An ELCB is an earth fault protective device that protects against electric shock by tripping a circuit breaker when a fault voltage is detected. RCDs are replacing ELCBs and rely on sensing current. Both devices prevent electrocution, fire, and equipment damage and should never be bypassed or tested regularly.
A residual current device (ELCB) is an earth fault protective device installed in a consumer unit (CU) or distribution board (DB) primarily to protect against electric shock. The ELCB is basically a conventional circuit breaker equipped with a sense coil and an interlock or latching mechanism. The coil is connected to the plant earth network, thus providing a return path to it for any fault induced voltages. Any fault voltage returning to the coil will trip it, activate the lockout mechanism, and trip or shut off the circuit breaker. Although still prevalent in many countries, the RCD is gradually being replaced by residual current devices (RCDs) which perform the same function but rely on sensing current rather than voltage.
Short circuits in unprotected domestic, commercial, and industrial electrical systems are a leading cause of electrocution, fire, and equipment damage. In most cases, a circuit fault, involving a live wire contacting a conductive part of an appliance or a person on an unprotected installation, will cause electric shock, severe local heating, and sparks. Unfortunately, in many cases this leads to death from electrocution or catastrophic fire and equipment damage. While these types of faults always occur, installing an earth leakage circuit interrupter and a complete earth or ground circuit in the installation can prevent resulting damage or loss of life. This protection is achieved by providing an “emergency isolation communication” line between supply and consumption points in a circuit via a grounding system.
The RCD variant is similar to a conventional main switch with the exception of the inclusion of a sensing coil connected to its contacts by a latching mechanism. This sensing coil receives the emergency messages mentioned above and instantly shuts off power to the system in the event of a fault. This is accomplished by an electromagnetic solenoid action that occurs when the coil is energized. This process activates the interlock or latch system which immediately turns off the circuit breaker.
For the operation of the RCD, however, it is essential that the communication line between the sensing coil and the rest of the installation is kept open. This is achieved by ensuring that all appliances, machines and sockets have a properly connected ground lead returning to the switchboard or distribution board. It is also essential that all earth connections within the CU are clean and that the ELCB earth leads are connected to both the circuit earth bus connector and the incoming supply ground point. If all of these requirements are met, any short between a live wire and a person, appliance, or fitting will send a voltage through the earth or earth wires to the coil, energizing it and cutting off power before serious damage or injury can result. .
The ELCB has been replaced in many countries by residual current sensing devices (RCDs) which are more sensitive and rely on fault current sensing rather than voltage feedback for their operation. However, both units perform the same function and are critical parts of any electrical installation. For this reason, RCD and RCD units should never be bypassed and tested regularly to ensure proper operation.
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