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I have a two-gang box where one of the switches is a single-pole switch, and the other one is a 3-way switch. I'm trying to replace the single-pole switch with a smart dimmer, the instructions don't quite match what I have in my wall. I want to makes sure I'm not doing anything wrong.

The switch I'm installing (Leviton DZ6HD) does not have any wires sticking out of it, so I have to install the wires directly into/onto it. The instructions show a neutral coming from the top of the box and tied together with a neutral going to the bottom of the box as shown below (2 is neutral).

Wiring to the switch in the instructions

In my wall, there are three white wires that all connect together and none of them to any switch. I assume that there is one neutral for each switch, and one return. Below is a diagram I made of how the wiring in my switch is (the orange one is bare copper wire).

Wiring to the switch in my box

So my question is, do I need to just go buy some white wire and run it from the switch where the neutral wire goes, to the bundle of 3 neutral wires (making it now a bundle of 4 wires). This makes sense to me, but I want to make 100% sure so I don't burn the house down.

Also, should I just completely ignore all the wires that are attached to the right 3-way switch as they seem all pretty isolated?

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In this case you will need to do as you suspected. This is a smart switch and needs power for its smarts and therefore needs a complete circuit. A normal switch doesn't need power for itself, it just passes power through (on) or interrupts power (off) using just the black wire (normally). Make sure you get the correct size wire. In your case it is most likely 14 but could be 12 in some older homes. If you are not sure of wire size, check the breaker. If 15 amp, most likely 14, if 20 amp, most likely 12. It's important to get the correct size wire. Not stranded, solid. Hope this helps... PS. You also asked about the 3way. If it is working ok and you ae not messing with it at all, then just leave it as is. If you are messing with the 3way, we need to have a longer discussion.

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  • Thanks for the response! Glad to know I was on the right track. I ran out to get some wire from Lowes since they were closing. I got 14 gauge "Primary Cable". It is stranded, but it's the right size (and I was told it was copper). Even if I'm just running a couple inches of it from the cap to the outlet, should I wait until tomorrow to go back and get solid wire?
    – scorgn
    Sep 18, 2021 at 2:26
  • @scorgn -- "Primary Wire" is useless for you -- get some THHN instead
    – ThreePhaseEel
    Sep 18, 2021 at 3:17
  • @ThreePhaseEel Thanks for letting me know, I don't know why the person at Lowes told me it would work
    – scorgn
    Sep 18, 2021 at 3:22
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Yes, because one of the neutrals shares a cable with a hot that is going to the switch. (If all the neutrals went into cables unrelated to this switch, then no... that can happen in a switch loop.)

The cheapest wire to get is THHN individual wires, they sell solid or stranded. Solid is the safe bet - stranded is illegal on backstabs and very hard to attach to side screws.

Get a red or tan wire nut while you're at it... yellow nuts are comfortable enough with 3 wires, but 4 wires goes easier with red or tan.

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  • Perfect thanks for the tip! I did buy some assorted caps, the green one fit well (seemed to be slightly smaller than red but bigger than the existing tan cap). I ended up cutting some of the existing wire out to make sure I was using the right type and twisting it back in there.
    – scorgn
    Sep 18, 2021 at 3:08
  • Another quick question while I have you. Is it normal that the hot wire is coming from two separate places, tied together? I tested the two black wires that were connected to the switch to see which one was hot, so I'm fairly sure I just treat it as if it were one hot wire. But I just wanted to make sure since I couldn't see any other examples where the hot wire was two separate wires pigtailed together.
    – scorgn
    Sep 18, 2021 at 3:15
  • Yes, it's normal for the "always-hot" and partner neutral to come in on one cable from supply (panel) and go onward to serve another switch box or receptacle. One circuit can support as many as a dozen or more... so why not? On the green wire nuts, watch it - they have a little hole in the top. Make sure no wires are sticking out of that. (If you inserted all the wires even, shouldn't be a problem).
    – Harper - Reinstate Monica
    Sep 18, 2021 at 5:44
  • Thank you so much for the help! I got it set up and working, I really doubted myself at first because of how much of a mess that cable box looked. Just mapping out the cables was the hardest part haha. I made sure to have all the wires even when twisting the wires together. It was harder than it seemed it be, but I was surprised at how well it actually acted as a screw with the screw cap.
    – scorgn
    Sep 18, 2021 at 5:58

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