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    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_529A378E1DAD35551871739992D5517D" xlink:type="locator" />
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    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_pwr_CanadianAndAustralianDollarsMember_A9C7F05DD2E11FEF5FCC4F939631C5A4" xlink:to="lab_pwr_CanadianAndAustralianDollarsMember_A9C7F05DD2E11FEF5FCC4F939631C5A4" xlink:type="arc" />
    <link:label id="lab_us-gaap_LineOfCreditFacilityLineItems_263138FA1DD43D23C3CA4F939632A418_terseLabel_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityLineItems_263138FA1DD43D23C3CA4F939632A418" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Line of Credit Facility [Line Items]</link:label>
    <link:label id="lab_us-gaap_LineOfCreditFacilityLineItems_263138FA1DD43D23C3CA4F939632A418_label_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityLineItems_263138FA1DD43D23C3CA4F939632A418" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Line of Credit Facility [Line Items]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityLineItems" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_263138FA1DD43D23C3CA4F939632A418" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_263138FA1DD43D23C3CA4F939632A418" xlink:to="lab_us-gaap_LineOfCreditFacilityLineItems_263138FA1DD43D23C3CA4F939632A418" xlink:type="arc" />
    <link:label id="lab_us-gaap_LineOfCredit_6052090A1DD62021301D4F93963297FD_terseLabel_en-US" xlink:label="lab_us-gaap_LineOfCredit_6052090A1DD62021301D4F93963297FD" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Amount borrowed under the credit facility</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCredit" xlink:label="loc_us-gaap_LineOfCredit_6052090A1DD62021301D4F93963297FD" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LineOfCredit_6052090A1DD62021301D4F93963297FD" xlink:to="lab_us-gaap_LineOfCredit_6052090A1DD62021301D4F93963297FD" xlink:type="arc" />
    <link:label id="lab_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_D72744825151001ADAC04F9396323EDD_terseLabel_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_D72744825151001ADAC04F9396323EDD" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Credit facility available for revolving loans or issuing new letters of credit</link:label>
    <link:label id="lab_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_D72744825151001ADAC04F9396323EDD_label_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_D72744825151001ADAC04F9396323EDD" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Line of Credit Facility, Remaining Borrowing Capacity</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_D72744825151001ADAC04F9396323EDD" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_D72744825151001ADAC04F9396323EDD" xlink:to="lab_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_D72744825151001ADAC04F9396323EDD" xlink:type="arc" />
    <link:label id="lab_currency_AUD_137E05BFD78FA09EC6BA5E4557B61FD8_terseLabel_en-US" xlink:label="lab_currency_AUD_137E05BFD78FA09EC6BA5E4557B61FD8" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Australian Dollars</link:label>
    <link:label id="lab_currency_AUD_137E05BFD78FA09EC6BA5E4557B61FD8_label_en-US" xlink:label="lab_currency_AUD_137E05BFD78FA09EC6BA5E4557B61FD8" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Australia, Dollars</link:label>
    <link:loc xlink:href="http://xbrl.sec.gov/currency/2017/currency-2017-01-31.xsd#currency_AUD" xlink:label="loc_currency_AUD_137E05BFD78FA09EC6BA5E4557B61FD8" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_currency_AUD_137E05BFD78FA09EC6BA5E4557B61FD8" xlink:to="lab_currency_AUD_137E05BFD78FA09EC6BA5E4557B61FD8" xlink:type="arc" />
    <link:label id="lab_us-gaap_DebtInstrumentAxis_5B484C58E7738261E1A05E4557B6E2CE_terseLabel_en-US" xlink:label="lab_us-gaap_DebtInstrumentAxis_5B484C58E7738261E1A05E4557B6E2CE" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Debt Instrument [Axis]</link:label>
    <link:label id="lab_us-gaap_DebtInstrumentAxis_5B484C58E7738261E1A05E4557B6E2CE_label_en-US" xlink:label="lab_us-gaap_DebtInstrumentAxis_5B484C58E7738261E1A05E4557B6E2CE" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Debt Instrument [Axis]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentAxis" xlink:label="loc_us-gaap_DebtInstrumentAxis_5B484C58E7738261E1A05E4557B6E2CE" xlink:type="locator" />
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    <link:label id="lab_us-gaap_DebtInstrumentNameDomain_39AAB087B508C7480F365E4557B6D4CB_terseLabel_en-US" xlink:label="lab_us-gaap_DebtInstrumentNameDomain_39AAB087B508C7480F365E4557B6D4CB" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Debt Instrument, Name [Domain]</link:label>
