Exhibit
      4


**AMENDMENT
        NO. 1**
 **TO**
 **AMENDED
        AND RESTATED CREDIT AGREEMENT**
  This
        AMENDMENT NO. 1, dated as of September 1, 2006 (this “ ***Amendment*** ”),
        is
        made by and among TUCSON ELECTRIC POWER COMPANY, an Arizona corporation (the
        “ ***Borrower*** ”),
        the
        lenders listed on the signature pages of this Amendment as “Lenders” (such
        lenders, together with their respective permitted assignees from time to
        time,
        being referred to herein, collectively, as the “ ***Lenders*** ”),
        the
        banks listed on the signature pages of this Amendment as “Issuing Banks”
(collectively, the “ ***Issuing
        Banks*** ”),
        UNION
        BANK OF CALIFORNIA, N.A., as administrative agent for the Lenders (in such
        capacity, the “ ***Administrative
        Agent*** ”),
        and
        WELLS FARGO BANK, NATIONAL ASSOCIATION and ABN AMRO BANK N.V., as New Issuing
        Banks (as defined herein).
  **PRELIMINARY
        STATEMENT:**
  The
        Borrower, the Lenders, the Issuing Banks, The Bank of New York and JPMorgan
        Chase Bank, N.A., as Co-Syndication Agents, Wells Fargo Bank, National
        Association and ABN AMRO Bank N.V., as Co-Documentation Agents, and the
        Administrative Agent previously entered into that certain Amended and Restated
        Credit Agreement, dated as of August 11, 2006 (the “ ***Existing
        Agreement*** ”,
        as
        amended by this Amendment, the “ ***Amended
        Agreement*** ”,
        and as
        the Amended Agreement may hereafter be amended, supplemented or otherwise
        modified from time to time, the “ ***Credit
        Agreement*** ”).
        The
        Borrower desires to amend the Existing Agreement in certain particulars to
        allow
        for the replacement from time to time of Revenue Bond Letters of Credit in
        accordance with the terms and conditions set forth in the Credit Agreement.
        Each
        of the Borrower, the Required Lenders, the Administrative Agent and the Issuing
        Banks has agreed to such amendment, on the terms and conditions set forth
        herein. The parties therefore agree as follows (capitalized terms used but
        not
        defined herein having the meanings assigned such terms in the Existing
        Agreement):
  ***SECTION
        1.  Amendments to Existing Agreement*** .
        The
        Existing Agreement is, effective
        as of the date hereof and subject to the satisfaction of the conditions
        precedent set forth in Section 2 hereof ,
        hereby
        amended as follows:
  (a) ***Revenue
        Bond Letters of Credit*** .
        The
        first sentence of Section 2.04(a)(ii) of the Existing Agreement is hereby
        amended and restated in its entirety to read as follows:
  “Subject
        to the terms and conditions set forth herein, the Borrower may request the
        issuance, amendment or replacement of Revenue Bond Letters of Credit, for
        its
        own account, during the period from the Effective Date
  S-2
 through
          and including the date that occurs ten (10) Business Days prior to the
          Final Maturity Date, in a form reasonably acceptable to the Administrative
          Agent
          and the applicable Issuing Bank.”
 (b) ***Amendment
        and Replacement of Revenue Bond Letters of Credit*** .
        Section
        2.04(b)(ii) of the Existing Agreement is hereby amended and restated in its
        entirety to read as follows:
  “(ii)  Any
        Revenue Bond Letter of Credit may be amended by the applicable Issuing Bank,
        or
        replaced with a new Revenue Bond Letter of Credit issued by another Issuing
        Bank, at the request of the Borrower and with the consent of the Administrative
        Agent; provided ,
        that no
        such amendment or replacement shall increase the stated amount of a Revenue
        Bond
        Letter of Credit or extend the expiration date thereof beyond the last
        permissible date referred to in paragraph (d) below. To request an amendment
        to
        or replacement of an outstanding Revenue Bond Letter of Credit, the Borrower
        shall hand deliver or telecopy to the applicable Issuing Bank and the
        Administrative Agent (no less than three Business Days (or such shorter period
        of time as acceptable to the applicable Issuing Bank and the Administrative
        Agent) in advance of the requested date of amendment or replacement, as the
        case
        may be) a notice identifying the Revenue Bond Letter of Credit to be amended
        or
        replaced (as the case may be) and specifying the date of amendment or
        replacement (which shall be a Business Day), the amount of such Revenue Bond
        Letter of Credit, the name and address of the beneficiary thereof and such
        other
        information as shall be necessary to amend or replace (as the case may be)
        such
        Revenue Bond Letter of Credit. The Administrative Agent shall, promptly after
        its receipt thereof, distribute a copy of each such notice to the Lenders.
        If
        requested by the applicable Issuing Bank, the Borrower also shall submit
        a
        letter of credit application on such Issuing Bank’s standard form in connection
        with any request for the replacement of a Revenue Bond Letter of Credit.
        Upon
        the amendment or replacement of any Revenue Bond Letter of Credit, the
        applicable Issuing Bank shall provide notice and a copy thereof to the
        Administrative Agent, which shall promptly furnish copies thereof to the
        Lenders.”
  (c) ***Participations
