<PAGE>
                                                                    EXHIBIT 4.12

                                SEVENTH AMENDMENT
             TO THIRD AMENDED AND RESTATED SECURED CREDIT AGREEMENT

         THIS SEVENTH AMENDMENT TO THIRD AMENDED AND RESTATED SECURED CREDIT
AGREEMENT (this "AMENDMENT") is entered into as of February 12, 2002, among
QUANTA SERVICES, INC., a Delaware corporation ("BORROWER"), the Lenders, as
defined below, and BANK OF AMERICA, N.A., f/k/a NationsBank, N.A., as
administrative agent for the Lenders (in such capacity, the "AGENT").
Capitalized terms used but not defined in this Amendment have the meaning given
such terms in the Credit Agreement (defined below).

                                    RECITALS

         A. The Borrower is party to that certain Third Amended and Restated
Secured Credit Agreement dated as of June 14, 1999 (as amended by the First
Amendment dated as of September 21, 1999, the Second Amendment dated as of March
21, 2000, the Third Amendment and Consent dated as of June 15, 2000, the Fourth
Amendment dated as of October 27, 2000, the Fifth Amendment dated as of November
9, 2000, the Sixth Amendment dated as of October 17, 2001, and as may be further
amended, restated or supplemented from time to time, the "CREDIT AGREEMENT"),
among the Borrower, Agent, and the lenders from time to time parties thereto
(each a "LENDER" collectively, "LENDERS").

         B. The Borrower has requested that certain provisions of the Credit
Agreement be amended to take into account certain adjustments to the
determination of Consolidated Net Worth in accordance with Statement of
Financial Accounting Standards No. 142 (Goodwill and Other Intangible Assets)
issued in June, 2001.

         C. The Borrower has also requested that (i) SECTION 6.6(e) of the
Credit Agreement be amended to increase the reporting threshold thereunder for
certain events from $1,000,000 to $5,000,000, (ii) SECTION 6.14(e) of the Credit
Agreement be amended to permit a Subordinated Debt Investment, and (iii) SECTION
6.15(k) of the Credit Agreement be amended to allow the Borrower the use of
funds thereunder to redeem Subordinated Debt Investments.

         D. The Borrower, Agent and the Lenders have agreed to amend the Credit
Agreement to accommodate the foregoing requests and to make other related
modifications, in each case subject to the terms and conditions set out in this
Amendment.

         NOW THEREFORE, in consideration of the premises herein contained and
other good and valuable consideration, the receipt and sufficiency of which are
hereby acknowledged, the undersigned agree as follows:

         1. Amendment to Section 1.1 (Definitions). SECTION 1.1 of the Credit
Agreement is hereby amended (a) to amend and restate the defined terms "EBIT"
and "EBITDA" (with the new or modified language underlined), and (b) to add the
following defined term of "SFAS 142" in its appropriate alphabetical order:

                  ""EBIT" means, for any period, on a trailing four fiscal
                  quarter basis, the sum of Consolidated Net Income plus each of
                  the following to the extent actually deducted in determining
                  Consolidated Net Income, (a) Consolidated Interest Expense,
                  (b) provisions for taxes based on income or revenues, and (c)
                  provisions made in




<PAGE>


                  accordance with SFAS 142, all calculated on a consolidated
                  basis for the Borrower and its Subsidiaries and as determined
                  in accordance with GAAP.

