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Up front, I do not know what I am doing.

I would like to replace two three-way switches with one smart single-pole switch, in a home without neutral wires. I believe my wiring configuration is best represented (with the exception of the neutral wires, which I do not have) by this diagram

enter image description here
Source: https://www.electrical101.com/3way-switch-wiring-using-nm-cable.html

based on the fact that one switch is in obvious proximity to the main panel and the other is on the opposite side of the room in question, with the fixture in between them. I would specifically like to eliminate the switch between the fixture and the main panel, and use the smart switch on the other side of the fixture.

From what I've gathered from Google results, what's needed is essentially

  1. Remove the panel-side switch, and join the line wire and one of the traveler wires with a wire nut; and
  2. At the other switch location, attach the black wire (connected to the black screw) to the "line" lead of the smart switch and the "same" traveler wire to the "load" lead on the smart switch.

What isn't clear about those two steps is how to determine which traveler wire at the other switch location corresponds to the one joined to the line wire at the panel-side switch, without trusting the wire colors to be meaningful. I would think I could determine that by turning on the light (from either switch) and noting which of the two traveler wires at each switch had voltage.

My questions:

  1. Is my presumption about what my wiring configuration is reasonable?
  2. Is what I want to achieve possible given that presumed wiring configuration?
  3. Should I be worried about whether doing this is safe?
  4. Am I right about how to determine which wires to join together, and which wires to connect to the smart switch?
  5. Given 4, do I even need to actually know 1, or would this plan work regardless of the wiring configuration?
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  • Your link downloads a file which nothing I own can open. Can you provide a regular web page link, or post the image itself here.
    – Tetsujin
    Dec 21, 2022 at 12:21
  • The image is a webp file, which is apparently some Google image format that loads fine for me in Chrome. I've added a link to the full page I took the image from, in case that renders better for you. (I don't want to infringe on the clearly-displayed copyright notice by simply copying the image here.)
    – cbmanica
    Dec 21, 2022 at 12:29
  • works with firefox too
    – Jasen
    Dec 21, 2022 at 12:30
  • OK, works on Chrome, not my version of Safari or the Mac it's on. I saved future issues by just inlining it.
    – Tetsujin
    Dec 21, 2022 at 12:38

2 Answers 2

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If you have that.

At the the first switch location connect the incoming black to the outgoing black. (you could use red instead of black, but why?) cap the unused red. leave the incoming white connected to the outgoing white.

At the lamp juction box, join the incoming and outgoing whites and a short wire together connect that to the lamp. remove any colored (or black)_ tape or paint marking from the white. connect the outgoing red to the lamp, cap the incoming red, connect the incoming black to the outgoing black.

At the far switch clean tape or paint markings off the white wire connect it to switch neutral. Connect black to line. connect red to load.

If you got the two traveler cables swapped, you only need to swap two wires (the reds in the lamp junction).

look for the marking on the white wire that goes to the far switch it should be there, and wioll clue you in as to which is which,

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What you're describing is bypassing the first switch and using the second one as a switch loop.

In the first box (which you want to bypass), connect black to black and white to white. Disconnect and cap (insulate) red so it won't cause trouble and is clearly not in use.

At the lamp, connect black to black, white to white, and the lamp between the whites and the right-hand red, which will be your switched hot. Cap the left-hand red.

In the last box, the connect black to the smart switch's Line terminal, white to it's Neutral terminal, and red to it's Load terminal so red can return switched power to the light.

Let me know if that's unclear and I'll post a modified version of your graphic.

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  • It's not exactly clear, but part of that is that I don't actually know (yet) what the wiring at the light actually looks like - I guess I thought I could do this without changing wiring at the fixture, which seems to be incorrect. I'll edit and possibly repost this question when I have a chance to see those wires (and will photograph).
    – cbmanica
    Dec 21, 2022 at 18:04
  • There are several ways a three-way could have been wired. My answer assumes that one of the switches has been wired as a drop rather than the two being in series before reaching the light , and that the colors are as shown in the diagram (which would be pretty much US standard). If something else was done, a different answer will apply. Knowing what wires actually come into the light fixture now and how it is connected to them would be a huge hint. If not sure, and not sure how to test, seriously consider hiring a pro.
    – keshlam
    Dec 21, 2022 at 19:17
  • You may indeed be able to avoid changing the wiring at the light -- but that requires either looking at that wiring to confirm how it was done, or doing some tests with a meter (and possibly some long wires) to confirm what's attached where. I would go with the former as less effort and less risk of error than probe-and-deduce, unless it is unreasonably hard to reach the fixture (ceiling fixture too high to reach without renting a bigger ladder or scaffolding or lift)
    – keshlam
    Dec 22, 2022 at 3:17
  • The fixture is reachable, and I'm able to test with a meter if needed. Assuming I get photos of the wires at the two switch locations and the fixture, what's the best way to post those to this old-ish question now? Should I re-ask or edit this one?
    – cbmanica
    Dec 23, 2022 at 19:58

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