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It is mechanically possible to install a standard new-work box in an existing wall by:

  1. Cutting hole in drywall adjacent to a stud

  2. Placing plastic box in the hole up against the stud

  3. Screwing through the plastic into the stud. The screws would need to be somewhat angled and as much as possible positioned to penetrate the meat of the stud.

However, is this acceptable practice? To be clear, I'm asking about using a box that was not specifically designed to be mounted in this way.

Once concern I have is just that the screw heads could be slightly in the way, maybe a small risk of nicking wire insulation. But this is probably avoidable and there are plenty of other similar circumstances where that has to be taken into consideration.

Second concern would be if this violates electrical code for some reason? (USA)


Note - there are a few reasons you might prefer to use a new-work box instead of an old-work box (which would not require this procedure):

  • Positioning
  • You don't have one on hand
  • Much more secure to attach to stud than to drywall, like for a large 240V plug
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    @FreeMan thank you for reading carefully... I edited to clarify I hope – StayOnTarget Nov 3 '20 at 17:37
  • @FreeMan and a second edit, why did I have to reread that 5 times before I saw my mistake? lol – StayOnTarget Nov 3 '20 at 17:39
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    Because it's much easier to note other people's mistakes than our own. :/ – FreeMan Nov 3 '20 at 17:43
  • @FreeMan true words of wisdom :) – StayOnTarget Nov 3 '20 at 17:43
  • my ele does this all the time - not that this means it is code compliant but it doesn't get flagged on inspection. – Fresh Codemonger Nov 3 '20 at 17:50
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Yes, as redlude97 mentions, they make boxes designed to mount this way. They're often sold as old/new work boxes since they can be used just as easily either way.

Here's a picture of a typical example. This one is made by Arlington and sold by Platt, (though this is not an endorsement of either of those companies; it just happened to be the first google result):

Old/New Work Electrical Box

Edit in response to your question edit:

Since you're asking specifically about using a new work box not designed for this purpose, that would most likely not be allowable unless the manufacturer specifically allows it in their instructions. One of the primary jobs of electrical boxes is keeping contained any fires that may try to start inside of them, and UL (or other testing labs) make sure they do -- provided they're unmodified. Once you start adding holes in them that the manufacturer didn't put there, then they can no longer guarantee their fire performance, and their UL listing is technically no longer valid. Now, an inspector might not notice, and just assumed you used one of the ones designed to be mounted this way, but it would still be a code violation. This falls under Sec. 110.3(B) of the electrical code -- you must follow manufacturers instructions when installing listed equiptment.

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    And why take any safety or liability risks? – Mark Gavagan Nov 4 '20 at 12:45
  • Plus, boxes designed for old work are generally easier to handle in such situations. – chrylis -cautiouslyoptimistic- Nov 4 '20 at 18:31
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Just use a metal box

You have much broader latitude to put additional holes in a metal box.

Just drill the holes that you require or prefer, fill them with screws, and you're all set. Metal boxes are UL-listed on the presumption that none of the manufacturer-supplied screw holes will be filled.

Metal boxes do a much better job containing heat from arc faults, and they also assure breaker trip if a hot wire gets loose and contacts the box. That is, after all, the purpose of a box.

Also, metal boxes provide several mechanisms for grounding switches and receps without having to run a ground wire to them. Switches ground through the mounting screws, and receps also can do that if they are "self-grounding".

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They make these boxes with preinstalled angled screws, without providing a product recommendation google smart box electrical 1 gang

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Making a hole in a box for a screw to mount it is acceptable. If you look at this box from Carlon for example

https://new.abb.com/low-voltage/products/wire-cable-management/electrical-boxes/carlon-deep-blue

it can be used for both old work (cutting a hole and installing in an existing finished wall) or for new work (installing in the studs before the drywall or other wall finish is applied).

For new work, you'd be snapping off the flange used for new work - it's perforated so it will snap off easily. Then you'd drill screws from inside the box into the stud. As mentioned in the question, you would have to make sure you don't make a sharp burr inside the box - you wouldn't use a drywall screw or other flathead screw made to use in wood.

There is a practical limitation to consider thought. Unless you have a right-angle adapter for your drill / driver

right angle adapter

driving screws inside the box is going to be a pain. I'd recommend a screw with a pan head that will let you use a square or star drive - phillips would be less than ideal, and slotted would be an exercise in frustration. I'd also recommend using a washer, so it's less likely to rip out of the plastic, and don't overtighten it.

The "smartbox" type boxes with the built-in angled screws inside

Madison smartbox

are more expensive, and have just a little less room inside for your wires and devices, but really easy to use, do not require a right-angle adapter, and easy to adjust the depth. They still have way more room inside than the metal old-work style boxes, which are tiny - barely big enough to fit dimmers, smart switches, and GFCI devices.

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