    <link:label id="lab_us-gaap_DebtInstrumentNameDomain_39AAB087B508C7480F365E4557B6D4CB_label_en-US" xlink:label="lab_us-gaap_DebtInstrumentNameDomain_39AAB087B508C7480F365E4557B6D4CB" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Debt Instrument, Name [Domain]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_39AAB087B508C7480F365E4557B6D4CB" xlink:type="locator" />
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    <link:label id="lab_pwr_FourthAmendedAndRestatedMember_C357F06EB29FE03690345E4557B69202_terseLabel_en-US" xlink:label="lab_pwr_FourthAmendedAndRestatedMember_C357F06EB29FE03690345E4557B69202" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Current Credit Agreement</link:label>
    <link:label id="lab_pwr_FourthAmendedAndRestatedMember_C357F06EB29FE03690345E4557B69202_label_en-US" xlink:label="lab_pwr_FourthAmendedAndRestatedMember_C357F06EB29FE03690345E4557B69202" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Fourth Amended And Restated [Member]</link:label>
    <link:label id="lab_pwr_FourthAmendedAndRestatedMember_C357F06EB29FE03690345E4557B69202_documentation_en-US" xlink:label="lab_pwr_FourthAmendedAndRestatedMember_C357F06EB29FE03690345E4557B69202" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Fourth amended and restated.</link:label>
    <link:loc xlink:href="pwr-20170930.xsd#pwr_FourthAmendedAndRestatedMember" xlink:label="loc_pwr_FourthAmendedAndRestatedMember_C357F06EB29FE03690345E4557B69202" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_pwr_FourthAmendedAndRestatedMember_C357F06EB29FE03690345E4557B69202" xlink:to="lab_pwr_FourthAmendedAndRestatedMember_C357F06EB29FE03690345E4557B69202" xlink:type="arc" />
    <link:label id="lab_pwr_RevolvingLoansAndLetterOfCreditInAlternativeCurrenciesMember_7C57ED73B05141DCF5195E4557B60271_terseLabel_en-US" xlink:label="lab_pwr_RevolvingLoansAndLetterOfCreditInAlternativeCurrenciesMember_7C57ED73B05141DCF5195E4557B60271" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Revolving Loans and Letters of Credit in Alternative Currencies</link:label>
    <link:label id="lab_pwr_RevolvingLoansAndLetterOfCreditInAlternativeCurrenciesMember_7C57ED73B05141DCF5195E4557B60271_label_en-US" xlink:label="lab_pwr_RevolvingLoansAndLetterOfCreditInAlternativeCurrenciesMember_7C57ED73B05141DCF5195E4557B60271" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Revolving Loans And Letter Of Credit In Alternative Currencies [Member]</link:label>
    <link:label id="lab_pwr_RevolvingLoansAndLetterOfCreditInAlternativeCurrenciesMember_7C57ED73B05141DCF5195E4557B60271_documentation_en-US" xlink:label="lab_pwr_RevolvingLoansAndLetterOfCreditInAlternativeCurrenciesMember_7C57ED73B05141DCF5195E4557B60271" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Revolving loans and letter of credit in alternative currencies.</link:label>
    <link:loc xlink:href="pwr-20170930.xsd#pwr_RevolvingLoansAndLetterOfCreditInAlternativeCurrenciesMember" xlink:label="loc_pwr_RevolvingLoansAndLetterOfCreditInAlternativeCurrenciesMember_7C57ED73B05141DCF5195E4557B60271" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_pwr_RevolvingLoansAndLetterOfCreditInAlternativeCurrenciesMember_7C57ED73B05141DCF5195E4557B60271" xlink:to="lab_pwr_RevolvingLoansAndLetterOfCreditInAlternativeCurrenciesMember_7C57ED73B05141DCF5195E4557B60271" xlink:type="arc" />
    <link:label id="lab_pwr_SwingLinesLoanMember_9D48342395906BA326E25E4557B64E63_terseLabel_en-US" xlink:label="lab_pwr_SwingLinesLoanMember_9D48342395906BA326E25E4557B64E63" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Swing Lines Loan</link:label>
    <link:label id="lab_pwr_SwingLinesLoanMember_9D48342395906BA326E25E4557B64E63_label_en-US" xlink:label="lab_pwr_SwingLinesLoanMember_9D48342395906BA326E25E4557B64E63" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Swing Lines Loan [Member]</link:label>
    <link:label id="lab_pwr_SwingLinesLoanMember_9D48342395906BA326E25E4557B64E63_documentation_en-US" xlink:label="lab_pwr_SwingLinesLoanMember_9D48342395906BA326E25E4557B64E63" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Swing Lines Loan [Member]</link:label>
    <link:loc xlink:href="pwr-20170930.xsd#pwr_SwingLinesLoanMember" xlink:label="loc_pwr_SwingLinesLoanMember_9D48342395906BA326E25E4557B64E63" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_pwr_SwingLinesLoanMember_9D48342395906BA326E25E4557B64E63" xlink:to="lab_pwr_SwingLinesLoanMember_9D48342395906BA326E25E4557B64E63" xlink:type="arc" />
    <link:label id="lab_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_09239C9F1B63D22349525E4557B635E9_terseLabel_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_09239C9F1B63D22349525E4557B635E9" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Senior secured revolving credit facility</link:label>
    <link:label id="lab_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_09239C9F1B63D22349525E4557B635E9_label_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_09239C9F1B63D22349525E4557B635E9" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Line of Credit Facility, Maximum Borrowing Capacity</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_09239C9F1B63D22349525E4557B635E9" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_09239C9F1B63D22349525E4557B635E9" xlink:to="lab_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_09239C9F1B63D22349525E4557B635E9" xlink:type="arc" />
