POWER OF ATTORNEY LETTER

Exhibit 24

POWER OF ATTORNEY

Know all by these present, that the undersigned hereby constitutes
and appoints Vincent A. Mercaldi, signing singly, the undersigned's true and
lawful attorney in fact to:

(1) execute for and on behalf of the undersigned, in the
undersigned's capacity as a director and/or officer of Quanta Services, Inc.
(the Company), Forms 3, 4, and 5 in accordance with Section 16(a) of the
Securities Exchange Act of 1934 and the rules thereunder;

(2) do and perform any and all acts for and on behalf of the
undersigned which may be necessary or desirable to complete and execute any
such Form 3, 4, or 5, complete and execute any amendment or amendments thereto,
and timely file such form with the United States Securities and Exchange
Commission and any stock exchange or similar authority; and

(3) take any other action of any type whatsoever in connection
with the foregoing which, in the opinion of such attorney in fact, may be of
benefit to, in the best interest of, or legally required by, the undersigned,
it being understood that the documents executed by such attorney in fact on
behalf of the undersigned pursuant to this Power of Attorney shall be in such
form and shall contain such terms and conditions as such attorney in fact may
approve in such attorney in fact's discretion.

The undersigned hereby grants to such attorney in fact full power
and authority to do and perform any and every act and thing whatsoever
requisite, necessary, or proper to be done in the exercise of any of the
rights and powers herein granted, as fully to all intents and purposes as
the undersigned might or could do if personally present, with full power of
substitution or revocation, hereby ratifying and confirming all that such
attorney in fact, or such attorney in fact's substitute or substitutes, shall
lawfully do or cause to be done by virtue of this power of attorney and the
rights and powers herein granted. The undersigned acknowledges that the
foregoing attorney in fact, in serving in such capacity at the request of
the undersigned, are not assuming, nor is the Company assuming, any of the
undersigned's responsibilities to comply with Section 16 of the Securities
Exchange Act of 1934.

This Power of Attorney shall remain in full force and effect until
the undersigned is no longer required to file Forms 3, 4, and 5 with respect
to the undersigned's holdings of and transactions in securities issued by the
Company, unless earlier revoked by the undersigned in a signed writing
delivered to the foregoing attorney in fact.

IN WITNESS WHEREOF, the undersigned has caused this Power of
Attorney to be executed as of this 24th day of May, 2006.

s/ Ralph R. DiSibio