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I have an old light switch that I want to upgrade. The old switch does not have a ground screw (see second image) so the bare copper ground wire is just tied to the metal box with a screw (see "B" in the first image).

My new switch comes with a ground screw and a ground wire pre-attached.

Also, there does not appear to be a neutral wire here (correct me if I'm wrong) so I made sure to just pick a new switch that does not require neutral.

I just want to make sure, when I install the new switch what is the best way to go about it:

  • Remove the existing copper wire from the box screw and attach it to the light switch's ground wire?
  • Leave the existing copper where it is (B) and attach the new switch's ground wire to the box at A?
  • Or pigtail the existing copper to the new switch and then put it all back at B?

I know there are other similar questions answered on the site, but I wanted to provide pics of my exact setup to make sure. Thanks.

(also, whatever the solution is here, would it also apply to something like smart relays?)

Front of box

Back of switch

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Leave the ground at B as it is, connect the ground of the new switch to A.

With metal boxes there is less need to connect a ground wire from a switch to the box, since the metal screw mounts of the switch act as a ground path.

White wire is usually used as neutral in circuits, but in your case the cable is being used as a switch loop. One wire is always hot/live(should be the white and is nice to put black tape on it) and the other wire is called switch hot, becomes hot when switch is on.

Newer smart switches do usually require a separate neutral and new code requires three wire plus ground cables for them(black, red, and white for neutral).

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  • Thanks. This is the new switch so I'm thinking that because it looks like mostly plastic housing, I'd better make use of the included ground wire. (Although from videos, it looks like there are metal strips going from the screws to the internals.)
    – orr
    Apr 4, 2022 at 10:35
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    If relying on the switch mounting screws to ground the circuit to the box, make sure to remove the tab that holds the screw on the backside. There needs to be metal on metal contact between the switch and the box.
    – Evil Elf
    Apr 4, 2022 at 12:17
  • @EvilElf Will do, thanks.
    – orr
    Apr 4, 2022 at 12:54
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There are a lot of problems there.

The left of the three cables has two unterminated wires in the box. What’s with that? At LEAST they should be capped off, but what are they, and why is their ground wire in use (but incorrectly)?

The left switch is grounded by a wire from that left cable. The box is grounded by a wire from the right cable. I can’t see where the ground wire goes from the middle cable. But none of these are connected together as they should be.

I'd like to suggest that whoever did this has so little understanding of electrical wiring that it should be inspected and rewired by a professional electrician.. If the same person did other wiring in this house you NEED to have it looked at by a professional.

At least in this box, all the ground wires need to be connected to each other and to all the switches and to the box. It’s not critically important HOW you do that. Ideally, the wire that is closest to the actual source of ground should be longer, should be connected to the box screw first, and then wire nutted to all the rest, and the switches should all be pigtailed to that. Usually in an existing box you can't be picky ... you use the available wire to connect everything together as best you can without breaking them, as long as they ARE ACTUALLY connected by proper nuts or devices.

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  • I don't know what the unterminated wires were intended for. In case it matters, the left device is a power outlet, not a light switch (does that make the grounding situation make sense for the left side?) The middle ground wire is tied to the screw behind that jumble of unterminated wires. Anyway, thanks for giving me a heads up, I'll get an electrician to check this out.
    – orr
    Apr 4, 2022 at 12:54
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    As it happens the ground wires are all connected to each other via the switch and outlet frames and their mounting screws so while in use, it won't make a difference. But it's not meant to be done that way and what scares me is that the installer probably had no sense of the function of the ground system. It appears the installer just thought each ground wire needs to be terminated somewhere, as if it is the wire itself whose needs we are serving. If the level of understanding was that poor, it's worth having the whole house inspected. If you quickly find that this box is an anomaly, GREAT
    – jay613
    Apr 4, 2022 at 13:12
  • Got it, thanks again @jay613
    – orr
    Apr 4, 2022 at 13:26
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    If that uncapped black wire is hot (or the white, for that matter) it's a potentially big issue. When you stuff everything back in, you can easily make the whole box hot. At the very least put caps on those wires. +1.
    – JimmyJames
    Apr 4, 2022 at 20:56

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