<PAGE>
      
                                                     Exhibit (4)-36
                                                     Commonwealth Edison Company
                                                     Form 10-K  File No. 1-1839






                         SECOND SUPPLEMENTAL INDENTURE

                          Dated as of January 24, 1997


                                    Between


                          COMMONWEALTH EDISON COMPANY

                                      and

                            WILMINGTON TRUST COMPANY


 

<PAGE>
 

ARTICLE I  DEFINITIONS  . . . . . . . . . . . . . . . . . . . . . . . . .     2
       Section 1.1.  Definition of Terms  . . . . . . . . . . . . . . . .     2
       Section 1.2.  Interpretation . . . . . . . . . . . . . . . . . . .     4

ARTICLE II  GENERAL TERMS AND CONDITIONS OFTHE DEBENTURES . . . . . . . .     5
       Section 2.1.  Designation and Principal Amount . . . . . . . . . .     5
       Section 2.2.  Maturity . . . . . . . . . . . . . . . . . . . . . .     5
       Section 2.3.  Form and Payment . . . . . . . . . . . . . . . . . .     5
       Section 2.4.  Global Debenture . . . . . . . . . . . . . . . . . .     5
       Section 2.5.  Interest . . . . . . . . . . . . . . . . . . . . . .     6

ARTICLE III  REDEMPTION OF THE DEBENTURES . . . . . . . . . . . . . . . .     6
       Section 3.1.  Tax Event Redemption . . . . . . . . . . . . . . . .     6
       Section 3.2.  Optional Redemption by Company . . . . . . . . . . .     7
       Section 3.3.  No Sinking Fund  . . . . . . . . . . . . . . . . . .     8

ARTICLE IV  EXTENSION OF INTEREST PAYMENT PERIOD  . . . . . . . . . . . .     8
       Section 4.1.  Extension of Interest Payment Period . . . . . . . .     8
       Section 4.2.  Notice of Extension  . . . . . . . . . . . . . . . .     8

ARTICLE V  EXPENSES . . . . . . . . . . . . . . . . . . . . . . . . . . .     9
       Section 5.1.  Payment of Expenses  . . . . . . . . . . . . . . . .     9

ARTICLE VI  SUBORDINATION . . . . . . . . . . . . . . . . . . . . . . . .     9
       Section 6.1.  Agreement to Subordinate . . . . . . . . . . . . . .     9
       Section 6.2.  Default on Senior Indebtedness . . . . . . . . . . .    10
       Section 6.3.  Liquidation; Dissolution; Bankruptcy . . . . . . . .    10
       Section 6.4.  Subrogation  . . . . . . . . . . . . . . . . . . . .    11
       Section 6.5.  Trustee to Effectuate Subordination  . . . . . . . .    12
       Section 6.6.  Notice by the Company  . . . . . . . . . . . . . . .    12
       Section 6.7.  Rights of the Trustee; Holders of Senior Indebtedness   13
       Section 6.8.  Subordination May Not Be Impaired  . . . . . . . . .    13

ARTICLE VII  FORM OF DEBENTURE  . . . . . . . . . . . . . . . . . . . . .    14
       Section 7.1.  Form of Debenture  . . . . . . . . . . . . . . . . .    14

ARTICLE VIII  ORIGINAL ISSUE OF DEBENTURES; EXCHANGE  . . . . . . . . . .    20
       Section 8.1.  Original Issue of Debentures . . . . . . . . . . . .    20
       Section 8.2  Exchange of Debentures for Series B Debentures  . . .    21

ARTICLE IX  MISCELLANEOUS . . . . . . . . . . . . . . . . . . . . . . . .    21
       Section 9.1.  Ratification of Indenture  . . . . . . . . . . . . .    21
       Section 9.2.  Trustee Not Responsible for Recitals . . . . . . . .    22
       Section 9.3.  Governing Law  . . . . . . . . . . . . . . . . . . .    22

                                      -i-
<PAGE>


       Section 9.4.  Separability . . . . . . . . . . . . . . . . . . . .    22
       Section 9.5.  Counterparts . . . . . . . . . . . . . . . . . . . .    22








                                      -ii-



<PAGE>
 
          THIS SECOND SUPPLEMENTAL INDENTURE, dated as of January 24, 1997
(the "SECOND SUPPLEMENTAL INDENTURE"), between Commonwealth Edison Company, an
Illinois corporation (the "COMPANY"), and Wilmington Trust Company, not in its
individual capacity but solely as trustee (the "TRUSTEE") under the Indenture
dated as of September 1, 1995 between the Company and the Trustee (the
"INDENTURE") as supplemented by the First Supplemental Indenture dated as of
September 19, 1995  between the Company and the Trustee  (the "FIRST
SUPPLEMENTAL INDENTURE").

                          W I T N E S S E T H:

          WHEREAS, the Company executed and delivered the Indenture to the
Trustee to provide, among other things, for the future issuance of the
Company's unsecured subordinated debt securities, to be issued from time to
time in one or more series as might be determined by the Company under the
Indenture, in an unlimited aggregate principal amount which may be
authenticated and delivered as provided in the Indenture; and

          WHEREAS, pursuant to the terms of the Indenture, the Company desires
to provide for the establishment of a new series of its debt securities to be
known as its 8.50% Subordinated Deferrable Interest Debentures due  January
15, 2027 (the "DEBENTURES"), the form and substance of such Debentures and the
terms, provisions and conditions thereof to be set forth as provided in the
Indenture and this Second Supplemental Indenture; and

          WHEREAS, ComEd Financing II, a Delaware statutory business trust
(the "TRUST"), has offered to the public $150,000,000 aggregate liquidation
amount of its 8.50 % Series A Capital Securities  (Liquidation Amount $1,000
per Capital Security) (the "CAPITAL SECURITIES") and has offered to the
Company $4,640,000 aggregate stated liquidation amount of its 8.50% Common
Securities  (Liquidation Amount $1,000 per Common Security) (the "COMMON
SECURITIES"), such Capital Securities and Common Securities representing
undivided beneficial interests in the assets of the Trust, and proposes to
invest the proceeds from such offering in $154,640,000 aggregate principal
amount of the Debentures; and

          WHEREAS, the Company has requested the Trustee to execute and
deliver this Second Supplemental Indenture, and all requirements necessary to
make this Second Supplemental Indenture a valid instrument, in accordance with
its terms, and to make the Debentures, when executed by the Company and
authenticated and delivered by the Trustee, the valid obligations of the
Company, have been performed, and the execution and delivery of this Second
Supplemental Indenture has been duly authorized in all respects;

          NOW, THEREFORE, in consideration of the purchase and acceptance of
the Debentures by the holders thereof, and for the purpose of setting forth,
as provided in the Indenture, the form and substance of the Debentures and the
terms, provisions and conditions thereof, the Company covenants and agrees
with the Trustee as follows:
<PAGE>
 
                               ARTICLE I
                              DEFINITIONS

          Section 1.1.  Definition of Terms.  Unless the context otherwise
requires, (a) a term defined in the Indenture has the same meaning when used
in this Second Supplemental Indenture, (b)  a term defined anywhere in this
Second Supplemental Indenture has the same meaning throughout and (c) the
following terms have the meanings given to them in the Declaration: (i)
Administrative Trustee; (ii) Capital Security Certificate; (iii) Clearing
Agency; (iv) Delaware Trustee; (v) Exchange Offer; (vi) No Recognition
Opinion; (vii) Property Trustee; (viii) Pro Rata; (ix) Series B Debentures;
(x) Sponsor;  and (xi) Tax Event.

