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I currently have a 12/3 Line providing power to a paddle switch that then provides power to an outlet where the pull tab has been removed. I would like to add a GFCI switch combo to replace the regular switch and provide power to the outlet.

The outlet currently powers my dishwasher and garbage disposal. The wires I have are currently setup to have the black line power the bottom outlet for the disposal and the red wire (that bypasses the switch) to power the top outlet for constant power to the dishwasher.

Any ideas on how to properly achieve this?

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    Can you post photos of the insides of the boxes involved please? – ThreePhaseEel Nov 3 '20 at 5:17
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    To turn off dishwasher and garbage disposal, is it a single circuit breaker or 2? If a single, is it two half-breakers with a handle-tie tying the handles together? Does the 12/3 line come from the service panel or go to the switch? – Harper - Reinstate Monica Nov 3 '20 at 7:21
  • The service panel for this is a two 15A half breaker that are tied together. The 12/3 comes from the service panel directly into the “switch box”. From there, it wired as follows, Neutrals “white” tied together, Hot “black” line to top of paddle switch, load “black” line to bottom of paddle switch which then provides power via turning on the switch to bottom part of duplex out, the two Red “hot” lines are tied together and then run to the top of duplex for constant power to the dishwasher. All Ground “bare” wires are tied together. – Ricky T. Nov 3 '20 at 14:25
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Install a 2-pole GFCI breaker in the panel

This is what's called a multi-wire branch circuit or MWBC. It is 2 sub-circuits fed off separate breakers. These 2 breakers are handle-tied because that is a safety requirement for MWBCs. That is also why neutral is pigtailed.

The split receptacle is a very typical use of an MWBC to deliver 2 sub-circuits to one recep. The switching is a neat trick.

The only way you can make this setup GFCI is to install a 2-pole GFCI breaker in the panel. Individual GFCI devices will not work because there isn't space for them.

Note that your current breakers are half-width (we call 'em "double-stuff") and that means you will need to find some more space in your panel. There's no such thing as a half-width GFCI breaker.


However, if you are able to run new cable between the switch and receptacle, and are able to blow out the under-sink receptacle into a 2-gang, then you could fit a GFCI+switch device in the current switch location, and a plain recep and GFCI downstairs. use either 2 cables or /2/2 cable; mark one of the cables' wires purple and gray (gray=neutral), and the other hot wire red.

  • In the under-sink box, red+white land on a GFCI receptacle that powers the dishwasher. Purple+gray land on a plain receptacle that powers the disposal.
  • In the switch box, Red + white wire as before. Black+white go to the LINE side of the GFCI+switch.
  • Purple to one of the switch pigtails. The other switch pigtail to LOAD hot. Gray to the LOAD neutral of the GFCI+switch.

The key to it is the separate neutrals past the first GFCI. That's why you can't do it with cables as-installed except by using a 2-pole GFCI breaker.

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  • Note that the second neutral in /2/2 cables comes with a red stripe on it from the factory, so you don't have to worry about remarking it yourself :) – ThreePhaseEel Nov 5 '20 at 0:02

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