##### 



Exhibit 4-3-1 This instrument was prepared by,
and when recorded should be
returned to: Richard W. Astle
Sidley Austin Brown & Wood LLP
Bank One Plaza
10 South Dearborn Street
Chicago, Illinois 60603   Supplemental Indenture Dated as of February 15, 2005 Commonwealth Edison Company to BNY Midwest Trust Company and D.G. Donovan Trustees Under Mortgage Dated July 1, 1923, and Certain Indentures Supplemental Thereto Providing for Issuance of FIRST MORTGAGE BONDS, POLLUTION CONTROL SERIES 2005 Due March 1, 2017




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This Supplemental Indenture, dated as of February 15, 2005, between Commonwealth
Edison Company, a corporation organized and existing under the laws of the State of Illinois
(hereinafter called the Company) having an address at 10 South Dearborn Street, 37th
floor, Chicago, Illinois 60603, party of the first part, BNY Midwest Trust Company, a
trust company organized and existing under the laws of the State of Illinois having an address at 2
North LaSalle Street, Suite 1020, Chicago, Illinois 60602, and D.G. Donovan, an individual
having an address at 2 North LaSalle Street, Suite 1020, Chicago, Illinois 60602, as Trustee and
Co-Trustee, respectively, under the Mortgage of the Company dated July 1, 1923, as amended and
supplemented by Supplemental Indenture dated August 1, 1944 and the subsequent supplemental
indentures hereinafter mentioned, parties of the second part (said Trustee being hereinafter called
the Trustee, the Trustee and said Co-Trustee being hereinafter together called the Trustees,
and said Mortgage dated July 1, 1923, as amended and supplemented by said Supplemental Indenture
dated August 1, 1944 and subsequent supplemental indentures, being hereinafter called the
"Mortgage), W I T N E S S E T H: WHEREAS, the Company duly executed and delivered the Mortgage to provide for the issue of, and
to secure, its bonds, issuable in series and without limit as to principal amount except as
provided in the Mortgage; and WHEREAS, the Company from time to time has executed and delivered supplemental indentures to
the Mortgage to provide for (i) the creation of additional series of bonds secured by the Mortgage,
(ii) the amendment of certain of the terms and provisions of the Mortgage and (iii) the
confirmation of the lien of the Mortgage upon property of the Company, such supplemental indentures
that are currently effective and the respective dates, parties thereto and purposes thereof, being
as follows: SupplementalIndenture Date
    
    Parties
    
    Providing ForAugust 1, 1944
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Edmond B.
Stofft, as Trustee and Co-Trustee
    
    Amendment and restatement of
Mortgage dated July 1, 1923August 1, 1946
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Edmond B.
Stofft, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienApril 1, 1953
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Edmond B.
Stofft, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienMarch 31, 1967
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Edward J.
Friedrich, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienApril 1, 1967
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Edward J.
Friedrich, as Trustee and Co-Trustee
    
    Amendment of Sections 3.01, 3.02,
3.05 and 3.14 of the Mortgage and
issuance of First Mortgage 5-3/8%
Bonds, Series Y
 2




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##### 



SupplementalIndenture Date
    
    Parties
    
    Providing ForFebruary 28, 1969
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Donald W.
Alfvin, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienMay 29, 1970
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Donald W.
Alfvin, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienJune 1, 1971
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Donald W.
Alfvin, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienApril 1, 1972
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Donald W.
Alfvin, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienMay 31, 1972
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Donald W.
Alfvin, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienJune 15, 1973
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Donald W.
Alfvin, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienMay 31, 1974
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Donald W.
Alfvin, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienJune 13, 1975
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Donald W.
Alfvin, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienMay 28, 1976
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Donald W.
Alfvin, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienJune 3, 1977
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Donald W.
Alfvin, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienMay 17, 1978
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Donald W.
Alfvin, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienAugust 31, 1978
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Donald W.
Alfvin, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienJune 18, 1979
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Donald W.
Alfvin, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienJune 20, 1980
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Donald W.
Alfvin, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienApril 16, 1981
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Donald W.
Alfvin, as Trustee and Co-Trustee
    
    Confirmation of mortgage lien
 3




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SupplementalIndenture Date
    
    Parties
    
    Providing ForApril 30, 1982
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Donald W.
Alfvin, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienApril 15, 1983
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Donald W.
Alfvin, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienApril 13, 1984
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Donald W.
Alfvin, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienApril 15, 1985
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and Donald W.
Alfvin, as Trustee and Co-Trustee
    
