Document:

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                                                                  EXHIBIT 4.2(b)

Sierra Pacific Power Company
6100 Neil Road
P.O. Box 10100
Reno, Nevada  89520-0400

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                         SIERRA PACIFIC POWER COMPANY

                                      TO

                             THE BANK OF NEW YORK
                                    Trustee

                                  ----------

                         FIRST SUPPLEMENTAL INDENTURE

                            Dated as of May 1, 2001

                                  ----------

          Supplementing the General and Refunding Mortgage Indenture
                            Dated as of May 1, 2001

        THIS INSTRUMENT GRANTS A SECURITY INTEREST BY A PUBLIC UTILITY

          THIS INSTRUMENT CONTAINS AFTER-ACQUIRED PROPERTY PROVISIONS

This instrument is being filed pursuant to Nevada Revised Statutes Chapter 105

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      FIRST SUPPLEMENTAL INDENTURE, dated as of May 1, 2001, between SIERRA
PACIFIC POWER COMPANY, a corporation organized and existing under the laws of
the State of Nevada (herein called the "Company"), having its principal office
at 6100 Neil Road, P.O. Box 10100, Reno, Nevada 89520, and THE BANK OF NEW YORK,
a banking corporation duly organized and existing under the laws of the State of
New York, as Trustee (herein called the "Trustee"), the office of the Trustee at
which on the date hereof its corporate trust business is principally
administered being 101 Barclay Street, New York, New York 10286.

                             RECITALS OF THE COMPANY

      WHEREAS, the Company has heretofore executed and delivered to the Trustee
a General and Refunding Mortgage Indenture dated as of May 1, 2001 (the
"Indenture") providing for the issuance by the Company from time to time of its
bonds, notes or other evidence of indebtedness to be issued in one or more
series (in the Indenture and herein called the "Securities") and to provide
security for the payment of the principal of and premium, if any, and interest;
if any, on the Securities; and

      WHEREAS, the Company, in the exercise of the power and authority conferred
upon and reserved to it under the provisions of the Indenture and pursuant to
appropriate resolutions of the Board of Directors, has duly determined to make,
execute and deliver to the Trustee this First Supplemental Indenture to the
Indenture as permitted by Sections 2.01, 3.01 and 14.01 of the Indenture in
order to establish the form or terms of, and to provide for the creation and
issuance of, the Initial Series of Securities under the Indenture in an initial
aggregate principal amount of $320,000,000 (such first series being hereinafter
and in the Indenture referred to as the "Initial Series"); and

      WHEREAS, all things necessary to make the Securities of the Initial
Series, when executed by the Company and authenticated and delivered by the
Trustee or any Authenticating Agent and issued upon the terms and subject to the
conditions hereinafter and in the Indenture set forth against payment therefor
the valid, binding and legal obligations of the Company and to make this First
Supplemental Indenture a valid, binding and legal agreement of the Company, have
been done;

      NOW, THEREFORE, THIS FIRST SUPPLEMENTAL INDENTURE WITNESSETH that, in
order to establish the terms of a series of Securities, and for and in
consideration of the premises and of the covenants contained in the Indenture
and in this First Supplemental Indenture and for other good and valuable
consideration the receipt and sufficiency of which are hereby acknowledged, it
is mutually covenanted and agreed as follows:
<PAGE>

                                   ARTICLE ONE

                        DEFINITIONS AND OTHER PROVISIONS
                             OF GENERAL APPLICATION

      Section 101. Definitions. Each capitalized term that is used herein and is
                   -----------
defined in the Indenture shall have the meaning specified in the Indenture
unless such term is otherwise defined herein.

                                   ARTICLE TWO

                       TITLE, FORM AND TERMS OF THE BONDS

      Section 201. Title of the Bonds. This First Supplemental Indenture hereby
                   ------------------
creates a series of Securities designated as the "8% General and Refunding
Mortgage Bonds, Series A, due June 1, 2008" of the Company (collectively
referred to herein as the "Bonds"). For purposes of the Indenture, the Bonds
shall constitute a single series of Securities and may be issued in an unlimited
principal aggregate amount, although the initial issuance of the Bonds shall be
in the aggregate principal amount of $320,000,000.

      Section 202. Form and Terms of the Bonds. The form and terms of the Bonds
                   ---------------------------
will be set forth in an Officer's Certificate delivered by the Company to the
Trustee pursuant to the authority granted by this First Supplemental Indenture
in accordance with Sections 2.01 and 3.01 of the Indenture.

