25-pair cable

Q: Where I can find documentation on Category 5 25-pair cable? Is it included in Telecommunications Industry Association/Electronic Industries Association standard 568A? Our computer people are saying that only one 100-megabit-per-second circuit can be installed in a 25-pair cable.

Q: Where I can find documentation on Category 5 25-pair cable? Is it included in Telecommunications Industry Association/Electronic Industries Association standard 568A? Our computer people are saying that only one 100-megabit-per-second circuit can be installed in a 25-pair cable.

Terry Evans

Pacific Gas and Electric

Davis, CA

A: TIA/EIA-568A`s Section 10.3 on backbone unshielded twisted-pair cabling describes categories of multi-pair cable (greater than four-pair), cautions you to separate services with different signal levels or impulse noise susceptibility into separate binder groups and then refers you to Annex D.

Annex D, "Shared sheath guidelines for multi-pair UTP cables," says: "Shared sheath guidelines for applications with data rates beyond 10 megabits per second need to be developed in conjunction with the applications standard committees, and is under study."

I contacted Geoff Thompson of Bay Networks and chair of the Institute of Electrical and Electronics Engineers` 802.3 committee. He also participates in TR-41.8.1 and SC 25/WG3. According to Thompson, "There has not been any formal work in the IEEE 802.3 100Base-T committee on the issue of 100Base-T in a 25-pair cable with any signals on the other pairs." Not very encouraging.

Specifications for Category 5 25-pair cable are spelled out in the standard, but guidelines for installing applications with data rates beyond 10 Mbits/sec are not, leaving cabling system designers to answer the "...but you said that Category 5 would support ..." questions. [See "Multi-pair UTP backbone cable," June 1994, page 10. Ed.]

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