EXHIBIT 10.21  MODIFICATION OF TERM LOAN
               REVOLVING CREDIT AND SECURITY AGREEMENT

        THIS  AGREEMENT  is made as of the 30 day of May,  1996,  by and between
SUNTRUST  BANK,  SOUTH  FLORIDA,  N.A.,  a  national  banking  association  (the
"Lender"),   ABLE  TELCOM  HOLDING  CORPORATION,   a  Florida  corporation  (the
"Borrower") and TRANSPORTATION SAFETY CONTRACTORS,  INC., a Florida corporation,
TRANSPORTATION SAFETY CONTRACTORS OF VIRGINIA, INC., a Virginia corporation, BCD
COMMUNICATIONS,   INC.,  a  Florida  corporation  and  TIPCO,  INC.,  a  Florida
corporation (singularly a "Guarantor" and collectively the "Guarantors").

                                         WITNESSETH:

        WHEREAS,  Lender,  Borrower  and  Guarantors  entered  into a Term Loan,
Revolving Credit and Security Agreement dated as of November 29, 1995 (the "Loan
Agreement") in connection  with which Lender made available to Borrower  certain
Loans as defined in the Loan  Agreement,  which are evidenced and secured by the
Loan Documents, as defined in the Loan Agreement; and

        WHEREAS,  Lender and Borrower have agreed to amend the Loan Agreement to
revise certain financial covenants; and

        WHEREAS,  the  Guarantors  have  agreed to  execute  this  Agreement  to
evidence their consent to the amendments to the Loan Agreement  contained herein
and to affirm the  continuing  validity of the  Guaranty  Agreements,  after the
amendments contained herein.

        NOW, THEREFORE, in consideration of the mutual promises and covenants of
this  agreement and for other good and valuable  consideration,  the receipt and
sufficiency  of which is hereby  acknowledged,  Lender,  Borrower and Guarantors
agree as follows:

        1.  RECITALS/TERMS.  All of the  recitals  set forth  above are true and
correct and by this  reference are made a material part of this  Agreement.  All
capitalized terms used herein which are defined in the Loan Agreement shall have
the same  meaning  when used herein  unless the  context  herein  shall  require
otherwise.

        2.     DEFINITIONS.

               (a)    The definition of "Debt Service" is hereby amended to read
                      as follows:

                      "DEBT  SERVICE" is defined as the  current  portion of all
                      long term debt, as calculated in accordance with generally
                      accepted  accounting   principles  and  reflected  in  the
                      consolidated  financial  statement  of  Borrower  and  the
                      Subsidiaries,   excluding  the  promissory   note(s)  from
                      Borrowers to (i) H.C.  Connell in the  original  principal
                      amount of $1,869,049.00  dated December 7, 1995; (ii) Bill
                      Caudill in the original  principal  amount of  $250,000.00
                      dated  December  7,  1995;  (iii)  Frazer  Gaines  in  the
                      original principal amount of $250,000.00 dated December 7,
                      1995;  and  (iv)  the  three  promissory  notes  from  the
                      Borrower   to  the   prior   principal   shareholders   of

<PAGE>

                      Transportation  Safety  Contractors,  Inc. in the original
                      aggregate  principal  amount of  $1,307,967.00  dated June
                      1994,  plus all interest  payments due on Borrower's  Debt
                      during the period in question.

               (b)    The definition of "Funded Debt" is hereby amended to read
                      as follows:

                      "FUNDED  DEBT"  is  defined  as  total   liabilities,   as
                      calculated   in   accordance   with   generally   accepted
                      accounting  principles  and reflected in the  consolidated
                      financial statement of Borrower and the Subsidiaries, less
                      (i) accounts  payable;  (ii) income taxes  payable;  (iii)
                      accrued  expenses;   (iv)  the  promissory  notes(s)  from
                      Borrowers to (a) H.C.  Connell in the  original  principal
                      amount of  $1,869,049.00  dated December 7, 1995; (b) Bill
                      Caudill in the original  principal  amount of  $250,000.00
                      dated  December 7, 1995; (c) Frazer Gaines in the original
                      principal  amount of  $250,000.00  dated December 7, 1995;
                      (v) the three  promissory  notes from the  Borrower to the
                      prior  principal  shareholders  of  Transportation  Safety
                      Contractors,  Inc.  in the  original  aggregate  principal
                      amount of  $1,307,967.00  dated  June  1994;  and (vi) the
                      equipment   and  revolving   loan  from   SunTrust   Bank,
                      Mid-Florida,  N.A. in the principal  amount of $340,000.00
                      and  $200,000.00,  respectively.  Funded  Debt  shall also
                      include the redemption amount with respect to any stock of
                      the Borrower or the  Subsidiaries  required to be redeemed
                      within the next twelve months.

