Document:

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                                                                   EXHIBIT 10.51

                             THIRD AMENDMENT TO THE
                           BELDEN WIRE & CABLE COMPANY
                  SUPPLEMENTAL EXCESS DEFINED CONTRIBUTION PLAN

WHEREAS, Belden Wire & Cable Company (hereinafter referred to as the "Company")
established the Belden Wire & Cable Company Supplemental Excess Defined
Contribution Plan (as amended from time to time, hereinafter referred to as the
"Plan") restated as of January 1, 1998, for the benefit of certain employees of
the Employer;

WHEREAS, Section 9.1 of Article IX of the Plan provides for the Company's
amending the Plan; and

WHEREAS, the Company deems it desirable to make certain amendments to the Plan
effective immediately before the Effective Time, as defined in the Agreement and
Plan of Merger by and among Cable Design Technologies Corporation, BC Merger
Corp. and Belden Inc. dated as of February 4, 2004, as amended;

NOW, THEREFORE, the Plan is amended effective immediately before the Effective
Time as follows:

1. The following definition is added in Article II as Section 2.1 (with the
remaining definitions to be renumbered accordingly):

"2.1  'BELDEN CDT' means Belden CDT Inc., a Delaware corporation."

2. The definition of "CHANGE OF CONTROL" in Article II is amended by (a)
changing each reference to "the Company" therein to a reference to "Belden CDT",
and (b) adding to the end thereof the following sentence: "For the avoidance of
doubt, the consummation of the transactions contemplated by the Agreement and
Plan of Merger by and among Cable Design Technologies Corporation, BC Merger
Corp. and Belden Inc. dated as of February 4, 2004, as amended, shall not
constitute a 'Change of Control' under the Plan."

3. The definition of "DEFERRAL PLAN" in Article II is deleted and replaced with
the following: "'DEFERRAL PLAN' means the Belden Inc. Deferred Compensation
Plan, as amended from time to time."

4. The definition of "PLAN" in Article II is amended by adding the words ", as
amended from time to time" to the end thereof.

5. The definition of "PLAN ADMINISTRATOR" is amended by changing the reference
to "Article VII" therein to a reference to "Article X".

                                       1
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6. The definition of "SAVINGS PLAN" in Article II is amended by adding the words
", as amended from time to time" to the end thereof.

7. The definition of "TRUST" in Article II is deleted and replaced with the
following:

"2.21 'TRUST' means the Trust Agreement Establishing the Trust by and between
Belden Wire & Cable Company (For the Supplemental Excess Defined Contribution
Plan) and CG Trust Company, now Prudential Bank & Trust, F.S.B., effective
January 1, 2001, as amended from time to time, and any successor agreement
thereto. Such Trust constitutes an unfunded arrangement and will not affect the
status of the Plan as an unfunded plan for purposes of Title I of ERISA."

8. Capitalized terms used herein, unless otherwise defined herein, have the
meaning ascribed to such terms in the Plan. Except as expressly provided herein
all provisions of the Plan shall remain in full force and effect.

         IN WITNESS WHEREOF, Belden Wire & Cable Company, by its duly authorized
officer, executes this amendment as of the 14th day of July, 2004.

                                            BELDEN WIRE & CABLE COMPANY

                                            By:  /s/ Cathy O. Staples
                                                 --------------------

                                            Its: Vice President, Human Resources
                                                 -------------------------------

Attest: /s/ Eivind J. Kolemainen
        ------------------------
         Eivind J. Kolemainen

                                       2<PAGE>
                                                                   EXHIBIT 10.52

                                 TRUST AGREEMENT

                                  Establishing

                                       THE

                                      TRUST

                                 BY AND BETWEEN

                           BELDEN WIRE & CABLE COMPANY

               (FOR THE SUPPLEMENTAL EXCESS DEFINED BENEFIT PLAN)

                                       and

                                CG TRUST COMPANY

<PAGE>

                                TABLE OF CONTENTS

<Table>
<Caption>

                                                                   PAGE
                                                                   ----
<S>           <C>                                                  <C>
Section 1     Establishment of Trust                                1

