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I have an issue similar to others wanting to add GFI to upgrade their kitchen outlets having multiple daisy-chained outlets with three wire service (220V with a neutral). I have a split phase wiring arrangement but I have two split outlet pairs at each position (total 4 plugs X 2) with split phase (220V across the red/black with a white common neutral). They are not GFI protected. Can I rewire them so the first set of 4 plugs in the line has two GFCI outlets such that the 'left' outlet pair is powered from one line (red) against neutral (white) and the other is powered from the other line (black) against the same neutral (white) then using the load terminals extend the lines to the other 4 outlet box with a similar arrangement with the 'left' outlet pair protected from the original 'left' and the same for the right pair? I would have to rewire the second set because currently the hot connecting tab is broken out such that the top and bottom of each plug is opposite phases. They would match the first set with left/right phases instead of top/bottom split. I'd replace that second outlet pair rather than wire in bridges to replace the broken out ones. Thanks Rob

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    Not without running a new neutral from the set of outlets with the GFCIs to the next outlets.
    – Ecnerwal
    Commented Apr 3 at 23:53
  • I think the easiest way with MWBC is to use a GFCI breaker in the panel. I have read that GFCI receptacles do not like/work well with MWBC.
    – crip659
    Commented Apr 3 at 23:54
  • It's been 240V and 120V for decades, by the way.
    – Ecnerwal
    Commented Apr 4 at 0:01

2 Answers 2

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In most houses, the practical solution to this will be a 2-pole 20A GFCI breaker in the breaker panel, which feeds the Multi-Wire Branch Circuit (MWBC) without further fuss.

To use GFCIs of the receptacle flavor, either every outlet needs to be a GFCI receptacle (no load connection) or you need a neutral wire you don't have from the GFCI Load to the following outlets. You have one neutral, and you need two neutrals - one for each side of the MWBC after the "split" - that's usually impractical (unless you have conduits), and the breaker, though expensive, quickly becomes less expensive than replacing every receptacle with a GFCI receptacle.

Attempting to share the neutral from single-pole GFCIs will guarantee GFCI trips, as GFCIs (RCDs in the rest of the world) look at the current going in and out of them, and if it differs by too much, they trip. The 2-Pole GFCI breaker can sum the current from both hot legs and the neutral to make that calculation work. Two single-pole GFCIs sharing a neutral wire cannot.

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You are on the right track. You can't split a GFCI, so each receptacle goes on an alternating phase.

Use a GFCI receptacle at each location. Leave the warning tape on the load terminals. Don't waste your time trying to cheap out on GFCIs by using one GFCI to protect other plain sockets, that will be way more trouble than it's worth.

At the first receptaclee,

  • connect the black wires to GFCI Line hot, read the instructions for how to put 2 wires on 1 screw.

  • pigtail neutral-this is mandatory.

  • connect the two red wires to each other with a wire nut.

At the next receptacle, do the same but swap the words red and black in what is said above.

Etc.

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