Residential question

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chrismarcellino

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Minnesota
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ee
Dennis Alwon said:
It didn't sound like that
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It was a question--if he can use NMC or UF-B, he is not limited to dry areas (short of any local amendments) and can use the 90C column when derating like NM. (NMC can be used in damp areas unlike NM, 334.10(B), if you can find a place to order it.) I would contend that behind an exterior rated panel 1/8" off the siding under a standard residential eave is a damp location.

Or am I misunderstanding what you mean? thx
 
Coppersmith

Coppersmith

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Tampa, FL, USA
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Electrical Contractor
chrismarcellino said:
I would contend that behind an exterior rated panel 1/8" off the siding under a standard residential eave is a damp location.
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I've been debating about whether I agree with this statement and have come to the conclusion that if the mounting surface is flat and a sufficiently thick bead of sealant (1/4") is installed surrounding the penetration (and thus the cables), and then the panel is installed over this sealing the area, then this is not a damp area. However, it is advisable to run this past the inspector before proceeding.

I frequently install Bell boxes on exterior walls with NM cable coming into the back hub. I put a bead of silicone on the box surrounding the connector. I've never had one turned down on inspection.

That said, I don't believe running cables into the back of the panel is the best method since there are limited KO's on the back and the penetrations will have to be quite large. Coming into the bottom of the panel or using a trough on the inside wall as I've already suggested above would be better.
 
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Hv&Lv

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chrismarcellino said:
The comment was regarding sealing entrances to panels, or the open end of the accessible short conduit allowed by 312.5(c), which the NEC stipulates must be sealed. In either case, a flammable foam (115 C ignition point for Great Stuff) is less useful than any other material, and more work to add future wiring work. (If the panel is designed to contain an arc flash or bolted on fault etc,. best to not make a cannon out of it.)

No issues in the walls, attic or outside of otherwise permitted fittings, etc. of course. Wasn't try to suggest against the use of spray foam as insulation or draft sealing, for which it is awesome. I'm no inspector, but if I can see the spray foam from inside the panel or conduit, I would fail it. Just my opinion though.
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F6B4B451-D9BE-4C8A-BB30-1C52A366443C.jpeg


would some thing like this pass? I’ll admit, it looks like crap, but it’s listed for conduit sealing. It’s a closed cell foam.
 
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