<PAGE>   1
                                                                    EXHIBIT 10.1


                            FIFTH AMENDMENT TO SECOND
                    AMENDED AND RESTATED FINANCING AGREEMENT

         THIS FIFTH AMENDMENT TO SECOND AMENDED AND RESTATED FINANCING AGREEMENT
(the "Amendment" ") dated as of May 10, 1999, is by and among ENCORE WIRE
CORPORATION, a Delaware corporation ("Borrower"), NATIONSBANK, N.A., dba BANK OF
AMERICA, NATIONAL ASSOCIATION (successor by merger to NationsBank of Texas,
N.A.), a national banking association, and COMERICA BANK-TEXAS (Comerica Bank"),
a state banking association, in their individual capacities as "Lenders" (as
such term is defined herein), and NATIONSBANK, N.A., dba BANK OF AMERICA,
NATIONAL ASSOCIATION (successor by merger to NationsBank of Texas, N.A.), a
national banking association, as agent for itself and the other Lenders (in such
capacity, together with its successors in such capacity, the "Agent").

                              W I T N E S S E T H:

         WHEREAS, the Borrower, the Agent, and the Lenders are parties to the
Second Amended and Restated Financing Agreement, dated as of June 9, 1997, as
amended by the First Amendment to Second Amended and Restated Financing
Agreement, dated as of February 20, 1998 (the "First Amendment"), by the
Second Amendment to Second Amended and Restated Financing Agreement, dated as of
June 15, 1998 (the "Second Amendment"), by the Third Amendment to Second
Amended and Restated Financing Agreement, dated as of August 28, 1998 (the
"Third Amendment") and by the Fourth Amendment to Second Amended and Restated
Financing Agreement, dated as of October 28, 1998 (the "Fourth Amendment") (as
so amended, the "Original Financing Agreement") relating to a $65,000,000
revolving credit facility ("Facility"), pursuant to which, inter alia, the
Lenders agreed to make certain loans available to the Borrower upon the terms
and conditions contained in the Original Financing Agreement;

         WHEREAS, the parties hereto desire to amend the Original Financing
Agreement in accordance with the terms and provisions of this Amendment;

         NOW, THEREFORE, for and in consideration of these premises and other
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the Borrower, the Agent and the Lenders hereby agree as follows:

         1. Terms. All capitalized terms defined in the Original Financing
Agreement and not otherwise defined herein shall have the same definitions when
used herein as set forth in the Original Financing Agreement as amended by this
Fifth Amendment.

         2. Amendment of Section 7.26. Section 7.26 of the Original Financing
Agreement is amended by deleting Section 7.26 in its entirety and replacing it
with the following:

         7.26 Limitation on Indebtedness. Borrower will not be obligated,
         directly or indirectly, for borrowed money or otherwise under any
         promissory note, bond, indenture or similar instrument, other than (a)
         in favor of Agent and the Lenders hereunder, (b) trade indebtedness
         incurred in the normal and ordinary course of Borrower's business and
         not more than ninety (90) days past due, and (c) (i) other indebtedness
         of Borrower, provided

<PAGE>   2

         that the payments required in respect of such indebtedness do not
         exceed $2,100,000.00 in the aggregate during any 12-month period and
         the Agent gives its consent to such other indebtedness, which shall not
         be unreasonably withheld.

         3. Amendment of Section 7.31. Section 7.31 of the Original Financing
Agreement is amended by deleting Section 7.31 in its entirety and replacing it
with the following:

         7.31 Redemptions and Acquisition of Shares. Borrower will not make any
         payment on account of the purchase, redemption or other acquisition or
         retirement of any shares of capital stock, provided, that
         notwithstanding the foregoing, for so long as no Event of Default shall
         have occurred and be continuing, and no other event or condition which
         is reasonably expected to result in a Material Adverse Effect or would
         be the subject of a required notice under paragraph 7.13 is in
         existence, Borrower shall not be prohibited from repurchasing shares to
         be held as treasury shares, provided further that (i) the aggregate
         number of such shares purchased after May 1, 1999, shall not exceed
         1,635,000 and the aggregate purchase price paid by Borrower for all
         such shares shall not exceed the maximum amount of $23,700,000.00, and
         (ii) no Event of Default shall result from, or exist immediately
         following, any such repurchase.