    Confirmation of mortgage lienApril 15, 1986
    
    Company to Continental Illinois National Bank
and Trust Company of Chicago and M.J. Kruger,
as Trustee and Co-Trustee
    
    Confirmation of mortgage lienJune 15, 1990
    
    Company to Continental Bank, National
Association and M.J. Kruger, as Trustee and
Co-Trustee
    
    Issuance of First Mortgage 9-7/8%
Bonds, Series 75October 1, 1991
    
    Company to Continental Bank, National
Association and M.J. Kruger, as Trustee and
Co-Trustee
    
    Issuance of First Mortgage 8-1/4%
Bonds, Series 76 and First
Mortgage 8-7/8% Bonds, Series 77October 15, 1991
    
    Company to Continental Bank, National
Association and M.J. Kruger, as Trustee and
Co-Trustee
    
    Issuance of First Mortgage 8-3/8%
Bonds, Series 78 and First
Mortgage 9-1/8% Bonds, Series 79May 15, 1992
    
    Company to Continental Bank, National
Association and M.J. Kruger, as Trustee and
Co-Trustee
    
    Issuance of First Mortgage 6-1/8%
Bonds, Series 82 and First
Mortgage 8% Bonds, Series 83April 15, 1993
    
    Company to Continental Bank, National
Association and M.J. Kruger, as Trustee and
Co-Trustee
    
    Issuance of First Mortgage 7-5/8%
Bonds, Series 92June 15, 1993
    
    Company to Continental Bank, National
Association and M.J. Kruger, as Trustee and
Co-Trustee
    
    Issuance of First Mortgage 7%
Bonds, Series 93 and First
Mortgage 7-1/2% Bonds, Series 94July 15, 1993
    
    Company to Continental Bank, National
Association and M.J. Kruger, as Trustee and
Co-Trustee
    
    Issuance of First Mortgage 6-5/8%
Bonds, Series 96 and First
Mortgage 7-3/4% Bonds, Series 97January 15, 1994
    
    Company to Continental Bank, National
Association and M.J. Kruger, as Trustee and
Co-Trustee
    
    Issuance of First Mortgage Bonds,
Pollution Control Series 1994A,
1994B and 1994CDecember 1, 1994
    
    Company to Bank of America Illinois and
Robert J. Donahue, as Trustee and Co-Trustee
    
    Issuance of First Mortgage Bonds,
Pollution Control Series 1994D
 4




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SupplementalIndenture Date
    
    Parties
    
    Providing ForJune 1, 1996
    
    Company to Harris Trust and Savings Bank and
D.G. Donovan, as Trustee and Co-Trustee
    
    Issuance of First Mortgage Bonds,
Pollution Control Series 1996A and
1996BMarch 1, 2002
    
    Company to BNY Midwest Trust Company and D.G.
Donovan, as Trustee and Co-Trustee
    
    Issuance of unregistered First
Mortgage 6.15% Bonds, Series 98May 20, 2002
    
    Company to BNY Midwest Trust Company and D.G.
Donovan, as Trustee and Co-Trustee
    
    Issuance of First Mortgage Bonds,
Pollution Control Series 2002June 1, 2002
    
    Company to BNY Midwest Trust Company and D.G.
Donovan, as Trustee and Co-Trustee
Bonds, Series 98
    
    Issuance of additional
unregistered First Mortgage 6.15%October 7, 2002
    
    Company to BNY Midwest Trust Company and D.G.
Donovan, as Trustee and Co-Trustee
    
    Issuance of registered First
Mortgage 6.15% Bonds, Series 98 in
exchange for unregistered First
Mortgage 6.15% Bonds, Series 98January 13, 2003
    
    Company to BNY Midwest Trust Company and D.G.
Donovan, as Trustee and Co-Trustee
    
    Issuance of First Mortgage 3.700%
Bonds, Series 99 and First
Mortgage 5.875% Bonds, Series 100March 14, 2003
    
    Company to BNY Midwest Trust Company and D.G.
Donovan, as Trustee and Co-Trustee
    
    Issuance of First Mortgage 4.70%
Bonds, Series 101April 23, 2003
    
    Company to BNY Midwest Trust Company and D.G.
Donovan, as Trustee and Co-Trustee
    
    Issuance of First Mortgage Bonds,
Pollution Control Series 2003August 13, 2003
    
    Company to BNY Midwest Trust Company and D.G.
Donovan, as Trustee and Co-Trustee
    
    Issuance of First Mortgage 4.74%
Bonds, Series 102September 10, 2003
    
    Company to BNY Midwest Trust Company and D.G.
Donovan, as Trustee and Co-Trustee
    
    Issuance of First Mortgage Bonds,
Pollution Control Series 2003BNovember 10, 2003
    
