2

When installing a split receptacle in a kitchen, where the top and bottom are each their own circuit, is there any way you can use an MWBC, or is your only option to run two normal circuits with two separate neutral wires? I can't think of any code-compliant way to do an MWBC here that wouldn't require a double-pole DFCI breaker, which to my knowledge doesn't exist for any type of panel. In the past, this was easy since AFCI wasn't required in kitchens, and double-pole GFCI breakers do exist. Also, if this is impossible now, is it also impossible now to install NEMA 6-15 or 6-20 receptacles in kitchens? Because I don't think 240V GFCI receptacles exist, and without them, wouldn't you need a double-pole DFCI for that too?

3

There are a couple of tricky ways to do what you're after, but they aren't all that great

It is still possible to run kitchen small appliance branch circuits as split-receptacle MWBCs (vs. double-duplex MWBCs or solutions based on separate branch circuits), but it takes some panel gymnastics to do so for the reason you describe (namely, the lack of two-pole DFCIs on the market). In particular, you have the choice of:

  • a GFCI protected common feeder using a 2-pole, 50A GFCI to protect a subpanel with 2-pole, 20A AFCIs in it
  • using individual "spa box" sized panels with GFCI breakers in them (you can even use actual spa panels for this) as subpanels off 2-pole, 20A AFCIs
  • or using a single large box to mount several unit mount GFCI breakers individually fed from 2-pole, 20A AFCIs in the panel.

The first approach is the simplest and cleanest to implement using "conventional" parts, but has the downside that a GFCI trip takes out all the kitchen receptacles. The second and third approaches avoid this, but at the cost of either multiplying boxes at the panel or using harder-to-get boxes and breakers (Eaton (QCGFT) and GE (THQC...GFT) make lug-lug/unit-mount GFCI breakers, but they're not exactly home-store items, and you'd need a cutout box and brackets to mount them in/with, too).

Given that, it's probably simpler to have a conduit run out to your kitchen receptacles, so you can pull in extra wires for 240V outlets (which don't need AFCI protection), more circuits, or what-have-you. This doesn't have to be terribly expensive, either, as it can be done using ENT ("smurf tube") since that's a mains-legal wiring method in most places that aren't Chicagoland (where you're already using conduit to begin with) or NYC.

5
  • With any of the approaches, does it matter whether the GFCI or AFCI is "first"? – Joseph Sible-Reinstate Monica Mar 18 at 1:01
  • 1
    @JosephSible-ReinstateMonica -- it does not, save for the GFCI-protects-a-subpanel-of-AFCIs approach (since 50A AFCis aren't a thing) – ThreePhaseEel Mar 18 at 1:17
  • 1
    I wonder if using an old split-bus panel as a kitchen subpanel could be another option. The lower section could be fed by a large 2 pole GFCI breaker, and would contain individual 2 pole AFCI breakers. Then any non-MWBCs could be fed from the top part, so that a single GFCI trip doesn't take out the whole kitchen at once. – Nate S. Mar 18 at 16:53
  • 1
    @NateS. -- I've considered that as split-bus panels are still a thing (Siemens and SqD make them for generator use), but that has the same downside as my plan #1 above in that a GFCI trip wipes out all the kitchen SABCs – ThreePhaseEel Mar 18 at 22:36
  • True, but I could imagine it being more convenient to put all kitchen circuits in one panel: the bottom section for the MWBC SABCs and the top section for other circuits, like the fridge, microwave, and any SABCs that are not also MWBCs. You could do the same thing by just taking the non-MWBC circuits back to the main panel, but then where to reset what circuit gets confusing. – Nate S. Mar 18 at 22:47
3

Well, 240V circuits don't...

240V circuits don't require AFCI. They do require GFCI in certain locations when your locality adopts (or copies) NEC 2020, but 240V GFCI breakers are readily available. So you are at leisure to fit all the NEMA 6-20 receps that you please at your kitchen countertops, provided you also provide the mandatory 120V receps.

I quite agree that concurrent AFCI and GFCI requirements put the last nail in the coffin of a traditional kitchen MWBC where you split each receptacle.*

An interesting question is what happens when you have a 240V circuit which is also MWBC. Is AFCI still required then? Which is a perfectly allowable combination; you're allowed to put both 120V and 240V sockets on a MWBC so long as the breaker is common-trip.

There is no question that the 240V portion is exempt from AFCI requirements. What I don't know is whether such a circuit washes away the requirement for AFCI protection on the 120V outlets as well. "Seems a bit too easy"...

But the point of splitting receptacles is lost on me, honestly.

However, in all honesty, I consider the "splitting receptacles" trick to be stupid. I don't see an advantage to having both circuits at every receptacle, versus each receptacle alternating which circuit it is on. What's really the practical benefit to the cook of having

 A            A              A               A
 B            B              B               B

vs

 A          B           A            B
 A          B           A            B

except box fill and difficulty of implementation? It's easier to communicate to the cook, I'll grant -- but a

Now if you were going

 A       C        E        G
 B       D        F        H

then I'm all for that, if your load calculation can stand the weight of eight 1500VA circuits. Even so, this seems like a more practical plan:

 A       B        C        D
 A       B        C        D

That's 4 fewer kitchen recep circuits, so 6000 VA less in the house's load calculation. And we don't really need MWBCs for that.

4
  • 1
    The main reason to prefer the first method is if the layout of the kitchen doesn't give you access to more than one in a given place. For example, in my kitchen, the (large) area to the left of my stove is served by a single duplex receptacle, and I'm not going to run a cord across the stove to get to a different one. My only options to get more than 20A there are to leave it as a grandfathered MWBC, or cut a bigger hole in the granite backsplash to get a second yolk in there, which I'd rather not do. – Nate S. Mar 18 at 16:18
  • 1
    @NateS. That's fair, but one-off's like that don't need to be MWBC... the other sockets could be [AA] [BB] [AA] [BB] and then each contribute a 12/2 to the problematic [AB] socket. Of course those 2 breakers would need handle-ties because of the shared yoke... – Harper - Reinstate Monica Mar 18 at 16:34
  • True. The trouble is mostly that it was wired as an MWBC originally, and changing it will require getting through the granite. I'm comfortable DIYing electrical, but I don't really have the tools or skills to work on granite. If I ever remodel, I'll do that, but for the moment it makes more sense to me to just live without AFCI. Though if anyone ever comes out with a two-pole DFCI, that would be even better... maybe someday. – Nate S. Mar 18 at 16:44
  • "a traditional kitchen MWBC where you split each receptacle.*" Is that asterisk meant to refer to a footnote? If so, where is it? – Joseph Sible-Reinstate Monica Mar 18 at 21:03

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

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