Raised-floor cabling standards

Q: In raised-floor systems, such as in campus computing centers, I have seen a smorgasbord of conduit and cabling types, including plastic, aluminum, steel, PVC, and plenum. Is there a standard or fire code that requires metal conduits? And also, does cabling that is not in conduit have to be plenum-rated?

Q: In raised-floor systems, such as in campus computing centers, I have seen a smorgasbord of conduit and cabling types, including plastic, aluminum, steel, PVC, and plenum. Is there a standard or fire code that requires metal conduits? And also, does cabling that is not in conduit have to be plenum-rated?

Scott English

Prewire Communications

Louisville, CO

A: I assume from your question that the underfloor space is used as a return-air plenum space. If the computer room meets the National Electrical Code (NEC) Article 645-2, special requirements for information technology equipment room, then the types of conduit and cable jacketing you describe are allowed. Should the computer room fail to comply with NEC 645-2, then NEC Articles 800-51 and 770-51 apply.

NEC 800-51 Listing Requirements states that Type CMP communications plenum cable be listed as suitable for use in ducts, plenums, and other spaces used for environmental air, and also be listed as having adequate fire-resistant and low smoke-producing characteristics. Likewise, NEC 770-51, Listing Requirements for Optical Fiber Cables and Raceways, (e) Plenum Optical Fiber Raceway, requires that plenum optical fiber raceways (the NEC`s definition of the flexible nonmetallic tubing commonly known as innerduct in our industry) be listed as having adequate fire- resistant and low smoke-producing characteristics.

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: ballast@utexas.edu.

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