I have a double pole 20A breaker feeding a 120V MWBC with 12/3 with ground, romex that goes up three levels to two separate 120V duplex GFCI receptacles with common neutral.

I want to have both 120V and 220V small appliances. Wanting to add a 220V 6 amp coffee maker to two small 120V appliances. This is not a kitchen, but indoors, off of a top deck. The MWBC feeds just the two 120V duplex GFCI's, nothing else.

What is best practice to do this?

I could run existing MWBC wires to a small panel, then install one double pole 15A 220V GFCI breaker and two single pole 15A 120V GFCI breakers, and new receptacles. Possible also to use the existing 120V GFCI receptacles and regular single pole breakers fed off this panel too, in this situation.

Or could leave the current two GFCI receptacles alone and take 12g wire pig-tailed from the ends of the MWBC to a 'spa' panel, change out the breaker in the 'spa' panel for a 15A or 20A 220V double pole GFCI breaker and then connect a 220V receptacle.

Or I could attach an inline 220V GFCI to the hot leads of the MWBC in a junction box.

Or I could use a 2000W step up/down transformer plugged into one of the 120V GFCI receptacles. It just seems redundant to convert the voltage when I already have it there, but a plug-in transformer may be the most code compliant and cheapest, way.

I can not run another wire from my main panel. I cannot replace the 20A double pole breaker in the main panel, with a GFCI breaker, as it is actually a quad breaker.

Any other ideas? Other than code won't allow any of it? Wife really wants the coffee maker so it is going to get done somehow.

  • What make/model is your quadruplex breaker? – ThreePhaseEel Nov 6 '18 at 0:11

You do not have a "120V MWBC".

You have a plain MWBC. 240V-only (no neutral) loads are allowed on MWBCs.

They even make receptacles for that.

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Note how there is no tab to break away on the visible side, since one must be neutral and the other L2. However you can see the tab peeking out from the other side, which could both be L1 of the same circuit.. Because this is legal on MWBCs.

As far as GFCI protection: It's an easy job for a 2-pole GFCI breaker. Replace the current non-GFCI 2-pole breaker in the service panel with a 2-pole GFCI breaker. Liberate the two GFCI receptacles and reuse them somewhere useful.

If you don't have space in your panel, then it's time to fit a subpanel somewhere. Since you're ready to do that, do that... just not out at the patio where it'll be a one-trick pony. Next to the main service is better. After all, you have this "out of spaces" problem all over your house. So fit it somewhere that makes sense for all your future loads.

I know adding a subpanel is a big job, "best" kicked on down the road for awhile longer... But the fact is you'll be right back here again when the wife wants an on-demand water heater or a plug-in hybrid. In this day and age, with so many amazing electrical gadgets, a full panel is no place to be.

  • One potential fly -- if he has a non-common-trip quadruplex breaker, he can't do this, because the rules about common trip for mixed 120/240V loads on a MWBC apply circuit-wide. – ThreePhaseEel Nov 6 '18 at 0:11
  • @ThreePhaseEel is there such a thing as a quadplex breaker (I assume on the outside breakers) that is "common maintenance shutoff" with the factory handle ties, and yet not common trip? – Harper Nov 6 '18 at 3:23
  • BR quadruplex breakers are available in common and independent trip versions (independent trip is BQxxxxxx, common trip is BQCxxxxxx) – ThreePhaseEel Nov 6 '18 at 3:24
  • @ThreePhaseEel but an independent trip breaker would not have handle ties and would not have any pretense to common maintenance shutoff, yes? Also, the coffee maker is not a 120/240 load, it is 240 only, I suspect from Europe. I thought that if alone, they didn't need common trip - do they need common trip when they are in an MWBC? Of course MWBCs that serve only line-to-neutral loads only need common maint.s/o, not common trip. – Harper Nov 6 '18 at 3:29
  • The BQ220220 for instance still has inner and outer handle ties even though it is independent trip. And it turns out that the rules in 210.4 only allow independent trip for line-to-line loads on a MWBC for a single device, as of 2017 (although they do allow independent trip for a single 120/240V load), which restricts the otherwise permissive rules in 240.15(B)(2) for line-to-line only loads – ThreePhaseEel Nov 6 '18 at 3:36

I would install a small "spa" panel then 2 breakers for each outlet and the double pole for the coffee maker. Because you are already feeding 12 AWG protected by 20 amps this would be legal as a sub. Make sure your neutrals are isolated from ground in the new panel, and install the panels prior to or at the split on the MWBC with there own breakers. For a clean install, you could continue with the MWBC from the spa panel but it needs to be a double pole if you do. I would take the easiest / least expensive path, but either will work.

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