Plenum or PVC The outer sheath of shielded and unshielded twisted cable comes in two kinds: PVC cable is the most common and least expensive type. Plenum cable is a special type of fire-retardant cable designated for use in the plenum space of a building. Plenum cable has a special Teflon coating that not only resists heat but also gives off fewer toxic fumes if it does burn. Unfortunately plenum cable costs more than twice as much as ordinary PVC cable. Most local building codes require plenum cable when the wiring is installed in the building's plenum space (a compartment that's part of building's air-distribution system, usually the space above a suspended ceiling or under a raised floor). The aria above a suspended ceiling is not a plenum space if both the delivery and return lines of the air-conditioning and heating systems are ducted. Plenum cable is required only if the air-conditioning and heating systems are not ducted. For AVAYA, NORSTAR, NEC, SAMSUNG, MITEL, PANASONIC, TOSHIBA telephone systems and voicemail call (866)206-2316 or email