    Company to BNY Midwest Trust Company and D.G.
Donovan, as Trustee and Co-Trustee
    
    Issuance of First Mortgage Bonds,
Pollution Control Series 2003CDecember 5, 2003
    
    Company to BNY Midwest Trust Company and D.G.
Donovan, as Trustee and Co-Trustee
    
    Issuance of First Mortgage Bonds,
Pollution Control Series 2003D
 WHEREAS, the respective designations, maturity dates and principal amounts of the bonds
of each series presently outstanding under, and secured by, the Mortgage and the several
supplemental indentures above referred to, are as follows: Designation
    
    Maturity Date
    
    Principal AmountFirst Mortgage 9-7/8% Bonds, Series 75
    
    June 15, 2020
    
    $
    54,171,000First Mortgage 8-1/4% Bonds, Series 76
    
    October 1, 2006
    
    
    95,000,000First Mortgage 8-3/8% Bonds, Series 78
    
    October 15, 2006
    
    
    31,021,000First Mortgage 8% Bonds, Series 83
    
    May 15, 2008
    
    
    120,000,000First Mortgage 7-5/8% Bonds, Series 92
    
    April 15, 2013
    
    
    125,000,000First Mortgage 7% Bonds, Series 93
    
    July 1, 2005
    
    
    162,910,000
 5




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Designation
    
    Maturity Date
    
    Principal AmountFirst Mortgage 7-1/2% Bonds, Series 94
    
    July 1, 2013
    
    
    127,000,000First Mortgage 5.7% Bonds, Pollution
Control Series 1994B
    
    January 15, 2009
    
    
    15,900,000First Mortgage 5.85% Bonds, Pollution
Control Series 1994C
    
    January 15, 2014
    
    
    17,000,000First Mortgage 6.75% Bonds, Pollution
Control Series 1994D
    
    March 1, 2015
    
    
    91,000,000First Mortgage 4.4% Bonds, Pollution
Control Series 1996A
    
    December 1, 2006
    
    
    110,000,000First Mortgage 4.4% Bonds, Pollution
Control Series 1996B
    
    December 1, 2006
    
    
    89,400,000First Mortgage 6.15% Bonds, Series 98
    
    March 15, 2012
    
    
    450,000,000First Mortgage Bonds, Pollution Control
Series 2002
    
    April 15, 2013
    
    
    100,000,000First Mortgage 3.700% Bonds, Series 99
    
    February 1, 2008
    
    
    295,000,000First Mortgage 5.875% Bonds, Series 100
    
    February 1, 2033
    
    
    253,600,000First Mortgage 4.70% Bonds, Series 101
    
    April 15, 2015
    
    
    260,000,000First Mortgage Bonds, Pollution Control
Series 2003
    
    May 15, 2017
    
    
    40,000,000First Mortgage 4.74% Bonds, Series 102
    
    August 15, 2010
    
    
    212,000,000First Mortgage Bonds, Pollution Control
Series 2003B
    
    November 1, 2019
    
    
    42,200,000First Mortgage Bonds, Pollution Control
Series 2003C
    
    March 1, 2020
    
    
    50,000,000First Mortgage Bonds, Pollution Control
Series 2003D
    
    January 15, 2014
    
    
    19,975,000Total
    
    $
    2,761,177,000
 WHEREAS, the Mortgage provides for the issuance from time to time thereunder, in series,
of bonds of the Company for the purposes and subject to the limitations therein specified; and WHEREAS, the Company desires, by this Supplemental Indenture, to create an additional series
of bonds to be issuable under the Mortgage, such bonds to be designated First Mortgage Bonds,
Pollution Control Series 2005 (hereinafter called the bonds of Series 2005) and the terms and
provisions to be contained in the bonds of Series 2005 or to be otherwise applicable thereto to be
as set forth in this Supplemental Indenture; and WHEREAS, the bonds of Series 2005 and the Trustees certificate to be endorsed thereon shall
be substantially in the forms included in Exhibit A hereto; and 6




