Earth Leakage Circuit Breaker (ELCB) is an automatic tripping switch that breaks the domestic power supply when it detects more than 25 milli ampere leakage current in the earth line. Earthing is provided in domestic power supply to drain leakage current to the earth if the phase line accidentally short with the metal body of the appliance. For this 3 pin plug is used in appliances. In the 3 pin plug, the earth pin is longer and larger than the other two pins. The longer earth pin first makes contact with socket so that if there is any leakage, the current will pass immediately through the earth line. The earth pin is larger in size to handle high current. If the ELCB is working well, it can immediately break the power supply to prevent shock hazard. It is necessary to confirm the working of ELCB occasionally by pressing its trigger switch.
ELCB is now called as GFCI (Ground Fault Circuit Interrupter). MCB is the Miniature Circuit Breaker used to break phase line, if a larger current passes through the wire. Tripping of MCB protects the wiring and connected appliances from damage.
It is a basic fact that, all current flowing to electrical equipment from the power generation station via its supply circuit’s phase or neutral wire should only return to the power station via that same circuit’s neutral wire. If there is no fault anywhere in a circuit supplying single-phase, the current flowing to the unit at any instant in the “live” wire should exactly match the current flowing away from the unit in the neutral wire. Similarly, there should be no current flowing in the unit’s safety “earth”. If any current is flowing in the ground wire, it must be caused by a fault condition and the supply of current to the circuit needs to be stopped urgently.
Before circuit breakers were invented, simple wire fuses were used: the wire in the fuses was deliberately made much thinner than the wires in the circuits they were intended to protect. Thus, if a fault condition occurred, as the current in the circuit grew higher and higher, a point would be reached at which the thin wire of the fuse would get so hot that it would melt – all safely contained within the body of the fuse – and thus break the flow of current in the circuit it was protecting.
The problem with fuses is that – depending on their design, as some are faster-acting than others – it can take a significantly longer amount of time for them to operate compared with today’s very-fast-acting circuit breakers. That fact means that, if a circuit overload current fault condition occurs, considerable damage can still occur both to the circuit wiring and/or to the unit it is supplying with power.