First Quality ~ First Time
Apparatus Repair & Engineering, Inc.
Hagerstown, MD 21740

Local: (301) 739-8285

  Toll Free: (800) 592-3100  

FAX: (301) 739-3804


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Useful Formulae

Rotational Speed

In the formula below, the "Poles" refer to the "Electrical Poles" that are wound into the electric motor when it is manufactured. This is a set value and, aside from "redesigning and rewinding" the motor, is basically a non-changeable number. Therefore, from a "law of physics" stand-point, the only thing that will change the speed of an electric motor is changing the "Frequency". This is where the AC Drive comes into the picture. This calculated value for speed is known as the "Synchronous Speed".

120 x Frequency

Synchronous RPM =



Synchronous RPM - Full Load RPM

 X 100
Percent Slip =

Synchronous RPM


5250 x HP

Torque (lb-ft) =



63000 x HP

Torque (lb-in) =


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Copyright 2002 - 2018 Apparatus Repair & Engineering, Inc. All rights reserved.
Revised: November 10, 2018.