I have a 1-pole Square D "QO" type 1-pole, 20A GFCI breaker (not AFCI). Plugged into it are:

  • Twenty-five CFL lights averaging ~15W each, so 375W nominal
  • A 1500W-nominal heater-fan, though, I suspect with the 100' of #14 extension cord, probably running a bit shy of 1500W

If the heater is on, and I plug in the lights, I get a breaker trip. Often I get a breaker trip just with the lights. I have tried splitting up and powering only sections of lights, with varying and inconclusive results.

It's not unheard of for CFLs to have a pretty serious inrush current, but I am mystified.

I really need to know whether this is a GFCI trip, or an overcurrent trip. The QO breaker has no lights whatsoever. Can I get the breaker to tell me somehow? Or should I dump this and go with GFCI receptacles?

  • Have you tried timing the trip yet? (i.e. from energization/reset to trip with a known faulty load placed on the breaker) Jan 1, 2020 at 19:18
  • Have you measured the inrush current?
    – Solar Mike
    Jan 1, 2020 at 19:19
  • 1
    I would use an amp clamp to see what the inrush is , my least expensive clamp has a inrush or peak hold so I can see what the max is on a 20 amp it should not trip under ~32a in under a second. I have not had issues in the past with cfl’s (harmonics causing this issue) but I have with larger ballasted fixtures.
    – Ed Beal
    Jan 1, 2020 at 20:47
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    @ThreePhaseEel The trip is instant. It first started doing it when I unscrewed a 30W CFL (really big one) with the power on. The moment the bulb broke contact, the breaker tripped, and continued tripping ever since, even after I removed the light fixture and capped off wires. It's a mystery! Jan 2, 2020 at 8:53
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    @ThreePhaseEel Not at this location, unfortunately. In this question I'm hoping to get the QO breaker to tell me what kind of trip it is; noting that the dual-function AFCI+GFCI+breakers have a "secret handshake" way of divining this info. Jan 2, 2020 at 18:07

2 Answers 2


Older Square D breakers

Square D does not provide any means to distinguish type/reason of trip.

Newer Square D breakers (date code 1130 and newer)

These breakers (at this writing) have white or purple TEST buttons.

The "Time Saver" (heh) diagnostics provide a method for the breaker to tell you the cause of the last trip.

Link.... link.

Generally the procedure is to turn the breaker off, hold down TEST, turn the breaker back on continuing to hold down TEST, and time the number of seconds until the breaker trips again. The amount of delay (if any) reveals the trip cause - ground fault, arc fault, or overcurrent.

Note that Square D arc fault breakers have weak ground fault detection (for the purpose of detecting hot-ground and neutral-ground parallel arc faults) — so they can in fact trip on a ground fault indication.


To answer your direct question, no, there is no way to differentiate the reason for the trip on a basic GFCI circuit breaker (regardless of the make). There is one trip mechanism and indicator, the only thing added to a GFCI breaker is an additional sensor system operating that trip mechanism.

  • 2
    That is not true for some makes; they have LEDs to indicate trip function. . I am looking for an answer for QO. Jan 3, 2020 at 3:12

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