Plenum wiring is permitted in ducts fabricated for environmental air-handling purposes if the total length of such wiring does not exceed how many feet?

Plenum wiring is permitted in ducts fabricated for environmental air-handling purposes if the total length of such wiring does not exceed how many feet?

• A. 4 ft
• B. 6 ft
• C. 8 ft
• D. 10 ft

Answer: (A)

In ducts or plenums that are part of environmental air handling, wiring is limited to reduce fire growth and smoke production in the air path. The NEC allows wiring that is rated for plenum use in these spaces, but the total length that can run inside the duct is strictly limited to four feet. This short length helps keep heat sources and fuel loads low within the air-handling path, improving safety and air quality. If more wiring is needed in the air-handling duct, it must be routed outside the duct or installed using an approved method that is permitted for plenum spaces, with the wiring properly listed for that use.

In ducts or plenums that are part of environmental air handling, wiring is limited to reduce fire growth and smoke production in the air path. The NEC allows wiring that is rated for plenum use in these spaces, but the total length that can run inside the duct is strictly limited to four feet. This short length helps keep heat sources and fuel loads low within the air-handling path, improving safety and air quality. If more wiring is needed in the air-handling duct, it must be routed outside the duct or installed using an approved method that is permitted for plenum spaces, with the wiring properly listed for that use.