What type of enclosure is required for electrical equipment installed in an air-handling space?

• A. A nonmetallic enclosure listed for use in a plenum
• B. A metallic enclosure
• C. A plastic enclosure
• D. An enclosure of any type

Answer: (A)

In air-handling spaces, the enclosure for electrical equipment must be nonmetallic and listed for use in plenum spaces. This environment is part of the building’s HVAC system, so materials here must be designed to limit smoke and toxic fumes and to minimize flame spread. A nonmetallic enclosure that is specifically listed for plenum use (often with a UL 2043 rating) meets these safety requirements. Metal enclosures aren’t acceptable in that environment unless they are specifically listed for plenum use, and a nonlisted enclosure isn’t allowed either. So the required enclosure is a nonmetallic enclosure listed for use in a plenum.