Difference between Leakage,Earth and Residual current

In considering for electrical protection all the three currents are mentioned in different situation and concepts considering type of faults.

A fault is termed Earth Fault when there is total or partial insulation failure causing large fault current to earth from the system which can cause total damage to system if the breaker is not tripped in time. For this purpose earth fault relays are incorporated in distribution panels.

An insulation deterioration due to ageing of regular insulation of equipments or wiring can cause low value regular leakage current of the range of milliamps to few amps which cannot be detected by over current relay or earth fault relay. But these currents can cause fatal accidents resulting to burning to loss of life to people working around and also results in regular energy loss.

These leakage current can be detected by residual current devices which provide earth leakage protection. These relays sense differential current or residual current and when it reach above a predefined value trips off the system. The current that operate these protection relays are termed residual current devises . In other words it is the difference between the input and output currents at the location of the relay. They are also called ELCB .

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