      Section 203. Treatment of Proceeds of Title Insurance Policy. Any moneys
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received by the Trustee as proceeds of any title insurance policy on Mortgaged
Property of the Company shall be subject to and treated in accordance with the
provisions of Section 6.07(b) of the Indenture (other than the last paragraph
thereof).

                                  ARTICLE THREE

                            MISCELLANEOUS PROVISIONS

      The Trustee makes no undertaking or representations in respect of, and
shall not be responsible in any manner whatsoever for and in respect of, the
validity or sufficiency of this First Supplemental Indenture or the proper
authorization or the due execution hereof by the Company or for or in respect of
the recitals and statements contained herein, all of which recitals and
statements are made solely by the Company.

      Except as expressly amended and supplemented hereby, the Indenture shall
continue in full force and effect in accordance with the provisions thereof and
the Indenture is in all respects hereby
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ratified and confirmed. This First Supplemental Indenture and all of its
provisions shall be deemed a part of the Indenture in the manner and to the
extent herein and therein provided.

      This First Supplemental Indenture shall be governed by, and construed in
accordance with, the laws of the State of New York (including without limitation
Section 5-1401 of the New York General Obligations Law or any successor to such
statute).

      This First Supplemental Indenture may be executed in any number of
counterparts, each of which so executed shall be deemed to be an original, but
all such counterparts shall together constitute but one and the same instrument.<PAGE>

                                                                  EXHIBIT 4.2(c)

                         SIERRA PACIFIC POWER COMPANY

                             OFFICER'S CERTIFICATE

      I, the undersigned officer of Sierra Pacific Power Company (the
"Company"), do hereby certify that I am an Authorized Officer of the Company as
such term is defined in the Indenture (as defined herein). I am delivering this
certificate pursuant to the authority granted in the Board Resolutions of the
Company dated May 22, 2001, and Sections 1.04, 2.01, 3.01 and 4.01(a) of the
General and Refunding Mortgage Indenture dated as of May 1, 2001 (the "Mortgage
Indenture"), as supplemented by a First Supplemental Indenture dated as of May
1, 2001 (the "Supplemental Indenture"; and collectively with the Mortgage
Indenture, the "Indenture"), between the Company and The Bank of New York, as
Trustee (the "Trustee"). Terms used herein and not otherwise defined herein
shall have the meanings assigned to them in the Indenture unless the context
clearly requires otherwise. Based upon the foregoing, I hereby certify on behalf
of the Company as follows:

      1. The terms and conditions of the Securities described in this Officer's
Certificate are as follows (the lettered subdivisions set forth in this
Paragraph 1 corresponding to the lettered subdivisions of Section 3.01 of the
Mortgage Indenture):

      (a) The Securities of the first series to be issued under the Indenture
      shall be designated "8% General and Refunding Mortgage Bonds, Series A,
      due 2008" (the "Series A Bonds").

      (b) There shall be no limit upon the aggregate principal amount of the
      Series A Bonds that may be authenticated and delivered under the
      Indenture. The Series A Bonds shall be initially authenticated and
      delivered in the aggregate principal amount of $350,000,000.

      (c) Interest on the Series A Bonds shall be payable to the Persons in
      whose names such Securities are registered at the close of business on the
      Regular Record Date for such interest, except as otherwise expressly
      provided in the form of such Securities attached hereto as Exhibit A.

      (d) The Series A Bonds shall mature and the principal thereof shall be due
      and payable together with all accrued and unpaid interest thereon on June
      1, 2008.

      (e) The Series A Bonds shall bear interest at the rate of 8% per annum.
      Interest shall accrue on the Series A Bonds from May 24, 2001, or the most
      recent date to which interest has been paid or duly provided for. The
      Interest Payment Dates for the Series A Bonds shall be June 1 and December
      1 in each year commencing December 1, 2001, and the Regular Record Dates
      with respect to the Interest Payment Dates for the Series A Bonds shall be
      May 17 and November 16 in each year, respectively (whether or not a
      Business Day).

      (f) The Corporate Trust Office of The Bank of New York in New York, New
      York shall be the place at which (i) the principal of, premium and
      interest on, the Series A
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      Bonds shall be payable, (ii) registration of transfer of the Series A
      Bonds may be effected, (iii) exchanges of the Series A Bonds may be
      effected and (iv) notices and demands to or upon the Company in respect of
      the Series A Bonds and the Indenture may be served; and The Bank of New
      York shall be the Security Registrar for the Series A Bonds; provided,
                                                                   --------
      however, that the Company reserves the right to change, by one or more
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      Officer's Certificates, any such place or the Security Registrar; and
      provided, further, that the Company reserves the right to designate, by
      one or more Officer's Certificates, its principal office in Las Vegas,
      Nevada as any such place or itself as the Security Registrar; provided,
      however, that there shall be only a single Security Registrar for the
      Series A Bonds.

