I posted a question about replacing three-way switches with Insteon switches last month and Stu bailed me out. Thanks! Today I went to replace two more three-ways and found the existing wiring is different. Whereas the last time there were five "pairs" of wires amongst the two switches and the wires were different gauges, this time there are only three "pair" and they're all the same thickness (see illustration).

 

FWIW, if I connect a volt meter between the ground and each of the wires, the black wire on switch #2 is hot, the black wire on switch #1 is cold, and the red and white wires on both switches are lukewarm (i.e., they move the needle, but not much). And it probably goes without saying (if you know what you're doing; I don't), but if I wire the red and black wires together at both switches, the lights turn on.

 

(If you reply, thank you very much, please be specific about the wiring of the new switches. I don't know which wires are going to the load, line, etc so I won't understand that terminology. Thank you!)

 

Edited December 24, 20168 yr by Sachelis

The diagram you posted is not possible. For one, there cannot be a cable with only one wire And a wire that goes "elsewhere" doesn't make sense if it's part of a 3-wire cable. Which wire is connected to the black screw at each switch.

 

BTW, the only way to get accurate reading on a meter is to remove the load (e.g., unscrew the bulb).

The black wire going "elsewhere" is connected to other stuff in a four-gang box, but not to the switch #1. The single black wire going into cable B also has a white neutral wire coming from the box (but not from switch #1). Unfortunately, I didn't look at the wiring before disassembly... (whereas last time I was wiser and took photos...).

I'm pretty sure cable A and C are the same cable, and that the "elsewhere" wire is the hot wire going to switch 2. That'd mean cable B is going to the load. That'd mean the white and red wires are the travellers. 

It's not possible for cables A and C to be opposite ends of the same cable. You'll need to remove the fixture.

If I had to guess based upon the diagram, I would say that the B cable is to the fixture, and the "elsewhere" wire is connected to a line supply cable somewhere in the back of the box.  Black B is connected to common screw, as is black C.  In other words...hot into black A to switch2, red/white are travelers back to switch1 and switch1 common to load.  No?

 

Is the white wire from B connected to a white bundle in the box somewhere?

If the black A wire is the line, then there must be a black & white wire cable not shown.

Yeah, that was right, oberkc. As in, A and C were the same cable, and contained the travelers plus a hot wire going to  switch #2. I only displayed wires that were connected to the two switches in my illustration, which made it more difficult to decode. The "fixture" is eight ceiling lights, so not so easy to inspect. In any case, I connected switch #2 to a neutral and hot (the hot was already there; the neutral I got from a nearby switch), and I stubbed off the red wire from the new switch #2. I connected the red (load) wire on switch #1 to the black wire in cable B and got a hot (black) and neutral (white) from the box near switch #1. It works! Whew. Merry Christmas Eve!

It's unsafe to pick up a neutral from another circuit. If you have a (not shown) 2-wire cable, one where the black connects to the "elsewhere" wire, then you can change some connections and wire safely and according to code.

 

 

It's unsafe to pick up a neutral from another circuit. If you have a (not shown) 2-wire cable, one where the black connects to the "elsewhere" wire, then you can change some connections and wire safely and according to code.

Adding to this. If you have the new-fangled AFCI breakers they will trip if the live/neutral are unbalanced. This means you cannot share a neutral without being unable to reset the breaker. Just don't do it!

Sachelis, of course I agree with the concerns expressed about stealing neutrals fro other circuits. It is my hope that, were you to find the cable that was originally connected to the "elsewhere" wire, you would find a white wire bundled together with the black wire connected to "elsewhere".. This is the neutral that you should use. If such a white wire is not there, be careful. Sometimes wires can get connected together and this can be hard to identify.

Edited December 25, 20168 yr by oberkc

The line and neutral were from the same circuit. Clearly. Thanks for the advice.

The line and neutral were from the same circuit. Clearly. Thanks for the advice.

 

That's not clear if you got the neutral from another switch.