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I am replacing three smart light switches in the following wire box with new smart light switches that don't need the neutral wire:

Wire box for three light switches The wire box has 4 sets of cables for only 3 light switches and I forgot to take a picture of how they were connected before. I remember that the two left white wires were connected together though.

I was able to connect the two right switches and they worked correctly, but the way I connected the left one fried when I turned it on.

How should I be connecting the left one correctly?

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  • The white wires weren't even connected to the switches. Why did you disturb them? – Harper - Reinstate Monica Sep 13 '20 at 15:33
  • In the picture, nothing is connected to the switches. The white wires were connected to the switch before I uninstalled them though – Mitchel Sep 13 '20 at 15:35
  • I was able to connect the two right switches by connecting the ground wire to the ground wire, the line wire to the white wire, and the load wire to the black wire. – Mitchel Sep 13 '20 at 15:38
  • ALL the switches? Was the earlier left switch a smart switch? Are the new switches going in smart switches? Do they require neutral? – Harper - Reinstate Monica Sep 13 '20 at 15:38
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    Wow, normally these "pic with every wire disconnected and splayed out" end badly. The reason is that in electrical wiring, color-coding is not used (even when Code requires it be used, as in here!!) All the information that tells you what wires do and how to connect them, is stored in how the wires are connected now. When someone splays em out and takes a photo, the information is already destroyed. However your followup comments contain enough info to solve this. – Harper - Reinstate Monica Sep 13 '20 at 15:58
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Easy enough here

The good news is that the two left cables aren't doing anything complicated. One of them is an incoming power feed, and the other is the onward feed to the light, providing both hot and neutral. Furthermore, since the white wires there were connected to each other as expected, we know the black wires are our line and load connections. So, I'd figure out which of those two black wires is the always-hot (line) connection, and wire that to the line-in terminal on the smart switch. Then, the other black wire is the switched-hot, which gets wired to the load-out terminal on the smart switch. The two neutrals get nutted to each other, and last but not least, the ground for the smart switch gets added to the existing grounding bundle in the box. Then you can button everything back up, turn the breaker on, and enjoy your new smartswitches!

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  • Thanks for the solution! I ordered new switches since I fried the ones I had and will be able to test this tomorrow. – Mitchel Sep 13 '20 at 18:15
  • And I assume the way I previously connected the two right switches was correct since they worked? (Ground in ground, line to white, load to black). Note that the load and line wires are interchangeable on the switch. – Mitchel Sep 13 '20 at 18:34
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    All the grounds should be bundled together in the back of the box, and you also need to have a ground pigtail to a screw on the box since it's a metal box – ThreePhaseEel Sep 13 '20 at 19:00
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Some cleanup necessary with grounds. All grounds need to connect to each other -- all ground wires, the metal box, and all switch grounds.

As you have it wired, you are taking cable 3 and 4's ground straight to the respective switch. That is not how grounds are done; the cable onward to the lamp can't ground the switch as it has no connection back to the panel.

I see what look like at many as six "ground screws" in the back of the metal box. You are free to terminate any ground wires there.

The switches themselves can ground through their mounting screws. If you want to run a ground wire from the switch to the box, you can do that too, but it's not necessary given the grounded metal boxes.

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