Section 2     Payments to Plan Participants                         2
              and Their Beneficiaries

Section 3     Trustee Responsibility Regarding                      3
              Payments to Trust Beneficiary
              When Company is Insolvent

Section 4     Payments to Company                                   4

Section 5     Investment Authority                                  4

Section 6     Disposition of Income                                 4

Section 7     Accounting by Trustee                                 5

Section 8     Responsibility of Trustee                             5

Section 9     Compensation and Expenses of Trustee                  6

Section 10    Resignation and Removal of Trustee                    6

Section 11    Appointment of Successor                              7

Section 12    Amendment or Termination                              7

Section 13    Payment of Incurred Expenses                          8

Section 14    Miscellaneous                                         8

Section 15    Effective Date                                        9
</Table>

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    (a)  This Agreement made this first day of January, 2001, by and between
         Belden Wire & Cable Company (the "Company") and CG Trust Company, a
         trust company organized under the laws of the State of Illinois with
         its principal office and place of business in Chicago, Illinois (the
         "Trustee");

    (b)  WHEREAS, Company has adopted the Belden Wire & Cable Company
         Supplemental Excess Defined Benefit Plan (the "Plan");

    (c)  WHEREAS, Company has incurred or expects to incur liability under the
         terms of such Plan with respect to the individuals participating in
         such Plan;

    (d)  WHEREAS, Company wishes to establish a trust (hereinafter called
         "Trust" or "Trust Fund") and to contribute to the Trust assets that
         shall be held herein, subject to the claims of Company's creditors in
         the event of Company's insolvency, as herein defined, until paid to
         Plan participants and their beneficiaries in such manner and at such
         times as specified in the Plan;

    (e)  WHEREAS, it is the intention of the parties that this Trust shall
         constitute an unfunded arrangement and shall not affect the status of
         the Plan as an unfunded plan maintained for the purpose of providing
         benefits for a select group of management or highly compensated
         employees for purposes of Title I of the Employee Retirement Income
         Security Act of 1974;

    (f)  WHEREAS, it is the intention of Company to make contributions to the
         Trust to provide itself with a source of funds to assist in the meeting
         of its liabilities under the Plan.

NOW, THEREFORE, the parties do hereby establish the Trust and agree that the
Trust shall be comprised, held and disposed of as follows:

Section 1.  Establishment of Trust.

    (a)  Company hereby deposits with Trustee in trust certain good and valuable
         consideration, which shall become the principal of the Trust to be
         held, administered and disposed of by Trustee as provided in this Trust
         Agreement.

    (b)  The Trust hereby established shall be revocable by the Company; it
         shall become irrevocable upon a Change of Control, as defined herein.

    (c)  The Trust is intended to be a grantor trust, of which Company is the
         grantor, within the meaning of subpart E, part I, subchapter J, chapter
         1, subtitle A of the Internal Revenue Code of 1986, as amended, and
         shall be construed accordingly.

                                                                               1

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    (d)  The principal of the Trust, and any earnings thereon shall be held
         separate and apart from other funds of Company and shall be used
         exclusively for the uses and purposes of Plan participants and general
         creditors as herein set forth. Before a Change in Control, (i) plan
         participants and their beneficiaries shall have no preferred claim on,
         or any beneficial ownership interest in, any assets of the Trust, (ii)
         any rights created under the Plan and this Trust Agreement shall be
         mere unsecured contractual rights of Plan participants and their
         beneficiaries against Company, (iii) any assets held by the Trust will
         be subject to the claims of Company's general creditors under federal
         and state law in the event of insolvency, as defined in Section 3(a)
         herein.

    (e)  Upon a Change of Control, Company shall, as soon as possible, but in no
         event longer than thirty (30) days following the Change of Control, as
         defined herein, make an irrevocable contribution to the Trust in an
         amount that is sufficient to pay all Plan participants and their
         beneficiaries the aggregate accrued benefits to which they would be
         entitled pursuant to the Plan as of the date of the Change of Control
         (whether or not they are then entitled to receive such accrued
         benefits), and shall thereafter make further irrevocable contributions
         to the Trust on a current basis as and in the amount that such benefits
         accrue. The Trustee shall have no responsibility for enforcing the
         Company's obligation to make payment of any contribution to the Trust,
         for the timing or amount thereof, or for the adequacy of the Trust to
         meet or discharge any liabilities of the Plan.

