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I have two circuits in my garage. One is a 15amp circuit that powers the garage door and has two outlets, the other is a dedicated 20amp fridge outlet. Both have GFCIs. I'm trying to run a kiln in the garage and it keeps tripping the GFCI. What's weird is that it keeps doing different things.

For context, the machine needs to be run for 14+ hours straight overnight when in use. I was able to achieve this cycle once, but the next time I tried it tripped the GFCI sometime in the night. After then, the kiln would trip the GFCI almost instantly when the kiln's heating element was turned on. The kiln seemed to be fine when turned on but not actively heating.

A couple days later I tried it again, and after 2 hours or so of heating, the GFCI had not tripped. Thinking the issue had somehow resolved itself, I did another night cycle only to find it had tripped sometime during the night. I am almost certain the furnace does not trip on normal circuits.

Relocating the kiln is out of the question. Obviously I can't have a kiln inside my home and the outside outlets all have GFCI as well.

I really wish to get this kiln working again soon so I've been debating bypassing or installing a regular outlet, although doing so does scare me a little bit. I'm just not sure what the issue can be here.

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    Have you tried switching to a different brand of GFCI (assuming this is GFCI/receptacle, not GFCI/breaker)? It is, of course, quite possible that there is an actual real ground fault in the kiln that only manifests itself when things heat up enough - e.g., perhaps some piece of grounded metal expands enough to eventually contact a (electrically) hot wire/component, causing a ground fault. Commented Mar 28, 2023 at 2:15
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    I would contact the "manufacturer". They're a jewelry supplies retailer in Kingston NY with a real honest-to-gosh showroom and a large warehouse, but still, most likely they private-label these from the far east. Regardless, they'll be far more responsible than some random Amazon seller that hides behind the Red Curtain, and who knows, maybe they make 'em right there on the Hudson and can send you out a heating element. Commented Mar 28, 2023 at 3:13
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    The most likely explanation is that your kiln has developed a Ground Fault, which is why the Ground Fault Circuit Interrupter is Interrupting the Circuit. If it's not that, next most likely is a faulty GFCI. Or (possible but unlikely) maybe the kiln isn't supposed to be on a GFCI circuit to begin with - did it come with an installation guide that you discarded? Commented Mar 28, 2023 at 7:56
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    BTW, you bought on Amazon, so there's no guarantee that you actually got something from PMC Supplies LLC. Commented Mar 28, 2023 at 7:56
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    Did the OP ever state which GFCI circuit it pops—the 15A or the 20A?
    – Huesmann
    Commented Mar 28, 2023 at 13:07

2 Answers 2

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  1. You have an actual ground fault. Think this first when a GFCI trips, it's usually the answer. Because kilns operate over a very wide temperature range, there's considerable potential for things to move so you can quite easily have an intermittent ground fault due to heat causing things to touch. If properly designed, built and maintained that should not happen, but it can happen. Usually that means maintenance is required. Also, a kiln kept in a damp area may have issues due to moisture in the firebrick insulation.
  2. One of the various issues with GFCIs mentioned in comments - particular ones tripping on heavy loads, or due to old age, or some other cause that's not an actual ground fault. If you try new/different GFCIs and the problem persists, see item 1.
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  • Yeah, ground faults on appliances like these are surprisingly common. But also, the heating elements aren't necessarily expensive. Commented Mar 28, 2023 at 20:05
  • This house is quite new and multiple gfci circuits were being tripped so I guess its probably #1. I've completely disassembled the electronics "box" of the kiln and didn't find anything awry, I contacted support and they asked me to take pictures of the inside of the kiln where the coils are and they didn't see anything off, so I just don't know what could be going wrong and lack the electrical knowledge to actually check. Commented Mar 29, 2023 at 21:44
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Resistance of the heating coils or elements in a kiln changes with the temperature of the kiln (and also as the elements age). If the kiln is fine when it's cold and shutting off when it's hot, that might help explain what's going on. Or if you've moved the kiln recently, it may also be a loose connection within the kiln that only shows up when it's hot. You could try running it up to temperature, empty, while you can watch it, to test for this.

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