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I wanted to change my breakers to AFCI, but don’t know if it possible. I have 4 20 amp circuits running to my kitchen. The wiring is 12-3, but this is where it gets weird for a DIYer, like myself. One black wire goes to one circuit, the red goes to another circuit, and the neutral goes to the neutral bar, so it is shared. The other 2 kitchen circuits are wired in the same way with one 12-3 romex. I haven’t seen anything like this in previous homes I owned. Were the builders of this 1970s condo complex being cheap and trying to save money on wiring?

So, is there a way to switch the breakers without rewiring given that there is one neutral for 2 circuits?

Thanks in advance.

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  • We really, really need to know the manufacturer of your panel, to see whether there are options for you. Also, we need a photo of the panel so we can see whether it is double-stuffed. Aug 3, 2022 at 19:31

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It's a MWBC, (multi wire branch circuit) and they are incredibly common (not unusual, not a sign of the builders cheaping out) in kitchens since kitchens have a required minimum of 2 20A countertop circuits.

They may be seen elsewhere, but if a house only has one or two, it's almost always the kitchen, IME.

You need a two-pole (240V) AFCI for each set of these - that gets each circuit hot and the single circuit neutral, then has a connection to the panel neutral (either via plug-on or via a pigtail.) If the circuits are not currently next to each other in the panel, you may have to do some rearranging so that you can change them to a double-breaker.

You may actually need a two-pole combined AFCI/GFCI for a kitchen, depending on your local applicable code.

Beware that it's also very common for kitchen receptacles on MWBCs to be wired with the hot tab broken and different circuits (halves of the MWBC) on the two outlets. You can't replace that directly with a GFCI receptacle.

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    Well, I learned something new today. Thanks Ecnerwal for the explanation and solution.
    – Vmarc
    Aug 3, 2022 at 6:10
  • Things are moving fast in the AFCI market, and there may be good news depending on the panel make. Also, "hot tab broken" outlets CAN be GFCId but you must put the entire socket on one circuit or the other. (or alternately use a 2-pole GFCI/AFCI breaker). Aug 3, 2022 at 19:40
  • ..exactly why I'm suggesting an AFCI/GFCI 2-pole, and saying they can't be replaced directly as in: wired the same way.
    – Ecnerwal
    Aug 3, 2022 at 20:05

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