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I moved a three way switch and (stupidly) did not take a picture of the original installation. I'm trying to put it back together and having difficulty. This was originally wired in 1980 and worked. I didn't remove or add any cables.

I have power, one light, 4 conductor cable, and 3-way switch in Box A.

I have two lights, 4 conductor cable, and 3-way switch in Box B.

I moved Box B but I've since taken apart Box A trying to figure this out so I'm re-wiring everything.

How should this go back together? I've wired a 3-way switch before and I can wire it OK if I omit the lights in Box B. I think the neutral in Box B needs to be connected to the grounding cable but I'm not sure.

  • Hot (black)
  • Neutral (dashed)
  • Red (traveler)
  • Green (bare ground)

my wiring

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    Can you run replacement wires between the two boxes? It seems the original installers did something nasty here... – ThreePhaseEel Mar 24 '17 at 22:16
  • Yes I can, I've open the wall to move box b. – Mike Marseglia Mar 25 '17 at 0:52
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The last guy used an illegal and unsafe technique to do that.

Smart switch method

  • Ground is ground in all cases
  • Neutral is neutral in all cases
  • Red is switched-hot in all cases
  • Black on a branch going to a lamp is always switched hot

Smart switch on box A switches the switched-hot. This leaves the black wire in the /3 (RBWg) spare. Smart switch remote in box B controls switch A using that wire as needed.

You need to select the smart switch pair carefully. Such a smart switch would either use the black as an always-hot and communicate via powerline or radio with the master. Or be battery or inline powered and use the black as a data cable.

Added wires method(s)

If you can switch to /4, you can have 2 messengers (red/black here), neutral (white), and a switched-hot (blue), and it will look like this.

enter image description here

If you can't get /4 you can just double back with a /2 cable and have the /2 carry switched-hot and its partner neutral for light A. It could transit through box A, but the hot and neutral would need to be separated from the other wires in the box. That is because in any cable, currents must be equal (cancel each other out).

enter image description here

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    Harper, I have the ability to run an additional cable since I opened the wall to move box b. Can i fix this by running a /4? After everything I've read I'm guessing the problem is there is no neutral from the fixtures in box b back to the power cable. Also, could you elaborate on the illegal technique? I'm just curious what it was and how to spot it. – Mike Marseglia Mar 25 '17 at 0:49
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    @MikeMarseglia -- the illegal technique was using ground as a neutral-substitute, and running a /4 using bare as ground, white as neutral, two of the other wires as travelers, and the remaining wire as a switched hot would work – ThreePhaseEel Mar 25 '17 at 0:55
  • @MikeMarseglia Yes, /4 would be an option; neutral, 2 messengers and switched hot. If /4 proves difficult to source, you could double-back with a /2 cable and have that carry switched-hot and its partner neutral back to light A. It could visit box A, but both the hot and neutral would have to go straight to light A without interacting with anything else. Currents must be equal (cancel each other out) on any given cable. – Harper - Reinstate Monica Mar 25 '17 at 5:53

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