Sizing Disconnect/Breaker for main feed 1

[elfman]

This may be a remedial question, but I can never seem to find exactly what I am looking for in the NEC.

I have a control panel that has the main 480VAC power feed into a breaker - (ABB Tmax) Power then branches into three motors and a transformer. Each motor and transformer is protected per NEC and manufacturer recomendations. I am trying to find how to size the main breaker. Is there a rule of thumb or a very specific formula/table? I am trying to master the process, not just answer this one situation.

Thanks in advance.

"To be or not to be, that is the question" - William Shakespeare via Hamlet

 

[dpc]

See NEC 430.63. This should be what you are looking for. It references some other sections you'll have to go to, but it should answer your question.

Post back if you have questions.

Cheers,

dpc

 

[SixOn]

I think it would be easier if you add up the individual current demand of each load to get the main breaker current rating.

But then you would also have to consider the maximum current each motor can draw when there is a voltage sag of about 10%

You might also have to consider the diversity factor of your loads