                  "EBITDA" means, for any period, on a trailing four fiscal
                  quarter basis (using the historical financial results of any
                  business acquired in an Acquisition through the Effective
                  Date, to the extent applicable, all on a pro forma basis,
                  consistent with SEC regulations), the sum of (i) Consolidated
                  Net Income plus each of the following to the extent actually
                  deducted in determining Consolidated Net Income, (a)
                  Consolidated Interest Expense, (b) provisions for taxes based
                  on income or revenues, and (c) provisions made in accordance
                  with SFAS 142, plus (ii) the amount of all depreciation and
                  amortization expense deducted in determining Consolidated Net
                  Income, and adjusted for (iii) Non-Cash Charges, all
                  calculated on a consolidated basis for the Borrower and its
                  Subsidiaries and as determined in accordance with GAAP. Upon
                  the consummation of any Acquisition after the Effective Date,
                  EBITDA may be calculated, subject to the immediately following
                  sentence, using a calculation which (y) includes the
                  historical financial results of the acquired business on a pro
                  forma trailing four fiscal quarter basis (consistent with SEC
                  regulations), and (z) assumes that the consummation of such
                  Acquisition (and the incurrence, refinancing, or assumption of
                  any Indebtedness in connection with such Acquisition) occurred
                  on the first day of the trailing four fiscal quarter period.
                  The foregoing adjustment to EBITDA to take into account an
                  Acquisition may only be made if the balance sheet and
                  statements of income, retained earnings, and cash flows of the
                  acquired Person (or the Person from whom the assets,
                  securities or other equity interests were acquired), are in
                  compliance with SEC regulations and requirements regarding the
                  preparation and presentation of historical financial
                  information and pro forma financial information.

                  "SFAS 142" means the Statement of Financial Accounting
                  Standards No. 142 (Goodwill and Other Intangible Assets), as
                  issued by the Financial Accounting Standards Board in June,
                  2001, and applicable to all fiscal years beginning after
                  December 15, 2001."

         2. Amendments to Section 6.6 (Financial Reports and Other Information).
SECTION 6.6(e) of the Credit Agreement is hereby amended and restated in its
entirety as follows (with the new or modified language underlined):

                  "(e) The Borrower will promptly and in any event, within ten
                  (10) days after an officer of the Borrower has knowledge
                  thereof, give written notice to the Agent of: (i) any pending
                  or threatened litigation or proceeding against the Borrower or
                  any of its Subsidiaries asserting any uninsured claim or
                  claims against any of same in excess of $5,000,000 in the
                  aggregate; (ii) the occurrence of any Default or Event of
                  Default; (iii) any circumstance that has had a Material
                  Adverse Effect; and (iv) any event which would result in a
                  breach of SECTIONS 6.20, 6.21, 6.22, 6.23, OR 6.24."

         3. Amendments to Section 6.11 (Restrictions on Fundamental Changes).
SECTION 6.11(a) of the Credit Agreement is hereby amended and restated in its
entirety as follows (with the new or modified language underlined):


                                       2
<PAGE>

                  "(a) the Borrower or any of its Subsidiaries may merge into or
                  consolidate with, make an Acquisition or otherwise purchase or
                  acquire all or substantially all of the assets or stock of any
                  other Person, if in respect of such merger, consolidation,
                  purchase or Acquisition, (i) the Borrower is the surviving
                  entity to any such merger or consolidation to which the
                  Borrower is a party, or, if the Borrower is not a party to
                  such transaction, a Subsidiary is the surviving entity to any
                  such merger or consolidation (or the other Person will thereby
                  become a Subsidiary), (ii) the nature of the business of such
                  acquired Person is a Permitted Business; (iii) no Default or
                  Event of Default shall have occurred and be continuing or
                  would otherwise be existing as a result of such merger,
                  consolidation, purchase or Acquisition, (iv) such merger,
                  consolidation, purchase or Acquisition is non-hostile in
                  nature; and (v) either (y) the aggregate amount of (without
                  duplication) (1) the cash purchase price paid, (2) the
                  Borrowings under this Agreement in respect of such
                  consolidation, purchase or Acquisition, and (3) the
                  Indebtedness of such acquired Person assumed or otherwise
                  refinanced by the Borrower or any of its Subsidiaries, does
                  not exceed, for any single Acquisition (after deducting the
                  amount of cash and Cash Equivalents held by such acquired
                  Person), an amount equal to 7.5% of Consolidated Net Worth as
                  of the end of the immediately preceding fiscal quarter
                  (without taking into account adjustments to the determination
                  of Consolidated Net Worth made in accordance with SFAS 142 in
                  accordance with GAAP), or (z) (1) prior to the consummation of
                  such merger, consolidation, purchase or Acquisition, the
                  Borrower shall have delivered to the Agent (which the Agent
                  shall promptly provide to each Lender) a report signed by an
                  executive officer of the Borrower which shall contain
                  calculations demonstrating the Borrower's compliance with
                  SECTIONS 6.20, 6.21, 6.22, and 6.23 (which calculation may use
                  historical financial results of the acquired business provided
                  the calculation (A) is made on a trailing four fiscal quarter
                  pro forma basis (consistent with SEC regulations), (B) assumes
                  that the consummation of such merger, consolidation, purchase
                  or Acquisition (and the incurrence, refinancing, or assumption
                  of any Indebtedness in connection with such Acquisition)
                  occurred on the first day of the trailing four-quarter fiscal
                  period, and (C) is based on a balance sheet and statements of
                  income, retained earnings, and cash flows of the acquired
                  Person (or the Person from whom the assets, securities or
                  other equity interests were acquired), which are in compliance
                  with SEC regulations and requirements regarding the
                  preparation and presentation of historical financial
                  information and pro forma financial information, and (2) the
                  Majority Lenders have given their prior written consent to
                  such merger, consolidation, purchase or Acquisition."

