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I have an old MWBC and I'd like to protect the circuits with GFCI and CACFI (they are general purpose 15A circuits and include receptacles and lights). Note, currently they just have their own 15A breaker (no dual pole, no ties, no GFCI, no (C)AFCI etc.).

My understanding is that MWBC's require dual pole breakers. Unfortunately I am not able to find a dual pole, dual function breaker for my Siemens panel.

Is it allowed to just get two Q115DFN (dual function CAFCI/GFCI 15A) and bridge them via handle tie?

If not, what are other options (other than re-pulling neutral wires)?

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  • Current code does require a handle tie. And it would be smart to install one even if the installation is grandfathered. A dual is not required by code unless there's a mix of 240 & 120V loads on the circuit. But if GFCI or AFCI is required, you need a dual anyway.
    – Ecnerwal
    Commented Aug 22, 2023 at 1:35

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It won't work.

Any GFCI and most, but not all, AFCI breakers serving an MWBC has to be a dual, because the breaker needs to know what's coming back on the (one) neutral .vs. what's on BOTH the hots so it can tell if they sum correctly, and trip if they don't. One two-pole unit can do that. Two single pole units cannot.

If you can't get dual function for your panel, you can decide if you have more likely problems with bad wiring (AFCI) or shock risk (GFCI) and choose that for the breaker. Or you can change out the panel [more likely just install a sub-panel for the circuits like this you need to service] for one that has what you want available. Or you can (by having each entire receptacle be on one side of the MWBC, not split) use an AFCI breaker and GFCI receptacles.

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  • If the single pole AFCI breakers don't require a load netural connection, then certainly having two of them without neutral connections would be the same thing and should work as expected with no common trip. Do they have handle ties available for the tandems?
    – Robert Chapin
    Commented Aug 22, 2023 at 2:20
  • Tandems (not two-pole) have not been mentioned here, and few if any tandem AFCI breakers exist, anyway. Most AFCI need neutral, anyway.
    – Ecnerwal
    Commented Aug 22, 2023 at 2:31
  • I have tandem AFCI breakers in my Siemens panel and they do not need load neutral. Just a couple of letters from UL explaining how they are compatible with the old listings.
    – Robert Chapin
    Commented Aug 22, 2023 at 2:33
  • Yeah -- current production Siemens and GE AFCIs don't need neutral, and the Siemens ones are indeed available as tandems
    – ThreePhaseEel
    Commented Aug 22, 2023 at 2:40
  • Makes sense that GFCI need load neutral, didn’t think of that. Seems CAFCI techno only need neutral but not load neutral?
    – divB
    Commented Aug 22, 2023 at 6:19

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