        of Revenue Bond Lenders*** .
        The
        first sentence of Section 2.04(e)(ii) of the Existing Agreement is hereby
        amended and restated in its entirety to read as follows:
  “On
        the
        Effective Date, without any further action on the part of any Issuing Bank
        or
        the Revenue Bond Lenders, each Issuing Bank issuing (or deemed to be issuing)
        one or more Revenue Bond Letters of Credit (whether on the Effective Date
        or at
        any time thereafter) pursuant to this Section hereby grants to each Revenue
        Bond
        Lender, and each Revenue Bond Lender hereby acquires from such Issuing Bank,
        a
        participation in each such Revenue Bond Letter of Credit equal to such Revenue
        Bond
  S-3
 Lender’s
          Applicable Percentage of the aggregate amount available to be drawn under
          such
          Revenue Bond Letter of Credit.”
 ***SECTION
        2.   Conditions of Effectiveness of
        Amendments*** .
        The
        amendments to the Existing Agreement set forth in Section 1 hereof shall
        become
        effective as of the date hereof when, and only when, the Administrative Agent
        shall have received counterparts of this Amendment executed by the Borrower,
        the
        Required Lenders, the Issuing Banks and the Administrative Agent (in sufficient
        quantity for each party to have a fully executed original).
  ***SECTION
        3.   Replacement of Issuing Bank*** .
  (a) ***Existing
        Issuing Bank*** .
        Pursuant to Section 2.04(j) of the Existing Agreement, the Borrower, the
        Administrative Agent, Credit Suisse (as successor to Credit Suisse First
        Boston,
        acting through its New York Branch) (“ ***Credit
        Suisse*** ”),
        Wells
        Fargo Bank, National Association (“ ***Wells
        Fargo*** ”)
        and
        ABN AMRO Bank N.V. (“ ***ABN
        AMRO*** ”,
        and
        together with Wells Fargo, the “ ***New
        Issuing Banks*** ”)
        hereby
        agree that, effective as of the date of satisfaction
        of the conditions precedent set forth in subsection (c) below, Credit
        Suisse, in its capacity as issuer of the Existing Letters of Credit listed
        as
        items 1, 2 and 3 on Schedule 2.04 to the Existing Agreement (the “ ***Replaced
        Letters of Credit*** ”)
        (in
        such capacity, the “ ***Existing
        Issuing Bank*** ”),
        shall
        be replaced as issuer of the Replaced Letters of Credit by (i) with respect
        to
        the Replaced Letters of Credit listed as items 1 and 3 on such Schedule 2.04,
        Wells Fargo, and (ii) with respect to the Replaced Letter of Credit listed
        as
        item 2 on such Schedule 2.04, ABN AMRO.
  (b) ***New
        Issuing Banks*** .
        Each
        New Issuing Bank acknowledges and agrees that, effective as of the date of satisfaction of
        the
        conditions precedent set forth in subsection (c) below, (i) it is an “Issuing
        Bank” under the Credit Agreement, (ii) by its execution and delivery of this
        Amendment, it is deemed a party to the Credit Agreement as if it were a
        signatory thereof in such capacity and (iii) with respect to Letters of Credit
        it issues, it assumes all obligations, and acquires all rights and remedies,
        of
        an “Issuing Bank” under the Credit Agreement.
  (c) ***Conditions
        to Replacement of Existing Issuing Bank*** .
        The
        replacement of the Existing Issuing Bank by the New Issuing Banks pursuant
        to
        subsection (a) above shall become effective on the date on which each of
        the
        following conditions is satisfied:
  (i)  Wells
        Fargo shall have issued Revenue Bond Letters of Credit, in replacement of
        (and
        in form and substance substantially identical to) the Replaced Letters of
        Credit
        listed as items 1 and 3 on Schedule 2.04 to the Existing Credit Agreement,
        to
        the applicable Revenue Bond Trustees, and all conditions to the issuance
        of such
        replacement Revenue Bond Letters of Credit set forth in the applicable Revenue
        Bond
  S-4
  Indentures
        and Revenue Bond Loan Agreements shall have been satisfied (or waived in
        accordance with the terms thereof).
  (ii)  ABN
        AMRO
        shall have issued a Revenue Bond Letter of Credit, in replacement of (and
        in
        form and substance substantially identical to) the Replaced Letter of Credit
        listed as item 2 on Schedule 2.04 to the Existing Credit Agreement, to the
        applicable Revenue Bond Trustee, and all conditions to the issuance of such
        replacement Revenue Bond Letter of Credit set forth in the applicable Revenue
        Bond Indenture and Revenue Bond Loan Agreement shall have been satisfied
        (or
        waived in accordance with the terms thereof).
  (iii)  Each
        of
        the Replaced Letters of Credit shall have been surrendered for cancellation
        by
        the applicable Revenue Bond Trustee and returned to the Existing Issuing
        Bank.
  (iv)  The
        Borrower shall have paid all unpaid fees accrued for the account of the Existing
        Issuing Bank pursuant to Section 2.10(b) of the Existing Agreement.
  (v)  The
        Borrower and the New Issuing Banks (and, if applicable, any “Custodian”, as
        defined in the applicable Revenue Bond Pledge Agreement) shall have executed
        and
        delivered Revenue Bond Pledge Agreements in replacement of the existing Revenue
        Bond Pledge Agreements to which the Existing Issuing Bank is a party, and
        all
