An RCD (residual current device) is an electrical safety device installed in your consumer unit or as a portable adapter. It monitors the flow of current through the live and neutral wires of a circuit. If these currents stop matching, even by a tiny amount like 30mA, the RCD triggers and cuts the power within milliseconds.
Why this matters: if you accidentally touch a live wire or a faulty appliance leaks current to earth, you receive a dangerous shock. An RCD detects this fault current and disconnects the circuit before serious injury or fire occurs. Standard circuit breakers and fuses do not provide this protection.
Modern UK homes are required to have RCDs fitted by Building Regulations. They are particularly important in kitchens, bathrooms, gardens and anywhere water is present, since wet conditions increase shock risk. You will typically find RCDs in your consumer unit protecting circuits, or you can use portable RCD adapters for extra protection on older ring circuits.
Common misconceptions: RCDs are not the same as circuit breakers or fuses. They protect people from electric shock, while circuit breakers protect wiring from overload. Many households benefit from having both. You should test RCDs monthly using the test button on the device. If the power does not cut when you press it, the RCD has failed and needs replacement.
What you should do: check your consumer unit to see which circuits have RCD protection. If critical circuits like lighting are not covered, consider having a qualified electrician add RCD protection. For temporary protection on older circuits, portable RCD units are affordable and effective, though not a permanent substitute for proper installation.