An earth leakage circuit breaker (ELCB) is a ground fault protection device installed in a consumer unit (CU) or distribution board (DB) primarily to protect against electric shocks. The ELCB is basically a conventional circuit breaker equipped with a sensing coil and interlock or latching mechanism. The coil is connected to the installation ground network, thereby providing a return path to it for any fault induced voltages. Any fault voltage returning to the coil will energize it, activate the latching mechanism, and trip or switch off the circuit breaker. Although still prevalent in many countries, the earth leakage circuit breaker is gradually being supplanted by residual current devices (RCDs) which fulfill the same function but rely on current instead of voltage sensing.
Short circuits in unprotected domestic, commercial, and industrial electrical installations are a major cause of electrocution, fire, and equipment damage. In most cases, a circuit fault, which involves a live wire contacting a conductive part of an appliance or a person on an unprotected installation, will cause electric shocks, severe localized heating, and sparking. Sadly, in many cases this leads to death by electrocution or catastrophic fires and damage to equipment. Although these types of faults always occur, the installation of an earth leakage circuit breaker and a comprehensive grounding or earth circuit in the installation may prevent the resultant damage or loss of life. This protection is achieved by providing a line of “emergency isolation communication” between the supply and consumer points in a circuit via an earthing system.
The earth leakage variant is similar to a conventional main breaker with the exception of the inclusion of a sensing coil connected to its contacts by means of a latching mechanism. This sensing coil receives the emergency messages mentioned above and instantly cuts the supply of power to the installation should a fault occur. This is achieved by means of an electromagnetic solenoid action that occurs when the coil is energized. This process activates the interlock or latching system which immediately switches the circuit breaker off.
For the earth leakage circuit breaker to work, however, it is essential that the line of communication between the sensing coil and the rest of the installation be kept open. This is achieved by ensuring that all appliances, machines, and outlets are equipped with a properly connected ground lead that returns to the consumer unit or distribution board. It is also essential that all ground connections within the CU are clean and that the ELCB ground leads are connected to both the circuit's ground bus connector and the incoming supply ground point. If all these requirements are met, any short circuit between a live lead and a person, appliance, or fitting will send a voltage back via the earth or ground leads to the coil, thereby energizing it and cutting the power before serious damage or injury can result.
The ELCB has been replaced in many countries by residual current detecting devices (RCDs) which are more sensitive and rely on fault current sensing rather than voltage returns for their operation. Both units fulfill the same function, however, and form critical parts of any electrical installation. For this reason, earth leakage circuit breaker and RCD units should never be bypassed and regularly tested to ensure proper functioning.