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WHEREAS, the Company is legally empowered and has been duly authorized by the necessary
corporate action and by order of the Illinois Commerce Commission to make, execute and deliver this
Supplemental Indenture, and to create, as an additional series of bonds of the Company, the bonds
of Series 2005, and all acts and things whatsoever necessary to make this Supplemental Indenture,
when executed and delivered by the Company and the Trustees, a valid, binding and legal instrument,
and to make the bonds of Series 2005, when authenticated by the Trustee and issued as provided in
the Mortgage and in this Supplemental Indenture, the valid, binding and legal obligations of the
Company, entitled in all respects to the security of the Mortgage, as amended and supplemented,
have been done and performed; NOW, THEREFORE, in consideration of the premises and of the sum of one dollar duly paid by the
Trustees to the Company, and for other good and valuable consideration, the receipt of which is
hereby acknowledged, the parties hereto do hereby agree as follows: ARTICLE I DEFINITIONS AND RULES OF CONSTRUCTION SECTION 1.01. Terms of the Mortgage.The terms used in this Supplemental Indenture which are
defined in the Mortgage, unless otherwise specified herein, are used herein with the same meanings
as in the Mortgage. SECTION 1.02. Definitions of New Terms.The following terms shall have the following
meanings in this Supplemental Indenture: IFA shall mean the Illinois Finance Authority, a political subdivision and
body politic and corporate duly organized and validly existing under and by virtue
of the laws of the State of Illinois. IFA Bonds shall mean those certain Pollution Control Revenue Refunding Bonds
(Commonwealth Edison Company Project) Series 2005 issued in the original aggregate
principal amount of $91,000,000 under and pursuant to the terms of the IFA
Indenture. IFA Indenture shall mean that certain Indenture of Trust dated as of February
15, 2005, between IFA, as issuer, and J.P. Morgan Trust Company, National
Association, as trustee. Multi-Mode Annex shall mean the Multi-Mode Annex relating to the IFA Bonds,
which is attached as Appendix B to the IFA Indenture. SECTION 1.03. Rules of Construction.All references to any agreement refer to such agreement
as modified, varied, or amended from time to time by the parties thereto (including any permitted
successors or assigns) in accordance with its terms. 7




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ARTICLE II SECTION 2.01. Designation and Issuance of Bonds.(a) The bonds of Series 2005 shall, as
hereinbefore recited, be designated as the Companys First Mortgage Bonds, Pollution Control
Series 2005. (b) Subject to the provisions of the Mortgage, the bonds of Series 2005 shall be issuable
without limitation as to the aggregate principal amount thereof. SECTION 2.02. Form, Date, Maturity Date, Interest Rate and Interest Payment Dates of Bonds.
(a) The definitive bonds of Series 2005 shall be in engraved, lithographed, printed or
type-written form and shall be registered bonds without coupons, and such bonds and the Trustees
certificate to be endorsed thereon shall be substantially in the forms included in Exhibit A
hereto. The bonds of Series 2005 shall be dated as provided in Section 3.01 of the Mortgage, as
amended by Supplemental Indenture dated April 1, 1967. All bonds of Series 2005 shall mature on
March 1, 2017. (b) The bonds of Series 2005 shall bear interest on each day that they are outstanding at a
rate per annum which is equal to the weighted-average interest rate borne on the IFA Bonds
outstanding on such date; provided, however, such interest rate on the bonds of Series 2005 shall
not exceed 12% per annum. The bonds of Series 2005 shall bear interest until the principal thereof
shall be paid in full. Interest on the bonds of Series 2005 shall be payable to the record holder
thereof on the dates that interest is payable on the IFA Bonds. (c) The interest on the bonds of Series 2005 so payable on any interest payment date shall,
subject to the exceptions provided in Section 3.01 of the Mortgage, as amended by said Supplemental
Indenture dated April 1, 1967, be paid to the person in whose name such bond is registered on such
interest payment date. SECTION 2.03. Bonds Issued as Collateral Security.The bonds of Series 2005 shall be issued,
delivered, and pledged to, and registered in the name of, the trustee under the IFA Indenture in
order to secure and provide for, and as collateral security for, the due and punctual payment of
the principal, premium, if any, and interest due from time to time on the IFA Bonds. SECTION 2.04. Credit for Payments on IFA Bonds.(a) The Company shall receive a credit
against its obligation to make any payment of interest on the bonds of Series 2005, whether on an
interest payment date, at maturity, upon redemption, upon acceleration or otherwise, in an amount
equal to the amount, if any, paid by or for the account of the Company in respect of any
corresponding payment of interest on the IFA Bonds. So long as all the bonds of Series 2005 are
pledged as described in Section 2.03, the obligation of the Company to make any payment with
respect to the principal of the bonds of Series 2005 shall be credited in full if, at the time that
any such payment of principal shall be due, there shall have been paid by or for the account of the
Company the then due principal of all IFA Bonds which are outstanding. (b) The Trustee may conclusively presume that the obligation of the Company to pay the
principal of, and premium, if any, and interest on, the bonds of Series 2005 as the same shall
become due and payable has been credited in accordance with this Section 2.04 unless 8




