Wiring in soffits?


Old 02-20-06, 08:07 AM
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Question Wiring in soffits?

I'm running some NMSC through a soffit. The soffit encloses some ductwork in my basement ceiling. Can I run the cables along the bottom of the soffit cavity or do I have to go up to the joists?

(It may seem a trivial difference, but the way the ducts are arranged, it would be a lot simpler if I could run the cables along the bottom of the cavity)

They would lie on top of the horizontal memebers that form the bottom side of the soffit. I'm not sure what the code requires for this (the 'simplified' code book I have doesn't mention anything about soffits).

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Old 02-20-06, 11:22 AM
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I don't know your answer but... The soffit you describe may be construed as a plenum by your local inspector. If so, the codes are much more strict. You may have a tough time getting a definitive answer to this one.

Good luck!
Old 02-20-06, 11:56 AM
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What is the ambient temperature?
Old 02-20-06, 12:57 PM
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The soffit is in a (soon-to-be) finished basement. There's no drywall around it yet, so it's hard to tell what the temperature would be when enclosed. That said, I'd find it difficult to believe that it would be higher than 90C (I'm using NM-90 cable). There's a fair amount of open space in the soffit since it spans the hot-air plenum, a cold air return, an I-beam, and some supply pipes. There aren't any lighting fixtures in the space.
Old 02-20-06, 01:00 PM
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I don't see any problem running your cable in that space. Just make sure you have proper clearance or protection so that a nail or screw can't pierce the cable.
Old 02-20-06, 01:07 PM
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Red face

Thanks for all your replies. Code specifies 1.25" from the nailing edge of a stud. Cable sitting on top of 2x3 soffit framing will be 1.5" from the nailing edge. By this reasoning I should be okay.

I suppose I could put a 1x4 running board or something in, but that may be overkill.

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