               (c)    The following definition is added to Article 1 of the Loan
                      Agreement:

                      "NONRECURRING   WRITE  OFF"  means  the  loss  from  Latin
                      American operations  ($3,308,149.00) charged to Borrower's
                      second quarter 1996 earnings taken in connection  with the
                      restructuring of Borrower's Latin American operations.

        3.     REVISIONS TO FINANCIAL COVENANTS.

               (a)    Section 6.20 is hereby amended to read as follows:

                      6.20  SUBSIDIARIES.  The Borrower and/or its  Subsidiaries
                      will not be permitted to make  acquisitions  or enter into
                      joint venture agreements without the prior written consent
                      of  the  Lender  until  Borrower  and  Guarantors  achieve
                      compliance with the financial  covenant  ratio(s) required
                      to be achieved by July 31, 1997, under Sections 6.21, 6.22
                      and  6.23  of the  Loan  Agreement,  as  modified  by this
                      Agreement.  Thereafter  new  Subsidiaries  may be acquired
                      without  the prior  written  consent of the Bank  provided
                      Borrower   provides  prior  written  notice  to  the  Bank
                      containing  a   certification   that  the  terms  of  this
                      Agreement  and the special  terms  outlined  below will be
                      complied  with after said  acquisition.  The special terms
                      are:

                      (a)    The  Subsidiary to be acquired is engaged in one of
                             the  three   primary  lines  of  business  for  the
                             Borrower -- highway signage,  telecommunications or
                             utility installation;
<PAGE>

                      (b)    The  ratio  of  the  combined   earnings   before 
                             deduction  of interest,  taxes,   depreciation,  
                             amortization and lease payments of Borrower and the
                             Subsidiary  to be acquired  calculated  on a 
                             trailing  four quarters basis for both the Borrower
                             and the Subsidiary  to be  acquired, divided by the
                             combined  projected interest,  principal  and lease
                             payments  of  Borrower  and the Subsidiary  to be 
                             acquired,  calculated  for the  four  quarters
                             after acquisition shall be greater than 1.75X; and

                        (c)  The total value of the  consideration  to be given,
                             debt to be assumed  and  expenses to be incurred by
                             Borrower and the  Subsidiaries  in connection  with
                             such acquisition shall not exceed $1,000,000.00.

               (b)    Section 6.21 is hereby amended to read as follows:

                      6.21. NET WORTH.  Shall maintain  Borrower's  Tangible Net
                      Worth to be not less  than  $8,300,000.00  as of April 30,
                      1996,  $8,500,000.00 as of July 31, 1996, $8,700,000.00 as
                      of October 31, 1996,  $8,900,00000 as of January 31, 1997,
                      $9,100,000.00  as of April 30, 1997 and  $9,300,000.00  at
                      all times after July 31, 1997.

               (c)    Section 6.22 is hereby amended to read as follows:

                      6.22 FUNDED DEBT/TANGIBLE NET WORTH. Shall assure that the
                      ratio of Borrower's Funded Debt to Borrower's Tangible Net
                      Worth shall be less than: 1.60X as of July 31, and October
                      31, 1996;  1.50X as of January 31 and April 30, 1997;  and
                      1.40x at the end of each fiscal quarter beginning July 31,
                      1997.

               (d)    Section 6.23 is hereby amended to read as follows:

                      6.23  DEBT  SERVICE.   Shall  assure  that  the  ratio  of
                      Borrower's earnings before deduction of interest payments,
                      taxes,  depreciation,  amortization  and the  Nonrecurring
                      Write  Off  shall  be  greater  than  1.20X  Debt  Service
                      measured  quarterly  beginning  April  30,  1996  for  the
                      trailing four quarters.

        4. WAIVER OF DEFAULTS.  Lender  agrees that Lender waives any default in
Borrower's  compliance with the covenants in Section 6.21, 6.22 and 6.23,  which
occurred prior to the date of this Agreement. Lender hereby reserves any and all
rights and remedies exercisable on the occurrence of an existing or future Event
of Default other than those expressly waived above.

        5.  GUARANTY  AGREEMENTS.  Guarantors  hereby  ratify  and  confirm  the
continuing  validity  of the  Guaranty  Agreements  and any other  documents  or
agreements  given  by any  Guarantor  in  connection  with  the  Loan  Documents
notwithstanding the amendments to the Loan Agreement contained herein and hereby
further consent to such amendments.
<PAGE>
6. NO DEFAULT.  Borrower and  Guarantors  hereby warrant and represent to Lender
that, after giving effect to this  Modification,  Borrower and Guarantors are in
compliance  with  all  provisions  of the  Loan  Agreement  and all  other  Loan
Documents  and that no default or Event of Default has occurred  thereunder  nor
has any event  occurred or failed to occur which with the passage of time or the
giving of notice or both would comprise such a default or Event of Default.

