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The GFI in our bathroom was tripping somewhat frequently when my wife used the blow dryer. Other than the vanity light there were not other things operating on this circuit. If the GFI did not trip, the plug to the hair dryer would be quite hot to the touch. To my limited knowledge, a danger sign.

After a ridiculous quote by an electrician to diagnosis the problem, I decided to watch some you tube videos. I bought a GFI tester and the outlet was hooked up correctly. However, I noticed that the circuit had a 20a breaker, but the GFI was 15a. So first step, I replaced it with a new 20a GFI. After testing all symptoms were gone. No hot hair dryer plug and no tripping.

I checked the other GFIs despite them working correctly. All were 15a GFIs but on a 20a circuit. One was the kitchen which get used very heavily. I went ahead and replaced them all, just to be safe but it left me with some questions:

  1. How bad is it to have a 15a GFI on a 20a circuit?

  2. Do you think that the problem in our bathroom was just a bad GFI? Related to the mismatch in circuit and outlet rating? Or something else?

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    What’s the gauge of the wires between the receptacle and the panel? Also, the 15A rating of the GFI receptacle doesn’t mean that there’s a “real” breaker inside. It is only tripping for ground faults, not an amount of current. Feb 22 at 16:56
  • @RibaldEddie it is the 20A wire. This house was formally a flip and it seems like they hired an electrician to do the rough work, and that seems right. The rest not so much.
    – Pete B.
    Feb 22 at 17:22
  • Define what "20A" wire means to you.
    – FreeMan
    Feb 22 at 17:29
  • There is a lot of low end stuff made overseas. Also, people often go for the cheapest, not the best. I did another remodel a number of years ago and nearly all of the outlets were $.69 cheapies many years old. They would hardly hold a plug. I replace ALL of them with high quality spec grade outlets and upgraded the GFCI outlets. One common misconception about GFCI outlets is they provide over-current protection....they don't, they only provide ground fault protection. Sounds to me like you solved the problem, the old one was worn out or defective. Feb 22 at 18:33

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My understanding is that you can have multiple 15 amp outlets on a 20 Amp circuit but not just one. GFCI's trip on a fault, not an overload so the existing GFCI was probably going bad. Hair dryers can easily use 15 amps and that would heat up the plug a bit. If the GFCI outlet was old and had been used a lot, the plug might not have been as tight as it should be but not enough to arc but would heat up more.

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  • The weird thing is, the outlet was not that old. The house was redone 6 years ago and the outlet looked very new.
    – Pete B.
    Feb 22 at 17:24
  • Outlets do go bad sometimes. Feb 22 at 17:26
  • @PeteB. Have you lived there the whole time? A previous owner could have used a 2200 watt dryer, 18.33 amps, and over time, toasted the outlet.
    – JACK
    Feb 22 at 17:32
  • Bathrooms are the worst place for GFCIs, in terms of longevity, but also the most important place to have GFCI. Both because of the water/heat/humidity/etc. I have some 20-year-old bathroom GFCIs that are doing just fine. But for one to fail in 6 years (assuming the warranty is 5 years :-) ) is not unheard of. Feb 23 at 0:52
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    @manassehkatz-Moving2Codidact Both my bathrooms have GFCI breakers protecting them, same with my outdoor outlets. I've had GFCI's fail right out of the box... Some DIYer replaced a bad one and returned the bad one to their home store for a refund. :-)
    – JACK
    Feb 23 at 13:15
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However, I noticed that the circuit had a 20a breaker, but the GFI was 15a. So first step, I replaced it with a new 20a GFI.
How bad is it to have a 15a GFI on a 20a circuit?

It's not bad at all and is totally legal. There was never a problem here; you reacted to this over nothing.

Do you think that the problem in our bathroom was just a bad GFI? Related to the mismatch in circuit and outlet rating? Or something else?

Fair chance there was nothing wrong with the old GFCI. The heating of the socket is the clue.

You fixed the problem "by accident" in the course of swapping the GFCI.

What you actually had was a bad connection on the "Line" terminals. Most likely, a screw was not torqued correctly, and the connection was loose. Loose connections cause series arcing and that creates a great deal of heat. Series arcing can also cause fires, which is why they have AFCI (Arc Fault) breakers now to catch these faults.

This is why NEC now requires torque screwdrivers to set torque wherever a torque is specified.

If that was an AFCI receptacle (e.g. an AFCI/GFCI dual-mode) then it may have been detecting this arcing. Because of the way the signal travels, an AFCI receptacle can "hear" a series arc fault in its supply wires.

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  • While swapping for 20A was unnecessary, and swapping in other locations really not needed, switching it out (whether for a 15A or 20A) definitely made sense. Even if the heating was from a bad connection and not from an internal problem, that heat would not have been good for the GFCIs electronics over an extended period of time. Feb 23 at 0:53
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    That is true @manassehkatz. That's a lot of heat if it's noticeable from the outside. Feb 23 at 3:25

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