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I would like to side-mount this double gang box as shown to install two switches. My concern is that the 1/4” holes in the back of the box will be a code violation. I have looked at other 2 gang metal boxes but all seem to have these large holes in the back, presumably for mounting the back of the box to concrete.

BTW I’m planning to run the conduit up from the left knockout so I can a attach it to the stud with a support bracket. I believe support is required within 3’ of a box for EMT, although I see some conduits in my basement that are only supported high above the box where they contact the ceiling joist.

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    Though note that this specific box will require a special cover plate to be able to mount switches on it, as the one in your picture is designed primarily to have a blank cover plate put on it. This is because there aren't places in the proper spots to directly mount switches.
    – Milwrdfan
    Mar 9 at 22:19
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    @Milwrdfan "is designed primarily to have a blank cover plate" is entirely in your own head. It's designed to have any number of covers to suit the many possible uses - an exposed work cover, a mud ring (of various depths and in one or two gang configuration), a box extension...blank covers are one option, but far from "the primary one."
    – Ecnerwal
    Mar 10 at 2:05
  • Why worry about tiny holes in the box when the holes in the receptacle you might be mounting in there are larger and far more inviting for prying fingers?
    – arne
    Mar 10 at 14:57

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This box is a welded version of the drawn 4" square box you have there. It comes, from the factory, with ears for nailing it to a (wooden) stud, yet still has the exact same pattern of open holes in the back as yours does.

4" welded steel box with mounting ears
Source: Lowes.com

If this box comes with a UL listing (which it does) to be mounted via the attached mount points with the holes in the back open, then yours meets UL requirements when mounted through the side, even if the holes in the back are open.

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  • Thanks. Does that mean I can use this box but not the original one that lacks the mounting bracket?
    – Michael D
    Mar 9 at 20:06
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    It means the small holes in your box (as most all metal boxes have) are not a problem.
    – kreemoweet
    Mar 9 at 21:08
  • @MichaelD as kreemoweet noted, this was simply used as an example of another box that is, essentially, the same as yours, to show that this one is specifically designed to side mount and leave the holes on the back exposed. If you look closely, you'll also see that it has holes on all 4 vertical edges that one could screw/nail through to mount it, yet those are left open when installed with the mfgr's intended mounting method.
    – FreeMan
    Mar 10 at 12:24
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You can just drill mounting holes as needed for a side mount. Do not drill on knockouts or contacting knockout edges. Being able to field-drill mounting holes is one of the many privileges of using a metal box! Can't do it with plastic.

The holes in the back of the box are not a code violation. It is normal for some of them to be unused. I keep a bag of #10-32 bolts and nuts in my electrical kit, I could always fill the holes with those if it bothered me. The smallest hole is already tapped #10-32.

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  • As noted in the link I added: Metal boxes can be mounted anywhere. If you don't have a screw hole in the place you need, drill one.
    – manassehkatz-Moving 2 Codidact
    Mar 9 at 21:24

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