Section 2. Payments to Plan Participants and Their Beneficiaries.

    (a)  Company shall deliver to Trustee a schedule (the "Payment Schedule")
         that indicates the amounts payable in respect of each Plan participant
         (and his or her beneficiaries), that provides a formula or other
         instructions acceptable to Trustee for determining the amounts so
         payable, the form in which such amount is to be paid (as provided for
         or available under the Plan), and the time of commencement for payment
         of such amounts. Except as otherwise provided herein, Trustee shall
         make payments to the Plan participants and their beneficiaries in
         accordance with such Payment Schedule. The Trustee shall make
         provisions for reporting and withholding of any federal, state or local
         taxes that may be required to be withheld with respect to the payment
         of benefits pursuant to the terms of the Plan and shall pay amounts
         withheld to the appropriate taxing authorities or determine that such
         amounts have been reported, withheld and paid by Company.

    (b)  The entitlement of a Plan participant or his or her beneficiaries to
         benefits under the Plan shall be determined by Company or such party as
         it shall designate under the Plan, and any claim for such benefits
         shall be considered and reviewed under the procedures set out in the
         Plan.

                                                                               2

<PAGE>

    (c)  Company may make payment of benefits directly to Plan participants or
         their beneficiaries as they become due under the terms of the Plan.
         Company shall notify Trustee of its decision to make payment of
         benefits directly prior to the time amounts are payable to participants
         or their beneficiaries. Trustee shall require Company to provide
         reasonable written documentation that such payments have been made
         directly to such participant or beneficiary. In addition, if the
         principal of the Trust, and any earnings thereon, are not sufficient to
         make payments of benefits in accordance with the terms of the Plan,
         Company shall make the balance of each such payment as it falls due.
         Trustee shall notify Company where principal and earnings are not
         sufficient.

Section 3. Trustee Responsibility Regarding Payments to Trust Beneficiary When
Company is Insolvent.

    (a)  Trustee shall cease payment of benefits to Plan participants and their
         beneficiaries if the Company is insolvent. Company shall be considered
         "insolvent" for purposes of this Trust Agreement if (i) Company is
         unable to pay its debts as they become due or (ii) Company is subject
         to a pending proceeding as a debtor under the United States Bankruptcy
         Code.

    (b)  At all times during the continuance of this Trust, as provided in
         Section 1(d) hereof, the principal and income of the Trust shall be
         subject to claims of general creditors of Company under federal and
         state law as set forth below.

         (1)  The Board of Directors and the Chief Executive Officer of Company
              shall have the duty to inform Trustee in writing of Company's
              insolvency. If a person claiming to be a creditor of Company
              alleges in writing to Trustee that Company has become insolvent,
              Trustee shall determine whether Company is insolvent and, pending
              such determination, Trustee shall discontinue payment of benefits
              to Plan participants or their beneficiaries.

         (2)  Unless Trustee has actual knowledge of Company's insolvency, or
              has received notice from Company or a person claiming to be a
              creditor alleging that Company is insolvent, Trustee shall have no
              duty to inquire whether Company is insolvent. Trustee may in all
              events rely on such evidence concerning Company's solvency as may
              be furnished to Trustee and that provides Trustee with a
              reasonable basis for making a determination concerning Company's
              solvency.

                                                                               3

<PAGE>

         (3)  If at any time Trustee has determined that Company is insolvent,
              Trustee shall discontinue payments to Plan participants or their
              beneficiaries and shall hold the assets of the Trust for the
              benefit of Company's general creditors. Nothing in this Trust
              Agreement shall in any way diminish any rights of Plan
              participants or their beneficiaries to pursue their rights as
              general creditors of Company with respect to benefits due under
              the Plan or otherwise.