    <link:label id="lab_pwr_OptionToIncreaseRevolvingCommitmentsUnderCreditAgreement_B3F013A90507957F48D85E4557B6DBAE_terseLabel_en-US" xlink:label="lab_pwr_OptionToIncreaseRevolvingCommitmentsUnderCreditAgreement_B3F013A90507957F48D85E4557B6DBAE" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Option to increase revolving commitments under the credit agreement</link:label>
    <link:label id="lab_pwr_OptionToIncreaseRevolvingCommitmentsUnderCreditAgreement_B3F013A90507957F48D85E4557B6DBAE_label_en-US" xlink:label="lab_pwr_OptionToIncreaseRevolvingCommitmentsUnderCreditAgreement_B3F013A90507957F48D85E4557B6DBAE" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Option To Increase Revolving Commitments Under Credit Agreement</link:label>
    <link:label id="lab_pwr_OptionToIncreaseRevolvingCommitmentsUnderCreditAgreement_B3F013A90507957F48D85E4557B6DBAE_documentation_en-US" xlink:label="lab_pwr_OptionToIncreaseRevolvingCommitmentsUnderCreditAgreement_B3F013A90507957F48D85E4557B6DBAE" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Option to increase revolving commitments under credit agreement.</link:label>
    <link:loc xlink:href="pwr-20170930.xsd#pwr_OptionToIncreaseRevolvingCommitmentsUnderCreditAgreement" xlink:label="loc_pwr_OptionToIncreaseRevolvingCommitmentsUnderCreditAgreement_B3F013A90507957F48D85E4557B6DBAE" xlink:type="locator" />
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    <link:label id="lab_us-gaap_ShortTermBorrowings_F3EA3D068C64E885D0AA5E45592F3FC1_terseLabel_en-US" xlink:label="lab_us-gaap_ShortTermBorrowings_F3EA3D068C64E885D0AA5E45592F3FC1" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Short-term debt</link:label>
    <link:label id="lab_us-gaap_ShortTermBorrowings_F3EA3D068C64E885D0AA5E45592F3FC1_label_en-US" xlink:label="lab_us-gaap_ShortTermBorrowings_F3EA3D068C64E885D0AA5E45592F3FC1" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Short-term Debt</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShortTermBorrowings" xlink:label="loc_us-gaap_ShortTermBorrowings_F3EA3D068C64E885D0AA5E45592F3FC1" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_ShortTermBorrowings_F3EA3D068C64E885D0AA5E45592F3FC1" xlink:to="lab_us-gaap_ShortTermBorrowings_F3EA3D068C64E885D0AA5E45592F3FC1" xlink:type="arc" />
    <link:label id="lab_us-gaap_LongTermDebtCurrent_7FC20AEA378055EF33295E45592F8F91_terseLabel_en-US" xlink:label="lab_us-gaap_LongTermDebtCurrent_7FC20AEA378055EF33295E45592F8F91" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Current maturities of long-term debt</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_LongTermDebtCurrent" xlink:label="loc_us-gaap_LongTermDebtCurrent_7FC20AEA378055EF33295E45592F8F91" xlink:type="locator" />
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    <link:label id="lab_us-gaap_DebtCurrent_43AAD31F25EDD198D8825E45592FE67B_totalLabel_en-US" xlink:label="lab_us-gaap_DebtCurrent_43AAD31F25EDD198D8825E45592FE67B" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xml:lang="en-US">Current maturities of long-term debt and short-term debt</link:label>
    <link:label id="lab_us-gaap_DebtCurrent_43AAD31F25EDD198D8825E45592FE67B_label_en-US" xlink:label="lab_us-gaap_DebtCurrent_43AAD31F25EDD198D8825E45592FE67B" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Debt, Current</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DebtCurrent" xlink:label="loc_us-gaap_DebtCurrent_43AAD31F25EDD198D8825E45592FE67B" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_DebtCurrent_43AAD31F25EDD198D8825E45592FE67B" xlink:to="lab_us-gaap_DebtCurrent_43AAD31F25EDD198D8825E45592FE67B" xlink:type="arc" />
    <link:label id="lab_pwr_ScheduleOfOperatingLeasesFutureMinimumPaymentsDueTable_7A9E58686AE48BF0329F59B6713B215E_terseLabel_en-US" xlink:label="lab_pwr_ScheduleOfOperatingLeasesFutureMinimumPaymentsDueTable_7A9E58686AE48BF0329F59B6713B215E" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Schedule Of Operating Leases Future Minimum Payments Due [Table]</link:label>
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    <link:label id="lab_pwr_ExcessOfFederalFundsRateMember_03B2CBBC7A46461F81ED59B672844E8D_terseLabel_en-US" xlink:label="lab_pwr_ExcessOfFederalFundsRateMember_03B2CBBC7A46461F81ED59B672844E8D" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Excess of Federal Funds Rate</link:label>
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    <link:label id="lab_pwr_ExcessOfEuroCurrencyRateMember_BD7B03321980F6E476EB59B6728496CD_terseLabel_en-US" xlink:label="lab_pwr_ExcessOfEuroCurrencyRateMember_BD7B03321980F6E476EB59B6728496CD" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Excess of Euro Currency Rate</link:label>
