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I want to make it clear that I am a complete and utter novice and know next to nothing about electrical wiring, I just about have a grasp of the basics. I've wired up a lot of other smart switches in my house without issue, and can usually figure them out.

I was aware that the wiring in our 1984 built house wasn't the best but just don't understand how things work sometimes.

Anyway I wired up this Kasa smart dimmer which is replacing a Leviton dimmer and joined the neutral to the 3 connected neutrals with a wire nut. When I turned the breaker back on the switch did not have any power. I separated one of the neutral wires and connected that to the smart switch, and then when it powered back on the switch had neutral power, but it seemed to interfere with another light I had nearby.

I read that I could pigtail a new white THHN wire in place of one of the neutrals, then connect that and the spare neutral to the smart switch. Is that a valid theory? I suppose my main confusion was why the switch didn't have power when I joined it to the three neutrals already wire nutted.

I've got no problem returning this switch and leaving it as it is I'm not going to get involved in something I know very little about, so hopefully someone can provide input.

I will attach a photo of the box. Also to add when I separated the neutral and the switch had power it was operating the light as it should.

enter image description here

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    Wire nuts are rated/sized for how many wires they can connect. The wires going into a wire nut must be all even. It looks easy, but not hard to mess up the connection to all four wires. Wagos/lever connectors might be easier.
    – crip659
    Feb 1 at 18:43
  • Okay good to know thank you. I'd say the kasa neutral was a few MM shorter than the three already grouped in the box. I'll take a bit more time with the neutral and maybe strip a bit more of the covering on the smart switch.
    – Polarbert
    Feb 1 at 18:59
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    I would also use a new wire nut. They are suppose to be reusable, but for a few cents, it does not make much sense.
    – crip659
    Feb 1 at 19:01
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    It's been my experience that the pre-stripped end on switches with wires (instead of screws) are usually too long, not too short. You want stranded wires to stick out a bit (1/8" or less) beyond the solid wires, but I find the pre-stripped ends are usually about 2x longer than they need to be. I just trim off the excess bare wire.
    – FreeMan
    Feb 1 at 19:03
  • Thanks again I will trim the neutral wires down a bit then. And get some new wirenuts.
    – Polarbert
    Feb 1 at 22:23

2 Answers 2

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You're saying "spare neutrals" as if you see multiple neutrals sitting there unused waiting for you. We hear that a lot. Actually, those spliced neutrals are working very hard, returning current from other parts of the circuit back to the panel. Current flows in loops, and neutral is the return line.

By separating them and taking one, you actually are denying neutral to other parts of the circuit, which will make them inoperative. Certainly not what you intended.

So yes, you need to keep the neutrals bundled and then add your neutral also. This might require using a larger wire nut, but a red nut should be OK for four wires. Always best to use wire nuts in the middle of their range - using them at extremes requires impeccable technique.

Remember to tighten nuts very tight. They are not caps, the tightening is what makes the electrical connection. Pre-twisting does absolutely nothing, because when you are tightening the nut enough, it is twisting the wires together MUCH tighter than you could possibly do with pliers.

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  • I got a new red wirenut and added the kasa neutral to the group of three. I tightened it as much as I could, but there is still no dice from the switch. This seems very odd.
    – Polarbert
    Feb 2 at 5:46
  • As an amateur, I pre-twist mostly to hold things stable while installing the nut...
    – keshlam
    Feb 2 at 14:17
  • That's what i did as well. Is there a possibility I could have too many switches on the neutral line? I'm really not sure why it isn't working. I checked the switch again and it powered up okay
    – Polarbert
    Feb 2 at 15:58
  • @PolarBert any chance you mixed up supply and lamp wire? Is the lamp LED and if so, can you temporarily change it to old incandescent for testing? Feb 4 at 2:25
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Well my father in law came over and despite him not being an electrician managed to help me resolve the issue. I dont know for sure what the problem was but I'm fair sure it was down to the smart switch neutral not connecting properly. All is well and I appreciate the input!

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    Could you ask him what he found, so you can change this into a real answer rather than "never mind, resolved now"?
    – keshlam
    Feb 3 at 2:02
  • I was stood next to him the entire time. It was a connection issue with the neutral wire.
    – Polarbert
    Feb 4 at 3:39

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