          In addition, the following terms have the following respective
meanings:

          "ADJUSTED TREASURY RATE"  means, with respect to any redemption
date, the rate per annum equal to (i) the yield, under the heading which
represents the average for the immediately prior week, appearing in the most
recently published statistical release designated "H.15 (519)" or any
successor publication which is published weekly by the Federal Reserve Board
and which establishes yields on actively traded United States Treasury
securities adjusted to constant maturity under the caption "Treasury Constant
Maturities," for the maturity corresponding to the Initial Optional Prepayment
Date (if no maturity is within three months before or after the Initial
Optional Prepayment Date, yields for the two published maturities most closely
corresponding to the Initial Optional Prepayment Date shall be determined and
the Adjusted Treasury Rate shall be interpolated or extrapolated from such
yields on a straight-line basis, rounding to the nearest month) or (ii) if
such release (or any successor release) is not published during the week
preceding the calculation date or does not contain such yields, the rate per
annum equal to the semi-annual equivalent yield to maturity of the Comparable
Treasury Issue, assuming a price for the Comparable Treasury Issue (expressed
as a percentage of its principal amount) equal to the Comparable Treasury
Price for such redemption date, in each case calculated on the third Business
Day preceding the redemption date, plus in each case (a) 1.25 % if such
redemption date occurs on or prior to January 15, 1998, and (b) 0.50% in all
other cases.

          "COMPARABLE TREASURY ISSUE" means the United States Treasury
security selected by the Quotation Agent as having a maturity date
corresponding to the Initial Optional Prepayment Date that would be utilized,
at the time of selection and in accordance with customary financial practice,
in pricing new issues of corporate debt securities with a maturity date
corresponding to the Initial Optional Prepayment Date.  If no United States
Treasury security has a maturity date which is within three months before or
after the Initial Optional Prepayment Date, the two most closely corresponding
United States Treasury securities shall be used as the Comparable Treasure
Issue, and the calculation of the Adjusted Treasury Rate pursuant to clause
(ii) of the definition thereof shall be interpolated or extrapolated on a
straight line basis, rounding to the nearest month.

          "COMPARABLE TREASURY PRICE" means, with respect any redemption date,
(i) the average of the bid and asked prices for the Comparable Treasury Issue
(expressed in each

                                  -2-
<PAGE>
 
case as a percentage of its principal amount) on the third Business Day
preceding such redemption date, as set forth in the daily statistical
release (or any successor release) published by the Federal Reserve Bank
of New York and designated "Composite 3:30 p.m. Quotations for U.S.
Government Securities" or (ii) if such release (or any successor
release) is not published or does not contain such prices on such
Business Day, (a) the average of three Reference Treasury Dealer
Quotations for such redemption date, after excluding the highest and
lowest of such Reference Treasury Dealer Quotations, or (b) if the
Trustee obtains fewer than three such Reference Treasury Dealer
Quotations, the average of all such quotations.

          "DECLARATION" means the Amended and Restated Declaration of Trust of
ComEd Financing II, a Delaware statutory business trust, dated as of January
24, 1997.

          "DISSOLUTION EVENT" means that, as a result of the occurrence and
continuation of a Tax Event, the Trust is to be dissolved in accordance with
the Declaration and the Debentures held by the Property Trustee are to be
distributed to the holders of the Trust Securities issued by the Trust Pro
Rata in accordance with the Declaration.

          "FEDERAL RESERVE BOARD" means the Board of Governors of the Federal
Reserve System.

          "INITIAL OPTIONAL PREPAYMENT DATE" means January 15, 2007.

          "GUARANTEES"  means the guarantees by the Company of the payment of
distributions of moneys held by the Trust and payments on liquidation of the
Trust.

          "INITIAL PURCHASERS" means the entities so identified in the
Purchase Agreement.

          "MATURITY DATE" means the date on which the Debentures mature and on
which the principal shall be due and payable together with all accrued and
unpaid interest thereon including Compounded Interest and Additional Interest,
if any.

          "QUOTATION AGENT" means the Reference Treasury Dealer appointed by
the Trustee after consultation with the Company.

          "REFERENCE TREASURY DEALER" means: (i) Merrill Lynch Government
Securities, Inc. and its successors; provided, however, that if the foregoing
shall cease to be a primary U.S. Government securities dealer in New York City
(a "PRIMARY TREASURY DEALER"), the Company shall substitute therefor another
Primary Treasury Dealer; and (ii) any other Primary Treasury Dealer selected
by the Trustee after consultation with the Company.

          "REFERENCE TREASURY DEALER QUOTATION" means, with respect to each
Reference Treasury Dealer and any redemption date, the average, as determined
by the Trustee, of the bid and asked prices for the Comparable Treasury Issue
(expressed in each case as a percentage of its principal amount) quoted in
writing to the Trustee by such Reference

                                  -3-
<PAGE>
 
Treasury Dealer at 5:00 p.m., New York City time, on the third Business
Day preceding such redemption date.

     "SENIOR INDEBTEDNESS" means (i) any payment in respect of (A)
indebtedness of the Company for money borrowed and (B) indebtedness evidenced
by securities, debentures, bonds, notes or other similar instruments issued by
the Company including, without limitation, indebtedness evidenced by
securities issued pursuant to the provisions of the Mortgage dated July 1,
1923, as supplemented by Supplemental Indenture dated August 1, 1944 and
subsequent supplemental indentures, between the Company, as mortgagor, and
Harris Trust and Savings Bank and D.G. Donovan, as trustees; the Indenture
dated as of September 1, 1987, as supplemented and amended, between the
Company and Citibank, N.A., as trustee; the Indentures dated April 1, 1949,
October 1, 1949, October 1, 1950, October 1, 1954, January 1, 1958, January 1,
1959 and December 1, 1961, between the Company and Amalgamated Bank, as
successor trustee to The First National Bank of Chicago; and the Indenture
dated February 15, 1973, as supplemented, between the Company and LaSalle
National Bank, as successor trustee to The First National Bank of Chicago;
(ii) all capital lease obligations of the Company; (iii) all obligations of
the Company issued or assumed as the deferred purchase price of property, all
conditional sale obligations of the Company and all obligations of such
obligor under any title retention agreement (but excluding trade accounts
payable arising in the ordinary course of business); (iv) all obligations of
the Company for reimbursement on any letter of credit, banker's acceptance,
security purchase facility or similar credit transaction; (v) all obligations
of the type referred to in clauses (i) through (iv) of other persons for the
payment of which the Company is responsible or liable as obligor, guarantor or
otherwise; and (vi) all obligations of the type referred to in clauses (i)
through (v) of other persons secured by any lien on any property or asset of
the Company (whether or not such obligation is assumed by such obligor),
except for (1) any such indebtedness that is by its terms subordinated to or
pari passu with the Debentures, as the case may be, including all other debt
securities and guarantees in respect of those debt securities, issued to any
other trusts, partnerships or any other entity affiliated with the Company
which is a financing vehicle of the Company ("Financing Entity") in connection
with an issuance of preferred securities by such Financing Entity or other
securities which rank pari passu with, or junior to, the Capital Securities,
and (2) any indebtedness between or among the Company and its Affiliates.

          Section 1.2.  Interpretation.  Each definition in this Second
Supplemental Indenture includes the singular and the plural, and references to
the neuter gender include the masculine and feminine where appropriate.  Terms
which relate to accounting matters shall be interpreted in accordance with
generally accepted accounting principles in effect from time to time.
References to any statute mean such statute as amended at the time and include
any successor legislation.  The word "or" is not exclusive, and the words
"herein," "hereof" and "hereunder" refer to this Second Supplemental Indenture
as a whole.  The headings to the Articles and Sections are for convenience of
reference and shall not affect the meaning or interpretation of this Second
Supplemental Indenture.  References to Articles and Sections mean the Articles
and Sections of this Second Supplemental Indenture.

                                  -4-
<PAGE>
 
                               ARTICLE II
                    GENERAL TERMS AND CONDITIONS OF
                             THE DEBENTURES

          Section 2.1.  Designation and Principal Amount.  There is hereby
authorized a series of Debt Securities designated the "8.50 % Series A
Subordinated Deferrable Interest Debentures due January  15, 2027," limited in
aggregate principal amount to $154,640,000, which amount shall be as set forth
in any written order of the Company for the authentication and delivery of
Debentures pursuant to Section 2.04 of the Indenture.

