Nate Core Practice Test

If you double the RPM of a motor, what happens to the horsepower requirement?

1. It remains the same

2. It doubles

3. It increases dramatically

4. It decreases

The correct answer is: It increases dramatically

When you double the RPM of a motor, the horsepower requirement increases dramatically due to the relationship between speed, torque, and power. Horsepower is calculated based on both the torque produced by the motor and its rotational speed (RPM). Specifically, horsepower can be expressed using the formula: Horsepower = (Torque × RPM) / 5252 In this formula, torque remains constant for the same load, but when you increase RPM, the horsepower required increases because the relationship is directly proportional. Doubling the RPM effectively means that the motor must do twice the amount of work in the same amount of time, which results in an increased demand for power—therefore, the horsepower requirement rises significantly. This understanding is crucial in HVAC applications, where selecting the right motor for the required speed and load is fundamental to system efficiency and performance. As a motor's speed is critical to its application, recognizing how changes in RPM affect horsepower helps in making informed decisions regarding equipment selection and energy consumption.