Sb1234 Posted August 27, 2008 Report Share Posted August 27, 2008 As per NEC 430-24 to size a busbar for a switch board with all motor loads the following formula is to be used - (25%of FLA of largest motor) + ( Sum of FLA of all motor ) Also as per NEC 430-52 and 53 and NEC -152 for incomer circuit breaker selection of the switchboard the following formula should be used . (250% of FLA of largest motor) + ( Sum of FLA of all other motors ) From the above formula it seems that the bus bar rating of a system will be less than the required circuit breaker ratings in terms of ampere. But it does not seem to be common. Is it okay to put an incomer circuit breaker with higher ampere rating than bus bar ampere rating.I generally see that circuit breaker ratings is switchboard are equal to bus bar rating. Any comment is welcome . Regards Link to comment Share on other sites More sharing options...
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