[Earth Leakage Circuit Breakers] The IEE regulations require that any socket likely to be used for equipment operated out of doors be protected by a residual current circuit breaker with an instantaneous tripping current of not more than 30mA. Think of it as a protection grading problem. But here you have to choose the protection settings upstream to grade with the equipment downstream. I haven't heard of such filters drawing 30mA, though. True. Any protective device is useful in a specific situation, and protects against specific faults. Anything can be used where it's inappropriate. But that doesn't make it per se a bad thing. See above. help. I disagree. I once said, joking, "I used to recommend steel toe-caps when moving large computers, but now I generally prefer bare feet - so you make damned well sure you don't drop it!" My view is: A protective device - any protective device - is there to get you out of trouble, not to get you into it. One should never take risks (because one knows there is protection there) that one wouldn't take without it. I disagree that the knowledge that there is an RCCB in the circuit will make me complacent. I'd rather work carefully, knowing that any mistake I make could be fatal, but also knowing that I have taken all reasonable steps to ensure that it won't. Our protection specialist at Power Tech often talks about prortection in terms of "the fence at the top of the cliff" and "the ambulance at the bottom of the cliff". When working with live high voltages, one should always try and put in place as many "fence" systems as possible - rubber gloves, isolating transformers, insulated screwdrivers, hands in pockets etc., but "ambulance" systems such as residual current devices have their place. Philip.