<?xml version="1.0" encoding="US-ASCII"?>
<!-- RR Donnelley Xcelerate Taxonomy Labels Linkbase, based on XBRL 2.1  http://www.rrdonnelley.com/ -->
<!-- Version: 6.23.6 -->
<!-- Round: 9 -->
<!-- Creation date: 2016-08-08T20:02:00Z -->
<!-- Copyright (c) 2005-2013 R.R. Donnelley &amp; Sons Company All Rights Reserved. -->
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    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_AcceleratedShareRepurchaseProgramMember" xlink:label="pwr_AcceleratedShareRepurchaseProgramMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_AcceleratedShareRepurchaseProgramMember_lbl" xml:lang="en-US" id="id_7861063_2243165_3_1">Accelerated Share Repurchase Program [Member]</label>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_AccountingChangesAndErrorCorrectionsAbstract_lbl" xml:lang="en-US" id="id_7861063_2027881_2_1">Accounting Changes and Error Corrections [Abstract]</label>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccountingPoliciesAbstract_lbl" xml:lang="en-US" id="id_7861063_2025283_1_1">Accounting Policies [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_AccountingPoliciesAbstract_lbl" xml:lang="en-US" id="id_7861063_2025283_2_1">Accounting Policies [Abstract]</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_lbl" xml:lang="en-US" id="id_7861063_2021602_1_1">Accounts Payable and Accrued Liabilities, Current</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_lbl" xml:lang="en-US" id="id_7861063_2021602_2_1">Accounts payable and accrued expenses</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent" xlink:to="us-gaap_AccountsPayableAndAccruedLiabilitiesCurrent_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="us-gaap_AccountsReceivableNetCurrent"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccountsReceivableNetCurrent_lbl" xml:lang="en-US" id="id_7861063_2025718_1_1">Accounts Receivable, Net, Current</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_AccountsReceivableNetCurrent_lbl" xml:lang="en-US" id="id_7861063_2025718_2_1">Accounts receivable, net of allowances of $2,719 and $5,226</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccountsReceivableNetCurrent" xlink:to="us-gaap_AccountsReceivableNetCurrent_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccruedPayrollTaxesCurrentAndNoncurrent" xlink:label="us-gaap_AccruedPayrollTaxesCurrentAndNoncurrent"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccruedPayrollTaxesCurrentAndNoncurrent_lbl" xml:lang="en-US" id="id_7861063_2021822_1_1">Accrued Payroll Taxes</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_AccruedPayrollTaxesCurrentAndNoncurrent_lbl" xml:lang="en-US" id="id_7861063_2021822_2_1">Pre-acquisition non-U.S.tax obligations and indemnification liability amount recorded</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccruedPayrollTaxesCurrentAndNoncurrent" xlink:to="us-gaap_AccruedPayrollTaxesCurrentAndNoncurrent_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_lbl" xml:lang="en-US" id="id_7861063_2022470_1_1">Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_lbl" xml:lang="en-US" id="id_7861063_2022470_2_1">Accumulated depreciation on property and equipment</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment" xlink:to="us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_lbl" xml:lang="en-US" id="id_7861063_2027239_1_1">Accumulated Other Comprehensive Income (Loss), Net of Tax</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_lbl" xml:lang="en-US" id="id_7861063_2027239_2_1">Accumulated other comprehensive loss</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax" xlink:to="us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_AcquiredCompanyMember" xlink:label="pwr_AcquiredCompanyMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_AcquiredCompanyMember_lbl" xml:lang="en-US" id="id_7861063_2067064_3_1">Acquired Company [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_AcquiredCompanyMember_lbl" xml:lang="en-US" id="id_7861063_2067064_1_1">Acquired Company [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_AcquiredCompanyMember_lbl" xml:lang="en-US" id="id_7861063_2067064_2_1">Acquired Company [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_AcquiredCompanyMember" xlink:to="pwr_AcquiredCompanyMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife" xlink:label="us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_lbl" xml:lang="en-US" id="id_7861063_2022472_1_1">Acquired Finite-lived Intangible Assets, Weighted Average Useful Life</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_lbl" xml:lang="en-US" id="id_7861063_2022472_2_1">Weighted Average Amortization Period at Acquisition Date in Years</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife" xlink:to="us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_Acquisitions2015Member" xlink:label="pwr_Acquisitions2015Member"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_Acquisitions2015Member_lbl" xml:lang="en-US" id="id_7861063_2297723_3_1">Acquisitions 2015 [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_Acquisitions2015Member_lbl" xml:lang="en-US" id="id_7861063_2297723_1_1">Acquisitions 2015 [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_Acquisitions2015Member_lbl" xml:lang="en-US" id="id_7861063_2297723_2_1">Acquisitions 2015 [Member]</label>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_Acquisitions2016Member_lbl" xml:lang="en-US" id="id_7861063_2143424_3_1">2016 Acquisitions [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_Acquisitions2016Member_lbl" xml:lang="en-US" id="id_7861063_2143424_1_1">Acquisitions 2016 [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_Acquisitions2016Member_lbl" xml:lang="en-US" id="id_7861063_2143424_2_1">Acquisitions 2016 [Member]</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AdditionalPaidInCapitalCommonStock" xlink:label="us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AdditionalPaidInCapitalCommonStock_lbl" xml:lang="en-US" id="id_7861063_2024642_1_1">Additional Paid in Capital, Common Stock</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_AdditionalPaidInCapitalCommonStock_lbl" xml:lang="en-US" id="id_7861063_2024642_2_1">Additional paid-in capital</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:label="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xml:lang="en-US" id="id_7861063_2025723_1_1">Adjustments, Noncash Items, to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl" xml:lang="en-US" id="id_7861063_2025723_2_1">Adjustments to reconcile net income to net cash provided by operating activities of continuing operations -</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract" xlink:to="us-gaap_AdjustmentsNoncashItemsToReconcileNetIncomeLossToCashProvidedByUsedInOperatingActivitiesAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_AlaskaPowerPlantConstructionProjectMember" xlink:label="pwr_AlaskaPowerPlantConstructionProjectMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_AlaskaPowerPlantConstructionProjectMember_lbl" xml:lang="en-US" id="id_7861063_2393987_3_1">Alaska power plant construction project.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_AlaskaPowerPlantConstructionProjectMember_lbl" xml:lang="en-US" id="id_7861063_2393987_1_1">Alaska Power Plant Construction Project [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_AlaskaPowerPlantConstructionProjectMember_lbl" xml:lang="en-US" id="id_7861063_2393987_2_1">Alaska Power Plant Construction Project [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_AlaskaPowerPlantConstructionProjectMember" xlink:to="pwr_AlaskaPowerPlantConstructionProjectMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_AlbertaPowerLineMember" xlink:label="pwr_AlbertaPowerLineMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_AlbertaPowerLineMember_lbl" xml:lang="en-US" id="id_7861063_2099307_3_1">Alberta Power Line [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_AlbertaPowerLineMember_lbl" xml:lang="en-US" id="id_7861063_2099307_1_1">Alberta Power Line [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_AlbertaPowerLineMember_lbl" xml:lang="en-US" id="id_7861063_2099307_2_1">Alberta Power Line [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_AlbertaPowerLineMember" xlink:to="pwr_AlbertaPowerLineMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/currency/2016/currency-2016-01-31.xsd#currency_AllCurrenciesDomain" xlink:label="currency_AllCurrenciesDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="currency_AllCurrenciesDomain_lbl" xml:lang="en-US" id="id_7861063_2023129_1_1">All Currencies [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="currency_AllCurrenciesDomain_lbl" xml:lang="en-US" id="id_7861063_2023129_2_1">All Currencies [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="currency_AllCurrenciesDomain" xlink:to="currency_AllCurrenciesDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="us-gaap_AllocatedShareBasedCompensationExpense"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AllocatedShareBasedCompensationExpense_lbl" xml:lang="en-US" id="id_7861063_2023781_1_1">Allocated Share-based Compensation Expense</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_AllocatedShareBasedCompensationExpense_lbl" xml:lang="en-US" id="id_7861063_2023781_2_1">Compensation expense related to Restricted Stock Units to be settled in cash</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AllocatedShareBasedCompensationExpense" xlink:to="us-gaap_AllocatedShareBasedCompensationExpense_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent" xlink:label="us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_lbl" xml:lang="en-US" id="id_7861063_2024866_1_1">Allowance for Doubtful Accounts Receivable, Current</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_lbl" xml:lang="en-US" id="id_7861063_2024866_2_1">Allowances for doubtful accounts on current receivable</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_lbl" xml:lang="en-US" id="id_7861063_2024866_12_1">Allowances on accounts receivable, current</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent" xlink:to="us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_AmendmentFlag" xlink:label="dei_AmendmentFlag"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_AmendmentFlag_lbl" xml:lang="en-US" id="id_7861063_2024215_1_1">Amendment Flag</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="dei_AmendmentFlag_lbl" xml:lang="en-US" id="id_7861063_2024215_2_1">Amendment Flag</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_AmendmentFlag" xlink:to="dei_AmendmentFlag_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AmortizationOfFinancingCosts" xlink:label="us-gaap_AmortizationOfFinancingCosts"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AmortizationOfFinancingCosts_lbl" xml:lang="en-US" id="id_7861063_2021624_1_1">Amortization of Debt Issuance Costs</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_AmortizationOfFinancingCosts_lbl" xml:lang="en-US" id="id_7861063_2021624_2_1">Amortization of debt issuance costs</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AmortizationOfFinancingCosts" xlink:to="us-gaap_AmortizationOfFinancingCosts_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AmortizationOfIntangibleAssets" xlink:label="us-gaap_AmortizationOfIntangibleAssets"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AmortizationOfIntangibleAssets_lbl" xml:lang="en-US" id="id_7861063_2025955_1_1">Amortization of Intangible Assets</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_AmortizationOfIntangibleAssets_lbl" xml:lang="en-US" id="id_7861063_2025955_2_1">Amortization of intangible assets</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AmortizationOfIntangibleAssets" xlink:to="us-gaap_AmortizationOfIntangibleAssets_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember_lbl" xml:lang="en-US" id="id_7861063_2035280_1_1">Arrangements and Non-arrangement Transactions [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ArrangementsAndNonarrangementTransactionsMember_lbl" xml:lang="en-US" id="id_7861063_2035280_2_1">Arrangements and Non-arrangement Transactions [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ArrangementsAndNonarrangementTransactionsMember" xlink:to="us-gaap_ArrangementsAndNonarrangementTransactionsMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_Assets" xlink:label="us-gaap_Assets"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_Assets_lbl" xml:lang="en-US" id="id_7861063_2023136_1_1">Assets</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_Assets_lbl" xml:lang="en-US" id="id_7861063_2023136_6_1">Total assets</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Assets" xlink:to="us-gaap_Assets_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="us-gaap_AssetsAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AssetsAbstract_lbl" xml:lang="en-US" id="id_7861063_2027910_1_1">Assets [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_AssetsAbstract_lbl" xml:lang="en-US" id="id_7861063_2027910_2_1">ASSETS</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsAbstract" xlink:to="us-gaap_AssetsAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AssetsCurrent" xlink:label="us-gaap_AssetsCurrent"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AssetsCurrent_lbl" xml:lang="en-US" id="id_7861063_2023790_1_1">Assets, Current</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_AssetsCurrent_lbl" xml:lang="en-US" id="id_7861063_2023790_6_1">Total current assets</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsCurrent" xlink:to="us-gaap_AssetsCurrent_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="us-gaap_AssetsCurrentAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AssetsCurrentAbstract_lbl" xml:lang="en-US" id="id_7861063_2027691_1_1">Assets, Current [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_AssetsCurrentAbstract_lbl" xml:lang="en-US" id="id_7861063_2027691_2_1">Current Assets:</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsCurrentAbstract" xlink:to="us-gaap_AssetsCurrentAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation" xlink:label="us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation_lbl" xml:lang="en-US" id="id_7861063_2025522_1_1">Disposal Group, Including Discontinued Operation, Assets</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation_lbl" xml:lang="en-US" id="id_7861063_2025522_2_1">Assets of fiber optic licensing operations</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation" xlink:to="us-gaap_AssetsOfDisposalGroupIncludingDiscontinuedOperation_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/country/2016/country-2016-01-31.xsd#country_AU" xlink:label="country_AU"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="country_AU_lbl" xml:lang="en-US" id="id_7861063_2022492_1_1">AUSTRALIA</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="country_AU_lbl" xml:lang="en-US" id="id_7861063_2022492_2_1">Australia [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="country_AU" xlink:to="country_AU_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/currency/2016/currency-2016-01-31.xsd#currency_AUD" xlink:label="currency_AUD"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="currency_AUD_lbl" xml:lang="en-US" id="id_7861063_2025094_1_1">Australia, Dollars</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="currency_AUD_lbl" xml:lang="en-US" id="id_7861063_2025094_2_1">Australian Dollars [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="currency_AUD" xlink:to="currency_AUD_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_AutoLiabilityInsuranceClaimsDeductible" xlink:label="pwr_AutoLiabilityInsuranceClaimsDeductible"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_AutoLiabilityInsuranceClaimsDeductible_lbl" xml:lang="en-US" id="id_7861063_2163801_3_1">Auto liability insurance claims deductible amount per occurrence.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_AutoLiabilityInsuranceClaimsDeductible_lbl" xml:lang="en-US" id="id_7861063_2163801_1_1">Auto Liability Insurance Claims Deductible</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_AutoLiabilityInsuranceClaimsDeductible_lbl" xml:lang="en-US" id="id_7861063_2163801_2_1">Auto liability insurance claims deductible</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_AutoLiabilityInsuranceClaimsDeductible" xlink:to="pwr_AutoLiabilityInsuranceClaimsDeductible_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_AvailabilityAmountToAllowDividendsAndStockRepurchases" xlink:label="pwr_AvailabilityAmountToAllowDividendsAndStockRepurchases"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_AvailabilityAmountToAllowDividendsAndStockRepurchases_lbl" xml:lang="en-US" id="id_7861063_2154278_3_1">Amount of availability under the credit agreement and/or cash and cash equivalents on hand that must be present to allow for cash payments of dividends and stock repurchases.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_AvailabilityAmountToAllowDividendsAndStockRepurchases_lbl" xml:lang="en-US" id="id_7861063_2154278_1_1">Availability Amount To Allow Dividends And Stock Repurchases</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_AvailabilityAmountToAllowDividendsAndStockRepurchases_lbl" xml:lang="en-US" id="id_7861063_2154278_2_1">Amount of availability under the credit agreement and/or cash and cash equivalents on hand that must be present to allow for cash payments of dividends and stock repurchases</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_AvailabilityAmountToAllowDividendsAndStockRepurchases" xlink:to="pwr_AvailabilityAmountToAllowDividendsAndStockRepurchases_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="us-gaap_AwardTypeAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_AwardTypeAxis_lbl" xml:lang="en-US" id="id_7861063_2025317_1_1">Award Type [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_AwardTypeAxis_lbl" xml:lang="en-US" id="id_7861063_2025317_2_1">Award Type [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_AwardTypeAxis" xlink:to="us-gaap_AwardTypeAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BasisOfAccountingPolicyPolicyTextBlock" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2026403_1_1">Basis of Accounting, Policy [Policy Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2026403_2_1">Interim Condensed Consolidated Financial Information</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BasisOfAccountingPolicyPolicyTextBlock" xlink:to="us-gaap_BasisOfAccountingPolicyPolicyTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BillingsInExcessOfCostCurrent" xlink:label="us-gaap_BillingsInExcessOfCostCurrent"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BillingsInExcessOfCostCurrent_lbl" xml:lang="en-US" id="id_7861063_2025323_1_1">Billings in Excess of Cost, Current</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BillingsInExcessOfCostCurrent_lbl" xml:lang="en-US" id="id_7861063_2025323_2_1">Billings in excess of costs and estimated earnings on uncompleted contracts</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BillingsInExcessOfCostCurrent" xlink:to="us-gaap_BillingsInExcessOfCostCurrent_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_BorrowingsUnderCreditFacilityMember" xlink:label="pwr_BorrowingsUnderCreditFacilityMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_BorrowingsUnderCreditFacilityMember_lbl" xml:lang="en-US" id="id_7861063_2096317_3_1">The borrowings under the credit facility.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_BorrowingsUnderCreditFacilityMember_lbl" xml:lang="en-US" id="id_7861063_2096317_1_1">Borrowings Under Credit Facility [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_BorrowingsUnderCreditFacilityMember_lbl" xml:lang="en-US" id="id_7861063_2096317_2_1">Borrowings Under Credit Facility [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_BorrowingsUnderCreditFacilityMember" xlink:to="pwr_BorrowingsUnderCreditFacilityMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessAcquisitionAcquireeDomain" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain_lbl" xml:lang="en-US" id="id_7861063_2022941_1_1">Business Acquisition, Acquiree [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BusinessAcquisitionAcquireeDomain_lbl" xml:lang="en-US" id="id_7861063_2022941_2_1">Business Acquisition, Acquiree [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BusinessAcquisitionAcquireeDomain" xlink:to="us-gaap_BusinessAcquisitionAcquireeDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessAcquisitionAxis" xlink:label="us-gaap_BusinessAcquisitionAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BusinessAcquisitionAxis_lbl" xml:lang="en-US" id="id_7861063_2027704_1_1">Business Acquisition [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BusinessAcquisitionAxis_lbl" xml:lang="en-US" id="id_7861063_2027704_2_1">Business Acquisition [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BusinessAcquisitionAxis" xlink:to="us-gaap_BusinessAcquisitionAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:label="us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_lbl" xml:lang="en-US" id="id_7861063_2025106_1_1">Business Acquisition, Equity Interest Issued or Issuable, Number of Shares</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_lbl" xml:lang="en-US" id="id_7861063_2025106_2_1">Number of shares granted for acquired companies</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued" xlink:to="us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableNumberOfSharesIssued_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessAcquisitionLineItems" xlink:label="us-gaap_BusinessAcquisitionLineItems"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BusinessAcquisitionLineItems_lbl" xml:lang="en-US" id="id_7861063_2022284_1_1">Business Acquisition [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BusinessAcquisitionLineItems_lbl" xml:lang="en-US" id="id_7861063_2022284_2_1">Business Acquisition [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BusinessAcquisitionLineItems" xlink:to="us-gaap_BusinessAcquisitionLineItems_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessAcquisitionProFormaEarningsPerShareDiluted" xlink:label="us-gaap_BusinessAcquisitionProFormaEarningsPerShareDiluted"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BusinessAcquisitionProFormaEarningsPerShareDiluted_lbl" xml:lang="en-US" id="id_7861063_2035300_1_1">Business Acquisition, Pro Forma Earnings Per Share, Diluted</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BusinessAcquisitionProFormaEarningsPerShareDiluted_lbl" xml:lang="en-US" id="id_7861063_2035300_2_1">Earnings per share from continuing operations attributable to common stock - basic and diluted</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BusinessAcquisitionProFormaEarningsPerShareDiluted" xlink:to="us-gaap_BusinessAcquisitionProFormaEarningsPerShareDiluted_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessAcquisitionProFormaInformationTextBlock" xlink:label="us-gaap_BusinessAcquisitionProFormaInformationTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BusinessAcquisitionProFormaInformationTextBlock_lbl" xml:lang="en-US" id="id_7861063_2027275_1_1">Business Acquisition, Pro Forma Information [Table Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BusinessAcquisitionProFormaInformationTextBlock_lbl" xml:lang="en-US" id="id_7861063_2027275_2_1">Unaudited Supplemental Pro Forma Results of Operations</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BusinessAcquisitionProFormaInformationTextBlock" xlink:to="us-gaap_BusinessAcquisitionProFormaInformationTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount" xlink:label="us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_lbl" xml:lang="en-US" id="id_7861063_2023155_1_1">Business Acquisition, Goodwill, Expected Tax Deductible Amount</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_lbl" xml:lang="en-US" id="id_7861063_2023155_2_1">Goodwill expected to be deductible for income tax</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount" xlink:to="us-gaap_BusinessAcquisitionPurchasePriceAllocationGoodwillExpectedTaxDeductibleAmount_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_BusinessAcquisitionsProFormaAmortizationOfIntangibleAssets" xlink:label="pwr_BusinessAcquisitionsProFormaAmortizationOfIntangibleAssets"/>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_BusinessAcquisitionsProFormaNetIncomeLossAttributableToCommonStock_lbl" xml:lang="en-US" id="id_7861063_2068729_3_1">The pro forma net income(loss) attributable to common stock for a period as if the business combination or combinations had been completed at the beginning of the period.</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessAcquisitionsProFormaRevenue" xlink:label="us-gaap_BusinessAcquisitionsProFormaRevenue"/>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BusinessAcquisitionsProFormaRevenue_lbl" xml:lang="en-US" id="id_7861063_2024024_2_1">Revenues</label>
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    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_BusinessAcquisitionsProFormaSellingGeneralAndAdministrativeExpenses" xlink:label="pwr_BusinessAcquisitionsProFormaSellingGeneralAndAdministrativeExpenses"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_BusinessAcquisitionsProFormaSellingGeneralAndAdministrativeExpenses_lbl" xml:lang="en-US" id="id_7861063_2359185_3_1">The pro forma selling, general and administrative expenses for a period as if the business combination or combinations had been completed at the beginning of the period.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_BusinessAcquisitionsProFormaSellingGeneralAndAdministrativeExpenses_lbl" xml:lang="en-US" id="id_7861063_2359185_1_1">Business Acquisitions Pro Forma Selling General And Administrative Expenses</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_BusinessAcquisitionsProFormaSellingGeneralAndAdministrativeExpenses_lbl" xml:lang="en-US" id="id_7861063_2359185_2_1">Selling, general and administrative expenses</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationAcquiredReceivablesFairValue" xlink:label="us-gaap_BusinessCombinationAcquiredReceivablesFairValue"/>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BusinessCombinationAcquiredReceivablesFairValue_lbl" xml:lang="en-US" id="id_7861063_2025107_2_1">Fair value of accounts receivable acquired</label>
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    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_BusinessCombinationAcquisitionOfLessThan100PercentNoncontrollingInterestFairValueLessThanZero" xlink:label="pwr_BusinessCombinationAcquisitionOfLessThan100PercentNoncontrollingInterestFairValueLessThanZero"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_BusinessCombinationAcquisitionOfLessThan100PercentNoncontrollingInterestFairValueLessThanZero_lbl" xml:lang="en-US" id="id_7861063_2159474_3_1">Business combination acquisition of less than 100 percent noncontrolling interest fair value less than zero.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_BusinessCombinationAcquisitionOfLessThan100PercentNoncontrollingInterestFairValueLessThanZero_lbl" xml:lang="en-US" id="id_7861063_2159474_1_1">Business Combination Acquisition Of Less Than 100 Percent Noncontrolling Interest Fair Value Less Than Zero</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_BusinessCombinationAcquisitionOfLessThan100PercentNoncontrollingInterestFairValueLessThanZero_lbl" xml:lang="en-US" id="id_7861063_2159474_2_1">Non-controlling interests</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferred1" xlink:label="us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BusinessCombinationConsiderationTransferred1_lbl" xml:lang="en-US" id="id_7861063_2026621_1_1">Business Combination, Consideration Transferred</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BusinessCombinationConsiderationTransferred1_lbl" xml:lang="en-US" id="id_7861063_2026621_2_1">Fair value of total consideration transferred or estimated to be transferred</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" xlink:label="us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_lbl" xml:lang="en-US" id="id_7861063_2025534_1_1">Business Combination, Consideration Transferred, Equity Interests Issued and Issuable</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_lbl" xml:lang="en-US" id="id_7861063_2025534_2_1">Value of Quanta common stock and exchangeable shares issued</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable" xlink:to="us-gaap_BusinessCombinationConsiderationTransferredEquityInterestsIssuedAndIssuable_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_BusinessCombinationConsiderationTransferredOrToBeTransferredCashAndLiabilitiesIncurred" xlink:label="pwr_BusinessCombinationConsiderationTransferredOrToBeTransferredCashAndLiabilitiesIncurred"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_BusinessCombinationConsiderationTransferredOrToBeTransferredCashAndLiabilitiesIncurred_lbl" xml:lang="en-US" id="id_7861063_2047216_3_1">Consideration transferred or to be transferred cash and liabilities incurred except for contingent consideration.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_BusinessCombinationConsiderationTransferredOrToBeTransferredCashAndLiabilitiesIncurred_lbl" xml:lang="en-US" id="id_7861063_2047216_1_1">Business Combination Consideration Transferred Or To Be Transferred Cash And Liabilities Incurred</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/positiveLabel" xlink:label="pwr_BusinessCombinationConsiderationTransferredOrToBeTransferredCashAndLiabilitiesIncurred_lbl" xml:lang="en-US" id="id_7861063_2047216_32_1">Consideration transferred or to be transferred cash and liabilities incurred except for contingent consideration</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_BusinessCombinationConsiderationTransferredOrToBeTransferredCashAndLiabilitiesIncurred_lbl" xml:lang="en-US" id="id_7861063_2047216_2_1">Aggregate consideration for acquisitions</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="pwr_BusinessCombinationConsiderationTransferredOrToBeTransferredCashAndLiabilitiesIncurred_lbl" xml:lang="en-US" id="id_7861063_2047216_12_1">Cash paid or payable</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_BusinessCombinationConsiderationTransferredOrToBeTransferredCashAndLiabilitiesIncurred" xlink:to="pwr_BusinessCombinationConsiderationTransferredOrToBeTransferredCashAndLiabilitiesIncurred_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:label="us-gaap_BusinessCombinationContingentConsiderationLiability"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BusinessCombinationContingentConsiderationLiability_lbl" xml:lang="en-US" id="id_7861063_2024231_1_1">Business Combination, Contingent Consideration, Liability</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BusinessCombinationContingentConsiderationLiability_lbl" xml:lang="en-US" id="id_7861063_2024231_2_1">Contingent consideration</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BusinessCombinationContingentConsiderationLiability" xlink:to="us-gaap_BusinessCombinationContingentConsiderationLiability_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate" xlink:label="us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate_lbl" xml:lang="en-US" id="id_7861063_2026184_1_1">Business Combination, Indemnification Assets, Amount as of Acquisition Date</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate_lbl" xml:lang="en-US" id="id_7861063_2026184_2_1">Pre-acquisition non-U.S.tax obligations and indemnification asset amount recorded</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate" xlink:to="us-gaap_BusinessCombinationIndemnificationAssetsAmountAsOfAcquisitionDate_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssets" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssets"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssets_lbl" xml:lang="en-US" id="id_7861063_2024234_1_1">Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssets_lbl" xml:lang="en-US" id="id_7861063_2024234_2_1">Current assets</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssets" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentAssets_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities_lbl" xml:lang="en-US" id="id_7861063_2025109_1_1">Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities_lbl" xml:lang="en-US" id="id_7861063_2025109_14_1">Current liabilities</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilitiesNoncurrent" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilitiesNoncurrent"/>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedDeferredTaxLiabilitiesNoncurrent_lbl" xml:lang="en-US" id="id_7861063_2022291_14_1">Deferred tax liabilities, net</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibleAssetsOtherThanGoodwill"/>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNetTangibleAssets_lbl" xml:lang="en-US" id="id_7861063_2059024_3_1">Amount of tangible assets acquired less liabilities assumed at the acquisition date.