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I've just installed an RO water filter under the kitchen sink and I need an electrical circuit for it. I was planning to share the existing GFI outlet with the garbage disposer, but I now realize that outlet is (obviously) switched. Inside that wall box are 2 hot lines — one switched and one always on (plus neutral and ground). I don’t have a photo handy but coming into the box is a single piece of 14/3 romex with black, white, red, ground. The black is capped off, unused. So if I could find a single gang double GFI that would be perfect. Does such a thing exist, where the top and bottom outlets are not connected to each other?

Maybe I could expand the wall box and make it a double-gang, then install 2 GFI outlets, but it would be very awkward trying to work under the sink.

I could replace the circuit breaker in the panel with a GFI breaker, and then use a regular duplex outlet with tabs broken off. But I'm not sure if that's allowed by code. And my breaker panel is a very old Square D, so Homeline breakers don't fit. I'm not sure what this style is called or if GFI breakers are even available.

Any other solutions? I'm in California if that matters.

Here's a photo of the breaker panel. The metal tab is wider than that of a Homeline.

enter image description here

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  • To my knowledge, there are no double-GFCI receptacles on the market.
    – DoxyLover
    Commented Dec 22, 2022 at 6:57
  • My RO doesn't use electricity. What does the electricity do for you?
    – mkeith
    Commented Dec 22, 2022 at 7:41
  • Can you provide a picture showing all the wires/cables in the GFCI box? In particular, could be one cable black/white + another black/white (power in + switch loop), or could be one black/white/red (coming from the switch), or could be one black/white + another black/white/red (power in + modern switch loop). Show how all the wires are connected currently to each other and/or to the GFCI. Without these details, it will be nearly impossible. With the details, it may be trivial. Commented Dec 22, 2022 at 16:26
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    @mkeith The electric water pump eliminates the need for a large pressure tank, saving space, and also reduces the amount of waste water.
    – Elliott B
    Commented Dec 22, 2022 at 17:23
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    Check for labeling on your electrical panel to be sure, but that looks like Square D QO breakers would fit. QO breakers are widely available and are upmarket from their Homeline stuff.
    – Chris O
    Commented Dec 22, 2022 at 17:32

6 Answers 6

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Just to point out the alternative: Replace the circuit breaker feeding that outlet with one that provides GFCI protection. That avoids having to muck about in the space under the sink. (I should look into doing this myself.)

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  • I had to do this very thing for an RO Filter kit (mine came with a booster pump because I'm on well water). . . The Outlet needed to be split to support both the Garbage Disposal and the RO Filter. Since the Disposal is switched, I've opted to keep the Disposal's outlet half only controlled by this switch, while the other half of the switch is powered/supplied by the GFCI's load line.
    – k1dfr0std
    Commented Sep 19, 2023 at 5:29
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Your panel is not too old, it's QO

You seem to be under the impression that Square-D's only current product line is their (aptly named) HomeLine of 1" breakers and matching panels. This is a very false assumption on your part -- your panel is a Square-D QO, which is still made today, widely considered one of the finest panels ever made, and just at home in an office, store, or even on a factory floor as it is in your house. In fact, current production QO breakers (with the obvious exception of PoN AF/GF/DF breakers) are backwards compatible to the very early days of the QO lineage.

You should have no trouble finding a QO115DF (since it'll need to be an AFCI in addition to a GFCI due to kitchen outlets requiring AFCI protection in this day and age) at any electrical supply house that stocks Square-D, as well as through industrial MRO suppliers (Grainger and the likes). Home Depot does carry them at some locations as well, and it's also worth trying your local hardware stores (Ace/TrueValue/...) if nothing else works.

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Inside that wall box are 2 hot lines — one switched and one always on (plus neutral and ground).

It sounds like you have an incoming line and a switched line. Here's how I would play this.

  1. Buy a double-gang old work box and a GFCI
  2. After shutting the power off, remove the existing receptacle and box. Your box is likely nailed and can be removed by marking and cutting the wall for your double gang box (identify which side has the stud first!). Once the hole is wider, use a pry bar to get the old box off the wall
  3. Feed your wires into the new box and attach to the wall
  4. Connect your GFCI on the LINE side to your incoming hot.
  5. Cut a short wire to connect the neutral on the LOAD side to your your switched outlet
  6. Hook one side of your switched wire to the LOAD hot of your GFCI. Connect the other side to the hot side of your switched outlet

This gives you GFCI protection for the whole setup.

So if I could find a single gang double GFI that would be perfect. Does such a thing exist, where the top and bottom outlets are not connected to each other?

