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(Apologies since this has been asked before, but I can't seem to decipher other answers)

I have a 3 way switch in my garage for overheard fluorescent lights. S1 is in a single gang box with no other wiring, S2 is in a 2 gang box with another independent light switch. I'd like to re-wire the 3-way with a tp-link smart switch (that requires a neutral) but from what I can tell (confirmed with a multi-meter) I do not have a neutral in S1. The wiring fits the image below, which has been referred to as a power-in-fixture installation.

enter image description here

S1 (top left) has a ground, a white always-hot wire, 2 travelers, no neutral, nothing else in the box. S2 has a ground, no always-hot wires (Though the other switch in box 2 has a hot wire), 2 travelers, and the load wire.

What are my options to get this to support a smart 3-way switch that requires a neutral? I've read about using the ground as a neutral but It's almost always cited as a bad idea.

I realize there are smart switches that do not require neutrals, but I've already bought a specific brand and installed them in the rest of the house and If possible I'd like to avoid dealing with multiple manufacturers and control apps.

Edit: I came up with an acceptable work-around. The 2-gang box has a neutral, so I can use the smart switch there, and I can leave a normal 3-way toggle switch at the single gang box. The 3-way smart switch works just as well being one-half of the circuit. So really the only difference is that the other switch is a toggle instead of an aesthetically matching paddle switch, but I think I can live with that for now. I'd still be interested in any tips that would allow me to replace the switch in the single gang box as well though.

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  • Is replacing the wiring between the fixture and the switches an option? Jul 25 at 15:37
  • If it comes down to that then I should be fine wiring the switches, since at that point I can ensure that I have all the necessary wires. For right now I'm just trying to see what's possible without having to run new wires. Jul 25 at 16:40
  • Is this NM cable or is it THHN in conduit? Is the ground wire bare copper or is it insulated green? If you decide to rewire, consider using /4 + gnd between the switch boxes.This would allow 3-wire control between the switches and would provide a neutral and a constant line hot in both switch boxes. Jul 25 at 19:10
  • Is this circuit wired in #14 copper and on a 15 A breaker? Are there receptacles on the same circuit? Jul 25 at 19:14
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S1 (top left) has a ground, a white always-hot wire, 2 travelers, no neutral, nothing else in the box. S2 has a ground, no always-hot wires (Though the other switch in box 2 has a hot wire), 2 travelers, and the load wire.

Correct, neither box has neutral in a "power at the light" configuration. You cannot use a neutral-needing smart switch here unless you dispense with the dual travelers, i.e. use smart switches at both switch locations that use wireless or powerline signaling.

Edit: I came up with an acceptable work-around. The 2-gang box has a neutral, so I can use the smart switch there,

NOT acceptable. You cannot poach neutral off a different leg of the circuit. Yes, I know it works, but it's no better than bootlegging ground, so why not just bootleg ground at that point.

Your best bet is to change to a smart switch tech such as Insteon that handles 3-ways with wireless or powerline signaling. At that point you re-task the 3 wires as:

  • Black = always-hot
  • White = neutral
  • Red = switched-hot (but only to the master switch)
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  • Why is it no better than using the ground? Using the ground is unsafe because it's essentially shared between many circuits, but neutral can be cutoff at the breaker box (these are on the same breaker). It's far safer, right? Jul 25 at 20:08
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    @TheShoeShiner It's true that it's a different problem, but it's still a problem. You can't poach neutrals out of unrelated cables, NEC 300.3. Jul 25 at 20:15
  • Wouldn't all of those neutrals be tied together anyway? (They were prior to this install) Jul 26 at 12:26
  • Found this: diy.stackexchange.com/questions/200100/… Seems like that answer explains why this shouldn't be done? Jul 26 at 12:37
  • But I still can't wrap my head around why the neutrals from the normal light switches can all be tied together, but the neutral from this switch can't be tied into it as well? I.e. If i replaced this with normal switch, the neutral would be tied together with the ohters. Yet we're saying that using this 3-way switch, that is unsafe? Jul 26 at 12:47
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Since the smart switch does not need travelers and you need only one switch, you can rewire it. White wire is neutral, black coming phase, red-phase out, connect to load. Second switch box no use, just cap the wires and blank cover.

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  • I'm trying to re-wire it to use a smart 3-way switch. So there are still two functional switches. Jul 25 at 13:15
  • The entire purpose of having a 3 way switch is to be able to activate it from 2 locations. Re-wiring it as a single location switch is only a work-around, which I am able to do, but doesn't solve the real problem. I'm not able to understand your solution unless you reference the wiring diagram which explains which wires I have available. Jul 25 at 14:23
  • I did not provide you with solution because you does not explain the principal's behind your project. Then you have Wi-Fi switch, you can control the load from an place you have Wi-Fi in you house or even trough Internet. I do not understand why you need the second switch.
    – user263983
    Jul 25 at 14:32
  • TP-link has a link to application, which can guide you through whole process of replacing devices.
    – user263983
    Jul 25 at 14:42
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    I need the second switch because If I'm walking into my garage from door #1 , I want a switch there to turn the lights on so that I don't run into stuff in the dark. If I'm walking in from door #2, I want a switch there as well for the same reason. In either case, I may not have my phone with me, thus the WiFi is not always an option. This is what 3-way switches were designed for. Jul 25 at 15:03
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Some active devices consumed so little power that their instructions allowed the use of the ground to carry the very small current that they drew. I don't know if the current applicable code allows that. The instructions for your device would of course have to allow that.

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    The tp-link kasa switches say that they do require a neutral. They don't explain exactly how much current is present across the neutral though. Jul 25 at 13:16

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