Residual Current Device (RCD)

The modern (and better) alternative to Earth Leakage Circuit Breakers and fuses in the Consumer Unit. RCDs are tripped if they detect a slight current imbalance between Neutral and Live wires above their trip value - typically 30 mA. RCDs can also be used at sockets to give specific protection (such as using an electric hedgetrimmer), their advantage here is that if they trip they will not shut down the whole house.