          Section 2.2.  Maturity.  The Maturity Date will be January 15,
2027.

          Section 2.3.  Form and Payment.  Except as provided in Section 2.4,
the Debentures shall be issued in fully registered certificated form without
interest coupons.  Principal and interest on the Debentures issued in
certificated form will be payable, the transfer of such Debentures will be
registrable and such Debentures will be exchangeable for Debentures bearing
identical terms and provisions at the office or agency of the Trustee in
Wilmington, Delaware, provided, however, that payment of interest may be made
at the option of the Company by check mailed to the registered holder at such
address as shall appear in the Security Register.  Notwithstanding the
foregoing, so long as the registered holder of any Debentures is the Property
Trustee, the payment of the principal of, premium (if any) and interest
(including Compounded Interest and Additional Interest, if any) on such
Debentures held by the Property Trustee will be made at such place and to such
account as may be designated by the Property Trustee.

          Section 2.4.  Global Debenture.  In the event that the Sponsor gives
notice of its election to liquidate the Trust pursuant to Section 8.1(a)(iii)
of the Declaration:

             (a)  the Debentures in certificated form may be presented
        to the Trustee by the Property Trustee in exchange for a Global
        Security in an aggregate principal amount equal to the aggregate
        principal amount of the Debentures so presented, to be
        registered in the name of the Depositary, or its nominee, and
        delivered by the Trustee to the Depositary for crediting to the
        accounts of its participants pursuant to the instructions of the
        Administrative Trustees. The Company, upon any such
        presentation, shall execute a Global Security in such aggregate
        principal amount and deliver the same to the Trustee for
        authentication and delivery in accordance with the Indenture and
        this Second Supplemental Indenture; and any  payments on the
        Debentures issued as a Global Security will be made to the
        Depositary; and

             (b)  if any Capital Securities are held in non book-entry
        certificated form, the Debentures in certificated form may be
        presented to the Trustee by the Property Trustee and any Capital
        Security Certificate which represents Capital Securities other
        than Capital Securities held by the Clearing Agency or its
        nominee ("NON BOOK-ENTRY CAPITAL SECURITIES") will be deemed to
        represent beneficial interests in Debentures presented to the
        Trustee by the Property Trustee having an aggregate principal
        amount equal to the aggregate stated liquidation amount of the
        Non Book-Entry Capital Securities until such

                                  -5-
<PAGE>
 
        Capital Security Certificates are presented to the Security
        Registrar for transfer or reissuance at which time such Capital
        Security Certificates will be canceled and a Debenture,
        registered in the name of the holder of such Capital Security
        Certificate or the transferee of the holder of such Capital
        Security Certificate, as the case may be, with an aggregate
        principal amount equal to the aggregate stated liquidation
        amount of the Capital Security Certificate canceled, will be
        executed by the Company and delivered to the Trustee for
        authentication and delivery in accordance with the Indenture and
        this Second Supplemental Indenture.  On issue of such
        Debentures, Debentures with an equivalent aggregate principal
        amount that were presented by the Property Trustee to the
        Trustee will be deemed to have been cancelled.

          Section 2.5.  Interest.  (a)  Each Debenture will bear interest at
the rate of 8.50% per annum (the "COUPON RATE") from the original date of
issuance until the principal thereof becomes due and payable, and on any
overdue principal and (to the extent that payment of such interest is
enforceable under applicable law) on any overdue installment of interest at
the Coupon Rate, compounded semi-annually, payable (subject to the provisions
of Article IV) semi-annually in arrears on July 15 and January 15 of each year
(each, an "INTEREST PAYMENT DATE"), commencing on July 15, 1997, to the Person
in whose name such Debenture or any predecessor Debenture is registered, at
the close of business on the first day of July and January, respectively.

          (b)  The amount of interest payable for any period will be computed
on the basis of a 360-day year consisting of twelve 30-day months.  In the
event that any date on which interest is payable on the Debentures is not a
Business Day, then payment of interest payable on such date will be made on
the next succeeding day which is a Business Day (and without any interest or
other payment in respect of any such delay).  The amount of interest payable
for any period shorter than a full calendar month for which interest is
computed, will be computed on the basis of the actual number of days elapsed
in such month.

          (c)  If at any time while the Property Trustee is the holder of any
Debentures, the Trust or the Property Trustee is required to pay any taxes,
duties, assessments or governmental charges of whatever nature (other than
withholding taxes) imposed by the United States, or any other taxing
authority, then, in any case, the Company will pay as additional interest
("ADDITIONAL INTEREST") on the Debentures held by the Property Trustee, such
additional amounts as shall be required so that the net amounts received and
retained by the Trust and the Property Trustee after paying such taxes,
duties, assessments or other governmental charges will be equal to the amounts
the Trust and the Property Trustee would have received had no such taxes,
duties, assessments or other government charges been imposed.


                              ARTICLE III
                      REDEMPTION OF THE DEBENTURES

          Section 3.1.  Tax Event Redemption.  If a Tax Event has occurred and
is continuing, then, notwithstanding Section 3.2, the Company shall have the
right, upon not less than 30 days' nor more than 60 days' notice to the
registered holders of the Debentures, to redeem the Debentures, in whole (but
not in part), for cash at any time prior to January 15, 2007

                                  -6-
<PAGE>
 
and within 90 days of the occurrence of such Tax Event (the "90 DAY
PERIOD") at a redemption price (the "TAX EVENT REDEMPTION PRICE") equal
to the greater for (i) 100% of the principal amount of such Debentures
or (ii) the sum, as determined by a Quotation Agent, of the present
values of the principal amount and premium payable as part of the
redemption price with respect to an optional redemption of such
Debentures on January 15, 2007, together with scheduled payments of
interest on the Debentures accruing from the redemption date to and
including January 15, 2007, in each case discounted to the redemption
date on a semi-annual basis (assuming a 360-day year consisting of
twelve 30-day months) at the Adjusted Treasury Rate, plus, in each case,
accrued interest thereon to the date of such redemption.  The Tax Event
Redemption Price shall be paid prior to 12:00 noon, New York time, on
the date of such redemption or at such earlier time as the Company
determines and specifies in the notice of redemption, provided the
Company shall deposit with the Trustee an amount sufficient to pay the
Tax Event Redemption Price by 11:00 a.m. on the date such Tax Event
Redemption Price is to be paid.

          Section 3.2.  Optional Redemption by Company.   Subject to the
provisions of Article III of the Indenture, except as otherwise specified in
this Second Supplemental Indenture, the Company shall have the right to redeem
the Debentures, in whole or in part, from time to time, on or after January
15, 2007, at a redemption price (the "OPTIONAL REDEMPTION PRICE") equal to the
percentage of the principal amount of the Debentures specified below, plus, in
each case, accrued and unpaid interest thereon to the date of such redemption
if redeemed  during the 12-month period beginning January 15 of the years
indicated below:

               YEAR                    PERCENTAGE
               ----                    ----------
               2007                    104.250%
               2008                    103.825
               2009                    103.400
               2010                    102.975
               2011                    102.550
               2012                    102.125
               2013                    101.700
               2014                    101.275
               2015                    101.850
               2016                    100.425
               2017 and thereafter     100.000

Any redemption pursuant to this Section 3.2 will be made upon not less than 30
days' nor more than 60 days' notice to the registered holder of the
Debentures, at the Optional Redemption Price.  If the Debentures are only
partially redeemed pursuant to this Section 3.2, the Debentures will be
redeemed pro rata or by lot or by any other method utilized by the Trustee;
provided, that if at the time of redemption, the Debentures are registered as
a Global Security, the Depositary shall determine by lot the principal amount
of such Debentures held by each Debenture holder to be redeemed.  The Optional
Redemption Price shall be paid prior to 12:00 noon, New York time, on the date
of such redemption or at such earlier time as the Company determines and
specifies in the notice of redemption, provided the Company shall deposit with
the Trustee an amount

                                  -7-
<PAGE>
 
sufficient to pay the Optional Redemption Price by 11:00 a.m. on the
date such Optional Redemption Price is to be paid. Section 3.3.  No
Sinking Fund.  The Debentures are not entitled to the benefit of any
sinking fund.


