Heating, Ventilation, and Air Conditioning (HVAC ) Electrical Practice Test

To determine the synchronous speed of a motor, you can use the formula:

\[

\text{Synchronous Speed} (N_s) = \frac{120 \times \text{Frequency (Hz)}}{\text{Number of Poles}}

\]

In this case, the motor has four poles and operates at a frequency of 60 Hz. Plugging in these values gives:

\[

N_s = \frac{120 \times 60}{4} = \frac{7200}{4} = 1800 \text{ rpm}

\]

This means that the synchronous speed of the four-pole, 60 Hz single-phase motor is 1800 revolutions per minute (rpm). This speed represents the rate at which the magnetic field rotates in the motor, which is essential for the operation of synchronous motors.

Understanding synchronous speed is crucial because it helps in determining the performance of the motor and its relation to the actual speed at which the rotor runs, which in many cases is less than the synchronous speed depending on the load and slip of the motor.