         4. Amendments to Section 6.14 (Indebtedness). SECTIONS 6.14 (e) and (f)
of the Credit Agreement are hereby amended and restated in their entirety as
follows (with the new or modified language underlined):

                  "(e) Indebtedness incurred in connection with Subordinated
                  Debt Investments, including any convertible Subordinated Debt
                  Investment not to exceed $250,000,000 (which amount includes
                  the Indebtedness under the Convertible Subordinated Notes), in
                  the aggregate, on terms subordinated in right of payment and
                  collection to, and with a maturity date beyond the Maturity
                  Date of, the Obligations and otherwise on terms acceptable to
                  the Agent;



                                       3
<PAGE>


                  (f) other Indebtedness not included within subsections (a)
                  through (e) above, provided that such Indebtedness shall not
                  exceed, at any one time outstanding, an amount equal to 8.5%
                  of Consolidated Net Worth as of the end of the immediately
                  preceding fiscal quarter (without taking into account
                  adjustments to the determination of Consolidated Net Worth in
                  accordance with SFAS 142 in accordance with GAAP);"

         5. Amendments to Section 6.15 (Loans, Advances and Investments).
SECTION 6.15(k) of the Credit Agreement is hereby amended and restated in its
entirety as follows (with the new or modified language underlined):

                  "(k) Investments up to an aggregate amount of $75,000,000 in
                  the Borrower in the form of (i) repurchasing of the Borrower's
                  common stock through a series of open-market transactions or
                  in privately negotiated, off-market transactions or through
                  one or more hedge, swap, exchange, forward, future, collar or
                  cap arrangements, fixed price agreements or other similar
                  arrangements or agreements, and (ii) refunding, repurchase,
                  discharge, defeasance or retirement any Subordinated Debt
                  Investment; and"

         6. Amendments to Section 6.19 (Capital Expenditures). SECTION 6.19 of
the Credit Agreement is hereby amended and restated in its entirety as follows
(with the new or modified language underlined):

                  "Section 6.19 Capital Expenditures. Neither the Borrower nor
                  any of its Subsidiaries shall make or commit to make Capital
                  Expenditures during any period of four consecutive fiscal
                  quarters in excess of 15% of Consolidated Net Worth, with
                  Consolidated Net Worth being determined as of the last day of
                  the last fiscal quarter of such period (without taking into
                  account adjustments to the determination of Consolidated Net
                  Worth made in accordance with SFAS 142 in accordance with
                  GAAP)."

         7. Amendments to Section 6.20 (Minimum Consolidated Net Worth). SECTION
6.20 of the Credit Agreement is hereby amended and restated in its entirety as
follows (with the new or modified language underlined):