</label>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilitiesOther_lbl" xml:lang="en-US" id="id_7861063_2025110_14_1">Other long-term liabilities</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets"/>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedOtherNoncurrentAssets_lbl" xml:lang="en-US" id="id_7861063_2022090_2_1">Other assets</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_lbl" xml:lang="en-US" id="id_7861063_2024026_1_1">Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_lbl" xml:lang="en-US" id="id_7861063_2024026_2_1">Property and equipment</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedPropertyPlantAndEquipment_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_lbl" xml:lang="en-US" id="id_7861063_2027707_1_1">Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Net</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_lbl" xml:lang="en-US" id="id_7861063_2027707_2_1">Fair value of total consideration transferred</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet" xlink:to="us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredGoodwillAndLiabilitiesAssumedNet_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_BusinessCombinationsAbstract" xlink:label="us-gaap_BusinessCombinationsAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_BusinessCombinationsAbstract_lbl" xml:lang="en-US" id="id_7861063_2024909_1_1">Business Combinations [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_BusinessCombinationsAbstract_lbl" xml:lang="en-US" id="id_7861063_2024909_2_1">Business Combinations [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_BusinessCombinationsAbstract" xlink:to="us-gaap_BusinessCombinationsAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/country/2016/country-2016-01-31.xsd#country_CA" xlink:label="country_CA"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="country_CA_lbl" xml:lang="en-US" id="id_7861063_2021866_1_1">CANADA</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="country_CA_lbl" xml:lang="en-US" id="id_7861063_2021866_2_1">Canada [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="country_CA" xlink:to="country_CA_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/currency/2016/currency-2016-01-31.xsd#currency_CAD" xlink:label="currency_CAD"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="currency_CAD_lbl" xml:lang="en-US" id="id_7861063_2027944_1_1">Canada, Dollars</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="currency_CAD_lbl" xml:lang="en-US" id="id_7861063_2027944_2_1">Canadian Dollars [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="currency_CAD" xlink:to="currency_CAD_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_CanadianAndAustralianDollarsMember" xlink:label="pwr_CanadianAndAustralianDollarsMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_CanadianAndAustralianDollarsMember_lbl" xml:lang="en-US" id="id_7861063_2062680_3_1">Canadian and Australian dollars [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_CanadianAndAustralianDollarsMember_lbl" xml:lang="en-US" id="id_7861063_2062680_1_1">Canadian and Australian dollars [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_CanadianAndAustralianDollarsMember_lbl" xml:lang="en-US" id="id_7861063_2062680_2_1">Canadian and Australian dollars [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_CanadianAndAustralianDollarsMember" xlink:to="pwr_CanadianAndAustralianDollarsMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis" xlink:label="us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis_lbl" xml:lang="en-US" id="id_7861063_2025997_1_1">Project [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis_lbl" xml:lang="en-US" id="id_7861063_2025997_2_1">Project [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis" xlink:to="us-gaap_CapitalizedCostsOfUnprovedPropertiesExcludedFromAmortizationByPropertyOrProjectAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CapitalLeaseObligations" xlink:label="us-gaap_CapitalLeaseObligations"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeaseObligations_lbl" xml:lang="en-US" id="id_7861063_2025115_1_1">Capital Lease Obligations</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CapitalLeaseObligations_lbl" xml:lang="en-US" id="id_7861063_2025115_2_1">Capital leases, interest rates ranging from 2.5% to 6.2%</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CapitalLeaseObligationsMember" xlink:label="us-gaap_CapitalLeaseObligationsMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CapitalLeaseObligationsMember_lbl" xml:lang="en-US" id="id_7861063_2021870_1_1">Capital Lease Obligations [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CapitalLeaseObligationsMember_lbl" xml:lang="en-US" id="id_7861063_2021870_2_1">Capital Leases [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CapitalLeaseObligationsMember" xlink:to="us-gaap_CapitalLeaseObligationsMember_lbl"/>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CashAndCashEquivalentsAbstract_lbl" xml:lang="en-US" id="id_7861063_2027715_1_1">Cash and Cash Equivalents [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CashAndCashEquivalentsAbstract_lbl" xml:lang="en-US" id="id_7861063_2027715_2_1">Cash and Cash Equivalents [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsAbstract" xlink:to="us-gaap_CashAndCashEquivalentsAbstract_lbl"/>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xml:lang="en-US" id="id_7861063_2025118_1_1">Cash and Cash Equivalents, at Carrying Value</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xml:lang="en-US" id="id_7861063_2025118_4_1">Cash and cash equivalents, end of period</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xml:lang="en-US" id="id_7861063_2025118_5_1">Cash and cash equivalents, beginning of period</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl" xml:lang="en-US" id="id_7861063_2025118_2_1">Cash and cash equivalents</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsAtCarryingValue" xlink:to="us-gaap_CashAndCashEquivalentsAtCarryingValue_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CashAndCashEquivalentsAxis" xlink:label="us-gaap_CashAndCashEquivalentsAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CashAndCashEquivalentsAxis_lbl" xml:lang="en-US" id="id_7861063_2025340_1_1">Cash and Cash Equivalents [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CashAndCashEquivalentsAxis_lbl" xml:lang="en-US" id="id_7861063_2025340_2_1">Cash and Cash Equivalents [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsAxis" xlink:to="us-gaap_CashAndCashEquivalentsAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CashAndCashEquivalentsLineItems" xlink:label="us-gaap_CashAndCashEquivalentsLineItems"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CashAndCashEquivalentsLineItems_lbl" xml:lang="en-US" id="id_7861063_2024249_1_1">Cash and Cash Equivalents [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CashAndCashEquivalentsLineItems_lbl" xml:lang="en-US" id="id_7861063_2024249_2_1">Cash and Cash Equivalents [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsLineItems" xlink:to="us-gaap_CashAndCashEquivalentsLineItems_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_lbl" xml:lang="en-US" id="id_7861063_2023171_1_1">Cash and Cash Equivalents, Period Increase (Decrease)</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_lbl" xml:lang="en-US" id="id_7861063_2023171_6_1">Net increase (decrease) in cash and cash equivalents</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease" xlink:to="us-gaap_CashAndCashEquivalentsPeriodIncreaseDecrease_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CashAndCashEquivalentsPolicyTextBlock" xlink:label="us-gaap_CashAndCashEquivalentsPolicyTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CashAndCashEquivalentsPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2025342_1_1">Cash and Cash Equivalents, Policy [Policy Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CashAndCashEquivalentsPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2025342_2_1">Cash and Cash Equivalents</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashAndCashEquivalentsPolicyTextBlock" xlink:to="us-gaap_CashAndCashEquivalentsPolicyTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CashEquivalentsAtCarryingValue" xlink:label="us-gaap_CashEquivalentsAtCarryingValue"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CashEquivalentsAtCarryingValue_lbl" xml:lang="en-US" id="id_7861063_2023832_1_1">Cash Equivalents, at Carrying Value</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CashEquivalentsAtCarryingValue_lbl" xml:lang="en-US" id="id_7861063_2023832_2_1">Cash equivalents</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashEquivalentsAtCarryingValue" xlink:to="us-gaap_CashEquivalentsAtCarryingValue_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_CashPaidForOtherIntangibles" xlink:label="pwr_CashPaidForOtherIntangibles"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_CashPaidForOtherIntangibles_lbl" xml:lang="en-US" id="id_7861063_2159218_3_1">Cash Paid For Other Intangibles</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_CashPaidForOtherIntangibles_lbl" xml:lang="en-US" id="id_7861063_2159218_1_1">Cash Paid For Other Intangibles</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="pwr_CashPaidForOtherIntangibles_lbl" xml:lang="en-US" id="id_7861063_2159218_14_1">Cash paid for intangibles</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_CashPaidForOtherIntangibles" xlink:to="pwr_CashPaidForOtherIntangibles_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations" xlink:label="us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_lbl" xml:lang="en-US" id="id_7861063_2022962_1_1">Cash Provided by (Used in) Investing Activities, Discontinued Operations</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_lbl" xml:lang="en-US" id="id_7861063_2022962_2_1">Net cash used in investing activities</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations" xlink:to="us-gaap_CashProvidedByUsedInInvestingActivitiesDiscontinuedOperations_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations" xlink:label="us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_lbl" xml:lang="en-US" id="id_7861063_2023604_1_1">Cash Provided by (Used in) Operating Activities, Discontinued Operations</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_lbl" xml:lang="en-US" id="id_7861063_2023604_2_1">Net cash provided by operating activities</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations" xlink:to="us-gaap_CashProvidedByUsedInOperatingActivitiesDiscontinuedOperations_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_CentralStatesPlanMember" xlink:label="pwr_CentralStatesPlanMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_CentralStatesPlanMember_lbl" xml:lang="en-US" id="id_7861063_2167449_3_1">2011 Central States Plan Withdrawal Liability, Quanta subsidiaries withdrew from the Central States, Southeast and Southwest Areas Pension Plan.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_CentralStatesPlanMember_lbl" xml:lang="en-US" id="id_7861063_2167449_1_1">Central States Plan [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_CentralStatesPlanMember_lbl" xml:lang="en-US" id="id_7861063_2167449_2_1">Central States Plan [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_CentralStatesPlanMember" xlink:to="pwr_CentralStatesPlanMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_ChangeInContractEstimatesImpactOnOperatingResults" xlink:label="pwr_ChangeInContractEstimatesImpactOnOperatingResults"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ChangeInContractEstimatesImpactOnOperatingResults_lbl" xml:lang="en-US" id="id_7861063_2105424_3_1">Change in contract estimates impact on operating results.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_ChangeInContractEstimatesImpactOnOperatingResults_lbl" xml:lang="en-US" id="id_7861063_2105424_1_1">Change in Contract Estimates Impact on Operating Results</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="pwr_ChangeInContractEstimatesImpactOnOperatingResults_lbl" xml:lang="en-US" id="id_7861063_2105424_14_1">Decrease in operating results due to change in contract estimates, percentage</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_ChangeInContractEstimatesImpactOnOperatingResults" xlink:to="pwr_ChangeInContractEstimatesImpactOnOperatingResults_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_ChangeInContractEstimatesImpactOnOperatingResultsValueGainsIdentifiedThatOffsetAgainstLossesDisclosed" xlink:label="pwr_ChangeInContractEstimatesImpactOnOperatingResultsValueGainsIdentifiedThatOffsetAgainstLossesDisclosed"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ChangeInContractEstimatesImpactOnOperatingResultsValueGainsIdentifiedThatOffsetAgainstLossesDisclosed_lbl" xml:lang="en-US" id="id_7861063_2393917_3_1">Change in contract estimates impact on operating results value gains identified that offset against losses disclosed.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_ChangeInContractEstimatesImpactOnOperatingResultsValueGainsIdentifiedThatOffsetAgainstLossesDisclosed_lbl" xml:lang="en-US" id="id_7861063_2393917_1_1">Change in Contract Estimates Impact on Operating Results Value Gains Identified That Offset Against Losses Disclosed</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_ChangeInContractEstimatesImpactOnOperatingResultsValueGainsIdentifiedThatOffsetAgainstLossesDisclosed_lbl" xml:lang="en-US" id="id_7861063_2393917_2_1">Change in contract estimates impact on operating results value gains identified that offset against losses disclosed</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_ChangeInContractEstimatesImpactOnOperatingResultsValueGainsIdentifiedThatOffsetAgainstLossesDisclosed" xlink:to="pwr_ChangeInContractEstimatesImpactOnOperatingResultsValueGainsIdentifiedThatOffsetAgainstLossesDisclosed_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ClassOfStockDomain" xlink:label="us-gaap_ClassOfStockDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ClassOfStockDomain_lbl" xml:lang="en-US" id="id_7861063_2027969_1_1">Class of Stock [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ClassOfStockDomain_lbl" xml:lang="en-US" id="id_7861063_2027969_2_1">Class of Stock [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfStockDomain" xlink:to="us-gaap_ClassOfStockDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ClassOfStockLineItems" xlink:label="us-gaap_ClassOfStockLineItems"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ClassOfStockLineItems_lbl" xml:lang="en-US" id="id_7861063_2035316_1_1">Class of Stock [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ClassOfStockLineItems_lbl" xml:lang="en-US" id="id_7861063_2035316_2_1">Class of Stock [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfStockLineItems" xlink:to="us-gaap_ClassOfStockLineItems_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ClassOfTreasuryStockTable" xlink:label="us-gaap_ClassOfTreasuryStockTable"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ClassOfTreasuryStockTable_lbl" xml:lang="en-US" id="id_7861063_2026640_1_1">Class of Treasury Stock [Table]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ClassOfTreasuryStockTable_lbl" xml:lang="en-US" id="id_7861063_2026640_2_1">Class of Treasury Stock [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ClassOfTreasuryStockTable" xlink:to="us-gaap_ClassOfTreasuryStockTable_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_CommitmentAndContingenciesLineItems" xlink:label="pwr_CommitmentAndContingenciesLineItems"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_CommitmentAndContingenciesLineItems_lbl" xml:lang="en-US" id="id_7861063_2244056_3_1">Commitment And Contingencies [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_CommitmentAndContingenciesLineItems_lbl" xml:lang="en-US" id="id_7861063_2244056_1_1">Commitment And Contingencies [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_CommitmentAndContingenciesLineItems_lbl" xml:lang="en-US" id="id_7861063_2244056_2_1">Commitment And Contingencies [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_CommitmentAndContingenciesLineItems" xlink:to="pwr_CommitmentAndContingenciesLineItems_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_CommitmentAndContingenciesTable" xlink:label="pwr_CommitmentAndContingenciesTable"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_CommitmentAndContingenciesTable_lbl" xml:lang="en-US" id="id_7861063_2170029_3_1">Commitment And Contingencies [Table]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_CommitmentAndContingenciesTable_lbl" xml:lang="en-US" id="id_7861063_2170029_1_1">Commitment And Contingencies [Table]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_CommitmentAndContingenciesTable_lbl" xml:lang="en-US" id="id_7861063_2170029_2_1">Commitment And Contingencies [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_CommitmentAndContingenciesTable" xlink:to="pwr_CommitmentAndContingenciesTable_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommitmentsAndContingencies" xlink:label="us-gaap_CommitmentsAndContingencies"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommitmentsAndContingencies_lbl" xml:lang="en-US" id="id_7861063_2022745_1_1">Commitments and Contingencies</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CommitmentsAndContingencies_lbl" xml:lang="en-US" id="id_7861063_2022745_2_1">Commitments and Contingencies</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommitmentsAndContingencies" xlink:to="us-gaap_CommitmentsAndContingencies_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommitmentsAndContingenciesDisclosureAbstract" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureAbstract_lbl" xml:lang="en-US" id="id_7861063_2026024_1_1">Commitments and Contingencies Disclosure [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureAbstract_lbl" xml:lang="en-US" id="id_7861063_2026024_2_1">Commitments and Contingencies Disclosure [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommitmentsAndContingenciesDisclosureAbstract" xlink:to="us-gaap_CommitmentsAndContingenciesDisclosureAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommitmentsAndContingenciesDisclosureTextBlock" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_lbl" xml:lang="en-US" id="id_7861063_2027090_1_1">Commitments and Contingencies Disclosure [Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_lbl" xml:lang="en-US" id="id_7861063_2027090_2_1">Commitments and Contingencies</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock" xlink:to="us-gaap_CommitmentsAndContingenciesDisclosureTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_CommonStockAvailableForAwardsPursuantToPlan" xlink:label="pwr_CommonStockAvailableForAwardsPursuantToPlan"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_CommonStockAvailableForAwardsPursuantToPlan_lbl" xml:lang="en-US" id="id_7861063_2221154_3_1">Common stock available for awards pursuant to the plan.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_CommonStockAvailableForAwardsPursuantToPlan_lbl" xml:lang="en-US" id="id_7861063_2221154_1_1">Common Stock Available For Awards Pursuant To Plan</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_CommonStockAvailableForAwardsPursuantToPlan_lbl" xml:lang="en-US" id="id_7861063_2221154_2_1">Aggregate number of shares of common stock that may be issued</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_CommonStockAvailableForAwardsPursuantToPlan" xlink:to="pwr_CommonStockAvailableForAwardsPursuantToPlan_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockNoParValue" xlink:label="us-gaap_CommonStockNoParValue"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockNoParValue_lbl" xml:lang="en-US" id="id_7861063_2024490_1_1">Common Stock, No Par Value</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CommonStockNoParValue_lbl" xml:lang="en-US" id="id_7861063_2024490_2_1">Exchangeable Shares, par value</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockNoParValue" xlink:to="us-gaap_CommonStockNoParValue_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockParOrStatedValuePerShare" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xml:lang="en-US" id="id_7861063_2021893_1_1">Common Stock, Par or Stated Value Per Share</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CommonStockParOrStatedValuePerShare_lbl" xml:lang="en-US" id="id_7861063_2021893_2_1">Common stock, par value</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockParOrStatedValuePerShare" xlink:to="us-gaap_CommonStockParOrStatedValuePerShare_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="us-gaap_CommonStockSharesAuthorized"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockSharesAuthorized_lbl" xml:lang="en-US" id="id_7861063_2024271_1_1">Common Stock, Shares Authorized</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CommonStockSharesAuthorized_lbl" xml:lang="en-US" id="id_7861063_2024271_2_1">Common stock, shares authorized</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesAuthorized" xlink:to="us-gaap_CommonStockSharesAuthorized_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockSharesIssued" xlink:label="us-gaap_CommonStockSharesIssued"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xml:lang="en-US" id="id_7861063_2022978_1_1">Common Stock, Shares, Issued</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CommonStockSharesIssued_lbl" xml:lang="en-US" id="id_7861063_2022978_2_1">Common stock, shares issued</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesIssued" xlink:to="us-gaap_CommonStockSharesIssued_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockSharesOutstanding" xlink:label="us-gaap_CommonStockSharesOutstanding"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xml:lang="en-US" id="id_7861063_2022748_1_1">Common Stock, Shares, Outstanding</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CommonStockSharesOutstanding_lbl" xml:lang="en-US" id="id_7861063_2022748_2_1">Common stock, shares outstanding</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockSharesOutstanding" xlink:to="us-gaap_CommonStockSharesOutstanding_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CommonStockValue" xlink:label="us-gaap_CommonStockValue"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CommonStockValue_lbl" xml:lang="en-US" id="id_7861063_2025780_1_1">Common Stock, Value, Issued</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CommonStockValue_lbl" xml:lang="en-US" id="id_7861063_2025780_2_1">Common stock, value</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CommonStockValue" xlink:to="us-gaap_CommonStockValue_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_CommonStockWithheldForSettlementOfEmployeeTaxLiabilitiesMember" xlink:label="pwr_CommonStockWithheldForSettlementOfEmployeeTaxLiabilitiesMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_CommonStockWithheldForSettlementOfEmployeeTaxLiabilitiesMember_lbl" xml:lang="en-US" id="id_7861063_2330542_3_1">Common stock withheld for settlement of employee tax liabilities.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_CommonStockWithheldForSettlementOfEmployeeTaxLiabilitiesMember_lbl" xml:lang="en-US" id="id_7861063_2330542_1_1">Common Stock Withheld For Settlement Of Employee Tax Liabilities [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_CommonStockWithheldForSettlementOfEmployeeTaxLiabilitiesMember_lbl" xml:lang="en-US" id="id_7861063_2330542_2_1">Common Stock Withheld for Settlement of Employee Tax Liabilities [Member]</label>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CompensationRelatedCostsPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2021436_1_1">Compensation Related Costs, Policy [Policy Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CompensationRelatedCostsPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2021436_2_1">Stock-Based Compensation</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CompensationRelatedCostsPolicyTextBlock" xlink:to="us-gaap_CompensationRelatedCostsPolicyTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTax" xlink:label="us-gaap_ComprehensiveIncomeNetOfTax"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ComprehensiveIncomeNetOfTax_lbl" xml:lang="en-US" id="id_7861063_2025782_1_1">Comprehensive Income (Loss), Net of Tax, Attributable to Parent</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_ComprehensiveIncomeNetOfTax_lbl" xml:lang="en-US" id="id_7861063_2025782_6_1">Total comprehensive income attributable to Quanta stockholders</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ComprehensiveIncomeNetOfTax" xlink:to="us-gaap_ComprehensiveIncomeNetOfTax_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest" xlink:label="us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest_lbl" xml:lang="en-US" id="id_7861063_2026427_1_1">Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest_lbl" xml:lang="en-US" id="id_7861063_2026427_2_1">Less: Comprehensive income attributable to non-controlling interests</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest" xlink:to="us-gaap_ComprehensiveIncomeNetOfTaxAttributableToNoncontrollingInterest_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest" xlink:label="us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_lbl" xml:lang="en-US" id="id_7861063_2035324_1_1">Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_lbl" xml:lang="en-US" id="id_7861063_2035324_6_1">Comprehensive income</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest" xlink:to="us-gaap_ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ComprehensiveIncomePolicyPolicyTextBlock" xlink:label="us-gaap_ComprehensiveIncomePolicyPolicyTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ComprehensiveIncomePolicyPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2025783_1_1">Comprehensive Income, Policy [Policy Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ComprehensiveIncomePolicyPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2025783_2_1">Comprehensive Income</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ComprehensiveIncomePolicyPolicyTextBlock" xlink:to="us-gaap_ComprehensiveIncomePolicyPolicyTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ConcentrationRiskBenchmarkDomain_lbl" xml:lang="en-US" id="id_7861063_2023409_1_1">Concentration Risk Benchmark [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ConcentrationRiskBenchmarkDomain_lbl" xml:lang="en-US" id="id_7861063_2023409_2_1">Concentration Risk Benchmark [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConcentrationRiskBenchmarkDomain" xlink:to="us-gaap_ConcentrationRiskBenchmarkDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:label="us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ConcentrationRiskByBenchmarkAxis_lbl" xml:lang="en-US" id="id_7861063_2021437_1_1">Concentration Risk Benchmark [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ConcentrationRiskByBenchmarkAxis_lbl" xml:lang="en-US" id="id_7861063_2021437_2_1">Concentration Risk Benchmark [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:to="us-gaap_ConcentrationRiskByBenchmarkAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskByTypeAxis" xlink:label="us-gaap_ConcentrationRiskByTypeAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ConcentrationRiskByTypeAxis_lbl" xml:lang="en-US" id="id_7861063_2021438_1_1">Concentration Risk Type [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ConcentrationRiskByTypeAxis_lbl" xml:lang="en-US" id="id_7861063_2021438_2_1">Concentration Risk Type [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConcentrationRiskByTypeAxis" xlink:to="us-gaap_ConcentrationRiskByTypeAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskLineItems" xlink:label="us-gaap_ConcentrationRiskLineItems"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ConcentrationRiskLineItems_lbl" xml:lang="en-US" id="id_7861063_2025786_1_1">Concentration Risk [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ConcentrationRiskLineItems_lbl" xml:lang="en-US" id="id_7861063_2025786_2_1">Concentration Risk [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConcentrationRiskLineItems" xlink:to="us-gaap_ConcentrationRiskLineItems_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskPercentage1" xlink:label="us-gaap_ConcentrationRiskPercentage1"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ConcentrationRiskPercentage1_lbl" xml:lang="en-US" id="id_7861063_2026029_1_1">Concentration Risk, Percentage</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ConcentrationRiskPercentage1_lbl" xml:lang="en-US" id="id_7861063_2026029_2_1">Concentration risk percentage</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConcentrationRiskPercentage1" xlink:to="us-gaap_ConcentrationRiskPercentage1_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskTable" xlink:label="us-gaap_ConcentrationRiskTable"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ConcentrationRiskTable_lbl" xml:lang="en-US" id="id_7861063_2022316_1_1">Concentration Risk [Table]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ConcentrationRiskTable_lbl" xml:lang="en-US" id="id_7861063_2022316_2_1">Concentration Risk [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConcentrationRiskTable" xlink:to="us-gaap_ConcentrationRiskTable_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="us-gaap_ConcentrationRiskTypeDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ConcentrationRiskTypeDomain_lbl" xml:lang="en-US" id="id_7861063_2027980_1_1">Concentration Risk Type [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ConcentrationRiskTypeDomain_lbl" xml:lang="en-US" id="id_7861063_2027980_2_1">Concentration Risk Type [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConcentrationRiskTypeDomain" xlink:to="us-gaap_ConcentrationRiskTypeDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ConsolidationPolicyTextBlock" xlink:label="us-gaap_ConsolidationPolicyTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ConsolidationPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2023415_1_1">Consolidation, Policy [Policy Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ConsolidationPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2023415_2_1">Principles of Consolidation</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ConsolidationPolicyTextBlock" xlink:to="us-gaap_ConsolidationPolicyTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ContractReceivableRetainageDueAfterOneYear" xlink:label="us-gaap_ContractReceivableRetainageDueAfterOneYear"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ContractReceivableRetainageDueAfterOneYear_lbl" xml:lang="en-US" id="id_7861063_2022547_1_1">Contract Receivable Retainage, after Next Twelve Months</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ContractReceivableRetainageDueAfterOneYear_lbl" xml:lang="en-US" id="id_7861063_2022547_2_1">Non-current retainage balances</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ContractReceivableRetainageDueAfterOneYear" xlink:to="us-gaap_ContractReceivableRetainageDueAfterOneYear_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ContractReceivableRetainageDueOneYearOrLess" xlink:label="us-gaap_ContractReceivableRetainageDueOneYearOrLess"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ContractReceivableRetainageDueOneYearOrLess_lbl" xml:lang="en-US" id="id_7861063_2022128_1_1">Contract Receivable Retainage, Next Twelve Months</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ContractReceivableRetainageDueOneYearOrLess_lbl" xml:lang="en-US" id="id_7861063_2022128_2_1">Current retainage balances</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ContractReceivableRetainageDueOneYearOrLess" xlink:to="us-gaap_ContractReceivableRetainageDueOneYearOrLess_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_ContractValueOfProject" xlink:label="pwr_ContractValueOfProject"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ContractValueOfProject_lbl" xml:lang="en-US" id="id_7861063_2384124_3_1">Represents a contract value.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_ContractValueOfProject_lbl" xml:lang="en-US" id="id_7861063_2384124_1_1">Contract Value Of Project</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_ContractValueOfProject_lbl" xml:lang="en-US" id="id_7861063_2384124_2_1">Contract value of project</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_ContractValueOfProject" xlink:to="pwr_ContractValueOfProject_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_CorporateAndNonAllocatedCostsMember" xlink:label="pwr_CorporateAndNonAllocatedCostsMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_CorporateAndNonAllocatedCostsMember_lbl" xml:lang="en-US" id="id_7861063_2269001_3_1">Corporate and non-allocated costs.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_CorporateAndNonAllocatedCostsMember_lbl" xml:lang="en-US" id="id_7861063_2269001_1_1">Corporate And Non Allocated Costs [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_CorporateAndNonAllocatedCostsMember_lbl" xml:lang="en-US" id="id_7861063_2269001_2_1">Corporate and Non-Allocated Costs [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_CorporateAndNonAllocatedCostsMember" xlink:to="pwr_CorporateAndNonAllocatedCostsMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CorporateJointVentureMember" xlink:label="us-gaap_CorporateJointVentureMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CorporateJointVentureMember_lbl" xml:lang="en-US" id="id_7861063_2022132_1_1">Corporate Joint Venture [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CorporateJointVentureMember_lbl" xml:lang="en-US" id="id_7861063_2022132_2_1">Corporate Joint Venture [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CorporateJointVentureMember" xlink:to="us-gaap_CorporateJointVentureMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CostOfServices" xlink:label="us-gaap_CostOfServices"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CostOfServices_lbl" xml:lang="en-US" id="id_7861063_2026439_1_1">Cost of Services</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CostOfServices_lbl" xml:lang="en-US" id="id_7861063_2026439_2_1">Cost of services (including depreciation)</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CostOfServices" xlink:to="us-gaap_CostOfServices_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear" xlink:label="us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear_lbl" xml:lang="en-US" id="id_7861063_2027320_1_1">Costs in Excess of Billings, Current</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear_lbl" xml:lang="en-US" id="id_7861063_2027320_2_1">Costs and estimated earnings in excess of billings on uncompleted contracts</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear" xlink:to="us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityAxis" xlink:label="us-gaap_CreditFacilityAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CreditFacilityAxis_lbl" xml:lang="en-US" id="id_7861063_2024073_1_1">Credit Facility [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CreditFacilityAxis_lbl" xml:lang="en-US" id="id_7861063_2024073_2_1">Credit Facility [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CreditFacilityAxis" xlink:to="us-gaap_CreditFacilityAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CreditFacilityDomain" xlink:label="us-gaap_CreditFacilityDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CreditFacilityDomain_lbl" xml:lang="en-US" id="id_7861063_2024074_1_1">Credit Facility [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CreditFacilityDomain_lbl" xml:lang="en-US" id="id_7861063_2024074_2_1">Credit Facility [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CreditFacilityDomain" xlink:to="us-gaap_CreditFacilityDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_CrossDefaultProvisions" xlink:label="pwr_CrossDefaultProvisions"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_CrossDefaultProvisions_lbl" xml:lang="en-US" id="id_7861063_2144935_3_1">Cross-default provisions.</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CurrencyAxis" xlink:label="us-gaap_CurrencyAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CurrencyAxis_lbl" xml:lang="en-US" id="id_7861063_2027995_1_1">Currency [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CurrencyAxis_lbl" xml:lang="en-US" id="id_7861063_2027995_2_1">Currency [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CurrencyAxis" xlink:to="us-gaap_CurrencyAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_CurrentFiscalYearEndDate" xlink:label="dei_CurrentFiscalYearEndDate"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_CurrentFiscalYearEndDate_lbl" xml:lang="en-US" id="id_7861063_2024507_1_1">Current Fiscal Year End Date</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="dei_CurrentFiscalYearEndDate_lbl" xml:lang="en-US" id="id_7861063_2024507_2_1">Current Fiscal Year End Date</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_CurrentFiscalYearEndDate" xlink:to="dei_CurrentFiscalYearEndDate_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CustomerConcentrationRiskMember" xlink:label="us-gaap_CustomerConcentrationRiskMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CustomerConcentrationRiskMember_lbl" xml:lang="en-US" id="id_7861063_2025387_1_1">Customer Concentration Risk [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CustomerConcentrationRiskMember_lbl" xml:lang="en-US" id="id_7861063_2025387_2_1">Customer Concentration Risk [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CustomerConcentrationRiskMember" xlink:to="us-gaap_CustomerConcentrationRiskMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_CustomerRelationshipsMember" xlink:label="us-gaap_CustomerRelationshipsMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_CustomerRelationshipsMember_lbl" xml:lang="en-US" id="id_7861063_2026047_1_1">Customer Relationships [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_CustomerRelationshipsMember_lbl" xml:lang="en-US" id="id_7861063_2026047_2_1">Customer Relationships [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_CustomerRelationshipsMember" xlink:to="us-gaap_CustomerRelationshipsMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtCurrent" xlink:label="us-gaap_DebtCurrent"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtCurrent_lbl" xml:lang="en-US" id="id_7861063_2027542_1_1">Debt, Current</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_DebtCurrent_lbl" xml:lang="en-US" id="id_7861063_2027542_2_1">Current maturities of long-term debt and short-term borrowings</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_DebtCurrent_lbl" xml:lang="en-US" id="id_7861063_2027542_6_1">Current maturities of long-term debt and short-term borrowings</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtCurrent" xlink:to="us-gaap_DebtCurrent_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtDisclosureAbstract" xlink:label="us-gaap_DebtDisclosureAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtDisclosureAbstract_lbl" xml:lang="en-US" id="id_7861063_2026667_1_1">Debt Disclosure [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_DebtDisclosureAbstract_lbl" xml:lang="en-US" id="id_7861063_2026667_2_1">Debt Disclosure [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtDisclosureAbstract" xlink:to="us-gaap_DebtDisclosureAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtDisclosureTextBlock" xlink:label="us-gaap_DebtDisclosureTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtDisclosureTextBlock_lbl" xml:lang="en-US" id="id_7861063_2022560_1_1">Debt Disclosure [Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_DebtDisclosureTextBlock_lbl" xml:lang="en-US" id="id_7861063_2022560_2_1">Debt Obligations</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtDisclosureTextBlock" xlink:to="us-gaap_DebtDisclosureTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="us-gaap_DebtInstrumentAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtInstrumentAxis_lbl" xml:lang="en-US" id="id_7861063_2025588_1_1">Debt Instrument [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_DebtInstrumentAxis_lbl" xml:lang="en-US" id="id_7861063_2025588_2_1">Debt Instrument [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentAxis" xlink:to="us-gaap_DebtInstrumentAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:label="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_lbl" xml:lang="en-US" id="id_7861063_2025392_1_1">Debt Instrument, Basis Spread on Variable Rate</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_lbl" xml:lang="en-US" id="id_7861063_2025392_2_1">Debt Instrument Basis Spread On Variable Rate</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1" xlink:to="us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:label="us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtInstrumentInterestRateStatedPercentage_lbl" xml:lang="en-US" id="id_7861063_2022149_1_1">Debt Instrument, Interest Rate, Stated Percentage</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_DebtInstrumentInterestRateStatedPercentage_lbl" xml:lang="en-US" id="id_7861063_2022149_2_1">Capital leases and Other long-term debt interest rates</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentInterestRateStatedPercentage" xlink:to="us-gaap_DebtInstrumentInterestRateStatedPercentage_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentLineItems" xlink:label="us-gaap_DebtInstrumentLineItems"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtInstrumentLineItems_lbl" xml:lang="en-US" id="id_7861063_2021687_1_1">Debt Instrument [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_DebtInstrumentLineItems_lbl" xml:lang="en-US" id="id_7861063_2021687_2_1">Debt Instrument [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentLineItems" xlink:to="us-gaap_DebtInstrumentLineItems_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="us-gaap_DebtInstrumentNameDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtInstrumentNameDomain_lbl" xml:lang="en-US" id="id_7861063_2035345_1_1">Debt Instrument, Name [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_DebtInstrumentNameDomain_lbl" xml:lang="en-US" id="id_7861063_2035345_2_1">Debt Instrument, Name [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentNameDomain" xlink:to="us-gaap_DebtInstrumentNameDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DebtInstrumentTable" xlink:label="us-gaap_DebtInstrumentTable"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DebtInstrumentTable_lbl" xml:lang="en-US" id="id_7861063_2023206_1_1">Schedule of Long-term Debt Instruments [Table]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_DebtInstrumentTable_lbl" xml:lang="en-US" id="id_7861063_2023206_2_1">Schedule of Long-term Debt Instruments [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DebtInstrumentTable" xlink:to="us-gaap_DebtInstrumentTable_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_DecreaseInFairValueOfReportingUnitsConsideredForImpairmentCalculation" xlink:label="pwr_DecreaseInFairValueOfReportingUnitsConsideredForImpairmentCalculation"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_DecreaseInFairValueOfReportingUnitsConsideredForImpairmentCalculation_lbl" xml:lang="en-US" id="id_7861063_2364611_3_1">Decrease in fair value of Reporting units considered, for impairment calculation.