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    <link:label id="lab_pwr_ExcessOfEuroCurrencyRateMember_BD7B03321980F6E476EB59B6728496CD_documentation_en-US" xlink:label="lab_pwr_ExcessOfEuroCurrencyRateMember_BD7B03321980F6E476EB59B6728496CD" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Excess Of Euro Currency Rate [Member]</link:label>
    <link:loc xlink:href="pwr-20170930.xsd#pwr_ExcessOfEuroCurrencyRateMember" xlink:label="loc_pwr_ExcessOfEuroCurrencyRateMember_BD7B03321980F6E476EB59B6728496CD" xlink:type="locator" />
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    <link:label id="lab_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_8865741BAF19266255A259B6728844C4_terseLabel_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_8865741BAF19266255A259B6728844C4" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Commitment fee</link:label>
    <link:label id="lab_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_8865741BAF19266255A259B6728844C4_label_en-US" xlink:label="lab_us-gaap_LineOfCreditFacilityUnusedCapacityCommitmentFeePercentage_8865741BAF19266255A259B6728844C4" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Line of Credit Facility, Unused Capacity, Commitment Fee Percentage</link:label>
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    <link:label id="lab_pwr_ReductionInCompanyMaximumFundedDebtAndMaximumSeniorDebtByAllCashAndCashEquivalentsInExcessOfAmount_C2E438429C915C4C887059B6728836AC_terseLabel_en-US" xlink:label="lab_pwr_ReductionInCompanyMaximumFundedDebtAndMaximumSeniorDebtByAllCashAndCashEquivalentsInExcessOfAmount_C2E438429C915C4C887059B6728836AC" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Reduction in Quanta's funded indebtedness reduced by cash and cash equivalents in excess of this amount</link:label>
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    <link:label id="lab_pwr_ReductionInCompanyMaximumFundedDebtAndMaximumSeniorDebtByAllCashAndCashEquivalentsInExcessOfAmount_C2E438429C915C4C887059B6728836AC_documentation_en-US" xlink:label="lab_pwr_ReductionInCompanyMaximumFundedDebtAndMaximumSeniorDebtByAllCashAndCashEquivalentsInExcessOfAmount_C2E438429C915C4C887059B6728836AC" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Reduction in Quanta's maximum funded debt and maximum senior debt by all cash and cash equivalents in excess of amount.</link:label>
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    <link:label id="lab_pwr_PercentageOfCapitalStockOfDirectForeignSubsidiariesRequiredToSecureCreditAgreement_ACA40F8809D69A59820E59B67288D57A_terseLabel_en-US" xlink:label="lab_pwr_PercentageOfCapitalStockOfDirectForeignSubsidiariesRequiredToSecureCreditAgreement_ACA40F8809D69A59820E59B67288D57A" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Percentage of capital stock of direct foreign subsidiaries of wholly owned U.S. subsidiaries to secure credit agreement</link:label>
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    <link:label id="lab_pwr_PercentageOfCapitalStockOfDirectForeignSubsidiariesRequiredToSecureCreditAgreement_ACA40F8809D69A59820E59B67288D57A_documentation_en-US" xlink:label="lab_pwr_PercentageOfCapitalStockOfDirectForeignSubsidiariesRequiredToSecureCreditAgreement_ACA40F8809D69A59820E59B67288D57A" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Percentage of capital stock of direct foreign subsidiaries required to secure credit agreement.</link:label>
    <link:loc xlink:href="pwr-20170930.xsd#pwr_PercentageOfCapitalStockOfDirectForeignSubsidiariesRequiredToSecureCreditAgreement" xlink:label="loc_pwr_PercentageOfCapitalStockOfDirectForeignSubsidiariesRequiredToSecureCreditAgreement_ACA40F8809D69A59820E59B67288D57A" xlink:type="locator" />
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    <link:label id="lab_pwr_DebtInstrumentCovenantLeverageRatioMaximum_E2ECEB1307C435A51D3559B672885489_terseLabel_en-US" xlink:label="lab_pwr_DebtInstrumentCovenantLeverageRatioMaximum_E2ECEB1307C435A51D3559B672885489" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Maximum consolidated leverage ratio</link:label>
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    <link:label id="lab_pwr_DebtInstrumentCovenantAcquisitionThresholdForLeverageRatio_FDE1ECE76D33FFDE8E6C59B6728A5934_terseLabel_en-US" xlink:label="lab_pwr_DebtInstrumentCovenantAcquisitionThresholdForLeverageRatio_FDE1ECE76D33FFDE8E6C59B6728A5934" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Acquisition threshold for leverage ratio</link:label>
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    <link:label id="lab_pwr_DebtInstrumentCovenantLeverageRatioAcquisitionCompletedInCurrentAndTwoSubsequentQuartersMaximum_E7C7DD0DCD16034154E459B6728A4497_terseLabel_en-US" xlink:label="lab_pwr_DebtInstrumentCovenantLeverageRatioAcquisitionCompletedInCurrentAndTwoSubsequentQuartersMaximum_E7C7DD0DCD16034154E459B6728A4497" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Maximum leverage ratio acquisition completed in current and two subsequent quarters</link:label>
