Sizing an Incoming Breaker

Steve,

I must make one assumption before I continue. It is;

1] all of the AC units are protected by "motor start" circuit breakers of the same brand & type.

If this is the case, your incoming breaker should be sized so that it does not trip under fault current conditions if any of the downstream breakers trip under fault current conditions. In order to do this, you may do 1 of 2 things;

1] contact the circuit breaker manufacturer & they should be able to answer your question.

2] consult the "time/current curves" of the downstream breakers in order to find out the characteristics of the incoming breaker.

If you don't know how to do 2], do 1].

One other thing...it's a very good idea if you know the prospective fault current of the supply circuit before you lauch into this because the circuit breaker manufacturer/distributor will probably ask you this question.

If there were to be some form of sequence start available, then the incomer needs to be sized only for up to 5 machines running and only 1 machine starting at any time. Such a start may result in economies of equipment and cables that are valuable.