        further actions required under any applicable law, or that the Administrative
        Agent may reasonably request, to perfect the Liens created or intended to
        be
        created by such replacement Revenue Bond Pledge Agreements shall have been
        taken.
  ***SECTION
        4*** **.** ***Representations
        and Warranties of the Borrower*** .
        The
        Borrower represents and warrants as follows:
  (a) The
        execution and delivery by the Borrower of this Amendment, and the performance
        by
        the Borrower of this Amendment and the Amended Agreement, are within the
        Borrower’s organizational powers and have been duly authorized by all necessary
        corporate and, if required, stockholder action, and do not and will not (i)
        violate any Requirement of Law, (ii) violate or result in a default under
        any
        indenture, agreement or other instrument binding upon the Borrower or any
        of its
        Consolidated Subsidiaries or its assets, or give rise to a right thereunder
        to
        require any payment to be made by the Borrower or any of its Consolidated
        Subsidiaries, or (iii) result in the creation or imposition of any Lien on
        any
        asset of the Borrower or any of its Consolidated Subsidiaries, except Liens
        created under the Loan Documents or under the Mortgage Indenture. This
        Amendment has
        been
        duly executed and delivered by the Borrower.
  S-5
  (b) The
        execution and delivery by the Borrower of this Amendment, and the performance
        by
        the Borrower of this Amendment and the Amended Agreement, do not
        require any consent or approval of, registration or filing with, or any other
        action by, any Governmental Authority, except as set forth in Section 3.03(a)
        of
        the Existing Agreement.
  (c) Each
        of
        t his
        Amendment and the Amended Agreement constitutes a legal, valid and binding
        obligation of the Borrower, enforceable in accordance with its terms, subject
        to
        applicable bankruptcy, insolvency, reorganization, moratorium or other laws
        affecting creditors’ rights generally and subject to general principles of
        equity, regardless of whether considered in a proceeding in equity or at
        law.
  (d) No
        Default or Event of Default has occurred and is continuing .
  ***SECTION
        5.   Reference to and Effect on the Existing
        Agreement*** .
        (a) Upon the effectiveness of this Amendment: (i) each reference in the
        Existing Agreement to “this Agreement”, “hereunder”, “hereof” or words of like
        import referring to the Existing Agreement shall mean and be a reference
        to the
        Credit Agreement; and (ii) each reference in any other Loan Document to “the
        Credit Agreement”, “thereunder”, “thereof” or words of like import referring to
        the Existing Agreement shall mean and be a reference to the Credit
        Agreement.
  (b) Except
        as
        specifically amended or waived above, the Existing Agreement shall continue
        to
        be in full force and effect and is hereby in all respects ratified and
        confirmed. Without limiting the generality of the foregoing, the Security
        Documents and all of the Collateral described therein do and shall continue
        to
        secure the payment of all Obligations.
  (c) The
        execution, delivery and effectiveness of this Amendment shall not, except
        as
        expressly provided herein, operate as a waiver of any right, power or remedy
        of
        the Lenders, the Issuing Banks or the Administrative Agent under the Existing
        Agreement or any other Loan Document, nor constitute a waiver of any provision
        of the Existing Agreement or any other Loan Document.
  ***SECTION
        6.   Costs and Expenses*** .
        The
        Borrower agrees to pay on demand all reasonable out-of-pocket expenses of
        the
        Administrative Agent in connection with the preparation, negotiation,
        syndication, execution and delivery of this Amendment and the other instruments
        and documents to be delivered hereunder, including, without limitation, the
        reasonable fees, charges and disbursements of counsel to the Administrative
        Agent with respect thereto and with respect to advising the Administrative
        Agent
        as to its rights and responsibilities hereunder and thereunder, and all
        out-of-pocket expenses incurred by the Administrative Agent, any Issuing
        Bank or
        any Lender (including, without limitation, the fees, charges and disbursements
        of any counsel for the Administrative Agent, any Issuing Bank or any Lender)
        in
        connection with the
  S-6
  enforcement
        (whether through negotiations, legal proceedings or otherwise) of this
        Amendment.
  ***SECTION
        7.   Execution in Counterparts*** .
        This
        Amendment may be executed in any number of counterparts and by different
        parties
        hereto in separate counterparts, each of which when so executed and delivered
        shall be deemed to be an original and all of which taken together shall
        constitute but one and the same instrument. In
        furtherance of the foregoing, it is understood and agreed that signatures
        hereto
        submitted by facsimile transmission shall be deemed to be, and shall constitute,
        original signatures.
  ***SECTION
        8.   Governing Law*** .
        This
        Amendment shall be governed by, and construed in accordance with, the laws
        of
        the State of the New York.
  [REMAINDER
        OF PAGE INTENTIONALLY LEFT BLANK]
 
