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I'm having trouble figuring out why my light switch box is wired the way it is. The place I'm living in is quite old (guessing built in the 80s?). Originally, I opened open the panel with the hope of installing a switch-outlet combo... which I can't do until I figure out why it's currently wired the way it is.

I've made a diagram (below). The large rectangles on the edges of the box are the ROMEX cables, while the smaller squares are wire nuts. W = white wire (neutral), B = black wire (hot), Gnd = bare copper (ground). The switch is on the far right of the diagram.

wiring diagram

As you can see, the wiring is quite strange. Two of the neutrals are connected to ground, with another neutral connected to a couple of the hot wires. If I had to guess, it looks like they wanted to make another power line without having to run separate cabling.

Can anyone tell what's going on here?

Thanks for the help!

  • Does the switch even work? The way its wired, seems like you won't get any voltage across the right outlet, because both connections are hot. – Jeff-Inventor ChromeOS Aug 9 '14 at 20:50
  • Yep... the switch definitely works. – david Aug 9 '14 at 21:00
  • Which black wire (or wires) is hot when the switch is off? Also, have you checked to see how the light fixture is wired? – Comintern Aug 9 '14 at 22:23
  • It would help if you included a diagram of the wiring at the end of each cable, especially the end of the cable connected to the switch. I'd be very interested to see where those wires terminate. – Tester101 Aug 11 '14 at 12:33
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You have some pretty weird wiring to the light fitting. It looks like at the light fitting (fed from top-right romex at box) you would find

  • the "ground" wire (green or bare copper in the US?) is being used as a neutral return from the light bulb.
  • the "hot" (black) is a switched hot to the light bulb.
  • the "neutral wire (white) is being used as a permanent hot for some other purpose.

So I'd expect an ordinary light fitting to be using the false "ground" and switched hot wires only.

The permanent hot (false neutral, white) might have been used (now or previously) to power some kind of device that needs live power. For example a remote light control or a ceiling fan that is operated by a pull-cord independently of the light bulb itself.

I would check the wiring in the light fitting controlled by that switch. Then I'd label the wires at each end to make clear what each wire is really used for. Alternatively, you could rewire it properly - that would be best if the light fitting is a normal conventional simple light only. I'd double check that something else (an extra outlet?) isn't already wired from the light fitting end - disconnect the white wire from the three black and see if an outlet or something stops working.

If you can't figure it out it might be best to call an electrician.

  • This was my hypothesis as well. Talked to an electrician friend of mine and he concurred. Thanks for the help. – david Aug 10 '14 at 22:37

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