Electrical – Possible to ground-fault protect both legs of a MWBC with two single-pole breakers

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To get a MWBC working, with both legs GF protected, I installed 2 Single Pole GFI breakers, on adjacent slots, with a handle-tie. Since there are 2 lugs for Neutral wires, and only one neutral coming in, I used two pieces of white 12 awg to wire nut to the neutral coming in.

It doesn't work, trips as soon as it's flipped on.

I even opened the circuit at the first box, (so i kknow it's not an actual ground-fault) and it still trips, even though neither leg of the circuit could possible be conducting at all!

I was told I could use 2 single-pole breakers w/ handle tie to get both legs of the circuit GF protected, but this appears to not be the case. Am I wiring it wrong? Also, how is it possible for them to both trip when neither is conducting?

Best Answer

Never gonna work. Sorry, but even if you might be able to get one at a time to work, GFCI on MWBC is based on the breaker comparing "all hot" to "all neutral". Two electrically separate breakers simply can't do that. The handle tie requirement satisfies the general MWBC safety issue of making sure that if one is off for maintenance then the other is off as well. Options:

  • Double GFCI breaker

  • Two single regular breakers with handle tie and install single GFCI where needed at point of use (e.g., kitchen or bathroom).

GFCI is perfectly effective at point of use. AFCI is best at breaker or very close to it.