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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

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  • "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.
    – Peter Duniho
    Commented 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
    – manassehkatz-Moving 2 Codidact
    Commented Jan 20, 2021 at 7:04
  • screw colors matched to wire colors and a lot of this will quickly make more sense.
    – manassehkatz-Moving 2 Codidact
    Commented 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.
    – Justin Randall
    Commented Jan 20, 2021 at 7:14

1 Answer 1

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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.

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  • 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?
    – Justin Randall
    Commented 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.
    – manassehkatz-Moving 2 Codidact
    Commented Jan 20, 2021 at 15:28

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