Also commonly called safety switches, these are designed to cut the power in a fraction of a second in the event of a fault, preventing electrocution. Some devices may not have built in RCD's (residual current device) or you may which to use a power tool outdoors. Essential safety measure for any DIYer.
Note: RCDs are not a substitute for common sense around mains electricity. While they will work in most situations, they may not in some cases and are not a substitute for current overload devices such as fuses and circuit breakers. Wiring, appliances, leads and power outlets must always be maintained in a safe condition.
10a 240v AC rated
Trip time < 30ms
Trip leakage current 30mA