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When a GFCI breaker pops, is there a way to tell whether it popped for the GFCI reason or because of excessive current?

  • Are you looking for advice on a specific model of breaker? Does this circuit have plug-in loads that could potentially be unplugged? – Harper - Reinstate Monica Feb 11 at 20:48
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If the GFCI breaker pops because of a ground fault it pops softly without a loud sound. When it pops due to an overload you can hear a sharp sound inside the breaker comming from the spark during the opening of the breaker contact

  • In my situation, the breaker is in the basement so there's no way to hear it when it pops. I'm wondering how one would determine the cause by inspecting the state. – Wynne Feb 10 at 20:35
  • Does the breaker pop directly if you put it back into operation? If so then you can hear the difference in sound. If not it might be a ground failure. There are clamp on differential amp meters to determine if there is a ground fault – Decapod Feb 10 at 20:37
  • No, stays on until a day later, it's popped again. – Wynne Feb 10 at 20:40
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If the circuit is under normal load - not over the limit, e.g. at 60% of the rate when the ground fault occurs, the sound of the breaker will not be very different from an overload - in case of no shortcut. Especially if inductive devices like big motors or transformers are interrupted.

There is a small chance to distinguish a GF (if the normal load is zero or low, say < 30% of the rate) from a current overload by measuring the wiring/panel connections/breakers with an infrared thermometer.

The breakers do only trip if the overload current (f.e. 2 times the rated current) is flowing for some seconds/minutes, during that time the wiring is heated up above the normal temperature. In case of a shortcut (f.e. 60 times the rated current), the breaker should trip within miliseconds. In that case it might be possible that the wires/connectors could have not enough time to heat up in order to distinguish the shortcut from a ground fault by measuring the temperature.

  • I think a warm breaker is the only evidence you can hope for, but that only shows the breaker was loaded pretty decently before it tripped. If there was a high-current device plugged in, and it happened to have a ground fault, this might be misleading. And as you mentioned, a short circuit won't heat the breaker at all just like a ground fault. – JPhi1618 Feb 10 at 21:23
  • @JPhi1618 Yes, with a high current consumer switched on during the tripping (e.g. >60% of the rate), the distinction could be very difficult. But in the case of low current, the wires do heat up significantly if an overload current should suddenly occur. The temperature of the wires could be 15 or more degree Celsius above normal temperature in case of a 200% current load for some minutes. – xeeka Feb 10 at 21:41
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    Right, but 200% isn't a short circuit, that's a standard overload. With a short circuit, the current spikes and a magnetic trip mechanism trips the breaker in milliseconds with no heat. Heat will be associated with overload. – JPhi1618 Feb 10 at 22:00
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I can say that for a Square D QO or Homeline GFI breaker, there's no visible difference. The trip indicator shows orange, and the handle moves to the middle regardless of the trip reason. This is the behavior of the GFI breakers that I have used, but it might be worth looking up an instruction manual for your exact brand to see if there is a hint to the trip reason.

Also, you can observe the breaker in its tripped state, then reset it, then use the TEST button to purposely create a GFI trip and see if there is any difference in appearance. This may or may not tell you anything, but its free and easy.

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Check on the breaker: RCD usually have an indicator telling if has been triggered the RCD or the MCB part.
ABB has a blue piece of plastic that remains invisible if MCB trigger and pops out if RCD triggered, BTicino has a little window changing color if MCP have opened the circuit.

These checks has to be done with the device still off after the fault (never re-armed).

Others have a blue or white lever that is for the RCD and a black lever for MCB, if both are down RCD tripped, if only the black one is down MCB has tripped.

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Breakers vary. Read their instructions/labeling

Every brand of breaker provides a way to distinguish between these. For some manufacturers, the method can be a little byzantine coughSquareDcough. Others have LED lights that plainly indicate; some even have flags. But if you read the instructions and labeling for that model of breaker, it will describe how.

If you don't like yours, check the latest breakers UL-Listed for your panel, and see if they've improved. Or you can look at breakers UL-Classified for your panel such as Eaton CL or CHQ.

Plug the appliance into a different circuit

Specifically one that has a plain breaker and a GFCI receptacle. Then it will be obvious whether the GFCI recep has tripped or the breaker.

Change the breaker to a plain breaker (temporarily)

If you are dealing with a hardwired situation, e.g. modifying wiring, and you just can't tease the trip type out of the breaker, then change the breaker to a plain one. Now, obviously, it won't be a GFCI breaker. Unfortunately this requires you to also move the neutral back to the neutral bar.

Change the breaker to plain (permanently) and fit a GFCI recep

In this case, you fit a plain breaker, and fit a GFCI receptacle at the first outlet location, protecting the rest of the run with the LOAD terminals on that GFCI. You could also fit a GFCI deadfront anywhere along the cable; my favorite place for a deadfront in utility space is right next to the service panel. I mount a 4-11/16" square box there with a 2-gang mud ring, and a conduit nipple into the panel, then fit up to 2 deadfronts in that large box.

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    I couldn't find how to tell on a Square D - if you know I would be interested to learn (looked at a few manuals and never found it). – JPhi1618 Feb 11 at 3:24
  • @JPhi1618 the instructions inside the breaker box are the final word, but I believe you turn the breaker off, hold down TEST, and turn the breaker on. It will trip; "0-2 sec." vs "5 sec." tells you which one tripped. But don't quote me, consult your breaker's labeling/instructions that came inside the box which is part of its UL listing. Sales literature does not help as UL doesn't approve that. You may need to call Square D. – Harper - Reinstate Monica Feb 11 at 13:15
  • @Harper-ReinstateMonica -- that's only true for SqD AFCI/DFCI breakers, their GFCIs don't have that feature (and likely never will) – ThreePhaseEel Feb 11 at 23:42

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