Load Calculation

[Electriman]

Greetings,

I have a project that has a couple motors and some other continues and non-continues loads. Some of the motors have VFDs. I have following options for load calculations:
A) I can use NEC 215 which says 125% of continues load plus 100% of non continues loads. The load can be motor too.
B) I can use NEC 430 to calculate the motor load and add 125% of continues and 100% of non-continues loads other than motors

What do you recommend?

As far as motors with VFD, should I consider the motor hp for load calculation or VFD input current?


Thanks in advance.

 

[Eddie702]

You have to use the VFD input rating

 

[Electriman]

Any more feedback?

 

[don_resqcapt19]

I see no reason to base the load calculation on the VFD input rating. Often the VFD has a horsepower rating that exceeds the horsepower of the motor that is being used. The VFD will never pull its rated input current in that type of applicator. The actual load is the motor and the small amount of losses in the VFD. I would use the motor currents as shown in the Article 430 tables for the load calcualtions.

 

[Eddie702]

430:22A says 125% of drive input current

 

[ptonsparky]

430:22A says 125% of drive input current

That is for conductors suppling a single motor. DC to boot.

 

[Eddie702]

That is for conductors suppling a single motor. DC to boot.

Yes, my mistake i did a typo.

Should have been 430:122 A