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I searched for similar but didn't find anything after a quick search. I have an existing GFCI with 12 gauge wire coming off 20 amp breaker. I want to add another gfci for an outdoor kitchen. Can I simply add a wire to the other side of the existing screws on existing gfci outlet and connect in the same manner on the new one? My experience level is novice so I apologize in advance! 🙂

The line coming in to the line screw is a 14 and the rest are 12.

existing gfci that I want to add another gfci to

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  • Not suppose to have 14 gauge on a 20 amp breaker. Should replace the 14 with 12 gauge or drop the breaker to 15 amp one. Neutral/white maybe okay, but don't think so. One of the experts soon should be around to check.
    – crip659
    Dec 4, 2021 at 20:31
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    No pass on Neutral. 20A = all 12 (or bigger - 10, 8, etc) ANY 14Ga = 15A breaker maximum. It's conduit, so it should be easy to pull the correct wires.
    – Ecnerwal
    Dec 4, 2021 at 21:42

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First, this wiring is THHN wires in conduit. I might guess that it's metal conduit.

The ground wire is improperly attached. The ground wire coming into the box MUST be attached to the grounding lug on the box itself. Connecting it to the receptacle only is illegal (yes I'm aware that's standard practice with plastic boxes).

Buy a foot or two of solid green #12 THHN wire "by the foot" - most better stores sell it that way for ~20 cents/foot. That way you can make any pigtails you want. Do not cut any wires from the wall shorter than 6 inches.

Once the box is grounded, the receptacle will pick up ground automatically, because of those funny wipers on the mounting screw holes. However, if you willingly choose to ALSO run a ground from box to receptacle, that is perfectly fine - it's just "belt and suspenders". (unnecessary but does no harm, and might help in rare conditions.)


Now, if you don't know anything about GFCI, don't want to know anything about GFCI, and just want to attach another outdoor GFCI receptacle to this circuit, attach the extension hot and neutral to the "Line" terminals, which happen to be black and white here. Note that each of the screws on this existing GFCI will accept 2 wires under each screw - read the instructions for how.

If you want to save yourself a bit of money, every GFCI device is able to protect downline outlets also. That's what the "Load" terminals do, and as you see there's already a black-red pair on your "Load" terminals. Wherever that goes, that is protected by this GFCI. A load there can trip this GFCI. So if you want to, you can use a plain receptacle at your new outlet, and attach its hot-neutral wires to this GFCI's "Load" terminals. That will cause this GFCI to protect that plain outlet, which must be labeled "GFCI Protected" in some durable way not handwritten. (I like P-touch or Brother label makers. I also like to put the location of the GFCI reset).

Never put a GFCI on "Load" terminals of another GFCI. It is a waste of GFCIs, and will create annoyances, confusion and possible wasted money on electrician service calls.


What to do about the additional ground wire from the circuit extension? It MUST be attached to this metal box, along with the incoming ground wire that must also be attached there. If there are several ground screws on the box feel free to use them all. Otherwise install a ground pigtail on the metal box, and then tie all the ground wires to the pigtail.

If you are tempted to do the extension with "Romex cable" like you've seen in all the Youtube videos, I would point out that the wiring around here is NOT Romex - it is conduit for some reason. That reason is most likely a city requirement for conduit construction. Check with your city, and if conduit is required, then do your extension in conduit. It's different from the Youtube videos but it's really not that hard.

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