Originally Posted by Vermilye
A fault between the neutral & ground will trip a modern GFCI. If this fault is present in the heater element of the refrigerator or water heater, it will cause a trip even with the circuit breaker off. The only way to identify which device is causing the problem is to disconnect both the hot & neutral wires.
While there could also be a fault in the converter, failed heater elements are often the problem.
Jon: I think that is what I was trying to say. I’m figuring that flipping the breakers is making the OP falsely accuse the converter because it just happens to be the item with no on/off switch so it is applying load when the breaker is flipped unlike the others that require the additional step of turning the appliance on. Easy enough to check if other AC loads on other circuits also trip the GFI. I knew it was the HWH element when I disconnected it outside in the access panel and the GFI no longer tripped.
The refrigerator could be unplugged to test, but the converter needs to be disconnected within the power center so I would check the other items first.