Motor Demand load calculation

[Sajid khan]

I have an Motor control centre (MCC) which has total connected load of 3x23.32kVA+15.98kVA+4x24.71kVA= 184.78kVA How can i calculate the Maximum demand?

I tried to find it in Article 430.26 for the demand factor of the motor but unable to find it. What demand factor shall i use?

cooperation of all forum members will be highly appreciated.

Thanks in advance

Regards,
Sajid

 

[kwired]

I have an Motor control centre (MCC) which has total connected load of 3x23.32kVA+15.98kVA+4x24.71kVA= 184.78kVA How can i calculate the Maximum demand?

I tried to find it in Article 430.26 for the demand factor of the motor but unable to find it. What demand factor shall i use?

cooperation of all forum members will be highly appreciated.

Thanks in advance

Regards,
Sajid

There is no demand factor for such application in the NEC.

NEC assumes those motors all are capable of running continuously at up to at least 100% of full load rating, but in reality even more then that is possible since overload settings are often in the 115% to 125% range of motor full load current.

Reality is not all of them run at that level, but is case by case for each and every motor. If you do have motors that by the nature of the load driven are not possible to run at same time (some will say there must be a physical or electrical interlock to prevent them from running at same time some don't) you will never see more then the larger load at any instant in time from those motors.

 

[Sajid khan]

There is no demand factor for such application in the NEC.

NEC assumes those motors all are capable of running continuously at up to at least 100% of full load rating, but in reality even more then that is possible since overload settings are often in the 115% to 125% range of motor full load current.

Reality is not all of them run at that level, but is case by case for each and every motor. If you do have motors that by the nature of the load driven are not possible to run at same time (some will say there must be a physical or electrical interlock to prevent them from running at same time some don't) you will never see more then the larger load at any instant in time from those motors.

Thanks Kwired. Yes you are wright, i have gone through a little more in Article 430.26 & 430.24 and found that there is no demand factor for the motors but the rules to find the main disconnect, main feeder and branch feeder is given. I think this info is enough to size the breakers and feeders.

Regards