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and until it shall have received a written notice (including a telex, telegram, telecopy or
other form of written telecommunication) from the trustee under the IFA Indenture stating that
payment of the principal of, or premium, if any, or interest on, the IFA Bonds has become due and
payable and has not been fully paid and specifying the amount of funds required to make such
payment. SECTION 2.05. Execution of Bonds.The bonds of Series 2005 shall be executed on behalf of
the Company by its President or one of its Vice Presidents, manually or by facsimile signature, and
shall have its corporate seal affixed thereto or a facsimile of such seal imprinted thereon,
attested by its Secretary or one of its Assistant Secretaries, manually or by facsimile signature,
all as may be provided by resolution of the Board of Directors of the Company. In case any officer
or officers whose signature or signatures, manual or facsimile, shall appear upon any bond of
Series 2005 shall cease to be such officer or officers before such bond shall have been actually
authenticated and delivered, such bond nevertheless may be issued, authenticated and delivered with
the same force and effect as though the person or persons whose signature or signatures, manual or
facsimile, appear thereon had not ceased to be such officer or officers of the Company. SECTION 2.06. Medium and Places of Payment of Principal of, and Premium, If Any, and Interest
on, Bonds; Transferability and Exchangeability.The principal of, and premium, if any, and the
interest on the bonds of Series 2005 shall be payable in any coin or currency of the United States
of America which at the time of payment is legal tender for the payment of public and private
debts, and such principal, premium, if any, and interest shall be payable at the office or agency
of the Company in the City of Chicago, State of Illinois, and such bonds shall be transferable and
exchangeable, in the manner provided in Sections 3.09 and 3.10 of the Mortgage, at said office or
agency. No charge shall be made by the Company to the registered owner of any bond of Series 2005
for the registration of transfer of such bond or for the exchange thereof for bonds of the same
series of other authorized denominations, except, in the case of any transfer, a charge sufficient
to reimburse the Company for any stamp or other tax or governmental charge required to be paid by
the Company or the Trustee. SECTION 2.07. Denominations and Numbering of Bonds. The bonds of Series 2005 shall be issued
in the denomination of $1,000 and in such multiples of $1,000 as shall from time to time hereafter
be determined and authorized by the Board of Directors of the Company or by any officer or officers
of the Company authorized to make such determination, the authorization of the denomination of any
bond of Series 2005 to be conclusively evidenced by the execution thereof on behalf of the Company.
Bonds of Series 2005 shall each be numbered R-1 and consecutively upwards. SECTION 2.08. Temporary Bonds.Until definitive bonds of Series 2005 are ready for delivery,
there may be authenticated and issued in lieu of any thereof and subject to all of the provisions,
limitations, and conditions set forth in Section 3.11 of the Mortgage, temporary registered bonds
of Series 2005 without coupons. SECTION 2.09. Optional Redemption of Bonds.Upon the notice and in the manner provided in
Sections 501 and 504 of the IFA Indenture and Section 4.01 of the Multi-Mode Annex, the bonds of
Series 2005 may be redeemed in whole or in part, at the option of the 9




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Company, on the date or dates determined under Section 4.01 of the Multi-Mode Annex, at the
redemption prices (expressed as percentages of the principal amount of each bond of Series 2005 or
portion thereof to be redeemed) set forth in Section 4.01 of the Multi-Mode Annex, plus accrued
interest to the redemption date. SECTION 2.10. Mandatory Redemption. Upon the notice and in the manner provided in Sections
502 and 504 of the IFA Indenture, the bonds of Series 2005 shall be redeemed by the Company in
whole, or as provided under such paragraphs in part, at 100% of the principal amount thereof plus
accrued interest to the redemption date. SECTION 2.11. Default Mandatory Redemption.The bonds of Series 2005 shall be redeemed
promptly, without notice, by the Company in whole at 100% of the principal amount thereof plus
accrued interest to the date of redemption following receipt by the Trustee of written notice from
the trustee under the IFA Indenture stating that the principal of the IFA Bonds has been declared
to be immediately due and payable as a result of an event of default under the IFA Indenture. ARTICLE III CONFIRMATION OF LIEN The Company, for the equal and proportionate benefit and security of the holders of all bonds
at any time issued under the Mortgage, hereby confirms the lien of the Mortgage upon, and hereby
grants, bargains, sells, transfers, assigns, pledges, mortgages, warrants and conveys unto the
Trustees, all property of the Company and all property hereafter acquired by the Company, other
than (in each case) property which, by virtue of any of the provisions of the Mortgage, is excluded
from such lien, and hereby confirms the title of the Trustees (as set forth in the Mortgage) in and
to all such property. Without in any way limiting or restricting the generality of the foregoing,
there is specifically included within the confirmation of lien and title hereinabove expressed the
property of the Company legally described on Exhibit B attached hereto and made a part hereof. ARTICLE IV MISCELLANEOUS The terms and conditions of this Supplemental Indenture shall be deemed to be a part of the
terms and conditions of the Mortgage for any and all purposes. The Mortgage, as supplemented by
the indentures supplemental thereto dated subsequent to August 1, 1944 and referred to in the first
paragraph of this Supplemental Indenture, and as further supplemented by this Supplemental
Indenture, is in all respects hereby ratified and confirmed. This Supplemental Indenture shall bind and, subject to the provisions of Article XIV of the
Mortgage, inure to the benefit of the respective successors and assigns of the parties hereto. 10




