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When I plug a high powered (1200W) device into my new GFCI outlet the GF circuit pops after 3 or 4 minutes. It does not pop if I plug the same device into a downstream outlet fed by the load terminals. It does not pop with smaller devices. This happens with a hair dryer and with a space heater.

Any ideas on how to diagnose this?

Some additional detail:

At first I blamed the hair dryer. I thought it might be faulty, or wet or something related to the additional GF breaker in its plug. But the problem also occurs with a space heater that has a plastic chassis, a two-pin plug without its own GFI, sitting on a ceramic tile floor with nobody touching it. It's hard to imagine how a current imbalance would occur with that one. The very strange thing is that it only occurs when the device is plugged directly into the GFCI outlet, not the downstream load ones, and it occurs reliably after a few minutes. Almost as if it's "heating up" although it's not hot to the touch. It resets and pops again quickly unless I let it rest a while.

It's brand new, an Eaton SGF20 on a 20A circuit. The hair dryer is 9A, the heater is 12. (I'm not using the at the same time obviously.) With smaller devices plugged in (maybe 1A) it runs forever.

Adding some test results further to comments in Harper's answer

Temperature scan of outlet before use is 78.8F :

enter image description here

After 6 minutes of use with a hair dryer and about 3 seconds after the GFCI trips, socket temp is 96.3. I attempted to measure the pin temperature of the plug, it was 88-ish but harder to capture with this device and only two hands. The body of the GFCI plug and the power cord were also in the mid to high eighties.

enter image description here

Note Within margin of error of my measurements we could have a 20 degree rise, which could be a trigger for the device's "self tests". Waiting for callback from Eaton.

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    That is very strange, indeed - bad contacts on the receptacle triggering some thermal overload we don't normally see? Is it the same for both sockets of the GFCI itself? I'd say give Eaton a call, it sounds defective.
    – Ecnerwal
    Commented Dec 4, 2022 at 16:46
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    Not to blame you, but did you do proper install using correct torque on the screws
    – Traveler
    Commented Dec 4, 2022 at 18:19
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    @Ruskes I tried blaming the user of the hair dryer. Can you imagine how THAT went? :)
    – jay613
    Commented Dec 4, 2022 at 18:56
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    14 inch-pound is probably in-spec. Commented Dec 4, 2022 at 22:29
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    @Ecnerwal your initial comment (10 minutes after I asked the question) is proven correct: It was defective. An identical unit from the same box is fine after a month of regular use.
    – jay613
    Commented Jan 25, 2023 at 17:34

3 Answers 3

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I suspect the problem is thermal, at the plug.

Eaton is notorious for making products that do a bit more than their specifications say they must. For instance, Eaton's newest AFCI and GFCI breakers have the computer also monitor voltage (trip if over 140-ish volts as you get with a Lost Neutral) and over-current (allowing motors to start up, but acting sooner than the thermal trip would in the event of a stalled/stuck motor).

So I suspect your Eaton GFCI has thermal detection at the sockets. These are all the rage of late, and are in fact mandatory for plug-in EV chargers (e.g. the travel units supplied with EVs). Don't look at the temperature of the unit face, look at the temperature of the plug blades.

Or, shrug who knows? It could just be a mystery of science LOL.

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    I had a hunch it was a thermal trip at the GFCI - makes logical sense. I just didn't know that it is not a bug, it is a feature. You can even another plain receptacle right next to this one if the downstream (could be 4 feet away) receptacle is not convenient. Just pigtail with the other Load wires. Commented Dec 5, 2022 at 0:23
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    It may a little too sensitive. But to be honest, I have seen a lot of space heaters & hair dryers (worst by far is space heaters because they run for hours at a time) that seem to have cords no thicker than a lamp cord. Those cords and plugs often do heat up quite a bit - which could be avoided simply by upsizing the conductors. But except at the high end, these are commodity items and manufacturers are literally counting pennies. Put "We use 14 AWG wire in the power cord!" on the space heater box and it won't sell any more than without it. So the minimum UL/ETL requires is all you get. Commented Dec 5, 2022 at 1:24
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    I don't think it's intentionally thermal -- it could be that heat is shifting some threshold in the electronics and causing it to be excessively sensitive to a small leak as a result? Commented Dec 5, 2022 at 3:15
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    The space heater cord definitely heats up a little, exactly as Manasseh describes, but very little. Maybe 90F, guessing by touch. If the GFCI is supposed to work in a hot garage in the summer, say 120 or 130F ... that alone can't be what triggers it. Do all Eaton breakers fail in hot weather? I doubt it. There is something in a tech spec on their site about "thermal rise". I wonder if the self-check includes something like X degrees increase in Y minutes. I called Eaton, a helpful person whose job was NOT to get rid of me said he'd have a specialist call me back.
    – jay613
    Commented Dec 5, 2022 at 20:09
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    @jay613 Hot sockets are very much a thing on plug-in travel EVSEs, and people find using the cheapie $12 14-50 sockets often results in their EVSE reducing power due to hot plug. The $80 Hubbell does not do that. But I would look closest at plug pin temperature. Because if this is getting too hot to touch, then take a close look at plug condition. Commented Dec 5, 2022 at 22:02
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The actual problem in this case was a faulty GFCI device. Replacing it solved the problem, and the replacement was an identical one, in fact from the same box.

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There's nothing to "diagnose". GFCI's have always been quirky, unreliable technology. They trip for endless, mysterious reasons with no connection to their ostensible function, including using them with higher loads, and just turning stuff on and off. Try a different brand.

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  • Although frustrating, I am increasingly feeling this is the best answer.
    – jay613
    Commented Dec 5, 2022 at 23:54
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    to be fair, between a regular socket that heats up and a GFCI socket that heats up and trip, I'll take the GFCI any time. Yeah, a regular socket that doesn't heat up is better, but still.... the diagnostic part did its job
    – Jeffrey
    Commented Dec 6, 2022 at 0:04
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    @Jeffrey I would like to think that a 20-degree rise in 20 minutes with ongoing increase would trigger some "let's stop this before it gets bad" reflex in the GFCI. I'm a fan of the attitude, "No, it REALLY IS a feature, you idiot, stop regarding it as a nuisance". The thing is, I phoned Eaton and asked them this very question and they did some research and couldn't come up with a "Yes, that's it". Not done yet, I'm going to do some tests they requested.
    – jay613
    Commented Dec 8, 2022 at 17:15

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