3

I want to wire the circuit shown in the attached image in my garage. I want to have two circuits, and they need to be GFCI protected due to being in the garage. I've read through a number of posts regarding MWBC and GFCI, and it seems like the best solution is to use a 2-pole GFCI breaker in the panel. However, I'm wondering if I can wire it using two separate neutral wires on the load terminals of the GFCIs in order to save the $$$ on the expensive breaker. (I already have two normal breakers that I can tie together).

In the image below, I have a 14/3 cable from the panel to my garage, with the one neutral from the panel splitting and feeding the line terminals of both GFCIs. Then, I have an additional white wire coming off the load of one GFCI to supply neutral for the outlets on that circuit. In addition, each circuit branches off in two directions from the GFCIs.

Garage MWBC

Improve this question
1
  • 1
    Do you already have the wire run? If not, are you drawn to this because you have a ton of 14/3?
    – Aloysius Defenestrate
    Commented Oct 29, 2023 at 2:34

1 Answer 1

Reset to default
3

Should work. You'll either need to run wire in conduit or buy 14-2-2 cable with 2 separate neutral wires (one marked with red) to do it as drawn. You can't use 14/3 "and an extra neutral wire."

Generally easier (and less expensive, using commodity cable .vs. oddball special order cable) to just separate the cable runs once it's split out so you can use 14-2, rather than mess about with keeping both halves running to one duplex in a quad box. Just put in a duplex from one and a duplex from the other in boxes near each other if you want both available, rather than "in the same box."

If you do conduit, gray neutral for one half is likely to be easier to source than red-striped white. Or you can tape-group the conductors.

Improve this answer
10
  • 1
    Two 14/2 cables into (and out of) each receptacle box downstream of the GFCIs would be 100% legal and code-compliant.
    – nobody
    Commented Oct 29, 2023 at 3:00
  • But does the box on the right side of the diagram violate the pigtail rule? I'm curious if it would only apply to the GFCIs in this case
    – Robert Chapin
    Commented Oct 29, 2023 at 3:24
  • 1
    @RobertChapin -- "pigtail rule"?
    – ThreePhaseEel
    Commented Oct 29, 2023 at 4:09
  • @ThreePhaseEel NEC 300.13(B) -- I don't know if it is enforceable beyond the split. It depends how you define where the MWBC begins and ends.
    – Robert Chapin
    Commented Oct 29, 2023 at 13:24
  • 1
    @AlexNorton Flat 14/3 is treated for fill purposes as one strand of 0000 (within 0.002 inches on diameter, with the flat cable actually being a hair larger, because it's treated as a round of the maximum size of the oval) and running that and one neutral would fall under 2-conductor fill rules which have a lower percentage (31 rather than 40) due to jamming. Let's do the math. You'd be good in 1-1/4" PVC 40. Meanwhile 1/2" PVC-40 or 80 would be plenty for 5 14AWG THHN wires, not in a cable. 9 would fit in schedule 80. Plan first, then buy wire/cable.
    – Ecnerwal
    Commented Oct 29, 2023 at 23:35

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.