      (g) The Series A Bonds shall be redeemable, at the option of the Company,
      at any time or from time to time, in whole or in part, at a price equal to
      100% of the principal amount of the Series A Bonds to be redeemed plus
      accrued and unpaid interest to the Redemption Date (subject to the right
      of Holders of record on a Regular Record Date occurring prior to such
      Redemption Date to receive interest paid on the applicable Interest
      Payment Date that is prior to the Redemption Date) plus the applicable
      make-whole premium (the "Make-Whole Premium").

            The amount of the Make-Whole Premium with respect to the Series A
      Bonds (or portion thereof) to be redeemed will be equal to the excess, if
      any, of:

            (i) the sum of the present values, calculated as of the Redemption
            Date, of:

                  (A) each interest payment that, but for such redemption, would
                  have been payable on the Series A Bonds (or portion thereof)
                  being redeemed on each Interest Payment Date occurring after
                  the Redemption Date (excluding any accrued and unpaid interest
                  for the period prior to the Redemption Date); and

                  (B) the principal amount that, but for such redemption, would
                  have been payable at the Stated Maturity of the Series A Bonds
                  (or portion thereof) being redeemed,

            over

            (ii) the principal amount of the Series A Bonds (or portion thereof)
            being redeemed.

            The present values of each interest and principal payment referred
      to in clause (i) above will be determined in accordance with generally
      accepted principles of financial analysis. Such present values will be
      calculated by discounting the amount of each payment of interest or
      principal from the date that each such payment would have been payable,
      but for such redemption, to the Redemption Date at a discount rate equal
      to the Treasury Yield (as defined below) plus 30 basis points.

            The Make-Whole Premium will be calculated by Credit Suisse First
      Boston Corporation or, if such firm is unwilling or unable to make such
      calculation, by an

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      independent investment banking institution of national standing
      appointed by the company (in any such case, an "Independent Investment
      Banker"). The Trustee shall have no responsibility for the calculation of
      the Make-Whole Premium and may conclusively presume the correctness of
      such calculation.

            For purposes of determining the Make-Whole Premium, "Treasury Yield"
      means a rate of interest per annum equal to the weekly average yield to
      maturity of United States Treasury Notes that have a constant maturity
      that corresponds to the remaining term to maturity of the Series A Bonds,
      calculated to the nearest 1/12 of a year (the "Remaining Term"). The
      Treasury Yield will be determined as of the third business day immediately
      preceding the applicable Redemption Date.

            The weekly average yields of United States Treasury Notes will be
      determined by reference to the most recent statistical release published
      by the Federal Reserve Bank of New York and designated "H.15(519) Selected
      Interest Rates" or any successor release (the "H.15 Statistical Release").
      If the H.15 Statistical Release sets forth a weekly average yield for
      United States Treasury Notes having a constant maturity that is the same
      as the Remaining Term, then the Treasury Yield will be equal to such
      weekly average yield. In all other cases, the Treasury Yield will be
      calculated by interpolation, on a straight-line basis, between the weekly
      average yields on the United States Treasury Notes that have a constant
      maturity closest to and greater than the Remaining Term and the United
      States Treasury Notes that have a constant maturity closest to and less
      than the Remaining Term (in each case as set forth in the H.15 Statistical
      Release). Any weekly average yields so calculated by interpolation will be
      rounded to the nearest 1/100th of 1%, with any figure of 1/200 of 1% or
      above being rounded upward. If weekly average yields for United States
      Treasury Notes are not available in the H.15 Statistical Release or
      otherwise, then the Treasury Yield will be calculated by interpolation of
      comparable rates selected by the Independent Investment Banker.

            If less than all of the Series A Bonds are to be redeemed, the
      Security Registrar will select the Series A Bonds to be redeemed by such
      method as the Security Registrar shall deem fair and appropriate. The
      Trustee may select for redemption Series A Bonds and portions of Series A
      Bonds in amounts of $1,000 or whole multiples of $1,000, subject to clause
      (i) of this Paragraph 1 (as to minimum denominations).

