Defining Hybrid Cable

Q: When the tia TR-41.8.1 working group on commercial cabling talks about hybrid cables, does it mean mixed Category 3 and 5, or mixed fiber-optic and copper cables, or what?

Robert Bailey

Bailey Consulting Inc.

Wilmington, DE

A: All of the above. tia/eia-568a, Section 3, defines hybrid cable as "an assembly of two or more cables of the same or different types or categories covered by one overall sheath." Section 13 describes composite cables as "hybrid cables consisting of optical fiber and copper conductors."

But the confusion does not stop there. Because Section 13.1 of tia/ eia-568a did not specifically address "bundled-cable" assemblies, and cross-talk requirements did not accurately ensure the expected performance of hybrid and bundled-cable constructions, TR-41.8.1 is currently revising the requirements for hybrid cable and drafting requirements for bundled- cable assemblies. The focus of this work is twofold:

- First, to define bundled cable, which, while similar to hybrid cable, does not have an overall sheath. According to TR-41.8.1, bundled cable is an assembly of two or more cables bound together to form a single unit prior to installation. More familiar names include loomed, speed-wrap, and whip-cable construction.

- Second, to establish a power-sum near-end crosstalk (ps-next) loss between all recognized non-fiber cable types. The ps-next must be better than the specified pair-to-pair next loss over the frequency range specified for each recognized cable type. How much better? They are still debating. Somewhere between 3 and 6 decibels is a good bet.

Donna Ballast is a communications analyst at the University of Texas at Austin and a bicsi reg-istered 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: [email protected].