 S-1
  IN
        WITNESS WHEREOF, the parties hereto have caused this Amendment to be executed
        by
        their respective officers thereunto duly authorized, as of the date first
        above
        written.
 
 TUCSON
                  ELECTRIC POWER COMPANYBy
              /s/
                  Kevin P. LarsonName: 
                  Kevin P. Larson
                Title:   
                  Sr. Vice President, CFO and TreasurerUNION
                  BANK OF CALIFORNIA, N.A.,
                asAdministrative
                  Agent and a LenderBy
              /s/
                  Jeffrey P. FesenmaierName: 
                  Jeffrey P. Fesenmaier, CFA
                Title:  
                  Assistant Vice President
 
 S-2
  WELLS
                  FARGO BANK, NATIONAL ASSOCIATION,
                as
                  a Lender and New Issuing BankBy
              /s/
                  Clyde GossertName: 
                  Clyde Gossert
                Title:   
                  Vice President
 
 S-3
  ABN
                  AMRO BANK N.V.,
                as
                  a Lender and New Issuing BankBy
              /s/
                  R. Scott DonaldsonName: 
                  R. Scott Donaldson
                Title:   
                  Vice PresidentBy
              /s/
                  Todd D. VaubelName: 
                  Todd D. Vaubel
                Title:   
                  Assistant Vice President
 