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    <link:loc xlink:href="pwr-20170930.xsd#pwr_DebtInstrumentCovenantLeverageRatioAcquisitionCompletedInCurrentAndTwoSubsequentQuartersMaximum" xlink:label="loc_pwr_DebtInstrumentCovenantLeverageRatioAcquisitionCompletedInCurrentAndTwoSubsequentQuartersMaximum_E7C7DD0DCD16034154E459B6728A4497" xlink:type="locator" />
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    <link:label id="lab_pwr_ElectricPowerInfrastructureMember_E5727CBAA3FEC7D58F175E4558EE3A61_terseLabel_en-US" xlink:label="lab_pwr_ElectricPowerInfrastructureMember_E5727CBAA3FEC7D58F175E4558EE3A61" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Electric Power Infrastructure Services</link:label>
    <link:label id="lab_pwr_ElectricPowerInfrastructureMember_E5727CBAA3FEC7D58F175E4558EE3A61_label_en-US" xlink:label="lab_pwr_ElectricPowerInfrastructureMember_E5727CBAA3FEC7D58F175E4558EE3A61" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Electric Power Infrastructure [Member]</link:label>
    <link:label id="lab_pwr_ElectricPowerInfrastructureMember_E5727CBAA3FEC7D58F175E4558EE3A61_documentation_en-US" xlink:label="lab_pwr_ElectricPowerInfrastructureMember_E5727CBAA3FEC7D58F175E4558EE3A61" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Electric Power Infrastructure [Member]</link:label>
    <link:loc xlink:href="pwr-20170930.xsd#pwr_ElectricPowerInfrastructureMember" xlink:label="loc_pwr_ElectricPowerInfrastructureMember_E5727CBAA3FEC7D58F175E4558EE3A61" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_pwr_ElectricPowerInfrastructureMember_E5727CBAA3FEC7D58F175E4558EE3A61" xlink:to="lab_pwr_ElectricPowerInfrastructureMember_E5727CBAA3FEC7D58F175E4558EE3A61" xlink:type="arc" />
    <link:label id="lab_pwr_OilAndGasInfrastructureServicesMember_B03BE6FA302AAE0DBC265E4558EE0818_terseLabel_en-US" xlink:label="lab_pwr_OilAndGasInfrastructureServicesMember_B03BE6FA302AAE0DBC265E4558EE0818" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Oil and Gas Infrastructure Services</link:label>
    <link:loc xlink:href="pwr-20170930.xsd#pwr_OilAndGasInfrastructureServicesMember" xlink:label="loc_pwr_OilAndGasInfrastructureServicesMember_B03BE6FA302AAE0DBC265E4558EE0818" xlink:type="locator" />
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    <link:label id="lab_pwr_CorporateAndNonAllocatedCostsMember_BD3CE7AEAF6B8F75C9545E4558EEFAD5_label_en-US" xlink:label="lab_pwr_CorporateAndNonAllocatedCostsMember_BD3CE7AEAF6B8F75C9545E4558EEFAD5" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Corporate And Non Allocated Costs [Member]</link:label>
    <link:label id="lab_pwr_CorporateAndNonAllocatedCostsMember_BD3CE7AEAF6B8F75C9545E4558EEFAD5_documentation_en-US" xlink:label="lab_pwr_CorporateAndNonAllocatedCostsMember_BD3CE7AEAF6B8F75C9545E4558EEFAD5" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">Corporate and non-allocated costs.</link:label>
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    <link:label id="lab_us-gaap_SegmentReportingInformationLineItems_77E0962051BE0330C4375E4558EE7116_terseLabel_en-US" xlink:label="lab_us-gaap_SegmentReportingInformationLineItems_77E0962051BE0330C4375E4558EE7116" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Segment Reporting Information [Line Items]</link:label>
    <link:label id="lab_us-gaap_SegmentReportingInformationLineItems_77E0962051BE0330C4375E4558EE7116_label_en-US" xlink:label="lab_us-gaap_SegmentReportingInformationLineItems_77E0962051BE0330C4375E4558EE7116" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Segment Reporting Information [Line Items]</link:label>
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    <link:label id="lab_us-gaap_OperatingIncomeLoss_6E113EE8036692D132AA5E4558EE688B_terseLabel_en-US" xlink:label="lab_us-gaap_OperatingIncomeLoss_6E113EE8036692D132AA5E4558EE688B" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Operating income (loss)</link:label>
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    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsRemainderOfFiscalYear" xlink:label="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsRemainderOfFiscalYear_C122A7F6638682D2FF345E455987BF56" xlink:type="locator" />
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    <link:label id="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears_311D0C498F437473BEAB5E455987B3F3_label_en-US" xlink:label="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears_311D0C498F437473BEAB5E455987B3F3" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Operating Leases, Future Minimum Payments, Due in Two Years</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears" xlink:label="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears_311D0C498F437473BEAB5E455987B3F3" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears_311D0C498F437473BEAB5E455987B3F3" xlink:to="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInTwoYears_311D0C498F437473BEAB5E455987B3F3" xlink:type="arc" />
