I am installing two new smart Eaton WFSW15-C2 smart switches. I have a new house, so it has the neutral wires required for a switch that requires the four wires. The two I am replacing are standard three-wire.

One problem is there are 4 neutral wires and they are all bundled up together under one red wire nut and the original switches have two black wires and the ground. Using a tester I was able to tell the hot. I guess the other black wire would be the load and goes to the outside light.

The biggest question I have is this:

Since I have a box with three switches and 4 neutral wires, should I use two of the neutral wires, one for each switch, and leave the other two twisted together and one to each of the new smart switches?

1 Answer 1


You have 1 neutral "in" and 3 "out". They aren't "spares". What you need to do here is to add the switch neutrals. You will likely need either a single new large wire nut or split into two but all connected together. If you need extra pieces of white wire, you can either buy some wire or pull some out if a cable. Should be 12 AWG for a 20A circuit, 12 or 14 for a 15A circuit. (You can't use black, green, bare copper or any other color except white or gray.)

You will have a total of seven neutrals:

  • 1 in from panel
  • 3 out to fixtures
  • 3 switches

They all need to connect together. So you can:

  • Use a single wire nut - if you can find one rated to handle 7 wires
  • Use two wire nuts - since this needs a wire to connect them together, you will effectively have nine wires, so one with 3 + wire to the other one, one with 4 + wire to the other one.
  • Use three wire nuts - which then means 10 altogether - one with 3 + wire to another one, one with 3 + wire to another one and one with 1 + wires from the other 2. This is, in some ways, the most logical: Panel + 2 groups; group of switches; group of fixtures. But really "whatever works".

Beware that switch boxes can get crowded. A typical smart switch is a bit deeper than a simple toggle switch, so it takes more room in the box. The extra wire nut(s) will take more room. So it may be a tight fit by the time you are done.

  • So with the four neutrals, I can split them into two, and then run a separate neutral copper wire from the two bundles into each of the two new smart switches?
    – Daniel K
    Commented Oct 3, 2021 at 19:05
  • But that they should remain wrapped together either in 4 bundle or two bundles of two with two wires coming from the neutral bundles to the switches?
    – Daniel K
    Commented Oct 3, 2021 at 19:06
  • 1
    @DanielK. Yes. The general idea is if you can't fit all the wires under 1 wire nut, to split them into 2 wire nuts, including a jumper wire between the 2 nuts so they are ALL connected. They also sell push-in connectors that take up to 8 wires. Some wire nuts say they are good for 6 wires, but I don't like using nuts very near the limits of their capacity, and I'm good at it. Commented Oct 3, 2021 at 20:45
  • 1
    Yeah, that was what I had to do. I used to do electrical back in the day, the early 90s and it's been a while. I had to create two separate bundles of two neutral wires with one wire as a jumper between the two bundles and one wire running from each neutral bundle to the proper switches.
    – Daniel K
    Commented Oct 3, 2021 at 21:23
  • 1
    @DanielK "with a third copper wire going to the switch" - just be 100% certain that it is not a bare copper wire! Bare wire can only be used for ground. Also, since you're dealing with the neutral, it must be white or grey as manassehkats mentioned in his answer.
    – FreeMan
    Commented Oct 4, 2021 at 14:57

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