In cabling, what does 'Plenum' designation indicate?

• A. Type of wiring conduit
• B. Color coding scheme
• C. Cables rated for use in air handling spaces due to fire safety considerations
• D. Shielding configuration

Answer: (C)

Plenum designation indicates the cable is rated for use in air handling spaces because of fire safety considerations. In buildings, spaces like return-air plenums and drop ceilings circulate air, so cables installed there must minimize flame spread and smoke production during a fire. Cables with a plenum rating use special flame-retardant jackets and low-smoke materials and are tested to standards such as UL 2043. This rating is more stringent than general-purpose or riser ratings. It’s not about the type of conduit, color coding, or shielding—the designation specifically concerns fire-safety performance in air-handling spaces.