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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?

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  • Can you post a link to the manual for your smartswitches please, as well as photos of the insides of the switch boxes involved? May 28 at 3:59
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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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  • "There should be a white wire together with the black switched hot wire, That white wire is a neutral", older switch boxes hardly ever have a neutral... May 28 at 5:57
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    @Jimmy switch loops wouldn't have neutral but switches in sequence between power and fixtures should. Cluster of blacks indicates there are other things connected via this box, so there should be a matching cluster of neutral whites. May 28 at 6:17
  • @manassehkatz-Moving2Codidact you are right that there's a white wire in the same sheath with the black switched hot wire! Here's the drawing: dropbox.com/s/41twvvabbx43xse/unnamed.jpg?dl=0 So if I connect the white wire from the incoming black hot wire and connect it instead to the black wire going to the light (the white wire becomes switched hot), the downstairs white wire would not be neutral anymore. The Brilliant Smart Switch needs a neutral line to function. What should I do in this case?
    – bei
    May 28 at 21:26
  • The white wire from downstairs was never neutral. It is currently hot and the idea is to change it to switched hot. If by "white wire from the incoming black hot wire" you mean the black wire currently connected to the upstairs switch, that white IS neutral. If you mean the white paired with the black hot wire (the black hot wire that currently connects to the white wire heading downstairs), that white IS neutral. The key is: You should have a WHITE CLUSTER very similar to the "Black cluster" - that is the bundle of neutrals. May 28 at 21:39
  • The white paired with the black hot wire is NOT neutral, right? Typo? There's a white cluster in the upstairs box, but there isn't a cluster in the downstairs box. I think the downstairs box only has the wires from the upstairs box (red, white, black, copper).
    – bei
    May 28 at 22:15
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Well, ground is easy.

Safety ground is a network connecting everything to everything, to ground and the grounding rods going into the dirt. It is there simply as a safety shield, and it performs no electrical function whatsoever. (except, obviously, when there is an electrical problem).

So with grounds, you hook them up, you hook them up FIRST (life goes better that way), and then you don't need to think about them at all.

Grounds are green, yellow/green, or bare.

Neutral.

Neutral is not ground. Neutral is the normal current return for 120V circuits. It handles 100% of the current that the hots do, it's just going the other direction.

We make best effort to keep neutral near ground voltage; however this effort is by no means perfect, so we insulate neutral.

We take advantage of the fact that you only have to interrupt one of the wires to turn stuff off. Because hot wires are not near ground and are dangerous more often, we switch those to reduce hazard downline of the switch or breaker. It's important to remember neutral doesn't have breakers!

Neutrals are white or gray.

Hots.

The color code for all hots is anything but the above. There are no required color codes for particular hots! That can make wiring very confusing. As such, I recommend to get some colored electrical tape and re-mark wires by their actual purpose/function.

When working in cables, sometimes you don't need neutral, but do need an extra hot. In that case, there are rules for re-tasking the white wire to be a hot. Not all these rules get followed.

  • The white wire must be re-marked a hot color (i.e. black electrical tape). This is a Code requirement, but widely ignored.
  • If neutral is not present in the cable... but "always-hot" is present, then the white must be used for always-hot.
  • White can never be used for switched-hot to a lamp.

Again, there are many kinds of "hot" wire, and they can be any color since there is no official color code distinguishing types of hot. They can even be white.

Wires that go to a switch are hot.

3-way circuits

And this is how 3-way circuits are wired.

enter image description here

Obviously here, wire colors have been chosen by function, and you can tape your wires to match if you want to. But 99% of people don't.

It sounds like in your case, the travelers are the black and red wires, with a non-remarked white wire carrying the always-hot.

Anyway, now that you have the vocabulary and layout, you can look at your switch's instructions and see what they are telling you to do. With smart switches, there isn't a standard; every switch does it differently.

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  • This is the clearest illustration of how a 3 way switch works that I have seen.
    – Kris
    May 28 at 11:38
  • I don't know how the proposed "Brilliant" switches work that the OP wants to put in -- I do know that those 3-way dimmers which communicate with each other usually use a red wire (perhaps of smaller gauge) for their comms line. May 28 at 14:05

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