                  "Section 6.20 Minimum Consolidated Net Worth. The Borrower
                  will maintain a minimum Consolidated Net Worth of not less
                  than an amount equal to the sum of (i) $296,000,000, plus (ii)
                  for each fiscal quarter ended prior to (but not on) such date
                  of determination, commencing with the fiscal quarter ended
                  June 30, 1999, (w) an amount equal to 50% of Consolidated Net
                  Income for such fiscal quarter, if positive, plus (x) an
                  amount equal to 100% of the amount of any equity issuance by
                  the Borrower, including equity issued in a secondary offering
                  or equity issued to acquire another entity in an Acquisition,
                  plus (y) an amount equal to 100% of the stockholders equity of
                  any entity acquired in an Acquisition for which the Borrower
                  uses the pooling of interest method of accounting to the
                  extent permitted by, and in accordance with Statement of
                  Financial Accounting Standards No. 141 (Business
                  Combinations), as adopted by the Financial Accounting
                  Standards Board in June, 2001,and GAAP, minus (z) any
                  distributions to shareholders of any Subchapter S corporation
                  acquired in an Acquisition as a result of operations of the
                  corporation acquired prior to the closing of the Acquisition
                  or the terms of the Acquisition,


                                       4
<PAGE>

                  provided that, the foregoing calculation shall take into
                  account, and be subject to, adjustments to the determination
                  of Consolidated Net Worth made in accordance with SFAS 142 in
                  accordance with GAAP."

         8. Amendments to Section 10.17 (Change in Accounting Principles or Tax
Laws). SECTION 10.17 of the Credit Agreement is hereby amended and restated in
its entirety as follows (with the new or modified language underlined):

                  "10.17 Change in Accounting Principles or Tax Laws. If (i) any
                  change in accounting principles from those used in the
                  preparation of the financial statements of the Borrower
                  referred to in SECTION 5.9 is hereafter occasioned by the
                  promulgation of rules, regulations, pronouncements and
                  opinions by or required by the Financial Accounting Standards
                  Board or the American Institute of Certified Public Accounts
                  (or successors thereto or agencies with similar functions) and
                  such change materially affects the calculation of any
                  component of any financial covenant, standard or term found in
                  this Agreement, or (ii) there is a material change in federal
                  or foreign tax laws which materially affects the Borrower's
                  ability to comply with the financial covenants, standards or
                  terms found in this Agreement, the Borrower, the Agent and the
                  Lenders agree to enter into negotiations in order to amend
                  such provisions so as to equitably reflect such changes with
                  the desired result that the criteria for evaluating the
                  Borrower's and its Subsidiaries' consolidated financial
                  condition shall be the same after such changes as if such
                  changes had not been made. Unless and until such provisions
                  have been so amended, the provisions of this Agreement shall
                  govern, provided that, for purposes of this SECTION 10.17, the
                  Borrower shall have 90 days from the date of any such change
                  to amend the appropriate provisions of this Agreement to
                  reflect such change in accordance with the immediately
                  preceding sentence."

         9. Conditions. This Amendment shall not be effective until (a) it has
been duly executed and delivered by Borrower, each Guarantor, and at least the
Majority Lenders, and (b) Borrower has delivered to Agent for the benefit of
Lenders (i) a certificate from the Borrower that no Default or Event of Default
exists under the Credit Agreement, and (ii) such other documents, if any, as the
Agent may reasonably request.

         10. Fees and Expenses. The Borrower agrees to pay (a) to Agent for the
benefit of each Lender that executes and delivers this Amendment on or before
February 12, 2002, an amendment fee equal to .05% of such Lender's Commitment,
and (b) the reasonable fees and expenses of counsel to Agent for services
rendered in connection with the preparation, negotiation and execution of this
Amendment.

         11. Representations and Warranties. The Borrower and the Guarantors
represent and warrant to the Lenders that they possess all requisite power and
authority to execute, deliver and comply with the terms of this Amendment, which
has been duly authorized and approved by all requisite corporate action on the
part of the Borrower and the Guarantors, for which no consent of any Person is
required, and which will not violate their respective organizational documents,
and agree to furnish the Agent with evidence of such authorization and approval
upon request. The Borrower and the Guarantors further represent and warrant to
the Agent and the Lenders that (a) the representations and warranties in each
Credit Document to which they are a party are true and correct in all material
respects on and as of the date of this Amendment as though made on the date of
this Amendment (except to the extent that (i) such representations and
warranties speak to a specific date or (ii) the facts on which such
representations and warranties are based have been


                                       5
<PAGE>

changed by transactions contemplated by the Credit Agreement), (b) it is in full
compliance with all covenants and agreements contained in each Credit Document
to which it is a party, and (c) no Default or Event of Default has occurred and
is continuing.