                               ARTICLE IV
                  EXTENSION OF INTEREST PAYMENT PERIOD

          Section 4.1.  Extension of Interest Payment Period.  So long as no
Event of Default has occurred and is continuing, the Company shall have the
right, at any time and from time to time during the term of the Debentures, to
extend the interest payment period of such Debentures for up to ten (10)
consecutive semi-annual periods (the "EXTENDED INTEREST PAYMENT PERIOD").  To
the extent permitted by applicable law, interest, the payment of which has
been deferred because of the extension of the interest payment period pursuant
to this Section 4.1, will bear interest compounded semi-annually at the Coupon
Rate for each semi-annual period of the Extended Interest Payment Period
("COMPOUNDED INTEREST").  At the end of the Extended Interest Payment Period,
the Company shall pay all interest accrued and unpaid on the Debentures,
including any Compounded Interest and Additional Interest ("DEFERRED
INTEREST") which shall be payable to the holders of the Debentures in whose
names the Debentures are registered in the Security Register on the record
date immediately preceding the end of the Extended Interest Payment Period.
Before the termination of any Extended Interest Payment Period, the Company
may further extend such period, provided that such period together with all
such further extensions thereof shall not exceed ten (10) consecutive
semi-annual periods or extend beyond the Maturity Date of the Debentures.
Upon the termination of any Extended Interest Payment Period and upon the
payment of all Deferred Interest then due, the Company may select a new
Extended Interest Payment Period, subject to the foregoing requirements.  No
interest shall be due and payable during an Extended Interest Payment Period,
except at the end thereof, but the Company may pay at any time all or any
portion of the interest accrued during an Extended Interest Payment Period.

          Section 4.2.  Notice of Extension.  (a)  If the Property Trustee is
the only registered holder of the Debentures at the time the Company selects
an Extended Interest Payment Period, the Company shall give written notice to
the Administrative Trustees, the Property Trustee and the Trustee of its
selection of such Extended Interest Payment Period on the earlier of (i) ten
days prior to the next succeeding date on which Distributions on the Trust
Securities issued by the Trust are payable, or (ii) the date the Trust or the
Administrative Trustees are required to give notice of the record or payment
date for such Distributions to the New York Stock Exchange or other applicable
self-regulatory organization or to holders of the Capital Securities issued by
the Trust, but in any event at least ten days before such record date.

          (b)  If the Property Trustee is not the only holder of the
Debentures at the time the Company selects an Extended Interest Payment
Period, the Company shall give the holders of the Debentures and the Trustee
written notice of its selection of such Extended Interest Payment Period ten
days before the earlier of (i) the next succeeding Interest Payment Date, or

                                  -8-
<PAGE>
 
(ii) the date the Company is  required to give notice of the record or payment
date of such interest payment to the New York Stock Exchange or other
applicable self-regulatory organization or to holders of the Debentures, but
in any event at least ten days before such record date.

          (c)  The period in which any notice is given pursuant to paragraphs
(a) or (b) of this Section 4.2 shall be counted as one of the 10 semi-annual
periods permitted in the maximum Extended Interest Payment Period permitted
under Section 4.1.


                               ARTICLE V
                                EXPENSES

          Section 5.1.  Payment of Expenses.  In connection with the offering,
sale and issuance of the Debentures to the Property Trustee in connection with
the sale of the Trust Securities by the Trust, the Company shall:

             (a)  pay all costs and expenses relating to the offering,
        sale and issuance of the Debentures, including compensation to
        the Initial Purchasers payable pursuant to the Purchase
        Agreement and compensation of the Trustee under the Indenture in
        accordance with the provisions of Section 7.06 of the Indenture;

             (b)  pay all costs and expenses of the Trust (including,
        but not limited to, costs and expenses relating to the
        organization of the Trust, the offering, sale and issuance of
        the Trust Securities (including compensation to the Initial
        Purchasers in connection therewith), the fees and expenses of
        the Property Trustee and the Delaware Trustee, the costs and
        expenses relating to the operation of the Trust, including
        without limitation, costs and expenses of accountants,
        attorneys, statistical or bookkeeping services, expenses for
        printing and engraving and computing or accounting equipment,
        paying agent(s), registrar(s), transfer agent(s), duplicating,
        travel and telephone and other telecommunications expenses and
        costs and expenses incurred in connection with the acquisition,
        financing, and disposition of Trust assets); and

             (c)  pay any and all taxes (other than United States
        withholding taxes attributable to the Trust or its assets) and
        all liabilities, costs and expenses with respect to such taxes
        of the Trust.


                               ARTICLE VI
                             SUBORDINATION

          Section 6.1.  Agreement to Subordinate.  The Company covenants and
agrees, and each holder of Debentures issued hereunder by such holder's
acceptance thereof likewise covenants and agrees, that all Debentures shall be
issued subject to the provisions of this Article VI; and each holder of a
Debenture, whether upon original issue or upon transfer or assignment thereof,
accepts and agrees to be bound by such provisions.

                                  -9-
<PAGE>
 
          The payment by the Company of the principal of, premium, if any, and
interest on all Debentures issued hereunder shall, to the extent and in the
manner hereinafter set forth, be subordinated and subject in right of payment
to the prior payment in full of all Senior Indebtedness of the Company,
whether outstanding at the date of this Second Supplemental Indenture or
thereafter incurred.

          No provision of this Article VI shall prevent the occurrence of any
default or Event of Default hereunder.

          Section 6.2.  Default on Senior Indebtedness.  In the event and
during the continuation of any default by the Company in the payment of
principal, premium, interest or any other payment due on any Senior
Indebtedness of the Company, or in the event that the maturity of any Senior
Indebtedness of the Company has been accelerated because of a default, then,
in either case, no payment shall be made by the Company with respect to the
principal (including redemption payments, if any) of premium, if any, or
interest on the Debentures.

          In the event that, notwithstanding the foregoing, any payment shall
be received by the Trustee or any holder when such payment is prohibited by
the preceding paragraph of this Section 6.2, such payment shall be held in
trust for the benefit of, and shall be paid over or delivered to, the holders
of Senior Indebtedness or their respective representatives, or to the trustee
or trustees under any indenture pursuant to which any of such Senior
Indebtedness may have been issued, as their respective interests may appear,
but only to the extent that the holders of the Senior Indebtedness (or their
representative or representatives or a trustee) notify the Trustee within 90
days of such payment of the amounts then due and owing on the Senior
Indebtedness and only the amounts specified in such notice to the Trustee
shall be paid to the holders of Senior Indebtedness.

          Section 6.3.  Liquidation; Dissolution; Bankruptcy.  Upon any
payment by the Company, or distribution of assets of the Company of any kind
or character, whether in cash, property or securities, to creditors upon any
dissolution or winding-up or liquidation or reorganization of the Company,
whether voluntary or involuntary or in bankruptcy, insolvency, receivership or
other proceedings, all amounts due upon all Senior Indebtedness of the Company
shall first be paid in full, or payment thereof provided for in money in
accordance with its terms, before any payment is made by the Company on
account of the principal (and premium, if any) or interest on the Debentures;
and upon any such dissolution or winding-up or liquidation or reorganization,
any payment by the Company, or distribution of assets of the Company of any
kind or character, whether in cash, property or securities, to which the
holders of the Debentures or the Trustee would be entitled to receive from the
Company, except for the provisions of this Article VI, shall be paid by the
Company or by any receiver, trustee in bankruptcy, liquidating trustee, agent
or other Person making such payment or distribution, or by the holders of the
Debentures or by the Trustee under this Indenture if received by them or it,
directly to the holders of Senior Indebtedness of the Company (pro rata to
such holders on the basis of the respective amounts of Senior Indebtedness
held by such holders, as calculated by the Company) or their representative or
representatives, or to the trustee or trustees under any indenture pursuant to
which any instruments evidencing such Senior Indebtedness may have been
issued, as their respective interests may appear, to the extent necessary to
pay such Senior Indebtedness in full,

                                  -10-
<PAGE>
 
in money or money's worth, after giving effect to any concurrent payment
or distribution to or for the holders of such Senior Indebtedness,
before any payment or distribution is made to the holders of Debentures
or to the Trustee.

