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I have an outlet box made of cheap PVC with worn out screw holes. It is located in a bedroom so dampness isn't really a big issue. The problem is: it's embedded in concrete so replacing the whole box would be difficult for me. I'm planning to just cover it with electrical tape but I have no idea if that's safe.

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    The screws are worn out, or the screw holes? What does that mean, seeing as plastic boxes don't have threads to begin with? Why can't you just use larger screws?
    – isherwood
    Commented Apr 13, 2022 at 20:36
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    I can't believe I'm endorsing plastic boxes, but they really are the best choice for inset into concrete. Concrete is inherently wet (when it dries out e.g. due to exposure to fire, it loses its strength and must be replaced. Those burnt tower blocks in Ukraine can't be saved.) However, that natural wetness makes metal boxes rust. Commented Apr 13, 2022 at 22:57
  • Isn't that one of the 7 signs, @Harper-ReinstateUkraine?
    – FreeMan
    Commented Apr 15, 2022 at 11:31

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If any electrical wires are in it, each one should have a wire nut on it.

Get a blank cover and put a dab of silicone on the holes in the box.

Push/screw the screws for the cover in and hold the cover with some tape till the silicone dries. Remove the tape.

Should look better than covering with electrical tape.

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  • Much better than my idea of "fill holes with epoxy, wait for it to cure, drill, tap, screw cover on".
    – FreeMan
    Commented Apr 13, 2022 at 20:02
  • Epoxy, drill and tap might be more code, since you just need to unscrew. Silicone might be more sticky to remove for code. If box still has wires in it.
    – crip659
    Commented Apr 13, 2022 at 20:07
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If you're not too concerned with appearance, you could pick up a pair of the next size up machine screws.

I'm not sure of the thread specification of a standard box cover screw, but I'd guess it's around a 4-40.Take one to the local hardware store and use their screw/thread sizer to find out for sure. A standard cover plate screw is 6-32 so go to the next larger size, 8-32. (assuming my guess was correct - it wasn't, thanks RibaldEddie).

Since the screw is larger than the old one, and the plastic of the box should be soft enough, the metal threads of the screw should cut their way in, and it would be a self-taping fix.

The screw heads would be "non-standard" looking, but how close they are depends on what screws are available easily and for a reasonable price.

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  • Tough choice, electrical tape or non standard screws. How will I choose?
    – crip659
    Commented Apr 13, 2022 at 21:43
  • Standard size for electrical box machine screws is 6-32. Commented Apr 14, 2022 at 5:10
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You might be able to stick a few toothpicks in the screw hole. Break them off even with the hole. Then you can screw away....well you know what I mean.

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  • That would work great on rigid screwholes (wood, steel, whatnot) but PVC will be a bit too soft for that, it might tear the box.
    – MiG
    Commented Apr 14, 2022 at 5:58
  • If the plastic hole is cracked...true, it wouldn't work. But the screw wouldn't be caring a load so I think this quick and dirty easy fix is worth a shot. Toothpicks are cheap! Commented Apr 14, 2022 at 14:09
  • It's a rigid object that resists the cutting action of the screw more than the plastic itself, which means it's likely to get pushed away more, potentially tearing the pvc inward... I would not try this unless I had exhausted all other options, especially considering the box is pretty much stuck in that concrete.
    – MiG
    Commented Apr 14, 2022 at 17:26

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