The following formula relates speed of the electric motor to number poles :
S = k x Hz x 60 / Number of Poles
where:
-
S = Motor speed
-
k = 2 for alternating current (AC electricity)
-
Hz = 60 for 60-Hertz electricity i.e. electricity moves (oscillates) at 60-waves per second
-
“Poles” are the positive and negative electromagnetic fields in the motor
Standard electric motor speeds at 60-Hz electricity.
- 2-pole motor = 3,600 RPM
- 4-pole motor = 1,800 RPM
- 6-pole motor = 1,200 RPM
- 8-pole motor = 900 RPM
Standard electric motor speeds at 50-Hz electricity.
- 2-pole motor = 3,000 RPM
- 4-pole motor = 1,500 RPM
- 6-pole motor = 1,000 RPM
- 8-pole motor = 750 RPM