What is the standard frequency of North American electrical power, and what effect does it have on AC motor control?

• A. 50 Hz; it has no significant impact on motor control.
• B. 50 Hz; it affects motor speed and timing in AC control applications.
• C. 60 Hz; it affects motor speed and timing in AC control applications.
• D. 60 Hz; it reduces motor efficiency.

Answer: (C)

The key idea is that the power supply frequency sets how fast an AC motor can run for a given number of poles, and this frequency is fundamental to how AC motor control works. The speed of an AC motor is tied to the supply frequency through the relationship with the number of poles: the synchronous speed is 120 times the frequency divided by the number of poles, and the actual speed is slightly lower due to slip. In motor control, frequency is the primary control parameter used by drives (such as V/f control or PWM-based drives) to set motor speed and the timing of electrical cycles. So with North America’s standard 60 Hz, motors have a higher potential speed (and different timing) than they would at 50 Hz, for the same pole count.

This is why the correct choice states 60 Hz and that it affects motor speed and timing in AC control applications. The option with 50 Hz would apply to other regions, not North America. Claims that 50 Hz has no significant impact or that 60 Hz reduces efficiency aren’t accurate reflections of how frequency governs speed and control timing in AC motors.