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_DecreaseInFairValueOfReportingUnitsConsideredForImpairmentCalculation_lbl" xml:lang="en-US" id="id_7861063_2364611_1_1">Decrease In Fair Value Of Reporting Units Considered For Impairment Calculation</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_DecreaseInFairValueOfReportingUnitsConsideredForImpairmentCalculation_lbl" xml:lang="en-US" id="id_7861063_2364611_2_1">Decrease in fair value of reporting units considered for impairment calculation</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_DecreaseInFairValueOfReportingUnitsConsideredForImpairmentCalculation" xlink:to="pwr_DecreaseInFairValueOfReportingUnitsConsideredForImpairmentCalculation_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DecreaseInRestrictedCash" xlink:label="us-gaap_DecreaseInRestrictedCash"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DecreaseInRestrictedCash_lbl" xml:lang="en-US" id="id_7861063_2028000_1_1">Decrease in Restricted Cash</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_DecreaseInRestrictedCash_lbl" xml:lang="en-US" id="id_7861063_2028000_2_1">Cash withdrawn from restricted cash</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DecreaseInRestrictedCash" xlink:to="us-gaap_DecreaseInRestrictedCash_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DecreaseInUnrecognizedTaxBenefitsIsReasonablyPossible" xlink:label="us-gaap_DecreaseInUnrecognizedTaxBenefitsIsReasonablyPossible"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DecreaseInUnrecognizedTaxBenefitsIsReasonablyPossible_lbl" xml:lang="en-US" id="id_7861063_2028001_1_1">Decrease in Unrecognized Tax Benefits is Reasonably Possible</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_DecreaseInUnrecognizedTaxBenefitsIsReasonablyPossible_lbl" xml:lang="en-US" id="id_7861063_2028001_2_1">Reasonably possible reduction to the balance of unrecognized tax benefits in succeeding 12 months</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DecreaseInUnrecognizedTaxBenefitsIsReasonablyPossible" xlink:to="us-gaap_DecreaseInUnrecognizedTaxBenefitsIsReasonablyPossible_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DeferredCompensationShareBasedArrangementsLiabilityCurrent" xlink:label="us-gaap_DeferredCompensationShareBasedArrangementsLiabilityCurrent"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredCompensationShareBasedArrangementsLiabilityCurrent_lbl" xml:lang="en-US" id="id_7861063_2024510_1_1">Deferred Compensation Share-based Arrangements, Liability, Current</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_DeferredCompensationShareBasedArrangementsLiabilityCurrent_lbl" xml:lang="en-US" id="id_7861063_2024510_2_1">Accrued liabilities under Compensation Plan</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredCompensationShareBasedArrangementsLiabilityCurrent" xlink:to="us-gaap_DeferredCompensationShareBasedArrangementsLiabilityCurrent_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit" xlink:label="us-gaap_DeferredIncomeTaxExpenseBenefit"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredIncomeTaxExpenseBenefit_lbl" xml:lang="en-US" id="id_7861063_2028007_1_1">Deferred Income Tax Expense (Benefit)</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_DeferredIncomeTaxExpenseBenefit_lbl" xml:lang="en-US" id="id_7861063_2028007_2_1">Deferred income tax provision (benefit)</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredIncomeTaxExpenseBenefit" xlink:to="us-gaap_DeferredIncomeTaxExpenseBenefit_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_DeferredTaxLiabilitiesGrossNoncurrent" xlink:label="us-gaap_DeferredTaxLiabilitiesGrossNoncurrent"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_DeferredTaxLiabilitiesGrossNoncurrent_lbl" xml:lang="en-US" id="id_7861063_2024097_1_1">Deferred Tax Liabilities, Gross, Noncurrent</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_DeferredTaxLiabilitiesGrossNoncurrent_lbl" xml:lang="en-US" id="id_7861063_2024097_2_1">Deferred income taxes</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_DeferredTaxLiabilitiesGrossNoncurrent" xlink:to="us-gaap_DeferredTaxLiabilitiesGrossNoncurrent_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_Depreciation" xlink:label="us-gaap_Depreciation"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_Depreciation_lbl" xml:lang="en-US" id="id_7861063_2025421_1_1">Depreciation</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_Depreciation_lbl" xml:lang="en-US" id="id_7861063_2025421_2_1">Depreciation</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Depreciation" xlink:to="us-gaap_Depreciation_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_DescriptionOfNewAccountingPronouncementsNotYetAdoptedPolicyTextBlock" xlink:label="pwr_DescriptionOfNewAccountingPronouncementsNotYetAdoptedPolicyTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_DescriptionOfNewAccountingPronouncementsNotYetAdoptedPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2137469_3_1">Description Of New Accounting Pronouncements Not Yet Adopted [Policy Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_DescriptionOfNewAccountingPronouncementsNotYetAdoptedPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2137469_1_1">Description Of New Accounting Pronouncements Not Yet Adopted [Policy Text Block]</label>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_DocumentAndEntityInformationAbstract_lbl" xml:lang="en-US" id="id_7861063_2260742_3_1">Document and entity information.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_DocumentAndEntityInformationAbstract_lbl" xml:lang="en-US" id="id_7861063_2260742_1_1">Document And Entity Information [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_DocumentAndEntityInformationAbstract_lbl" xml:lang="en-US" id="id_7861063_2260742_2_1">Document And Entity Information [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_DocumentAndEntityInformationAbstract" xlink:to="pwr_DocumentAndEntityInformationAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentFiscalPeriodFocus" xlink:label="dei_DocumentFiscalPeriodFocus"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_DocumentFiscalPeriodFocus_lbl" xml:lang="en-US" id="id_7861063_2025647_1_1">Document Fiscal Period Focus</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="dei_DocumentFiscalPeriodFocus_lbl" xml:lang="en-US" id="id_7861063_2025647_2_1">Document Fiscal Period Focus</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentFiscalPeriodFocus" xlink:to="dei_DocumentFiscalPeriodFocus_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentFiscalYearFocus" xlink:label="dei_DocumentFiscalYearFocus"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_DocumentFiscalYearFocus_lbl" xml:lang="en-US" id="id_7861063_2024142_1_1">Document Fiscal Year Focus</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="dei_DocumentFiscalYearFocus_lbl" xml:lang="en-US" id="id_7861063_2024142_2_1">Document Fiscal Year Focus</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentFiscalYearFocus" xlink:to="dei_DocumentFiscalYearFocus_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentInformationLineItems" xlink:label="dei_DocumentInformationLineItems"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_DocumentInformationLineItems_lbl" xml:lang="en-US" id="id_7861063_2022382_1_1">Document Information [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="dei_DocumentInformationLineItems_lbl" xml:lang="en-US" id="id_7861063_2022382_2_1">Document Information [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentInformationLineItems" xlink:to="dei_DocumentInformationLineItems_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentInformationTable" xlink:label="dei_DocumentInformationTable"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_DocumentInformationTable_lbl" xml:lang="en-US" id="id_7861063_2025014_1_1">Document Information [Table]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="dei_DocumentInformationTable_lbl" xml:lang="en-US" id="id_7861063_2025014_2_1">Document Information [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentInformationTable" xlink:to="dei_DocumentInformationTable_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentPeriodEndDate" xlink:label="dei_DocumentPeriodEndDate"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_DocumentPeriodEndDate_lbl" xml:lang="en-US" id="id_7861063_2023078_1_1">Document Period End Date</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="dei_DocumentPeriodEndDate_lbl" xml:lang="en-US" id="id_7861063_2023078_2_1">Document Period End Date</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentPeriodEndDate" xlink:to="dei_DocumentPeriodEndDate_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_DocumentType" xlink:label="dei_DocumentType"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_DocumentType_lbl" xml:lang="en-US" id="id_7861063_2022383_1_1">Document Type</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="dei_DocumentType_lbl" xml:lang="en-US" id="id_7861063_2022383_2_1">Document Type</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_DocumentType" xlink:to="dei_DocumentType_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_DomesticBankAccountsMember" xlink:label="pwr_DomesticBankAccountsMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_DomesticBankAccountsMember_lbl" xml:lang="en-US" id="id_7861063_2231885_3_1">Domestic Bank Accounts [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_DomesticBankAccountsMember_lbl" xml:lang="en-US" id="id_7861063_2231885_1_1">Domestic Bank Accounts [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_DomesticBankAccountsMember_lbl" xml:lang="en-US" id="id_7861063_2231885_2_1">Domestic Bank Accounts [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_DomesticBankAccountsMember" xlink:to="pwr_DomesticBankAccountsMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_DomesticJointVenturesMember" xlink:label="pwr_DomesticJointVenturesMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_DomesticJointVenturesMember_lbl" xml:lang="en-US" id="id_7861063_2343364_3_1">Domestic Joint Ventures [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_DomesticJointVenturesMember_lbl" xml:lang="en-US" id="id_7861063_2343364_1_1">Domestic Joint Ventures [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_DomesticJointVenturesMember_lbl" xml:lang="en-US" id="id_7861063_2343364_2_1">Domestic Joint Ventures [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_DomesticJointVenturesMember" xlink:to="pwr_DomesticJointVenturesMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EarningsPerShareAbstract" xlink:label="us-gaap_EarningsPerShareAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EarningsPerShareAbstract_lbl" xml:lang="en-US" id="id_7861063_2022611_1_1">Earnings Per Share [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_EarningsPerShareAbstract_lbl" xml:lang="en-US" id="id_7861063_2022611_2_1">Earnings Per Share [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareAbstract" xlink:to="us-gaap_EarningsPerShareAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EarningsPerShareBasicAndDiluted" xlink:label="us-gaap_EarningsPerShareBasicAndDiluted"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EarningsPerShareBasicAndDiluted_lbl" xml:lang="en-US" id="id_7861063_2023257_1_1">Earnings Per Share, Basic and Diluted</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_EarningsPerShareBasicAndDiluted_lbl" xml:lang="en-US" id="id_7861063_2023257_6_1">Net income attributable to common stock</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareBasicAndDiluted" xlink:to="us-gaap_EarningsPerShareBasicAndDiluted_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EarningsPerShareBasicAndDilutedAbstract" xlink:label="us-gaap_EarningsPerShareBasicAndDilutedAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EarningsPerShareBasicAndDilutedAbstract_lbl" xml:lang="en-US" id="id_7861063_2027160_1_1">Earnings Per Share, Basic and Diluted [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_EarningsPerShareBasicAndDilutedAbstract_lbl" xml:lang="en-US" id="id_7861063_2027160_2_1">Earnings per share attributable to common stock - basic and diluted:</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareBasicAndDilutedAbstract" xlink:to="us-gaap_EarningsPerShareBasicAndDilutedAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EarningsPerSharePolicyTextBlock" xlink:label="us-gaap_EarningsPerSharePolicyTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EarningsPerSharePolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2025461_1_1">Earnings Per Share, Policy [Policy Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_EarningsPerSharePolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2025461_2_1">Earnings Per Share</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerSharePolicyTextBlock" xlink:to="us-gaap_EarningsPerSharePolicyTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EarningsPerShareTextBlock" xlink:label="us-gaap_EarningsPerShareTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EarningsPerShareTextBlock_lbl" xml:lang="en-US" id="id_7861063_2027799_1_1">Earnings Per Share [Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_EarningsPerShareTextBlock_lbl" xml:lang="en-US" id="id_7861063_2027799_2_1">Per Share Information</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EarningsPerShareTextBlock" xlink:to="us-gaap_EarningsPerShareTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EffectOfExchangeRateOnCashAndCashEquivalents" xlink:label="us-gaap_EffectOfExchangeRateOnCashAndCashEquivalents"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EffectOfExchangeRateOnCashAndCashEquivalents_lbl" xml:lang="en-US" id="id_7861063_2023673_1_1">Effect of Exchange Rate on Cash and Cash Equivalents</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_EffectOfExchangeRateOnCashAndCashEquivalents_lbl" xml:lang="en-US" id="id_7861063_2023673_2_1">Effect of foreign exchange rate changes on cash and cash equivalents</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EffectOfExchangeRateOnCashAndCashEquivalents" xlink:to="us-gaap_EffectOfExchangeRateOnCashAndCashEquivalents_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_ElectricPowerDivisionMember" xlink:label="pwr_ElectricPowerDivisionMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ElectricPowerDivisionMember_lbl" xml:lang="en-US" id="id_7861063_2291499_3_1">Electric power division.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_ElectricPowerDivisionMember_lbl" xml:lang="en-US" id="id_7861063_2291499_1_1">Electric Power Division [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_ElectricPowerDivisionMember_lbl" xml:lang="en-US" id="id_7861063_2291499_2_1">Electric Power Division [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_ElectricPowerDivisionMember" xlink:to="pwr_ElectricPowerDivisionMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_ElectricPowerInfrastructureMember" xlink:label="pwr_ElectricPowerInfrastructureMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ElectricPowerInfrastructureMember_lbl" xml:lang="en-US" id="id_7861063_2078747_3_1">Electric Power Infrastructure [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_ElectricPowerInfrastructureMember_lbl" xml:lang="en-US" id="id_7861063_2078747_1_1">Electric Power Infrastructure [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_ElectricPowerInfrastructureMember_lbl" xml:lang="en-US" id="id_7861063_2078747_2_1">Electric Power Infrastructure Services [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_ElectricPowerInfrastructureMember" xlink:to="pwr_ElectricPowerInfrastructureMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_ElectricPowerInfrastructureServicesBusinessMember" xlink:label="pwr_ElectricPowerInfrastructureServicesBusinessMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ElectricPowerInfrastructureServicesBusinessMember_lbl" xml:lang="en-US" id="id_7861063_2294785_3_1">Electric Power Infrastructure Services Business [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_ElectricPowerInfrastructureServicesBusinessMember_lbl" xml:lang="en-US" id="id_7861063_2294785_1_1">Electric Power Infrastructure Services Business [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_ElectricPowerInfrastructureServicesBusinessMember_lbl" xml:lang="en-US" id="id_7861063_2294785_2_1">Electric Power Infrastructure Services Business [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_ElectricPowerInfrastructureServicesBusinessMember" xlink:to="pwr_ElectricPowerInfrastructureServicesBusinessMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EmployeeBenefitsAndShareBasedCompensation" xlink:label="us-gaap_EmployeeBenefitsAndShareBasedCompensation"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EmployeeBenefitsAndShareBasedCompensation_lbl" xml:lang="en-US" id="id_7861063_2022394_1_1">Employee Benefits and Share-based Compensation</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_EmployeeBenefitsAndShareBasedCompensation_lbl" xml:lang="en-US" id="id_7861063_2022394_2_1">Compensation costs</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EmployeeBenefitsAndShareBasedCompensation" xlink:to="us-gaap_EmployeeBenefitsAndShareBasedCompensation_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationCashFlowEffectCashUsedToSettleAwards" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationCashFlowEffectCashUsedToSettleAwards"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationCashFlowEffectCashUsedToSettleAwards_lbl" xml:lang="en-US" id="id_7861063_2023500_1_1">Employee Service Share-based Compensation, Cash Flow Effect, Cash Used to Settle Awards</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationCashFlowEffectCashUsedToSettleAwards_lbl" xml:lang="en-US" id="id_7861063_2023500_2_1">Payments to settle liabilities under compensation plan</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationCashFlowEffectCashUsedToSettleAwards" xlink:to="us-gaap_EmployeeServiceShareBasedCompensationCashFlowEffectCashUsedToSettleAwards_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_lbl" xml:lang="en-US" id="id_7861063_2024350_1_1">Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_lbl" xml:lang="en-US" id="id_7861063_2024350_2_1">Unrecognized compensation cost, related to unvested restricted stock, total</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized" xlink:to="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_lbl" xml:lang="en-US" id="id_7861063_2027807_1_1">Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_lbl" xml:lang="en-US" id="id_7861063_2027807_2_1">Expected weighted average period to recognize compensation cost on restricted stock and RSUs to be settled in stock (in years)</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:to="us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_EmployersLiabilityInsuranceClaimsDeductible" xlink:label="pwr_EmployersLiabilityInsuranceClaimsDeductible"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_EmployersLiabilityInsuranceClaimsDeductible_lbl" xml:lang="en-US" id="id_7861063_2055997_3_1">Employer's liability claims deductible amount per occurrence.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_EmployersLiabilityInsuranceClaimsDeductible_lbl" xml:lang="en-US" id="id_7861063_2055997_1_1">Employers Liability Insurance Claims Deductible</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_EmployersLiabilityInsuranceClaimsDeductible_lbl" xml:lang="en-US" id="id_7861063_2055997_2_1">Employer's liability claims subject to deductible per occurrence</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_EmployersLiabilityInsuranceClaimsDeductible" xlink:to="pwr_EmployersLiabilityInsuranceClaimsDeductible_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityCentralIndexKey" xlink:label="dei_EntityCentralIndexKey"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityCentralIndexKey_lbl" xml:lang="en-US" id="id_7861063_2022397_1_1">Entity Central Index Key</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="dei_EntityCentralIndexKey_lbl" xml:lang="en-US" id="id_7861063_2022397_2_1">Entity Central Index Key</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityCentralIndexKey" xlink:to="dei_EntityCentralIndexKey_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityCommonStockSharesOutstanding" xlink:label="dei_EntityCommonStockSharesOutstanding"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityCommonStockSharesOutstanding_lbl" xml:lang="en-US" id="id_7861063_2025882_1_1">Entity Common Stock, Shares Outstanding</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="dei_EntityCommonStockSharesOutstanding_lbl" xml:lang="en-US" id="id_7861063_2025882_2_1">Entity Common Stock, Shares Outstanding</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityCommonStockSharesOutstanding" xlink:to="dei_EntityCommonStockSharesOutstanding_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityDomain" xlink:label="dei_EntityDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityDomain_lbl" xml:lang="en-US" id="id_7861063_2026748_1_1">Entity [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="dei_EntityDomain_lbl" xml:lang="en-US" id="id_7861063_2026748_2_1">Entity [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityDomain" xlink:to="dei_EntityDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityFilerCategory" xlink:label="dei_EntityFilerCategory"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityFilerCategory_lbl" xml:lang="en-US" id="id_7861063_2025883_1_1">Entity Filer Category</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="dei_EntityFilerCategory_lbl" xml:lang="en-US" id="id_7861063_2025883_2_1">Entity Filer Category</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityFilerCategory" xlink:to="dei_EntityFilerCategory_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_EntityRegistrantName" xlink:label="dei_EntityRegistrantName"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_EntityRegistrantName_lbl" xml:lang="en-US" id="id_7861063_2021744_1_1">Entity Registrant Name</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="dei_EntityRegistrantName_lbl" xml:lang="en-US" id="id_7861063_2021744_2_1">Entity Registrant Name</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_EntityRegistrantName" xlink:to="dei_EntityRegistrantName_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EquityAbstract" xlink:label="us-gaap_EquityAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EquityAbstract_lbl" xml:lang="en-US" id="id_7861063_2025026_1_1">Equity [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_EquityAbstract_lbl" xml:lang="en-US" id="id_7861063_2025026_2_1">Equity [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EquityAbstract" xlink:to="us-gaap_EquityAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EquityClassOfTreasuryStockLineItems" xlink:label="us-gaap_EquityClassOfTreasuryStockLineItems"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EquityClassOfTreasuryStockLineItems_lbl" xml:lang="en-US" id="id_7861063_2025663_1_1">Equity, Class of Treasury Stock [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_EquityClassOfTreasuryStockLineItems_lbl" xml:lang="en-US" id="id_7861063_2025663_2_1">Equity, Class of Treasury Stock [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EquityClassOfTreasuryStockLineItems" xlink:to="us-gaap_EquityClassOfTreasuryStockLineItems_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="us-gaap_EquityComponentDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EquityComponentDomain_lbl" xml:lang="en-US" id="id_7861063_2027813_1_1">Equity Component [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_EquityComponentDomain_lbl" xml:lang="en-US" id="id_7861063_2027813_2_1">Equity Component [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EquityComponentDomain" xlink:to="us-gaap_EquityComponentDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage" xlink:label="us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_EquityMethodInvestmentOwnershipPercentage_lbl" xml:lang="en-US" id="id_7861063_2024573_1_1">Equity Method Investment, Ownership Percentage</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_EquityMethodInvestmentOwnershipPercentage_lbl" xml:lang="en-US" id="id_7861063_2024573_2_1">Equity method investment ownership</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_EquityMethodInvestmentOwnershipPercentage" xlink:to="us-gaap_EquityMethodInvestmentOwnershipPercentage_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_EscrowedFundsToCoverMultipleEmployerPlansLiabilityOfAcquiredCompany" xlink:label="pwr_EscrowedFundsToCoverMultipleEmployerPlansLiabilityOfAcquiredCompany"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_EscrowedFundsToCoverMultipleEmployerPlansLiabilityOfAcquiredCompany_lbl" xml:lang="en-US" id="id_7861063_2291008_3_1">Escrowed funds to cover multiple employer plans liability of acquired company.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_EscrowedFundsToCoverMultipleEmployerPlansLiabilityOfAcquiredCompany_lbl" xml:lang="en-US" id="id_7861063_2291008_1_1">Escrowed Funds To Cover Multiple Employer Plans Liability Of Acquired Company</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_EscrowedFundsToCoverMultipleEmployerPlansLiabilityOfAcquiredCompany_lbl" xml:lang="en-US" id="id_7861063_2291008_2_1">Cash proceeds deposited in Escrow account</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_EscrowedFundsToCoverMultipleEmployerPlansLiabilityOfAcquiredCompany" xlink:to="pwr_EscrowedFundsToCoverMultipleEmployerPlansLiabilityOfAcquiredCompany_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_EstimatedCostToCompleteBondedProjects" xlink:label="pwr_EstimatedCostToCompleteBondedProjects"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_EstimatedCostToCompleteBondedProjects_lbl" xml:lang="en-US" id="id_7861063_2259926_3_1">Estimated cost to complete bonded projects.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_EstimatedCostToCompleteBondedProjects_lbl" xml:lang="en-US" id="id_7861063_2259926_1_1">Estimated Cost To Complete Bonded Projects</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_EstimatedCostToCompleteBondedProjects_lbl" xml:lang="en-US" id="id_7861063_2259926_2_1">Estimated cost to complete bonded projects</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_EstimatedCostToCompleteBondedProjects" xlink:to="pwr_EstimatedCostToCompleteBondedProjects_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_ExcessOfBaseRateDomesticBorrowingsOnlyMember" xlink:label="pwr_ExcessOfBaseRateDomesticBorrowingsOnlyMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ExcessOfBaseRateDomesticBorrowingsOnlyMember_lbl" xml:lang="en-US" id="id_7861063_2067935_3_1">Excess Of Base Rate Domestic Borrowings Only [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_ExcessOfBaseRateDomesticBorrowingsOnlyMember_lbl" xml:lang="en-US" id="id_7861063_2067935_1_1">Excess Of Base Rate Domestic Borrowings Only [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_ExcessOfBaseRateDomesticBorrowingsOnlyMember_lbl" xml:lang="en-US" id="id_7861063_2067935_2_1">Excess of Base Rate Domestic Borrowings Only [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_ExcessOfBaseRateDomesticBorrowingsOnlyMember" xlink:to="pwr_ExcessOfBaseRateDomesticBorrowingsOnlyMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_ExcessOfEurocurrencyRateApplicableToDomesticBorrowingsOnlyMember" xlink:label="pwr_ExcessOfEurocurrencyRateApplicableToDomesticBorrowingsOnlyMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ExcessOfEurocurrencyRateApplicableToDomesticBorrowingsOnlyMember_lbl" xml:lang="en-US" id="id_7861063_2049875_3_1">Excess Of Eurocurrency Rate Applicable To Domestic Borrowings Only [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_ExcessOfEurocurrencyRateApplicableToDomesticBorrowingsOnlyMember_lbl" xml:lang="en-US" id="id_7861063_2049875_1_1">Excess Of Eurocurrency Rate Applicable To Domestic Borrowings Only [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_ExcessOfEurocurrencyRateApplicableToDomesticBorrowingsOnlyMember_lbl" xml:lang="en-US" id="id_7861063_2049875_2_1">Excess of Eurocurrency Rate Applicable to Domestic Borrowings Only [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_ExcessOfEurocurrencyRateApplicableToDomesticBorrowingsOnlyMember" xlink:to="pwr_ExcessOfEurocurrencyRateApplicableToDomesticBorrowingsOnlyMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_ExcessOfEuroCurrencyRateMember" xlink:label="pwr_ExcessOfEuroCurrencyRateMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ExcessOfEuroCurrencyRateMember_lbl" xml:lang="en-US" id="id_7861063_2097298_3_1">Excess Of Euro Currency Rate [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_ExcessOfEuroCurrencyRateMember_lbl" xml:lang="en-US" id="id_7861063_2097298_1_1">Excess Of Euro Currency Rate [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_ExcessOfEuroCurrencyRateMember_lbl" xml:lang="en-US" id="id_7861063_2097298_2_1">Excess of Euro Currency Rate [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_ExcessOfEuroCurrencyRateMember" xlink:to="pwr_ExcessOfEuroCurrencyRateMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_ExcessOfEuroCurrencyRateOfCreditAgreementForForeignBorrowingsMember" xlink:label="pwr_ExcessOfEuroCurrencyRateOfCreditAgreementForForeignBorrowingsMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ExcessOfEuroCurrencyRateOfCreditAgreementForForeignBorrowingsMember_lbl" xml:lang="en-US" id="id_7861063_2192317_3_1">Excess Of Euro Currency Rate Of Credit Agreement For Foreign Borrowings [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_ExcessOfEuroCurrencyRateOfCreditAgreementForForeignBorrowingsMember_lbl" xml:lang="en-US" id="id_7861063_2192317_1_1">Excess Of Euro Currency Rate Of Credit Agreement For Foreign Borrowings [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_ExcessOfEuroCurrencyRateOfCreditAgreementForForeignBorrowingsMember_lbl" xml:lang="en-US" id="id_7861063_2192317_2_1">Excess of Euro Currency Rate of Credit Agreement for Foreign Borrowings [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_ExcessOfEuroCurrencyRateOfCreditAgreementForForeignBorrowingsMember" xlink:to="pwr_ExcessOfEuroCurrencyRateOfCreditAgreementForForeignBorrowingsMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_ExcessOfFederalFundsRateMember" xlink:label="pwr_ExcessOfFederalFundsRateMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ExcessOfFederalFundsRateMember_lbl" xml:lang="en-US" id="id_7861063_2111393_3_1">Excess Of Federal Funds Rate [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_ExcessOfFederalFundsRateMember_lbl" xml:lang="en-US" id="id_7861063_2111393_1_1">Excess Of Federal Funds Rate [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_ExcessOfFederalFundsRateMember_lbl" xml:lang="en-US" id="id_7861063_2111393_2_1">Excess of Federal Funds Rate [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_ExcessOfFederalFundsRateMember" xlink:to="pwr_ExcessOfFederalFundsRateMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities" xlink:label="us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities_lbl" xml:lang="en-US" id="id_7861063_2022224_1_1">Excess Tax Benefit from Share-based Compensation, Financing Activities</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities_lbl" xml:lang="en-US" id="id_7861063_2022224_2_1">Tax impact of stock-based equity awards</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities" xlink:to="us-gaap_ExcessTaxBenefitFromShareBasedCompensationFinancingActivities_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ExcessTaxBenefitFromShareBasedCompensationOperatingActivities" xlink:label="us-gaap_ExcessTaxBenefitFromShareBasedCompensationOperatingActivities"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ExcessTaxBenefitFromShareBasedCompensationOperatingActivities_lbl" xml:lang="en-US" id="id_7861063_2027823_1_1">Excess Tax Benefit from Share-based Compensation, Operating Activities</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_ExcessTaxBenefitFromShareBasedCompensationOperatingActivities_lbl" xml:lang="en-US" id="id_7861063_2027823_14_1">Tax impact of stock-based equity awards</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ExcessTaxBenefitFromShareBasedCompensationOperatingActivities" xlink:to="us-gaap_ExcessTaxBenefitFromShareBasedCompensationOperatingActivities_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_ExchangeableSharesAssociatedWithSeriesFPreferredStockMember" xlink:label="pwr_ExchangeableSharesAssociatedWithSeriesFPreferredStockMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ExchangeableSharesAssociatedWithSeriesFPreferredStockMember_lbl" xml:lang="en-US" id="id_7861063_2133705_3_1">Exchangeable shares associated with series F preferred stock.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_ExchangeableSharesAssociatedWithSeriesFPreferredStockMember_lbl" xml:lang="en-US" id="id_7861063_2133705_1_1">Exchangeable Shares Associated With Series F Preferred Stock [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_ExchangeableSharesAssociatedWithSeriesFPreferredStockMember_lbl" xml:lang="en-US" id="id_7861063_2133705_2_1">Exchangeable Shares Associated with Series F Preferred Stock [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_ExchangeableSharesAssociatedWithSeriesFPreferredStockMember" xlink:to="pwr_ExchangeableSharesAssociatedWithSeriesFPreferredStockMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_ExchangeableSharesAssociatedWithSeriesGPreferredStockMember" xlink:label="pwr_ExchangeableSharesAssociatedWithSeriesGPreferredStockMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ExchangeableSharesAssociatedWithSeriesGPreferredStockMember_lbl" xml:lang="en-US" id="id_7861063_2206611_3_1">Exchangeable shares associated with series G preferred stock.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_ExchangeableSharesAssociatedWithSeriesGPreferredStockMember_lbl" xml:lang="en-US" id="id_7861063_2206611_1_1">Exchangeable Shares Associated With Series G Preferred Stock [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_ExchangeableSharesAssociatedWithSeriesGPreferredStockMember_lbl" xml:lang="en-US" id="id_7861063_2206611_2_1">Exchangeable Shares Associated with Series G Preferred Stock [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_ExchangeableSharesAssociatedWithSeriesGPreferredStockMember" xlink:to="pwr_ExchangeableSharesAssociatedWithSeriesGPreferredStockMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_ExchangeableSharesForCommonStockMember" xlink:label="pwr_ExchangeableSharesForCommonStockMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ExchangeableSharesForCommonStockMember_lbl" xml:lang="en-US" id="id_7861063_2334712_3_1">In connection with certain Canadian acquisitions, the former owners of the acquired companies received exchangeable shares of certain Canadian subsidiaries of Quanta, which may be exchanged at the option of the holders for Quanta common stock on a one-for-one basis. The holders of exchangeable shares can make an exchange only once in any calendar quarter and must exchange a minimum of either 50,000 shares or, if less, the total number of remaining exchangeable shares registered in the name of the holder making the request.</label>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ExchangeableSharesNotAssociatedWithPreferredStockMember_lbl" xml:lang="en-US" id="id_7861063_2161004_3_1">Exchangeable Shares Not Associated With Preferred Stock [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_ExchangeableSharesNotAssociatedWithPreferredStockMember_lbl" xml:lang="en-US" id="id_7861063_2161004_1_1">Exchangeable Shares Not Associated With Preferred Stock [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_ExchangeableSharesNotAssociatedWithPreferredStockMember_lbl" xml:lang="en-US" id="id_7861063_2161004_2_1">Exchangeable Shares Not Associated with Preferred Stock [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_ExchangeableSharesNotAssociatedWithPreferredStockMember" xlink:to="pwr_ExchangeableSharesNotAssociatedWithPreferredStockMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_ExchangeableStockSharesOutstanding" xlink:label="pwr_ExchangeableStockSharesOutstanding"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ExchangeableStockSharesOutstanding_lbl" xml:lang="en-US" id="id_7861063_2058642_3_1">Exchangeable Stock Shares Outstanding</label>
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    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_ExchangeableStockSharesOutstanding" xlink:to="pwr_ExchangeableStockSharesOutstanding_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FairValueOfFinancialInstrumentsPolicy" xlink:label="us-gaap_FairValueOfFinancialInstrumentsPolicy"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FairValueOfFinancialInstrumentsPolicy_lbl" xml:lang="en-US" id="id_7861063_2028091_1_1">Fair Value of Financial Instruments, Policy [Policy Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_FairValueOfFinancialInstrumentsPolicy_lbl" xml:lang="en-US" id="id_7861063_2028091_2_1">Fair Value Measurements</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FairValueOfFinancialInstrumentsPolicy" xlink:to="us-gaap_FairValueOfFinancialInstrumentsPolicy_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_FiberOpticLicensingMember" xlink:label="pwr_FiberOpticLicensingMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_FiberOpticLicensingMember_lbl" xml:lang="en-US" id="id_7861063_2225971_3_1">Fiber Optic Licensing.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_FiberOpticLicensingMember_lbl" xml:lang="en-US" id="id_7861063_2225971_1_1">Fiber Optic Licensing [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_FiberOpticLicensingMember_lbl" xml:lang="en-US" id="id_7861063_2225971_2_1">Fiber Optic Licensing Division [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_FiberOpticLicensingMember" xlink:to="pwr_FiberOpticLicensingMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedAndIndefiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTableTextBlock" xlink:label="us-gaap_FiniteLivedAndIndefiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTableTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FiniteLivedAndIndefiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTableTextBlock_lbl" xml:lang="en-US" id="id_7861063_2024193_1_1">Finite-Lived and Indefinite-Lived Intangible Assets Acquired as Part of Business Combination [Table Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_FiniteLivedAndIndefiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTableTextBlock_lbl" xml:lang="en-US" id="id_7861063_2024193_2_1">Estimated Fair Values of Identifiable Intangible Assets and Related Weighted Average Amortization</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedAndIndefiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTableTextBlock" xlink:to="us-gaap_FiniteLivedAndIndefiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTableTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_lbl" xml:lang="en-US" id="id_7861063_2029393_1_1">Finite-Lived Intangible Assets, Accumulated Amortization</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_lbl" xml:lang="en-US" id="id_7861063_2029393_2_1">Accumulated amortization on other intangible assets</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_lbl" xml:lang="en-US" id="id_7861063_2029393_14_1">Accumulated Amortization</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_lbl" xml:lang="en-US" id="id_7861063_2026353_1_1">Finite-Lived Intangible Assets, Amortization Expense, after Year Five</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_lbl" xml:lang="en-US" id="id_7861063_2026353_2_1">Thereafter</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_lbl" xml:lang="en-US" id="id_7861063_2025929_1_1">Finite-Lived Intangible Assets, Amortization Expense, Remainder of Fiscal Year</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_lbl" xml:lang="en-US" id="id_7861063_2025929_2_1">Remainder of 2016</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_lbl" xml:lang="en-US" id="id_7861063_2026354_1_1">Finite-Lived Intangible Assets, Amortization Expense, Year Five</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_lbl" xml:lang="en-US" id="id_7861063_2026354_2_1">2020</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_lbl" xml:lang="en-US" id="id_7861063_2025281_1_1">Finite-Lived Intangible Assets, Amortization Expense, Year Four</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_lbl" xml:lang="en-US" id="id_7861063_2025281_2_1">2019</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_lbl" xml:lang="en-US" id="id_7861063_2023313_1_1">Finite-Lived Intangible Assets, Amortization Expense, Year Three</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_lbl" xml:lang="en-US" id="id_7861063_2023313_2_1">2018</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_lbl" xml:lang="en-US" id="id_7861063_2023314_1_1">Finite-Lived Intangible Assets, Amortization Expense, Year Two</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_lbl" xml:lang="en-US" id="id_7861063_2023314_2_1">2017</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo" xlink:to="us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_lbl" xml:lang="en-US" id="id_7861063_2035448_1_1">Finite-Lived Intangible Assets by Major Class [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_lbl" xml:lang="en-US" id="id_7861063_2035448_2_1">Finite-Lived Intangible Assets by Major Class [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis" xlink:to="us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsGross" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross_lbl" xml:lang="en-US" id="id_7861063_2021793_1_1">Finite-Lived Intangible Assets, Gross</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_FiniteLivedIntangibleAssetsGross_lbl" xml:lang="en-US" id="id_7861063_2021793_2_1">Intangible assets subject to amortization</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetsGross" xlink:to="us-gaap_FiniteLivedIntangibleAssetsGross_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:label="us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FiniteLivedIntangibleAssetsLineItems_lbl" xml:lang="en-US" id="id_7861063_2024610_1_1">Finite-Lived Intangible Assets [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_FiniteLivedIntangibleAssetsLineItems_lbl" xml:lang="en-US" id="id_7861063_2024610_2_1">Finite-Lived Intangible Assets [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetsLineItems" xlink:to="us-gaap_FiniteLivedIntangibleAssetsLineItems_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_lbl" xml:lang="en-US" id="id_7861063_2027645_1_1">Finite-Lived Intangible Assets, Major Class Name [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_lbl" xml:lang="en-US" id="id_7861063_2027645_2_1">Finite-Lived Intangible Assets, Major Class Name [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain" xlink:to="us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetsNet" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" xml:lang="en-US" id="id_7861063_2031338_1_1">Finite-Lived Intangible Assets, Net</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_FiniteLivedIntangibleAssetsNet_lbl" xml:lang="en-US" id="id_7861063_2031338_6_1">Intangible Assets, Net</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetsNet" xlink:to="us-gaap_FiniteLivedIntangibleAssetsNet_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:label="us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_FiniteLivedIntangibleAssetUsefulLife_lbl" xml:lang="en-US" id="id_7861063_2034841_1_1">Finite-Lived Intangible Asset, Useful Life</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_FiniteLivedIntangibleAssetUsefulLife_lbl" xml:lang="en-US" id="id_7861063_2034841_2_1">Remaining Weighted Average Amortization Period in Years</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_FiniteLivedIntangibleAssetUsefulLife" xlink:to="us-gaap_FiniteLivedIntangibleAssetUsefulLife_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_ForecastedReturnsOfCapitalFromUnconsolidatedAffiliatesInOneYear" xlink:label="pwr_ForecastedReturnsOfCapitalFromUnconsolidatedAffiliatesInOneYear"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ForecastedReturnsOfCapitalFromUnconsolidatedAffiliatesInOneYear_lbl" xml:lang="en-US" id="id_7861063_2114326_3_1">Forecasted returns of capital from unconsolidated affiliates in two years.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_ForecastedReturnsOfCapitalFromUnconsolidatedAffiliatesInOneYear_lbl" xml:lang="en-US" id="id_7861063_2114326_1_1">Forecasted Returns Of Capital From Unconsolidated Affiliates In One Year</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_ForecastedReturnsOfCapitalFromUnconsolidatedAffiliatesInOneYear_lbl" xml:lang="en-US" id="id_7861063_2114326_2_1">Return of capital from unconsolidated affiliates anticipated for 2017</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_ForecastedReturnsOfCapitalFromUnconsolidatedAffiliatesInOneYear" xlink:to="pwr_ForecastedReturnsOfCapitalFromUnconsolidatedAffiliatesInOneYear_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_ForeignBankAccountsMember" xlink:label="pwr_ForeignBankAccountsMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ForeignBankAccountsMember_lbl" xml:lang="en-US" id="id_7861063_2227816_3_1">Foreign Bank Accounts [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_ForeignBankAccountsMember_lbl" xml:lang="en-US" id="id_7861063_2227816_1_1">Foreign Bank Accounts [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_ForeignBankAccountsMember_lbl" xml:lang="en-US" id="id_7861063_2227816_2_1">Foreign Bank Accounts [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_ForeignBankAccountsMember" xlink:to="pwr_ForeignBankAccountsMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ForeignCurrencyTransactionGainLossUnrealized" xlink:label="us-gaap_ForeignCurrencyTransactionGainLossUnrealized"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ForeignCurrencyTransactionGainLossUnrealized_lbl" xml:lang="en-US" id="id_7861063_2027650_1_1">Foreign Currency Transaction Gain (Loss), Unrealized</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_ForeignCurrencyTransactionGainLossUnrealized_lbl" xml:lang="en-US" id="id_7861063_2027650_14_1">Foreign currency loss</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ForeignCurrencyTransactionGainLossUnrealized" xlink:to="us-gaap_ForeignCurrencyTransactionGainLossUnrealized_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ForeignCurrencyTransactionsAndTranslationsPolicyTextBlock" xlink:label="us-gaap_ForeignCurrencyTransactionsAndTranslationsPolicyTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ForeignCurrencyTransactionsAndTranslationsPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2027002_1_1">Foreign Currency Transactions and Translations Policy [Policy Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ForeignCurrencyTransactionsAndTranslationsPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2027002_2_1">Functional Currency and Translation of Financial Statements</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ForeignCurrencyTransactionsAndTranslationsPolicyTextBlock" xlink:to="us-gaap_ForeignCurrencyTransactionsAndTranslationsPolicyTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_ForeignOperationsMember" xlink:label="pwr_ForeignOperationsMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ForeignOperationsMember_lbl" xml:lang="en-US" id="id_7861063_2057752_3_1">Foreign Operations [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_ForeignOperationsMember_lbl" xml:lang="en-US" id="id_7861063_2057752_1_1">Foreign Operations [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_ForeignOperationsMember_lbl" xml:lang="en-US" id="id_7861063_2057752_2_1">Foreign Operations [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_ForeignOperationsMember" xlink:to="pwr_ForeignOperationsMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_FourthAmendedAndRestatedMember" xlink:label="pwr_FourthAmendedAndRestatedMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_FourthAmendedAndRestatedMember_lbl" xml:lang="en-US" id="id_7861063_2393671_3_1">Fourth amended and restated.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_FourthAmendedAndRestatedMember_lbl" xml:lang="en-US" id="id_7861063_2393671_1_1">Fourth Amended And Restated [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_FourthAmendedAndRestatedMember_lbl" xml:lang="en-US" id="id_7861063_2393671_2_1">Current Credit Agreement [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_FourthAmendedAndRestatedMember" xlink:to="pwr_FourthAmendedAndRestatedMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GainLossOnSaleOfPropertyPlantEquipment" xlink:label="us-gaap_GainLossOnSaleOfPropertyPlantEquipment"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GainLossOnSaleOfPropertyPlantEquipment_lbl" xml:lang="en-US" id="id_7861063_2033049_1_1">Gain (Loss) on Disposition of Property Plant Equipment</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_GainLossOnSaleOfPropertyPlantEquipment_lbl" xml:lang="en-US" id="id_7861063_2033049_14_1">(Gain) loss on sale of property and equipment</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GainLossOnSaleOfPropertyPlantEquipment" xlink:to="us-gaap_GainLossOnSaleOfPropertyPlantEquipment_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_GeneralLiabilityInsuranceClaimsDeductible" xlink:label="pwr_GeneralLiabilityInsuranceClaimsDeductible"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_GeneralLiabilityInsuranceClaimsDeductible_lbl" xml:lang="en-US" id="id_7861063_2119060_3_1">General liability insurance claims deductible amount per occurrence.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_GeneralLiabilityInsuranceClaimsDeductible_lbl" xml:lang="en-US" id="id_7861063_2119060_1_1">General Liability Insurance Claims Deductible</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_GeneralLiabilityInsuranceClaimsDeductible_lbl" xml:lang="en-US" id="id_7861063_2119060_2_1">General liability insurance claims deductible</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_GeneralLiabilityInsuranceClaimsDeductible" xlink:to="pwr_GeneralLiabilityInsuranceClaimsDeductible_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_Goodwill" xlink:label="us-gaap_Goodwill"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_Goodwill_lbl" xml:lang="en-US" id="id_7861063_2031370_1_1">Goodwill</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_Goodwill_lbl" xml:lang="en-US" id="id_7861063_2031370_4_1">Goodwill, ending balance</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_Goodwill_lbl" xml:lang="en-US" id="id_7861063_2031370_5_1">Goodwill, beginning balance</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_Goodwill_lbl" xml:lang="en-US" id="id_7861063_2031370_2_1">Goodwill</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Goodwill" xlink:to="us-gaap_Goodwill_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GoodwillAcquiredDuringPeriod" xlink:label="us-gaap_GoodwillAcquiredDuringPeriod"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GoodwillAcquiredDuringPeriod_lbl" xml:lang="en-US" id="id_7861063_2034625_1_1">Goodwill, Acquired During Period</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_GoodwillAcquiredDuringPeriod_lbl" xml:lang="en-US" id="id_7861063_2034625_2_1">Goodwill</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_GoodwillAcquiredDuringPeriod_lbl" xml:lang="en-US" id="id_7861063_2034625_12_1">Goodwill acquired</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GoodwillAcquiredDuringPeriod" xlink:to="us-gaap_GoodwillAcquiredDuringPeriod_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract" xlink:label="us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract_lbl" xml:lang="en-US" id="id_7861063_2024406_1_1">Goodwill and Intangible Assets Disclosure [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract_lbl" xml:lang="en-US" id="id_7861063_2024406_2_1">Goodwill and Intangible Assets Disclosure [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract" xlink:to="us-gaap_GoodwillAndIntangibleAssetsDisclosureAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock" xlink:label="us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock_lbl" xml:lang="en-US" id="id_7861063_2022883_1_1">Goodwill and Intangible Assets Disclosure [Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock_lbl" xml:lang="en-US" id="id_7861063_2022883_2_1">Goodwill and Other Intangible Assets</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock" xlink:to="us-gaap_GoodwillAndIntangibleAssetsDisclosureTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GoodwillAndIntangibleAssetsPolicyTextBlock" xlink:label="us-gaap_GoodwillAndIntangibleAssetsPolicyTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GoodwillAndIntangibleAssetsPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2021808_1_1">Goodwill and Intangible Assets, Policy [Policy Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_GoodwillAndIntangibleAssetsPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2021808_2_1">Goodwill and Other Intangibles</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GoodwillAndIntangibleAssetsPolicyTextBlock" xlink:to="us-gaap_GoodwillAndIntangibleAssetsPolicyTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GoodwillForeignCurrencyTranslationGainLoss" xlink:label="us-gaap_GoodwillForeignCurrencyTranslationGainLoss"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GoodwillForeignCurrencyTranslationGainLoss_lbl" xml:lang="en-US" id="id_7861063_2032225_1_1">Goodwill, Foreign Currency Translation Gain (Loss)</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_GoodwillForeignCurrencyTranslationGainLoss_lbl" xml:lang="en-US" id="id_7861063_2032225_14_1">Foreign currency translation adjustments</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GoodwillForeignCurrencyTranslationGainLoss" xlink:to="us-gaap_GoodwillForeignCurrencyTranslationGainLoss_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GoodwillGross" xlink:label="us-gaap_GoodwillGross"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GoodwillGross_lbl" xml:lang="en-US" id="id_7861063_2021809_1_1">Goodwill, Gross</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodEndLabel" xlink:label="us-gaap_GoodwillGross_lbl" xml:lang="en-US" id="id_7861063_2021809_4_1">Goodwill gross, ending balance</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/periodStartLabel" xlink:label="us-gaap_GoodwillGross_lbl" xml:lang="en-US" id="id_7861063_2021809_5_1">Goodwill gross, beginning balance</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GoodwillGross" xlink:to="us-gaap_GoodwillGross_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GoodwillImpairedAccumulatedImpairmentLoss" xlink:label="us-gaap_GoodwillImpairedAccumulatedImpairmentLoss"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GoodwillImpairedAccumulatedImpairmentLoss_lbl" xml:lang="en-US" id="id_7861063_2034626_1_1">Goodwill, Impaired, Accumulated Impairment Loss</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_GoodwillImpairedAccumulatedImpairmentLoss_lbl" xml:lang="en-US" id="id_7861063_2034626_14_1">Accumulated impairment</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GoodwillImpairedAccumulatedImpairmentLoss" xlink:to="us-gaap_GoodwillImpairedAccumulatedImpairmentLoss_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GoodwillImpairmentLoss" xlink:label="us-gaap_GoodwillImpairmentLoss"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GoodwillImpairmentLoss_lbl" xml:lang="en-US" id="id_7861063_2034628_1_1">Goodwill, Impairment Loss</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_GoodwillImpairmentLoss_lbl" xml:lang="en-US" id="id_7861063_2034628_2_1">Non-cash charge for impairment of goodwill</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GoodwillImpairmentLoss" xlink:to="us-gaap_GoodwillImpairmentLoss_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GoodwillLineItems" xlink:label="us-gaap_GoodwillLineItems"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GoodwillLineItems_lbl" xml:lang="en-US" id="id_7861063_2022884_1_1">Goodwill [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_GoodwillLineItems_lbl" xml:lang="en-US" id="id_7861063_2022884_2_1">Goodwill [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GoodwillLineItems" xlink:to="us-gaap_GoodwillLineItems_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GoodwillPurchaseAccountingAdjustments" xlink:label="us-gaap_GoodwillPurchaseAccountingAdjustments"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GoodwillPurchaseAccountingAdjustments_lbl" xml:lang="en-US" id="id_7861063_2035461_1_1">Goodwill, Purchase Accounting Adjustments</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_GoodwillPurchaseAccountingAdjustments_lbl" xml:lang="en-US" id="id_7861063_2035461_2_1">Purchase price allocation adjustments</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GoodwillPurchaseAccountingAdjustments" xlink:to="us-gaap_GoodwillPurchaseAccountingAdjustments_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GrossProfit" xlink:label="us-gaap_GrossProfit"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GrossProfit_lbl" xml:lang="en-US" id="id_7861063_2029419_1_1">Gross Profit</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_GrossProfit_lbl" xml:lang="en-US" id="id_7861063_2029419_6_1">Gross profit</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GrossProfit" xlink:to="us-gaap_GrossProfit_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_GuaranteeObligationsMaximumExposure" xlink:label="us-gaap_GuaranteeObligationsMaximumExposure"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_GuaranteeObligationsMaximumExposure_lbl" xml:lang="en-US" id="id_7861063_2024410_1_1">Guarantor Obligations, Maximum Exposure, Undiscounted</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_GuaranteeObligationsMaximumExposure_lbl" xml:lang="en-US" id="id_7861063_2024410_2_1">Maximum guaranteed residual value</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_GuaranteeObligationsMaximumExposure" xlink:to="us-gaap_GuaranteeObligationsMaximumExposure_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_HealthCareDeductible" xlink:label="pwr_HealthCareDeductible"/>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_InsuranceSettlementsReceivableCurrent_lbl" xml:lang="en-US" id="id_7861063_2029208_1_1">Insurance Settlements Receivable, Current</label>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_IntangibleAssetsDisclosureAbstract_lbl" xml:lang="en-US" id="id_7861063_2326881_3_1">Intangible Assets Disclosure [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_IntangibleAssetsDisclosureAbstract_lbl" xml:lang="en-US" id="id_7861063_2326881_1_1">Intangible Assets Disclosure [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_IntangibleAssetsDisclosureAbstract_lbl" xml:lang="en-US" id="id_7861063_2326881_2_1">Intangible Assets Disclosure [Abstract]</label>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_InventoryNet_lbl" xml:lang="en-US" id="id_7861063_2030508_1_1">Inventory, Net</label>
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    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InventoryNet" xlink:to="us-gaap_InventoryNet_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_InvestmentAxis" xlink:label="invest_InvestmentAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="invest_InvestmentAxis_lbl" xml:lang="en-US" id="id_7861063_2030755_1_1">Investment [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="invest_InvestmentAxis_lbl" xml:lang="en-US" id="id_7861063_2030755_2_1">Investment [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="invest_InvestmentAxis" xlink:to="invest_InvestmentAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_InvestmentDomain" xlink:label="invest_InvestmentDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="invest_InvestmentDomain_lbl" xml:lang="en-US" id="id_7861063_2028983_1_1">Investment [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="invest_InvestmentDomain_lbl" xml:lang="en-US" id="id_7861063_2028983_2_1">Investment [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="invest_InvestmentDomain" xlink:to="invest_InvestmentDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_InvestmentIncomeInterest" xlink:label="us-gaap_InvestmentIncomeInterest"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_InvestmentIncomeInterest_lbl" xml:lang="en-US" id="id_7861063_2033310_1_1">Investment Income, Interest</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_InvestmentIncomeInterest_lbl" xml:lang="en-US" id="id_7861063_2033310_2_1">Interest income</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_InvestmentIncomeInterest" xlink:to="us-gaap_InvestmentIncomeInterest_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_InvestmentsInAffiliatesAndOtherEntitiesPolicyTextBlock" xlink:label="pwr_InvestmentsInAffiliatesAndOtherEntitiesPolicyTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_InvestmentsInAffiliatesAndOtherEntitiesPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2172746_3_1">Investments in affiliates and other entities policy.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_InvestmentsInAffiliatesAndOtherEntitiesPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2172746_1_1">Investments In Affiliates And Other Entities [Policy Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_InvestmentsInAffiliatesAndOtherEntitiesPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2172746_2_1">Investments in Affiliates and Other Entities</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_InvestmentsInAffiliatesAndOtherEntitiesPolicyTextBlock" xlink:to="pwr_InvestmentsInAffiliatesAndOtherEntitiesPolicyTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_InvestmentsInJointVenturesMember" xlink:label="pwr_InvestmentsInJointVenturesMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_InvestmentsInJointVenturesMember_lbl" xml:lang="en-US" id="id_7861063_2312812_3_1">Investments In Joint Ventures [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_InvestmentsInJointVenturesMember_lbl" xml:lang="en-US" id="id_7861063_2312812_1_1">Investments In Joint Ventures [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_InvestmentsInJointVenturesMember_lbl" xml:lang="en-US" id="id_7861063_2312812_2_1">Investments in Joint Ventures [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_InvestmentsInJointVenturesMember" xlink:to="pwr_InvestmentsInJointVenturesMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LeaseAndRentalExpense" xlink:label="us-gaap_LeaseAndRentalExpense"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LeaseAndRentalExpense_lbl" xml:lang="en-US" id="id_7861063_2028813_1_1">Operating Leases, Rent Expense</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LeaseAndRentalExpense_lbl" xml:lang="en-US" id="id_7861063_2028813_2_1">Rent expense related to operating leases</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LeaseAndRentalExpense" xlink:to="us-gaap_LeaseAndRentalExpense_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LeasesAbstract" xlink:label="us-gaap_LeasesAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LeasesAbstract_lbl" xml:lang="en-US" id="id_7861063_2030961_1_1">Leases [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LeasesAbstract_lbl" xml:lang="en-US" id="id_7861063_2030961_2_1">Leases [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LeasesAbstract" xlink:to="us-gaap_LeasesAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LegalCostsPolicyTextBlock" xlink:label="us-gaap_LegalCostsPolicyTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LegalCostsPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2030099_1_1">Legal Costs, Policy [Policy Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LegalCostsPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2030099_2_1">Litigation Costs and Reserves</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LegalCostsPolicyTextBlock" xlink:to="us-gaap_LegalCostsPolicyTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_LegalEntityAxis" xlink:label="dei_LegalEntityAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_LegalEntityAxis_lbl" xml:lang="en-US" id="id_7861063_2033330_1_1">Legal Entity [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="dei_LegalEntityAxis_lbl" xml:lang="en-US" id="id_7861063_2033330_2_1">Legal Entity [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="dei_LegalEntityAxis" xlink:to="dei_LegalEntityAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_LengthOfTransmissionLine" xlink:label="pwr_LengthOfTransmissionLine"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_LengthOfTransmissionLine_lbl" xml:lang="en-US" id="id_7861063_2123240_3_1">Length of transmission line.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_LengthOfTransmissionLine_lbl" xml:lang="en-US" id="id_7861063_2123240_1_1">Length Of Transmission Line</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_LengthOfTransmissionLine_lbl" xml:lang="en-US" id="id_7861063_2123240_2_1">Length of electrical transmission line to be constructed under contract</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_LengthOfTransmissionLine" xlink:to="pwr_LengthOfTransmissionLine_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_LettersOfCreditAndBankGuaranteesMember" xlink:label="pwr_LettersOfCreditAndBankGuaranteesMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_LettersOfCreditAndBankGuaranteesMember_lbl" xml:lang="en-US" id="id_7861063_2140464_3_1">The Letters Of Credit and Bank Guarantees.