         (4)  Trustee shall resume the payment of benefits to Plan participants
              or their beneficiaries in accordance with Section 2 of this Trust
              Agreement only after Trustee has determined that Company is not
              insolvent (or is no longer insolvent).

    (c)  Provided that there are sufficient assets, if Trustee discontinues the
         payment of benefits from the Trust pursuant to Section 3(b) hereof and
         subsequently resumes such payments, the first payment following such
         discontinuance shall include the aggregate amount of all payments due
         to Plan participants or their beneficiaries under the terms of the Plan
         for the period of such discontinuance, less the aggregate amount of any
         payments made to Plan participants and their beneficiaries by Company
         in lieu of the payments provided for hereunder during any such period
         of discontinuance.

Section 4. Payments to Company.

Except as provided in Section 3 hereof, after the Trust has become irrevocable,
Company shall have no right or power to direct Trustee to return to Company or
to divert to others any of the Trust assets before all payment[s] of accrued
benefits (present and future) have been made to Plan participants and their
beneficiaries pursuant to the terms of the Plan.

Section 5. Investment Authority.

Trustee shall have the power to invest the assets of the Trust Fund in such
investment vehicles as directed by the Company, including insurance policies or
securities (including stock or rights to acquire stock) or obligations issued by
Company. All rights associated with assets of the Trust shall be exercised by
Trustee or the person designated by Trustee pursuant to the Company's direction,
and shall in no event be exercisable by or rest with Plan participants.

Section 6. Disposition of Income.

During the term of this Trust, all income received by the Trust, net of expenses
and taxes, shall be accumulated and reinvested.

                                                                               4

<PAGE>

Section 7. Accounting by Trustee.

The Trustee has accepted this Trust on the condition that the Company has
entered or is entering into a service agreement with Connecticut General Life
Insurance Company ("Connecticut General") whereby Connecticut General will
provide recordkeeping services for all assets held pursuant to this Trust
Agreement. The Trustee shall be required to forward to the Company, or require
Connecticut General to forward to the Company, the recordkeeping reports and
related financial information provided by Connecticut General, but the Trustee
shall not otherwise be required to provide Trust accounts.

Section 8. Responsibility of Trustee.

         (a)   Trustee shall act with the care, skill, prudence and diligence
               under the circumstances then prevailing that a prudent person
               acting in like capacity and familiar with such matters would use
               in the conduct of an enterprise of a like character and with like
               aims, provided, however, that Trustee shall incur no liability to
               any person for any action taken pursuant to a direction, request
               or approval given by Company or any delegate appointed by the
               Company which is contemplated by, and in conformity with, the
               terms of the Plan or this Trust and is given in writing by
               Company or its delegate. In the event of a dispute between
               Company and a party, Trustee may apply to a court of competent
               jurisdiction to resolve the dispute.

         (b)   If Trustee undertakes or defends any litigation arising in
               connection with this Trust, Company agrees to indemnify Trustee
               against Trustee's costs, expenses and liabilities (including,
               without limitation, attorneys' fees and expenses) relating
               thereto and to be primarily liable for such payments. If Company
               does not pay such costs, expenses and liabilities in a reasonably
               timely manner, Trustee may obtain payment from the Trust.

         (c)   Trustee may hire agents, accountants, actuaries, investment
               advisors, financial consultants or other professionals to assist
               it in performing any of its duties or obligations hereunder,
               including recordkeeping, reporting, custody of assets or proxy
               voting. Such agents may include affiliates of the Trustee.

         (d)   Trustee shall have, without exclusion, all powers conferred in
               Trustees in accordance with applicable law, unless expressly
               provided otherwise herein, provided, however, that if an
               insurance policy is held as an asset of the Trust, Trustee shall
               have no power to name a beneficiary other than the Trust, to
               assign the policy (as distinct from conversion of the policy to a
               different form) other than to a successor trustee, or to loan to
               any person the proceeds of any borrowing against such policy.