         12. Scope of Amendment and Consent; Reaffirmation; Release. Except as
affected by this Amendment, the Credit Documents are unchanged and continue in
full force and effect. However, in the event of any inconsistency between the
terms of the Credit Agreement as hereby amended and any other Credit Document,
the terms of the Credit Agreement shall control and such other document shall be
deemed to be amended hereby to conform to the terms of the Credit Agreement. All
references to the Credit Agreement shall refer to the Credit Agreement as
amended by this Amendment. The Borrower and the Guarantors hereby reaffirm their
respective obligations under, and agree that, all Credit Documents to which they
are a party remain in full force and effect and continue to evidence their
respective legal, valid and binding obligations enforceable in accordance with
their terms (as the same are affected by this Amendment). The Borrower and the
Guarantors hereby release the Agent and the Lenders from any liability for
actions or failures to act in connection with the Credit Documents prior to the
date hereof. This Amendment shall be binding upon and inure to the benefit of
each of the undersigned and their respective successors and permitted assigns.

         13.      Miscellaneous.

                  (a) No Waiver of Defaults. This Amendment does not constitute
         a waiver of, or a consent to, any present or future violation of or
         default under, any provision of the Credit Documents, or a waiver of
         the Lenders' right to insist upon future compliance with each term,
         covenant, condition and provision of the Credit Documents, and the
         Credit Documents shall continue to be binding upon, and inure to the
         benefit of, the Borrower, the Guarantors, the Agent, and the Lenders
         and their respective successors and assigns.

                  (b) Form. Each agreement, document, instrument or other
         writing to be furnished to the Agent under any provision of this
         instrument must be in form and substance satisfactory to the Agent and
         its counsel.

                  (c) Multiple Counterparts. This Amendment may be executed in
         any number of counterparts with the same effect as if all signatories
         have signed the same document. All counterparts must be construed
         together to constitute one and the same instrument.

                  (d) Governing Law. This Amendment and the other Credit
         Documents must be construed-and their performance enforced-under Texas
         law.

                  (e) Entirety. THE CREDIT DOCUMENTS, AS AMENDED HEREBY,
         REPRESENT THE FINAL AGREEMENT BETWEEN THE BORROWER, GUARANTORS, THE
         AGENT AND THE LENDERS AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,
         CONTEMPORANEOUS, OR SUBSEQUENT ORAL AGREEMENTS BY THE PARTIES. THERE
         ARE NO UNWRITTEN ORAL AGREEMENTS AMONG THE PARTIES.

 [SIGNATURES AND GUARANTORS' CONSENT AND AGREEMENT APPEAR ON FOLLOWING PAGES.]


                                       6

<PAGE>


         EXECUTED as of the date first written above.


                                   QUANTA SERVICES, INC.


                                   By: /s/ Nick Grindstaff
                                       -----------------------------------------
                                           Nick Grindstaff
                                           Treasurer


                                  BANK OF AMERICA, N.A., as Administrative Agent


                                  By: /s/ Suzanne M. Paul
                                      ------------------------------------------
                                          Suzanne M. Paul, Vice President


                                  BANK OF AMERICA, N.A., as a Lender

                                  By: /s/ Albert L. Welch
                                     -------------------------------------------
                                          Albert L. Welch
                                          Senior Vice President

                                  BANK ONE, NA, as a Documentation Agent and
                                  as a Lender


                                  By: /s/ John A. Horst
                                      ------------------------------------------
                                         John A. Horst
                                         Director

                                  FLEET NATIONAL BANK (F/K/A BANK BOSTON, N.A.),
                                  as a Documentation Agent and as a Lender


                                  By:
                                     -------------------------------------------
                                       Name:
                                            ------------------------------------
                                       Title:
                                             -----------------------------------


                                  CREDIT LYONNAIS NEW YORK BRANCH, as a Managing
                                  Agent and as a Lender


