What is the wiring rating called when conductors pass through ducts?

• A. Riser rated
• B. Plenum rated
• C. General purpose
• D. Wet location rated

Answer: (B)

Wiring that runs through air-handling spaces like ducts must be plenum-rated. In ducts and plenums, air is circulated to ventilate the building, so any insulation or jacket material on the conductors needs to minimize smoke production and limit toxic gas release if a fire occurs. Plenum-rated cables are tested to meet stricter fire and smoke safety standards for these spaces, helping keep the ventilation paths from becoming highways for smoke and harmful fumes.

Riser-rated is for vertical runs between floors, not specifically for air-handling spaces. General-purpose wiring isn’t designed for use in plenums and may emit more smoke. Wet-location rated is for damp or submerged environments, which isn’t the primary concern in a ducted air system. So, plenum-rated is the appropriate choice for conductors passing through ducts.