In an air duct area, which type of wire would you most likely encounter?

• A. NM Cable
• B. MI Cable
• C. MC Cable
• D. Plenum Cable

Answer: (D)

In air duct areas you need wiring that is specifically rated for air-handling spaces. Plenum-rated cable is designed for these environments because its jacket materials are formulated to limit flame spread and produce low smoke and toxic gases if it burns. Ducts and other plenums can move air and spread smoke quickly, so using CMP-rated cable helps keep the ventilation paths safer during a fire. Other cable types, like NM, MI, or MC, aren’t intended for use inside ducts and don’t meet the strict plenum fire-and-smoke performance required for those spaces. So the best choice for an air duct area is plenum cable.