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I've recently replaced all my incandescents with LEDs and found that the dimmer switches were of a type that... disagreed with the dimmable LEDs. While I was replacing the switches I noticed that 2/3 dimmers had unconnected ground wires. These were notably the ganged boxes, with the single-switch box having the ground properly connected, the other switch boxes grounds were simply bundled together off to the side.

That said, the switch ground is simply connected to the metal mounting bracket, and the bracket is connected to the switch box via the mounting screw, and the box itself is grounded.

I know that it is not ideal, but is it acceptable to leave the situation as-is rather than digging all the old wiring out of the back of the switch boxes? I've already destroyed my hands getting to this point, and also the ground wires are inexplicably painted over.

Yes, they are inexplicably both crammed into the back of the box and painted over, and I know neither how nor why.

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    Most switches/outlets are grounded to metal boxes by their mounting screws, and having a ground wire on the ground screw is just an option. If the switch has a ground wire attached from the maker would used it and attach to ground.
    – crip659
    Nov 28, 2022 at 20:37

3 Answers 3

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It is correct already.

On metal boxes, ground from cables must be routed to the metal box FIRST. That is a Code requirement. It also provides a useful benefit: if a hot wire gets loose or pinched in the box, it will result in an instant breaker trip instead of a lingering hazard.

Once the box is grounded, switches pick up ground automagically via their mounting screws. There is no need for hard, flush, metal-metal contact for switches (nor for receptacles labeled "Self-Grounding").

This is a break from what you may have learned with plastic boxes.

You can run a ground wire if you really really want to, but you must not disrupt the mandatory grounding to the box. So you can run a wire to an additional ground screw on the box, use a ground clip, or add to the pigtail already going to the box. Do Not disconnect grounds from the metal box and place them on the switch. That would leave the box ungrounded (except through a serpentine path that might not suffice for grounding a hard short). And the grounding would be lost when the device is removed.

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  • no need for hard, flush, metal-metal contact Really? Because without that, and especially a bit paint-splattered, it is just the screw (not necessarily as fine as the -32 ground screw) doing the job. (Well, 2 screws at least, presumably that helps a bit.) Nov 29, 2022 at 0:49
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    Good lord, why on earth would they make switch boxes out of plastic? I can't think of a single benefit over metal. Anyhow, thanks for the explanation. I'm a sub-apprentice electrician at best, but I have a basic idea of how wiring is supposed to work and figured "this is all probably fine, but I should double-check".
    – Sammitch
    Nov 29, 2022 at 1:31
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    @manassehkatz Devices use 6-32 screws to mount; the -32 thread pitch satisfies Code for thread engagement to the metal. The question of the hour is "what about the screw head-to-yoke contact?" NEC says good enough for switches only, probably due to their low need for grounding. Right out for a receptacle, as one might expect. Nov 29, 2022 at 1:54
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I cannot say with any authority what the code says about your grounding situation, but I believe I know the answer to your paint mystery. When the house was constructed, I am going to guess the painter sprayed before the outlets and switches were installed, and couldn't be bothered to mask off the open boxes with the rough electrical in them.

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  • This sufficiently explains the mystery, but manassehkatz answers the question. Also I'm less concerned with strictly adhering to building code than I am with simply not burning down the building or zapping a finger off.
    – Sammitch
    Nov 28, 2022 at 22:15
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As long as you have metal boxes and the boxes are properly grounded and the switch yokes have good metal-to-metal contact with the boxes, you are OK.

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