I have an older house that was wired with no ground wires on some circuits. I have changed all outlets to 3 prong outlets. I have installed a GFCI breaker on a two-wire circuit and when I turn on a light it trips the breaker. I can disconnect the neutral on the breaker and all seems fine.

What are the possible problems?

  • 1
    You have a ground fault on that circuit. Good chance the ground fault is between the switch and the light or somewhere on that circuit. Older house equals greater chance of loose connections and/or bad wire insulation. The breaker is doing it's job to protect you.
    – crip659
    Oct 23, 2023 at 21:20
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    "that was wire[d] with no ground..." "I have change[d] all outlet[s] to 3 prong outlets." Does that mean that the ground of those outlets is disconnected? If so, then that is deceptive, dangerous and invites electrocution. Oct 23, 2023 at 22:36
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    Did you check that the GFCI breaker/s you installed in the panel are made for it? Panels can only use certain makes of breakers.
    – crip659
    Oct 23, 2023 at 22:58
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    @crip659, that's irrelevant. If the apparently grounded outlets are wired with the original 2-wire (no ground), that is very dangerous. Clarification needed. Oct 24, 2023 at 0:59
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    Are you installing the GFCI according to instructions including hooking up both neutral wires (the one from the circuit and the GFCI curly pigtail)? Follow the hot wire back to the cable it comes in on, is there another red or black wire in that cable tha goes to a different breaker? Oct 24, 2023 at 1:24

1 Answer 1


In an older house, the most likely explanation is that you have a multi-wire branch circuit.

You may be able to resolve this with a dual-pole GFCI breaker; however, this is just speculation, and any specific solutions are going to require an electrician to check on the wiring in person.

  • 1
    If the OP were to provide pictures of his actual wiring, I'm betting we could determine from right here whether it was a MWBC or not.
    – FreeMan
    Oct 24, 2023 at 16:35

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