Q: I have done research on running Category 5 wire in the home, but I have not seen anything on the allocation of pairs. If I run a Category 5 wire to support an Integrated Services Digital Network (isdn) line, can I use the spare pairs for other things, like a dial line or a fax machine, or would there be some coupling between the two circuits? On the other hand, there could also be coupling in the cable the local exchange carrier provides to the home, since separation between the pairs is minimal. Any ideas?
Donald L. Wilson
United States Postal Service
Mascoutah, IL
A: isdn does not require Category 5 performance. The cabling coming into your house from your local service provider is "almost" Category 3. You can certainly install an additional line for a telephone or fax in the same cable.
The TR-41.8.2 working group of the Telecommunications Industry Association (tia--Arlington, VA) is currently revising PN-3490, "Residential Tele-communications Cabling Standard." Draft 7 of PN-3490 describes a grading system that is intended to help with selecting a cabling system for the residence, based on the services that will be installed.
Grade 1, which represents the minimum requirements for basic telecommunications, consists of a minimum of 2-pair unshielded twisted-pair (utp) cable that meets the electrical specifications of Category 3 cable, and 75-ohm coaxial cabling. Grade 2, which represents the minimum requirements for a better grade of premises cabling, specifies a minimum of Category 3, 4-pair utp cable, and 75-ohm coaxial cabling. Grade 3, which represents the minimum requirements for the highest grade of premises cabling, specifies a minimum of Category 5, 4-pair utp cable, as well as 75-ohm coaxial cabling. Optical fiber is recommended where applicable.
Working group chair Bob Jensen, who is with dbi (Austin, TX), says the group is optimistic that the revised standard would be ready for publication by year`s end. The revised standard will be published as ansi/tia/eia-570a and will retire ansi/eia/tia-570, "Residential and Light Commercial Telecommunications Wiring Standard" (June 1991).
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, University of Texas, Austin, TX 78713; tel: (512) 471-0112, fax: (512) 471-8883, e-mail: [email protected].