          In the event that, notwithstanding the foregoing, any payment or
distribution of assets of the Company of any kind or character, whether in
cash, property or securities, prohibited by the foregoing, shall be received
by the Trustee or the holders of the Debentures before all Senior Indebtedness
of the Company is paid in full, or provision is made for such payment in money
in accordance with its terms, such payment or distribution shall be held in
trust for the benefit of and shall be paid over or delivered to the holders of
such Senior Indebtedness or their representative or representatives, or to the
trustee or trustees under any indenture pursuant to which any instruments
evidencing such Senior Indebtedness may have been issued, as their respective
interests may appear, as calculated by the Company, for application to the
payment of all Senior Indebtedness of the Company remaining unpaid to the
extent necessary to pay such Senior Indebtedness in full in money in
accordance with its terms, after giving effect to any concurrent payment or
distribution to or for the benefit of the holders of such Senior Indebtedness.

          For purposes of this Article VI, the words "cash, property or
securities" shall not be deemed to include shares of stock of the Company as
reorganized or readjusted, or securities of the Company or any other
corporation provided for by a plan of reorganization or readjustment, the
payment of which is subordinated at least to the extent provided in this
Article VI with respect to the Debentures to the payment of all Senior
Indebtedness of the Company that may at the time be outstanding, provided that
(i) such Senior Indebtedness is assumed by the new corporation, if any,
resulting from any such reorganization or readjustment, and (ii) the rights of
the holders of such Senior Indebtedness are not, without the consent of such
holders, altered by such reorganization or readjustment.  The consolidation of
the Company with, or the merger of the Company into, another corporation or
the liquidation or dissolution of the Company following the conveyance or
transfer of its property as an entirety, or substantially as an entirety, to
another corporation upon the terms and conditions provided for in Article X of
the Indenture shall not be deemed a dissolution, winding-up, liquidation or
reorganization for the purposes of this Section 6.3 if such other corporation
shall, as a part of such consolidation, merger, conveyance or transfer, comply
with the conditions stated in Article X of the Indenture.  Nothing in Section
6.2 or in this Section 6.3 shall apply to claims of, or payments to, the
Trustee under or pursuant to Section 7.06 of the Indenture.

          Section 6.4.  Subrogation.  Subject to the payment in full of all
Senior Indebtedness of the Company, the rights of the holders of the
Debentures shall be subrogated to the rights of the holders of such Senior
Indebtedness to receive payments or distributions of cash, property or
securities of the Company applicable to such Senior Indebtedness until the
principal of (and premium, if any) and interest on the Debentures shall be
paid in full; and, for the purposes of such subrogation, no payments or
distributions to the holders for such Senior Indebtedness of any cash,
property or securities to which the holders of the Debentures or the Trustee
would be entitled except for the provisions of this Article VI, and no payment
over pursuant to the provisions of this Article VI, to or for the benefit of
the holders of such Senior Indebtedness by holders of the Debentures or the
Trustee, shall, as between the Company, its

                                  -11-
<PAGE>
 
creditors other than holders of Senior Indebtedness of the Company, and
the holders of the Debentures be deemed to be a payment by the Company
to or on account of such Senior Indebtedness.  It is understood that the
provisions of this Article VI are and are intended solely for the
purposes of defining the relative rights of the holders of the
Debentures, on the one hand, and the holders of such Senior Indebtedness
on the other hand.

          Nothing contained in this Article VI or elsewhere in this Indenture
or in the Debentures is intended to or shall impair, as between the Company,
its creditors other than the holders of Senior Indebtedness of the Company,
and the holders of the Debentures, the obligation of the Company which is
absolute and unconditional, to pay to the holders of the Debentures the
principal of (and premium, if any) and interest on the Debentures as and when
the same shall become due and payable in accordance with their terms, or is
intended to or shall affect the relative rights of the holders of the
Debentures and creditors of the Company, other than the holders of Senior
Indebtedness of the Company, nor shall anything herein or therein prevent the
Trustee or the holder of any Debenture from exercising all remedies otherwise
permitted by applicable law upon default under the Indenture, subject to the
rights, if any, under this Article VI of the holders of such Senior
Indebtedness in respect of cash, property or securities of the Company,
received upon the exercise of any such remedy.

          Upon any payment or distribution of assets of the Company referred
to in this Article VI, the Trustee, subject to the provisions of Section 7.01
of the Indenture, and the holders of the Debentures, shall be entitled to rely
upon any order or decree made by any court of competent jurisdiction in which
such dissolution, winding-up, liquidation or reorganization proceedings are
pending, or a certificate of the receiver, trustee in bankruptcy, liquidation
trustee, agent or other Person making such payment or distribution, delivered
to the Trustee or to the holders of the Debentures, for the purposes of
ascertaining the Persons entitled to participate in such distribution, the
holders of Senior Indebtedness and other indebtedness of the Company, the
amount thereof or payable thereon, the amount or amounts paid or distributed
thereon and all other facts pertinent thereto or to this Article VI.

          Section 6.5.  Trustee to Effectuate Subordination.  Each holder of a
Debenture by such holder's acceptance thereof authorizes and directs the
Trustee on such holder's behalf to take such action as may be necessary or
appropriate to effectuate the subordination provided in this Article VI and
appoints the Trustee such holder's attorney-in-fact for any and all such
purposes.

          Section 6.6.  Notice by the Company.  The Company shall give prompt
written notice to a Responsible Officer of the Trustee of any fact known to
the Company that would prohibit the making of any payment of monies to or by
the Trustee in respect of the Debentures pursuant to the provisions of this
Article VI.  Notwithstanding the provisions of this Article VI or any other
provision of the Indenture and this Second Supplemental Indenture, the Trustee
shall not be charged with knowledge of the existence of any facts that would
prohibit the making of any payment of monies to or by the Trustee in respect
of the Debentures pursuant to the provisions of this Article VI unless and
until a Responsible Officer of the Trustee shall have received written notice
thereof at the Principal Office of the Trustee from the Company or a holder or
holders of Senior Indebtedness or from any trustee therefor; and before the
receipt of any such written notice, the Trustee, subject to the provisions of
Section 7.01 of the Indenture,

                                  -12-
<PAGE>
 
shall be entitled in all respects to assume that no such facts exist;
provided, however, that if the Trustee shall not have received the
notice provided for in this Section 6.6 at least two Business Days prior
to the date upon which by the terms hereof any money may become payable
for any purpose (including, without limitation, the payment of the
principal of (or premium, if any) or interest on any Debenture), then,
anything herein contained to the contrary notwithstanding, the Trustee
shall have full power and authority to receive such money and to apply
the same to the purposes for which they were received, and shall not be
affected by any notice to the contrary that may be received by it within
two Business Days prior to such date.

          The Trustee, subject to the provisions of Section 7.01 of the
Indenture, shall be entitled to rely on the delivery to it of a written notice
by a Person representing himself to be a holder of Senior Indebtedness of the
Company (or a trustee on behalf of such holder) to establish that such notice
has been given by a holder of such Senior Indebtedness or a trustee on behalf
of any such holder or holders.  In the event that the Trustee determines in
good faith that further evidence is required with respect to the right of any
Person as a holder of such Senior Indebtedness to participate in any payment
or distribution pursuant to this Article VI, the Trustee may request such
Person to furnish evidence to the reasonable satisfaction of the Trustee as to
the amount of such Senior Indebtedness held by such Person, the extent to
which such Person is entitled to participate in such payment or distribution
and any other facts pertinent to the rights of such Person under this Article
VI, and if such evidence is not furnished, the Trustee may defer any payment
to such Person pending judicial determination as to the right of such Person
to receive such payment.

