Electrical equipment with low smoke and heat release properties, and wiring material suitable for the ambient temperature can be installed within an air-handling space if the enclosure is what?

• A. A metallic enclosure
• B. A nonmetallic enclosure listed for use within an air-handling (plenum) space
• C. A plastic enclosure
• D. Any enclosure

Answer: (B)

In air-handling spaces, only equipment and enclosures that are specifically listed for use in plenums and that have low smoke and heat release properties may be installed. The enclosure must be listed for plenum use, and the option that matches this requirement specifies a nonmetallic enclosure that is listed for use within an air-handling (plenum) space. The listing ensures the enclosure material, construction, and any joints meet the plenum safety requirements, preventing excessive smoke or heat from propagating through the air system and ensuring compatibility with the ambient temperature. Without that explicit listing for plenum use, the enclosure does not meet the NEC’s safety criteria for plenums.