Final answer:
Wiring in air handling spaces must be run in a conduit or be rated as plenum-rated cable, which is designed to resist fire and emit fewer toxic fumes. Plenum spaces in buildings require special attention to fire safety, and the NEC specifies the use of conduit or plenum-rated cabling in these areas.
Step-by-step explanation:
Wiring in air handling spaces must adhere to strict fire safety codes and regulations. When wiring is not run in some type of conduit, it must be rated for the specific environmental conditions of the air handling spaces. Specifically, the wiring must be rated as plenum-rated cable which includes plenum-rated power cables, network cables, and other communication wiring that resist fire and emit fewer toxic fumes.
Plenum spaces are parts of a building that can facilitate air circulation for heating and air conditioning systems, and because they have a potential for increased fire hazard due to the volume of air passing through, the National Electrical Code (NEC) requires either conduit or plenum-rated cabling. Conduit provides a physical barrier protecting the wiring, but where conduit is not used, plenum-rated cable is necessary to meet safety standards. This type of cable is coated with fire-resistant material that reduces the amount of smoke and hazardous fumes in case of a fire.