<PAGE>   1
                                                                  EXHIBIT 10.8.2

                      FIRST AMENDMENT TO CREDIT AGREEMENT

     This FIRST AMENDMENT TO CREDIT AGREEMENT (this "Amendment") is made and
entered into effective as of November 18, 1999, by and among TELERGY, INC. (the
"Borrower"), a New York corporation, each of the lending entities which is a
party hereto (as evidenced by the signature pages of this Agreement) or which
may from time to time become a party hereto as a lender or any successor or
assignee thereof (individually, a "Lender" and, collectively, the "Lenders"),
and NORTEL NETWORKS INC., a Delaware corporation formerly known as Northern
Telecom Inc., as administrative agent for itself and the other Lenders (in such
capacity, together with its successors in such capacity, the "Administrative
Agent").

                                   RECITALS:

     A.   Pursuant to that certain Credit Agreement dated as of February 26,
1999, by and among the Borrower, the Lenders, and the Administrative Agent
("Credit Agreement"), the Lenders agreed to provide to the Borrower a senior
secured credit facility in the maximum aggregate principal amount of
$45,000,000.

     B.   Pursuant to the request of the Borrower, the Administrative Agent and
the Lenders have agreed, subject to the terms and conditions of this Amendment,
to amend the Credit Agreement.

                                  AGREEMENTS:

     NOW, THEREFORE, in consideration of the premises and mutual covenants and
agreements contained herein and for other good and valuable consideration, the
receipt and sufficiency of which are hereby acknowledged, the parties hereto
hereby agree as follows:

     1.   Terms Defined. Unless otherwise defined or stated in this Amendment,
each capitalized term used in this Amendment has the meaning given to such term
in the Credit Agreement (as amended by this Amendment).

     2.   Amendments to Certain Definitions.

          (a)  The following terms and definitions thereof set forth in Section
     1.1 of the Credit Agreement is hereby amended and restated to read in their
     entirety as follows:

               "Tranche A Commitment Termination Date" means the earliest to
          occur of (a) the third anniversary of the Closing Date, (b) the
          initial date upon which the Tranche A Loans have become fully funded
          in an aggregate amount equal to the Tranche A Commitments (as such
          Commitments may be reduced or terminated pursuant to Section 2.13 or
          11.2), or (c) June 15, 2000, if (but only if) the aggregate principal
          amount of Tranche A Loans outstanding as of June 15, 2000 is less than
          $15,000,000.



FIRST AMENDMENT TO CREDIT AGREEMENT - Page 1

<PAGE>   2
               "TRANCHE B MATURITY DATE" means November 22, 1999.

     3.  AMENDMENT TO SCHEDULE 10. Schedule 10 to the Credit Agreement is
hereby amended and restated to read in it entirety as set forth on Exhibit A
hereto.

     4.  CONDITIONS PRECEDENT. The effectiveness of this Amendment is subject
to the satisfaction of each of the following conditions precedent, all of which
conditions precedent must be satisfied on or before November 22, 1999:

       (a)  The Administrative Agent shall have received all of the following,
     each dated (where applicable and unless otherwise indicated) the date of
     this Amendment, in form and substance satisfactory to the Administrative
     Agent:

            (i)  AMENDMENT DOCUMENTS. This Amendment as executed by the parties
       hereto;

           (ii)  RESOLUTIONS. Resolutions of the Board of Directors of the
        Borrower and the other Loan Parties certified by its Secretary or an
        Assistant Secretary which authorize the execution, delivery and
        performance by the Borrower and the other Loan Parties of this Amendment
        and the other Amendment Documents to which the Borrower or such Loan
        Party is or is to be a party;

          (iii)  REPAYMENT OF TRANCHE B LOAN. The Tranche B Loan shall have been
        repaid in full with in two business days of Agent's execution hereof;
        and

           iv)  FEES, COSTS AND EXPENSES. All fees, costs and expenses
        (including, without limitation, attorneys' fees and expenses) incurred
        by the Administrative Agent, incident to this Amendment or required to
        be paid in accordance with Section 13.1 of the Credit Agreement, to the
        extent incurred and submitted to the Borrower, shall have been paid in
        full by the Borrower.


       (b) The representations and warranties contained herein and in all other
  Loan Documents, as amended hereby, shall be true and correct as of the date
  hereof as if made again on and as of the date hereof (except if and to the
  extent that such representations and warranties are or were expressly made
  only as of another specific date); and

       (c) No Default or Event of Default shall have occurred and be
   continuing.


