Switch – The strangest 3-way light switches

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I live in a 2-story house. There is a set of staircase lights that was being controlled by two regular Leviton switches, one upstairs and one downstairs.

The downstairs gang box has only one socket for the switch, upon opening up the box I found that there are only four wires. White, Green, Black, and Red. It's missing the second black wire I usually see in other gang boxes. The WHITE wire is connected to the black screw of the Leviton switch. The red wire is connected to the gold screw above the black screw, the black wire is connected to the other gold screw, and the copper wire is connected to the green screw.

The upstairs gang box is also interesting. For the switch in question, the black screw is connected to a black black wire that's in its own sheath. The gold screw above it is connected to a black wire, which comes out from the same sheath from the red wire that's connected to the other gold screw, and the copper wire is connected to the green screw. The interesting part is that this socket's WHITE wire is twisted together with a cluster of BLACK wires which I think are the LINE wires for the other sockets.

When I was testing for line and load wires, the downstairs black screw was the LINE, but like I said the black screw is connected to the WHITE wire. I suspect the WHITE wire is carrying the LINE power from the upstairs cluster.

How should I install two smart (Brilliant) switches that have a black, red, white, and green wire and control the staircase lights?

Best Answer

This sounds normal:

"/3" cables have 4 wires - black, red, white, bare ground. So the color (except bare ground = green = ground etc.) is almost meaningless. Where in a normal setup, black = hot and white = neutral, with 3-ways you have a common wire (hot or switched-hot, depending on configuration) and two travelers. Since the travelers are "the same", they normally get the two non-white colors: black and red. And that is what you have. From the top:

  • Power comes in to the upstairs switch box on black, as usual. That is connected to the white wire (common = hot in this case) going down to the downstairs switch.
  • The white goes down to the downstairs switch and black and red travelers come back from the downstairs switch to the upstairs switch, all in one cable (and they must be all together, can't use a black/white cable + an extra separate wire).
  • The downstairs switch has white = common (black screw) and black/red = travelers (brass screws)
  • The upstairs switch gets black/red = travelers (brass screws) and black = switched hot (black screw). Note that the white that is "with" the travelers does not touch this switch.

One piece you didn't mention that is very important: There should be a white wire together with the black switched hot wire. That white wire is a neutral and should be connected to all other whites in the box except for the white that heads to the downstairs switch. If that is correct, then this is a standard setup.

The catch with replacing with smart switches is that most (not all) expect to have hot & neutral available in the same place. You have that possible but not as currently configured. The upstairs switch has travelers and switched hot and has neutral available. The downstairs switch has travelers and hot but it does not have neutral available.

The solution is to rearrange things a bit. Instead of the downstairs switch being "1" and the upstairs "2", make the upstairs "1" and the downstairs "2".

  • Disconnect the black wire going to the light from the black screw of the upstairs switch.
  • Disconnect the white wire from the incoming black hot wire and connect it instead to the black wire going to the light. That white wire becomes switched hot instead of hot.
  • Connect the incoming black hot wire (you'll need to add a pigtail) to the black screw on the upstairs switch.

Now the upstairs switch is connected to hot + travelers, and neutral is in the same box. That should allow for a "standard" replacement with a smart switch.

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