This weekend, I decided to sort out the confusing wiring to some of the lights in the house. I've been wanting to install some HomeKit light switches and remotes, and there are two problematic light switches I'd run into.
First, was some old wiring that didn't have neutral wires in the switch box. I'd given up on those; you need neutral and power in order to give the online switch constant power, otherwise when you turn the light off, the switch loses power and can't be turned back on. But, this article pointed toward one dimmer that doesn't need a neutral wire, the Lutron Caseta Smart Dimmer. Turns out, it never completely turns off the lights, letting a trickle of power flow, enough that it doesn't get shut off. I got one, and was planning on trying it ... but got hung up on another set of lights.
We have some 3-way light switches for our basement lights (each has a switch in the basement, and a switch at the top of the basement stairs). When I looked in the past, the wiring didn't seem to correspond to anything I found online describing "typical" ways of wiring 3-way switches. Compare those wiring diagrams to this one I ended up with after failing to match those diagrams to what I was seeing in the box.
After sorting that out, I could see how to install the Leviton Homekit Switch (fortunately, the neutral wire was passing through switch box 1 on the way to the light). I ended up abandoning using the Leviton Remote I'd bought because the neutral wire wasn't being sent to that box (I ended up removing the switch and connecting the wires together in that box, and using a spare Hue Dimmer Switch I had laying about.)
What a pain. We won't even talk about the other 3-way switched light that I couldn't sort out at all (which is, amazingly, on the same circuit as a few outlets and our kitchen fridge!).
But, at least I now have a better handle on how these lights are wired, and am thrilled to discover at least one Homekit-capable dimmer that works on old switch wiring with no neutral wire.
(Disclosure: The Amazon links above have a tag in them pointing at this site, so if you buy things using those links, Amazon will pay me a small amount.)