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I have a Multi-wire branch circuit & would like to connect GFCI receptacles. The MWBC currently powers dimmable LED lights in basement. In process of finishing basement. I would like to extend MWBC to GFCI receptacles in basement. So each half-circuit would have gfci receptacles. Each half-circuit would include a few extra non-gfci receptacles which should have gfci protection since they will be connected to the load side of up-stream gfci receptacle.

GFCI receptacle instructions has warning: 'do not install gfci receptacle in an electrical box containing (a) more than 3 wires (not including ground) or (b) cables with more than two wires (not including ground)'.

Can GFCI receptacle be installed to Multi-Branch Wire Circuit as long as I pig tail Neutral before connecting to GFCI receptacle?

Will Neutral pig tail satisfy NEC 300.13 (B) device removal? 300.13 (B) says: 'In MWBC, continuity of grounded conductor shall not depend on device connection such as lampholder or receptacle where removal of device would interrupt continuity.'

Any issues expected if non-gfci receptacles are installed on load side of gfci receptacles on each half-circuit so they have gfci protection as well?

Any feedback will be greatly appreciated!

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  • I believe this other question answers most of your questions pretty well diy.stackexchange.com/questions/123696/…. The only thing left open is whether the post-split GFCIs can coreside in the same box. I believe the code pros will say that since the device instructions say not to do that, you mustn't do that.
    – jay613
    Aug 17, 2021 at 19:23

2 Answers 2

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The LOAD side of a GFCI receptacle has two terminals: Protected Hot and Protected Neutral. The Protected Neutral is not the same as the supply neutral.

The "Protected Hot" will go onward to serve certain loads.

In order for the GFCI to work, the "Protected Neutral" must serve exactly, and only, the same loads as the Protected Hot supplies.

The "Protected Neutral" cannot share a wire with another GFCI's Protected Neutral. That means you cannot continue to use a shared neutral downstream of a 120V GFCI.

The only way that is possible is if you have a GFCI which is savvy to current on all of the hot wires + the neutral. That would be a 2-pole GFCI in your case, which only comes in the "circuit breaker" form-factor.

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    Thank you for the reply! Only the supply neutral will be shared prior to both GFCI's. The protected neutral will not be shared with another GFCI. The neutral will not be shared downstream of GFCI receptacle. The intention is for the protected neutral to serve only the same loads as the protected hot. Based on others feedback, it seems possible for neutral on MWBC to be shared prior to GFCI receptacles (one GFCI receptacle for red wire circuit & another for black wire circuit) & satisfy requirement you mention above. Do you agree?
    – jjcarey44
    Aug 17, 2021 at 22:45
  • @jjcarey44 yup, that's how it works.
    – Harper - Reinstate Monica
    Aug 18, 2021 at 1:42
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An MWBC can be used in essentially two ways:

  • Both half-circuits to each Duplex Receptacle - aka Top/Bottom split

This makes some sense in kitchens, as the same section of counter might be used with multiple appliances and this doubles the power available at each location.

Note that this would be done using a GFCI breaker, because a GFCI duplex receptacle (two receptacles and TEST/RESET between them) can't split power between the two receptacles - they have to share both hot & neutral.

  • Each half-circuit to a separate set of receptacles - aka Split the circuit

This is what you need to do here. The basic pattern is:

  • Breaker -> first box - /3 black/red/white
  • In first box, two /2 cables. One connects to black & white, the other connects to red & white. In other words, each hot goes to one place but the neutrals (incoming + 2 outgoing) are all tied together.
  • Second box on circuit A - black/white to GFCI LINE, second black/white to GFCI LOAD - which extends to additional ordinary receptacles in other boxes.
  • Second box on circuit B - black/white to GFCI LINE, second black/white to GFCI LOAD - which extends to additional ordinary receptacles in other boxes.

Note that the "first box" and one of the "second box" can actually be one large box. But conceptually you are splitting the circuit and then taking each branch to a GFCI.

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  • Why can the first two boxes be combined but not all three? You could obviously wire things this way in one box except for the noted instructions about more than three wires. Hence three boxes. Where is there a middle ground to combine two of them? Probably unimportant to OP as they want to create a couple of new protected daisy chains and so it'll be easy to do the split and then put the first GFCI in the first new box of each chain. Still ... curious.
    – jay613
    Aug 17, 2021 at 19:29
  • You could combine all 3. But why? That would put both GFCI receptacles in one place. In other words, the boxes I describe are "conceptual". They can be combined or not. For example, if the MWBC comes in at the middle of the ceiling and the receptacles are all to be on right wall and left wall, it might make sense to split in a ceiling box - maybe the same one that has the lights - and send right and left to wall boxes that each have a GFCI/duplex receptacle. But if the circuit comes in one side of the room split + GFCI in one box makes sense and the other 1/2 circuit goes to a box on the
    – manassehkatz-Moving 2 Codidact
    Aug 17, 2021 at 20:08
  • opposite side of the room. Stuff can always be together - just a matter of keeping things straight (partner neutrals, etc.).
    – manassehkatz-Moving 2 Codidact
    Aug 17, 2021 at 20:09
  • Thank you very much! The GFCI 's for each circuit will not nuisance trip because circuit A neutral will have different current than circuit B neutral? The GFCI's remain isolated from the other circuits current even though the neutral is shared?
    – jjcarey44
    Aug 17, 2021 at 20:24
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    The key is that the neutral is shared only before the GFCIs. It splits to go to two separate GFCIs. After that, each hot/neutral is tied only to the LOAD side of one GFCI.
    – manassehkatz-Moving 2 Codidact
    Aug 17, 2021 at 20:28

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