What is the formula for calculating the speed of a motor?

The correct formula for calculating the speed of a motor is 60 x Hertz/poles. This formula relates to synchronous speed, which is the speed at which the magnetic field rotates in the stator of the motor.

The formula is derived from the relationship between the frequency of the electrical supply (measured in Hertz) and the number of poles in the motor. Specifically, the synchronous speed in revolutions per minute (RPM) can be calculated as follows:

Synchronous Speed (RPM) = (120 x Frequency in Hertz) / Number of poles.

This equation illustrates that as the frequency increases, the speed of the motor also increases, while a higher number of poles will decrease the speed, as the motor requires more time to complete one full cycle.

In the context of the options given, while others suggest subtracting or adding Hertz per poles which do not conform to the fundamental relationships defined by electromagnetic principles, the correct formulation utilizes multiplication and a divisor of poles, confirming the dependency of motor speed on both frequency and the design of the motor itself.