I am having trouble knowing what type of electrical boxes to use on smaller metal studs.

I recently purchased a new construction that has an unfinished walk out basement. On the three sides of the house that are underground they used these walls that, as far as I understand it, are prefabricated with concrete, insulation, and metal studs. Here is a sideview of the wall where you can see all three sections.

The problem I am facing is that the metal studs are not very deep, they are a little more than 1 1/2" deep.

I found some low profile boxes which I think would do the job. I just need to run outlets on these walls, nothing fancy. I was concerned because I saw in the reviews of this box that this did not have the cubic inches needed to meet some NEC safety requirements and was wondering if there was someone on here with more knowledge than me that would be able to confirm or deny that this is what I should be using. Thanks!

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    Aesthetically, how do you feel about external conduit and surface mounted boxes? (It’s not clear if you have drywall yet, but if you did, the wiring would be much easier this way.) Commented Jun 18, 2022 at 13:30

1 Answer 1


The box you want to use is stamped for 8 cu-in.. If you install a single outlet with 14 AWG cable, the fill would be: two cables times 2 cu-in each, the outlet, 2 times 2 cu-in and a ground, 1 times 2 cu-in for a total of 10 cu-in.

An alternative would be to use a common 4" metal box (21 cubic inches) with a single gang mud ring. If using Romex, use cable clamps to enter a knockout hole. See pictures below.

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    Don’t forget to protect the beginning of the chain of outlets with a gfci (breaker or properly wired receptacle). Commented Jun 18, 2022 at 14:31
  • Thank you this has been very helpful. One follow up question, do electrical box extensions count towards the cubic in? For example, if I were to purchase something like this half inch box extender would that get me to 12 cu in that would allow me to daisy chain? homedepot.com/p/…
    – Weltall
    Commented Jun 18, 2022 at 17:00
  • Smart people will weigh in, but I don’t think daisy chaining off the receptacle ‘costs’ anything in box fill. And I think grounds are ‘free’, but could be wrong. The 2 gang solution will make things markedly easier just fitting stuff in. Commented Jun 18, 2022 at 18:19
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    A bog-standard 4x4 box is 21 cubic inches, and 3-10 more for the mud ring depending on thickness. (you can see it stamped right on the mud ring). Yes the mud ring cubic inches count in your favor. All wires count except pigtails, and grounds are "4 for the price of 1". This larger box (with a 1-gang mud ring) will be a lifesaver if a GFCI is involved, as 1-gang boxes are awfully tight for that. Commented Jun 18, 2022 at 18:33
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    @AloysiusDefenestrate If this was a conduit installation and the loops were less than 12", unbroken wires with insulation stripped off and connected to the outlet would not affect fill but NM in and out, cut, does affect fill.
    – JACK
    Commented Jun 18, 2022 at 18:38

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