300.22 Plenum Space Wiring Methods – https://www.MikeHolt.com/code. Nowhere is the risk of the spread of fire more apparent than in the spaces and ductwork that distribute environmental air, or the ductwork that provides different types of exhaust. The types of ducts, plenums, and the special wiring and electrical installation considerations contained within section 300.22 of the NEC are the topics of this podcast.