The speed a synchronous motor will run can be determined by the number of poles of the motor and the frequency of the electrical service using the formula:

RPM = Hz* (2 / poles) * 60

			
					2
					4
					6
					8
					10
					12
					14
					16
					18
				

			
					Frequency
					Number Of Poles
				

			
					60-cycles
					3600
					1800
					1200
					900
					720
					600
					514
					450
					400
				

					50-cycles
					3000
					1500
					1000
					750
					600
					500
					428
					375
					334
				

		

where

RPM = shaft rotation speed or revolutions per minute

Hz = frequency or cycles/sec

Poles = number of poles of your motor.

So, for example, if you have a 4 pole motor on 60 Hz then RPM=60*(2/4)*60=1800 rpm.

60Hz is the most common frequency in the US

50Hz is the most common frequency outside the US

Motor Poles & RPM

The speed a synchronous motor will run can be determined by the number of poles of the motor and the frequency of the electrical service using the formula: