Industrial service calc.

[JLH182]

If you have several motors in a facility, all 480 three phase, do you calculate them at 125%. Some are continous duty some are not. I meen some will be used for more than three hours at a time. I'm trying to make a load calculation for the power company.

 

[tish53]

When I do load letters for utilities, I just use the motor hp. No need for the 125% that you may use via NEC to size cable, etc.
If you know the average run time on each motor, that can help the utility engineer with transformer sizing. Our utilities are very willing to overload a transformer for 6 hours and then have it cool down for 18 hours.