Neutral across circuits?

Devices & Integrations
1

I have just installed a GE Enbrighten 3-Way (ZWave) switch and its remote. The master switch is in a 3-gang box with two dumb, single-pole switches that are on a separate circuit. The smart switches are working fine. However, the circuit breaker on the other circuit (with the two dumb switches) keeps tripping. Should the neutrals of the two circuits be connected together?

2

No. They should not. They should be two separate neutral bundles unless they are one 220 circuit with the breakers bonded together. (Some municipalities dont even allow two separate circuits in the same box.)

When two separate circuits share a neutral it is theoretically possible for both to send the full amperage load of both curcuits back to the breaker box over one wire. Assuming standard North American setups of 110v/15a thats 110v/30a - which wouod exceed the rating of the wire itself unless you ran 10 guage copper for your wiring…

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3

Thank you for the reply.

That makes complete sense to me. The neutrals were already connected together, but we had no smart switches. I’ll separate the neutrals and see if the breakers like it better.

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4

This 3 way circuit is for outdoor soffit can lights. One switch is inside by the front door, and one switch is in the garage. The circuit that they are on controls the other garage lights. So, I would assume that the primary switch is the one in the garage. However, it is the front door switch that has a voltage across common and ground.

The problem is that the switch at the front door has one cable coming into it from the top of the box. One black, one red, one white, one copper. If the white wire is used as a traveler, there is nothing to connect the neutral of the switch to. Whether this is the primary or remote, I need one more wire.

What the heck?

5

Tagging @ritchierich who might be able to help out.

6

Can you please post clear pictures of your 3 gang box? Given the Aux location has a single 14-3 Romex it doesn’t matter. I need to be able to see the wires coming into the box and where they go to the switches you you will need to loosen the other 2 dumb switches as well.

7

Meaning they control different loads or do they come from different breakers?

8

Usually, black - line, red - switched power, white - neutral, copper - ground. However, in a 3-way circuit white could also be carrying power but it should be marked with black tape (or permanent marker).

9

I don’t have a picture to share, and I have already put everything back the way it was. However, it is a pretty simple configuration.

  1. The cable from the breaker comes into box 1.
  2. The black wire (line) is connected directly to the black wire of a 14-3 cable that goes to box 2.
  3. In box 2, the black wire from the incoming cable is connected to the common terminal on a 3-way switch. The red and white wires from the incoming cable are connected to the traveler / load terminals of the switch. The ground is connected to the ground terminal.
  4. Back in box 1, the red and white wires from the cable (from box 2) are connected to the traveler terminals of a 3-way switch.
  5. The black wire of a 14-2 cable (that goes to the lights) is connected to the load (black) terminal on the 3-way switch.
  6. The white wire of the 14-2 cable (from the lights) is connected to the white wire of the 14-2 cable from the breaker.

Bottom line is that all three of the wires fed over to box 2 are used as line and travelers. There is no neutral available.

Now, box 2 also happens to have a simple light switch wired on a separate circuit. So, there is a neutral in box 2, but it is on a different circuit. That is why I posed the original question.

I think I am out of luck, as far as putting in a smart 3-way pair. I could get creative and put a smart switch back in box 1 with no connection at all (e.g. single pole) to box 2. Then, I could put a smart button over in box 2 that runs on the other circuit. I could put an event listener in my Smartthings configuration to signal the switch whenever the button is pressed.

For now, I’m just going to ponder the situation.

Thanks for the input! At least I didn’t burn the house down!

10

Assuming you are using the ge aux/remote switch (such as the 12723), it switches signal between one “traveler” and neutral, so doesn’t need the second traveler that a dumb switch uses.

11

OK this description is good and good news is you can use a smart switch in your “box 1”/2 gang box. You will need to change a bit of wiring to “send” neutral to the other box as I have described many times in the GE 3-Way Wiring FAQ. Since both line and load are in Box 1 the smart switch has to go here because Box 2 doesn’t have enough wires - 4 are needed for a master switch

Box 1

  • Disconnect the 14-2 line black wire from the black wire of the 14-3 running to Box 2
  • Connect the 14-2 line black wire to the line terminal on your smart switch
  • Put a wire cap on the 14-3 black wire as you no longer need it
  • Connect the 14-2 load black wire to the load terminal on your smart switch
  • Connect the 14-3 red wire to the traveler terminal of the smart switch
  • Connect the 14-3 white wire to one of the neutral terminals of the smart switch - this will send neutral to your Aux switch
  • Your smart switch should have come with a short white pigtail wire, add it to the 14-2 line and load white wire nut and connect the other end to the other neutral terminal of the smart switch

Box 2:

  • Put a wire nut on the black wire as you no longer need it
  • Connect the white wire to the neutral terminal of your Aux switch
  • Connect the red wire to the traveler terminal of your Aux switch

Test and enjoy your new smart switch!

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12

Interesting. I’m sketching that up to try tomorrow.

Thanks!

13

Excellent description, and it works as advertised!

All switches and lights are working, and nothing is crossing a circuit anywhere.

Thank you very much for your help!

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