     5.  REPRESENTATIONS AND WARRANTIES.  Each of the Borrower and the other
Loan Parties hereby jointly and severally represent and warrant to, and agrees
with, the Agent and the Lenders that, as of the date of and after giving effect
to this Amendment (a) the execution, delivery and performance of this Amendment
and any and all other Amendment Documents executed and/or delivered in
connection herewith have been authorized by all requisite corporate action on
the part


PAST AMENDMENT TO CREDIT AGREEMENT - Page 2
<PAGE>   3
of the Borrower and the other Loan Parties and will not violate the Borrower's
or any Loan Party's corporate charter or bylaws; (b) the term Loan Documents as
defined in the Credit Agreement and as used in any of the Loan Documents
includes, without limitation, the Amendment Documents; (c) all representations
and warranties set forth in the Credit Agreement and in the Security Documents
are true and correct as if made again on and as of such date (except if and to
the extent that such representations and warranties were expressly made only as
of another specific date); (d) no Default or Event of Default has occurred and
is continuing; (e) the Loan Parties do not have any unasserted right of setoff,
counterclaim or deduction to the Obligations owning pursuant to the Loan
Documents; and (f) the Credit Agreement, the Notes, the Guaranties, the
Security Documents and the other Loan Documents (as amended by this Amendment)
are and remain legal, valid, binding and enforceable obligations of the
Borrower and the other Loan Parties (as applicable) which are parties thereto
in accordance with their terms, except as limited by bankruptcy, insolvency or
other laws of general application relating to the enforcement of creditors'
rights and general principles of equity.

     6. Governing Law. THIS AMENDMENT AND THE OTHER LOAN DOCUMENTS SHALL BE
GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF NEW
YORK (WITHOUT REGARD TO CONFLICTS OF LAWS PRINCIPLES) AND APPLICABLE LAWS OF
THE U.S.

     7. Counterparts. This Amendment may be executed in any number of
counterparts, all of which when taken together shall constitute one agreement,
and any of the parties hereto may execute this Amendment by signing any such
counterpart.

     8. No Oral Agreements. THIS AMENDMENT, TOGETHER WITH THE CREDIT AGREEMENT
AND THE OTHER LOAN DOCUMENTS AS WRITTEN, REPRESENT THE FINAL AGREEMENTS BETWEEN
AND AMONG THE PARTIES HERETO AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,
CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES. THERE ARE NO
UNWRITTEN ORAL AGREEMENTS BETWEEN (A) THE BORROWER OR ANY OTHER LOAN PARTY AND
(B) THE ADMINISTRATIVE AGENT OR ANY LENDER.


FIRST AMENDMENT TO CREDIT AGREEMENT -- Page 3
<PAGE>   4
     9.   Agreement Remains in Effect: No Waiver. Except as expressly provided
herein, all terms and provisions of the Credit Agreement and the other the Loan
Documents shall remain unchanged and in full force and effect and are hereby
ratified and confirmed. No waiver by the Administrative Agent or any Lender of
any Default or Event of Default shall be deemed to be a waiver of any other
Default or Event of Default. No delay or omission by the Administrative Agent or
any Lender in exercising any power, right or remedy shall impair such power,
right or remedy or be construed as a waiver thereof or an acquiescence therein,
and no single or partial exercise of any such power, right or remedy shall
preclude other or further exercise thereof or the exercise of any other power,
right or remedy under the Agreement, the Loan Documents or otherwise.


     10.  Survival of Representations and Warranties.  All representations and
warranties made in this Amendment or any other Loan Document shall survive the
execution and delivery of this Amendment and the other Loan Documents, and no
investigation by the Administrative Agent or any Lender or any closing shall
affect the representations and warranties or the right of the Administrative
Agent and the Lenders to rely upon such representations and warranties.


     11.  Reference to Credit Agreement. This Amendment shall constitute a Loan
Document. Each of the Loan Documents, including the Credit Agreement, the
Amendment Documents and any and all other agreements, documents or instruments
now or hereafter executed and/or delivered pursuant to the terms hereof or
pursuant to the terms of the Credit Agreement as amended hereby, are (if and to
the extent necessary) hereby amended so that any reference in such Loan
Documents to the Credit Agreement shall mean a reference to the Credit
Agreement as amended hereby.


     12.  Severability.  Any provision of this Amendment held by a court of
competent jurisdiction to be invalid or unenforceable shall not impair or
invalidate the remainder of this Amendment and the effect thereof shall be
confined to the provision so held to be invalid or unenforceable.


     13.  Successors and Assigns.  This Amendment is binding upon and shall
inure to the benefit of the Agent, the Lenders, the Borrower and the other Loan
Parties and their respective successors and assigns; provided, however, that
neither the Borrower nor any of the other Loan Parties may assign or transfer
any of its rights or obligations hereunder without the prior written consent of
the Lenders.


     14.  Headings. The headings, captions and arrangements used in this
Amendment are for convenience only and shall not affect the interpretation of
this Amendment.



PROXY AMENDMENT TO CREDIT AGREEMENT - Page 4
<PAGE>   5
     IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed and delivered by their duly authorized officers effective as of the day
and year first above written.



                                 BORROWER:

                                 TELERGY, INC.


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


                                 ADMINISTRATIVE AGENT:
                                 NORTEL NETWORKS INC., formerly known as
                                 Northern Telecom Inc., as Administrative Agent


                                 By:
                                     ------------------------------------------
                                     Vice President, Customer Finance


                                 LENDERS:

                                 NORTEL NETWORKS INC.


                                 By:
                                     ------------------------------------------
                                     Vice President, Customer Finance






FIRST AMENDMENT TO CREDIT AGREEMENT - Page 5