1. 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 unequal, unbalanced in phase, rather placed at random phase displacement, may be filled with harmonics and even some d.c. components, connected in star with common neutral (earthed) as shown in below vector diagram.
2. A situation arises here –whether the same set of mixed 1-phase consumer circuits protected by several MCBs and 4-pole type ELCBs shall work efficiently and without any harm?
N (All the 3 neutrals,N1,N2 & N3 joined and earthed) is the common neutral.
The neutral circuit of N may carry maximum current as Ip1+Ip2+Ip3, hence, provide higher rating for neutral conductor, N.
The answer is–yes. After segregating the original 3-phase, 4-wire balanced supply source, feeding the 4 Nos Bus-bars with P1, P2, P3 & N and taking the supply to various sets of switch-boards work very satisfactorily with full protection secured by 4-pole ELCBs. Kirchhoff’s Law work here and sensitive torroid of the ELCB picks up smartly any unbalance in total sum of all forward and return currents in 4-wire configuration in the order of 5-30-50—-mA.