Block heater tripping the GFI

[MikeP]

One of my block heaters (immersion type) suddenly is tripping the GFI for ships service #2 at the master panel at the helm. It worked fine this morning for about 2 hours, then tripped the circuit. All subsequent resets/switching on the heater results in an immediate GFI trip The actual circuit breaker to the heater(s), which is located in a separate panel is not tripping. I disconnected the leads to the heater and cycled the switch and the GFI won't trip so obviously it's related to the block heater, not the wiring.

I would ASSUME that if there was a direct short, the circuit breaker itself would trip but this seems to be a GFI related trip so I'm ASSUMING that there may be a break in the heater element inside the water jacket that is allowing the current to leak directly into the water, thus tripping the GFI. Before I start draining coolant, moving the alternator and bracket to get to the heater, does this sound right/plausible?

I get a 6 MegOhm reading between engine ground and either terminal of the block heater. I guess I should check the other heater the same way and see what my readings are...

 

[MikeP]

Disregard - found the problem.

It was just a bit of mineral deposit that had bridged from the neutral connection on the heater to the eng block. The repair? A spritz of WD 40 and a wipe with a paper towel of the the block heater terminals/adjacent eng block. Those GFIs are sensitive!