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_LettersOfCreditAndBankGuaranteesMember_lbl" xml:lang="en-US" id="id_7861063_2140464_1_1">Letters Of Credit and Bank Guarantees [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_LettersOfCreditAndBankGuaranteesMember_lbl" xml:lang="en-US" id="id_7861063_2140464_2_1">Letters Of Credit and Bank Guarantees [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_LettersOfCreditAndBankGuaranteesMember" xlink:to="pwr_LettersOfCreditAndBankGuaranteesMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LettersOfCreditOutstandingAmount" xlink:label="us-gaap_LettersOfCreditOutstandingAmount"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LettersOfCreditOutstandingAmount_lbl" xml:lang="en-US" id="id_7861063_2033331_1_1">Letters of Credit Outstanding, Amount</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LettersOfCreditOutstandingAmount_lbl" xml:lang="en-US" id="id_7861063_2033331_2_1">Letters of credit and bank guarantees under the credit facility</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LettersOfCreditOutstandingAmount" xlink:to="us-gaap_LettersOfCreditOutstandingAmount_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_Liabilities" xlink:label="us-gaap_Liabilities"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_Liabilities_lbl" xml:lang="en-US" id="id_7861063_2031177_1_1">Liabilities</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_Liabilities_lbl" xml:lang="en-US" id="id_7861063_2031177_6_1">Total liabilities</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Liabilities" xlink:to="us-gaap_Liabilities_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquity" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xml:lang="en-US" id="id_7861063_2031178_1_1">Liabilities and Equity</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_LiabilitiesAndStockholdersEquity_lbl" xml:lang="en-US" id="id_7861063_2031178_6_1">Total liabilities and equity</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesAndStockholdersEquity" xlink:to="us-gaap_LiabilitiesAndStockholdersEquity_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" xml:lang="en-US" id="id_7861063_2034137_1_1">Liabilities and Equity [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl" xml:lang="en-US" id="id_7861063_2034137_2_1">LIABILITIES AND EQUITY</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesAndStockholdersEquityAbstract" xlink:to="us-gaap_LiabilitiesAndStockholdersEquityAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LiabilitiesCurrent" xlink:label="us-gaap_LiabilitiesCurrent"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesCurrent_lbl" xml:lang="en-US" id="id_7861063_2031608_1_1">Liabilities, Current</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_LiabilitiesCurrent_lbl" xml:lang="en-US" id="id_7861063_2031608_6_1">Total current liabilities</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesCurrent" xlink:to="us-gaap_LiabilitiesCurrent_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LiabilitiesCurrentAbstract" xlink:label="us-gaap_LiabilitiesCurrentAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesCurrentAbstract_lbl" xml:lang="en-US" id="id_7861063_2028362_1_1">Liabilities, Current [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LiabilitiesCurrentAbstract_lbl" xml:lang="en-US" id="id_7861063_2028362_2_1">Current Liabilities:</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesCurrentAbstract" xlink:to="us-gaap_LiabilitiesCurrentAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationCurrent" xlink:label="us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationCurrent"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationCurrent_lbl" xml:lang="en-US" id="id_7861063_2033926_1_1">Disposal Group, Including Discontinued Operation, Liabilities, Current</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationCurrent_lbl" xml:lang="en-US" id="id_7861063_2033926_2_1">Current liabilities of discontinued operations</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationCurrent_lbl" xml:lang="en-US" id="id_7861063_2033926_12_1">Total current liabilities of discontinued operations</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationCurrent" xlink:to="us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationCurrent_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationCurrentAbstract" xlink:label="us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationCurrentAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationCurrentAbstract_lbl" xml:lang="en-US" id="id_7861063_2029237_1_1">Disposal Group, Including Discontinued Operation, Liabilities, Current [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationCurrentAbstract_lbl" xml:lang="en-US" id="id_7861063_2029237_2_1">Current liabilities:</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationCurrentAbstract" xlink:to="us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationCurrentAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationNoncurrent" xlink:label="us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationNoncurrent"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationNoncurrent_lbl" xml:lang="en-US" id="id_7861063_2032299_1_1">Disposal Group, Including Discontinued Operation, Liabilities, Noncurrent</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationNoncurrent_lbl" xml:lang="en-US" id="id_7861063_2032299_2_1">Non-current liabilities of discontinued operations</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationNoncurrent" xlink:to="us-gaap_LiabilitiesOfDisposalGroupIncludingDiscontinuedOperationNoncurrent_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense" xlink:label="us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_lbl" xml:lang="en-US" id="id_7861063_2031456_1_1">Liability for Claims and Claims Adjustment Expense</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_lbl" xml:lang="en-US" id="id_7861063_2031456_2_1">Gross amount accrued for insurance claims</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense" xlink:to="us-gaap_LiabilityForClaimsAndClaimsAdjustmentExpense_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCredit" xlink:label="us-gaap_LineOfCredit"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LineOfCredit_lbl" xml:lang="en-US" id="id_7861063_2034338_1_1">Long-term Line of Credit</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LineOfCredit_lbl" xml:lang="en-US" id="id_7861063_2034338_2_1">Amount borrowed under the credit facility</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_LineOfCredit_lbl" xml:lang="en-US" id="id_7861063_2034338_12_1">Borrowings under credit facility</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LineOfCredit" xlink:to="us-gaap_LineOfCredit_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityAbstract" xlink:label="us-gaap_LineOfCreditFacilityAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LineOfCreditFacilityAbstract_lbl" xml:lang="en-US" id="id_7861063_2031190_1_1">Line of Credit Facility [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LineOfCreditFacilityAbstract_lbl" xml:lang="en-US" id="id_7861063_2031190_2_1">Line of Credit Facility [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LineOfCreditFacilityAbstract" xlink:to="us-gaap_LineOfCreditFacilityAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityAverageOutstandingAmount" xlink:label="us-gaap_LineOfCreditFacilityAverageOutstandingAmount"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LineOfCreditFacilityAverageOutstandingAmount_lbl" xml:lang="en-US" id="id_7861063_2032473_1_1">Line of Credit Facility, Average Outstanding Amount</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LineOfCreditFacilityAverageOutstandingAmount_lbl" xml:lang="en-US" id="id_7861063_2032473_2_1">Average daily amount outstanding under the credit facility</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LineOfCreditFacilityAverageOutstandingAmount" xlink:to="us-gaap_LineOfCreditFacilityAverageOutstandingAmount_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityExpirationDate1" xlink:label="us-gaap_LineOfCreditFacilityExpirationDate1"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LineOfCreditFacilityExpirationDate1_lbl" xml:lang="en-US" id="id_7861063_2030975_1_1">Line of Credit Facility, Expiration Date</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LineOfCreditFacilityExpirationDate1_lbl" xml:lang="en-US" id="id_7861063_2030975_2_1">Maturity date of senior secured revolving credit facility</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LineOfCreditFacilityExpirationDate1" xlink:to="us-gaap_LineOfCreditFacilityExpirationDate1_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityLineItems" xlink:label="us-gaap_LineOfCreditFacilityLineItems"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LineOfCreditFacilityLineItems_lbl" xml:lang="en-US" id="id_7861063_2032712_1_1">Line of Credit Facility [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LineOfCreditFacilityLineItems_lbl" xml:lang="en-US" id="id_7861063_2032712_2_1">Line of Credit Facility [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LineOfCreditFacilityLineItems" xlink:to="us-gaap_LineOfCreditFacilityLineItems_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumAmountOutstandingDuringPeriod" xlink:label="us-gaap_LineOfCreditFacilityMaximumAmountOutstandingDuringPeriod"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LineOfCreditFacilityMaximumAmountOutstandingDuringPeriod_lbl" xml:lang="en-US" id="id_7861063_2029691_1_1">Line of Credit Facility, Maximum Amount Outstanding During Period</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LineOfCreditFacilityMaximumAmountOutstandingDuringPeriod_lbl" xml:lang="en-US" id="id_7861063_2029691_2_1">Maximum amount outstanding during the period</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LineOfCreditFacilityMaximumAmountOutstandingDuringPeriod" xlink:to="us-gaap_LineOfCreditFacilityMaximumAmountOutstandingDuringPeriod_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_lbl" xml:lang="en-US" id="id_7861063_2032317_1_1">Line of Credit Facility, Maximum Borrowing Capacity</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_lbl" xml:lang="en-US" id="id_7861063_2032317_2_1">Senior secured revolving credit facility</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:to="us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity" xlink:label="us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_lbl" xml:lang="en-US" id="id_7861063_2032062_1_1">Line of Credit Facility, Remaining Borrowing Capacity</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_lbl" xml:lang="en-US" id="id_7861063_2032062_2_1">Credit facility available for revolving loans or issuing new letters of credit</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity" xlink:to="us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityTable" xlink:label="us-gaap_LineOfCreditFacilityTable"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LineOfCreditFacilityTable_lbl" xml:lang="en-US" id="id_7861063_2040957_1_1">Line of Credit Facility [Table]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LineOfCreditFacilityTable_lbl" xml:lang="en-US" id="id_7861063_2040957_2_1">Line of Credit Facility [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LineOfCreditFacilityTable" xlink:to="us-gaap_LineOfCreditFacilityTable_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage" xlink:label="us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_lbl" xml:lang="en-US" id="id_7861063_2030551_1_1">Line of Credit Facility, Unused Capacity, Commitment Fee Percentage</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_lbl" xml:lang="en-US" id="id_7861063_2030551_2_1">Commitment fee</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage" xlink:to="us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LitigationCaseAxis" xlink:label="us-gaap_LitigationCaseAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LitigationCaseAxis_lbl" xml:lang="en-US" id="id_7861063_2029493_1_1">Litigation Case [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LitigationCaseAxis_lbl" xml:lang="en-US" id="id_7861063_2029493_2_1">Litigation Case [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LitigationCaseAxis" xlink:to="us-gaap_LitigationCaseAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LitigationCaseTypeDomain" xlink:label="us-gaap_LitigationCaseTypeDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LitigationCaseTypeDomain_lbl" xml:lang="en-US" id="id_7861063_2030977_1_1">Litigation Case [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LitigationCaseTypeDomain_lbl" xml:lang="en-US" id="id_7861063_2030977_2_1">Litigation Case [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LitigationCaseTypeDomain" xlink:to="us-gaap_LitigationCaseTypeDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermDebt" xlink:label="us-gaap_LongTermDebt"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LongTermDebt_lbl" xml:lang="en-US" id="id_7861063_2029027_1_1">Long-term Debt</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LongTermDebt_lbl" xml:lang="en-US" id="id_7861063_2029027_2_1">Total long-term debt obligations</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_LongTermDebt_lbl" xml:lang="en-US" id="id_7861063_2029027_6_1">Total long-term debt obligations</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebt" xlink:to="us-gaap_LongTermDebt_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermDebtCurrent" xlink:label="us-gaap_LongTermDebtCurrent"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LongTermDebtCurrent_lbl" xml:lang="en-US" id="id_7861063_2029699_1_1">Long-term Debt, Current Maturities</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LongTermDebtCurrent_lbl" xml:lang="en-US" id="id_7861063_2029699_2_1">Current maturities of long-term debt</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_LongTermDebtCurrent_lbl" xml:lang="en-US" id="id_7861063_2029699_12_1">Less - Current maturities of long-term debt</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtCurrent" xlink:to="us-gaap_LongTermDebtCurrent_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermDebtNoncurrent" xlink:label="us-gaap_LongTermDebtNoncurrent"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LongTermDebtNoncurrent_lbl" xml:lang="en-US" id="id_7861063_2028655_1_1">Long-term Debt, Excluding Current Maturities</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LongTermDebtNoncurrent_lbl" xml:lang="en-US" id="id_7861063_2028655_2_1">Long-term debt and notes payable, net of current maturities</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_LongTermDebtNoncurrent_lbl" xml:lang="en-US" id="id_7861063_2028655_12_1">Total long-term debt obligations, net of current maturities</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermDebtNoncurrent" xlink:to="us-gaap_LongTermDebtNoncurrent_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongtermDebtTypeAxis" xlink:label="us-gaap_LongtermDebtTypeAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LongtermDebtTypeAxis_lbl" xml:lang="en-US" id="id_7861063_2033594_1_1">Long-term Debt, Type [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LongtermDebtTypeAxis_lbl" xml:lang="en-US" id="id_7861063_2033594_2_1">Long-term Debt, Type [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongtermDebtTypeAxis" xlink:to="us-gaap_LongtermDebtTypeAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongtermDebtTypeDomain" xlink:label="us-gaap_LongtermDebtTypeDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LongtermDebtTypeDomain_lbl" xml:lang="en-US" id="id_7861063_2032331_1_1">Long-term Debt, Type [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LongtermDebtTypeDomain_lbl" xml:lang="en-US" id="id_7861063_2032331_2_1">Long-term Debt, Type [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongtermDebtTypeDomain" xlink:to="us-gaap_LongtermDebtTypeDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_LongTermDebtWeightedAverageInterestRateDuringPeriod" xlink:label="pwr_LongTermDebtWeightedAverageInterestRateDuringPeriod"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_LongTermDebtWeightedAverageInterestRateDuringPeriod_lbl" xml:lang="en-US" id="id_7861063_2259152_3_1">Long Term Debt Weighted Average Interest Rate During Period</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_LongTermDebtWeightedAverageInterestRateDuringPeriod_lbl" xml:lang="en-US" id="id_7861063_2259152_1_1">Long Term Debt Weighted Average Interest Rate During Period</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_LongTermDebtWeightedAverageInterestRateDuringPeriod_lbl" xml:lang="en-US" id="id_7861063_2259152_2_1">Weighted-average interest rate</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_LongTermDebtWeightedAverageInterestRateDuringPeriod" xlink:to="pwr_LongTermDebtWeightedAverageInterestRateDuringPeriod_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis" xlink:label="us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis_lbl" xml:lang="en-US" id="id_7861063_2040972_1_1">Category of Item Purchased [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis_lbl" xml:lang="en-US" id="id_7861063_2040972_2_1">Category of Item Purchased [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis" xlink:to="us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain" xlink:label="us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain_lbl" xml:lang="en-US" id="id_7861063_2034941_1_1">Long-term Purchase Commitment, Category of Item Purchased [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain_lbl" xml:lang="en-US" id="id_7861063_2034941_2_1">Long-term Purchase Commitment, Category of Item Purchased [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain" xlink:to="us-gaap_LongTermPurchaseCommitmentCategoryOfItemPurchasedDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_LorenzoBentonvTelecomNetworkSpecialistsIncMember" xlink:label="pwr_LorenzoBentonvTelecomNetworkSpecialistsIncMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_LorenzoBentonvTelecomNetworkSpecialistsIncMember_lbl" xml:lang="en-US" id="id_7861063_2114300_3_1">Lorenzo Benton v. Telecom Network Specialists Inc [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_LorenzoBentonvTelecomNetworkSpecialistsIncMember_lbl" xml:lang="en-US" id="id_7861063_2114300_1_1">Lorenzo Bentonv Telecom Network Specialists Inc [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_LorenzoBentonvTelecomNetworkSpecialistsIncMember_lbl" xml:lang="en-US" id="id_7861063_2114300_2_1">Lorenzo Benton v Telecom Network Specialists Inc [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_LorenzoBentonvTelecomNetworkSpecialistsIncMember" xlink:to="pwr_LorenzoBentonvTelecomNetworkSpecialistsIncMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LossContingenciesByNatureOfContingencyAxis" xlink:label="us-gaap_LossContingenciesByNatureOfContingencyAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LossContingenciesByNatureOfContingencyAxis_lbl" xml:lang="en-US" id="id_7861063_2032333_1_1">Loss Contingency Nature [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LossContingenciesByNatureOfContingencyAxis_lbl" xml:lang="en-US" id="id_7861063_2032333_2_1">Loss Contingency Nature [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LossContingenciesByNatureOfContingencyAxis" xlink:to="us-gaap_LossContingenciesByNatureOfContingencyAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LossContingenciesLineItems" xlink:label="us-gaap_LossContingenciesLineItems"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LossContingenciesLineItems_lbl" xml:lang="en-US" id="id_7861063_2033181_1_1">Loss Contingencies [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LossContingenciesLineItems_lbl" xml:lang="en-US" id="id_7861063_2033181_2_1">Loss Contingencies [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LossContingenciesLineItems" xlink:to="us-gaap_LossContingenciesLineItems_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LossContingenciesTable" xlink:label="us-gaap_LossContingenciesTable"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LossContingenciesTable_lbl" xml:lang="en-US" id="id_7861063_2030134_1_1">Loss Contingencies [Table]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LossContingenciesTable_lbl" xml:lang="en-US" id="id_7861063_2030134_2_1">Loss Contingencies [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LossContingenciesTable" xlink:to="us-gaap_LossContingenciesTable_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_LossContingencyAccrualPaymentsAmount" xlink:label="pwr_LossContingencyAccrualPaymentsAmount"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_LossContingencyAccrualPaymentsAmount_lbl" xml:lang="en-US" id="id_7861063_2386139_3_1">Loss contingency accrual payments amount.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_LossContingencyAccrualPaymentsAmount_lbl" xml:lang="en-US" id="id_7861063_2386139_1_1">Loss Contingency Accrual Payments Amount</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_LossContingencyAccrualPaymentsAmount_lbl" xml:lang="en-US" id="id_7861063_2386139_2_1">Payment of withdrawal liability assessment amount</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_LossContingencyAccrualPaymentsAmount" xlink:to="pwr_LossContingencyAccrualPaymentsAmount_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_LossContingencyDamagesSoughtValueByPlaintiffForClassDamages" xlink:label="pwr_LossContingencyDamagesSoughtValueByPlaintiffForClassDamages"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_LossContingencyDamagesSoughtValueByPlaintiffForClassDamages_lbl" xml:lang="en-US" id="id_7861063_2050520_3_1">The value of the class damages the plaintiff seeks in the legal matter.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_LossContingencyDamagesSoughtValueByPlaintiffForClassDamages_lbl" xml:lang="en-US" id="id_7861063_2050520_1_1">Loss Contingency, Damages Sought, Value By Plaintiff for Class Damages</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_LossContingencyDamagesSoughtValueByPlaintiffForClassDamages_lbl" xml:lang="en-US" id="id_7861063_2050520_2_1">Amount sought by plaintiff for class damages</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_LossContingencyDamagesSoughtValueByPlaintiffForClassDamages" xlink:to="pwr_LossContingencyDamagesSoughtValueByPlaintiffForClassDamages_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_LossContingencyDamagesSoughtValueByPlaintiffForLegalFees" xlink:label="pwr_LossContingencyDamagesSoughtValueByPlaintiffForLegalFees"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_LossContingencyDamagesSoughtValueByPlaintiffForLegalFees_lbl" xml:lang="en-US" id="id_7861063_2073844_3_1">The value of the legal fees the plaintiff seeks in the legal matter.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_LossContingencyDamagesSoughtValueByPlaintiffForLegalFees_lbl" xml:lang="en-US" id="id_7861063_2073844_1_1">Loss Contingency, Damages Sought, Value By Plaintiff for Legal Fees</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_LossContingencyDamagesSoughtValueByPlaintiffForLegalFees_lbl" xml:lang="en-US" id="id_7861063_2073844_2_1">Amount sought by plaintiff for legal fees</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_LossContingencyDamagesSoughtValueByPlaintiffForLegalFees" xlink:to="pwr_LossContingencyDamagesSoughtValueByPlaintiffForLegalFees_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LossContingencyNatureDomain" xlink:label="us-gaap_LossContingencyNatureDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LossContingencyNatureDomain_lbl" xml:lang="en-US" id="id_7861063_2028170_1_1">Loss Contingency, Nature [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LossContingencyNatureDomain_lbl" xml:lang="en-US" id="id_7861063_2028170_2_1">Loss Contingency, Nature [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LossContingencyNatureDomain" xlink:to="us-gaap_LossContingencyNatureDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_LossOnContracts" xlink:label="us-gaap_LossOnContracts"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_LossOnContracts_lbl" xml:lang="en-US" id="id_7861063_2030351_1_1">Loss on Contracts</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_LossOnContracts_lbl" xml:lang="en-US" id="id_7861063_2030351_2_1">Loss on Contracts</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_LossOnContracts" xlink:to="us-gaap_LossOnContracts_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MaximumMember" xlink:label="us-gaap_MaximumMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_MaximumMember_lbl" xml:lang="en-US" id="id_7861063_2033371_1_1">Maximum [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_MaximumMember_lbl" xml:lang="en-US" id="id_7861063_2033371_2_1">Maximum [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MaximumMember" xlink:to="us-gaap_MaximumMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MergersAcquisitionsAndDispositionsDisclosuresTextBlock" xlink:label="us-gaap_MergersAcquisitionsAndDispositionsDisclosuresTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_MergersAcquisitionsAndDispositionsDisclosuresTextBlock_lbl" xml:lang="en-US" id="id_7861063_2034727_1_1">Mergers, Acquisitions and Dispositions Disclosures [Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_MergersAcquisitionsAndDispositionsDisclosuresTextBlock_lbl" xml:lang="en-US" id="id_7861063_2034727_2_1">Acquisitions</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MergersAcquisitionsAndDispositionsDisclosuresTextBlock" xlink:to="us-gaap_MergersAcquisitionsAndDispositionsDisclosuresTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MinimumGuaranteesPolicy" xlink:label="us-gaap_MinimumGuaranteesPolicy"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_MinimumGuaranteesPolicy_lbl" xml:lang="en-US" id="id_7861063_2040987_1_1">Minimum Guarantees, Policy [Policy Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_MinimumGuaranteesPolicy_lbl" xml:lang="en-US" id="id_7861063_2040987_2_1">Collective Bargaining Agreements</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MinimumGuaranteesPolicy" xlink:to="us-gaap_MinimumGuaranteesPolicy_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MinimumMember" xlink:label="us-gaap_MinimumMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_MinimumMember_lbl" xml:lang="en-US" id="id_7861063_2030148_1_1">Minimum [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_MinimumMember_lbl" xml:lang="en-US" id="id_7861063_2030148_2_1">Minimum [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MinimumMember" xlink:to="us-gaap_MinimumMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_MinimumNumberOfSharesThatCanBeExchangedByExchangeableShareholdersUnlessNumberOfRemainingExchangeableSharesRegisteredInNameOfHolderIsLess" xlink:label="pwr_MinimumNumberOfSharesThatCanBeExchangedByExchangeableShareholdersUnlessNumberOfRemainingExchangeableSharesRegisteredInNameOfHolderIsLess"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_MinimumNumberOfSharesThatCanBeExchangedByExchangeableShareholdersUnlessNumberOfRemainingExchangeableSharesRegisteredInNameOfHolderIsLess_lbl" xml:lang="en-US" id="id_7861063_2135300_3_1">Minimum number of shares that can be exchanged by exchangeable shareholders unless number of remaining exchangeable shares registered in name of holder is less.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_MinimumNumberOfSharesThatCanBeExchangedByExchangeableShareholdersUnlessNumberOfRemainingExchangeableSharesRegisteredInNameOfHolderIsLess_lbl" xml:lang="en-US" id="id_7861063_2135300_1_1">Minimum Number Of Shares That Can Be Exchanged By Exchangeable Shareholders Unless Number Of Remaining Exchangeable Shares Registered In Name Of Holder Is Less</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_MinimumNumberOfSharesThatCanBeExchangedByExchangeableShareholdersUnlessNumberOfRemainingExchangeableSharesRegisteredInNameOfHolderIsLess_lbl" xml:lang="en-US" id="id_7861063_2135300_2_1">Minimum number of shares that can be exchanged by exchangeable shareholders unless the number of remaining exchangeable shares registered in the name of the holder is less</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_MinimumNumberOfSharesThatCanBeExchangedByExchangeableShareholdersUnlessNumberOfRemainingExchangeableSharesRegisteredInNameOfHolderIsLess" xlink:to="pwr_MinimumNumberOfSharesThatCanBeExchangedByExchangeableShareholdersUnlessNumberOfRemainingExchangeableSharesRegisteredInNameOfHolderIsLess_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MinorityInterest" xlink:label="us-gaap_MinorityInterest"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_MinorityInterest_lbl" xml:lang="en-US" id="id_7861063_2031641_1_1">Stockholders' Equity Attributable to Noncontrolling Interest</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_MinorityInterest_lbl" xml:lang="en-US" id="id_7861063_2031641_2_1">Non-controlling interests</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MinorityInterest" xlink:to="us-gaap_MinorityInterest_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders" xlink:label="us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_lbl" xml:lang="en-US" id="id_7861063_2032344_1_1">Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_lbl" xml:lang="en-US" id="id_7861063_2032344_2_1">Distributions to non-controlling interests</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders" xlink:to="us-gaap_MinorityInterestDecreaseFromDistributionsToNoncontrollingInterestHolders_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MultiemployerPlanNameAxis" xlink:label="us-gaap_MultiemployerPlanNameAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_MultiemployerPlanNameAxis_lbl" xml:lang="en-US" id="id_7861063_2029939_1_1">Multiemployer Plan Name [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_MultiemployerPlanNameAxis_lbl" xml:lang="en-US" id="id_7861063_2029939_2_1">Multiemployer Plan Name [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MultiemployerPlanNameAxis" xlink:to="us-gaap_MultiemployerPlanNameAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MultiemployerPlanNameDomain" xlink:label="us-gaap_MultiemployerPlanNameDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_MultiemployerPlanNameDomain_lbl" xml:lang="en-US" id="id_7861063_2032749_1_1">Multiemployer Plan Name [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_MultiemployerPlanNameDomain_lbl" xml:lang="en-US" id="id_7861063_2032749_2_1">Multiemployer Plan Name [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MultiemployerPlanNameDomain" xlink:to="us-gaap_MultiemployerPlanNameDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_MultiemployerPlansWithdrawalObligation" xlink:label="us-gaap_MultiemployerPlansWithdrawalObligation"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_MultiemployerPlansWithdrawalObligation_lbl" xml:lang="en-US" id="id_7861063_2034960_1_1">Multiemployer Plans, Withdrawal Obligation</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_MultiemployerPlansWithdrawalObligation_lbl" xml:lang="en-US" id="id_7861063_2034960_2_1">Amount of withdrawal liability</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_MultiemployerPlansWithdrawalObligation" xlink:to="us-gaap_MultiemployerPlansWithdrawalObligation_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_MultiemployerPlanWithdrawalObligationAmountSuggestedByPlanDifferentThanAmountRecordedByCompany" xlink:label="pwr_MultiemployerPlanWithdrawalObligationAmountSuggestedByPlanDifferentThanAmountRecordedByCompany"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_MultiemployerPlanWithdrawalObligationAmountSuggestedByPlanDifferentThanAmountRecordedByCompany_lbl" xml:lang="en-US" id="id_7861063_2288834_3_1">Multiemployer plan withdrawal obligation amount suggested by plan different than amount recorded by company.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_MultiemployerPlanWithdrawalObligationAmountSuggestedByPlanDifferentThanAmountRecordedByCompany_lbl" xml:lang="en-US" id="id_7861063_2288834_1_1">Multiemployer Plan Withdrawal Obligation Amount Suggested By Plan Different Than Amount Recorded By Company</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_MultiemployerPlanWithdrawalObligationAmountSuggestedByPlanDifferentThanAmountRecordedByCompany_lbl" xml:lang="en-US" id="id_7861063_2288834_2_1">Multiemployer plan withdrawal obligation, amount suggested by Plan which is different than amount recorded by company</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_MultiemployerPlanWithdrawalObligationAmountSuggestedByPlanDifferentThanAmountRecordedByCompany" xlink:to="pwr_MultiemployerPlanWithdrawalObligationAmountSuggestedByPlanDifferentThanAmountRecordedByCompany_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NetCashProvidedByUsedInDiscontinuedOperations" xlink:label="us-gaap_NetCashProvidedByUsedInDiscontinuedOperations"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInDiscontinuedOperations_lbl" xml:lang="en-US" id="id_7861063_2031495_1_1">Net Cash Provided by (Used in) Discontinued Operations</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetCashProvidedByUsedInDiscontinuedOperations_lbl" xml:lang="en-US" id="id_7861063_2031495_6_1">Net cash used in discontinued operations</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInDiscontinuedOperations" xlink:to="us-gaap_NetCashProvidedByUsedInDiscontinuedOperations_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NetCashProvidedByUsedInDiscontinuedOperationsAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInDiscontinuedOperationsAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInDiscontinuedOperationsAbstract_lbl" xml:lang="en-US" id="id_7861063_2029292_1_1">Net Cash Provided by (Used in) Discontinued Operations [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_NetCashProvidedByUsedInDiscontinuedOperationsAbstract_lbl" xml:lang="en-US" id="id_7861063_2029292_2_1">Discontinued operations:</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInDiscontinuedOperationsAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInDiscontinuedOperationsAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations_lbl" xml:lang="en-US" id="id_7861063_2032942_1_1">Net Cash Provided by (Used in) Financing Activities, Continuing Operations</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations_lbl" xml:lang="en-US" id="id_7861063_2032942_6_1">Net cash used in financing activities of continuing operations</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperations_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_lbl" xml:lang="en-US" id="id_7861063_2033388_1_1">Net Cash Provided by (Used in) Financing Activities, Continuing Operations [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_lbl" xml:lang="en-US" id="id_7861063_2033388_2_1">Cash Flows from Financing Activities of Continuing Operations:</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations_lbl" xml:lang="en-US" id="id_7861063_2030371_1_1">Net Cash Provided by (Used in) Investing Activities, Continuing Operations</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations_lbl" xml:lang="en-US" id="id_7861063_2030371_6_1">Net cash used in investing activities of continuing operations</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperations_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_lbl" xml:lang="en-US" id="id_7861063_2030817_1_1">Net Cash Provided by (Used in) Investing Activities, Continuing Operations [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_lbl" xml:lang="en-US" id="id_7861063_2030817_2_1">Cash Flows from Investing Activities of Continuing Operations:</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations_lbl" xml:lang="en-US" id="id_7861063_2034376_1_1">Net Cash Provided by (Used in) Operating Activities, Continuing Operations</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations_lbl" xml:lang="en-US" id="id_7861063_2034376_6_1">Net cash provided by operating activities of continuing operations</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperations_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_lbl" xml:lang="en-US" id="id_7861063_2029047_1_1">Net Cash Provided by (Used in) Operating Activities, Continuing Operations [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_lbl" xml:lang="en-US" id="id_7861063_2029047_2_1">Cash Flows from Operating Activities of Continuing Operations:</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract" xlink:to="us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NetIncomeLossAttributableToNoncontrollingInterest" xlink:label="us-gaap_NetIncomeLossAttributableToNoncontrollingInterest"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_lbl" xml:lang="en-US" id="id_7861063_2030162_1_1">Net Income (Loss) Attributable to Noncontrolling Interest</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_lbl" xml:lang="en-US" id="id_7861063_2030162_2_1">Less: Net income attributable to non-controlling interests</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetIncomeLossAttributableToNoncontrollingInterest" xlink:to="us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_lbl" xml:lang="en-US" id="id_7861063_2032110_1_1">Net Income (Loss) Available to Common Stockholders, Basic</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_lbl" xml:lang="en-US" id="id_7861063_2032110_6_1">Net income attributable to common stock</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic" xlink:to="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_lbl" xml:lang="en-US" id="id_7861063_2028680_1_1">Net Income (Loss) Available to Common Stockholders, Basic [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_lbl" xml:lang="en-US" id="id_7861063_2028680_2_1">Amounts attributable to common stock:</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract" xlink:to="us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_NetPositionMember" xlink:label="pwr_NetPositionMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_NetPositionMember_lbl" xml:lang="en-US" id="id_7861063_2184083_3_1">Represents concentrations of credit risk related to accounts receivable, including amounts related to unbilled accounts receivable and costs and estimated earnings in excess of billings on uncompleted contracts, less billings in excess of costs and estimated earnings on uncompleted contracts.