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I have a 1-gang duplex outlet under the sink in my kitchen. The two outlets are on separate phases of a single MWBC circuit. One of them powers the garbage disposal, and is controlled by a switch. The other powers the dishwasher.

I want to put them behind CAFCI/GFCI. But for whatever reason, 2-pole dual-function breakers do not seem to exist, even though both 2-pole CAFCI and 2-pole GFCI are available. (That sounds completely illogical to me, by the way.)

I suppose one way is to use a 2-pole CAFCI breaker with a GFCI outlet. But I couldn't find duplex GFCI receptacles where the GFCI mechanism can handle MWBC (either with two independent GFCI or with a 2-pole GFCI). Do they exist?

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  • Why do you want to add dual function? And I have not seen a GFCI receptacle that can handle a mwbc. You may find problems with the dishwasher depending on its controls. – Ed Beal Aug 24 '20 at 20:20
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    Reasonable, very. Available, hit and miss. Don’t use an alien breaker though. – Harper - Reinstate Monica Aug 24 '20 at 20:47
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    Although they in theory should be great we have had a few call backs because of nuisance tripping what panel do you have ? – Ed Beal Aug 24 '20 at 21:11
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    I have a new QO panel (recently installed to replace Federal Pacific). I don't believe 2-pole dual-function is available for either Siemens or Square D. – Haozhun Aug 24 '20 at 21:46
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    @NateS. are you sure about Siemens having two-pole DFCIs? I don't see them in the current Siemens catalog (last update date 3/31/2020) – ThreePhaseEel Aug 24 '20 at 23:00
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Generally speaking, unless you are making changes, you don't need to add AFCI or GFCI to existing circuits. That being said, GFCI is of potentially major benefit in the kitchen. As you have found, you generally won't find AFCI + GFCI in a double-pole breaker, and you also won't find a GFCI/dual-receptacle that supports MWBC.

Assuming you don't need AFCI, my recommendation is to add the GFCI at the panel - a double-pole GFCI breaker. That gives you the really important human-safety part.

The flip side is, you may not need the same GFCI protection for your dishwasher, particularly if it can be hard-wired. Actually, you may not need it for the disposal if hard-wired, but my gut feeling is that the disposal is (because you touch the sink and the switch when the disposal is in use) is far more of a real-world ground fault concern than the dishwasher. In which case the other realistic alternative if you really want AFCI is:

  • Double-pole AFCI breaker
  • Change the dishwasher from cord & plug to hard-wired (which is usually a standard installation option)
  • Install a GFCI/receptacle for the disposal.

If you do this, you will connect split the neutral before the GFCI. Assuming black/red/white:

  • Black hardwired to dishwasher hot
  • Red to GFCI Line/Hot
  • White pigtailed to dishwasher neutral and to GFCI Line/Neutral
  • Nothing connected to GFCI Load
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  • Thanks. I have a question: as I understand it, putting the garbage disposal behind GFCI outlet won't protect me from being electrocuted by the garbage disposal switch. My switch controls the power to the garbage disposal receptacle. Is that correct? – Haozhun Aug 24 '20 at 20:36
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    Forgot about the switch. Yes, that does complicate things a little bit - GFCI breaker would be better for that reason. Or you can go with an air switch. – manassehkatz-Moving 2 Codidact Aug 24 '20 at 20:47
  • I would agree with the GFCI breaker recommendation garbage disposals are hard on them but it seams the breakers last longer. I don’t know if it’s the distance helps to dampen the motor spikes but that was my guess. – Ed Beal Aug 24 '20 at 21:15
  • Dishwasher outlets need GFCI by the NEC regardless of whether the dishwasher is cord-and-plug connected or hardwired. – ThreePhaseEel Aug 24 '20 at 22:58
  • Aha. Just looked it up 1996 for countertop receptacles. 2014 Dishwasher & Disposal and AFCI. – manassehkatz-Moving 2 Codidact Aug 24 '20 at 23:35

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