My welder has been tripping the GFI on the circuit in the garage after I have been using it a while. I finally took the cover off and discovered the electrician saved himself, what? $2 and used a 15amp GFI, even though the circuit breaker is 20A like I specified. (Why didn't the building inspector catch this? Is it to code?)

Anyway, that is not my question. I turned the circuit breaker off in prep to replace the GFI with a 20A one. Went back to the outlet, and pressed the test button, as a quick test to make sure I had disconnected the correct breaker. The GFI trips. I'm like, doggonit, I didn't flip the right breaker. I hit the reset button, and it will not reset. Weird, I did flip the right circuit breaker, the GFI receptacle is tripping even though the circuit is dead.

Well, thats crazy! If the GFI is not tripping because of an imbalance of current going through hot to neutral, but instead tripping because the button itself is mechanically tripping the reset, what is the point of having a test button? It is not really testing the GFI, it is only testing the mechanical tripping function of the test button!

Am I mis-understanding what a test button is supposed to indicate?

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    I think that's normal, especially the part about not resetting w/o power.
    – dandavis
    Commented Apr 7, 2021 at 17:45
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    Trust pros more. 15A GFCIs are internally rated for 20A (as are all 15A receps per a UL requirement), can power two loads totaling 20A, and are perfectly appropriate on 20A breakers. The only time you really need a 20A GFCI is when you have a NEMA 5-20P (sideways neutral) plug to plug in. Commented Apr 8, 2021 at 1:33
  • Yep, I understand that some GFI receptacles pass through 20A, in fact your reply confirmed in my mind that I should not replace one labelled 15A with one labelled 15A internal 20A pass-thru. I suppose by its nature, welding machines are going to trip GFI's since essentially some voltage is going to leak to the ground.
    – Netmammal
    Commented Apr 8, 2021 at 19:00
  • RE: Trust the pros. Unfortunately, I have yet to find an electrician I like (actually I like my brother-in-law,oddly enough, I have yet to find a plumber I did not like) Every electrician I have ever had do work for me has cut corners on every single little thing they can. I blame the business model, not the people Fixed price bidding when you don't know how complicated an outlet or switch is going to be to install does not reward thoroughness or care, it rewards speed. I asked for 20-amp outlets, and yet I can not plug a 20A cord in to them. 'nuff said.
    – Netmammal
    Commented Apr 8, 2021 at 19:38

2 Answers 2


Ok 2 parts, yes you are misunderstanding how a (listed) GFCI completes its test. The test is completed by the internal circuitry creating an imbalance.

The clicking noise you hear is the mechanical debounce that helps the reset function work better (not all GFCI’s use this method but many do because who would trust a micro switch smaller than a pencil eraser that you can not feel it click?

As for your welder if it is plug in with 2 parallel blades you only need a 15 amp receptacle having 2 receptacles it is legal on a 20 amp circuit (the feed through is rated for 20 amp). So it would not have been a code violation.

A 15 amp and 20 amp GFCI have the same circuitry the only difference is the shape of the receptacle itself. They both trip at ~5ma and have 20 amp feed through if supplying other receptacles.

  • Re-read my question. I do understand how GFI works, why would I use the word imbalance? Do you know for a fact that 15 and 20A receptacles use the same circuits? Can you give me a reference? It would seem that the 15A ones must be cheaper for a reason, if they are identical, then the 20A version should be cheaper (miniscule bit less plastic) The clicking noise I heard was really the GFI tripping, and not some goofy clicker. Turn the power back on, and what was getting power no longer gets power until I hit the reset.
    – Netmammal
    Commented Apr 8, 2021 at 19:14
  • Re read my answer and comments as far as 15 and 20 amp receptacles being 20 amp it is a code requirement for them to be 20 amp. The trip level is a requirement also. Not only do I play an internet electrician on this site I am a licensed professional electrician. Note you may hear clicks as one of my comments mentions, listed GFCI’s require power to reset and are shipped in the tripped state to verify proper wiring. Your knowledge base was not obvious since you did not know the ampacity of your gfci A 20 amp device will have the neutral horizontal and vertical receptacle a 15 amp will vertical
    – Ed Beal
    Commented Apr 8, 2021 at 19:30
  • I will also add that you are using the word to debounce to mean something other than what the first 20 google search items turned up take it to mean. Debouncing is usually (always?) done either in the electronics or the software, I've never heard of it being done mechanically as you suggest. As for microswitches, how does adding a second mechanical click increase the reliability of the microswitch? Instead it masks the true feel of a mushy/bad microswitch, so you really don't know when the microswitch has gone bad. I'm sure you are right, the manufacturers did it for that bad reason.
    – Netmammal
    Commented Apr 8, 2021 at 20:49
  • Debounce to eliminate switch contact bounce so it is a mechanical method to eliminate chatter in power electronics the original contact bounce prior to electronic controls. but I am sure your googlf fu is top notch. Mechanical locking of the contact also is called the same thing. And as I have mentioned the click was there an an indicator. Do you have power on the receptacle or load feed nope you just heard a click so you are misunderstanding as I said.
    – Ed Beal
    Commented Apr 8, 2021 at 21:49

No. You are correct. Pressing the test button is an electrical test which should do absolutely nothing without power. If that is happening, either the wiring is not what you expect or the GFI outlet is defective. I suggest completely unwiring the GFI outlet to determine which is the cause.

PS. It should not be necessary to remove the cover to determine if an outlet is 15A or 20A. That should be visually apparent from the slot configuration. See the image. 15A vs 20A

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    Some mfg’s have mechanical clicks so Folks would feel something and quit returning perfectly good devices. Also many devices now latch to the test position so a power fault won’t require a reset . As I explained the test button creates a click and most GFCI devices are shipped in the tripped position so they must be reset to turn on. However I do agree with the 15a vs 20 but either is code compliant on a 20 amp circuit. See table 210.21.B.3 for code reference.
    – Ed Beal
    Commented Apr 7, 2021 at 22:01
  • The outlet type is no indication of the breaker value on a circuit. Commented Apr 8, 2021 at 17:47
  • Thanks! Time for me to ditch these two GFI receptacles with this weird testing bug. I'll probably get 20A replacements with audible alerts (this is for my garage) I can only hope that this fault was being caused by more than 15A being pulled and not purely because of current leaking to ground. It does seem suspicious that I'd have to weld for a while before it would trip, that makes me think it was overheating related. I wish I could get them free of tamper-free. (Whats that called? Tamperable? :-)
    – Netmammal
    Commented Apr 8, 2021 at 19:21

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