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New member here, and wrangling with a very common problem: how to properly upgrade a 20A MWBC serving DW and GD to include both AFCI and GFCI protection without nuisance tripping. Disposal is plug-in, so easy enough to wire in a GFCI outlet at LINE only; DW is hard-wired, with a simple single-pole switch disconnect in same j-box as GD plug. Now, would a replacement 20A deadfront GFCI work here in lieu of the current disconnect, then install a double-pole 20A CACFI breaker at the load center to complete the upgrade?
Thanks in advance for any helpful suggestions.

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    How about a few pictures of what you're dealing with.
    – JACK
    Commented Mar 25, 2022 at 17:36
  • Amazingly, there are these things called "cameras" that are designed for taking pictures. Some of them aren't even attached to cell phones...
    – FreeMan
    Commented Mar 25, 2022 at 18:42
  • Sorry, don’t have a Smartphone, but layout is quite typical of these sorts of MWBC for dishwasher/disposal: 12/3 from panel to below-sink cabinet j-box, L1 to disposal counter-top switch, then to duplex outlet > disposal; L2 to dishwasher disco. switch > hard-wired DW. Checked with Schneider Electric this a.m., rep confirmed NO double-pole dual-function breaker available, which would immediately fix the problem…so, it’s work-arounds, per my query.
    – the_hamster
    Commented Mar 25, 2022 at 18:49
  • Doesn't a dishwasher disconnect have to be accessible? And how do you switch the disposal on and off? Which edition of NEC has your locality adopted? Only a minority are on NEC 2020.
    – Harper - Reinstate Monica
    Commented Mar 25, 2022 at 20:40

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GFCI and AFCI both need to see an entire circuit. For a 120V circuit (hot/neutral), that can be done anywhere. For a 240V/120V circuit (MWBC, hot/hot/neutral), there are normally two options:

  • Double-breaker - This is generally the only practical option for the AFCI part of things. It is fine for GFCI, but depending on the panel, you may or may not be able to get a combination AFCI + GFCI double breaker. (Not to be confused with CAFCI which combines two types of AFCI, but not GFCI.)
  • Split and protect at outlets - This is common for the GFCI, but gets tricky with MWBC. Since deadfront and receptacle GFCIs are normally for a 120V (hot/neutral) circuit, you must split the MWBC before any GFCI (except double-breaker).

So for your situation:

  • Double-breaker AFCI
  • Somewhere near the disposal and dishwasher, split the circuit so you have hot 1/neutral going to the disposal and hot 2/neutral going to the dishwasher.
  • For the disposal (plug-in) install a standard GFCI/receptacle in place of the plain receptacle.
  • For the dishwasher install a deadfront GFCI (no receptacle) after the split. The dishwasher gets wired to the load side of the GFCI.

The end result is:

  • Double-breaker 20A AFCI
  • Two 20A GFCI - one deadfront, one with receptacle
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    Ah, thanks very much…the circuit is currently wired as you outlined, and you answered the question about DW deadfront GFCI and wiring to LOAD side. Items on order and hope it all comes together w/o any nuisance tripping.
    – the_hamster
    Commented Mar 25, 2022 at 19:38
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    @the_hamster and I just checked Eaton CL line (specifically made and UL-CLassified for HOM), but they don't offer any 2-pole AFCIs at all. Schneider has had a bunch of supply problems with HOM, and they may also have had an ill-timed model change which was then disrupted by COVID. HOM is the shoemaker's son for Schneider; it's literally their "home line" and they care more about QO and other industrial lines. Well, unavailability is a defense, so I would plan for a future 2-pole AFCI and then proceed without it.
    – Harper - Reinstate Monica
    Commented Mar 25, 2022 at 21:01
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    @manassehkatz: Well, perhaps it’s an overzealous reading of 2020 NEC and extending AFCI coverage to all kitchen outlets…on several other electrician blogs, people were commenting on hazards of end-of-life dishwashers and electronics failures that could be handled by AFCI protection. For me, the arguments presented on this thread plus NEC requirements for GFCI protection for dishwashers now lead me back to your point about deadfront GFCI for DW, and that will do it, full stop.
    – the_hamster
    Commented Mar 25, 2022 at 23:15
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    @the_hamster that's not "accessible" LOL. The Code reason for the dishwasher disconnect is for when it starts belching smoke and you need to de-energize it PDQ. I suggest adding a gang to the disposal switch box, and then, fit a GFCI deadfront SWITCH there. The weird UX means people won't mistake it for a regular light or disposal switch, so won't switch off the DW by accident. If you're in NEC 2017 then AFCI is not required.
    – Harper - Reinstate Monica
    Commented Mar 26, 2022 at 4:12
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    For the record, house had final inspection signoff in Dec., 2003, and presumably the EC was working to 1999 or 2002 NEC. The DW disconnect inside cabinet area under the sink apparently was considered “accessible” then…the inspector passed it. But, your point is taken re: 2017 NEC and accessibility.
    – the_hamster
    Commented Mar 26, 2022 at 5:56

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