LV Motor feeder & Earthfault protection
LV Motor feeder & Earthfault protection
(OP)
Is it correct to employ Earth Leakage Relay (ELR) for earthfault protection of an LV motor.
The 415V system is solidly earthed and the motor is rated 128kW.
The ELRs are governed by IEC60947-2 which stipulates 'Non operate current' for the ELR to be not less than 50%, which means, the ELR can operate at any current above 50% of the set threshold.
I am curious to know the practice followed in other utilities.
Appreciate sharing your experience / views.
Thanks in anticipation.
The 415V system is solidly earthed and the motor is rated 128kW.
The ELRs are governed by IEC60947-2 which stipulates 'Non operate current' for the ELR to be not less than 50%, which means, the ELR can operate at any current above 50% of the set threshold.
I am curious to know the practice followed in other utilities.
Appreciate sharing your experience / views.
Thanks in anticipation.






RE: LV Motor feeder & Earthfault protection
If you wish you can prove the above to yourself by superimposing imposing the motor O/C time-current curves on the incomer E/F curves. Repeat the exercise with E/F protection added to the motor circuit.