Earth-leakage circuit breaker

An earth-leakage circuit breaker disconnects an electrical circuit when current flowing to earth exceeds a set threshold. It reduces electric-shock and fire risks but does not necessarily protect against overloads or short circuits.

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Residual-current device: A protective switch that disconnects a circuit when it detects an imbalance between outgoing and returning current. Modern earth-leakage protection commonly uses this differential-current principle.
Electric shock: A physiological response caused by electric current passing through the body. Preventing dangerous shock is a central purpose of earth-leakage protection.
Residual-current circuit breaker: A circuit breaker that detects residual current and opens a circuit, generally without built-in overcurrent protection. It is a common modern form of earth-leakage protection, distinct from older voltage-operated designs.
Electrical wiring regulations: Rules governing the safe design, installation, and inspection of electrical wiring systems. They specify where earth-leakage protection is required and how it must be selected.
Current transformer: An instrument transformer that produces a smaller current proportional to the current in a conductor. A zero-sequence current transformer detects imbalance among the circuit conductors.
Ground fault: An unintended electrical connection between a live conductor and earth or grounded equipment. It is a common fault that can produce the leakage current the breaker detects.
Earth-leakage circuit breaker (voltage-operated): An earth-leakage breaker that trips when voltage develops between its earth terminal and a reference earth. This older design detects earth-potential rise rather than comparing conductor currents.
Electrical distribution board: An enclosure that distributes electrical power to multiple circuits and houses protective devices. Earth-leakage breakers are installed there to protect one or more downstream circuits.
Zero-sequence current: The residual component of a set of phase currents, equal to their vector sum divided by three. Leakage to earth appears as a nonzero residual current in the monitored conductors.
Overcurrent protection: Protection that interrupts current exceeding a circuit's safe rating, including overload and short-circuit current. Earth-leakage detection alone does not necessarily provide this separate protection.