Electrical – Is it acceptable to retrofit a new-work plastic electrical box by screwing through it into a stud


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

Best Answer

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didn't put there, then they can no longer guarantee their fire performance, and their UL listing is technically no longer valid.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.