          Section 6.7.  Rights of the Trustee; Holders of Senior
Indebtedness.  The Trustee in its individual capacity shall be entitled to all
the rights set forth in this Article VI in respect of any Senior Indebtedness
at any time held by it, to the same extent as any other holder of Senior
Indebtedness, and nothing in the Indenture or this Second Supplemental
Indenture shall deprive the Trustee of any of its rights as such holder.

          With respect to the holders of Senior Indebtedness of the Company,
the Trustee undertakes to perform or to observe only such of its covenants and
obligations as are specifically set forth in this Article VI, and no implied
covenants or obligations with respect to the holders of such Senior
Indebtedness shall be read into the  Indenture or this Second Supplemental
Indenture against the Trustee.  The Trustee shall not be deemed to owe any
fiduciary duty to the holders of such Senior Indebtedness and, subject to the
provisions of Section 7.01 of the Indenture, the Trustee shall not be liable
to any holder of such Senior Indebtedness if it shall pay over or deliver to
holders of Debentures, the Company or any other Person money or assets to
which any holder of such Senior Indebtedness shall be entitled by virtue of
this Article VI or otherwise.

          Section 6.8.  Subordination May Not Be Impaired.  No right of any
present or future holder of any Senior Indebtedness of the Company to enforce
subordination as herein provided shall at any time in any way be prejudiced or
impaired by any act or failure to act on the part of the Company or by any act
or failure to act, in good faith, by any such holder, or by any noncompliance
by the Company with the terms, provisions and covenants of the Indenture,
regardless of any knowledge thereof that any such holder may have or otherwise
be charged with.

                                  -13-
<PAGE>
 
          Without in any way limiting the generality of the foregoing
paragraph, the holders of Senior Indebtedness of the Company may, at any time
and from time to time, without the consent of or notice to the Trustee or the
holders of the Debentures, without incurring responsibility to the holders of
the Debentures and without impairing or releasing the subordination provided
in this Article VI or the obligations hereunder of the holders of the
Debentures to the holders of such Senior Indebtedness, do any one or more the
following: (i) change the manner, place or terms of payment or extend the time
of payment of, or renew or alter, such Senior Indebtedness, or otherwise amend
or supplement in any manner such Senior Indebtedness or any instrument
evidencing the same or any agreement under which such Senior Indebtedness is
outstanding; (ii) sell, exchange, release or otherwise deal with any property
pledged, mortgaged or otherwise securing such Senior Indebtedness; (iii)
release any Person liable in any manner for the collection of such Senior
Indebtedness; and (iv) exercise or refrain from exercising any rights against
the Company and any other Person.


                              ARTICLE VII
                           FORM OF DEBENTURE

          Section 7.1.  Form of Debenture.  The Debentures and the Trustee's
Certificate of Authentication to be endorsed thereon are to be substantially
in the following forms:

                      (FORM OF FACE OF DEBENTURE)

          [IF THE DEBENTURE IS TO BE A GLOBAL SECURITY, INSERT:  This
Debenture is a Global Security within the meaning of the Indenture hereinafter
referred to and is registered in the name of a Depository or a nominee of a
Depository.  This Debenture is exchangeable for Debentures registered in the
name of a person other than the Depository or its nominee only in the limited
circumstances described in the Indenture, and no transfer of this Debenture
(other than a transfer of this Debenture as a whole by the Depository to a
nominee of the Depository or by a nominee of the Depository to the Depository
or another nominee of the Depository) may be registered except in limited
circumstances.

          Unless this Debenture is presented by an authorized representative
of The Depository Trust Company (55 Water Street, New York, New York) to the
issuer or its agent for registration of transfer, exchange or payment, and any
Debenture issued is registered in the name of Cede & Co. or such other name as
requested by an authorized representative of The Depository Trust Company and
any payment hereon is made to Cede & Co., ANY TRANSFER, PLEDGE OR OTHER USE
HEREOF FOR VALUE OR OTHERWISE BY A PERSON IS WRONGFUL since the registered
owner hereof, Cede & Co., has an interest herein.]

                                  -14-
<PAGE>
 
No.                                             $

                                                CUSIP No.


                      COMMONWEALTH EDISON COMPANY

       8.50% SERIES A SUBORDINATED DEFERRABLE INTEREST DEBENTURE
                          DUE JANUARY 15, 2027


          COMMONWEALTH EDISON COMPANY, an Illinois corporation (the
"COMPANY", which term includes any successor corporation under the
Indenture hereinafter referred to), for value received, hereby promises
to pay to _______ or registered assigns, the principal sum of
____________  Dollars on January 15, 2027, and to pay interest on said
principal sum from January 24, 1997 or from the most recent interest
payment date (each such date, an "INTEREST PAYMENT DATE") to which
interest has been paid or duly provided for, semi-annually (subject to
deferral as set forth herein) in arrears on July 15 and January 15 of
each year commencing, July 15, 1997, at the rate of  8.50% per annum
until the principal hereof shall have become due and payable, and on any
overdue principal and premium, if any, and (without duplication and to
the extent that payment of such interest is enforceable under applicable
law) on any overdue installment of interest compounded semi-annually at
the same rate per annum. The amount of interest payable on any Interest
Payment Date shall be computed on the basis of a 360-day year consisting
of twelve 30-day months.  In the event that any date on which interest
is payable on this Debenture is not a Business Day, then payment of
interest payable on such date will be made on the next succeeding day
which is a Business Day (and without any interest or other payment in
respect of any such delay).  The interest installment so payable, and
punctually paid or duly provided for, on any Interest Payment Date will,
as provided in the Indenture, be paid to the person in whose name this
Debenture (or one or more Predecessor Securities, as defined in said
Indenture) is registered at the close of business on the first day of
the month in which such Interest Payment Date occurs.  Any such interest
installment not punctually paid or duly provided for shall forthwith
cease to be payable to the registered holders on such regular record
date, and may be paid to the person in whose name this Debenture (or one
or more Predecessor Securities) is registered at the close of business
on a special record date to be fixed by the Trustee for the payment of
such defaulted interest, notice whereof shall be given to the registered
holders of this series of Debentures not less than ten (10) days prior
to such special record date, or may be paid at any time in any other
lawful manner not inconsistent with the requirements of any securities
exchange on which the Debentures may be listed, and upon such notice as
may be required by such exchange, all as more fully provided in the
Indenture.  The principal of (and premium, if any) and the interest on
this Debenture shall be payable at the office or agency of the Trustee
maintained for that purpose in Wilmington, Delaware, in any coin or
currency of the United States of America which at the time of payment is
legal tender for payment of public and private debts; provided, however,
that payment of interest may be made at the option of the Company by
check mailed to the registered holder at such address as shall appear in
the Security Register. Notwithstanding the foregoing, so long as the
Holder of this Debenture is the Property Trustee, the payment of the
principal of (and premium, if any) and


                                  -15-
<PAGE>
 
interest on this Debenture will be made at such place and to such
account as may be designated by the Property Trustee.

          The indebtedness evidenced by this Debenture is, to the extent
provided in the Indenture, subordinate and junior in right of payment to the
prior payment in full of all Senior Indebtedness, and this Debenture is issued
subject to the provisions of the Indenture with respect thereto.  Each Holder
of this Debenture, by accepting the same, (a) agrees to and shall be bound by
such provisions, (b) authorizes and directs the Trustee on his behalf to take
such action as may be necessary or appropriate to acknowledge or effectuate
the subordination so provided and (c) appoints the Trustee his
attorney-in-fact for any and all such purposes.  Each Holder hereof, by his
acceptance hereof, hereby waives all notice of the acceptance of the
subordination provisions contained herein and in the Indenture by each holder
of Senior Indebtedness, whether now outstanding or hereafter incurred, and
waives reliance by each such Holder upon said provisions.

          This Debenture shall not be entitled to any benefit under the
Indenture hereinafter referred to, be valid or become obligatory for any
purpose until the Certificate of Authentication hereon shall have been signed
by or on behalf of the Trustee.

