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Can you stack a handybox with an extension outside of the drywall? This puts the total box size at just shy for 4". I know handyboxes can be used with conduit, but can they be double-stacked in a garage location? I am wondering if I should re-do this, but I'd like to put in a dimmer switch that likely won't fit in a normal-sized handybox.

See image:

enter image description here

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It will be ugly, but I am aware of no code rule that would stop you from using an extension on a surface mounted handy box.

However I can't imagine why you would; it would be just as easy to switch to say a 4x4 box with a raised industrial cover, plenty of room inside, and it would protrude less, and it wouldn't be so ugly.

4-square box with industrial switch cover

As mentioned in @Harper's answer, you will have to trim the tabs on a Decora device to get it to fit in an industrial cover.

4-square box with industrial decora cover

If you'd rather not trim the decora dimmer to fit the industrial cover, you could use a mud ring on the 4x4 box, but I wouldn't - the plate will not lay flat and the corners will stick out like they do in the current handy box. I don't like that appearance, it's prone to chipping and cracking the cover, catching on things, etc.

If you really don't want to trim the tabs on the decora device, bump up to an even bigger box - a 4-11/16" square box, sometimes called a 2100 box. A 4-11/16" flat device cover is big enough that the plate will lie flat with no corners sticking out

4-11/16 box with flat device cover

or for a really finished appearance, spend a few more dollars and use a 4-11/16" decora industrial cover.

4-11/16 box with industrial cover

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    If those horizontal boxes are an extension from an embedded box please consider getting a RACO 187. – NoSparksPlease Dec 2 '19 at 2:34
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    The 187 extension is nice but I the picture shows a surface mounted handy box - you don't often see them flush. – batsplatsterson Dec 2 '19 at 10:52
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Yes, that's fine anywhere the aesthetics are acceptable, but please don't.

I'd much rather see you install either a 4 x 4 x 2-1/8 junction box, or a 4-11/16" square junction box, and fit a 1-gang mud ring. If it's a Decora device, use a mud ring with at least 1/4" of bump. Otherwise they make flat plates with 0" bump.

enter image description here

You can also use one with a domed cover (as in BatPlasterson's answer), but I wouldn't do that if it's a Decora device. They won't fit on a domed cover and you must mutilate a Decora device to make it fit, which means it can never go anywhere else.

On a bare/exposed mud ring like this, too-large cover plates like in your original photo will tend to snag. They make metal cover plates that are very minimal - they are designed to be caps for, and just cover a 1-gang handy-box like in your question's picture. That is also the right thing to use over a mud ring like this.

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  • You nailed it - the target is a caseta device with a decora casing. Thanks for the tip! – user3732386 Dec 2 '19 at 3:43
  • That's true, you have to trim the tabs of the Decora device to make it fit under the dome cover, but with a mud ring, the regular cover still doesn't lie flat on the plate. I hate those protruding corners. I do know another alternative and will update my answer. – batsplatsterson Dec 2 '19 at 10:27

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