Q: As cabling contractors, we run into requests for proposals that require plenum or polyvinyl chloride (pvc)-jacketed cable. Most building inspectors are consistent in what they require, but fire inspectors seem to vary with their moods. We have been asked, primarily by our customers, what the requirements are for running pvc-jacketed cable or riser-rated cable into a building. I am aware that, according to the National Electrical Code (nec), no pvc-jacketed cable can run in an air-return space for more that 50 feet, unless it is in conduit. I believe this but cannot find any documentation in the nec or tia standards. Both specifications refer to an authority called umc for exact codes and specifications, but I have been unable to find any documentation specifically stating how far and what requirements there are for this application.
Ed Kofol
Pacific States Communications
Reno, NV
A: The 50-foot rule is in nec 800-50, Listing, Marking, and Installation of Communications Wires and Cables, which says that communications cables installed in buildings shall be listed as being suitable for the purpose. There are some exceptions:
Listing is not required where the cable enters the building from the outside and is continuously enclosed in a rigid or an intermediate metal conduit.
Listing is not required where the cable enters the building from the outside and is terminated in an enclosure or on a listed primary protector and the length of the cable within the building, measured from its point of entrance, does not exceed 50 feet.
But these exceptions all address outside-plant distribution cable, not plenum- or riser-rated cable. Within the nec, there is zero tolerance for a riser-rated cable in a plenum environment. The tia standards address performance issues, but plenum- versus riser-rated cable is a safety issue.
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].