How to size the main circuit breaker and feeder for MCC

[dahualin]

I just give a simple one section MCC with 3 pumps to control, rated 460v 3 phase 5hp; 5hp; 15hp. The FLA for 5hp motor and 15hp motor are 6.6A and 18A respectively. The total load (FLA) is 18x1.25+6.6+6.6=35.7. So the feeder will be 3#8 + #10G. The main circuit breaker will be sized as 18x2.5+6.6+6.6=58.2, so the breaker is 50amps because 2.5 is the maximum rating or setting of Motor Branch circuit short-circuit and ground-fault protective devices. We cannot go next size up for the breaker.

Am I right? Thanks.

 

[bob]

I just give a simple one section MCC with 3 pumps to control, rated 460v 3 phase 5hp; 5hp; 15hp. The FLA for 5hp motor and 15hp motor are 6.6A and 18A respectively. The total load (FLA) is 18x1.25+6.6+6.6=35.7. So the feeder will be 3#8 + #10G. The main circuit breaker will be sized as 18x2.5+6.6+6.6=58.2, so the breaker is 50amps because 2.5 is the maximum rating or setting of Motor Branch circuit short-circuit and ground-fault protective devices. We cannot go next size up for the breaker.

Am I right? Thanks.

See 430.52.C.(1) exception #1. You do not have to go that high but
the exception will allow it.