What is the formula to calculate RPM in relation to frequency and number of poles?

The formula for calculating revolutions per minute (RPM) of an electric motor is based on the relationship between the frequency of the electrical supply and the number of poles in the motor. This calculation is essential for understanding the speed of the motor in relation to the electrical supply conditions.

The correct formula is RPM = (120 x f) / P. In this equation, "f" represents the frequency of the electrical supply in hertz (Hz), and "P" stands for the total number of poles in the motor. The constant 120 is derived from the fact that there are 60 seconds in a minute, so it accounts for converting from cycles per second to revolutions per minute.

In practical terms, as the frequency increases, the RPM of the motor will also increase if the number of poles remains constant. Conversely, a higher number of poles will reduce the RPM for a given frequency. This relationship is critical in selecting motors for specific applications where the required speed of operation is known.

Understanding this formula is vital for electrical tradespeople, as it aids in selecting and configuring motors appropriately for different tasks in various electrical systems.