An RCD (Residual Current Device) is an electrical safety device designed to protect against the risk of electric shock.
An RCD works by continuously monitoring the flow of electric current through a circuit. It compares the amount of current flowing into the circuit with the amount of current returning from the circuit. If the RCD detects an imbalance between the incoming and outgoing currents, it will quickly switch off the circuit.
This imbalance can occur when electricity is leaking from the circuit to earth, which can happen when someone touches a live wire or a faulty appliance with a damaged cable. The RCD detects this leakage of current and shuts off the circuit in a fraction of a second, preventing a potentially dangerous electrical shock.
In summary, an RCD works by continuously monitoring the current flowing in and out of a circuit, and quickly switching off the circuit if it detects an imbalance that suggests a leakage of current to earth.