While at a house from the early 90's in Wisconsin, USA, I encountered the below setup. This switch, to my knowledge, controls a single-light fixture - so could wire #3 be an oddly-colored ground?

Thanks in advance.

Picture of the wiring

Reference Post

3 Answers 3


It is not a ground. The ground screw on this switch is on the little metal protrusion above the switch body near the top of the yoke. There is no ground wire connected.

The red wire is probably the "switched" power to the light fixture.

Regarding the two black wires at the bottom, it looks like the person who wired that switch just wanted to save a few cents on wire nuts.

The two black wires at the bottom are both hot - one of them coming from upstream (i.e. back to the breaker panel) and the other going downstream to another device somewhere else in the house. (Note that the upstream might also come from another switch that is wired just like this too.) One wire is connected to the screw terminal and the other is connected to the "backstab" hole next to it. It was a quick and easy alternative to having a wire nut in the box that connects both of those black wires along with a pigtail that goes to the switch.

The easiest way to confirm that this is what you have is to observe whether each of those black wires leaves the box together with a white wire.

It is important to note that this wiring method is now considered unreliable and unsafe (though I don't think it is explicitly banned). If you look at the backstabbed wire, you can see one reason why -- there is a gap (looks like around 1/4”) of exposed conductor at the backstab: either the wire insulation was stripped too far, or the wire has worked loose from the teeth inside the hole (by being shaken or pulled).

(If you are replacing the switch, note that most modern switches no longer have a backstab hole. However, some nicer switches have two holes in the back that come out behind the screw - you can insert a wire into each hole and then tighten the screw to secure both wires. Do not secure two wires under a single screw from the outside, since the screws are not designed for that and one or both wires could come loose.)

  • 1
    It looks like the switch you have there is a three-way switch (because the terminals are color-coded), but from the angle of the picture it does not look like it is being used as a three-way switch. This answer is only correct if the second black wire is NOT connected to a screw on the opposite side of the switch.
    – Moshe Katz
    Dec 31, 2021 at 10:14
  • To help confirm, there are other ways to tell from the back, but all the 2-way switches I’ve ever seen in the US have “on” and “off” molded into the switch toggle, where 3 and 4 way do not. The picture doesn’t show the other side, but the back surface doesn’t show the inset I’d expect to see if there another screw on the non-visible side.
    – Tim B
    Dec 31, 2021 at 17:21
  • Thank you both. Apologies, I've been traveling. I can confirm that the second black wire is not connected to a screw. This entire discovery was disappointing as there is also no neutral wire that seems to have been run, leaving me to go back to a professional if I want to address this...
    – NJL
    Jan 7 at 4:58

Backstabs are internally connected to the nearest screw

That's the puzzle piece you're missing. On receptacles, you see 2 screws and you can plainly see they are connected to each other, so it is simply serving as a splice between the two wires (and feeding the receptacle too). You can't see backstab connections, so this isn't obvious, but the backstab+screw here are simply being used as a splice, to join the 2 wires to each other (and the switch too).

I suspect both black wires are "always-hot" (energized in any switch position). One of them comes from the supply, and the other takes power onward to another point-of-use.

The red wire is the "switched-hot" (energized when you want the light to be on). That coincidentally matches the preferred color code; usually you have to re-mark wires with colored tape lol.

This is a 3-way switch. But it's not being used as a 3-way switch, just as a 1-way. Which is fine.

  • This looks like a plastic box to me, given the bump for the screws.
    – Edwin
    Dec 31, 2021 at 19:57
  • @Edwin oh you're right, I missed that. Dec 31, 2021 at 20:07

No, that black wire is not a ground wire. Here are some things about this three-way switch that stand out to me:

  1. The ground wire is not connected. There is what looks like bare copper wire in the box. That needs to be connected to the other bare copper wires and, since this is a plastic box, to the switch, under the green screw. Since this home was constructed in the early 90s, there may be other switches in the home that don't have a green ground screw. That's fine, but if the switch has a ground terminal, you should use it.

  2. The black wire behind the switch - if it's connected to the switch - there is way too much copper exposed. That wire ether needs to be capped with a wire nut, or fastened correctly to the switch.

  3. It's possible this is a mis-wired three-way switch, and not a three-way switch used as a standard switch. A properly-wired three-way switch with a red wire under the common terminal (the black colored screw) doesn't make sense without either a second red wire or a white wire with black tape on it in the box. Under the common terminal (black screw) should be either the "line" conductor from the panel (hot wire) or the "load" conductor to the light fixtures. Usually, the cable with the three conductors (black, red, and white) goes to the other three-way switch. If this is the case, the red and black wires from that cable get connected to the traveler terminals (the ones that are not black). The other black wire (the one that comes from a cable with just a black and a white conductor) goes under the common screw.

  • 2
    Your "point 3" ignores the fact that a three-way switch can be (and appears to be, in this case) used as a regular switch. Indeed, the cost differential is small enough (if any) that stocking only 3-ways can make all sorts of economic sense for the person wiring the house. It's still "properly wired" as such with one traveler connection unused.
    – Ecnerwal
    Dec 31, 2021 at 18:13
  • @Ecnerwal - agreed. From a practical standpoint, this screams to me miss-wired three-way switch. The black wire in the back has no evidence of twisting, and it's too long to have been cut. This is a newer switch and looks, by the tidiness of things and not-connected ground, to have been done by a non-professional who would not be stocking switches. If there was intent to remove the second switch from the three-way scenario, I think it'd be a little neater, plus the OP is likely having issues, otherwise why create the post? I'll put a caveat in my answer, though.
    – Edwin
    Dec 31, 2021 at 18:28

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