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I've seen some similar questions but not my exact situation (forgive me if I missed it).

I am wanting to replace a switch that controls the light in my swimming pool with a smart switch.

Background...

  • 3-gang box with 2 light switches
  • 2 of the light switches are connected to the main circuit panel (Panel A) and have the expected hot, neutral, and ground wires.
  • 1 of the light switches is connected to an outdoor sub-panel (Panel B) and only has two wires (line and load). This controls the light in the pool and is currently working fine.

The (TP-Link Kasa) smart switch I want to install has 4 wires (line, load, neutral, ground). Obviously I would connect the switch line and load lines to the existing line and load cables (coming from Panel B). My question is if I can connect the switches' neutral and ground cables to the feed for the light switches connected to the main circuit panel (coming from Panel A)?

I hope my question comes across clear. Thank you in advance.

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  • 1
    A picture showing the wires will help. I have a feeling that the white wires for the two switches are not neutral, especially if the white is connected to the screw on the switch. You might have the right neutrals connected together behind the switch for the pool. Black wires usually have a matching white wire with them.
    – crip659
    Commented Aug 1, 2023 at 17:31
  • Is there GFCI at Panel B protecting the light? (Or equivalently: do the actual light fixtures in the pool run directly off 120V, or is the voltage to them stepped down by a transformer, and if it's the latter, is the switch on the primary (120V) or secondary (low voltage) side of the transformer?) Also, is this switch located inside or outside? Commented Aug 2, 2023 at 2:21

2 Answers 2

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Nope, absolutely not. Neutral not only needs to come from the same panel.... it not only needs to come from the same circuit... it also needs to come from the same cable as at least one of the hot wires going to the switch!

In this scenario you have a few options.

You can change to a smart switch which does not require neutral (this make make your choice of LED light more fidgety, or you may need a LUT-MLC helper capacitor out at the light fixture).

Or sometimes, depending on topology, you can flip the lighting circuit around. Right now the switch in this box is a switch loop from another supply elsewhere. However, since you do have supply here, flip it so the light is supplied from here and it's not a switch loop anymore. The supply into that other place it goes would be capped off and unused, at least, for that light. The switched-hot and neutral would need to not interact with any other hot (of any kind) or neutral wires in the other box(es) it goes through.

However, the complication here is that the other circuit is in the pool. That absolutely needs GFCI protection! In fact I am concerned with that circuit's wires being in the same box with non-GFCI-protected wires, since a problem in this box could put non-protected power onto those wires that feed lights at/in the pool! So at the very least I would want physical separation of those wires through at least a physical divider in the box.

However, since you're after smart switches anyway, we could certainly put a smart switch over in the pool area, and use a smart remote in this box - and this smart remote uses either radio communication to talk to the master (e.g. Insteon does this) or is a "literal wireless remote" that goes anywhere and has internal batteries. (it either mounts in the box with zero wires connected, or sticks to a wall anywhere you want it).

Some smart switch remotes use powerline-coded communication, but since the remote will be in a different panel, possibly different phase and certainly on the wrong side of a GFCI, I wouldn't count on powerline-coded signals working.

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  • Thank you for taking the time to explain the reasons that I just declared to be true. Take my upvote.
    – KMJ
    Commented Aug 1, 2023 at 20:42
  • Thank you for the detailed response. This is very helpful and informative. Commented Aug 4, 2023 at 15:59
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You can't reuse a neutral like that. Either rewire to add a neutral from that panel, or skip the smart switch for that one switch.

One specific reason is that this is in a pool area. It really should have GFCI, and GFCI won't work with a shared neutral.

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  • Thank you for the detailed response. This is very helpful and informative. Commented Aug 4, 2023 at 15:59
  • Harper deserves it more than me. :) Good luck with the project.
    – KMJ
    Commented Aug 4, 2023 at 16:05
  • Yeah, I'm only 13k rep away from being able to reinstate Monica ;) Commented Aug 6, 2023 at 20:02

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