Many years ago when I worked in new power plant site for doing of auxiliary system commissioning, we fronted a wonder accident in low voltage switchgear. One of withdrawable outgoing of switchgear (200 A feeder) burned due to a sever fault. Related outgoing protection device was a 200A molded case circuit breaker (MCCB) which could not have suitable action against mentioned fault. The space of drawable compartment failed due to sever arcing current. That sever fault current interrupted via, 4000 A - 4 pole ACB, MCC incoming with a long delay time instead of related outgoing protection. Indeed the incoming circuit breaker had prevented to fault extension in switchgear but it could not prevent to outgoing failure. Later investigation and verification shown, 200 A MCCB which made by an effectual manufacturer had suitable protection setting and it must be tripped against huge fault current instantaneously.
How can you explain that outgoing feeder protection inactivity?