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                                                                     EXHIBIT 3.5

                           CERTIFICATE OF DESIGNATION

                                       of

                  SERIES B JUNIOR PARTICIPATING PREFERRED STOCK

                                       of

                              QUANTA SERVICES, INC.

             PURSUANT TO SECTION 151 OF THE GENERAL CORPORATION LAW
                            OF THE STATE OF DELAWARE

         QUANTA SERVICES, INC., a corporation organized and existing under the
General Corporation Law of the State of Delaware (the "Corporation"), in
accordance with the provisions of Section 103 thereof, DOES HEREBY CERTIFY:

         That pursuant to the authority vested in the Board of Directors in
accordance with the provisions of the Restated Certificate of Incorporation of
the said Corporation, the said Board of Directors adopted the following
resolution creating a series of 700,000 shares of Preferred Stock designated as
"Series B Junior Participating Preferred Stock":

         RESOLVED, that pursuant to the authority vested in the Board of
Directors of this Corporation in accordance with the provisions of the Restated
Certificate of Incorporation, a series of Preferred Stock, par value $0.00001
per share, of the Corporation be and hereby is created, and that the designation
and number of shares thereof and the voting and other powers, preferences and
relative, participating, optional or other rights of the shares of such series
and the qualifications, limitations and restrictions thereof are as follows:

         SERIES B JUNIOR PARTICIPATING PREFERRED STOCK

         1. Designation and Amount. There shall be a series of Preferred Stock
that shall be designated as "Series B Junior Participating Preferred Stock," and
the number of shares constituting such series shall be 700,000. Such number of
shares may be increased or decreased by resolution of the Board of Directors;
provided, however, that no decrease shall reduce the number of shares of Series
B Junior Participating Preferred Stock to less than the number of shares then
issued and outstanding plus the number of shares issuable upon exercise of
outstanding rights, options or warrants or upon conversion of outstanding
securities issued by the Corporation.


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         2. Dividends and Distribution.

         (A) Subject to the prior and superior rights of the holders of any
shares of any class or series of stock of the Corporation ranking prior and
superior to the shares of Series B Junior Participating Preferred Stock
(including, without limitation, the Series A Convertible Preferred Stock) with
respect to dividends, the holders of shares of Series B Junior Participating
Preferred Stock, in preference to the holders of shares of any class or series
of stock of the Corporation ranking junior to the Series B Junior Participating
Preferred Stock in respect thereof, shall be entitled to receive, when, as and
if declared by the Board of Directors out of funds legally available for the
purpose, quarterly dividends payable in cash on the first day of January, April,
July and October, in each year (each such date being referred to herein as a
"Quarterly Dividend Payment Date"), commencing on the first Quarterly Dividend
Payment Date after the first issuance of a share or fraction of a share of
Series B Junior Participating Preferred Stock, in an amount per share (rounded
to the nearest cent) equal to the greater of (a) $1.00, or (b) the Adjustment
Number (as defined below) times the aggregate per share amount of all cash
dividends, and the Adjustment Number times the aggregate per share amount
(payable in kind) of all non-cash dividends or other distributions other than a
dividend payable in shares of Common Stock or a subdivision of the outstanding
shares of Common Stock (by reclassification or otherwise), declared on the
Common Stock, par value $0.00001 per share, of the Corporation (the "Common
Stock") since the immediately preceding Quarterly Dividend Payment Date, or,
with respect to the first Quarterly Dividend Payment Date, since the first
issuance of any share or fraction of a share of Series B Junior Participating
Preferred Stock. The "Adjustment Number" shall initially be 1,000. In the event
the Corporation shall at any time after March 8, 2000 (i) declare and pay any
dividend on Common Stock payable in shares of Common Stock (other than the 3 for
2 stock dividend payable on April 7, 2000), (ii) subdivide the outstanding
Common Stock, or (iii) combine the outstanding Common Stock into a smaller
number of shares, then in each such case the Adjustment Number in effect
immediately prior to such event shall be adjusted by multiplying such Adjustment
Number by a fraction the numerator of which is the number of shares of Common
Stock outstanding immediately after such event and the denominator of which is
the number of shares of Common Stock that were outstanding immediately prior to
such event.

         (B) The Corporation shall declare a dividend or distribution on the
Series B Junior Participating Preferred Stock as provided in paragraph (A) above
immediately after it declares a dividend or distribution on the Common Stock
(other than a dividend payable in shares of Common Stock).