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    <link:label id="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears_5769AB6EA82F574EB9265E455987A677_label_en-US" xlink:label="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears_5769AB6EA82F574EB9265E455987A677" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Operating Leases, Future Minimum Payments, Due in Three Years</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears" xlink:label="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears_5769AB6EA82F574EB9265E455987A677" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears_5769AB6EA82F574EB9265E455987A677" xlink:to="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInThreeYears_5769AB6EA82F574EB9265E455987A677" xlink:type="arc" />
    <link:label id="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears_D568FFE1F32F563BD3BA5E455987729A_terseLabel_en-US" xlink:label="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears_D568FFE1F32F563BD3BA5E455987729A" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Minimum lease payments, 2020</link:label>
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    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears" xlink:label="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFourYears_D568FFE1F32F563BD3BA5E455987729A" xlink:type="locator" />
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    <link:label id="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears_009279DA47D6099CC5875E455987C94D_label_en-US" xlink:label="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears_009279DA47D6099CC5875E455987C94D" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Operating Leases, Future Minimum Payments, Due in Five Years</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears" xlink:label="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears_009279DA47D6099CC5875E455987C94D" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears_009279DA47D6099CC5875E455987C94D" xlink:to="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsDueInFiveYears_009279DA47D6099CC5875E455987C94D" xlink:type="arc" />
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    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter" xlink:label="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter_634564A6308C19F69D715E455987C52F" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter_634564A6308C19F69D715E455987C52F" xlink:to="lab_us-gaap_OperatingLeasesFutureMinimumPaymentsDueThereafter_634564A6308C19F69D715E455987C52F" xlink:type="arc" />
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    <link:label id="lab_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_5828B553FF2EAF33604C5E45576891A9_verboseLabel_en-US" xlink:label="lab_us-gaap_NetIncomeLossAttributableToNoncontrollingInterest_5828B553FF2EAF33604C5E45576891A9" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xml:lang="en-US">Net income attributable to non-controlling interests</link:label>
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    <link:label id="lab_us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssetsAndLiabilitiesNet_F5DCBA61E27DEC2223395E455768DB0F_terseLabel_en-US" xlink:label="lab_us-gaap_VariableInterestEntityConsolidatedCarryingAmountAssetsAndLiabilitiesNet_F5DCBA61E27DEC2223395E455768DB0F" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Carrying value of the investments held by Quanta in variable interest entities</link:label>
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    <link:label id="lab_us-gaap_MinorityInterest_91FF98B7AD45CED0CAFE5E455768E159_terseLabel_en-US" xlink:label="lab_us-gaap_MinorityInterest_91FF98B7AD45CED0CAFE5E455768E159" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Non-controlling interests</link:label>
    <link:label id="lab_us-gaap_MinorityInterest_91FF98B7AD45CED0CAFE5E455768E159_label_en-US" xlink:label="lab_us-gaap_MinorityInterest_91FF98B7AD45CED0CAFE5E455768E159" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Stockholders' Equity Attributable to Noncontrolling Interest</link:label>
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    <link:label id="lab_us-gaap_WithdrawalFromMultiemployerDefinedBenefitPlanMember_9B436787C0408937BEA95E455943C7D1_terseLabel_en-US" xlink:label="lab_us-gaap_WithdrawalFromMultiemployerDefinedBenefitPlanMember_9B436787C0408937BEA95E455943C7D1" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Withdrawal from Multiemployer Defined Benefit Plan</link:label>
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    <link:label id="lab_pwr_CentralStatesPlanMember_F211F2EFA1A61503E07C5E4559431F0A_terseLabel_en-US" xlink:label="lab_pwr_CentralStatesPlanMember_F211F2EFA1A61503E07C5E4559431F0A" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Central States Plan</link:label>