         4. Costs. The Borrower shall pay all reasonable out-of-pocket costs and
expenses incurred by the Agent or any Lender in connection with the negotiation,
preparation, execution and consummation of this Amendment and the transactions
contemplated by this Amendment, including, without limitation, the reasonable
fees and expenses of counsel to the Agent and the Lenders.

         5.   Miscellaneous.

         5.1 Headings. Section headings are for reference only and shall not
affect the interpretation or meanings of any provision of this Amendment.

         5.2 Effect of this Amendment. The Original Financing Agreement, as
amended by this Amendment, shall remain in full force and effect except that any
reference therein, or in any other Loan Document referring to the Original
Financing Agreement, shall be deemed to refer to the Original Financing
Agreement as amended by this Amendment.

         5.3 GOVERNING LAW. THIS AMENDMENT SHALL BE GOVERNED BY, AND CONSTRUED
IN ACCORDANCE WITH, THE LAWS OF THE STATE OF TEXAS AND APPLICABLE FEDERAL LAW.

         5.4 Counterparts. This Amendment may be executed by the different
parties hereto on separate counterparts, each of which, when so executed, shall
be deemed an original but all such counterparts shall constitute but one and the
same Amendment.

         5.5 NO ORAL AGREEMENTS. THE Original Financing Agreement, AS AMENDED BY
THIS AMENDMENT, TOGETHER WITH THE OTHER LOAN DOCUMENTS, REPRESENTS THE ENTIRE
AGREEMENT AMONG THE PARTIES AND MAY NOT BE


                                        2
<PAGE>   3

CONTRADICTED BY EVIDENCE OF PRIOR CONTEMPORANEOUS, OR SUBSEQUENT ORAL
AGREEMENTS OF THE PARTIES. THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN OR
AMONG THE PARTIES.


                      REST OF PAGE INTENTIONALLY LEFT BLANK


                                       3
<PAGE>   4

         IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
executed by their respective duly authorized officers as of the date first above
written.

BORROWER:

ENCORE WIRE CORPORATION

By: /s/ SCOTT WEAVER
    -----------------------------------
    Scott Weaver, Vice President

LENDERS AND AGENT:

NATIONSBANK, N.A.,
dba BANK OF AMERICA,
NATIONAL ASSOCIATION,
Individually and as Agent

By:
    -----------------------------------
    Todd M. Bums, Vice President

COMERICA BANK-TEXAS

By:
    -----------------------------------
    William J. Rolley, Vice President


                                       4
<PAGE>   5

                            CONFIRMATION OF GUARANTY

         EWC Leasing Corp. ("Guarantor"), a wholly-owned subsidiary of Encore
Wire Corporation, hereby acknowledges the matters covered by the Fifth Amendment
to Second Amended and Restated Financing Agreement to which this Confirmation of
Guaranty is attached and confirms that, notwithstanding such matters, the
Guaranty By Corporation dated as of June 9, 1997 issued by Guarantor to and in
favor of NationsBank of Texas, N.A., (and now in favor of NationsBank, N.A., dba
Bank of America, National Association as a result of the merger of NationsBank
of Texas, N.A. with and into NationsBank, N.A.) and the Guaranty By Corporation
dated as of June 9, 1997 issued by Guarantor to and in favor of Bank of America,
Texas, N.A., assigned to Comerica Bank, National Association, remain in full
force and effect as continuing obligations of Guarantor, enforceable against
Guarantor in accordance with their respective terms.

         In Witness Whereof, this Confirmation of Guaranty is executed and
delivered as of the ___ day of May, 1999.

                                  EWC LEASING CORP.

                                  By: /s/ SCOTT D. WEAVER
                                      ------------------------------
                                      Scott D. Weaver
                                      Vice President


                                       5