The GFI trips under any load (although I haven't tried a very low load like a 10 watt lamp). I tried the heat gun and a rotary tool and it tripped under each load. It does not trip without a load.
I am plugging the load into a new receptacle installed at the end of the circuit (at the pump location in a shed). I read 118 volts across the receptacle and also from the hot lead to ground. I read no voltage from the receptacle neutral to ground. The circuit worked fine before water got into the conduit but I changed the receptacle in order to raise it off the pump shed floor. The source of water was not in the pump shed, it was rain infiltration in the pull box near the house. The only other access I have to the wires is an intermediate pull box about half way from the house to the pump shed. I read the same voltages there.
I'll try it. If there is a fault in the circuit, will it eventually dry out or will I need to pull new wire?
Hard to remember, it was 20 years ago. Up to the first pull box where the water infiltrated it appears to be regular 3 conductor #12 wire (it has a white outer sheath). From that connection I pulled individual #12 wires because of the long run (it was easier to pull individual wires). None of it is gray covered outdoor cable.
I'm 99% certain it's THHW or THW. The fact that it worked fine for 20 years until the rain infiltration is somewhat revealing. If it's THHW or THW should I give it more drying time before biting the bullet and pulling all new wire?
I will try the test. What I don't understand is why it only trips under load. If there is a fault in the circuit, wouldn't it trip without a load?
How do I get ahold of you after I try the test? It might be tomorrow.
Ok - I'll let you know. Thanks for your help.