RCD s (residual current devices), also commonly know as safety switches to help to prevent electrocution. If your house does not have RCD s fitted of you want to use a power tool outdoors on an outlet that doesn't have an RCD fitted you can use this portable one instead.

Note: This RCD  Safety Switch is 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 should always be maintained in a safe condition.