          The provisions of this Debenture are continued on the reverse side
hereof and such continued provisions shall for all purposes have the same
effect as though fully set forth at this place.

           IN WITNESS WHEREOF, the Company has caused this instrument to be
executed.


Dated
                                   COMMONWEALTH EDISON COMPANY

                                   By

                                        [Title]

Attest:


By
     [Title]





                                  -16-
<PAGE>
 
                [FORM OF CERTIFICATE OF AUTHENTICATION]

                     CERTIFICATE OF AUTHENTICATION

     This is one of the Debentures of the series of Debentures described in
the within-mentioned Indenture.



          WILMINGTON TRUST COMPANY,            ______________________________
          Not in Its Individual Capacity But   as Authentication Agent
          Solely as Trustee

          By                               By
               Authorized Signatory                    Authorized Signatory



                     (FORM OF REVERSE OF DEBENTURE)

          This Debenture is one of a duly authorized series of Debt Securities
of the Company (herein sometimes referred to as the "DEBENTURES"), specified
in the Indenture, all issued or to be issued in one or more series under and
pursuant to an Indenture dated as of September 1, 1995, duly executed and
delivered between the Company and Wilmington Trust Company, not in its
individual capacity but solely as trustee (the "TRUSTEE"), as supplemented by
the First Supplemental Indenture dated as of September 19, 1995 between the
Company and the Trustee, and the Second Supplemental Indenture dated as of
January 24, 1997 between the Company and the Trustee (the Indenture as so
supplemented, the "INDENTURE"), to which Indenture and all indentures
supplemental thereto reference is hereby made for a description of the rights,
limitations of rights, obligations, duties and immunities thereunder of the
Trustee, the Company and the holders of the Debentures.  By the terms of the
Indenture, the Debt Securities are issuable in series which may vary as to
amount, date of maturity, rate of interest and in other respects as in the
Indenture provided.  This series of Debt Securities is limited in aggregate
principal amount as specified in said Second Supplemental Indenture.

          If  a Tax Event has occurred and is continuing, the Company shall
have the right to redeem this Debenture in whole (but not in part) at any time
prior to January 15, 2007 and within 90 days of the occurrence of such Tax
Event, at a redemption price (the "TAX EVENT REDEMPTION PRICE") equal to the
greater of (i) 100% of the principal amount of this Debenture or (ii) the sum,
as determined by a Quotation Agent, of the present values of the principal
amount and premium payable as part of the redemption price with respect to an
optional redemption of this Debenture on January 15, 2007, together with
scheduled payments of interest on this Debenture accruing from the redemption
date to and including January 15, 2007, in each case discounted to the
redemption date on a semi-annual basis (assuming a 360-day year consisting of
twelve 30-day months) at the Adjusted Treasury Rate, plus, in each case,
accrued interest thereon to the date of such redemption.  The Tax Event
Redemption Price shall be paid

                                  -17-
<PAGE>
 
prior to 12:00 noon, New York time, on the date of such redemption or at
such earlier time as the Company determines and specifies in the notice
of redemption.

           The Company shall have the right to redeem this Debenture, in whole
or in part, from time to time, at any time on or after January 15, 2007 (an
"OPTIONAL REDEMPTION"), at a redemption price (the "OPTIONAL REDEMPTION
PRICE") equal to the percentage of the principal amount of this Debenture
specified below, plus, in each case, accrued and unpaid interest thereon to
the date of such redemption if redeemed during the 12-month period beginning
January 15 of the years indicated below:

               YEAR               PERCENTAGE
               ----               ----------
               2007               104.250%
               2008               103.825
               2009               103.400
               2010               102.975
               2011               102.550
               2012               102.125
               2013               101.700
               2014               101.275
               2015               100.850
               2016               100.425
               2017 and thereafter     100.000

Any  redemption pursuant to this paragraph will be made upon not less than 30
days' nor more than 60 days' notice, at the Optional Redemption Price.  If the
Debentures are only partially redeemed by the Company pursuant to an Optional
Redemption, the Debentures will be redeemed pro rata or by lot or by any other
method utilized by the Trustee; provided that if at the time of redemption,
the Debentures are registered as a Global Security, the Depositary shall
determine by lot the principal amount of such Debentures held by each
Debenture holder to be redeemed.

          In the event of redemption of this Debenture in part only, a new
Debenture or Debentures of this series for the unredeemed portion hereof will
be issued in the name of the holder hereof upon the cancellation hereof.

          In case an Event of Default, as defined in the Indenture, shall have
occurred and be continuing, the principal of all of the Debentures may be
declared, and upon such declaration shall become, due and payable, in the
manner, with the effect and subject to the conditions provided in the
Indenture.

          The Indenture contains provisions permitting the Company and the
Trustee, with the consent of the holders of not less than a majority in
aggregate principal amount of the Debt Securities of each series affected at
the time outstanding, as defined in the Indenture, to execute supplemental
indentures for the purpose of adding any provisions to or changing in any
manner or eliminating any of the provisions of the Indenture or of any
supplemental indenture or of modifying in any manner the rights of the Holders
of such Debt Securities; provided, however,

                                  -18-
<PAGE>
 
that no such supplemental indenture shall (i) extend the fixed maturity
of this Debenture, or reduce the principal amount hereof, or reduce the
rate or extend the time of payment of interest hereon, or reduce any
premium payable upon the redemption hereof, without the consent of the
Holder hereof or (ii) reduce the aforesaid percentage of Debt
Securities, the Holders of which are required to consent to any such
supplemental indenture, without the consent of the Holders of each Debt
Security then outstanding and affected thereby.  The Indenture also
contains provisions permitting the Holders of a majority in aggregate
principal amount of the Debt Securities of any series at the time
outstanding affected thereby, on behalf of all of the Holders of the
Debt Securities of such series, to waive any past default in the
performance of any of the covenants contained in the Indenture, or
established pursuant to the Indenture with respect to such series, and
its consequences, except a default in the payment of the principal of or
premium, if any, or interest on any of the Debt Securities of such
series.  Any such consent or waiver by the registered Holder of this
Debenture (unless revoked as provided in the Indenture) shall be
conclusive and binding upon such Holder and upon all future Holders and
owners of this Debenture and of any Debenture issued in exchange
therefor or in place hereof (whether by registration of transfer or
otherwise), irrespective of whether or not any notation of such consent
or waiver is made upon this Debenture.

          No reference herein to the Indenture and no provision of this
Debenture or of the Indenture shall alter or impair the obligation of the
Company, which is absolute and unconditional, to pay the principal of and
premium, if any, and interest on this Debenture at the time and place and at
the rate and in the money herein prescribed.

          The Company shall have the right, at any time and from time to time
during the term of the Debentures, to extend the interest payment period of
the Debentures (including this Debenture) for up to ten (10) consecutive
semi-annual periods (an "EXTENDED INTEREST PAYMENT PERIOD"), at the end of
which period the Company shall pay all interest then accrued and unpaid
(together with interest thereon at the rate specified for the Debentures to
the extent that payment of such interest is enforceable under applicable
law).  Before the termination of any such Extended Interest Payment Period,
the Company may further extend such Extended Interest Payment Period, provided
that such Extended Interest Payment Period together with all such further
extensions thereof shall not exceed ten (10) consecutive semi-annual periods
or extend beyond the Maturity Date of the Debentures.  At the termination of
any such Extended Interest Payment Period and upon the payment of all Deferred
Interest then due, the Company may select a new Extended Interest Payment
Period, subject to the foregoing requirements.

          As provided in the Indenture and subject to certain limitations
therein set forth, this Debenture is transferable by the registered holder
hereof on the Security Register of the Company, upon surrender of this
Debenture for registration of transfer at the office or agency of the Trustee
in Wilmington, Delaware accompanied by a written instrument or instruments of
transfer in form satisfactory to the Company or the Trustee duly executed by
the registered holder hereof or his attorney duly authorized in writing, and
thereupon one or more new Debentures of authorized denominations and for the
same aggregate principal amount and series will be issued to the designated
transferee or transferees.  No service charge will be made for any such
transfer, but the Company may require payment of a sum sufficient to cover any
tax or other governmental charge payable in relation thereto.

