Motor demand load for panel schedule

[PowerdT]

There is 250A, 480V panel. The existing motor loads or the breakers inside are (3)
60A and (1) 40A. All the loads are 3 phase.

I assumed (3) 480V*1.73*60*0.8 = 119578 VA
(1) 480V*1.73*40*0.8 = 26573 VA

Total connected load = 146151 VA

How would you calculate the demand load?

 

[tom baker]

For a motor, the branch ckt breaker is oversized to allow to start. Take the fla of largest motor x 1.25% and 100 % of others
Please review Art 220

 

[petersonra]

There is 250A, 480V panel. The existing motor loads or the breakers inside are (3)
60A and (1) 40A. All the loads are 3 phase.

I assumed (3) 480V*1.73*60*0.8 = 119578 VA
(1) 480V*1.73*40*0.8 = 26573 VA

Total connected load = 146151 VA

How would you calculate the demand load?

If you use the rating of the circuit breaker you will get some weird numbers. Use the full load current chart found in the code book.

 

[PowerdT]

For a motor, the branch ckt breaker is oversized to allow to start. Take the fla of largest motor x 1.25%100 % of others
Please review Art 220

That gives me demand load. Sorry on my question. I meant to say to calculate the demand factor

 

[electrofelon]

That gives me demand load. Sorry on my question. I meant to say to calculate the demand factor

I am not aware of any demand factor that would apply. Welcome to the NEC where your calculated load will be 3 times higher than actual.

 

[PowerdT]

I am not aware of any demand factor that would apply. Welcome to the NEC where your calculated load will be 3 times higher than actual.

How do u determine your panel has the capacity to add more load?

 

[electrofelon]

How do u determine your panel has the capacity to add more load?

An article ,220 load calc. The best way is to use measured demand per 220.87 and get away from calcs.

 

[kwired]

As mentioned with motors the breaker value alone is not going to tell you the load with a motor, it generally needs sized at least twice the motor rated current to help assure it won't trip while starting.

@ 480 three phase a 60 amp breaker would be typical for maybe a 20 HP motor and 40 amp maybe a 15 HP motor.

The 20 hp motor full load rating might only be around 24 amps and the 15 hp motor rating might be around 17 amps.

Actual loading could be less than those values. Actual demand is potentiually continuous and you can't apply a demand factor to something that never varies.

Without more information worst case load calculation would be NEC full load values and at continuous operation.