Ansi/tia/eia-607, the Commercial Building Grounding and Bonding Requirements for Telecommunications standard, was published in August 1994. Section 5.3.4 regarding bonding and sizing the telecommunications bonding busbar (TBB) states: "A TBB shall be an insulated copper conductor"...and the quest began. In my very first "Ask Donna" column (see January 1994, page 45), I was asked where to find a plenum-rated ground wire. There wasn`t any then, and there isn`t any now. But in the most recent committee draft, TR-41.7.2 has agreed to remove the word "insulated," hence allowing the designer to choose.
Another issue that has plagued our industry--sizing the TBB--is also being discussed within TR-41.7.2. Currently, tia/eia-607 requires the minimum TBB conductor size to be a No. 6 AWG with consideration given to a conductor as large as a No. 3/0 AWG; The IEEE Std. 241-1990 Grey Book requires a minimum of 2 MCM (thousand circular mils)/linear foot of run; The IEEE Std. 142-1991 Green Book gives an example of a 500-MCM copper conductor for the building; and The ABC of the Telephone provides the table on the right. It is a safe bet that there will be a conductor-diameter-to-length-of-run ratio provided in tia/eia-607a.
Also on the topic of tia/eia-607 revisions, BICSI will be submitting suggested configurations for the telecommunications main grounding busbar and TGB (telecommunications grounding busbar) developed by a BICSI Standards Committee Task Force. If adopted, this part of the revision would allow manufacturers to stock ground bars rather than make them to order, reducing the procurement delays that we are currently experiencing.
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Donna Ballast is a communications analyst at the University of Texas at Austin and a bicsi registered communications distribution designer (rcdd). Questions can be sent to her at Cabling Installation & Maintenance or at PO Drawer 7580, the University of Texas, Austin, TX 78713; tel: (512) 471-0112, fax: (512) 471-8883, e-mail: ballast@utexas.edu.
