What is the "earth fault current"?

Earth fault current is a current that flows directly from phase conductors to earth. It may also refer to a current that flows from protective conductors from the point of an insulation breakdown.

To avoid earth fault current, a protection is implemented by professionals. Protection requires interruption to the supply of a current to a circuit or system. Interruption is only set to occur when current leakage to the Earth is detected. The current leakage must be higher than the pre-determined threshold, if it exceeds it, than interruption occur. The effects of earth fault current were not fully realized until the 1970s.