4-pair vs. 25-pair cabling

Q: I attended the "Do we need zone cabling?" panel discussion at the bicsi conference in June. I left with the message that individual 4-pair drops were a better design choice than a 25-pair Category 5 cable. Comments?

Ross Bedbrook, RCDD

Bell Canada

Moose Creek, ON, Canada

A: Ah, yes, as moderator of that session, I remember it well. Brian Moffitt of Lucent Technologies presented a slide depicting a "600-Pair Consolidation Point," which George Weller of Steelcase later described as a "King Kong" consolidation point. amp`s Ken Hall concluded that "bicsi should drive zone cabling practices to ensure [that they are] designed and installed properly." Terry Cobb of Datacom Technologies explained that in a 4-pair cable, near-end crosstalk is measured from pair to pair, but in a 25-pair cable, near-end crosstalk is measured using a power-sum technique. Bob Jensen of dbi then reminded the group that there are no 25-pair connectors recognized in the tia/eia-568a standard; no field-test instruments available to test power-sum near-end crosstalk on 25 pair-cable; and no cabling install-ation requirements provided on how to break out the 25-pair into 4-pair bundles while minimizing crosstalk.

As for me, I am sticking to my closing statement at the session: "It sounds as if we still have some work to do on this one."

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].