Bradford Sherman
Interlink Communication Services of Florida
Miami, FL
Some confusion exists in the industry over the use of the terms describing the contents of cable with dissimilar structures. "Composite" and "hybrid" are used inconsistently throughout the telecommunications industry by installers, technicians, consultants, registered communications distribution designers (RCDDs) and cable manufacturers. Even the standards organizations disagree with each others` definitions.
- BICSI`s Telecommunications Distribution Methods Manual (issue 7, section 4, page 16) specifies that a "hybrid cable is one consisting of a common sheath containing two or more cable types, or two or more units of the same cable type."
- The 1996 National Electrical Code (section 770-4, optical-fiber cables) states that a composite cable contains optical fibers and current-carrying conductors.
- The ANSI/TIA/EIA-568A standard for commercial telecommunications cabling defines composite cable as a product that contains two or more elements of the same transmission medium.
- In "Composite and hybrid cabling systems suit innovative applications" (see March 1996, page 25), Tom Debiec, RCDD, from Berk-Tek Inc. sums it up in a logical way: composite--all copper or fiber; hybrid--metallic and fiber.
BICSI uses the term hybrid for both types of cable, while the NEC uses the term composite. I hope that cable manufacturers eventually create two distinct categories, thus preventing confusion among all involved.
Tom Debiec, RCDD, applications engineer at Berk-Tek Inc. (New Holland, PA) offers this additional information on hybrid/composite cables:
I understand that TIA`s TR 41.8.1 committee, responsible for ANSI/TIA/ EIA-568A, is in the process of refining the requirements for hybrid and composite cables. As part of this action, the committee is working to define the meaning of each term. Although the definitions may be different than those in Mr. Sherman`s letter, whatever the committee agrees to will become standard and may help to end the confusion about the terms "hybrid" and "composite" in the cabling industry.