Can I side-mount metal box with holes in the back?

Question

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.

Answer 1

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.

^{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.

Answer 2

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.