A 4-pole ELCB, providing passage to balanced 3 phase & 1 neutral through it’s torroid forming the primary winding of the sensitive current transformer, serves very effectively to guard against leaking current of the order of 5 mA – 30 mA -50 mA and beyond , with prompt clearance of the leaking circuit in a matter of 30-50-100….m.seconds.The consumer side is distributed 3-phase loads plus some single-phase loads. Problem arises when the main 3-phase, 4 wire balanced supply line is switched off by the supply agency and alternative stand-by 3-phase balanced supply is not available.

The gap may be asked to fulfill with 3 Nos separate sources of 1-phase diesel generators, the voltage of which shall be