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I've just discovered what looks like some crazy wiring. Our basement staircase has a light at the top of the stairs and a light at the bottom, as well as 3-way switches at both the top and the bottom. The 3-way switch at the top of the stairs was damaged by the tenant in the basement so I went to replace it with a new one making sure I connected all the wires as they were previously. When testing, I realized the two lights don't operate at the same time and the top light is not controlled by the bottom switch, so I decided to investigate and figure out how they were wired.

It looks like the bottom light is correctly wired for 3-way operation, but the top light is simply connected to the black and one of the brass screws in the top switch, such that it is effectively using the bottom light fixture as a neutral.

I've attached a diagram which I'm pretty sure is accurate. diagram of wiring

Edit: and here's my attempt at a wiring diagram wiring diagram

FYI: the top light is an LED fixture and the bottom light is a regular lamp/bulb fixture. When the top light is on and the bottom light off, I read 12V on the hot wire of the bottom light.

Is this allowed or even safe, and if not what is the best fix?

Whoever owned this house previously seems to have done crazy stuff all over the place.

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    That can't be right. As drawn, you have 4 logic possibilities: #1 light the lower light only. #2 same. #3 light both lights dimly and #4 nothing. You have drawn a schematic, I would focus on drawing a wiring diagram showing cables in each box.
    – Harper - Reinstate Monica
    Commented May 28, 2022 at 3:10
  • When both switches are down, only the bottom light is on; when the bottom switch is down and top switch is up, only the top light is on; when the bottom switch is up and the top switch is down, both lights are off; and when both switches are up, only the bottom light is on.
    – Matt
    Commented May 28, 2022 at 3:39
  • I've drawn a wiring diagram, added to the original post. Thanks
    – Matt
    Commented May 28, 2022 at 4:06
  • OK that correllates. If the top light lights, it must necessarily be pulling current through the bottom light, since the bottom light is in series with supply. "both lights dimly" isn't working because of a mismatch between the lights (which might be from them being LED). If they were equal size incandescents they would both be dim. Anyway, probably best not to dwell on 'crazy'.
    – Harper - Reinstate Monica
    Commented May 28, 2022 at 4:11
  • Is pulling replacement cabling an option here? Also, is the downstairs light in a position that's required by the NEC?
    – ThreePhaseEel
    Commented May 28, 2022 at 4:44

1 Answer 1

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This seems to be an attempt to install "three-way" switches to control two lights simultaneously. You do not have enough conductors installed to wire this circuit properly.

You have several choices to remediate this circuit.

  1. Replace some cables. The second leg, between the bottom light and the bottom switch, needs to have 3 conductors instead of 2, and the third leg, between the two switches, needs to have 4 conductors instead of 3. If your walls are closed up then you probably don't want to do this.
  2. Add a cable. Run a 2-conductor cable all the way from one light to the other. This would allow wiring the lights in parallel. This would be my preferred choice, even though it requires some wallboard repair.
  3. Abandon the top light. Cap the wires, remove the light, cover the old light box with a blank plate, and stick a battery & LED pull-chain light on the blank plate. Then you can control the bottom light with the two switches in a "three-way" switch loop.
  4. Abandon the bottom light. In this case the hot and neutral would be fed straight through the bottom light box without connecting to anything else there. The top light would be controlled by the two switches in a "three-way" feed through.
  5. Convert the bottom light to always-hot, and control it with a pull-chain or other local switch. This is a good choice if the top light provides enough illumination to safely use the stairs. The top light would be controlled by the two switches in a "three-way" feed through.

The "three-way" switch loop and the "three-way" feed through are both well-known circuits. You can probably find lots of diagrams on line.

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  • Option 5 would require wiring changes still, as power comes in at the upstairs lamp
    – ThreePhaseEel
    Commented May 28, 2022 at 16:04
  • @ThreePhaseEel: Querent's circuit diagram shows power entering at the bottom light.
    – A. I. Breveleri
    Commented May 28, 2022 at 16:49
  • Ah, yeah, that'd work then
    – ThreePhaseEel
    Commented May 28, 2022 at 18:44

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