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Outdoor GFCI with HD extension cord feeding Mosquito Magnet bug light (total load about 20W) fell to ground and was covered by water during storm. Current proceeded to travel through side of cord socket/ receptacle and melted plastic body. Eventually panel breaker tripped, but GFCI never did.

Thoughts???

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    Either it's faulty or miswired. What's the question? – isherwood Mar 2 at 16:12
  • Faulty is what I am thinking too. Flying down this weekend and will be replacing. Builder did not put ground wire to this box. Also going to add ground to GFCI. – sd105 Mar 2 at 17:11
  • @sd105 While you're there, check the house's ground connection (neutral bonded to ground in the main panel, and ground wire bonded to actual earth ground outside the house). Pick a convenient outlet and check for voltage between the outlet's neutral wire and the house's ground rod. It should be zero. Then check for continuity. They should be connected. If the ground connection isn't working, then the extension cord in the mud might not have leaked enough current to ground to cause a GFCI outlet to trip. – mrog Mar 2 at 18:52
  • "Thoughts???" leads to an open-ended discussion question which is not a good fit for this particular forum. If you'll take the tour, then browse the help center, especially the "how to ask a good question" section, I'm sure you can come up with a good, specific question that we can & will happily answer. – FreeMan Mar 3 at 12:01
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GFCIs are not magic everything-fixers

It's like asking an ambulance crew "why didn't you arrest those graffiti artists?" "That's not what we do".

GFCIs do one specific task that is related to human safety, and they do it well. They detect current leakage between the intended hot-neutral loop and anywhere else. However they do nothing about any fault that stays inside the hot-neutral loop.

Hence their name, "Ground Fault Circuit Interruptor", which is ironic since they don't interact with ground at all. It's presumed that the "anywhere else" must be ground.

Those other bailiwicks

It sounds like you had more of a "poor connection/arcing/overheat" problem. That is more in the bailiwick of an AFCI. (Arc Fault Circuit interruptor). Those work by listening to the power line for that familiar "crinkle-crunch" sound of hooking up speakers with the amplifier turned on, or a shoddy headphone jack, etc.

You note also that the GFCI did not trip and the breaker did. That's another thing GFCIs aren't. Some people think if they put a 15A GFCI on a 20A circuit, they can extend from there with 15A wire and the GFCI will protect it. The opposite is true, 15A GFCIs are specifically rated for 20A pass-through. (because of a NEC technicality).

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  • Exactly like Harper said. If you're extra stupid, you can kill yourself by doing a hot-neural electrocution on an insulated surface and the GFCI will never trip. The fuse will eventually trip but you'll be LONG dead, and you might even burn down the house. These things only protect against some faults, and pure stupidity will still kill you just fine. – Nelson Mar 4 at 4:58
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It is possible that the GFCI device did not function as designed. Impossible to say without forensic analysis (which is kind of hard for random people on the internet). But it is quite likely that it did not fail:

GFCI protects exactly one thing - an imbalance between hot and neutral (on a 120V circuit) or between the two hots & neutral (on a 240V circuit). It does nothing to limit the total flow of current, as long as all of the current going through hot also goes through neutral.

A device on an ordinary circuit is designed to use a certain amount of power (current & voltage) and is designed so that under normal circumstances the heat generated will not cause any problems. But that doesn't mean problems can't happen. For example, a rolled up extension cord can easily overheat, even when used at the design (for unrolled) specifications. A toaster run in an enclosed space can overheat and easily start a fire. A heavy load (e.g., a full 15A) run for an extended period of time on a thin extension cord (perhaps designed & rated for max. 10A) can overheat the extension cord - causing it to melt - without tripping the breaker because the current is less than the breaker rating. In many of these cases, a regular breaker will trip once things start melting because then there is a short circuit == high current flow. In some cases - e.g., a 3-wire cord where the melting happens first between the ground wire & hot or neutral instead of between hot & neutral, a GFCI will trip.

Back to the specific example:

If everything is sealed sufficiently that, despite the outside being wet, no current is able to "escape", then the GFCI will not trip. However, overheating will gradually happen because mud is an insulator, leading to melting, short circuit and a regular breaker trip.

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  • Doesn't the melted female end of the extension cord point toward stray current traveling through it and not returning to the neutral on GFCI? – sd105 Mar 2 at 16:49
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    Not necessarily. A functioning toaster will melt (burn) all kinds of things. Stick a running hair dryer inside a drawer and you can start a fire without tripping the bathroom GFCI. etc. Electricity normally produces heat. Enough heat = melting or burning. It is only when the electricity goes where it shouldn't that it trips a GFCI. If it goes to the right place but at high resistance = high heat, that is a problem, but it isn't a ground fault. – manassehkatz-Moving 2 Codidact Mar 2 at 16:54
  • In both of those examples the current going out and returning is equal unless the power makes contact with housing and someone touches and creates alternate path to ground. – sd105 Mar 2 at 17:10
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    Yeah, I've seen plenty of cases on construction sites where worn plugs or undersized extension cords were used for long periods on high-current tools and got very hot. – isherwood Mar 2 at 17:17
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    You could push the TEST button on the GFCI and see what happens. It's a darned good test, as ThreePhaseEel recently explained. Not every fault is a GFCI fault. – Harper - Reinstate Monica Mar 3 at 19:54

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