panel that has an RCD. As part of that, I've been reading up on the subject since I'm not electrically gifted. With that in mind, I'd suggest that you could have a loose,chafed or corroded connection in the hot or neutral wires since (remember, I'm book learned only...) the RCD measures the difference between the HOT and NEUTRAL wires and any difference exceeding 30ma triggers the cutoff. The ground(greenwire) is there to route the stray current safely away and ideally is dormant unless there is a leak elsewhere. Is this a new condition that just started or have you had something changed or added to your system? Does it trip if you have the breakers for the charger and hot water off when you plug in? Try to isolate the issue i.e; Water heater working OK? the element could be shot if this just started. Nigel Calders book has quite a bit on this as well as test instructions. Good luck with it, hopefully, more knowlegable than me will chime in! David