All this out of my head - probably approximately correct but don't trust your life to it: Defibrillation (or more properly here, fibrillation) depends not only on current but also on duration. RCDs are designed to disconnect power within a critical period. I think it's within 50mS (which fortunately makes sense in the context of 50Hz (or higher) mains frequencies) and corresponds to a critical period during the heart's cycle. In fibrillation the normal voltage patterns of the heart are disturbed and while it may still oscillate it may subsequently do so in a mode which is not conducive to pumping blood. The television (and real life) "300, joules, clear, zap" routine is designed to polarise the muscle, clear all oscillation patterns and let the oscillator try and start clean again. (Master Reset). As you'll well appreciate if you've "field tested" one, an RCD does not stop you receiving a shock (the kick is not necessarily pleasant) but strictly limits the duration. RM From: G.C. >I think that these figures air on the side of caution. An RCD usually has a trip of 30mA all though you can get them in many sizes. >When I last looked at these type of figures I recall a statement that 30mA at 40V was sufficient to cause defiblaration. > >Jim Main wrote: >> >> I found the following pertinent info in a mag the other day, detailing >> whether or not you'd be able to let go a live source - it depends on the >> amount of current that's flowing through the muscle.. and gave the following >> rough guidelines.. >> >> 1mA - tingling feeling - no problem letting go >> >> 10mA - probably still able to let go >> >> 16mA - borderline able to let go >> >> 20mA - you're locked to it! >> >> Jim