I have an existing 3-way switch setup that I'm trying to convert to "smart" switches and I'm feeling "not smart" after mapping out where I think the wires are going. Unfortunately I don't have a good wiring diagram to share with you besides this back of the napkin drawing where yellow = white wire.

back of the napkin drawing

Box A: This is a double gang box. There are 2 switches and 4 cables in this box. The first switch is a leg of the 3-way switch to entryway chandelier (20 feet overhead, I have no access to the fixture box so I don't know how it's wired). The other switch (referred to as switch 3) is to an outside light. I only mention it for completeness and the fact that it's using the same 14/2 line as the 3-way switches of interest.

Box A two gang
    cable 1 - 14/3 romex
        black - switch 1 traveler (switched hot)
        red - switch 1 traveler (always hot)
        white - nutted to cable 2 red
    cable 2 - 14/3 romex
        black - wired to switch 1 oddball/common terminal (always hot)
        red - nutted to cable 1 white
        white - neutral

    cable 3 - 14/2 romex
        black - line (always hot)
        white - neutral
    cable 4 - 14/2 romex
        black - switch 3 load (to outside light)
        white - neutral (from outside light)

all neutrals in box nutted together (cable 2, cable 3, cable 4)
cable 3 black (line) nutted to: (cable 2 black, switch 1 oddball, switch 3 line)

Box B: This is a single gang box. There is only 1 cable in this box. This is the other leg of the 3-way switch to entryway chandelier. Presumably this cable is the other end of cable 1 in Box A, since when the circuit is off that wire behaves the same in each box (red is hot, black and white are off).

Box B single gang
    cable 1 - 14/3 romex (presumably other end of Box A wire 1)
        black - switch 2 (switched hot)
        red - switch 2 (always hot)
        white - switch 2 oddball/common terminal (switched hot)

Okay... so now my question is ultimately twofold: What is most probable wiring diagram for the chandelier fixture box, and can I rewire for a smart switch & add on without having to change the wiring at the fixture?

I am presuming that Box A cable 2 is going up to the fixture. If that's true, I'm at a loss as to why 14/3 is used for this purpose.

Edited: Here are some photos of the switch boxes. Switch Box B Switch Box A

  • "I don't have a good wiring diagram to share with you" -- please fix that. Anyone else who would like to help is going to have to translate all of the words above into a diagram anyway, either in their head, or on actual paper. You should respect the community enough to do that work once yourself, instead of making each reader repeat the effort. Jan 20, 2021 at 6:18
  • a) What you are referring to as Wire 1, 2, 3, 4 are normally referred to as cables. Please rewrite as it will be less confusing since there are actual individual colored wires. b) With the exception of cable 2 (incoming power), how are you determining "switched hot" and "always hot"? c) PICTURES Please upload pictures showing all these cables/wires and switches - that will help a lot; d) On 3-way switches, normally the 2 travelers will have one color screw and the 1 other wire (hot or switched hot) has a different color (typical colors are black, silver, brass) - please list those Jan 20, 2021 at 7:04
  • screw colors matched to wire colors and a lot of this will quickly make more sense. Jan 20, 2021 at 7:04
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    @manassehkatz-Moving2Codidact sorry about the cable/wires thing. I'll see if I can clean it up. I will try to get some pictures, but it's a rat's nest in there. Yes the common/oddball terminal is depicted in my drawing. Jan 20, 2021 at 7:14

1 Answer 1


Based on the diagram (with yellow => white), it looks pretty straightforward, but actual pictures instead of drawings would confirm the details:

Box A:

  • Cable 1 = 3-way. Red & Black = travelers. White = switched hot.
  • Cable 2 = Light fixture. Red = switched hot. Black = always hot for use in other stuff past the light fixture. White = neutral.
  • Cable 3 = Incoming power. Black = hot. White = neutral.
  • Cable 4 = Outside light. Black = switched hot. White = neutral.

Box B:

  • Red & Black = travelers. White = switched hot.

For your smart switch, install it in Box A. You will probably need a neutral - just add it to the bunch of existing neutrals.

  • Thanks for this! Your explanation about the 14/3 to the fixture for future use makes sense. If my add-on switch requires just a neutral and traveler, do I just cap off the other traveler in each box and repurpose white as neutral? Jan 20, 2021 at 7:23
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    Hard to say what the 2nd switch (Box B) will need - depends on the design of the smart switch. But yes, if the end result is that it takes a neutral then neutral must be white and if the end result is that it does not take a neutral but that it also only needs 2 wires then you should rearrange the wires so that white is capped both ends and black & red used instead. Jan 20, 2021 at 15:28

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