                                                                               5

<PAGE>

         (e)   The Company shall indemnify and hold harmless the Trustee from
               and against any and all claims, losses, damages, expenses
               (including reasonable counsel fees) and liability to which the
               Trustee may be subject by reason of any act done or omitted to be
               done, except where the same is finally adjudicated to be due to
               the negligence or willful misconduct of the Trustee.

         (f)   In addition to and in no way in limitation of the indemnification
               of paragraph (e) of this section, the Company hereby agrees to
               indemnify and hold harmless the Trustee from and against any
               claims, losses, damages, expenses (including reasonable counsel
               fees) and liability to which the Trustee may be subject by reason
               of any act or omission of any prior, subsequent or existing
               trustee of the Plan.

         (g)   The Trustee shall be responsible only for such assets as are
               actually received by it as Trustee hereunder. The Trustee shall
               have no duty or authority to ascertain whether any contributions
               should be made to it pursuant to the Plan or to bring any action
               to enforce any obligation to make any such contribution, nor
               shall it have any responsibility concerning the amount of any
               contribution or the application of the Plan's contribution
               formula. The Trustee shall have no responsibility for any assets
               not held under this Trust, even if those assets are held as
               assets of the Plan under a separate trust agreement.
               Responsibility for any such assets shall be solely that of the
               trustees named in such separate trust agreement, or, in the event
               no such separate trust exists, the Company.

Section 9. Compensation and Expenses of Trustee.

Company shall pay all administrative and Trustees' fees and expenses in
accordance with a fee schedule provided to the Company. In addition, Trustee
shall be paid its reasonable expenses, including reasonable expenses of counsel
and other agents employed by the Trustee, incurred in connection with
administration of the Trust Fund. If the Trustee proposes an amended fee
schedule and the Company fails to object thereto within ninety (90) days of its
receipt, the amended fee schedule shall be deemed accepted by the Company. If
not paid, the fees and expenses shall be paid from the Trust.

Section 10. Resignation and Removal of Trustee.

         (a)   Trustee may resign at any time by written notice to Company,
               which shall be effective 30 (thirty) days after receipt of such
               notice unless Company and Trustee agree otherwise.

         (b)   Trustee may be removed by Company on 30 (thirty) days notice or
               upon shorter notice accepted by Trustee.

                                                                               6

<PAGE>

         (c)   The Trustee's service pursuant to this Agreement is conditioned
               upon the existence of one or more contracts between the Company
               and Connecticut General providing for full Plan recordkeeping
               services. In the event the contract providing for such
               recordkeeping services is discontinued or terminated, this Trust
               Agreement shall be terminated as well with no further notice from
               either party to the other as of the date of discontinuance or
               termination of the contract providing for Plan recordkeeping
               services.

         (d)   Upon resignation or removal of Trustee and appointment of a
               successor Trustee, all assets shall subsequently be transferred
               to the successor Trustee. The transfer shall be completed within
               30 days after receipt of notice of resignation, removal or
               transfer, unless Company extends the time limit.

         (e)   If Trustee resigns or is removed, a successor shall be appointed,
               in accordance with Section 11 hereof, by the effective date of
               resignation or removal under paragraph(s) (a), (b) or (c) of this
               section. If no such appointment has been made, Trustee may apply
               to a court of competent jurisdiction for appointment of a
               successor or for instructions. All expenses of Trustee in
               connection with the proceeding shall be allowed as administrative
               expenses of the Trust.

Section 11. Appointment of Successor.

If Trustee resigns or is removed in accordance with Section 10(a), (b) or (c)
hereof, Company may appoint any third party, such as a bank trust department or
other party that may be granted corporate trustee powers under state law, as a
successor to replace Trustee upon resignation or removal. The appointment shall
be effective when accepted in writing by the new Trustee, who shall have all of
the rights and powers of the former Trustee, including ownership rights in the
Trust assets. The former Trustee shall execute any instrument necessary or
reasonably requested by Company or the successor Trustee to evidence the
transfer.

Section 12. Amendment or Termination.

         (a)   This Trust Agreement may be amended by a written instrument
               executed by Trustee and Company. Notwithstanding the foregoing,
               no such amendment shall conflict with the terms of the Plan or
               shall make the Trust revocable after it has become irrevocable in
               accordance with Section 1(b) hereof.