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_NetPositionMember_lbl" xml:lang="en-US" id="id_7861063_2184083_1_1">Net Position [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_NetPositionMember_lbl" xml:lang="en-US" id="id_7861063_2184083_2_1">Net Position [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_NetPositionMember" xlink:to="pwr_NetPositionMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock" xlink:label="us-gaap_NewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock_lbl" xml:lang="en-US" id="id_7861063_2031651_1_1">New Accounting Pronouncements and Changes in Accounting Principles [Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_NewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock_lbl" xml:lang="en-US" id="id_7861063_2031651_2_1">New Accounting Pronouncements</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock" xlink:to="us-gaap_NewAccountingPronouncementsAndChangesInAccountingPrinciplesTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2032113_1_1">New Accounting Pronouncements, Policy [Policy Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2032113_2_1">Adoption of New Accounting Pronouncements</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock" xlink:to="us-gaap_NewAccountingPronouncementsPolicyPolicyTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NoncompeteAgreementsMember" xlink:label="us-gaap_NoncompeteAgreementsMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NoncompeteAgreementsMember_lbl" xml:lang="en-US" id="id_7861063_2034191_1_1">Noncompete Agreements [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_NoncompeteAgreementsMember_lbl" xml:lang="en-US" id="id_7861063_2034191_2_1">Non-compete Agreements [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NoncompeteAgreementsMember" xlink:to="us-gaap_NoncompeteAgreementsMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NoncontrollingInterestAbstract" xlink:label="us-gaap_NoncontrollingInterestAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NoncontrollingInterestAbstract_lbl" xml:lang="en-US" id="id_7861063_2029296_1_1">Noncontrolling Interest [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_NoncontrollingInterestAbstract_lbl" xml:lang="en-US" id="id_7861063_2029296_2_1">Noncontrolling Interest [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NoncontrollingInterestAbstract" xlink:to="us-gaap_NoncontrollingInterestAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NoncontrollingInterestInNetIncomeLossJointVenturePartnersNonredeemable" xlink:label="us-gaap_NoncontrollingInterestInNetIncomeLossJointVenturePartnersNonredeemable"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NoncontrollingInterestInNetIncomeLossJointVenturePartnersNonredeemable_lbl" xml:lang="en-US" id="id_7861063_2032522_1_1">Noncontrolling Interest in Net Income (Loss) Joint Venture Partners, Nonredeemable</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_NoncontrollingInterestInNetIncomeLossJointVenturePartnersNonredeemable_lbl" xml:lang="en-US" id="id_7861063_2032522_2_1">Income attributable to the other joint venture members</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NoncontrollingInterestInNetIncomeLossJointVenturePartnersNonredeemable" xlink:to="us-gaap_NoncontrollingInterestInNetIncomeLossJointVenturePartnersNonredeemable_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_NumberOfAgencies" xlink:label="pwr_NumberOfAgencies"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_NumberOfAgencies_lbl" xml:lang="en-US" id="id_7861063_2346838_3_1">Number Of Agencies</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_NumberOfAgencies_lbl" xml:lang="en-US" id="id_7861063_2346838_1_1">Number Of Agencies</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_NumberOfAgencies_lbl" xml:lang="en-US" id="id_7861063_2346838_2_1">Number of staffing Agency</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_NumberOfAgencies" xlink:to="pwr_NumberOfAgencies_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NumberOfBusinessesAcquired" xlink:label="us-gaap_NumberOfBusinessesAcquired"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NumberOfBusinessesAcquired_lbl" xml:lang="en-US" id="id_7861063_2031660_1_1">Number of Businesses Acquired</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_NumberOfBusinessesAcquired_lbl" xml:lang="en-US" id="id_7861063_2031660_2_1">Number of business acquisitions</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NumberOfBusinessesAcquired" xlink:to="us-gaap_NumberOfBusinessesAcquired_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_NumberOfCommonStockSharesReceivedByRsuHolder" xlink:label="pwr_NumberOfCommonStockSharesReceivedByRsuHolder"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_NumberOfCommonStockSharesReceivedByRsuHolder_lbl" xml:lang="en-US" id="id_7861063_2251995_3_1">Number of common stock shares received by RSU holder.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_NumberOfCommonStockSharesReceivedByRsuHolder_lbl" xml:lang="en-US" id="id_7861063_2251995_1_1">Number Of Common Stock Shares Received By RSU Holder</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_NumberOfCommonStockSharesReceivedByRsuHolder_lbl" xml:lang="en-US" id="id_7861063_2251995_2_1">Number of common stock shares that may be received by RSU holder</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_NumberOfCommonStockSharesReceivedByRsuHolder" xlink:to="pwr_NumberOfCommonStockSharesReceivedByRsuHolder_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_NumberOfCustomersRepresentingTenPercentOrMoreOfConcentrationRisk" xlink:label="pwr_NumberOfCustomersRepresentingTenPercentOrMoreOfConcentrationRisk"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_NumberOfCustomersRepresentingTenPercentOrMoreOfConcentrationRisk_lbl" xml:lang="en-US" id="id_7861063_2074549_3_1">Number of customers representing ten percent or more of consolidated revenues.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_NumberOfCustomersRepresentingTenPercentOrMoreOfConcentrationRisk_lbl" xml:lang="en-US" id="id_7861063_2074549_1_1">Number Of Customers Representing Ten Percent Or More Of Concentration Risk</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_NumberOfCustomersRepresentingTenPercentOrMoreOfConcentrationRisk_lbl" xml:lang="en-US" id="id_7861063_2074549_2_1">Number of customers representing ten percent or more of concentration risk</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_NumberOfCustomersRepresentingTenPercentOrMoreOfConcentrationRisk" xlink:to="pwr_NumberOfCustomersRepresentingTenPercentOrMoreOfConcentrationRisk_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_NumberOfProjectsWithSignificantLosses" xlink:label="pwr_NumberOfProjectsWithSignificantLosses"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_NumberOfProjectsWithSignificantLosses_lbl" xml:lang="en-US" id="id_7861063_2323254_3_1">Number of projects.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_NumberOfProjectsWithSignificantLosses_lbl" xml:lang="en-US" id="id_7861063_2323254_1_1">Number Of Projects With Significant Losses</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_NumberOfProjectsWithSignificantLosses_lbl" xml:lang="en-US" id="id_7861063_2323254_2_1">Number of projects with significant losses</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_NumberOfProjectsWithSignificantLosses" xlink:to="pwr_NumberOfProjectsWithSignificantLosses_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_NumberOfReportableSegments" xlink:label="us-gaap_NumberOfReportableSegments"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_NumberOfReportableSegments_lbl" xml:lang="en-US" id="id_7861063_2034760_1_1">Number of Reportable Segments</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_NumberOfReportableSegments_lbl" xml:lang="en-US" id="id_7861063_2034760_2_1">Number of reportable segments</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_NumberOfReportableSegments" xlink:to="us-gaap_NumberOfReportableSegments_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_NumberOfReportingUnitsImpactedByImpairmentCharges" xlink:label="pwr_NumberOfReportingUnitsImpactedByImpairmentCharges"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_NumberOfReportingUnitsImpactedByImpairmentCharges_lbl" xml:lang="en-US" id="id_7861063_2310747_3_1">Represents the number of reporting units impacted by impairment charges.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_NumberOfReportingUnitsImpactedByImpairmentCharges_lbl" xml:lang="en-US" id="id_7861063_2310747_1_1">Number of Reporting Units Impacted by Impairment Charges</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_NumberOfReportingUnitsImpactedByImpairmentCharges_lbl" xml:lang="en-US" id="id_7861063_2310747_2_1">Number of reporting units impacted impairment charge</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_NumberOfReportingUnitsImpactedByImpairmentCharges" xlink:to="pwr_NumberOfReportingUnitsImpactedByImpairmentCharges_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_NumberOfSharesOfCommonStockReceivedForEachExchangeableShare" xlink:label="pwr_NumberOfSharesOfCommonStockReceivedForEachExchangeableShare"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_NumberOfSharesOfCommonStockReceivedForEachExchangeableShare_lbl" xml:lang="en-US" id="id_7861063_2088062_3_1">Number of shares of common stock received for each exchangeable share.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_NumberOfSharesOfCommonStockReceivedForEachExchangeableShare_lbl" xml:lang="en-US" id="id_7861063_2088062_1_1">Number Of Shares Of Common Stock Received For Each Exchangeable Share</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_NumberOfSharesOfCommonStockReceivedForEachExchangeableShare_lbl" xml:lang="en-US" id="id_7861063_2088062_2_1">Number of shares of Common stock received for each exchangeable share</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_NumberOfSharesOfCommonStockReceivedForEachExchangeableShare" xlink:to="pwr_NumberOfSharesOfCommonStockReceivedForEachExchangeableShare_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_OilAndGasInfrastructureServicesBusinessMember" xlink:label="pwr_OilAndGasInfrastructureServicesBusinessMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_OilAndGasInfrastructureServicesBusinessMember_lbl" xml:lang="en-US" id="id_7861063_2351715_3_1">Oil and Gas Infrastructure [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_OilAndGasInfrastructureServicesBusinessMember_lbl" xml:lang="en-US" id="id_7861063_2351715_1_1">Oil and Gas Infrastructure Services Business [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_OilAndGasInfrastructureServicesBusinessMember_lbl" xml:lang="en-US" id="id_7861063_2351715_2_1">Oil and Gas Infrastructure Services Business [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_OilAndGasInfrastructureServicesBusinessMember" xlink:to="pwr_OilAndGasInfrastructureServicesBusinessMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_OilAndGasInfrastructureServicesMember" xlink:label="pwr_OilAndGasInfrastructureServicesMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_OilAndGasInfrastructureServicesMember_lbl" xml:lang="en-US" id="id_7861063_2196281_3_1">Oil and Gas Infrastructure Services [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_OilAndGasInfrastructureServicesMember_lbl" xml:lang="en-US" id="id_7861063_2196281_1_1">Oil And Gas Infrastructure Services [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_OilAndGasInfrastructureServicesMember_lbl" xml:lang="en-US" id="id_7861063_2196281_2_1">Oil and Gas Infrastructure Services [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_OilAndGasInfrastructureServicesMember" xlink:to="pwr_OilAndGasInfrastructureServicesMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_OilAndGasMember" xlink:label="pwr_OilAndGasMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_OilAndGasMember_lbl" xml:lang="en-US" id="id_7861063_2117511_3_1">Oil And Gas [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_OilAndGasMember_lbl" xml:lang="en-US" id="id_7861063_2117511_1_1">Oil And Gas [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_OilAndGasMember_lbl" xml:lang="en-US" id="id_7861063_2117511_2_1">Oil and Gas Infrastructure Division [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_OilAndGasMember" xlink:to="pwr_OilAndGasMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OperatingIncomeLoss" xlink:label="us-gaap_OperatingIncomeLoss"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingIncomeLoss_lbl" xml:lang="en-US" id="id_7861063_2032376_1_1">Operating Income (Loss)</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OperatingIncomeLoss_lbl" xml:lang="en-US" id="id_7861063_2032376_2_1">Operating income (loss)</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_OperatingIncomeLoss_lbl" xml:lang="en-US" id="id_7861063_2032376_6_1">Operating income</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingIncomeLoss" xlink:to="us-gaap_OperatingIncomeLoss_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDue" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDue"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDue_lbl" xml:lang="en-US" id="id_7861063_2028198_1_1">Operating Leases, Future Minimum Payments Due</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDue_lbl" xml:lang="en-US" id="id_7861063_2028198_6_1">Total minimum lease payments</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDue" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDue_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears_lbl" xml:lang="en-US" id="id_7861063_2028693_1_1">Operating Leases, Future Minimum Payments, Due in Five Years</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears_lbl" xml:lang="en-US" id="id_7861063_2028693_2_1">2020</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears_lbl" xml:lang="en-US" id="id_7861063_2028879_1_1">Operating Leases, Future Minimum Payments, Due in Four Years</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears_lbl" xml:lang="en-US" id="id_7861063_2028879_2_1">2019</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears_lbl" xml:lang="en-US" id="id_7861063_2032535_1_1">Operating Leases, Future Minimum Payments, Due in Three Years</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears_lbl" xml:lang="en-US" id="id_7861063_2032535_2_1">2018</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears_lbl" xml:lang="en-US" id="id_7861063_2034763_1_1">Operating Leases, Future Minimum Payments, Due in Two Years</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears_lbl" xml:lang="en-US" id="id_7861063_2034763_2_1">2017</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter_lbl" xml:lang="en-US" id="id_7861063_2031666_1_1">Operating Leases, Future Minimum Payments, Due Thereafter</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter_lbl" xml:lang="en-US" id="id_7861063_2031666_2_1">Thereafter</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsRemainderOfFiscalYear" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsRemainderOfFiscalYear"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsRemainderOfFiscalYear_lbl" xml:lang="en-US" id="id_7861063_2032379_1_1">Operating Leases, Future Minimum Payments, Remainder of Fiscal Year</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OperatingLeasesFutureMinimumPaymentsRemainderOfFiscalYear_lbl" xml:lang="en-US" id="id_7861063_2032379_2_1">Remainder of 2016</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesFutureMinimumPaymentsRemainderOfFiscalYear" xlink:to="us-gaap_OperatingLeasesFutureMinimumPaymentsRemainderOfFiscalYear_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OperatingLeasesOfLesseeDisclosureTextBlock" xlink:label="us-gaap_OperatingLeasesOfLesseeDisclosureTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OperatingLeasesOfLesseeDisclosureTextBlock_lbl" xml:lang="en-US" id="id_7861063_2033411_1_1">Operating Leases of Lessee Disclosure [Table Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OperatingLeasesOfLesseeDisclosureTextBlock_lbl" xml:lang="en-US" id="id_7861063_2033411_2_1">Minimum Lease Payments</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OperatingLeasesOfLesseeDisclosureTextBlock" xlink:to="us-gaap_OperatingLeasesOfLesseeDisclosureTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_OptionToIncreaseRevolvingCommitmentsUnderCreditAgreement" xlink:label="pwr_OptionToIncreaseRevolvingCommitmentsUnderCreditAgreement"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_OptionToIncreaseRevolvingCommitmentsUnderCreditAgreement_lbl" xml:lang="en-US" id="id_7861063_2071127_3_1">Option to increase revolving commitments under credit agreement.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_OptionToIncreaseRevolvingCommitmentsUnderCreditAgreement_lbl" xml:lang="en-US" id="id_7861063_2071127_1_1">Option To Increase Revolving Commitments Under Credit Agreement</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_OptionToIncreaseRevolvingCommitmentsUnderCreditAgreement_lbl" xml:lang="en-US" id="id_7861063_2071127_2_1">Option to increase revolving commitments under the credit agreement</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_OptionToIncreaseRevolvingCommitmentsUnderCreditAgreement" xlink:to="pwr_OptionToIncreaseRevolvingCommitmentsUnderCreditAgreement_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OrderOrProductionBacklogMember" xlink:label="us-gaap_OrderOrProductionBacklogMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OrderOrProductionBacklogMember_lbl" xml:lang="en-US" id="id_7861063_2032960_1_1">Order or Production Backlog [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OrderOrProductionBacklogMember_lbl" xml:lang="en-US" id="id_7861063_2032960_2_1">Backlog [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OrderOrProductionBacklogMember" xlink:to="us-gaap_OrderOrProductionBacklogMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_OrganizationAndDescriptionOfBusinessLineItems" xlink:label="pwr_OrganizationAndDescriptionOfBusinessLineItems"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_OrganizationAndDescriptionOfBusinessLineItems_lbl" xml:lang="en-US" id="id_7861063_2336089_3_1">Organization And Description Of Business [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_OrganizationAndDescriptionOfBusinessLineItems_lbl" xml:lang="en-US" id="id_7861063_2336089_1_1">Organization And Description Of Business [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_OrganizationAndDescriptionOfBusinessLineItems_lbl" xml:lang="en-US" id="id_7861063_2336089_2_1">Organization And Description Of Business [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_OrganizationAndDescriptionOfBusinessLineItems" xlink:to="pwr_OrganizationAndDescriptionOfBusinessLineItems_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_OrganizationAndDescriptionOfBusinessTable" xlink:label="pwr_OrganizationAndDescriptionOfBusinessTable"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_OrganizationAndDescriptionOfBusinessTable_lbl" xml:lang="en-US" id="id_7861063_2135130_3_1">Organization And Description Of Business [Table]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_OrganizationAndDescriptionOfBusinessTable_lbl" xml:lang="en-US" id="id_7861063_2135130_1_1">Organization And Description Of Business [Table]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_OrganizationAndDescriptionOfBusinessTable_lbl" xml:lang="en-US" id="id_7861063_2135130_2_1">Organization And Description Of Business [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_OrganizationAndDescriptionOfBusinessTable" xlink:to="pwr_OrganizationAndDescriptionOfBusinessTable_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract" xlink:label="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract_lbl" xml:lang="en-US" id="id_7861063_2032787_1_1">Organization, Consolidation and Presentation of Financial Statements [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract_lbl" xml:lang="en-US" id="id_7861063_2032787_2_1">Organization, Consolidation and Presentation of Financial Statements [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract" xlink:to="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock" xlink:label="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock_lbl" xml:lang="en-US" id="id_7861063_2034201_1_1">Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock_lbl" xml:lang="en-US" id="id_7861063_2034201_2_1">Business and Organization</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock" xlink:to="us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsDisclosureTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherAssetsNoncurrent" xlink:label="us-gaap_OtherAssetsNoncurrent"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherAssetsNoncurrent_lbl" xml:lang="en-US" id="id_7861063_2033988_1_1">Other Assets, Noncurrent</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OtherAssetsNoncurrent_lbl" xml:lang="en-US" id="id_7861063_2033988_2_1">Other assets, net</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherAssetsNoncurrent" xlink:to="us-gaap_OtherAssetsNoncurrent_lbl"/>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherCommitment_lbl" xml:lang="en-US" id="id_7861063_2033645_1_1">Other Commitment</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OtherCommitment_lbl" xml:lang="en-US" id="id_7861063_2033645_2_1">Outstanding capital commitment</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherCommitmentDueInFourthYear" xlink:label="us-gaap_OtherCommitmentDueInFourthYear"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherCommitmentDueInFourthYear_lbl" xml:lang="en-US" id="id_7861063_2030608_1_1">Other Commitment, Due in Fourth Year</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OtherCommitmentDueInFourthYear_lbl" xml:lang="en-US" id="id_7861063_2030608_2_1">Capital commitments, 2019</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherCommitmentDueInFourthYear" xlink:to="us-gaap_OtherCommitmentDueInFourthYear_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherCommitmentDueInSecondYear" xlink:label="us-gaap_OtherCommitmentDueInSecondYear"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherCommitmentDueInSecondYear_lbl" xml:lang="en-US" id="id_7861063_2032789_1_1">Other Commitment, Due in Second Year</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OtherCommitmentDueInSecondYear_lbl" xml:lang="en-US" id="id_7861063_2032789_2_1">Capital commitments, 2017</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherCommitmentDueInSecondYear" xlink:to="us-gaap_OtherCommitmentDueInSecondYear_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherCommitmentDueInThirdYear" xlink:label="us-gaap_OtherCommitmentDueInThirdYear"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherCommitmentDueInThirdYear_lbl" xml:lang="en-US" id="id_7861063_2029759_1_1">Other Commitment, Due in Third Year</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OtherCommitmentDueInThirdYear_lbl" xml:lang="en-US" id="id_7861063_2029759_2_1">Capital commitments, 2018</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherCommitmentDueInThirdYear" xlink:to="us-gaap_OtherCommitmentDueInThirdYear_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherCommitmentsAxis" xlink:label="us-gaap_OtherCommitmentsAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherCommitmentsAxis_lbl" xml:lang="en-US" id="id_7861063_2030609_1_1">Other Commitments [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OtherCommitmentsAxis_lbl" xml:lang="en-US" id="id_7861063_2030609_2_1">Other Commitments [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherCommitmentsAxis" xlink:to="us-gaap_OtherCommitmentsAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherCommitmentsDomain" xlink:label="us-gaap_OtherCommitmentsDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherCommitmentsDomain_lbl" xml:lang="en-US" id="id_7861063_2032790_1_1">Other Commitments [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OtherCommitmentsDomain_lbl" xml:lang="en-US" id="id_7861063_2032790_2_1">Other Commitments [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherCommitmentsDomain" xlink:to="us-gaap_OtherCommitmentsDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_OtherCommitmentsEngineeringProcurementAndConstructionElectricTransmissionProjectMember" xlink:label="pwr_OtherCommitmentsEngineeringProcurementAndConstructionElectricTransmissionProjectMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_OtherCommitmentsEngineeringProcurementAndConstructionElectricTransmissionProjectMember_lbl" xml:lang="en-US" id="id_7861063_2058040_3_1">Other future obligation related engineering, procurement and construction (EPC) electric transmission project.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_OtherCommitmentsEngineeringProcurementAndConstructionElectricTransmissionProjectMember_lbl" xml:lang="en-US" id="id_7861063_2058040_1_1">Other Commitments, Engineering, Procurement and Construction Electric Transmission Project [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_OtherCommitmentsEngineeringProcurementAndConstructionElectricTransmissionProjectMember_lbl" xml:lang="en-US" id="id_7861063_2058040_2_1">Other Commitments, Engineering, Procurement and Construction Electric Transmission Project [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_OtherCommitmentsEngineeringProcurementAndConstructionElectricTransmissionProjectMember" xlink:to="pwr_OtherCommitmentsEngineeringProcurementAndConstructionElectricTransmissionProjectMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherCommitmentsFutureMinimumPaymentsRemainderOfFiscalYear" xlink:label="us-gaap_OtherCommitmentsFutureMinimumPaymentsRemainderOfFiscalYear"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherCommitmentsFutureMinimumPaymentsRemainderOfFiscalYear_lbl" xml:lang="en-US" id="id_7861063_2033990_1_1">Other Commitments, Future Minimum Payments, Remainder of Fiscal Year</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OtherCommitmentsFutureMinimumPaymentsRemainderOfFiscalYear_lbl" xml:lang="en-US" id="id_7861063_2033990_2_1">Capital commitments, Remainder of 2016</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherCommitmentsFutureMinimumPaymentsRemainderOfFiscalYear" xlink:to="us-gaap_OtherCommitmentsFutureMinimumPaymentsRemainderOfFiscalYear_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherCommitmentsLineItems" xlink:label="us-gaap_OtherCommitmentsLineItems"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherCommitmentsLineItems_lbl" xml:lang="en-US" id="id_7861063_2033228_1_1">Other Commitments [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OtherCommitmentsLineItems_lbl" xml:lang="en-US" id="id_7861063_2033228_2_1">Other Commitments [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherCommitmentsLineItems" xlink:to="us-gaap_OtherCommitmentsLineItems_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_OtherCommitmentsPlannedOilAndGasInfrastructureProjectsMember" xlink:label="pwr_OtherCommitmentsPlannedOilAndGasInfrastructureProjectsMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_OtherCommitmentsPlannedOilAndGasInfrastructureProjectsMember_lbl" xml:lang="en-US" id="id_7861063_2392998_3_1">Other commitments planned oil and gas infrastructure projects.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_OtherCommitmentsPlannedOilAndGasInfrastructureProjectsMember_lbl" xml:lang="en-US" id="id_7861063_2392998_1_1">Other Commitments, Planned Oil And Gas Infrastructure Projects [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_OtherCommitmentsPlannedOilAndGasInfrastructureProjectsMember_lbl" xml:lang="en-US" id="id_7861063_2392998_2_1">Other Commitments, Planned Oil and Gas Infrastructure Projects [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_OtherCommitmentsPlannedOilAndGasInfrastructureProjectsMember" xlink:to="pwr_OtherCommitmentsPlannedOilAndGasInfrastructureProjectsMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherCommitmentsTable" xlink:label="us-gaap_OtherCommitmentsTable"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherCommitmentsTable_lbl" xml:lang="en-US" id="id_7861063_2028433_1_1">Other Commitments [Table]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OtherCommitmentsTable_lbl" xml:lang="en-US" id="id_7861063_2028433_2_1">Other Commitments [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherCommitmentsTable" xlink:to="us-gaap_OtherCommitmentsTable_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherCommitmentsTableTextBlock" xlink:label="us-gaap_OtherCommitmentsTableTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherCommitmentsTableTextBlock_lbl" xml:lang="en-US" id="id_7861063_2028204_1_1">Other Commitments [Table Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OtherCommitmentsTableTextBlock_lbl" xml:lang="en-US" id="id_7861063_2028204_2_1">Outstanding Capital Commitments Associated with Investments in Unconsolidated Affiliates</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherCommitmentsTableTextBlock" xlink:to="us-gaap_OtherCommitmentsTableTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax" xlink:label="us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_lbl" xml:lang="en-US" id="id_7861063_2030613_1_1">Other Comprehensive Income (Loss), Foreign Currency Transaction and Translation Adjustment, Net of Tax</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_lbl" xml:lang="en-US" id="id_7861063_2030613_2_1">Foreign currency translation adjustment, net of tax of $0, $0, $0 and $0</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax" xlink:to="us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax" xlink:label="us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax_lbl" xml:lang="en-US" id="id_7861063_2034771_1_1">Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Tax</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax_lbl" xml:lang="en-US" id="id_7861063_2034771_2_1">Foreign currency translation adjustment, tax</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax" xlink:to="us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTax" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTax"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTax_lbl" xml:lang="en-US" id="id_7861063_2032132_1_1">Other Comprehensive Income (Loss), Net of Tax</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTax_lbl" xml:lang="en-US" id="id_7861063_2032132_6_1">Other comprehensive income (loss)</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherComprehensiveIncomeLossNetOfTax" xlink:to="us-gaap_OtherComprehensiveIncomeLossNetOfTax_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_lbl" xml:lang="en-US" id="id_7861063_2028212_1_1">Other Comprehensive Income (Loss), Net of Tax [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_lbl" xml:lang="en-US" id="id_7861063_2028212_2_1">Other comprehensive income (loss), net of tax provision:</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract" xlink:to="us-gaap_OtherComprehensiveIncomeLossNetOfTaxPeriodIncreaseDecreaseAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherComprehensiveIncomeOtherNetOfTax" xlink:label="us-gaap_OtherComprehensiveIncomeOtherNetOfTax"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherComprehensiveIncomeOtherNetOfTax_lbl" xml:lang="en-US" id="id_7861063_2034407_1_1">Other Comprehensive Income, Other, Net of Tax</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OtherComprehensiveIncomeOtherNetOfTax_lbl" xml:lang="en-US" id="id_7861063_2034407_2_1">Other, net of tax of $0, $(3), $0 and $(2)</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherComprehensiveIncomeOtherNetOfTax" xlink:to="us-gaap_OtherComprehensiveIncomeOtherNetOfTax_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_OtherComprehensiveIncomeOtherTax" xlink:label="pwr_OtherComprehensiveIncomeOtherTax"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_OtherComprehensiveIncomeOtherTax_lbl" xml:lang="en-US" id="id_7861063_2197722_3_1">Other comprehensive income other tax.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_OtherComprehensiveIncomeOtherTax_lbl" xml:lang="en-US" id="id_7861063_2197722_1_1">Other Comprehensive Income Other Tax</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="pwr_OtherComprehensiveIncomeOtherTax_lbl" xml:lang="en-US" id="id_7861063_2197722_14_1">Other comprehensive income other tax</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_OtherComprehensiveIncomeOtherTax" xlink:to="pwr_OtherComprehensiveIncomeOtherTax_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherLiabilitiesNoncurrent" xlink:label="us-gaap_OtherLiabilitiesNoncurrent"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherLiabilitiesNoncurrent_lbl" xml:lang="en-US" id="id_7861063_2031520_1_1">Other Liabilities, Noncurrent</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OtherLiabilitiesNoncurrent_lbl" xml:lang="en-US" id="id_7861063_2031520_2_1">Insurance and other non-current liabilities</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherLiabilitiesNoncurrent" xlink:to="us-gaap_OtherLiabilitiesNoncurrent_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherLongTermDebt" xlink:label="us-gaap_OtherLongTermDebt"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherLongTermDebt_lbl" xml:lang="en-US" id="id_7861063_2034412_1_1">Other Long-term Debt</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OtherLongTermDebt_lbl" xml:lang="en-US" id="id_7861063_2034412_2_1">Other long-term debt, interest rates ranging from 3.5% to 4.3%</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherLongTermDebt" xlink:to="us-gaap_OtherLongTermDebt_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_OtherLongTermDebtMember" xlink:label="pwr_OtherLongTermDebtMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_OtherLongTermDebtMember_lbl" xml:lang="en-US" id="id_7861063_2200995_3_1">Other Long Term Debt [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_OtherLongTermDebtMember_lbl" xml:lang="en-US" id="id_7861063_2200995_1_1">Other Long Term Debt [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_OtherLongTermDebtMember_lbl" xml:lang="en-US" id="id_7861063_2200995_2_1">Other Long Term Debt [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_OtherLongTermDebtMember" xlink:to="pwr_OtherLongTermDebtMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_OtherNonoperatingIncomeExpense" xlink:label="us-gaap_OtherNonoperatingIncomeExpense"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_OtherNonoperatingIncomeExpense_lbl" xml:lang="en-US" id="id_7861063_2029084_1_1">Other Nonoperating Income (Expense)</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_OtherNonoperatingIncomeExpense_lbl" xml:lang="en-US" id="id_7861063_2029084_2_1">Other income (expense), net</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_OtherNonoperatingIncomeExpense" xlink:to="us-gaap_OtherNonoperatingIncomeExpense_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_OutstandingPerformanceBondsAmount" xlink:label="pwr_OutstandingPerformanceBondsAmount"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_OutstandingPerformanceBondsAmount_lbl" xml:lang="en-US" id="id_7861063_2233325_3_1">Outstanding performance bonds amount.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_OutstandingPerformanceBondsAmount_lbl" xml:lang="en-US" id="id_7861063_2233325_1_1">Outstanding Performance Bonds Amount</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_OutstandingPerformanceBondsAmount_lbl" xml:lang="en-US" id="id_7861063_2233325_2_1">Total amount of outstanding performance bonds</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_OutstandingPerformanceBondsAmount" xlink:to="pwr_OutstandingPerformanceBondsAmount_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PaymentsForProceedsFromInvestments" xlink:label="us-gaap_PaymentsForProceedsFromInvestments"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PaymentsForProceedsFromInvestments_lbl" xml:lang="en-US" id="id_7861063_2028232_1_1">Payments for (Proceeds from) Investments</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_PaymentsForProceedsFromInvestments_lbl" xml:lang="en-US" id="id_7861063_2028232_14_1">Investments in and return of equity from unconsolidated affiliates</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsForProceedsFromInvestments" xlink:to="us-gaap_PaymentsForProceedsFromInvestments_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PaymentsForProceedsFromOtherInvestingActivities" xlink:label="us-gaap_PaymentsForProceedsFromOtherInvestingActivities"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PaymentsForProceedsFromOtherInvestingActivities_lbl" xml:lang="en-US" id="id_7861063_2028913_1_1">Payments for (Proceeds from) Other Investing Activities</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_PaymentsForProceedsFromOtherInvestingActivities_lbl" xml:lang="en-US" id="id_7861063_2028913_14_1">Cash received from (paid for) other investments, net</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsForProceedsFromOtherInvestingActivities" xlink:to="us-gaap_PaymentsForProceedsFromOtherInvestingActivities_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:label="us-gaap_PaymentsForRepurchaseOfCommonStock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PaymentsForRepurchaseOfCommonStock_lbl" xml:lang="en-US" id="id_7861063_2031533_1_1">Payments for Repurchase of Common Stock</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_PaymentsForRepurchaseOfCommonStock_lbl" xml:lang="en-US" id="id_7861063_2031533_2_1">Payments for repurchase of common stock</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_PaymentsForRepurchaseOfCommonStock_lbl" xml:lang="en-US" id="id_7861063_2031533_14_1">Repurchase of common stock</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsForRepurchaseOfCommonStock" xlink:to="us-gaap_PaymentsForRepurchaseOfCommonStock_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PaymentsOfDividendsMinorityInterest" xlink:label="us-gaap_PaymentsOfDividendsMinorityInterest"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PaymentsOfDividendsMinorityInterest_lbl" xml:lang="en-US" id="id_7861063_2034789_1_1">Payments of Ordinary Dividends, Noncontrolling Interest</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_PaymentsOfDividendsMinorityInterest_lbl" xml:lang="en-US" id="id_7861063_2034789_14_1">Distributions to non-controlling interests</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsOfDividendsMinorityInterest" xlink:to="us-gaap_PaymentsOfDividendsMinorityInterest_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired" xlink:label="us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_lbl" xml:lang="en-US" id="id_7861063_2031535_1_1">Payments to Acquire Businesses, Net of Cash Acquired</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_lbl" xml:lang="en-US" id="id_7861063_2031535_14_1">Cash paid for acquisitions, net of cash acquired</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired" xlink:to="us-gaap_PaymentsToAcquireBusinessesNetOfCashAcquired_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PaymentsToAcquireEquityMethodInvestments" xlink:label="us-gaap_PaymentsToAcquireEquityMethodInvestments"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PaymentsToAcquireEquityMethodInvestments_lbl" xml:lang="en-US" id="id_7861063_2029786_1_1">Payments to Acquire Equity Method Investments</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_PaymentsToAcquireEquityMethodInvestments_lbl" xml:lang="en-US" id="id_7861063_2029786_2_1">Aggregate contributions to this unconsolidated affiliate</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsToAcquireEquityMethodInvestments" xlink:to="us-gaap_PaymentsToAcquireEquityMethodInvestments_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xml:lang="en-US" id="id_7861063_2034791_1_1">Payments to Acquire Property, Plant, and Equipment</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl" xml:lang="en-US" id="id_7861063_2034791_14_1">Additions of property and equipment</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:to="us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_PercentageOfCapitalStockOfDirectForeignSubsidiariesRequiredToSecureCreditAgreement" xlink:label="pwr_PercentageOfCapitalStockOfDirectForeignSubsidiariesRequiredToSecureCreditAgreement"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_PercentageOfCapitalStockOfDirectForeignSubsidiariesRequiredToSecureCreditAgreement_lbl" xml:lang="en-US" id="id_7861063_2046564_3_1">Percentage of capital stock of direct foreign subsidiaries required to secure credit agreement.