When should I use a residual current device?
It is advisable to use a residual current device (RCD) whenever possible but particularly in wet or damp locations, such as outdoors. An RCD rated at no more than 30 mA limits the energy in a particular type of electric shock and can save your life. However, an RCD cannot protect you from every type of electric shock, so you should still make sure that circuits are securely isolated before you work on them.
It is best to use an RCD that is incorporated into the switchboard of your installation. This means that all circuits fed from that RCD are protected by it. An RCD that is incorporated into an ordinary mains socket, or plugged into it, will protect anything attached to that socket, but it is possible that equipment may be plugged into another, unprotected socket.
RCDs should be regularly tested by pressing the ‘test’ button and making sure the RCD trips. Faulty or inoperative RCDs should be removed from use.
RCDs rated above 30 mA provide very limited protection against harm from an electric shock. For further guidance, see: information on RCDs.
If you use electrical equipment in particularly harsh conditions, it is worth selecting lower voltage equipment powered by a transformer with an output centre tapped to earth, or powered by a battery. Additional precautions may also be required, depending on the specific location. See Section 7 of BS7671 ‘Requirements for Electrical Installations, IET Wiring Regulations. Seventeenth edition’ for guidance on this. For details, see:British Standards Institution .