What is the primary function of an RCD in relation to earth leakage?

The primary function of a Residual Current Device (RCD) is to detect and interrupt earth leakage currents. RCDs are designed to monitor the electrical current flowing through live and neutral wires. If there is a discrepancy, meaning that some of the current is escaping to the ground (which can happen due to insulation failure or contact with moisture), the device quickly detects this imbalance. When it detects an earth leakage current that exceeds its predefined threshold, the RCD acts within milliseconds to disconnect the circuit, thus preventing potential electric shock or fire hazards.

The ability to quickly cut off the power is crucial for protecting individuals from serious electrical accidents, making the detection of earth leakage currents a vital safety feature of RCDs in electrical installations.