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_PercentageOfCapitalStockOfDirectForeignSubsidiariesRequiredToSecureCreditAgreement_lbl" xml:lang="en-US" id="id_7861063_2046564_1_1">Percentage Of Capital Stock Of Direct Foreign Subsidiaries Required To Secure Credit Agreement</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_PercentageOfCapitalStockOfDirectForeignSubsidiariesRequiredToSecureCreditAgreement_lbl" xml:lang="en-US" id="id_7861063_2046564_2_1">Percentage of capital stock of direct foreign subsidiaries required to secure credit agreement</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_PercentageOfCapitalStockOfDirectForeignSubsidiariesRequiredToSecureCreditAgreement" xlink:to="pwr_PercentageOfCapitalStockOfDirectForeignSubsidiariesRequiredToSecureCreditAgreement_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_PercentageOfForeignRevenue" xlink:label="pwr_PercentageOfForeignRevenue"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_PercentageOfForeignRevenue_lbl" xml:lang="en-US" id="id_7861063_2057717_3_1">Percentage of foreign revenue.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_PercentageOfForeignRevenue_lbl" xml:lang="en-US" id="id_7861063_2057717_1_1">Percentage Of Foreign Revenue</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_PercentageOfForeignRevenue_lbl" xml:lang="en-US" id="id_7861063_2057717_2_1">Percentage of foreign revenues</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_PercentageOfForeignRevenue" xlink:to="pwr_PercentageOfForeignRevenue_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_PercentChangeInContractEstimatesImpactOnOperatingResultsIsLessThanThisPercentage" xlink:label="pwr_PercentChangeInContractEstimatesImpactOnOperatingResultsIsLessThanThisPercentage"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_PercentChangeInContractEstimatesImpactOnOperatingResultsIsLessThanThisPercentage_lbl" xml:lang="en-US" id="id_7861063_2306761_3_1">Percent change in contract estimates impact on operating results is less than this percentage.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_PercentChangeInContractEstimatesImpactOnOperatingResultsIsLessThanThisPercentage_lbl" xml:lang="en-US" id="id_7861063_2306761_1_1">Percent Change In Contract Estimates Impact On Operating Results Is Less than This Percentage</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_PercentChangeInContractEstimatesImpactOnOperatingResultsIsLessThanThisPercentage_lbl" xml:lang="en-US" id="id_7861063_2306761_2_1">Percent change in contract estimates impact on operating results is less than this percentage</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_PercentChangeInContractEstimatesImpactOnOperatingResultsIsLessThanThisPercentage" xlink:to="pwr_PercentChangeInContractEstimatesImpactOnOperatingResultsIsLessThanThisPercentage_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_PerformanceBasedAwardPerformancePercentage" xlink:label="pwr_PerformanceBasedAwardPerformancePercentage"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_PerformanceBasedAwardPerformancePercentage_lbl" xml:lang="en-US" id="id_7861063_2066207_3_1">Performance Based Award Performance Percentage</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_PerformanceBasedAwardPerformancePercentage_lbl" xml:lang="en-US" id="id_7861063_2066207_1_1">Performance Based Award Performance Percentage</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_PerformanceBasedAwardPerformancePercentage_lbl" xml:lang="en-US" id="id_7861063_2066207_2_1">Performance units performance percentage</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_PerformanceBasedAwardPerformancePercentage" xlink:to="pwr_PerformanceBasedAwardPerformancePercentage_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_PerformanceLettersOfCreditMember" xlink:label="pwr_PerformanceLettersOfCreditMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_PerformanceLettersOfCreditMember_lbl" xml:lang="en-US" id="id_7861063_2152709_3_1">Performance Letters Of Credit [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_PerformanceLettersOfCreditMember_lbl" xml:lang="en-US" id="id_7861063_2152709_1_1">Performance Letters Of Credit [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_PerformanceLettersOfCreditMember_lbl" xml:lang="en-US" id="id_7861063_2152709_2_1">Performance Letters of Credit [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_PerformanceLettersOfCreditMember" xlink:to="pwr_PerformanceLettersOfCreditMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_PerformanceUnitsMember" xlink:label="pwr_PerformanceUnitsMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_PerformanceUnitsMember_lbl" xml:lang="en-US" id="id_7861063_2103894_3_1">Performance units.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_PerformanceUnitsMember_lbl" xml:lang="en-US" id="id_7861063_2103894_1_1">Performance Units [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_PerformanceUnitsMember_lbl" xml:lang="en-US" id="id_7861063_2103894_2_1">Performance Units [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_PerformanceUnitsMember" xlink:to="pwr_PerformanceUnitsMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_PeriodAfterAccountsReceivableAreTreatedAsDelinquent" xlink:label="pwr_PeriodAfterAccountsReceivableAreTreatedAsDelinquent"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_PeriodAfterAccountsReceivableAreTreatedAsDelinquent_lbl" xml:lang="en-US" id="id_7861063_2185509_3_1">Period after accounts receivable are treated as delinquent.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_PeriodAfterAccountsReceivableAreTreatedAsDelinquent_lbl" xml:lang="en-US" id="id_7861063_2185509_1_1">Period After Accounts Receivable Are Treated As Delinquent</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_PeriodAfterAccountsReceivableAreTreatedAsDelinquent_lbl" xml:lang="en-US" id="id_7861063_2185509_2_1">Number of days after accounts receivable are treated as delinquent</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_PeriodAfterAccountsReceivableAreTreatedAsDelinquent" xlink:to="pwr_PeriodAfterAccountsReceivableAreTreatedAsDelinquent_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_PeriodRelatedToOutstandingAccountsReceivableForAnalysisOfAllowanceForDoubtfulAccounts" xlink:label="pwr_PeriodRelatedToOutstandingAccountsReceivableForAnalysisOfAllowanceForDoubtfulAccounts"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_PeriodRelatedToOutstandingAccountsReceivableForAnalysisOfAllowanceForDoubtfulAccounts_lbl" xml:lang="en-US" id="id_7861063_2122046_3_1">Number of days related to outstanding accounts receivable for analysis of the allowance for doubtful accounts.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_PeriodRelatedToOutstandingAccountsReceivableForAnalysisOfAllowanceForDoubtfulAccounts_lbl" xml:lang="en-US" id="id_7861063_2122046_1_1">Period Related To Outstanding Accounts Receivable For Analysis Of Allowance For Doubtful Accounts</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_PeriodRelatedToOutstandingAccountsReceivableForAnalysisOfAllowanceForDoubtfulAccounts_lbl" xml:lang="en-US" id="id_7861063_2122046_2_1">Number of days related to outstanding accounts receivable for analysis of the allowance for doubtful accounts</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_PeriodRelatedToOutstandingAccountsReceivableForAnalysisOfAllowanceForDoubtfulAccounts" xlink:to="pwr_PeriodRelatedToOutstandingAccountsReceivableForAnalysisOfAllowanceForDoubtfulAccounts_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="us-gaap_PlanNameAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PlanNameAxis_lbl" xml:lang="en-US" id="id_7861063_2029102_1_1">Plan Name [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_PlanNameAxis_lbl" xml:lang="en-US" id="id_7861063_2029102_2_1">Plan Name [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PlanNameAxis" xlink:to="us-gaap_PlanNameAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="us-gaap_PlanNameDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PlanNameDomain_lbl" xml:lang="en-US" id="id_7861063_2039004_1_1">Plan Name [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_PlanNameDomain_lbl" xml:lang="en-US" id="id_7861063_2039004_2_1">Plan Name [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PlanNameDomain" xlink:to="us-gaap_PlanNameDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PreferredStockParOrStatedValuePerShare" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare_lbl" xml:lang="en-US" id="id_7861063_2028253_1_1">Preferred Stock, Par or Stated Value Per Share</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_PreferredStockParOrStatedValuePerShare_lbl" xml:lang="en-US" id="id_7861063_2028253_2_1">Preferred stock, par value</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockParOrStatedValuePerShare" xlink:to="us-gaap_PreferredStockParOrStatedValuePerShare_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PreferredStockSharesAuthorized" xlink:label="us-gaap_PreferredStockSharesAuthorized"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PreferredStockSharesAuthorized_lbl" xml:lang="en-US" id="id_7861063_2028472_1_1">Preferred Stock, Shares Authorized</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_PreferredStockSharesAuthorized_lbl" xml:lang="en-US" id="id_7861063_2028472_2_1">Preferred stock, shares authorized</label>
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    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockSharesIssued" xlink:to="us-gaap_PreferredStockSharesIssued_lbl"/>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PreferredStockSharesOutstanding_lbl" xml:lang="en-US" id="id_7861063_2030412_1_1">Preferred Stock, Shares Outstanding</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_PreferredStockSharesOutstanding_lbl" xml:lang="en-US" id="id_7861063_2030412_2_1">Number of preferred Stock issued to voting trust</label>
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    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PreferredStockSharesOutstanding" xlink:to="us-gaap_PreferredStockSharesOutstanding_lbl"/>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PreferredStockValue_lbl" xml:lang="en-US" id="id_7861063_2034043_1_1">Preferred Stock, Value, Issued</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_PrepaidExpenseAndOtherAssetsCurrent_lbl" xml:lang="en-US" id="id_7861063_2037836_2_1">Prepaid expenses and other current assets</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:to="us-gaap_PrepaidExpenseAndOtherAssetsCurrent_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProceedsFromDivestitureOfBusinessesNetOfCashDivested" xlink:label="us-gaap_ProceedsFromDivestitureOfBusinessesNetOfCashDivested"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromDivestitureOfBusinessesNetOfCashDivested_lbl" xml:lang="en-US" id="id_7861063_2033015_1_1">Proceeds from Divestiture of Businesses, Net of Cash Divested</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ProceedsFromDivestitureOfBusinessesNetOfCashDivested_lbl" xml:lang="en-US" id="id_7861063_2033015_2_1">Net cash proceeds from sale of fiber optic licensing operations</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital" xlink:label="us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital_lbl" xml:lang="en-US" id="id_7861063_2031300_1_1">Proceeds from Equity Method Investment, Dividends or Distributions, Return of Capital</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital_lbl" xml:lang="en-US" id="id_7861063_2031300_2_1">Proceeds from return of capital</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital" xlink:to="us-gaap_ProceedsFromEquityMethodInvestmentDividendsOrDistributionsReturnOfCapital_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProceedsFromIncomeTaxRefunds" xlink:label="us-gaap_ProceedsFromIncomeTaxRefunds"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromIncomeTaxRefunds_lbl" xml:lang="en-US" id="id_7861063_2033466_1_1">Proceeds from Income Tax Refunds</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ProceedsFromIncomeTaxRefunds_lbl" xml:lang="en-US" id="id_7861063_2033466_2_1">Income tax refunds related to continuing operations</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromIncomeTaxRefunds" xlink:to="us-gaap_ProceedsFromIncomeTaxRefunds_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProceedsFromLongTermLinesOfCredit" xlink:label="us-gaap_ProceedsFromLongTermLinesOfCredit"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromLongTermLinesOfCredit_lbl" xml:lang="en-US" id="id_7861063_2028264_1_1">Proceeds from Long-term Lines of Credit</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ProceedsFromLongTermLinesOfCredit_lbl" xml:lang="en-US" id="id_7861063_2028264_2_1">Borrowings under credit facility</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromLongTermLinesOfCredit" xlink:to="us-gaap_ProceedsFromLongTermLinesOfCredit_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment" xlink:label="us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_lbl" xml:lang="en-US" id="id_7861063_2035020_1_1">Proceeds from Sale of Property, Plant, and Equipment</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_lbl" xml:lang="en-US" id="id_7861063_2035020_2_1">Proceeds from sale of property and equipment</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment" xlink:to="us-gaap_ProceedsFromSaleOfPropertyPlantAndEquipment_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProceedsFromStockOptionsExercised" xlink:label="us-gaap_ProceedsFromStockOptionsExercised"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProceedsFromStockOptionsExercised_lbl" xml:lang="en-US" id="id_7861063_2039031_1_1">Proceeds from Stock Options Exercised</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ProceedsFromStockOptionsExercised_lbl" xml:lang="en-US" id="id_7861063_2039031_2_1">Exercise of stock options</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProceedsFromStockOptionsExercised" xlink:to="us-gaap_ProceedsFromStockOptionsExercised_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProfitLoss" xlink:label="us-gaap_ProfitLoss"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProfitLoss_lbl" xml:lang="en-US" id="id_7861063_2039475_1_1">Net Income (Loss), Including Portion Attributable to Noncontrolling Interest</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ProfitLoss_lbl" xml:lang="en-US" id="id_7861063_2039475_2_1">Net income</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_ProfitLoss_lbl" xml:lang="en-US" id="id_7861063_2039475_6_1">Net income</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProjectMember" xlink:label="us-gaap_ProjectMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProjectMember_lbl" xml:lang="en-US" id="id_7861063_2037853_1_1">Project [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ProjectMember_lbl" xml:lang="en-US" id="id_7861063_2037853_2_1">Project [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProjectMember" xlink:to="us-gaap_ProjectMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="us-gaap_PropertyPlantAndEquipmentNet"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xml:lang="en-US" id="id_7861063_2035024_1_1">Property, Plant and Equipment, Net</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xml:lang="en-US" id="id_7861063_2035024_2_1">Property and equipment</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_PropertyPlantAndEquipmentNet_lbl" xml:lang="en-US" id="id_7861063_2035024_12_1">Property and equipment, net of accumulated depreciation of $824,108 and $755,272</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ProvisionForDoubtfulAccounts" xlink:label="us-gaap_ProvisionForDoubtfulAccounts"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ProvisionForDoubtfulAccounts_lbl" xml:lang="en-US" id="id_7861063_2030245_1_1">Provision for Doubtful Accounts</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ProvisionForDoubtfulAccounts_lbl" xml:lang="en-US" id="id_7861063_2030245_2_1">Provision for (recovery of) doubtful accounts</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ProvisionForDoubtfulAccounts" xlink:to="us-gaap_ProvisionForDoubtfulAccounts_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_QuantaElectricPowerInfrastructureServicesSegmentMember" xlink:label="pwr_QuantaElectricPowerInfrastructureServicesSegmentMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_QuantaElectricPowerInfrastructureServicesSegmentMember_lbl" xml:lang="en-US" id="id_7861063_2315483_3_1">Quanta Electric Power Infrastructure Services Segment [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_QuantaElectricPowerInfrastructureServicesSegmentMember_lbl" xml:lang="en-US" id="id_7861063_2315483_1_1">Quanta Electric Power Infrastructure Services Segment [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_QuantaElectricPowerInfrastructureServicesSegmentMember_lbl" xml:lang="en-US" id="id_7861063_2315483_2_1">Quanta's Electric Power Infrastructure Services Segment [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_QuantaElectricPowerInfrastructureServicesSegmentMember" xlink:to="pwr_QuantaElectricPowerInfrastructureServicesSegmentMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeAxis" xlink:label="us-gaap_RangeAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RangeAxis_lbl" xml:lang="en-US" id="id_7861063_2028497_1_1">Range [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_RangeAxis_lbl" xml:lang="en-US" id="id_7861063_2028497_2_1">Range [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RangeAxis" xlink:to="us-gaap_RangeAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RangeMember" xlink:label="us-gaap_RangeMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RangeMember_lbl" xml:lang="en-US" id="id_7861063_2030442_1_1">Range [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_RangeMember_lbl" xml:lang="en-US" id="id_7861063_2030442_2_1">Range [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RangeMember" xlink:to="us-gaap_RangeMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ReceivablesAbstract" xlink:label="us-gaap_ReceivablesAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ReceivablesAbstract_lbl" xml:lang="en-US" id="id_7861063_2038046_1_1">Receivables [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ReceivablesAbstract_lbl" xml:lang="en-US" id="id_7861063_2038046_2_1">Receivables [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ReceivablesAbstract" xlink:to="us-gaap_ReceivablesAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ReceivablesPolicyTextBlock" xlink:label="us-gaap_ReceivablesPolicyTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ReceivablesPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2028958_1_1">Receivables, Policy [Policy Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ReceivablesPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2028958_2_1">Current and Long-Term Accounts and Notes Receivable and Allowance for Doubtful Accounts</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ReceivablesPolicyTextBlock" xlink:to="us-gaap_ReceivablesPolicyTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_ReductionInCompanyMaximumFundedDebtAndMaximumSeniorDebtByAllCashAndCashEquivalentsInExcessOfAmount" xlink:label="pwr_ReductionInCompanyMaximumFundedDebtAndMaximumSeniorDebtByAllCashAndCashEquivalentsInExcessOfAmount"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_ReductionInCompanyMaximumFundedDebtAndMaximumSeniorDebtByAllCashAndCashEquivalentsInExcessOfAmount_lbl" xml:lang="en-US" id="id_7861063_2341066_3_1">Reduction in Quanta's maximum funded debt and maximum senior debt by all cash and cash equivalents in excess of amount.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_ReductionInCompanyMaximumFundedDebtAndMaximumSeniorDebtByAllCashAndCashEquivalentsInExcessOfAmount_lbl" xml:lang="en-US" id="id_7861063_2341066_1_1">Reduction In Company Maximum Funded Debt And Maximum Senior Debt By All Cash And Cash Equivalents In Excess Of Amount</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_ReductionInCompanyMaximumFundedDebtAndMaximumSeniorDebtByAllCashAndCashEquivalentsInExcessOfAmount_lbl" xml:lang="en-US" id="id_7861063_2341066_2_1">Reduction in Quanta's maximum funded debt and maximum senior debt by all cash and cash equivalents in excess of amount</label>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RegulatedOperationsAbstract_lbl" xml:lang="en-US" id="id_7861063_2038828_1_1">Regulated Operations [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_RegulatedOperationsAbstract_lbl" xml:lang="en-US" id="id_7861063_2038828_2_1">Regulated Operations [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RegulatedOperationsAbstract" xlink:to="us-gaap_RegulatedOperationsAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RepaymentsOfLongTermLinesOfCredit" xlink:label="us-gaap_RepaymentsOfLongTermLinesOfCredit"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RepaymentsOfLongTermLinesOfCredit_lbl" xml:lang="en-US" id="id_7861063_2039500_1_1">Repayments of Long-term Lines of Credit</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_RepaymentsOfLongTermLinesOfCredit_lbl" xml:lang="en-US" id="id_7861063_2039500_14_1">Payments under credit facility</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RepaymentsOfLongTermLinesOfCredit" xlink:to="us-gaap_RepaymentsOfLongTermLinesOfCredit_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RepaymentsOfOtherLongTermDebt" xlink:label="us-gaap_RepaymentsOfOtherLongTermDebt"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RepaymentsOfOtherLongTermDebt_lbl" xml:lang="en-US" id="id_7861063_2038656_1_1">Repayments of Other Long-term Debt</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_RepaymentsOfOtherLongTermDebt_lbl" xml:lang="en-US" id="id_7861063_2038656_14_1">Payments on other long-term debt</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RepaymentsOfOtherLongTermDebt" xlink:to="us-gaap_RepaymentsOfOtherLongTermDebt_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RepaymentsOfShortTermDebt" xlink:label="us-gaap_RepaymentsOfShortTermDebt"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RepaymentsOfShortTermDebt_lbl" xml:lang="en-US" id="id_7861063_2040268_1_1">Repayments of Short-term Debt</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_RepaymentsOfShortTermDebt_lbl" xml:lang="en-US" id="id_7861063_2040268_14_1">Payments on short-term debt</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RepaymentsOfShortTermDebt" xlink:to="us-gaap_RepaymentsOfShortTermDebt_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_RepurchaseProgram2015OpenMarketPurchasesAndAcceleratedShareRepurchaseProgramMember" xlink:label="pwr_RepurchaseProgram2015OpenMarketPurchasesAndAcceleratedShareRepurchaseProgramMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_RepurchaseProgram2015OpenMarketPurchasesAndAcceleratedShareRepurchaseProgramMember_lbl" xml:lang="en-US" id="id_7861063_2128491_3_1">Represents the 2015 Repurchase Program.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_RepurchaseProgram2015OpenMarketPurchasesAndAcceleratedShareRepurchaseProgramMember_lbl" xml:lang="en-US" id="id_7861063_2128491_1_1">Repurchase Program, 2015 Open Market Purchases And Accelerated Share Repurchase Program [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_RepurchaseProgram2015OpenMarketPurchasesAndAcceleratedShareRepurchaseProgramMember_lbl" xml:lang="en-US" id="id_7861063_2128491_2_1">2015 Repurchase Plan Open Market Purchases And Accelerated Share Repurchase Agreement [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_RepurchaseProgram2015OpenMarketPurchasesAndAcceleratedShareRepurchaseProgramMember" xlink:to="pwr_RepurchaseProgram2015OpenMarketPurchasesAndAcceleratedShareRepurchaseProgramMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:label="us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_lbl" xml:lang="en-US" id="id_7861063_2031755_1_1">Cash and Cash Equivalents [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_lbl" xml:lang="en-US" id="id_7861063_2031755_2_1">Cash and Cash Equivalents [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember" xlink:to="us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_RestrictedStockAndRestrictedStockUnitsToBeSettledInCommonStockMember" xlink:label="pwr_RestrictedStockAndRestrictedStockUnitsToBeSettledInCommonStockMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_RestrictedStockAndRestrictedStockUnitsToBeSettledInCommonStockMember_lbl" xml:lang="en-US" id="id_7861063_2256074_3_1">Restricted Stock And Restricted Stock Units To Be Settled In Common Stock [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_RestrictedStockAndRestrictedStockUnitsToBeSettledInCommonStockMember_lbl" xml:lang="en-US" id="id_7861063_2256074_1_1">Restricted Stock And Restricted Stock Units To Be Settled In Common Stock [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_RestrictedStockAndRestrictedStockUnitsToBeSettledInCommonStockMember_lbl" xml:lang="en-US" id="id_7861063_2256074_2_1">Restricted Stock and Restricted Stock Units to be Settled in Common Stock [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_RestrictedStockAndRestrictedStockUnitsToBeSettledInCommonStockMember" xlink:to="pwr_RestrictedStockAndRestrictedStockUnitsToBeSettledInCommonStockMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_RestrictedStockUnitsToBeSettledInCashMember" xlink:label="pwr_RestrictedStockUnitsToBeSettledInCashMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_RestrictedStockUnitsToBeSettledInCashMember_lbl" xml:lang="en-US" id="id_7861063_2299465_3_1">Restricted Stock Units To Be Settled In Cash [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_RestrictedStockUnitsToBeSettledInCashMember_lbl" xml:lang="en-US" id="id_7861063_2299465_1_1">Restricted Stock Units To Be Settled In Cash [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_RestrictedStockUnitsToBeSettledInCashMember_lbl" xml:lang="en-US" id="id_7861063_2299465_2_1">Restricted Stock Units to be Settled in Cash [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_RestrictedStockUnitsToBeSettledInCashMember" xlink:to="pwr_RestrictedStockUnitsToBeSettledInCashMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RetainedEarningsAccumulatedDeficit" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xml:lang="en-US" id="id_7861063_2037317_1_1">Retained Earnings (Accumulated Deficit)</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_RetainedEarningsAccumulatedDeficit_lbl" xml:lang="en-US" id="id_7861063_2037317_2_1">Retained earnings</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RetainedEarningsAccumulatedDeficit" xlink:to="us-gaap_RetainedEarningsAccumulatedDeficit_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RevenueRecognitionAbstract" xlink:label="us-gaap_RevenueRecognitionAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RevenueRecognitionAbstract_lbl" xml:lang="en-US" id="id_7861063_2039882_1_1">Revenue Recognition [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_RevenueRecognitionAbstract_lbl" xml:lang="en-US" id="id_7861063_2039882_2_1">Revenue Recognition [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenueRecognitionAbstract" xlink:to="us-gaap_RevenueRecognitionAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_RevenueRecognitionPercentageOfCompletionPercentComplete" xlink:label="pwr_RevenueRecognitionPercentageOfCompletionPercentComplete"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_RevenueRecognitionPercentageOfCompletionPercentComplete_lbl" xml:lang="en-US" id="id_7861063_2384151_3_1">Represents revenue recognition for long-term contracts accounted for using the completed-contract method stated, as a percent complete.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_RevenueRecognitionPercentageOfCompletionPercentComplete_lbl" xml:lang="en-US" id="id_7861063_2384151_1_1">Revenue Recognition Percentage Of Completion Percent Complete</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_RevenueRecognitionPercentageOfCompletionPercentComplete_lbl" xml:lang="en-US" id="id_7861063_2384151_2_1">Project completion percentage</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_RevenueRecognitionPercentageOfCompletionPercentComplete" xlink:to="pwr_RevenueRecognitionPercentageOfCompletionPercentComplete_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RevenueRecognitionPolicyTextBlock" xlink:label="us-gaap_RevenueRecognitionPolicyTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RevenueRecognitionPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2039697_1_1">Revenue Recognition, Policy [Policy Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_RevenueRecognitionPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2039697_2_1">Revenue Recognition</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RevenueRecognitionPolicyTextBlock" xlink:to="us-gaap_RevenueRecognitionPolicyTextBlock_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_RevenueRecognitionTable" xlink:label="pwr_RevenueRecognitionTable"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_RevenueRecognitionTable_lbl" xml:lang="en-US" id="id_7861063_2115665_3_1">Revenue Recognition [Table]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_RevenueRecognitionTable_lbl" xml:lang="en-US" id="id_7861063_2115665_1_1">Revenue Recognition [Table]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_RevenueRecognitionTable_lbl" xml:lang="en-US" id="id_7861063_2115665_2_1">Revenue Recognition [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_RevenueRecognitionTable" xlink:to="pwr_RevenueRecognitionTable_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_RevenueRecognizedForCurrentPeriodLossesLineItems" xlink:label="pwr_RevenueRecognizedForCurrentPeriodLossesLineItems"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_RevenueRecognizedForCurrentPeriodLossesLineItems_lbl" xml:lang="en-US" id="id_7861063_2393994_3_1">Revenue recognized for current period losses [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_RevenueRecognizedForCurrentPeriodLossesLineItems_lbl" xml:lang="en-US" id="id_7861063_2393994_1_1">Revenue recognized for current period losses [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_RevenueRecognizedForCurrentPeriodLossesLineItems_lbl" xml:lang="en-US" id="id_7861063_2393994_2_1">Revenue recognized for current period losses [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_RevenueRecognizedForCurrentPeriodLossesLineItems" xlink:to="pwr_RevenueRecognizedForCurrentPeriodLossesLineItems_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_Revenues" xlink:label="us-gaap_Revenues"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_Revenues_lbl" xml:lang="en-US" id="id_7861063_2028297_1_1">Revenues</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_Revenues_lbl" xml:lang="en-US" id="id_7861063_2028297_2_1">Revenues</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_Revenues" xlink:to="us-gaap_Revenues_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_RevolvingLoansAndLetterOfCreditInAlternativeCurrenciesMember" xlink:label="pwr_RevolvingLoansAndLetterOfCreditInAlternativeCurrenciesMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_RevolvingLoansAndLetterOfCreditInAlternativeCurrenciesMember_lbl" xml:lang="en-US" id="id_7861063_2185645_3_1">Revolving loans and letter of credit in alternative currencies.</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_RevolvingLoansAndLetterOfCreditInAlternativeCurrenciesMember_lbl" xml:lang="en-US" id="id_7861063_2185645_1_1">Revolving Loans And Letter Of Credit In Alternative Currencies [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_RevolvingLoansAndLetterOfCreditInAlternativeCurrenciesMember_lbl" xml:lang="en-US" id="id_7861063_2185645_2_1">Revolving Loans and Letter of Credit in Alternative Currencies [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_RevolvingLoansAndLetterOfCreditInAlternativeCurrenciesMember" xlink:to="pwr_RevolvingLoansAndLetterOfCreditInAlternativeCurrenciesMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_RisksAndUncertaintiesAbstract" xlink:label="us-gaap_RisksAndUncertaintiesAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_RisksAndUncertaintiesAbstract_lbl" xml:lang="en-US" id="id_7861063_2036229_1_1">Risks and Uncertainties [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_RisksAndUncertaintiesAbstract_lbl" xml:lang="en-US" id="id_7861063_2036229_2_1">Risks and Uncertainties [Abstract]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_RisksAndUncertaintiesAbstract" xlink:to="us-gaap_RisksAndUncertaintiesAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SalesRevenueNetMember" xlink:label="us-gaap_SalesRevenueNetMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SalesRevenueNetMember_lbl" xml:lang="en-US" id="id_7861063_2037489_1_1">Sales Revenue, Net [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_SalesRevenueNetMember_lbl" xml:lang="en-US" id="id_7861063_2037489_2_1">Sales Revenue, Net [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SalesRevenueNetMember" xlink:to="us-gaap_SalesRevenueNetMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SalesRevenueServicesNet" xlink:label="us-gaap_SalesRevenueServicesNet"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SalesRevenueServicesNet_lbl" xml:lang="en-US" id="id_7861063_2039302_1_1">Sales Revenue, Services, Net</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_SalesRevenueServicesNet_lbl" xml:lang="en-US" id="id_7861063_2039302_2_1">Revenues</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SalesRevenueServicesNet" xlink:to="us-gaap_SalesRevenueServicesNet_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScenarioForecastMember" xlink:label="us-gaap_ScenarioForecastMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScenarioForecastMember_lbl" xml:lang="en-US" id="id_7861063_2038269_1_1">Scenario, Forecast [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ScenarioForecastMember_lbl" xml:lang="en-US" id="id_7861063_2038269_2_1">Scenario Forecast [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScenarioForecastMember" xlink:to="us-gaap_ScenarioForecastMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScenarioUnspecifiedDomain" xlink:label="us-gaap_ScenarioUnspecifiedDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScenarioUnspecifiedDomain_lbl" xml:lang="en-US" id="id_7861063_2036952_1_1">Scenario, Unspecified [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ScenarioUnspecifiedDomain_lbl" xml:lang="en-US" id="id_7861063_2036952_2_1">Scenario, Unspecified [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScenarioUnspecifiedDomain" xlink:to="us-gaap_ScenarioUnspecifiedDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_lbl" xml:lang="en-US" id="id_7861063_2035694_1_1">Schedule of Business Acquisitions, by Acquisition [Table]</label>