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Although this Supplemental Indenture is dated as of February 15, 2005, it shall be effective
only from and after the actual time of its execution and delivery by the Company and the Trustees
on the date indicated by their respective acknowledgments hereto annexed. This Supplemental Indenture may be simultaneously executed in any number of counterparts, and
all such counterparts executed and delivered, each as an original, shall constitute but one and the
same instrument. 11




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IN WITNESS WHEREOF, Commonwealth Edison Company has caused this Supplemental Indenture to be
executed in its name by its Senior Vice President, Treasurer and Chief Financial Officer, and
attested by one of its Assistant Secretaries, and BNY Midwest Trust Company, as Trustee under the
Mortgage, has caused this Supplemental Indenture to be executed in its name by one of its Vice
Presidents, and attested by one of its Assistant Vice Presidents, and D.G. Donovan, as Co-Trustee
under the Mortgage, has hereunto affixed his signature, all as of the day and year first above
written. COMMONWEALTH EDISON COMPANYBy:J. Barry MitchellSenior Vice President, Treasurer
and Chief Financial Officer
 ATTEST: Scott N. PetersAssistant Secretary BNY MIDWEST TRUST COMPANYBy:J. BartoliniVice President
 ATTEST: M. CallahanAssistant Vice President D.G. Donovan
 12




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STATE OF ILLINOIS
    
    
    ))COUNTY OF COOK
    
    
    )
 I, DONALD M. SALAZAR, a Notary Public in and for said County, in the State aforesaid, DO
HEREBY CERTIFY that J. Barry Mitchell, Senior Vice President, Treasurer and Chief Financial Officer
of Commonwealth Edison Company, an Illinois corporation, one of the parties described in and which
executed the foregoing instrument, and Scott N. Peters, Assistant Secretary of said corporation,
who are both personally known to me to be the same persons whose names are subscribed to the
foregoing instrument as such Senior Vice President, Treasurer and Chief Financial Officer and
Assistant Secretary, respectively, and who are both personally known to me to be Senior Vice
President, Treasurer and Chief Financial Officer and an Assistant Secretary, respectively, of said
corporation, appeared before me this day in person and severally acknowledged that they signed,
executed and delivered said instrument as their free and voluntary act as such Senior Vice
President, Treasurer and Chief Financial Officer and Assistant Secretary, respectively, of said
corporation, and as the free and voluntary act of said corporation, for the uses and purposes
therein set forth. GIVEN under my hand and notarial seal this 15th day of February, A.D. 2005. Donald M. SalazarNotary Public (NOTARIAL SEAL) My Commission expires January 25, 2009. 13




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STATE OF ILLINOIS
    
    
    ))COUNTY OF COOK
    
    
    )
 I, A. HERNANDEZ, a Notary Public in and for said County, in the State aforesaid, DO HEREBY
CERTIFY that J. BARTOLINI, Vice President of BNY Midwest Trust Company, an Illinois trust company,
one of the parties described in and which executed the foregoing instrument, and M. CALLAHAN,
Assistant Vice President of said trust company, who are both personally known to me to be the same
persons whose names are subscribed to the foregoing instrument as such Vice President and Assistant
Vice President, respectively, and who are both personally known to me to be a Vice President and an
Assistant Vice President, respectively, of said trust company, appeared before me this day in
person and severally acknowledged that they signed, executed and delivered said instrument as their
free and voluntary act as such Vice President and Assistant Vice President, respectively, of said
trust company, and as the free and voluntary act of said trust company, for the uses and purposes
therein set forth. GIVEN under my hand and notarial seal this 15th day of February, A.D. 2005. A. HernandezNotary Public {SEAL} My Commission expires July 8, 2006. 14




