It’s not the immersion element…

[doraymefa]

On launching I refilled the water tanks, pressurised the water system and plugged into shore power. All seemed fine until I closed the switches on the circuit board before leaving for the day.
When switching off the hot water, the on board circuit breaker tripped as did the pontoon circuit breaker.
I have since changed the immersion element for new and changed the shore power cable for new. I established that there was nothing wrong with the old immersion element which is now a spare.
This weekend I plugged into a different marina shore power and everything worked perfectly in that circuit until I turned the hot water off. Again the on board circuit breaker tripped as did the pontoon circuit breaker.
As a test I re-set the breakers, switched the hot water back on and all worked fine. This time I simply unplugged the shore power and nothing tripped. I switched off at the panel, reconnected shore power and turned on the hot water without an issue.
What should I do now to work out what is causing the circuit breakers to trip? Thanks.

 

[Stemar]

Is it the RCD that's tripping, or the X amp circuit breaker? If the first, it's probably a small current finding its way to earth (faulty switch?), if the latter, it's a short somewhere, but again, something that only happens as the switch moves.

I think my first thing would be to check the wiring behind the panel for anything that shouldn't be touching the back of the switch, and swap out the switch.

 

[ProDave]

It it's the RCD that is tripping it means there is some small neutral to earth leakage somewhere, not enough on it's own to trip an RCD.

Than what happens is turning off a double pole switch, sometimes the neutral contact can open first, and then the leakage becomes live to earth (via some appliance load) and is verymuch greater tripping the RCD.

Seen it many times (in houses) and only solved with proper testing with an insulation resistance meter.

 

[doraymefa]

It is the RCD. I will investigate the connection on the switch panel which is both scary and rather beautiful at the same time.
I will not be back on board for a while though.
Thanks for the advice.

 

[Boater Sam]

Look for an insulation fault on the neutral.
As you switch off, if the live opens last, the neutral comes up live for a fraction of a second and an insulation defect to earth will trip an RCD.