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                                                                  EXHIBIT 10.8.3


                      SECOND AMENDMENT TO CREDIT AGREEMENT

      This SECOND AMENDMENT TO CREDIT AGREEMENT (this "Amendment") is made and
entered into effective as of December 31, 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, 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, as
amended by that certain First Amendment to Credit Agreement dated effective as
of November 18, 1999, and as the same may be further amended from time to time
(the "Credit Agreement"), the Lenders agreed to provide to the Borrower a senior
secured credit facility.

      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. Amendment to Section 2.5. Section 2.5 to the Credit Agreement is hereby
amended and restated to read in its entirety as follows:

            Section 2.5 Borrowing Procedure.

            (a) Standard Procedure. The Borrower shall give the Administrative
      Agent notice of each borrowing hereunder in accordance with Section 2.9.
      Not later than 12:00 noon (New York, New York time) on the date specified
      for each borrowing hereunder, each Lender will make available the amount
      of the Loan to be made by it on such date to the Administrative Agent, at
      the Principal Office, in immediately available funds, for the account of
      the Borrower. The amount of each borrowing hereunder so received by the
      Administrative Agent shall, subject to the terms and conditions of this
      Agreement, be made available, for and on behalf of the
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      Borrower, in immediately available funds by no later than 2:00 p.m. (New
      York, New York time); provided, however, that the Administrative Agent
      may, in its discretion, cause such amount to be made available directly to
      or for the benefit of the Person who is to receive the proceeds of such
      Loan in accordance with Section 2.10. Notwithstanding anything to the
      contrary contained in this Agreement, if and to the extent that Nortel
      Networks is a Tranche A Lender under this Agreement, the Borrower further
      hereby irrevocably agrees that each Tranche A Loan to be advanced by
      Nortel Networks to the Borrower in accordance with this Agreement (and
      only in accordance with this Agreement and after the Administrative
      Agent's receipt of a Notice of Borrowing executed by the Borrower) may (in
      the discretion of Nortel Networks and if and to the extent that the
      proceeds of such Loan are to be paid to Nortel Networks) be effectively
      disbursed on the date set forth in the Notice of Borrowing for such
      disbursement to the Borrower by virtue of a credit in the amount of such
      Loan given to the Guarantor under the Supply Agreement.

            (b) Automatic Advancement of Loans. Notwithstanding anything to the
      contrary contained in this Agreement, the Administrative Agent shall, at
      the request of Nortel Networks so long as it is the only Lender hereunder,
      cause Loans to be advanced by the Lenders for and on behalf of the
      Borrower whether or not (i) any Notice of Borrowing is given in accordance
      with Section 2.9, (ii) any of the conditions precedent set forth in
      Article 6 hereof are satisfied, (iii) any Default exists, or (iv) any
      other fact or circumstance exists, if Nortel Networks shall have given
      five Business Day's prior written notice to the Administrative Agent and
      the Borrower of Nortel Networks' desire to cause the Lenders to make such
      Loans and all proceeds of such Loans are used to pay the purchase price
      for Nortel Networks Goods and Services which has not been disputed and
      which has not been paid when due. All Loans advanced pursuant to this
      Section 2.5(b) shall be initially advanced as Eurodollar Loans with a one
      month Interest Period (unless the Borrower has requested in writing, at
      least three Business Days prior to such advance, that any of such Loans
      have an Interest Period with a different duration in accordance with the
      requirements of this Agreement) or, if the maximum number of Interest
      Periods for Eurodollar Loans is already then in effect, as Base Rate
      Loans, and shall be advanced as Tranche A Loans (but after such
      advancement, may be Converted or Continued in accordance with this
      Agreement).

      3. Amendment to Schedule 10. Schedule 10 to the Credit Agreement is hereby
amended and restated to read in its 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 May 5, 2000:


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            (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 and any other agreement, document, instrument or
            certificate reasonably required by the Administrative Agent or the
            Lenders to be executed or delivered by the Borrower or any other
            Loan Party in connection with this Amendment;

                  (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) 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; and

                  (iv) Additional Information. The Administrative Agent shall
            have received such additional agreements, documents, instruments and
            information as the Administrative Agent or its legal counsel,
            Jenkens & Gilchrist, a Professional Corporation, may reasonably
            request to effect the transactions contemplated hereby.

            (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);

            (c) All corporate proceedings taken in connection with this
      Amendment and the other Amendment Documents, and all legal matters
      incident thereto, shall be reasonably satisfactory to the Administrative
      Agent and its legal counsel, Jenkens & Gilchrist, a Professional
      Corporation; and

            (d) No Default or Event of Default shall have occurred and be
      continuing (after giving effect to this Amendment).

      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 Administrative 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


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action on the part 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.

      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.

      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


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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 Administrative 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.


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      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 AND LENDER:
                                    NORTEL NETWORKS INC., as Administrative
                                    Agent and the sole Lender



                                    By: /s/ Mitchell L. Stone
                                        --------------------------------------
                                    Name:  Mitchell L. Stone
                                          ------------------------------------
                                    Title: Director
                                          ------------------------------------


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