7.      MISCELLANEOUS.

               (a)  This  agreement  shall  be  governed  by  and  construed  in
        accordance  with the law of the  State of  Florida.  In the event of any
        dispute hereunder, the prevailing party shall be entitled to recover all
        costs and  attorney's  fees  from the  non-prevailing  party.  Paragraph
        headings used herein are for  convenience  only and shall not be used to
        interpret any term hereof.  The Loan  Agreement  shall  continue in full
        force and  effect as  modified  by this  Modification.  In the event the
        terms  of  this  Modification  conflict  with  the  terms  of  the  Loan
        Agreement, the terms of this Modification shall control.

               (b) This Modification  constitutes the entire agreement among the
        parties  hereto and  supersedes  all prior  agreements,  understandings,
        negotiations  and  discussions,  both written and oral among the parties
        hereto with  respect to the subject  matter  hereof,  all of which prior
        agreements,  understanding,  negotiations and discussions,  both written
        and oral,  are  merged  into this  Modification.  Except as  hereinabove
        specifically  amended,  all other  provisions of the Loan  Agreement and
        each of the other Loan Documents  amended hereby shall remain  unchanged
        and in full force and effect.  Without limiting the generality of any of
        the provisions of this Modification, nothing herein or in any instrument
        or  agreement  shall be deemed or  construed  to  constitute a novation,
        satisfaction  or refinancing of all or any portion of the Loan or in any
        manner  affect or impair the lien or priority of the Loan  Agreement  or
        any of the Loan Documents as amended hereby.

               (c)  This   Modification   may  be  executed  in  any  number  of
        counterparts  with each executed  counterpart  constituting an original,
        but altogether constituting but one and the same instrument.

               (d) This  Modification  shall be  binding  upon and  inure to the
        benefit  of the  Borrower,  the  Guarantors  and the  Lender  and  their
        respective  heirs,  legal  representatives,  executors,  successors  and
        assigns.

        8. RELEASE. IN CONSIDERATION OF THE ACCOMMODATIONS PROVIDED HEREIN, EACH
OF THE BORROWER  AND THE  GUARANTORS  HEREBY  UNCONDITIONALLY,  IRREVOCABLY  AND
FOREVER  RELEASES,  ACQUITS AND  DISCHARGES  THE LENDER AND EACH OF THE LENDER'S
RESPECTIVE OFFICERS,  DIRECTORS,  EMPLOYEES, AGENTS AND COUNSEL FROM ANY AND ALL

<PAGE>

CLAIMS, DEMANDS AND CAUSES OF ACTION THAT ANY OF THEM HAD, NOW HAS OR MAY IN THE
FUTURE  HAVE  AGAINST  ANY ONE OR MORE OF THE  LENDER  OR ANY ONE OR MORE OF THE
LENDER'S  OFFICERS,  DIRECTORS,  EMPLOYEES,  AGENTS OR  COUNSEL  FOR THE ACTS OR
OMISSIONS OF ANY OF THE FOREGOING PARTIES FROM THE BEGINNING OF TIME THROUGH, TO
AND  INCLUDING  THE  DATE OF THE  EFFECTIVENESS  OF THIS  AGREEMENT,  INCLUDING,
WITHOUT  LIMITATION,  ANY CLAIMS  ARISING OUT OF OR CONNECTED IN ANY MANNER WITH
THE TRANSACTIONS CONTEMPLATED HEREIN OR IN THE LOAN AGREEMENT, AS AMENDED HEREBY
OR ANY OTHER LOAN DOCUMENTS,  AS THE SAME MAY BE AMENDED HEREBY, AS THE CASE MAY
BE.

