All, Just finished off testing a new install (well nearly finished testing). Fitted a Starbreaker board, came to test one of the lighting ciruits. Didn't matter what I tried I couldn't get an ELI reading without tripping the damn breaker. I'm using a 1502 tester, tried two wire, three wire methods, all the time it would trip the MCB. The other 6A breaker'ed circuits tested fine. Me thinks duff breaker. The other thing I found, when one of the other breakers tripped, the reset lever didn't move!!! The breakers tripped, but the reset lever stayed in the on position!! Didn't do it all the time only once or twice. Time for 2 replacement breakers J.