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My house has two unused bedrooms that each have their own dedicated circuits in my panel. Both circuits are on 15 amp AFCI breakers.

Since these are never used, and certainly never used at any level anywhere near 15 amps, I am going to combine them to free up a slot in the panel.

My understanding is that if these were not AFCI circuits, I could just combine the two hot wires in a pigtail to a single 15-amp breaker, and I could leave the grounds and neutral wires separately connected to the ground and neutral bus bars.

But this is an AFCI circuit so I'm questioning what exactly needs to be pigtailed. Obviously the hots need to be pigtailed and connected to the single 15-amp AFCI breaker. But do the 2 neutral wires also need to be pigtailed and connected to one terminal on the neutral bar? Do the 2 ground wires need to be pigtailed?

Thanks for any input.

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The neutrals do, the grounds don't.

Ground never sees current except during fault conditions, so it doesn't need to feed into the AFCI.

But do the 2 neutral wires also need to be pigtailed and connected to one terminal on the neutral bar?

You haven't looked inside your panel yet, have you? :)

The vast majority of AFCIs include, among their other abilities a GFPE, which is a weak GFCI. As such, it needs to be wired like a GFCI, with both hot and neutral coming from the breaker.

Thus your neutrals won't be going to the neutral bar but to the AFCIs, and as such you will need to pigtail, obviously.

If your arrangement does not have neutral going to the AFCIs, then you have some of the very newest AFCIs from certain specific manufacturers, and then you wire as you expected. If you have room on the neutral bar it is not necessary to pigtail.

However, one cannot as a rule pigtail unrelated circuits - the pigtail could carry the sum of all currents, and it's not big enough. If one is in a jam for neutral spaces, read the panel labeling and either stack grounds as the labeling authorizes, or use one of the accessory ground bars listed.

You can count on the fact that there are enough neutral bar spots for the maximum number of circuits allowed in the panel. UL would not have listed the panel if that were not so.

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  • Thanks for the response. You are correct re the neutrals going to the breaker itself, of course -- thanks for the reminder. Question re "one cannot as a rule pigtail unrelated circuits." See, e.g., diy.stackexchange.com/questions/155730/…. I've consistently seen that two circuits of the same amperage can be combined.
    – aunsafe2015
    Jan 13, 2023 at 14:28
  • @aunsafe2015 that's not what they're discussing there. They're discussing combining the hots, with the neutrals remaining where they are on the neutral bar. I'm saying you can't solve a "neutral bar full" problem by picking 2 random neutrals and pigtailing them.
    – Harper - Reinstate Monica
    Jan 13, 2023 at 22:26
  • Ah, so what you meant when you said "one cannot as a rule pigtail unrelated circuits" is that you cannot pigtail the neutrals of unrelated circuits? Understood.
    – aunsafe2015
    Jan 17, 2023 at 14:59
  • @aunsafe2015 exactly.
    – Harper - Reinstate Monica
    Jan 17, 2023 at 19:49

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