                                  By: /s/  Attila Koc
                                      ------------------------------------------
                                           Attila Koc
                                           Senior Vice President



                                       7

<PAGE>


                                  THE BANK OF NOVA SCOTIA, as a Managing Agent
                                  and as a Lender


                                  By: /s/ M.D. Smith
                                      ------------------------------------------
                                          M.D. Smith
                                          Agent

                                  NATIONAL CITY BANK, as a Lender


                                  By: /s/ Michael Aurbon
                                      ------------------------------------------
                                          Michael Aurbon
                                          Vice President


                                  LASALLE BANK NATIONAL ASSOCIATION, as a Lender


                                  By: /s/ Richard J. Kress
                                      ------------------------------------------
                                          Richard J. Kress
                                          First Vice President


                                  FIRST UNION NATIONAL BANK, as a Lender


                                  By: /s/ Laura B. Smith
                                      ------------------------------------------
                                          Laura B. Smith
                                          Vice President


                                  COMERICA BANK, as a Lender

                                  By: /s/ Gerald R. Finney, Jr.
                                      ------------------------------------------
                                          Gerald R. Finney, Jr.
                                          Vice President


THE BANK OF TOKYO-MITSUBISHI,     THE BANK OF TOKYO-MITSUBISHI, LTD., as a
LTD., as a Lender                 Lender

By: /s/ J. Fort                   By: /s/ John Mearns
    ------------------------          ------------------------------------------
        J. Fort                           J. Mearns
        Vice President                    VP and Manager


                                       8

<PAGE>


                                  THE CHASE MANHATTAN BANK, as a Lender


                                  By: /s/ James R. Dolphin
                                      ------------------------------------------
                                          James R. Dolphin
                                          Senior Vice President


                                  GUARANTY FEDERAL BANK, F.S.B., as a Lender


                                  By:
                                     -------------------------------------------
                                      Name:
                                           -------------------------------------
                                      Title:
                                            ------------------------------------


                                  SUNTRUST BANK, ATLANTA, as a Lender

                                  By:
                                     -------------------------------------------
                                      Name:
                                           -------------------------------------
                                      Title:
                                            ------------------------------------



                                  BANKERS TRUST COMPANY, as a Lender


                                  By: /s/ Scottye Lindsey
                                      ------------------------------------------
                                          Scottye Lindsey
                                          Vice President




                                       9
<PAGE>


                        GUARANTORS' CONSENT AND AGREEMENT

         As an inducement to the Lenders to execute, and in consideration of the
Lenders' execution of this Amendment, each of the undersigned hereby consents to
this Amendment and agrees that the same shall in no way release, diminish,
impair, reduce or otherwise adversely affect the obligations and liabilities of
the undersigned under their respective Guaranties described in the Credit
Agreement executed by the undersigned, or any agreements, documents or
instruments executed by any of the undersigned, all of which obligations and
liabilities are, and shall continue to be, in full force and effect. This
consent and agreement shall be binding upon the undersigned, and their
respective successors and assigns, and shall inure to the benefit of the
Lenders, and their respective successors and assigns.

