Spray foam around electrical box?


Old 09-27-19, 03:58 PM
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Spray foam around electrical box?


Hopefully this is a simple question. I replaced a metal electrical box with a plastic one, but there's quite a gap around the new box. I was going to spackle around it to fill the gap, but I think the gaps might be too big for spackle. On the other hand, I can go around to the back of the outlet from the garage side and use spray foam from that side to fill the gaps, and then just use an oversized outlet cover to cover the "ugly" on the room side. Attached are some pictures. I guess my question is (1) is this just crazy?, and (2) does spray foam and "electrical" not mix (although I'm not foaming inside the box, but around the outside).


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Last edited by PJmax; 09-27-19 at 05:58 PM. Reason: resized pictures
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Old 09-27-19, 04:21 PM
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IF this is an inside wall just use an oversize face plate. no need to fill in the gaps. If you're getting cold air from the garage use one of those insulating foam pads made for outlets.

But to answer your question, yes you can foam it but I would not. I would rather used blanket insulation.
Old 09-27-19, 05:58 PM
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You could tape the back off and use spackle too.
Old 09-27-19, 06:34 PM
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The code require the gap around the box to be no more than 1/8". Use 5 or 20 minute compound to fix the gap.
Old 09-27-19, 07:14 PM
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You said it was a garage wall. I would foam it. You want an air seal to keep fumes out of the house.
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Old 09-27-19, 11:04 PM
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Thanks for all of the replies guys. I think my picture from the garage side (the backside of the box) was a little misleading. The garage is in-fact sheetrocked and I had cut a hole in the sheetrock to get to the box. So I do plan on putting that sheetrock back. Thereís definitely going to be a draft from the garage to this room (and I completely forgot about the fumes), so Iíll probably do a little bit of everything.
Old 09-28-19, 12:00 PM
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I see from the pictures you provided you have the old cloth covered NM cable powering the grounding receptacle. I don't recall seeing much of that old stuff that ever had a ground wire in it, it mostly was all without ground. If you have no ground wire that receptacle should be GFCI protected or changed to a 2 wire receptacle.
Old 09-28-19, 12:28 PM
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That asphalt NM, when it has a ground wire, is usually 16awg, in my experience.

Iíd consider fibertape under any drywall mud. Or even fireblock caulk instead of brittle mud.
Old 09-28-19, 12:56 PM
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There are three cables coming into that box. Each cable has three wires: black, white, and bare copper. In the previous set up, the box was metal. So all of the grounding wires were wire-nutted together ( including one wire from the grounding screw on the outlet), then a pigtail came out to a metal clip on the metal box. Since the new box is plastic, I just put all of the grounding wires together in one wire nut, and then had a pigtail come out to the green screw on the outlet. Hope thatís correct?
Old 09-28-19, 01:45 PM
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It's not that old. It was common around here until at least the 70s. I have it in my house built in 1958 and it has ground wires.

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