         (b)   The Trust shall not terminate until the date on which Plan
               participants and their beneficiaries are no longer entitled to
               benefits pursuant to the terms of the Plan. Upon termination of
               the Trust any assets remaining in the Trust shall be returned to
               Company.

         (c)   If and when the Trust becomes irrevocable as provided herein, any
               amendment of this Agreement will require the approval of at least
               80 percent of the Plan Participants (or their beneficiaries).

                                                                               7

<PAGE>

Section 13. Payment of Incurred Expenses

So long as the Participant is not acting in bad faith, the Company shall
promptly pay as they are incurred by each Plan Participant any Expenses arising
from or related to any action, suit, or proceeding filed by a Participant to
enforce his or her rights under this Agreement or Plan ("Claim"). "Expenses"
shall mean all costs, expenses (including attorney's fees, witness fees and
investigative costs) and obligations paid or incurred in connection with or
relating to a Claim (including all interest, assessments and other charges paid
or payable in connection with or in respect of any of the foregoing).

Section 14. Miscellaneous.

         (a)   Any provision of this Trust Agreement prohibited by law shall be
               ineffective to the extent of any such prohibition, without
               invalidating the remaining provisions hereof.

         (b)   Benefits payable to Plan participants and their beneficiaries
               under this Trust Agreement may not be anticipated, assigned
               (either at law or in equity), alienated, pledged, encumbered or
               subjected to attachment, garnishment, levy, execution or other
               legal or equitable process.

         (c)   This Trust Agreement and the Trust hereby created shall be
               governed, construed, administered and regulated in all respects
               in accordance with the laws of Illinois.

         (d)   For purposes of this Trust, the term "Change of Control" shall
               mean (i) the occurrence of a Triggering Event under the Rights
               Agreement of July 6, 1995 between Belden, Inc. and the Chase
               Mellon Shareholder Services, LLC, (successor to First Chicago
               Trust Company of New York), as such Rights Agreement may be
               assigned or amended, or (ii) the purchase or other acquisition by
               any person, entity or group thereof, within the meaning of
               Section 13(d) or 14(d) of the Securities Exchange act of 1934
               ("Act"), or any comparable successor provisions, of beneficial
               ownership (within the meaning of Rule 13d-3 promulgated under the
               Act) of 25 percent or more of either outstanding shares of common
               stock or the combined voting power of Company's then outstanding
               voting securities entitled to vote generally, (iii) the approval
               by the stockholders of the Company of a reorganization, merger,
               or consolidation, in each case, with respect to which persons who
               were stockholders of the Company immediately prior to such
               reorganization, merger or consolidation do not, immediately
               thereafter, own more than 60 percent of the combined voting power
               entitled to vote generally in the election of directors of the
               reorganized, merged or consolidated Company's then outstanding
               securities, or (iv) a liquidation or dissolution of Company or of
               the sale of all or substantially all of the Company's assets.

                                                                               8
<PAGE>

               The Board of Directors and the Chief Executive Officer of the
               Company shall have a duty to inform Trustee in writing of any
               Change of Control. Unless Trustee has actual knowledge of
               Company's Change of Control, or has received notice from the
               Company that a Change of Control has occurred, Trustee shall have
               no duty to inquire whether a Change of Control has occurred.

         (e)   In the event of any conflict between provisions of the Plan and
               those of this Trust Agreement, this Trust Agreement shall
               prevail.

Section 15.  Effective Date.

The effective date of this Trust Agreement shall be January 1, 2001.

Attest:                                         BELDEN WIRE & CABLE COMPANY

/s/ Eivind J. Kolemainen                  By /s/ Cathy O. Staples
------------------------                     ---------------------

                                          Its Vice President
                                             ---------------------

                                          Date March 26, 2001
                                               -------------------

Attest:                                         CG TRUST COMPANY

/s/                                       By /s/
-------------------------                    ------------------------------

                                          Its
                                             -------------------------------

                                          Date
                                              ------------------------------

                                                                               9

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