                                 ADVANCED TECHNOLOGIES AND INSTALLATION, INC.
                                 ALLTECK LINE CONTRACTORS (USA), INC.
                                 ALLTECK LINE CONTRACTORS, INC.
                                 ARBY CONSTRUCTION, INC.
                                 AUSTIN TRENCHER, INC.
                                 BRADFORD BORTHERS, INC.
                                 CCLC, INC.
                                 COMMUNICATION MANPOWER, INC.
                                 COMPUTAPOLE, INC.
                                 CONTI COMMUNICATIONS, INC.
                                 CROCE ELECTRIC COMPANY, INC.
                                 CROWN FIBER COMMUNICATIONS, INC.
                                 DILLARD SMITH CONSTRUCTION COMPANY
                                 DRIFTWOOD ELECTRICAL CONTRACTORS, INC.
                                 EDWARDS PIPELINE COMPANY,  INC.
                                 ENVIRONMENTAL PROFESSIONAL ASSOCIATES, LIMITED
                                 FIVE POINTS CONSTRUCTION COMPANY
                                 GEM ENGINEERING CO., INC.
                                 GOLDEN STATE UTILITY CO.
                                 H.L. CHAPMAN PIPELINE CONSTRUCTION, INC.
                                 HAINES CONSTRUCTION COMPANY
                                 INTERMOUNTAIN ELECTRIC, INC.
                                 IRBY CONSTRUCTION COMPANY
                                 LINE EQUIPMENT SALES CO., INC.
                                 LOGICAL LINK, INC.
                                 MANUEL BROS., INC.
                                 MEARS GROUP, INC.
                                 MEJIA PERSONNEL SERVICES, INC.
                                 METRO UNDERGROUND SERVICES, INC.
                                 NETWORK COMMUNICATIONS SERVICES, INC.
                                 NETWORK ELECTRIC COMPANY
                                 NORTH PACIFIC CONSTRUCTION CO., INC.
                                 NORTH SKY COMMUNICATIONS, INC.
                                 NORTHERN LINE LAYERS, INC.
                                 OKAY CONSTRUCTION COMPANY, INC.
                                 PAC WEST CONSTRUCTION, INC.
                                 PAR ELECTRICAL CONTRACTORS, INC.
                                 PARKSIDE SITE & UTILITY COMPANY CORPORATION
                                 PARKSIDE UTILITY CONSTRUCTION CORP.
                                 P.D.G. ELECTRIC COMPANY
                                 POTELCO, INC.
                                 PROFESSIONAL TELECONCEPTS, INC. (IL)



                                       10
<PAGE>


                                 PROFESSIONAL TELECONCEPTS, INC. (NY)
                                 PWR FINANCIAL COMPANY QPC, INC.
                                 QSI, INC.
                                 QUANTA HOLDINGS, INC.
                                 QUANTA LI ACQUISITION, INC.
                                 QUANTA LIV ACQUISITION, INC.
                                 QUANTA LV ACQUISITION, INC.
                                 QUANTA LVII ACQUISITION, INC.
                                 QUANTA LVIII ACQUISITION, INC.
                                 QUANTA LIX ACQUISITION, INC.
                                 QUANTA LX ACQUISITION, INC.
                                 QUANTA LXI ACQUISITION, INC.
                                 QUANTA LXII ACQUISITION, INC.
                                 QUANTA LXIII ACQUISITION, INC.
                                 QUANTA LXIV ACQUISITION, INC.
                                 QUANTA LXV ACQUISITION, INC.
                                 QUANTA LXVI ACQUISITION, INC.
                                 QUANTA LXVII ACQUISITION, INC.
                                 QUANTA LXVIII ACQUISITION, INC.
                                 QUANTA LXIX ACQUISITION, INC.
                                 QUANTA LXX ACQUISITION, INC.
                                 QUANTA LXXI ACQUISITION, INC.
                                 QUANTA LXXII ACQUISITION, INC.
                                 QUANTA LXXIII ACQUISITION, INC.
                                 QUANTA UTILITY INSTALLATION CO., INC,
                                 R. A. WAFFENSMITH & CO., INC.
                                 RANGER DIRECTIONAL, INC.
                                 SEAWARD CORPORATION
                                 SOUTHEAST PIPELINE CONSTRUCTION, INC.
                                 SOUTHWEST TRENCHING COMPANY, INC.
                                 SOUTHWESTERN COMMUNICATIONS, INC.
                                 SPALJ CONSTRUCTION COMPANY
                                 SPECIALTY DRILLING TECHNOLOGY, INC.
                                 SUMTER UTILITIES, INC.
                                 THE RYAN COMPANY, INC.
                                 TOM ALLEN CONSTRUCTION COMPANY
                                 TRANS TECH ACQUISITION, INC.
                                 TRAWICK CONSTRUCTION COMPANY, INC.
                                 TTGP, INC.
                                 TTLP, INC.
                                 TTM, INC.
                                 TXLP, INC.
                                 UNDERGROUND CONSTRUCTION CO., INC.
                                 UTILCO, INC.
                                 VCI TELCOM, INC.
                                 W.C. COMMUNICATIONS, INC.
                                 W.H.O.M. CORPORATION