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STATE OF ILLINOIS
    
    
    ))COUNTY OF COOK
    
    
    )
 I, A. HERNANDEZ, a Notary Public in and for said County, in the State aforesaid, DO HEREBY
CERTIFY that D.G. DONOVAN, one of the parties described in and which executed the foregoing
instrument, who is personally known to me to be the same person whose name is subscribed to the
foregoing instrument, appeared before me this day in person and acknowledged that he signed,
executed and delivered said instrument as his free and voluntary act for the uses and purposes
therein set forth. GIVEN under my hand and notarial seal this 15th day of February, A.D. 2005. A. HernandezNotary Public {SEAL} My Commission expires July 8, 2006. 15




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EXHIBIT A
to
Supplemental Indenture COMMONWEALTH EDISON COMPANY First Mortgage Bond, Pollution Control Series 2005 Due March 1, 2017 COMMONWEALTH EDISON COMPANY, an Illinois corporation (hereinafter called the Company), for
value received, hereby promises to pay to ___, as trustee under that certain
Indenture of Trust dated as of February 15, 2005 (the IFA Indenture) between Illinois Finance
Authority (IFA) and said trustee, or registered assigns, on the first day of March, 2017, the sum
of ___Dollars, and to pay interest on said sum from the date hereof until said sum shall be
paid, at a rate per annumon each day which is equal to the weighted-average interest rate borne on
the IFA Bonds (as hereinafter defined) outstanding on such date, until the principal thereof shall
be paid in full, subject to Section 2.04 of the Supplemental Indenture dated as of February 15,
2005 (the Supplemental Indenture), executed and delivered by the Company to the Trustees (as
hereinafter defined), which provides for certain credits towards payment of principal of and
interest on the bonds of this Series. Interest shall accrue on the bonds of this Series from the
date of issuance hereof, and the payment thereof shall be credited as provided in Section 2.04(a)
of the Supplemental Indenture unless and until the Trustee receives the notice contemplated by
Section 2.04(b) of the Supplemental Indenture, whereupon the interest on the bonds of this Series
shall become and remain due and payable until such time as the Trustee receives a further written
notice (including a telex, telegram, telecopy or other form of written telecommunication) from the
trustee under the IFA Indenture stating that such payments need not continue. When interest is due
and payable as described above, interest on the bonds of this Series shall be payable at the same
time as interest on the IFA Bonds and upon maturity, redemption, or acceleration of the bonds of
this Series, subject to Section 2.04 of the Supplemental Indenture. The interest on each bond of
this Series so payable on any interest payment date shall, subject to the exceptions provided in
Section 3.01 of the Mortgage (as hereinafter defined), as amended by a supplemental indenture dated
April 1, 1967, be paid to the person in whose name such bond is registered on the date of such
payment. The principal of, and premium, if any, and the interest on, this bond shall be payable at
the office or agency of the Company in the City of Chicago, State of Illinois in any coin or
currency of the United States of America which at the time of payment is legal tender for the
payment of public and private debts. This bond is one of the bonds of the Company, issued and to be issued in series from time to
time under and in accordance with and, irrespective of the time of issue, equally and ratably
secured by the Mortgage dated July 1, 1923, and indentures supplemental thereto, under which BNY
Midwest Trust Company and D.G. Donovan (collectively, the Trustees) are now the Trustees, and is
one of the First Mortgage Bonds, Pollution Control Series 2005 of the A-1




