Old 03-11-08, 01:52 PM
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Are you allowed to use a cold air returns or forced air duct as raceways?........Is mc cable allowed in a plastic box?

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Old 03-11-08, 02:26 PM
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Originally Posted by ThomasB View Post
Are you allowed to use a cold air returns or forced air duct as raceways?
Only if metal raceways are installed. You can use MC/AC cable, EMT conduit, etc through an air-handling space. No PVC boxes, plastic conduit, Romex cable, etc.

I would really not consider using the heat ducts as the warm environment in the duct will require derating the ampacity of the wire.

Romex is allowed through the perpendicular dimension of cold-air returns if you seal the penetrations with fire-rated caulk.

Is mc cable allowed in a plastic box?
No. With metal-sheathed cables, you need to use a metal box with a fitting rated for that cable type to ensure integrity of the grounding system.

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