In-Line RCD Safety Device A sensible addition to any electrical tool or existing cable reel. Employing some form of RCD is a must whenever using a tool out of doors. The device is simply added to the power line (this should be done by a competent electrician) and ensures that the unit is used every time, unlike a cable extension or plug socket adaptor. Rated at 13A, the RCD trips in no more than 30ms, cutting the power, should a leakage current of less than 30mA flow.