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    <link:label id="lab_pwr_CentralStatesPlanMember_F211F2EFA1A61503E07C5E4559431F0A_documentation_en-US" xlink:label="lab_pwr_CentralStatesPlanMember_F211F2EFA1A61503E07C5E4559431F0A" xlink:role="http://www.xbrl.org/2003/role/documentation" xlink:type="resource" xml:lang="en-US">2011 Central States Plan Withdrawal Liability, Quanta subsidiaries withdrew from the Central States, Southeast and Southwest Areas Pension Plan.</link:label>
    <link:loc xlink:href="pwr-20170930.xsd#pwr_CentralStatesPlanMember" xlink:label="loc_pwr_CentralStatesPlanMember_F211F2EFA1A61503E07C5E4559431F0A" xlink:type="locator" />
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    <link:label id="lab_us-gaap_MultiemployerPlansWithdrawalObligation_1E65B8DF218FAD95DF6F5E455944B08A_terseLabel_en-US" xlink:label="lab_us-gaap_MultiemployerPlansWithdrawalObligation_1E65B8DF218FAD95DF6F5E455944B08A" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Amount of withdrawal liability</link:label>
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    <link:label id="lab_pwr_MultiemployerPlanWithdrawalObligationAmountSuggestedByPlanDifferentThanAmountRecordedByCompany_D4E12B7F40DC848610885E4559442E7B_terseLabel_en-US" xlink:label="lab_pwr_MultiemployerPlanWithdrawalObligationAmountSuggestedByPlanDifferentThanAmountRecordedByCompany_D4E12B7F40DC848610885E4559442E7B" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Amount of withdrawal liability, amount suggested by Plan which is different than amount recorded by company</link:label>
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    <link:label id="lab_us-gaap_PaymentsToAcquireBusinessesGross_3B6071BCC6F23C53E3F092926C7744E7_terseLabel_en-US" xlink:label="lab_us-gaap_PaymentsToAcquireBusinessesGross_3B6071BCC6F23C53E3F092926C7744E7" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Aggregate consideration paid</link:label>
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    <link:label id="lab_us-gaap_SalesRevenueServicesNet_2D078CE4FAABD5BC4C5492926C78369C_verboseLabel_en-US" xlink:label="lab_us-gaap_SalesRevenueServicesNet_2D078CE4FAABD5BC4C5492926C78369C" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xml:lang="en-US">Revenues included in consolidated results of operations</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SalesRevenueServicesNet" xlink:label="loc_us-gaap_SalesRevenueServicesNet_2D078CE4FAABD5BC4C5492926C78369C" xlink:type="locator" />
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    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_AC245ED95A273A52713A92926C783807" xlink:type="locator" />
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    <link:label id="lab_us-gaap_BusinessCombinationAcquisitionRelatedCosts_329D34F9DE3D4421CEE992926C78DEF1_terseLabel_en-US" xlink:label="lab_us-gaap_BusinessCombinationAcquisitionRelatedCosts_329D34F9DE3D4421CEE992926C78DEF1" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Acquisition costs</link:label>
    <link:label id="lab_us-gaap_BusinessCombinationAcquisitionRelatedCosts_329D34F9DE3D4421CEE992926C78DEF1_label_en-US" xlink:label="lab_us-gaap_BusinessCombinationAcquisitionRelatedCosts_329D34F9DE3D4421CEE992926C78DEF1" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Business Combination, Acquisition Related Costs</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BusinessCombinationAcquisitionRelatedCosts" xlink:label="loc_us-gaap_BusinessCombinationAcquisitionRelatedCosts_329D34F9DE3D4421CEE992926C78DEF1" xlink:type="locator" />
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    <link:label id="lab_us-gaap_AssetsAbstract_B4B45668CADBE14669B14A83FA8F32BC_terseLabel_en-US" xlink:label="lab_us-gaap_AssetsAbstract_B4B45668CADBE14669B14A83FA8F32BC" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">ASSETS</link:label>
    <link:label id="lab_us-gaap_AssetsAbstract_B4B45668CADBE14669B14A83FA8F32BC_label_en-US" xlink:label="lab_us-gaap_AssetsAbstract_B4B45668CADBE14669B14A83FA8F32BC" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Assets [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsAbstract" xlink:label="loc_us-gaap_AssetsAbstract_B4B45668CADBE14669B14A83FA8F32BC" xlink:type="locator" />
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    <link:label id="lab_us-gaap_AssetsCurrentAbstract_0D3DC0CC6F756E6742AC4A83FA8FDE7B_terseLabel_en-US" xlink:label="lab_us-gaap_AssetsCurrentAbstract_0D3DC0CC6F756E6742AC4A83FA8FDE7B" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Current Assets:</link:label>
    <link:label id="lab_us-gaap_AssetsCurrentAbstract_0D3DC0CC6F756E6742AC4A83FA8FDE7B_label_en-US" xlink:label="lab_us-gaap_AssetsCurrentAbstract_0D3DC0CC6F756E6742AC4A83FA8FDE7B" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Assets, Current [Abstract]</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsCurrentAbstract" xlink:label="loc_us-gaap_AssetsCurrentAbstract_0D3DC0CC6F756E6742AC4A83FA8FDE7B" xlink:type="locator" />