                                 By: /s/  Dana Gordon
                                     -------------------------------------------
                                     Dana Gordon, President or Vice President of
                                        each Guarantor


                                       11
<PAGE>


                                 QDE LLC
                                 QUANTA DELAWARE, INC.
                                 QUANTA ASSET MANAGEMENT LLC

                                 By: /s/  Linda Bubacz
                                     -------------------------------------------
                                          Linda Bubacz, President

                                 BROWN ENGINEERING, LLC

                                 By: Haines Construction Company, Its Member

                                     By: /s/  Dana Gordon
                                         ---------------------------------------
                                              Dana Gordon, Vice President

                                 COAST TO COAST, LLC

                                 By: Environmental Professional Associates,
                                     Limited, a Californiacorporation,
                                     Its Member

                                     By: /s/  Dana Gordon
                                         ---------------------------------------
                                         Dana Gordon, Vice President

                                 DOT 05, LLC

                                 By: Spalj Construction Company, Its Member

                                     By: /s/ Dana Gordon
                                         ---------------------------------------
                                             Dana Gordon, Vice President

                                 LAKE NORMAN PIPELINE, LLC

                                 By:  Edwards Pipeline Company, Inc., Its Member

                                      By: /s/ Dana Gordon
                                         ---------------------------------------
                                              Dana Gordon, Vice President

                                 MEARS/CPG, LLC
                                 MEARS ENGINEERING, LLC
                                 MEARS/HDD, LLC
                                 MEARS SERVICES, LLC

                                 By: Mears Group, Inc., The Sole Member of each
                                     of the foregoing limited liability
                                     companies

                                     By: /s/ Dana Gordon
                                         ---------------------------------------
                                         Dana Gordon, Vice President




                                       12
<PAGE>


                                 S.K.S. PIPELINERS, LLC

                                 By: Arby Construction, Inc., Its Member

                                     By: /s/ Dana Gordon
                                         ---------------------------------------
                                         Dana Gordon, Vice President




                                       13
<PAGE>



                                 TJADER, L.L.C.

                                 By: Spalj Construction Company, Its Member

                                     By: /s/ Dana Gordon
                                         ---------------------------------------
                                             Dana Gordon, Vice President

                                 TNS-VA, LLC

                                 By: Professional Teleconcepts, Inc., Its Member

                                     By: /s/ Dana Gordon
                                         --------------------------------------
                                         Dana Gordon, Vice President

                                 AIRLAN TELECOM SERVICES, L.P.
                                 NORTH HOUSTON POLE LINE, L.P.
                                 LINDSEY ELECTRIC, L.P.
                                 DIGCO UTILITY CONSTRUCTION, L.P.

                                 By: Mejia Personnel Services, Inc., Its General
                                     Partner


                                     By: /s/ Dana Gordon
                                         ---------------------------------------
                                         Dana Gordon, Vice President

                                 QUANTA SERVICES MANAGEMENT PARTNERSHIP, L.P.
                                 QUANTA ASSOCIATES, L.P.

                                 By: QSI, Inc., Its General Partner


                                     By: /s/ Dana Gordon
                                         ---------------------------------------
                                         Dana Gordon, Vice President

                                 TRANS TECH ELECTRIC, L.P.

                                 By: TTGP, Inc., Its General Partner


                                     By: /s/ Dana Gordon
                                         ---------------------------------------
                                         Dana Gordon, Vice President

                                 PWR NETWORK, LLC

                                 By: PWR Financial Company, Its Sole Member

                                     By: /s/ Dana Gordon
                                         ---------------------------------------
                                         Dana A. Gordon, Vice President




                                       14

<PAGE>




                                Q RESOURCES, LLC

                                By: Quanta Holdings, Inc.

                                    By: /s/ Dana Gordon
                                        ----------------------------------------
                                        Dana A. Gordon, Vice President

                                QUANTA RECEIVABLES, L.P.

                                By: PWR Network, LLC, Its General Partner

                                    By: PWR Financial Company, Its Sole Member

                                        By: /s/ Dana Gordon
                                            ------------------------------------
                                            Dana A. Gordon, Vice President



                                       15