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    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable" xlink:to="us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionTable_lbl"/>
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    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SegmentReportingInformationLineItems" xlink:to="us-gaap_SegmentReportingInformationLineItems_lbl"/>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_SegmentReportingPolicyPolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2035536_2_1">Segment Reporting</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SelfInsuranceReservePolicyTextBlock" xlink:label="us-gaap_SelfInsuranceReservePolicyTextBlock"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SelfInsuranceReservePolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2036067_1_1">Self Insurance Reserve [Policy Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_SelfInsuranceReservePolicyTextBlock_lbl" xml:lang="en-US" id="id_7861063_2036067_2_1">Self-Insurance</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SellingGeneralAndAdministrativeExpense" xlink:label="us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SellingGeneralAndAdministrativeExpense_lbl" xml:lang="en-US" id="id_7861063_2036068_1_1">Selling, General and Administrative Expense</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_SellingGeneralAndAdministrativeExpense_lbl" xml:lang="en-US" id="id_7861063_2036068_2_1">Selling, general and administrative expenses</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SellingGeneralAndAdministrativeExpense" xlink:to="us-gaap_SellingGeneralAndAdministrativeExpense_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_SeriesFAndSeriesGPreferredStockMember" xlink:label="pwr_SeriesFAndSeriesGPreferredStockMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_SeriesFAndSeriesGPreferredStockMember_lbl" xml:lang="en-US" id="id_7861063_2113193_3_1">Series F- and Series G- Preferred Stock [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_SeriesFAndSeriesGPreferredStockMember_lbl" xml:lang="en-US" id="id_7861063_2113193_1_1">Series F- and Series G- Preferred Stock [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_SeriesFAndSeriesGPreferredStockMember_lbl" xml:lang="en-US" id="id_7861063_2113193_2_1">Series F- and Series G- Preferred Stock [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_SeriesFAndSeriesGPreferredStockMember" xlink:to="pwr_SeriesFAndSeriesGPreferredStockMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SeriesFPreferredStockMember" xlink:label="us-gaap_SeriesFPreferredStockMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SeriesFPreferredStockMember_lbl" xml:lang="en-US" id="id_7861063_2037173_1_1">Series F Preferred Stock [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_SeriesFPreferredStockMember_lbl" xml:lang="en-US" id="id_7861063_2037173_2_1">Series F Preferred Stock [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SeriesFPreferredStockMember" xlink:to="us-gaap_SeriesFPreferredStockMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SeriesGPreferredStockMember" xlink:label="us-gaap_SeriesGPreferredStockMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SeriesGPreferredStockMember_lbl" xml:lang="en-US" id="id_7861063_2037508_1_1">Series G Preferred Stock [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_SeriesGPreferredStockMember_lbl" xml:lang="en-US" id="id_7861063_2037508_2_1">Series G Preferred Stock [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SeriesGPreferredStockMember" xlink:to="us-gaap_SeriesGPreferredStockMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember" xlink:label="us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_lbl" xml:lang="en-US" id="id_7861063_2037929_1_1">Series of Individually Immaterial Business Acquisitions [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_lbl" xml:lang="en-US" id="id_7861063_2037929_2_1">Acquisitions [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember" xlink:to="us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensation" xlink:label="us-gaap_ShareBasedCompensation"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensation_lbl" xml:lang="en-US" id="id_7861063_2039916_1_1">Share-based Compensation</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ShareBasedCompensation_lbl" xml:lang="en-US" id="id_7861063_2039916_2_1">Non-cash stock compensation expense</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ShareBasedCompensation_lbl" xml:lang="en-US" id="id_7861063_2039916_12_1">Non-cash stock-based compensation</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensation" xlink:to="us-gaap_ShareBasedCompensation_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_lbl" xml:lang="en-US" id="id_7861063_2040492_1_1">Share-based Compensation Arrangement by Share-based Payment Award, Award Requisite Service Period</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_lbl" xml:lang="en-US" id="id_7861063_2040492_2_1">Required performance period</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardRequisiteServicePeriod1_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_lbl" xml:lang="en-US" id="id_7861063_2036265_1_1">Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_lbl" xml:lang="en-US" id="id_7861063_2036265_2_1">Vesting period for restricted stock and restricted stock units</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_lbl" xml:lang="en-US" id="id_7861063_2038710_1_1">Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_lbl" xml:lang="en-US" id="id_7861063_2038710_2_1">Granted, shares</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_lbl" xml:lang="en-US" id="id_7861063_2038710_12_1">Performance units granted</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl" xml:lang="en-US" id="id_7861063_2035122_1_1">Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl" xml:lang="en-US" id="id_7861063_2035122_2_1">Granted, weighted average grant date fair value, per share</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_lbl" xml:lang="en-US" id="id_7861063_2037346_1_1">Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_lbl" xml:lang="en-US" id="id_7861063_2037346_2_1">Awards vested</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_lbl" xml:lang="en-US" id="id_7861063_2037346_12_1">Performance units vested</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue_lbl" xml:lang="en-US" id="id_7861063_2036268_1_1">Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue_lbl" xml:lang="en-US" id="id_7861063_2036268_2_1">Fair value of restricted stock, vested</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodTotalFairValue_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xml:lang="en-US" id="id_7861063_2035719_1_1">Share-based Compensation Arrangement by Share-based Payment Award [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl" xml:lang="en-US" id="id_7861063_2035719_2_1">Share-based Compensation Arrangement by Share-based Payment Award [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_lbl" xml:lang="en-US" id="id_7861063_2036270_1_1">Share-based Compensation Arrangement by Share-based Payment Award, Shares Issued in Period</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_lbl" xml:lang="en-US" id="id_7861063_2036270_2_1">Number of common shares issued in connection with performance units</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedInPeriod_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardTermsOfAward" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardTermsOfAward"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardTermsOfAward_lbl" xml:lang="en-US" id="id_7861063_2038871_1_1">Share-based Compensation Arrangement by Share-based Payment Award, Terms of Award</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardTermsOfAward_lbl" xml:lang="en-US" id="id_7861063_2038871_2_1">Performance units vesting conditions</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardTermsOfAward" xlink:to="us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardTermsOfAward_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_lbl" xml:lang="en-US" id="id_7861063_2036771_2_1">Equity Award [Domain]</label>
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    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementBusinessSegmentsAxis" xlink:to="us-gaap_StatementBusinessSegmentsAxis_lbl"/>
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    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_StatementGeographicalAxis" xlink:to="us-gaap_StatementGeographicalAxis_lbl"/>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_StatementOfFinancialPositionAbstract_lbl" xml:lang="en-US" id="id_7861063_2039336_2_1">Statement of Financial Position [Abstract]</label>
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    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SubsequentEventLineItems" xlink:to="us-gaap_SubsequentEventLineItems_lbl"/>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_SubsequentEventsTextBlock_lbl" xml:lang="en-US" id="id_7861063_2040768_2_1">Subsequent Events</label>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_SubsequentEventTable_lbl" xml:lang="en-US" id="id_7861063_2039938_2_1">Subsequent Event [Table]</label>
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    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_SummaryOfSignificantAccountingPoliciesLineItems" xlink:label="pwr_SummaryOfSignificantAccountingPoliciesLineItems"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_SummaryOfSignificantAccountingPoliciesLineItems_lbl" xml:lang="en-US" id="id_7861063_2153280_3_1">Summary Of Significant Accounting Policies [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_SummaryOfSignificantAccountingPoliciesLineItems_lbl" xml:lang="en-US" id="id_7861063_2153280_1_1">Summary Of Significant Accounting Policies [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_SummaryOfSignificantAccountingPoliciesLineItems_lbl" xml:lang="en-US" id="id_7861063_2153280_2_1">Summary Of Significant Accounting Policies [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_SummaryOfSignificantAccountingPoliciesLineItems" xlink:to="pwr_SummaryOfSignificantAccountingPoliciesLineItems_lbl"/>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_SummaryOfSignificantAccountingPoliciesTable_lbl" xml:lang="en-US" id="id_7861063_2317292_3_1">Summary Of Significant Accounting Policies [Table]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_SummaryOfSignificantAccountingPoliciesTable_lbl" xml:lang="en-US" id="id_7861063_2317292_1_1">Summary Of Significant Accounting Policies [Table]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_SummaryOfSignificantAccountingPoliciesTable_lbl" xml:lang="en-US" id="id_7861063_2317292_2_1">Summary Of Significant Accounting Policies [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_SummaryOfSignificantAccountingPoliciesTable" xlink:to="pwr_SummaryOfSignificantAccountingPoliciesTable_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_SupplementalCashFlowInformationAbstract" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract_lbl" xml:lang="en-US" id="id_7861063_2036634_1_1">Supplemental Cash Flow Information [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_SupplementalCashFlowInformationAbstract_lbl" xml:lang="en-US" id="id_7861063_2036634_2_1">Supplemental disclosure of cash flow information:</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_SupplementalCashFlowInformationAbstract" xlink:to="us-gaap_SupplementalCashFlowInformationAbstract_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_SwingLinesLoanMember" xlink:label="pwr_SwingLinesLoanMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_SwingLinesLoanMember_lbl" xml:lang="en-US" id="id_7861063_2094791_3_1">Swing Lines Loan [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_SwingLinesLoanMember_lbl" xml:lang="en-US" id="id_7861063_2094791_1_1">Swing Lines Loan [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_SwingLinesLoanMember_lbl" xml:lang="en-US" id="id_7861063_2094791_2_1">Swing Lines Loan [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_SwingLinesLoanMember" xlink:to="pwr_SwingLinesLoanMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TaxPeriodAxis" xlink:label="us-gaap_TaxPeriodAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TaxPeriodAxis_lbl" xml:lang="en-US" id="id_7861063_2038123_1_1">Tax Period [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_TaxPeriodAxis_lbl" xml:lang="en-US" id="id_7861063_2038123_2_1">Tax Period [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TaxPeriodAxis" xlink:to="us-gaap_TaxPeriodAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TaxPeriodDomain" xlink:label="us-gaap_TaxPeriodDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TaxPeriodDomain_lbl" xml:lang="en-US" id="id_7861063_2038317_1_1">Tax Period [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_TaxPeriodDomain_lbl" xml:lang="en-US" id="id_7861063_2038317_2_1">Tax Period [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TaxPeriodDomain" xlink:to="us-gaap_TaxPeriodDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TaxYear2010Member" xlink:label="us-gaap_TaxYear2010Member"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TaxYear2010Member_lbl" xml:lang="en-US" id="id_7861063_2037013_1_1">Tax Year 2010 [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_TaxYear2010Member_lbl" xml:lang="en-US" id="id_7861063_2037013_2_1">Tax Year 2010 [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TaxYear2010Member" xlink:to="us-gaap_TaxYear2010Member_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TaxYear2011Member" xlink:label="us-gaap_TaxYear2011Member"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TaxYear2011Member_lbl" xml:lang="en-US" id="id_7861063_2039146_1_1">Tax Year 2011 [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_TaxYear2011Member_lbl" xml:lang="en-US" id="id_7861063_2039146_2_1">Tax Year 2011 [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TaxYear2011Member" xlink:to="us-gaap_TaxYear2011Member_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TaxYear2012Member" xlink:label="us-gaap_TaxYear2012Member"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TaxYear2012Member_lbl" xml:lang="en-US" id="id_7861063_2039946_1_1">Tax Year 2012 [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_TaxYear2012Member_lbl" xml:lang="en-US" id="id_7861063_2039946_2_1">Tax Year 2012 [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TaxYear2012Member" xlink:to="us-gaap_TaxYear2012Member_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TradeNamesMember" xlink:label="us-gaap_TradeNamesMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TradeNamesMember_lbl" xml:lang="en-US" id="id_7861063_2035164_1_1">Trade Names [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_TradeNamesMember_lbl" xml:lang="en-US" id="id_7861063_2035164_2_1">Trade Names [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TradeNamesMember" xlink:to="us-gaap_TradeNamesMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/dei/2014/dei-2014-01-31.xsd#dei_TradingSymbol" xlink:label="dei_TradingSymbol"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="dei_TradingSymbol_lbl" xml:lang="en-US" id="id_7861063_2038518_1_1">Trading Symbol</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="dei_TradingSymbol_lbl" xml:lang="en-US" id="id_7861063_2038518_2_1">Trading Symbol</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TreasuryStockMember" xlink:label="us-gaap_TreasuryStockMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TreasuryStockMember_lbl" xml:lang="en-US" id="id_7861063_2037023_1_1">Treasury Stock [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_TreasuryStockMember_lbl" xml:lang="en-US" id="id_7861063_2037023_2_1">Treasury Stock [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TreasuryStockMember" xlink:to="us-gaap_TreasuryStockMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TreasuryStockShares" xlink:label="us-gaap_TreasuryStockShares"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TreasuryStockShares_lbl" xml:lang="en-US" id="id_7861063_2037739_1_1">Treasury Stock, Shares</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_TreasuryStockShares_lbl" xml:lang="en-US" id="id_7861063_2037739_2_1">Treasury stock, common shares</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TreasuryStockShares" xlink:to="us-gaap_TreasuryStockShares_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TreasuryStockSharesAcquired" xlink:label="us-gaap_TreasuryStockSharesAcquired"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TreasuryStockSharesAcquired_lbl" xml:lang="en-US" id="id_7861063_2038134_1_1">Treasury Stock, Shares, Acquired</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_TreasuryStockSharesAcquired_lbl" xml:lang="en-US" id="id_7861063_2038134_2_1">Treasury stock acquired</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TreasuryStockSharesAcquired" xlink:to="us-gaap_TreasuryStockSharesAcquired_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TreasuryStockValue" xlink:label="us-gaap_TreasuryStockValue"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TreasuryStockValue_lbl" xml:lang="en-US" id="id_7861063_2039161_1_1">Treasury Stock, Value</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2009/role/negatedLabel" xlink:label="us-gaap_TreasuryStockValue_lbl" xml:lang="en-US" id="id_7861063_2039161_14_1">Treasury stock, 84,757,044 and 74,991,343 common shares, at cost</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod" xlink:label="us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TreasuryStockValueAcquiredCostMethod_lbl" xml:lang="en-US" id="id_7861063_2035576_1_1">Treasury Stock, Value, Acquired, Cost Method</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_TreasuryStockValueAcquiredCostMethod_lbl" xml:lang="en-US" id="id_7861063_2035576_2_1">Value of treasury stock acquired, cost method</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TreasuryStockValueAcquiredCostMethod" xlink:to="us-gaap_TreasuryStockValueAcquiredCostMethod_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_TwoThousandAndElevenPlanMember" xlink:label="pwr_TwoThousandAndElevenPlanMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_TwoThousandAndElevenPlanMember_lbl" xml:lang="en-US" id="id_7861063_2353833_3_1">Two Thousand And Eleven Plan [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_TwoThousandAndElevenPlanMember_lbl" xml:lang="en-US" id="id_7861063_2353833_1_1">Two Thousand And Eleven Plan [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_TwoThousandAndElevenPlanMember_lbl" xml:lang="en-US" id="id_7861063_2353833_2_1">2011 Plan [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_TwoThousandAndElevenPlanMember" xlink:to="pwr_TwoThousandAndElevenPlanMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_TwoThousandAndSevenPlanMember" xlink:label="pwr_TwoThousandAndSevenPlanMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_TwoThousandAndSevenPlanMember_lbl" xml:lang="en-US" id="id_7861063_2058015_3_1">Two Thousand And Seven Plan [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_TwoThousandAndSevenPlanMember_lbl" xml:lang="en-US" id="id_7861063_2058015_1_1">Two Thousand And Seven Plan [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_TwoThousandAndSevenPlanMember_lbl" xml:lang="en-US" id="id_7861063_2058015_2_1">2007 Plan [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_TwoThousandAndSevenPlanMember" xlink:to="pwr_TwoThousandAndSevenPlanMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_TwoThousandFifteenRepurchaseProgramMember" xlink:label="pwr_TwoThousandFifteenRepurchaseProgramMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_TwoThousandFifteenRepurchaseProgramMember_lbl" xml:lang="en-US" id="id_7861063_2077418_3_1">2015 Repurchase Program [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_TwoThousandFifteenRepurchaseProgramMember_lbl" xml:lang="en-US" id="id_7861063_2077418_1_1">Two Thousand Fifteen Repurchase Program [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_TwoThousandFifteenRepurchaseProgramMember_lbl" xml:lang="en-US" id="id_7861063_2077418_2_1">2015 Repurchase Program [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_TwoThousandFifteenRepurchaseProgramMember" xlink:to="pwr_TwoThousandFifteenRepurchaseProgramMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_TwoThousandFifteenRepurchaseProgramOpenMarketPurchasesMember" xlink:label="pwr_TwoThousandFifteenRepurchaseProgramOpenMarketPurchasesMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_TwoThousandFifteenRepurchaseProgramOpenMarketPurchasesMember_lbl" xml:lang="en-US" id="id_7861063_2385037_3_1">Two Thousand Fifteen Repurchase Program Open Market Purchases [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_TwoThousandFifteenRepurchaseProgramOpenMarketPurchasesMember_lbl" xml:lang="en-US" id="id_7861063_2385037_1_1">Two Thousand Fifteen Repurchase Program Open Market Purchases [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_TwoThousandFifteenRepurchaseProgramOpenMarketPurchasesMember_lbl" xml:lang="en-US" id="id_7861063_2385037_2_1">2015 Repurchase Program Open Market Purchases [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_TwoThousandFifteenRepurchaseProgramOpenMarketPurchasesMember" xlink:to="pwr_TwoThousandFifteenRepurchaseProgramOpenMarketPurchasesMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_TwoThousandThirteenRepurchaseProgramAndOpenMarketRepurchasesMember" xlink:label="pwr_TwoThousandThirteenRepurchaseProgramAndOpenMarketRepurchasesMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_TwoThousandThirteenRepurchaseProgramAndOpenMarketRepurchasesMember_lbl" xml:lang="en-US" id="id_7861063_2384120_3_1">Two Thousand Thirteen Repurchase Program And Open Market Repurchases [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_TwoThousandThirteenRepurchaseProgramAndOpenMarketRepurchasesMember_lbl" xml:lang="en-US" id="id_7861063_2384120_1_1">Two Thousand Thirteen Repurchase Program And Open Market Repurchases [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_TwoThousandThirteenRepurchaseProgramAndOpenMarketRepurchasesMember_lbl" xml:lang="en-US" id="id_7861063_2384120_2_1">2013 Repurchase Program Open Market Repurchases [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_TwoThousandThirteenRepurchaseProgramAndOpenMarketRepurchasesMember" xlink:to="pwr_TwoThousandThirteenRepurchaseProgramAndOpenMarketRepurchasesMember_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_TwoThousandThirteenRepurchaseProgramMember" xlink:label="pwr_TwoThousandThirteenRepurchaseProgramMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_TwoThousandThirteenRepurchaseProgramMember_lbl" xml:lang="en-US" id="id_7861063_2224005_3_1">Two Thousand Thirteen Repurchase Program [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_TwoThousandThirteenRepurchaseProgramMember_lbl" xml:lang="en-US" id="id_7861063_2224005_1_1">Two Thousand Thirteen Repurchase Program [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_TwoThousandThirteenRepurchaseProgramMember_lbl" xml:lang="en-US" id="id_7861063_2224005_2_1">2013 Repurchase Program [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_TwoThousandThirteenRepurchaseProgramMember" xlink:to="pwr_TwoThousandThirteenRepurchaseProgramMember_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_TypeOfArrangementAxis" xlink:label="us-gaap_TypeOfArrangementAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_TypeOfArrangementAxis_lbl" xml:lang="en-US" id="id_7861063_2036820_1_1">Type of Arrangement and Non-arrangement Transactions [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_TypeOfArrangementAxis_lbl" xml:lang="en-US" id="id_7861063_2036820_2_1">Type of Arrangement and Non-arrangement Transactions [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_TypeOfArrangementAxis" xlink:to="us-gaap_TypeOfArrangementAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_UnapprovedChangeOrdersAmount" xlink:label="us-gaap_UnapprovedChangeOrdersAmount"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_UnapprovedChangeOrdersAmount_lbl" xml:lang="en-US" id="id_7861063_2036115_1_1">Unapproved Change Orders, Amount</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_UnapprovedChangeOrdersAmount_lbl" xml:lang="en-US" id="id_7861063_2036115_2_1">Change orders and/or claims</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnapprovedChangeOrdersAmount" xlink:to="us-gaap_UnapprovedChangeOrdersAmount_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_UnbilledContractsReceivable" xlink:label="us-gaap_UnbilledContractsReceivable"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_UnbilledContractsReceivable_lbl" xml:lang="en-US" id="id_7861063_2037746_1_1">Unbilled Contracts Receivable</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_UnbilledContractsReceivable_lbl" xml:lang="en-US" id="id_7861063_2037746_2_1">Unbilled receivables</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnbilledContractsReceivable" xlink:to="us-gaap_UnbilledContractsReceivable_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_UnrecognizedTaxBenefits" xlink:label="us-gaap_UnrecognizedTaxBenefits"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_UnrecognizedTaxBenefits_lbl" xml:lang="en-US" id="id_7861063_2037031_1_1">Unrecognized Tax Benefits</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_UnrecognizedTaxBenefits_lbl" xml:lang="en-US" id="id_7861063_2037031_2_1">Total amount of unrecognized tax benefits relating to uncertain tax positions</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnrecognizedTaxBenefits" xlink:to="us-gaap_UnrecognizedTaxBenefits_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions_lbl" xml:lang="en-US" id="id_7861063_2038141_1_1">Unrecognized Tax Benefits, Increase Resulting from Current Period Tax Positions</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions_lbl" xml:lang="en-US" id="id_7861063_2038141_2_1">Unrecognized tax benefits, increase resulting from current period tax positions</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions" xlink:to="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromCurrentPeriodTaxPositions_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions_lbl" xml:lang="en-US" id="id_7861063_2036826_1_1">Unrecognized Tax Benefits, Increase Resulting from Prior Period Tax Positions</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions_lbl" xml:lang="en-US" id="id_7861063_2036826_2_1">Unrecognized tax benefits, increase due to tax positions taken in prior period</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions" xlink:to="us-gaap_UnrecognizedTaxBenefitsIncreasesResultingFromPriorPeriodTaxPositions_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_UnrecognizedTaxBenefitsPeriodIncreaseDecrease" xlink:label="us-gaap_UnrecognizedTaxBenefitsPeriodIncreaseDecrease"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_UnrecognizedTaxBenefitsPeriodIncreaseDecrease_lbl" xml:lang="en-US" id="id_7861063_2038142_1_1">Unrecognized Tax Benefits, Period Increase (Decrease)</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_UnrecognizedTaxBenefitsPeriodIncreaseDecrease_lbl" xml:lang="en-US" id="id_7861063_2038142_2_1">Amount of unrecognized tax benefits change from year end relating to uncertain tax positions</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnrecognizedTaxBenefitsPeriodIncreaseDecrease" xlink:to="us-gaap_UnrecognizedTaxBenefitsPeriodIncreaseDecrease_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceOnFirstAnniversary" xlink:label="us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceOnFirstAnniversary"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceOnFirstAnniversary_lbl" xml:lang="en-US" id="id_7861063_2039579_1_1">Unrecorded Unconditional Purchase Obligation, Due in Next Twelve Months</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceOnFirstAnniversary_lbl" xml:lang="en-US" id="id_7861063_2039579_2_1">Estimated committed capital in next fiscal year</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceOnFirstAnniversary" xlink:to="us-gaap_UnrecordedUnconditionalPurchaseObligationBalanceOnFirstAnniversary_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_UnrecordedUnconditionalPurchaseObligationLineItems" xlink:label="us-gaap_UnrecordedUnconditionalPurchaseObligationLineItems"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_UnrecordedUnconditionalPurchaseObligationLineItems_lbl" xml:lang="en-US" id="id_7861063_2033768_1_1">Unrecorded Unconditional Purchase Obligation [Line Items]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_UnrecordedUnconditionalPurchaseObligationLineItems_lbl" xml:lang="en-US" id="id_7861063_2033768_2_1">Unrecorded Unconditional Purchase Obligation [Line Items]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnrecordedUnconditionalPurchaseObligationLineItems" xlink:to="us-gaap_UnrecordedUnconditionalPurchaseObligationLineItems_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_UnrecordedUnconditionalPurchaseObligationTable" xlink:label="us-gaap_UnrecordedUnconditionalPurchaseObligationTable"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_UnrecordedUnconditionalPurchaseObligationTable_lbl" xml:lang="en-US" id="id_7861063_2037564_1_1">Unrecorded Unconditional Purchase Obligation [Table]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_UnrecordedUnconditionalPurchaseObligationTable_lbl" xml:lang="en-US" id="id_7861063_2037564_2_1">Unrecorded Unconditional Purchase Obligation [Table]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UnrecordedUnconditionalPurchaseObligationTable" xlink:to="us-gaap_UnrecordedUnconditionalPurchaseObligationTable_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/country/2016/country-2016-01-31.xsd#country_US" xlink:label="country_US"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="country_US_lbl" xml:lang="en-US" id="id_7861063_2037985_1_1">UNITED STATES</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="country_US_lbl" xml:lang="en-US" id="id_7861063_2037985_2_1">United States [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="country_US" xlink:to="country_US_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.sec.gov/currency/2016/currency-2016-01-31.xsd#currency_USD" xlink:label="currency_USD"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="currency_USD_lbl" xml:lang="en-US" id="id_7861063_2035181_1_1">United States of America, Dollars</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="currency_USD_lbl" xml:lang="en-US" id="id_7861063_2035181_2_1">U S Dollar [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="currency_USD" xlink:to="currency_USD_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_UseOfEstimates" xlink:label="us-gaap_UseOfEstimates"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_UseOfEstimates_lbl" xml:lang="en-US" id="id_7861063_2035182_1_1">Use of Estimates, Policy [Policy Text Block]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_UseOfEstimates_lbl" xml:lang="en-US" id="id_7861063_2035182_2_1">Use of Estimates and Assumptions</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_UseOfEstimates" xlink:to="us-gaap_UseOfEstimates_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssetsAndLiabilitiesNet" xlink:label="us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssetsAndLiabilitiesNet"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssetsAndLiabilitiesNet_lbl" xml:lang="en-US" id="id_7861063_2039586_1_1">Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssetsAndLiabilitiesNet_lbl" xml:lang="en-US" id="id_7861063_2039586_2_1">Carrying value of the investments held by Quanta in variable interest entities</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssetsAndLiabilitiesNet" xlink:to="us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssetsAndLiabilitiesNet_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_VariableRateAxis" xlink:label="us-gaap_VariableRateAxis"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_VariableRateAxis_lbl" xml:lang="en-US" id="id_7861063_2039383_1_1">Variable Rate [Axis]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_VariableRateAxis_lbl" xml:lang="en-US" id="id_7861063_2039383_2_1">Variable Rate [Axis]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_VariableRateAxis" xlink:to="us-gaap_VariableRateAxis_lbl"/>
    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_VariableRateDomain" xlink:label="us-gaap_VariableRateDomain"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_VariableRateDomain_lbl" xml:lang="en-US" id="id_7861063_2037226_1_1">Variable Rate [Domain]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_VariableRateDomain_lbl" xml:lang="en-US" id="id_7861063_2037226_2_1">Variable Rate [Domain]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="us-gaap_VariableRateDomain" xlink:to="us-gaap_VariableRateDomain_lbl"/>
    <loc xlink:type="locator" xlink:href="pwr-20160630.xsd#pwr_VehicleFleetCommittedCapitalMember" xlink:label="pwr_VehicleFleetCommittedCapitalMember"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:label="pwr_VehicleFleetCommittedCapitalMember_lbl" xml:lang="en-US" id="id_7861063_2274575_3_1">Vehicle Fleet Committed Capital [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="pwr_VehicleFleetCommittedCapitalMember_lbl" xml:lang="en-US" id="id_7861063_2274575_1_1">Vehicle Fleet Committed Capital [Member]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="pwr_VehicleFleetCommittedCapitalMember_lbl" xml:lang="en-US" id="id_7861063_2274575_2_1">Vehicle Fleet Committed Capital [Member]</label>
    <labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="pwr_VehicleFleetCommittedCapitalMember" xlink:to="pwr_VehicleFleetCommittedCapitalMember_lbl"/>
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    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xml:lang="en-US" id="id_7861063_2035931_2_1">Weighted average diluted shares outstanding</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:label="us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_lbl" xml:lang="en-US" id="id_7861063_2035931_6_1">Weighted average shares outstanding for diluted earnings per share</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_lbl" xml:lang="en-US" id="id_7861063_2038760_1_1">Weighted Average Number of Shares Outstanding, Diluted [Abstract]</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_lbl" xml:lang="en-US" id="id_7861063_2038760_2_1">Shares used in computing earnings per share:</label>
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    <loc xlink:type="locator" xlink:href="http://xbrl.fasb.org/us-gaap/2016/elts/us-gaap-2016-01-31.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/label" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xml:lang="en-US" id="id_7861063_2038354_1_1">Weighted Average Number of Shares Outstanding, Basic</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xml:lang="en-US" id="id_7861063_2038354_2_1">Weighted average basic shares outstanding</label>
    <label xlink:type="resource" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:label="us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_lbl" xml:lang="en-US" id="id_7861063_2038354_12_1">Weighted average shares outstanding for basic earnings per share</label>
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