Finding Motor Speed

A squirrel cage induction motor is a constant speed motor. It must operate at the speed specified on the nameplate or it will burn out.

To Calculate the speed of an induction motor:

Srpm = (120 x F) /p


Srpm = synchronous revolutions per minute.
120 = constant
F = power supply frequency (in cycles/sec)
P = number of motor winding poles

• Example: What is the synchronous of a motor having 2 poles connected to a 60 hz power supply?

Srpm = (120 x F)/p

Srpm = (120 x 60)/2

Srpm = 7200/2

Srpm = 3600 rpm