        9. WAIVER OF JURY TRIAL.  THE BORROWER,  THE  GUARANTORS  AND THE LENDER
HEREBY KNOWINGLY,  VOLUNTARILY AND INTENTIONALLY WAIVE THE RIGHT ANY OF THEM MAY
HAVE TO A TRIAL BY JURY IN RESPECT OF ANY  LITIGATION  BASED HEREON,  OR ARISING
OUT OF, UNDER OR IN CONNECTION WITH THIS AGREEMENT OR ANY AGREEMENT  EXECUTED IN
CONJUNCTION HEREWITH, OR ANY COURSE OF CONDUCT,  COURSE OF DEALING,  STATEMENTS,
(WHETHER  VERBAL OR  WRITTEN)  OR  ACTIONS  BY ANY PARTY.  THIS  PROVISION  IS A
MATERIAL  INDUCEMENT TO THE LENDER  ENTERING INTO THIS  AGREEMENT AND MAKING ANY
LOAN, ADVANCE OR OTHER EXTENSION OF CREDIT TO THE BORROWER. FURTHER, EACH OF THE
BORROWER AND THE GUARANTOR HEREBY CERTIFIES THAT NO  REPRESENTATIVE  OR AGENT OF
THE LENDER, NOR THE LENDER'S COUNSEL,  HAS REPRESENTED,  EXPRESSLY OR OTHERWISE,
THAT THE  LENDERS  WOULD NOT, IN THE EVENT OF SUCH  LITIGATION,  SEEK TO ENFORCE
THIS WAIVER OF RIGHT TO JURY TRIAL PROVISION. NO


<PAGE>


REPRESENTATIVE  OR  AGENT  OF THE  LENDER,  NOR  THE  LENDER'S  COUNSEL  HAS THE
AUTHORITY TO WAIVE, CONDITION, OR MODIFY THIS PROVISION.

        IN WITNESS  WHEREOF,  Borrower,  Lender and  Guarantor  have caused this
agreement to be executed as of the day and year set forth above.

Witnesses:                                  LENDER:
                                            SUNTRUST BANK, SOUTH FLORIDA, N.A.,
                                            a national banking association

/S/GRETCHEN W. SOLAR                   By /S/PAUL BERRYMAN
------------------------------------   ---------------------------------------
Print Name: GRETCHEN W. SOLAR          Print Name:  PAUL R. BERRYMAN
            ------------------------                --------------------------
                                       Its: SENIOR VICE PRESIDENT
                                            ----------------------------------
/S/MERCEDES ALVAREZ
------------------------------------
Print Name: MERCEDES ALVAREZ
            ------------------------

                                            BORROWER:
                                            ABLE TELCOM HOLDING CORPORATION, a
                                            Florida corporation

/S/DANIEL L. OSBORNE                
------------------------------------   By: /S/WILLIAM J. MERCURIO
Print Name: DANIEL L. OSBORNE              -----------------------------------
            ------------------------   Print Name: WILLIAM J. MERCURIO
                                                   ---------------------------
                                       Its: CHIEF EXECUTIVE OFFICER
                                            ----------------------------------
/S/ROSEMARIE MULHOLLAND
------------------------------------
Print Name: ROSEMARIE MULHOLLAND
            ------------------------
                                            GUARANTORS:
                                            TRANSPORTATION SAFETY CONTRACTORS,
                                            INC., a Florida corporation

/S/DANIEL L. OSBORNE                        
-----------------------------------    By: /S/WILLIAM J. MERCURIO
Print Name: DANIEL L. OSBORNE          ---------------------------------------
                                       Print Name: WILLIAM J. MERCURIO
                                                   ---------------------------
                                       Its: CHAIRMAN
/S/ROSEMARIE MULHOLLAND                     ----------------------------------
-----------------------------------
Print Name: ROSEMARIE MULHOLLAND
            -----------------------

                           [SIGNATURES CONTINUED ON FOLLOWING PAGE]
<PAGE>

                                            TRANSPORTATION SAFETY CONTRACTORS OF
                                            VIRGINIA, a Virginia corporation

/S/DANIEL L. OSBORNE                
------------------------------------
Print Name: DANIEL L. OSBORNE               By:/S/WILLIAM J. MERCURIO
            -----------------------         ---------------------------------
                                            Print Name: WILLIAM J. MERCURIO
                                                        ---------------------
                                            Its: CHAIRMAN                    
                                                 ----------------------------
/S/ROSEMARIE MULHOLLAND
------------------------------------
Print Name: ROSEMARIE MULHOLLAND
            ------------------------
                                            BCD COMMUNICATIONS, INC., a Florida
                                            corporation

/S/DANIEL L. OSBORNE                    
------------------------------------        By:/S/ WILLIAM J. MERCURIO  
Print Name: DANIEL L. OSBORNE               ---------------------------------
                                            Print Name: WILLIAM J. MERCURIO
                                                         --------------------
                                            Its:CHAIRMAN   
                                                -----------------------------

/S/ROSEMARIE MULHOLLAND
-----------------------------------
Print Name: ROSEMARIE MULHOLLAND
            -----------------------
                                            TIPCO, INC., a Florida corporation

