ABB REF615 Backup Relay:
Fault Current = Multiplication Factor (obtained from relay) X CT ratio.
For eg: If Multiplication factor is 1.2 and CT ratio is 400/1, then -
Fault current is 1.2X400 = 480Amps.

NOTE: In these kind of relays the indication LEDs and Programmable LEDs need to be reset first, after a fault, before attempting to close the breaker.