This is my situation also!
Old wiring:
Line in (circuit 40) in box w/ 3 way >
14/2 (no red and white) to 4 way >
14/2 to 3 way >
Light fixture - BORROWING neutral from circuit 33, but powered by circuit 40.
From my research, it doesn’t seem possible to use smart switches without 14/3. Need that red wire between switches.
Moved to a new thread . . .
Before you even think about wiring switches you need to fix the borrowed neutral. That not only presents a safety hazard, but it will may prevent proper switch operation.
Do you have Romex or individual conductors in conduit? I can understand how you might not have a neutral in a switch box, but how do you wind up with no neutral in the light box???
In older homes, the hot and neutral are present in the light box and there is a switch loop to the switch box. If that’s the case, you can either wire as a non-neutral or re-wire to provide a hot and neutral to the switch if smart bulbs are being used.
Thanks for the reply!
The correct neutral of the line (circuit 40) doesn’t exit the first box, since there’s only the two conductors of 14/2 to carry the voltage to the next switchbox.
The neutral of 33 is found in the junction box in the ceiling where the light fixture hangs.
Having done some AI research via perplexity, this was apparently OK to do, as long as the neutrals were on different phases. My understanding is it was considered safe as is because the circuits are odd (33) and even (40). Source: 4 Way Switch Wiring Methods – Electrician 101
Currently I’ve just closed up the boxes with a dumb 3 way, 4 way, and 3 way. At least they are decora instead of toggles. In the future I could either rewire to 14/3 or I could use 3 smart Innovelli Reds and pass current all the way from 40 through each box, letting only the 3rd smart switch control the load - the others would use zwave association to control that third one.
Open to other ideas!
You are correct that you can share a neutral as long as they are on separate phases. So while that is theoretically correct, there are practical aspects that are critical for SAFETY. The current NEC requires a method through which a simultaneous disconnect can be accomplished. That means a double-pole breaker, or two singles with a handle tie. You can only implement that with two breaker slots that are adjacent vertically. In your case, I’m guessing 33 and 40 are not. So while you may be theoretically correct, your application of that theory remains a safety hazard.
That aside, with a shared neutral, there is still the issue of whether or not a smart switch will function correctly. We’ve had cases here where users (probably improperly) shared a neutral to power a switch and then complained about the switch not working correctly. I can’t say what it was about the shared neutral that caused the problem, but in those cases it was clear the shared neutral was the problem.
You didn’t answer my question about if you have individual conductors or Romex. How is it that with power originating at a light box that the light box only gets the hot but not the corresponding neutral (and presumably ground)?