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I have an outlet near a kitchen sink that, as part of a reno, would like to convert to GFCI, and tap into to power a dishwasher.

The existing box has a 12/3 line coming in, and I fished and added 12/2 for the dishwasher. The 12/3 line appears to be a dedicated circuit on a double breaker.

How would I connect the line's black and red, both hot, to the GFCI Outlet.

diagram

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    Is replacing the box with a two-gang box, or adding an extension out from it, an option? – ThreePhaseEel Mar 31 at 0:14
  • Not an option. Backsplash already installed – zigbeee Mar 31 at 1:17
  • Understood that a box change isn't an option -- as to an extension though? Also, where does the cable going to the dishwasher lead...? – ThreePhaseEel Mar 31 at 1:18
  • An extension to increase the depth will be needed, as the box is now 3/4 inch recessed behind the quartz stone. The romex for the dishwasher was fished behind the drywall and sticks out at the bottom to connect directly to the dishwasher – zigbeee Mar 31 at 1:24
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    Two key questions: 1 - Are any other receptacles controlled by this double breaker? 2 - How many, if any, breakers control other kitchen countertop receptacles? – manassehkatz-Moving 2 Codidact Mar 31 at 3:38
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There are basically two options:

New Breaker

This is the simplest option, though probably not the least expensive. And may not even be possible, depending on the breaker panel. Replace the existing 20A double breaker with a GFCI 20A double breaker. If you can do that, then the wiring is easy:

  • Blacks together
  • Red to hot on new (ordinary) duplex receptacle
  • Whites (neutral) together and with a pigtail to neutral on new receptacle

GFCI Receptacle

This gets a little tricky, and also depends on your dishwasher circuit not required to be on a GFCI circuit. According to this page of code changes this is required as of the 2014 NEC. Which according to this page of NEC adoption by state means pretty much everywhere except Kansas and Indiana. There may be specific exemptions in some areas as well. So if it is allowed:

  • Blacks together
  • Red to hot line on new GFCI duplex receptacle
  • Whites (neutral) together and with a pigtail to neutral line on new receptacle
  • Load side of new receptacle is not used at all.

The reason you can't use the load side, which would provide GFCI protection for the dishwasher, is that you can't have kitchen countertop receptacles shared with hardwired appliances (with some very limited exceptions).

If you could put in a two-gang box then there would be a compliant with newer code solution:

  • GFCI receptacle on one hot
  • GFCI dead front on the other hot, wired to the dishwasher

GFCI devices have to be accessible (so you can reset them), so you can't just bury it behind the dishwasher.

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    can't have kitchen countertop receptacles shared with hardwired appliances It's about 99% certain that both sides of the MWBC feeding an outlet near the sink (above countertop level) are the required two countertop receptacle circuits, so any way you slice this it's either going to share the dishwasher with half the countertop, or else remove one of the required countertop circuits and send it to the dishwasher. i.e it won't pass a competent inspection unless a new circuit is pulled or found to supply either the dishwasher or half the countertop outlets. – Ecnerwal Mar 31 at 2:17
  • @Ecnerwal That is a valid point. But it appears that this existing 12/3 MWBC is not being used for anything else. Which should mean there are already other circuits feeding other countertop receptacles - but that may not turn out to be the case. – manassehkatz-Moving 2 Codidact Mar 31 at 2:47
  • It appears to me that the MWBC was feeding both halves of the existing outlet separately, as is very common for countertop MWBC receptacles. That's "being used." I see no evidence that it's not also feeding other countertop receptacles - the 99% odds that it is doing exactly that are because that's the very common way to do that (pre-GFCI or with GFCI 240 breaker rather than GFCI receptacles.) More circuits would be good, but code minimum is mostly what you see, if that. – Ecnerwal Mar 31 at 3:22
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    There is a 2nd coutertop receptacle also 12/3 wire, but is controlled by a separate double breaker. – zigbeee Mar 31 at 12:00

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