List of standard NEMA motors
List of standard NEMA motors
(OP)
I have a few questions regarding motor selection for pump applications.
1/ For a North American application sshould I be specifying in HP or kW?
2/ Could someone point me to a list of standard NEMA motor HP/(kW) ratings in the range 1 - 400 HP
3/ I have one application for a motor where I want to run a centrifual pump on a VFD at a reduced speed. Do I have to de-rate the motor (ie install a larger horsepower motor) because it needs to deliver the calculated horsepower at a slower speed and a given horsepower at lower speed requires a larger torque.
Note: The mechanical engineer calculated the HP required at the lower speed.
Thanks in advance
Roy
1/ For a North American application sshould I be specifying in HP or kW?
2/ Could someone point me to a list of standard NEMA motor HP/(kW) ratings in the range 1 - 400 HP
3/ I have one application for a motor where I want to run a centrifual pump on a VFD at a reduced speed. Do I have to de-rate the motor (ie install a larger horsepower motor) because it needs to deliver the calculated horsepower at a slower speed and a given horsepower at lower speed requires a larger torque.
Note: The mechanical engineer calculated the HP required at the lower speed.
Thanks in advance
Roy





RE: List of standard NEMA motors
2 - Standard ratings are given in NEMA MG-1. You can get a free condensed version at the NEMA website. You can also see the standard ratings on page14 of 25 here:
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3 - I think generally you would derate by the factor below rated speed since voltage is reduced by the same factor to keep constant volts/hz. Very low speed would require additional derating due to cooling reduction which occurs at low speed. Maybe others can comment.
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RE: List of standard NEMA motors
Thanks for the quick response and the link.
The pump will be running 24/7 at a fixed speed somewhere around 3,000 RPM. Am I correct in thinking that if we require 200 HP at 3,000 then I need a motor 200 * 3600/3000
Roy
RE: List of standard NEMA motors
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RE: List of standard NEMA motors
Technically, you might be able to get away with a 200HP motor that has a 1.15 Service Factor, but only if you don't care about the long term life of the motor.
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RE: List of standard NEMA motors
The old standard Equation of 5252.1*HP / RPM = Torque as a base then HP = Torque * RPM /5252.1
5252.1*200 / 3000 = 350 ft-lbs of torque.
Many motor suppliers sell a typical Premium efficiency design motor with Constant Torque Ranges on the nameplate. Typical ranges are 10-60 Hz, 6-60 Hz, 3-60Hz etc. As you are looking to run this motor at a 50 Hz equivalent any of the above would be proper. As the motor is capable of handling the load as a constant torque, you simply size the motor around the same torque number.
The HP motor you want to request would be in the 350*3600/5252.1 = 240HP Range, with a NEMA std break point of 250HP. Consult with the motor suppliers applications engineering and they will confirm the number or perhaps recommend one horsepower higher.
Regards,
RE: List of standard NEMA motors
This question stems from your April 12, 2008 inquiry about electrical immersion heaters having a NEMA 4 terminal box that the manufacturer claims to be suitable for a Class 1 Div. 2.
I am faced with the same question. What did you end up doing?
RE: List of standard NEMA motors
The NEMA 4 box was accepted without a purge.
Roy
RE: List of standard NEMA motors
Who was the manufacturer of the 120KW electrical immersion heater? Perhaps they can help me with my delima.