                                  -19-
<PAGE>
 
          Prior to due presentment for registration of transfer of this
Debenture, the Company, the Trustee, any paying agent and any Security
Registrar may deem and treat the registered holder hereof as the absolute
owner hereof (whether or not this Debenture shall be overdue and notwithstanding
 any notice of ownership or writing hereon made by anyone other than the
Security Registrar) for the purpose of receiving payment of or on account of
the principal hereof and premium, if any, and interest due hereon and for all
other purposes, and neither the Company nor the Trustee nor any paying agent
nor any Security Registrar shall be affected by any notice to the contrary.

          No recourse shall be had for the payment of the principal of,
premium (if any) or the interest on this Debenture, or for any claim based
hereon, or otherwise in respect hereof, or based on or in respect of the
Indenture, against any incorporator, stockholder, officer or director, past,
present or future, as such, of the Company or of any predecessor or successor
corporation, whether by virtue of any constitution, statute or rule of law, or
by the enforcement of any assessment or penalty or otherwise, all such
liability being, by the acceptance hereof and as part of the consideration for
the issuance hereof, expressly waived and released.

          [The Debentures of this series are issuable only in registered form
without coupons in denominations of $[1,000] and any integral multiple
thereof.] [This Global Security is exchangeable for Debentures in definitive
form only under certain limited circumstances set forth in the Indenture.
Debentures of this series so issued are issuable only in registered form
without coupons in denominations of $[1,000] and any integral multiple
thereof.] As provided in the Indenture and subject to certain limitations
[herein and] therein set forth, Debentures of this series [so issued] are
exchangeable for a like aggregate principal amount of Debentures of this
series of a different authorized denomination, as requested by the Holder
surrendering the same.

          All terms used in this Debenture which are defined in the Indenture
shall have the meanings assigned to them in the Indenture.

          THE INTERNAL LAWS OF THE STATE OF NEW YORK SHALL GOVERN THE
INDENTURE AND THE DEBENTURES WITHOUT REGARD TO CONFLICT OF LAW PROVISIONS
THEREOF.

                              ARTICLE VIII
                 ORIGINAL ISSUE OF DEBENTURES; EXCHANGE

          Section 8.1.  Original Issue of Debentures.  Debentures in the
aggregate principal amount of $154,640,000 may, upon execution of this Second
Supplemental Indenture, be executed by the Company and delivered to the
Trustee for authentication, and the Trustee shall thereupon authenticate and
deliver said Debentures to or upon the written order of the Company, signed by
its Chairman, its President or any Vice President and its Treasurer or an
Assistant Treasurer, without any further action by the Company.

          Section 8.2  Exchange of Debentures for Series B Debentures.  The
Debentures may be exchanged for Series B Debentures pursuant to the terms of
the Exchange Offer.  The Trustee shall make the exchange as follows:

                                  -20-
<PAGE>
 
          The Company shall present the Trustee with an Officers' Certificate
certifying the following:

          (a)   upon issuance of the Series B Debentures, the
                transactions contemplated by the Exchange Offer have
                been consummated; and

          (b)   the principal amount of Debentures properly tendered in
                the Exchange Offer that are represented by a Global
                Security and the principal amount of Debentures properly
                tendered in the Exchange Offer that are represented by
                definitive securities, the name of each holder of such
                definitive securities, the principal amount properly
                tendered in the Exchange Offer by each such holder and
                the name and address to which definitive securities for
                Series B Debentures shall be registered and sent for
                each such holder.

          The Trustee, upon receipt of (i) such Officers' Certificate, (ii) an
Opinion of Counsel (x) to the effect that the Series B Debentures have been
registered under Section 5 of the Securities Act and the Indenture has been
qualified under the Trust Indenture Act and (y) with respect to the matters
set forth in Section 3(o) of the Registration Rights Agreement and (iii) a
Company Order, shall authenticate (A) a Global Security for Series B
Debentures in aggregate principal amount equal to the aggregate principal
amount of Debentures represented by a Global Security indicated in such
Officers' Certificate as having been properly tendered and (B) definitive
securities representing Series B Debentures registered in the names of, and in
the principal amounts indicated in, such Officers' Certificate.

          If the principal amount of the Global Security for the Series B
Debentures is less than the principal amount of the Global Security for the
Debentures, the Trustee shall make an endorsement on such Global Security for
Debentures indicating a reduction in the principal amount represented thereby.

          The Trustee shall deliver such definitive securities for Series B
Debentures to the holders thereof as indicated in such Officers' Certificate.


                               ARTICLE IX
                             MISCELLANEOUS

          Section 9.1.  Ratification of Indenture.  The Indenture, as
supplemented by the First Supplemental Indenture and this Second Supplemental
Indenture, is in all respects ratified and confirmed, and this Second
Supplemental Indenture shall be deemed part of the Indenture in the manner and
to the extent herein and therein provided.

          Section 9.2.  Trustee Not Responsible for Recitals.  The recitals
herein contained are made by the Company and not by the Trustee, and the
Trustee assumes no responsibility for the correctness thereof.  The Trustee
makes no representation as to the validity or sufficiency of this Second
Supplemental Indenture.

                                  -21-
<PAGE>
 
          Section 9.3.  Governing Law.  This Second Supplemental Indenture and
each Debenture shall be deemed to be a contract made under the internal laws
of the State of New York, and for all purposes shall be construed in
accordance with the laws of said State.

          Section 9.4.  Separability.  In case any one or more of the
provisions contained in this Second Supplemental Indenture or in the
Debentures shall for any reason be held to be invalid, illegal or
unenforceable in any respect, such invalidity, illegality or unenforceability
shall not affect any other provisions of this Second Supplemental Indenture or
of the Debentures, but this Second Supplemental Indenture and the Debentures
shall be construed as if such invalid or illegal or unenforceable provision
had never been contained herein or therein.

          Section 9.5.  Counterparts.  This Second Supplemental Indenture may
be executed in any number of counterparts each of which shall be an original;
but such counterparts shall together constitute but one and the same
instrument.

                                  -22-
<PAGE>
 
          IN WITNESS WHEREOF, the parties hereto have caused this Second
Supplemental Indenture to be duly executed, and their respective corporate
seals to be hereunto affixed and attested, on the date or dates indicated in
the acknowledgments and as of the day and year first above written.

                         COMMONWEALTH EDISON COMPANY


                         By:
                              Vice President


[Corporate Seal]

Attest:


     Secretary


                         WILMINGTON TRUST COMPANY,
                         Not in Its Individual Capacity
                         But Solely as Trustee


                         By:
                              Title:


[Corporate Seal]

Attest:


     Title:
<PAGE>
 
STATE OF ILLINOIS   )
COUNTY OF COOK      ) ss:


          On the 24th day of January, 1997, before me personally came John C.
Bukovski, to me known, who, being by me duly sworn, did depose and say that
he is a Vice President of COMMONWEALTH EDISON COMPANY, one of the corporations
described in and which executed the above instrument; that he knows the
corporate seal of said corporation; that the seal affixed to the said
instrument is such corporate seal; that it was so affixed by authority of the
Board of Directors of said corporation, and that he signed his name thereto by
like authority.



                         NOTARY PUBLIC


[seal]                   Commission expires






STATE OF DELAWARE    )
COUNTY OF NEW CASTLE ):


          On the ________ day of January, 1997, before me personally came W.
Chris Sponenberg, to me known, who, being by me duly sworn, did depose and say
that he is a Senior Financial Services Officer of WILMINGTON TRUST COMPANY,
one of the corporations described in and which executed the above instrument;
that he knows the corporate seal of said corporation; that the seal affixed to
the said instrument is such corporate seal; that it was so affixed by
authority of the Board of Directors of said corporation, and that he signed
his name thereto by like authority.



                         NOTARY PUBLIC


[seal]                   Commission expires