/S/ DANIEL L. OSBORNE                    
-----------------------------------         By: /S/ WILLIAM J. MERCURIO        
Print Name: DANIEL L. OSBORNE               -------------------------------
                                            Print Name: WILLIAM J. MERCURIO
                                                        -------------------
                                            Its:CHAIRMAN       
                                                ---------------------------
/S/ROSEMARIE MULHOLLAND
----------------------------------
Print Name: ROSEMARIE MULHOLLAND
            ---------------------- 

STATE OF FLORIDA                    )
                                    )  SS:
COUNTY OF PALM BEACH                )

        The foregoing  instrument was acknowledged before me this 8 day of JULY,
1996,  by PAUL R.  BERRYMAN as SENIOR VICE  PRESIDENT  of SUNTRUST  BANK,  SOUTH
FLORIDA, N.A., a national banking association,  on behalf of the bank. HE/She IS
PERSONALLY   KNOWN   TO  ME  or  has   produced   _________________________   as
identification.

                                /S/ MINDY J. GABRIEL...........................
                                MINDY J. GABRIEL..................Printed Name:
                                 Notary Public
                                 CC497982........................Commission No.:
                                 My Commission Expires:  NOV. 02, 1999
<PAGE>

STATE OF FLORIDA                    )
                                    )  SS:
COUNTY OF PALM BEACH                )

        The foregoing  instrument  was  acknowledged  before me this 30TH day of
MAY, 1996, by WILLIAM J. MERCURIO as CHIEF EXEC.  OFFICER of ABLE TELCOM HOLDING
CORPORATION,  a Florida  corporation,  on behalf of the  corporation.  He/She is
personally   known   to  me  or  has   produced   _________________________   as
identification.

                             /S/ STACEY C. MCKISSICK........................
                             STACEY C. MCKISSICK...............Printed Name:
                               Notary Public
                               CC555959........................Commission No.:
                               My Commission Expires:  MAY 19, 2000

STATE OF FLORIDA                    )
                                    )  SS:
COUNTY OF PALM BEACH                )

        The foregoing  instrument  was  acknowledged  before me this 30TH day of
MAY,  1996,  by  WILLIAM  J.  MERCURIO  as  CHAIRMAN  of  TRANSPORTATION  SAFETY
CONTRACTORS,  INC., a Florida corporation, on behalf of the corporation.  He/She
is  personally  known  to  me  or  has  produced   _________________________  as
identification.

                             /S/ STACEY C. MCKISSICK.......................
                             STACEY C. MCKISSICK..............Printed Name:
                              Notary Public
                              CC555959........................Commission No.:
                              My Commission Expires:  MAY 19, 2000
<PAGE>

STATE OF FLORIDA                    )
                                    )  SS:
COUNTY OF PALM BEACH                )

        The foregoing  instrument  was  acknowledged  before me this 30TH day of
MAY,  1996,  by  WILLIAM  J.  MERCURIO  as  CHAIRMAN  of  TRANSPORTATION  SAFETY
CONTRACTORS  OF  VIRGINIA,  INC.,  a  Virginia  corporation,  on  behalf  of the
corporation.    He/She   is   personally   known   to   me   or   has   produced
_________________________ as identification.

                              /S/STACEY C. MCKISSICK.........................
                              STACEY C. MCKISSICK...............Printed Name:
                               Notary Public
                               CC555959........................Commission No.:
                               My Commission Expires:  MAY 19, 2000

STATE OF FLORIDA                    )
                                    )  SS:
COUNTY OF PALM BEACH                )

        The foregoing  instrument  was  acknowledged  before me this 30TH day of
MAY,  1996,  by WILLIAM J. MERCURIO as CHAIRMAN of BCD  COMMUNICATIONS,  INC., a
Florida corporation, on behalf of the corporation. He/She is personally known to
me or has produced _________________________ as identification.

                              /S/STACEY C. MCKISSICK..........................
                              STACEY C. MCKISSICK................Printed Name:
                                  Notary Public
                                  CC555959......................Commission No.:
                                  My Commission Expires:  MAY 19, 2000
<PAGE>

STATE OF FLORIDA                    )
                                    )  SS:
COUNTY OF PALM BEACH                )

        The foregoing  instrument  was  acknowledged  before me this 30TH day of
MAY,  1996,  by  WILLIAM J.  MERCURIO  as  CHAIRMAN  of TIPCO,  INC.,  a Florida
corporation,  on behalf of the corporation.  He/She is personally known to me or
has produced _________________________ as identification.

                              /S/STACEY C. MCKISSICK..........................
                              STACEY C. MCKISSICK................Printed Name:
                                  Notary Public
                                  CC555959......................Commission No.:
                                  My Commission Expires:  MAY 19, 2000

WPALM/41434_1.DOC