I'll start by acknowledging that I know this violates NEC. As I understand it, the reason that a 20 amp outlet can't be connected to a 15 amp circuit is that someone could potentially connect a 20 amp device, overload the circuit, and cause a fire. That makes sense.

Now, here's the question. Suppose all you have on hand is a 20 amp GFCI and you need to replace an outlet on a 15 amp circuit. (You will get a correct 15 amp outlet eventually, but you don't have it right now.) This circuit is on your own, private property - no one else will use it but you. You also don't own any 20 amp devices, so there is zero chance of one being connected to the circuit. (For sake of discussion, exclude situations like forgetting you did this, contractors using the circuit, sale of the property to an unaware party, etc. I acknowledge those are more good reasons for the NEC rule.)

Does connecting the 20 amp GFCI to the 15 amp circuit pose a danger just by its existence? That is, will it pose some risk just by being connected to the circuit, even if unused, or only used for 15 amp devices? Or, is it only potentially dangerous, because someone could connect something to it that they shouldn't?

  • You're chasing a fantasy, as detailed in the answers you've already gotten. And I can safely say that as a person who runs basically all outlet circuits at 20A, the only items I've ever used with a 20A plug on them were ones that I myself had put that plug on. So I rarely bother with 20A receptacles OTHER than the 20A GFCI's on those circuits.
    – Ecnerwal
    Oct 21, 2020 at 21:16
  • 1
    STOP. Does the GFCI device actually have an obvious T-shaped neutral pin? Or do you think it's 20A only because its labeling and documentation says something about that? Oct 22, 2020 at 0:39

2 Answers 2


First off, connecting a 20 Amp load to a 15 Amp circuit will overload the circuit but shouldn't cause a fire because the 15 Amp breaker will trip.

A 20 amp GFCI doesn't pose any threat just by being there. The threat comes from people thinking it's on a 20 amp circuit and loading it as such.... which will trip a 15 Amp breaker.

  • 1
    As I understood it, you shouldn't count on a breaker. 20 amps may trip a 15 amp breaker, but it could take a long time, whereas 200 amps would trip it very quickly. Oct 21, 2020 at 20:34
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    @SouthShoreAK We've got 328 million people depending on breakers, and fuses, to do their job so I think it's safe to count on them. Plus, #14 awg is actually good for 20 Amps.... but you're only allowed to protect it for 15 Amps. Plus, 20 Amps would trip a 15 Amp breaker fairly fast if a constant load.
    – JACK
    Oct 21, 2020 at 21:02
  • You said it yourself: if you don't plug a 20A device into it because you don't own one, there is no potential danger. The ONLY possible hazard is in "someone" plugging in a device that actually draws more than 15A continuously. And most likely, the breaker will trip and prevent a fire. I bought a bunch of 20A duplex receptacles at a garage sale years ago for 10 cents each, I used them in making up my own extension cords. The plug end of the cord is 15A, so I can't plug it into a 20A circuit anyway, but in theory I could plug in a 20A device to the box. I just know not to...
    – JRaef
    Oct 21, 2020 at 21:47

Let's look at it a slightly different way:

  • Which is more dangerous, a 20 Amp GFCI on a 15 Amp circuit, or a 15 Amp non-GFCI on a 15 Amp circuit that should have GFCI, such as a kitchen or bathroom receptacle?

I would argue that given those two choices, the risk of using the 20 Amp GFCI (an edge case of 20 Amp device overloading 14 AWG wire and causing a problem before the 15 Amp breaker trips) is very, very low. But the risk of using the 15 Amp (i.e., matched exactly) non-GFCI in a place where water hazards exist that can be made safe by using GFCI is huge.

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