         (C) Dividends shall begin to accrue and be cumulative on outstanding
shares of Series B Junior Participating Preferred Stock from the Quarterly
Dividend Payment Date next preceding the date of issue of such shares of Series
B Junior Participating Preferred Stock, unless the date of issue of such shares
is prior to the record date for the first Quarterly Dividend Payment Date, in
which case dividends on such shares shall begin to accrue from the date of issue
of such shares, or unless the date of issue is a Quarterly Dividend Payment Date
or is a date


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after the record date for the determination of holders of shares of Series B
Junior Participating Preferred Stock entitled to receive a quarterly dividend
and before such Quarterly Dividend Payment Date, in either of which events such
dividends shall begin to accrue and be cumulative from such Quarterly Dividend
Payment Date. Accrued but unpaid dividends shall not bear interest. Dividends
paid on the shares of Series B Junior Participating Preferred Stock in an amount
less than the total amount of such dividends at the time accrued and payable on
such shares shall be allocated pro rata on a share-by-share basis among all such
shares at the time outstanding. The Board of Directors may fix a record date for
the determination of holders of shares of Series B Junior Participating
Preferred Stock entitled to receive payment of a dividend or distribution
declared thereon, which record date shall be no more than 60 days prior to the
date fixed for the payment thereof.

         3. Voting Rights. The holders of shares of Series B Junior
Participating Preferred Stock shall have the following voting rights:

         (A) Each share of Series B Junior Participating Preferred Stock shall
entitle the holder thereof to a number of votes equal to the Adjustment Number
on all matters submitted to a vote of the stockholders of the Corporation.

         (B) Except as required by law, by Section 3(C) and by Section 10
hereof, holders of Series B Junior Participating Preferred Stock shall have no
special voting rights and their consent shall not be required (except to the
extent they are entitled to vote with holders of Common Stock as set forth
herein) for taking any corporate action.

         (C) If, at the time of any annual meeting of stockholders for the
election of directors, the equivalent of six quarterly dividends (whether or not
consecutive) payable on any share or shares of Series B Junior Participating
Preferred Stock are in default, the Corporation shall take all steps which are
necessary, including the calling of a special meeting of stockholders, to cause
the number of directors constituting the Board of Directors of the Corporation
to be increased by two as contemplated by the following sentence. In addition to
voting together with the holders of Common Stock for the election of other
directors of the Corporation, the holders of record of the Series B Junior
Participating Preferred Stock, voting separately as a class to the exclusion of
the holders of Common Stock, shall be entitled at said meeting of stockholders
(and at each subsequent annual meeting of stockholders), unless all dividends in
arrears on the Series B Junior Participating Preferred Stock have been paid or
declared and set apart for payment prior thereto, to vote for the election of
two directors of the Corporation, the holders of any Series B Junior
Participating Preferred Stock being entitled to cast a number of votes per share
of Series B Junior Participating Preferred Stock as is specified in paragraph
(A) of this Section 3. Until the default in payments of all dividends which
permitted the election of said directors shall cease to exist, any director who
shall have been so elected pursuant to the provisions of this Section 3(C) may
be removed at any time without cause only by the affirmative vote of the holders
of the shares of Series B Junior Participating Preferred Stock at the time
entitled to cast a majority of the votes entitled to be cast for the election of
any such


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director at a special meeting of such holders called for that purpose, and any
vacancy thereby created may be filled by the vote of such holders. If and when
such default shall cease to exist, the holders of the Series B Junior
Participating Preferred Stock shall be divested of the foregoing special voting
rights, subject to revesting in the event of each and every subsequent like
default in payments of dividends. Upon the termination of the foregoing special
voting rights, the terms of office of all persons who may have been elected
directors pursuant to said special voting rights shall forthwith terminate, and
the number of directors constituting the Board of Directors shall be reduced by
two. The voting rights granted by this Section 3(C) shall be in addition to any
other voting rights granted to the holders of the Series B Junior Participating
Preferred Stock in this Section 3.

         4. Certain Restrictions.

         (A) Whenever quarterly dividends or other dividends or distributions
payable on the Series B Junior Participating Preferred Stock as provided in
Section 2 are in arrears, thereafter and until all accrued and unpaid dividends
and distributions, whether or not declared, on shares of Series B Junior
Participating Preferred Stock outstanding shall have been paid in full, the
Corporation shall not:

                  (i) declare or pay dividends on, make any other distributions
         on, or redeem or purchase or otherwise acquire for consideration any
         shares of stock ranking junior (either as to dividends or upon
         liquidation, dissolution or winding up) to the Series B Junior
         Participating Preferred Stock;

                  (ii) declare or pay dividends on or make any other
         distributions on any shares of stock ranking on a parity (either as to
         dividends or upon liquidation, dissolution or winding up) with the
         Series B Junior Participating Preferred Stock, except dividends paid
         ratably on the Series B Junior Participating Preferred Stock and all
         such parity stock on which dividends are payable or in arrears in
         proportion to the total amounts to which the holders of all such shares
         are then entitled; or

                  (iii) purchase or otherwise acquire for consideration any
         shares of Series B Junior Participating Preferred Stock, or any shares
         of stock ranking on a parity with the Series B Junior Participating
         Preferred Stock, except in accordance with a purchase offer made in
         writing or by publication (as determined by the Board of Directors) to
         all holders of Series B Junior Participating Preferred Stock, or to
         such holders and holders of any such shares ranking on a parity
         therewith, upon such terms as the Board of Directors, after
         consideration of the respective annual dividend rates and other
         relative rights and preferences of the respective series and classes,
         shall determine in good faith will result in fair and equitable
         treatment among the respective series or classes.

