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After carefully considering and measuring the layout of two proposed recessed medicine cabinets over my bathroom vanity, I've discovered that the spec homebuilder carefully considered how they might stymie that future project.

In particular -- for this question today -- is the light switch gang box seen on the right of picture 1. It leaves me only 2.5 inches of wall cavity, when my recessed cabinet needs 3.5 inches.

Ideally I would move the light switch horizontally leftward (as seen from the bedroom, in photo 2), but I can't because it is already up against the cluster of studs that make up the doorway of that bedroom.

Next option is to lower the light switch on the wall to be below the rectangle needed for the mirror. But I don't know what electrical code has to say about that. It would certainly be unusual compared to the rest of this 2001 house.

Moving it farther away from the door or to the adjacent wall (the one the door swings against) would feel awkward.

I've seen shallow single-gang boxes, but they

  • Seem too shallow for a standard 1-way switch, 3 cables and associated wire nuts
  • Seem intended just for splicing runs

(No I cannot just shift the proposed recess cabinet to the left, because that will ruin my feng shui careful centering of both mirrors over the vanity.)

enter image description here enter image description here

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    They are quite picky about light switches at doorways. Basically you should just need to find the switch in the pitch blackness, so very limited choice to common placement. Think shallow boxes used more than just junction box, but need the experts to say more.
    – crip659
    Commented Oct 15, 2022 at 0:21
  • Have you considered either lowering the switch or raising the cabinet. Maybe both would work.
    – Gil
    Commented Oct 15, 2022 at 15:53

1 Answer 1

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Steel boxes to the rescue

Better installations use steel boxes. They use a standard "knockout" into which you fit connectors for the particular cable or conduit type you are using (here, NM-B).

Here's the cool thing: the boxes come in many shapes, including some surprisingly shallow ones.

So I would start with the bog-standard 4x4 steel box.

enter image description here

This particular one has stud flanges which is good, but also built-in FMC conduit connectors which is very wrong for your application. Forget built-in connectors, just get standard knockouts as seen on the side of that box.

Now, what you notice about the steel box is it's only 1-1/2" deep. Muuuuuch better!

The 1-1/2" x 4x4" steel box is 21 cubic inches, and the mud ring gives another 3-6 cubic inches. More room than a plastic 1-gang box.

Into the knockouts, use NM-B connectors (oddly called "3/8").

enter image description here

These boxes can also be put back-to-back in a 2x4 stud wall, with a "box spacing connector" both physically bracing them and allowing wire pass-thru.

What you may also notice is it doesn't have standard attachment points. That's correct; you add a Mud Ring the thickness of your drywall. They make them in 1-gang or 2-gang. 2-gang here may save you some drywall work, and then just come up with something to put in the other space - they also make one-side-blank cover plates.

enter image description here

Also available in 2-gang.

Code requires you land all cable ground wires on the box first.

Now fun fact, you notice how the mud ring makes flush contact with the box? That means ground is carried to the mud ring. And then, via the mounting screws, ground is carried to switches and self-grounding rated receptacles. So that's one less wire to wrestle into the box.

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  • "... So that's one less wire to wrestle into the box." Thank you for that detail in particular. I made use of it (and tested continuity between switch and ground, to be sure). Commented Oct 31, 2022 at 4:16

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