They don't really make GFCI outlets like that. Unlike a normal outlet (where you can break a tab), GFCIs are designed to protect downstream outlets (hence the LINE and LOAD sides). They also protect the outlets on the device itself. You'd essentially need two GFCIs (since the second receptacle could potentially be on a second circuit) built into one form factor, which means two circuit monitors and two sets of test and reset buttons. That's probably too impractical (and expensive) to build.

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As I understand it, disposals do not currently require GFCI. However, receptacles in a kitchen within 6 feet of sink, which I believe includes under a sink, do require GFCI.

As I understand the original question and comments, you have a single cable going to the switch and then to the receptacle with:

  • Black = Hot (currently unused)
  • Red = Switched Hot
  • White = Neutral
  • Ground

I'll ignore ground - everything should have it, all grounds need to be connected together, etc.

I see two plausible alternatives:

Hardwire disposal

My disposals are hardwired. Unless the disposal requires plug/cord installation (the ones I've dealt with do not, but I don't know what make/model you have) or local code requires plug/cord installation, this is definitely my recommendation.

  • Remove the cord/plug from the disposal. The end should be in a small junction box that is an integral part of the disposal.
  • Use a short piece of 14/2 NM cable to go from the disposal junction box to the wall box.
  • Assuming the existing wall box is flush rather than surface mount, you may have to drill a hole in the back of the cabinet to get the cable through so that it can properly go into box. If it is a plastic box there should be integral clamps. If it is a metal box you'll knock out a knockout cover and put in a clamp.

In the box:

  • Connect disposal black to switch cable red.
  • Connect disposal white to switch cable white and add a white pigtail which goes to the receptacle line neutral.
  • Connect switch cable black to receptacle line hot. (The same place that had the red.)

The switch will turn the disposal on/off, the receptacle will be on all the time, but the disposal will not be GFCI protected.

Plug-in Disposal

If you can easily remove the existing box and replace it with a two-gang box, great. But that probably isn't so easy to do, in which case add another single-gang box near the existing one. Alternatively, you could use a surface-mount metal box, which will be ugly (not inherently, but having a mix will look strange, *but it is under the sink, so who cares!).

Unless you go with a two-gang box (in which case there is more work to remove and replace the existing receptacle, but you can use simple wires (remove the outside of 14/3 cable if you want - that's legitimate for inside the box use) to connect the receptacles), you will need to run a short cable between the old box and the new box - pretty much the same as if you were going to hardwire the disposal, but a much shorter distance.

  • Install a GFCI/receptacle in the new box (or 2nd half of replacement box). It doesn't have to be the same brand as the original.
  • Leave the red wire as is.
  • Connect the black wire to line hot on the new GFCI/receptacle.
  • Remove the white wire from the original receptacle. Add two white pigtails and attach one to each receptacle's line neutral.

The original receptacle will continue to be for the disposal. The new receptacle will be on all the time. The disposal will still be GFCI protected.

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  • NEC 210.8 specifies distance not piercing a barrier. So I guess this was allowed in 2014 and 2017... here is some more discussion electricallicenserenewal.com/… Commented Dec 22, 2022 at 23:17
  • @RobertChapin In a quick search, it isn't 100% clear to me. Definitely if it was above the sink it would need GFCI. Under? Not so clear. Commented Dec 22, 2022 at 23:21
  • It’s a flush mount box, so for the hard wire option, how would you pass the romex through the drywall?
    – Elliott B
    Commented Dec 23, 2022 at 16:14
  • I would cut a small hole. If it is just drywall, that's trivial. If it is an actual wood (or MDF or whatever) cabinet back then it is a little harder, but not a big deal. No clamp needed - that is specifically when entering a box so that you can't pull on the cable and mess up the connections inside the box. Should be secured to the drywall - staples or similar will do the job. Commented Dec 23, 2022 at 16:36
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Maybe I could expand the wall box and make it a double-gang, then install 2 GFI outlets, but it would be very awkward trying to work under the sink.

This is one way to do it, yes. But remember, there is no requirement for GFIs under the sink nor for disposers in NEC 2017. This definitely changed with NEC 2023 where the GFCI requirement applies to all receptacles in "Kitchens".

It would be much easier to remove the GFI and use a single gang receptacle if you are not subject to the new rules of NEC 2023. Just make sure the disposer and RO pump are rated less than the existing circuit rating.

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  • Wow, really?! That’s definitely the easiest option. I never would have guessed GFI is not required here, where you could have potential water leaks right next to it.
    – Elliott B
    Commented Dec 22, 2022 at 17:22
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It might be worthwhile reconsidering expanding the existing box, using a surface mounted extension box like a Raco 187: enter image description here and 809C cover. enter image description here

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