Earth leakage circuit breaker

An Earth-leakage circuit breaker (ELCB) is a safety device used in electrical installations with high Earth impedance to prevent shock. It detects small stray voltages on the metal enclosures of electrical equipment, and interrupts the circuit if a dangerous voltage is detected. Once widely used, more recent installations instead use residual current circuit breakers which instead detect leakage current directly.

The main purpose of Earth leakage protectors is to prevent injury to humans and animals due to electric shock.

This is a category of devices, which are used to protect instruments, circuits and operators, while Earth leakage. Early ELCBs are voltage sensing devices, which are now replaced by current sensing devices (RCD/RCCB). Usually voltage sensing devices termed as ELCB and Current sensing devices termed as RCCB.

Voltage ELCBs were first introduced about sixty years ago and current ELCB was first introduced about forty years ago. For many years, the voltage operated ELCB and the differential current operated ELCB were both referred to as ELCBs because it was a simpler name to remember. But the use of a common name for two different devices gave rise to considerable confusion in the electrical industry.

If the wrong type was used on an installation, the level of protection given could be substantially less than that intended.

To eliminate this confusion, IEC decided to apply the term residual current device (RCD) to differential-current-operated ELCBs. Residual current refers to any current over and above the load current.

ELCB manufacturers include: Major Tech, Fuji Electric, Schneider Electric, Legrand, Havells, ABB, Siemens AG, Areva T&D, Camsco, Telemecanique, Orion Italia, Crabtree, MEM, Terasaki,Vguard.

An ELCB is a specialised type of latching relay that has a building's incoming mains power connected through its switching contacts so that the ELCB disconnects the power in an Earth leakage (unsafe) condition.

The ELCB detects fault currents from live to the Earth (ground) wire within the installation it protects. If sufficient voltage appears across the ELCB's sense coil, it will switch off the power, and remain off until manually reset. A voltage-sensing ELCB does not sense fault currents from live to any other Earthed body.

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