      (h) Not applicable.

      (i) The Series A Bonds are issuable only in denominations of $250,000 and
      integral multiples of $1000 in excess thereof.

      (j) Not applicable.

      (k) Not applicable.

      (l) Not applicable.

      (m) Not applicable.

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      (n) Not applicable.

      (o) Pursuant to the terms of a registration rights agreement with one or
      more of the initial purchasers of the Series A Bonds (a "Registration
      Rights Agreement"), the Company has agreed to file an exchange offer
      registration statement to exchange the Series A Bonds for substantially
      identical Securities registered under the Securities Act of 1933, as
      amended (the "Securities Act") as evidence of the same underlying
      indebtedness. Unless otherwise specified by the Company in a supplement to
      this Officer's Certificate, the Securities so registered and offered and
      issued in exchange shall be additional Series A Bonds.The Company has also
      agreed to file a shelf registration statement to cover resales of the
      Series A Bonds, as initially issued and sold, under certain circumstances.
      If the Company fails to satisfy those obligations, the Company has agreed
      to pay liquidated damages to the holders of the Series A Bonds under
      certain circumstances. The terms relating to the exchange of the Series A
      Bonds are set forth in the Registration Rights Agreement attached hereto
      as Exhibit B.

      (p) Not applicable.

      (q) Certificates representing Series A Bonds offered and sold in reliance
      on Rule 144A (and only such Series A Bonds) shall be in the form of a
      permanent certificate in global form (a "Global Certificate") registered
      in the name of Cede & Co., as nominee for The Depository Trust Company
      (the "Depositary") to be delivered to the Depositary or its custodian, by
      or on behalf of the Company. The Global Certificate shall not be
      transferable or exchangeable, nor shall any purported transfer be
      registered, except as follows:

            (i) the Global Certificate may be transferred in whole, and
            appropriate registration of transfer effected, if such transfer is
            by such nominee to the Depositary, or by the Depositary to another
            nominee thereof, or by any nominee of the Depositary to any other
            nominee thereof, or by the Depositary or any nominee thereof to any
            successor securities depositary or any nominee thereof; and

            (ii) the Global Certificate may be exchanged for Series A Bonds in
            the form of definitive certificates registered in the respective
            names of the beneficial owners thereof, and thereafter shall be
            transferable without restriction, if:

                  (A) the Depositary, or any successor securities depositary,
                  shall have notified the Company and the Trustee that (i) it is
                  unwilling or unable to continue to act as securities
                  depositary with respect to the Series A Bonds, (ii) has ceased
                  to be qualified to act as such, or (iii) has ceased to be a
                  clearing agency registered under the Exchange Act, and the
                  Trustee shall not have been notified by the Company within
                  ninety (90) days of the identity of a successor securities
                  depositary with respect to such Securities;

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<PAGE>

                  (B) the Company shall have delivered to the Trustee a Company
                  Order to the effect that the Company has elected to terminate
                  the book-entry system; or

                  (C) an Event of Default shall have occurred and be continuing.

            Unless and until definitive, fully registered certificates shall
      have been issued to beneficial owners as provided in subclause (ii) of
      this clause (g) of Paragraph 1 hereof:

                  (a) the provisions of this clause (q) shall be in full force
            and effect;

                  (b) the Company and the Trustee and any agent of either shall
            be entitled to deal with the Depositary for all purposes of the
            indenture and such Series A Bonds (including payment of principal
            of, and premium and interest thereon, the giving of notice and
            receiving approvals, votes or consents thereunder) as the Holder of
            such Securities and the sole holder of the Global Certificate and
            shall have no obligation to the beneficial owners of such
            Securities;

                  (c) to the extent that the provisions of clause (q) of
            paragraph 1 conflicts with any other provisions of the Indenture or
            the Series A Bonds, the provisions of this clause (q) of Paragraph 1
            shall control; and

                  (d) the rights of such beneficial owners shall be exercised
            only through the Depositary and shall be limited to those
            established by law and agreements between such beneficial owners or
            of any agent member of, or direct or indirect participants in, the
            Depositary and the Depositary or the depositary participants. The
            Depositary will make book-entry transfers among depositary
            participants and receive and transmit payments of principal, premium
            and interest, if any, to such depositary participants.