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Company, the issuance of which is provided for by the Supplemental Indenture, executed and
delivered by the Company to such Trustees, to which Mortgage and all indentures supplemental
thereto reference is hereby made for a description of the property mortgaged and pledged, the
nature and extent of the security, the rights of the holders and registered owners of said bonds,
of the Company and of the Trustees in respect of the security, and the terms and conditions
governing the issuance and security of said bonds. The term Mortgage, as hereinafter used, shall
mean said Mortgage dated July 1, 1923, and all indentures supplemental thereto. With the consent of the Company and to the extent permitted by and as provided in the
Mortgage, modifications or alterations of the Mortgage or of any indenture supplemental thereto and
of the rights and obligations of the Company and of the holders and registered owners of the bonds
may be made, and compliance with any provision of the Mortgage or any such supplemental indenture
may be waived, by the affirmative vote of the holders and registered owners of not less than eighty
per centum(80%) in principal amount of the bonds then outstanding under the Mortgage, and by the
affirmative vote of the holders and registered owners of not less than eighty per centum(80%) in
principal amount of the bonds of any series then outstanding under the Mortgage and affected by
such modification or alteration, in case one or more but less than all of the series of bonds then
outstanding under the Mortgage are so affected, but in any case excluding bonds disqualified from
voting by reason of the Companys interest therein as provided in the Mortgage; subject, however,
to the condition, among other conditions stated in the Mortgage, that no such modification or
alteration shall be made which will permit the extension of the time or times of payment of the
principal of or the interest or the premium, if any, on this bond, or the reduction in the
principal amount hereof or in the rate of interest or the amount of any premium hereon, or any
other modification in the terms of payment of such principal, interest or premium, which terms of
payment are unconditional, or, otherwise than as permitted by the Mortgage, the creation of any
lien ranking prior to or on a parity with the lien of the Mortgage with respect to any of the
mortgaged property, all as more fully provided in the Mortgage. The bonds of this Series are subject to redemption, as provided in the Supplemental Indenture. In case of certain completed defaults specified in the Mortgage, the principal of this bond
may be declared or may become due and payable in the manner and with the effect provided in the
Mortgage. No recourse shall be had for the payment of the principal of or the interest on this bond, or
for any claim based hereon, or otherwise in respect hereof or of the Mortgage, to or against any
incorporator, stockholder, officer or director, past, present or future, of the Company or of any
successor corporation, either directly or through the Company or such successor corporation, under
any constitution or statute or rule of law, or by the enforcement of any assessment or penalty, or
otherwise, all such liability of incorporators, stockholders, directors and officers being waived
and released by the registered owner hereof by the acceptance of this bond and being likewise
waived and released by the terms of the Mortgage, all as more fully provided therein. A-2




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This bond is transferable by the registered owner hereof, in person or by duly authorized
attorney, at the office or agency of the Company in the City of Chicago, State of Illinois, upon
surrender and cancellation of this bond; and thereupon a new registered bond or bonds without
coupons of the same aggregate principal amount and series will, upon the payment of charges as
provided in the Mortgage, be issued to the transferee in exchange herefor. Bonds of this Series are issuable only in registered form without coupons and in the
denominations of $1,000 each and any authorized multiple thereof. As provided in the Mortgage,
such bonds are exchangeable for registered bonds of the same series as between authorized
denominations. Any such exchange may be made by the registered owner of any such bond or bonds
upon presentation thereof for that purpose at the office or agency of the Company in the City of
Chicago, State of Illinois. This bond shall not be entitled to any security or benefit under the Mortgage or be valid or
become obligatory for any purpose unless and until it shall have been authenticated by the
execution by the corporate Trustee, or its successor in trust under the Mortgage, of the
certificate endorsed hereon. A-3




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IN WITNESS WHEREOF, Commonwealth Edison Company has caused this bond to be executed in its
name by its President or one of its Vice Presidents, and has caused its corporate seal to be hereto
affixed, attested by its Secretary or one of its Assistant Secretaries, as of the ___day of
___, 20___. COMMONWEALTH EDISON COMPANY[SEAL]By:President
 ATTEST: Secretary (General Form of Trustees Certificate) This bond is one of the bonds of the series designated herein, referred to and described in
the within mentioned Supplemental Indenture dated as of February 15, 2005. BNY MIDWEST TRUST COMPANYBy:Authorized Officer
 Illinois Commerce Commission Identification No. 6235 A-4




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ABBREVIATIONS The following abbreviations, when used in the inscription on the face of this instrument,
shall be construed as though they were written out in full according to applicable laws or
regulations: TEN COM
    
    -
    
    as tenants in commonTEN ENT
    
    -
    
    as tenants by the entiretiesJT TEN
    
    -
    
    as joint tenants with right of survivorship and not as
tenants in commonUNIF GIFT MIN ACT - ......... Custodian .............(Cust)      (Minors)under Uniform Gifts to Minors Act............................(State)
 Additional abbreviations may also be used though not in the above list. FOR VALUE RECEIVED the undersigned hereby sell(s), assign(s), and transfer(s) unto PLEASE INSERT SOCIAL SECURITY OROTHER IDENTIFYING NUMBER OF ASSIGNEE
 
 (Please print or typewrite name and address including postal zip code of assignee) the within Bond and all rights thereunder, hereby irrevocably constituting and appointing
attorney to transfer said Bond on the books of the Company, with full power of
substitution in the premises. Dated:NOTICE: The signature to this assignment must
correspond with the name as written upon the face of
the within instrument in every particular, without
alteration or enlargement or any change whatever.
 A-5




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EXHIBIT B
to
Supplemental Indenture Legal Descriptions [omitted] B-1