I've just finished up wiring an old heater in my sauna. It has laid around in a shed for a decade or so and am wondering if it's spent. It powered on fine and heated for about 5 minutes until the GFCI tripped. I tried to reset the GFCI and it instantly trips.
I pulled the lid from the panel below the heater and with the supply wires disconnected, tested for continuity around the element, and then from each end to ground. The element tests ok at about 15Ω which is what I'd expect (4000W element at 240V). My concern is I have found a varying resistance between the element and ground. I checked it at 3 different points in time, first it was 150KΩ and increasing, the second it was 140KΩ and decreasing, the last just now was down to 10KΩ.
Does anybody know what this is a symptom of? Could it be a case of contamination on the element conducting to ground or is there a fault? I'm sure the element leaking current onto ground and the heater chassis is a big problem and the GFCI was right to trip.