            Notwithstanding the foregoing, with respect to any Global
      Certificate, nothing contained herein or in the Indenture shall prevent
      the Company, the Trustee or any agent of the Company or the Trustee, from
      giving effect to any written certification, proxy or other authorization
      furnished by the Depositary (or its nominee), as a Holder, with respect to
      such Global Certificate or impair, as between such Depositary and the
      related beneficial owner, the operation of customary practices governing
      the exercise of rights of the Depositary (or its nominee) as Holder of
      such global certificate. Except for the Global Certificate, any and all of
      the Series A Bonds shall be in the form of a non-global, definitive
      physical certificate.

      (r) Not applicable.

      (s) The Series A Bonds have not been registered under the Securities Act
      and may not be offered, sold or otherwise transferred in the absence of
      such registration or an applicable exemption therefrom. No service charge
      shall be made for the registration of transfer or exchange of the Series A
      Bonds, or any Tranche thereof; provided, however,

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<PAGE>

      that the Company may require payment of a sum sufficient to cover any tax
      or other governmental charge payable in connection with the exchange or
      transfer.

      (t) For purposes of the Series A Bonds, "Business Day" shall mean any day,
      other than a Saturday or Sunday, on which commercial banks and foreign
      exchange markets are open for business, including dealings in deposits in
      U.S. dollars, in New York.

      (u) Notwithstanding the provisions of Section 9.01 of the Indenture, no
      Series A Bond shall be deemed to have been paid ,and the indebtedness of
      the Company in respect thereof deemed to have been satisfied and
      discharged as contemplated therein, unless the Company shall have
      delivered to the Trustee either:

            (i) an opinion of counsel in the United States reasonably acceptable
            to the Trustee confirming that (A) the Company has received from, or
            there has been published by, the Internal Revenue Service a ruling
            or (B) since the date of the Indenture, there has been a change in
            the applicable federal income tax law, in either case to the effect
            that, and based thereon such opinion of counsel shall confirm that,
            the Holders of the outstanding Bonds will not recognize income, gain
            or loss for federal income tax purposes as a result of such
            defeasance and will be subject to federal income tax on the same
            amounts, in the same manner and at the same times as would have been
            the case if such defeasance had not occurred; or

            (ii) (A) an instrument wherein the Company, notwithstanding the
            satisfaction and discharge of its Indebtedness in respect of the
            Bonds, shall assume the obligation (which shall be absolute and
            unconditional) to irrevocably deposit with the Trustee such
            additional sums of money, if any, or additional Government
            Obligations, if any, or any combination thereof, at such time or
            times, as shall be necessary, together with the money and/or
            Government Obligations theretofore so deposited, to pay when due the
            principal of and premium, if any, and interest due and to become due
            on such bonds or portions thereof; provided, however, that such
            instrument may state that the obligation of the Company to make
            additional deposits as aforesaid shall be subject to the delivery to
            the Company by the Trustee of a notice asserting the deficiency
            accompanied by an opinion of an independent public accountant of
            nationally recognized standing showing the calculation thereof; and
            (B) an opinion of tax counsel in the United States reasonably
            acceptable to the Trustee to the effect that the Holders of the
            outstanding Bonds will not recognize income, gain or loss for
            federal income tax purposes as a result of such defeasance and will
            be subject to federal income tax on the same amounts, in the same
            manner and at the same times as would have been the case if such
            defeasance had not occurred.

      The Series A Bonds shall have such other terms and provision as are
provided in the form thereof attached hereto as Exhibit A, and shall be issued
                                                ---------
in substantially such form.

      2. All conditions precedent provided for in the Mortgage Indenture and the
Indenture (including any covenants compliance with which constitutes a condition
precedent)

                                       6
<PAGE>

relating to the execution and delivery of the Supplemental Indenture and the
authentication and delivery of the Series A Bonds have been complied with.

      3. The undersigned has read all of the covenants and conditions contained
in the Indenture, and the definitions in the Indenture relating thereto,
relating to the issuance of the Series A Bonds and in respect of compliance with
which this certificate is made.

      4. The statements contained in this certificate are based upon the
familiarity of the undersigned with the Indenture, the documents accompanying
this certificate, and upon discussions by the undersigned with officers and
employees of the Company familiar with the matters set forth herein.

      5. In the opinion of the undersigned, he has made such examination or
investigation as is necessary to enable him to express an informed opinion as to
whether or not such covenants and conditions have been complied with.

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<PAGE>

      IN WITNESS WHEREOF, the undersigned has executed this Officer's
Certificate on this 24th day of May, 2001.

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

Acknowledged and Received on
May __, 2001

THE BANK OF NEW YORK,
as Trustee

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

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