Non-Latching In-Line RCD Safety Unit - 

The Masterplug Safety in-line RCD continuously monitors the power supply to an electrical appliance and cuts off the power within 40 milliseconds if an earth current fault is detected. This is fast enough to prevent a fatal electrical shock. Specifically designed for heavy duty applications, the water resistant casing of the unit is rated at IP65 when used with plugs, sockets and connectors of an equivalent rating. The RCD is a non-latching type so when power to the RCD is disconnected, due to a power cut or switching off the mains, the RCD will trip & have to be re-set when power returns. Designed with outdoor activities in mind it's ideal for power tools and garden equipment.