    <link:labelArc order="1" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="loc_us-gaap_AssetsCurrentAbstract_0D3DC0CC6F756E6742AC4A83FA8FDE7B" xlink:to="lab_us-gaap_AssetsCurrentAbstract_0D3DC0CC6F756E6742AC4A83FA8FDE7B" xlink:type="arc" />
    <link:label id="lab_us-gaap_AccountsReceivableNetCurrent_A913C8069ACF94244B054A83FA8FACEA_terseLabel_en-US" xlink:label="lab_us-gaap_AccountsReceivableNetCurrent_A913C8069ACF94244B054A83FA8FACEA" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Accounts receivable, net of allowances of $5,066 and $2,752</link:label>
    <link:label id="lab_us-gaap_AccountsReceivableNetCurrent_A913C8069ACF94244B054A83FA8FACEA_label_en-US" xlink:label="lab_us-gaap_AccountsReceivableNetCurrent_A913C8069ACF94244B054A83FA8FACEA" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Accounts Receivable, Net, Current</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsReceivableNetCurrent" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_A913C8069ACF94244B054A83FA8FACEA" xlink:type="locator" />
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    <link:label id="lab_us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear_91791BD1C6B0F42232384A83FA8F19C6_terseLabel_en-US" xlink:label="lab_us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear_91791BD1C6B0F42232384A83FA8F19C6" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Costs and estimated earnings in excess of billings on uncompleted contracts</link:label>
    <link:label id="lab_us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear_91791BD1C6B0F42232384A83FA8F19C6_label_en-US" xlink:label="lab_us-gaap_CostsInExcessOfBillingsOnUncompletedContractsOrProgramsExpectedToBeCollectedWithinOneYear_91791BD1C6B0F42232384A83FA8F19C6" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Costs in Excess of Billings, Current</link:label>
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    <link:label id="lab_us-gaap_InventoryNet_3CBEBB94D6C79BF9F9E74A83FA8F7AEF_terseLabel_en-US" xlink:label="lab_us-gaap_InventoryNet_3CBEBB94D6C79BF9F9E74A83FA8F7AEF" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Inventories</link:label>
    <link:label id="lab_us-gaap_InventoryNet_3CBEBB94D6C79BF9F9E74A83FA8F7AEF_label_en-US" xlink:label="lab_us-gaap_InventoryNet_3CBEBB94D6C79BF9F9E74A83FA8F7AEF" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Inventory, Net</link:label>
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    <link:label id="lab_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_B3A285D5ABB9255D548F4A83FA8F0D67_label_en-US" xlink:label="lab_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_B3A285D5ABB9255D548F4A83FA8F0D67" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Prepaid Expense and Other Assets, Current</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_B3A285D5ABB9255D548F4A83FA8F0D67" xlink:type="locator" />
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    <link:label id="lab_us-gaap_AssetsCurrent_DAC3DC13A813A21AD09A4A83FA902229_totalLabel_en-US" xlink:label="lab_us-gaap_AssetsCurrent_DAC3DC13A813A21AD09A4A83FA902229" xlink:role="http://www.xbrl.org/2003/role/totalLabel" xlink:type="resource" xml:lang="en-US">Total current assets</link:label>
    <link:label id="lab_us-gaap_AssetsCurrent_DAC3DC13A813A21AD09A4A83FA902229_label_en-US" xlink:label="lab_us-gaap_AssetsCurrent_DAC3DC13A813A21AD09A4A83FA902229" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Assets, Current</link:label>
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AssetsCurrent" xlink:label="loc_us-gaap_AssetsCurrent_DAC3DC13A813A21AD09A4A83FA902229" xlink:type="locator" />
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    <link:label id="lab_us-gaap_PropertyPlantAndEquipmentNet_AD2A417C29285183DE674A83FA906DD7_verboseLabel_en-US" xlink:label="lab_us-gaap_PropertyPlantAndEquipmentNet_AD2A417C29285183DE674A83FA906DD7" xlink:role="http://www.xbrl.org/2003/role/verboseLabel" xlink:type="resource" xml:lang="en-US">Property and equipment, net of accumulated depreciation of $966,387 and $862,825</link:label>
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    <link:label id="lab_us-gaap_OtherAssetsNoncurrent_8A7BDD2B8A50B1637B704A83FA904CBA_terseLabel_en-US" xlink:label="lab_us-gaap_OtherAssetsNoncurrent_8A7BDD2B8A50B1637B704A83FA904CBA" xlink:role="http://www.xbrl.org/2003/role/terseLabel" xlink:type="resource" xml:lang="en-US">Other assets, net</link:label>
    <link:label id="lab_us-gaap_OtherAssetsNoncurrent_8A7BDD2B8A50B1637B704A83FA904CBA_label_en-US" xlink:label="lab_us-gaap_OtherAssetsNoncurrent_8A7BDD2B8A50B1637B704A83FA904CBA" xlink:role="http://www.xbrl.org/2003/role/label" xlink:type="resource" xml:lang="en-US">Other Assets, Noncurrent</link:label>
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