On a substation breaker that is coming off of a 13200v bus down to 7620v through the breaker I would like to know after you get your average amperage per phase on the 7620 side (Distribution Side) say 420 amps for example do you use the 13200 or the 7620 to figure your Mega-Watts? How is the best way to calculate and if you don't mind could you give an example. Thanks!