         (B) The Corporation shall not permit any subsidiary of the Corporation
to

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purchase or otherwise acquire for consideration any shares of stock of the
Corporation unless the Corporation could, under paragraph (A) of this Section 4,
purchase or otherwise acquire such shares at such time and in such manner.

         5. Reacquired Shares. Any shares of Series B Junior Participating
Preferred Stock purchased or otherwise acquired by the Corporation in any manner
whatsoever shall be retired promptly after the acquisition thereof. All such
shares shall upon their retirement become authorized but unissued shares of
Preferred Stock and may be reissued as part of a new series of Preferred Stock
to be created by resolution or resolutions of the Board of Directors, subject to
any conditions and restrictions on issuance set forth herein.

         6. Liquidation, Dissolution or Winding Up.

                  (A) Upon any liquidation, dissolution or winding up of the
         Corporation, voluntary or otherwise, no distribution shall be made to
         the holders of shares of stock ranking junior (either as to dividends
         or upon liquidation, dissolution or winding up) to the Series B Junior
         Participating Preferred Stock unless, prior thereto, the holders of
         shares of Series B Junior Participating Preferred Stock shall have
         received an amount per share (the "Series B Liquidation Preference")
         equal to the greater of (i) $10.00, plus an amount equal to accrued and
         unpaid dividends and distributions thereon, whether or not declared, to
         the date of such payment, or (ii) the Adjustment Number times the per
         share amount of all cash and other property to be distributed in
         respect of the Common Stock upon such liquidation, dissolution or
         winding up of the Corporation.

                  (B) In the event, however, that there are not sufficient
         assets available to permit payment in full of the Series B Liquidation
         Preference and the liquidation preferences of all other classes and
         series of stock of the Corporation, if any, that rank on a parity with
         the Series B Junior Participating Preferred Stock in respect thereof,
         then the assets available for such distribution shall be distributed
         ratably to the holders of the Series B Junior Participating Preferred
         Stock and the holders of such parity shares in proportion to their
         respective liquidation preferences.

                  (C) Neither the merger or consolidation of the Corporation
         into or with another corporation nor the merger or consolidation of any
         other corporation into or with the Corporation shall be deemed to be a
         liquidation, dissolution or winding up of the Corporation within the
         meaning of this Section 6.

         7. Consolidation, Merger, Etc. In case the Corporation shall enter into
any consolidation, merger, combination or other transaction in which the
outstanding shares of Common Stock are exchanged for or changed into other stock
or securities, cash and/or any other property, then in any such case each share
of Series B Junior Participating Preferred Stock shall at the same time be
similarly exchanged or changed in an amount per share equal to the Adjustment
Number times the aggregate amount of stock, securities, cash and/or any other


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property (payable in kind), as the case may be, into which or for which each
share of Common Stock is changed or exchanged.

         8. No Redemption. Shares of Series B Junior Participating Preferred
Stock shall not be subject to redemption by the Corporation.

         9. Ranking. The Series B Junior Participating Preferred Stock shall
rank junior to all other series of the Preferred Stock as to the payment of
dividends and as to the distribution of assets upon liquidation, dissolution or
winding up, unless the terms of any such series shall provide otherwise, and
shall rank senior to the Common Stock as to such matters.

         10. Amendment. At any time that any shares of Series B Junior
Participating Preferred Stock are outstanding, the Restated Certificate of
Incorporation of the Corporation shall not be amended in any manner which would
materially alter or change the powers, preferences or special rights of the
Series B Junior Participating Preferred Stock so as to affect them adversely
without the affirmative vote of the holders of two-thirds of the outstanding
shares of Series B Junior Participating Preferred Stock, voting separately as a
class.

         11. Fractional Shares. Series B Junior Participating Preferred Stock
may be issued in fractions of a share that shall entitle the holder, in
proportion to such holder's fractional shares, to exercise voting rights,
receive dividends, participate in distributions and to have the benefit of all
other rights of holders of Series B Junior Participating Preferred Stock.

         IN WITNESS WHEREOF, the undersigned has executed this Certificate this
21st day of March, 2000.

QUANTA SERVICES, INC.


By:
   ---------------------------------
   Brad Eastman, Vice President


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