I have had an elcb protecting the garden supply(pump, lights etc) without problem for the last 10-11 years, which has now started nuisance tripping. I have read that this is common with elcb's but given it previously being ok, I wondered if it may be a sign that it is on it's last legs. I have insulation tested all the circuits which showed no problems & the fish in the pond seem happy enough, but I have no means of actually testing the elcb unless someone can tell me how to do it with a megger ( very old) or a multi meter( the only testers I have access to these days). Thanks.