 S-4
  THE
                  BANK OF NEW YORK,
                as
                  an Issuing Bank and a LenderBy
              /s/
                  John-Paul MarottaName: 
                  John-Paul Marotta
                Title:   
                  Managing Director
  S-5
  CREDIT
                  SUISSE, Cayman Islands Branch,
                as
                  an Issuing BankBy
              /s/
                  David DoddName: 
                  David Dodd
                Title:    Vice
                  PresidentBy
              /s/
                  Mikhail FaybusovichName: 
                  Mikhail Faybusovich
                Title:   
                  Associate
 
 S-6
  JPMORGAN
                  CHASE BANK, N.A.,
                as
                  a LenderBy
              /s/
                  Nancy R. BarwigName: 
                  Nancy R. Barwig
                Title:   
                  Vice President
 
 S-7
  BANK
                  HAPOALIM B.M.,
                as
                  a LenderBy
              /s/
                  Shaun BreidbartName: 
                  Shaun Breidbart
                Title:   
                  Vice PresidentBy
              /s/
                  Laura Anne RaffaName: 
                  Laura Anne Raffa
                Title:   
                  Executive Vice President & Corporate
                  Manager
 
 S-8
  BAYERISCHE
                  LANDESBANK, NEW YORK BRANCH,
                as
                  a LenderBy
              /s/
                  John GregoryName: 
                  John Gregory
                Title:   
                  Vice PresidentBy
              /s/
                  Norman McClaveName: 
                  Norman McClave
                Title:   
                  First Vice President
 
 S-9
  BNP
                  PARIBAS,
                as
                  a LenderBy
              /s/
                  Mark A. RenaudName: 
                  Mark A. Renaud
                Title:   
                  Managing DirectorBy
              /s/
                  Leonardo OsorioName: 
                  Leonardo Osorio
                Title:   
                  Director
 
 S-10
  COBANK,
                  ACB,
                as
                  a LenderBy
              /s/
                  Raymond HaleyName: 
                  Raymond Haley
                Title:   
                  Vice President
 
 S-11
  COMERICA
                  WEST INCORPORATED,
                as
                  a LenderBy
              /s/
                  Fatima ArshadName: 
                  Fatima Arshad
                Title:   
                  Corporate Banking Representative
 
 S-12
  COMMERZBANK
                  AG, NEW YORK AND CAYMAN BRANCHES,
                as
                  a LenderBy
              /s/
                  Andrew CampbellName: 
                  Andrew Campbell
                Title:   
                  Senior Vice PresidentBy
              /s/
                  Andrew KjollerName: 
                  Andrew Kjoller
                Title:   
                  Vice President
 
 S-13
  DRESDNER
                  BANK AG, NEW YORK AND CAYMAN BRANCHES,
                as
                  a LenderBy
              /s/
                  Thomas R. BradyName: 
                  Thomas R. Brady
                Title:   
                  DirectorBy
              /s/
                  Brian SmithName: 
                  Brian Smith
                Title:   
                  Managing Director
 
 S-14
  KBC
                  BANK, N.V.,
                as
                  a LenderBy
              /s/
                  Jean-Pierre DielsName: 
                  Jean-Pierre Diels
                Title:   
                  First Vice PresidentBy
              /s/
                  Eric RaskinName: 
                  Eric Raskin
                Title:    Vice
                  President
 
 S-15
  LLOYDS
                  TSB BANK PLC,
                as
                  a LenderByName:
                Title:ByName:
                Title:
 
 S-16
  SOVEREIGN
                  BANK,
                as
                  a LenderBy
              /s/
                  Robert D. LaniganName: 
                  Robert D. Lanigan
                Title:   
                  Senior Vice President
 
 S-17
  THE
                  BANK OF TOKYO-MITSUBISHI, UFJ, LTD.,
                NEW
                  YORK BRANCH (as successor to UFJ BANK LIMITED),
                as
                  a LenderBy
              /s/
                  Chi-Cheng ShenName: 
                  Chi-Cheng Shen
                Title:   
                  Authorized SignatoryByName:
                Title:
 
 S-18
  U.S.
                  BANK NATIONAL ASSOCIATION,
                as
                  a LenderBy
              /s/
                  Dale ParshallName: 
                  Dale Parshall
                Title:   
                  Vice President
  S-19
  WACHOVIA
                  BANK, NATIONAL ASSOCIATION,
                as
                  a LenderBy
              /s/ Paul
                PritchettName: 
                  Paul Pritchett
                Title:   
                  Vice President