MCC Main and Feeder Breaker Coordination

[botz]

Hello, I am designing a distribution system and the client(due to economical reasons) wants to get rid of power circuit breaker switchgear and feed the transformer(4160 to 480V) directly to MCC main breaker. I have been trying (in vain) to figure out how to coordinate the MCC feeder breakers and the main breaker tied to MCC in instantaneous region, since they will be on the same 2000A bus, with 3 cycles. Square D says, it can be done using 1600A electronic trip breaker. GE says it cannot be done for instantaneous faults and thats why ppl use 30 cycle power breaker....really confused at this point....:-? HELP!!!

 

[jim dungar]

Some manufacturers have molded case circuit breakers (including Square D's Powerpact family) that can "disable" their instantaneous protection yet it will become active again to self protect itself. This is not a completely accurate description but it covers the basic concept.