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Replacing old switches with kasa 220. Replaced almost 20 of them without any issues. Finally opened this switch box that controls the pool light and pool waterfall and I am stumped. Please help.

Here is a diagram (Actual PICS at the bottom of the post, they are too cluttered) of all the stuff in the box with the voltage readings against the ground wire:
enter image description here

My main points of confusion are :

a) The three capped wires are all by themselves, not connected.

b) Which is the neutral wire than I can use for the two smart switches?

c) Why is there a low (approx 20 V) voltage in the white wire in the lower left sheath ?

Thanks.

ACTUAL IMAGES :

enter image description here enter image description here enter image description here

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  • do not understand those cups. What are they? Take a picture please.
    – asinine
    Jun 7, 2022 at 4:48
  • @Ruskes Sorry for the confusion. Updated the diagram and also added pictures. Thanks.
    – Testingtest
    Jun 7, 2022 at 5:05
  • Are the pool light and waterfall on the same breaker, or different breakers?
    – ThreePhaseEel
    Jun 7, 2022 at 11:48
  • Stock advice regarding "spare, extra, or 'weirdly connected' wires" in switch/light boxes. If it was working before you started, leave them that way / connect to new switch or light the same wires the same terminals" - if it's not working you might need to dig deeper.
    – Ecnerwal
    Jun 7, 2022 at 12:47
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    Please re-wire the old switches in the configuration you found them, and thorougly test to confirm that all switches work in all respects no excuses. Then take new photos indicating which switch you wish to replace. All due respect, just because you did 20 "successfully" doesn't mean you know what you're doing. Switches are complicated.
    – Harper - Reinstate Monica
    Jun 7, 2022 at 19:54

1 Answer 1

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a) The three capped wires are all by themselves, not connected.

It appears that you have one disconnected cable (top of the diagram), showing phantom voltage when one of the switches is turned on. You can't do anything with this without figuring out where the other end of the cable is.

b) Which is the neutral wire than I can use for the two smart switches?

The only likely usable neutral wire is the white of the black/red/white cable. In that cable, black and red are a modern switch loop and white is the required unused neutral.

c) Why is there a low (approx 20 V) voltage in the white wire in the lower left sheath?

Phantom voltage. That happens with long wires next to other wires, particular if one end of the wire is not connected to anything.

To finish up the explanation:

S2 is a traditional switch loop, where white is used as a hot (preferred) or switched hot (which may be the case here based on your voltage readings). That is not allowed in newer circuits because code now requires a neutral (in order to handle smart switches, among other things), and since neutral must be white (at last in a standard cable), that means black and red get used for hot and switched hot. So S2 has no neutral available.

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  • Thanks. Follow-up question: Can I use the white of the black/red/white cable, as neutral for both smart switches? or just one ?
    – Testingtest
    Jun 7, 2022 at 18:23
  • That's where it gets a bit tricky. The problem is that wires in any cable have to "match". First step is: Are both switches/devices on the same circuit? If so, then the problem is that for S1 you have hot/switched-hot/neutral in one cable (great) but for S2 you will have to do some rewiring at the waterfall to change it to get neutral and switched-hot instead of hot and switched-hot.
    – manassehkatz-Moving 2 Codidact
    Jun 7, 2022 at 18:30
  • Actually, this can be done even if they are on separate circuits provided they can be rearranged to be on one circuit. Which depends on power requirements and installation instructions - if the waterfall says "dedicated circuit required" then you are out of luck.
    – manassehkatz-Moving 2 Codidact
    Jun 7, 2022 at 18:31

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