NATE Air Conditioning and Heat Pumps Practice Exam

Of the motors commonly used in HVACR systems, which type typically has the lowest starting torque?

1. PSC motor

2. Shaded-pole motor

3. Split-phase motor

4. Three-phase motor

The correct answer is: Shaded-pole motor

The shaded-pole motor is known for its low starting torque, making it suitable primarily for small fan and blower applications where high starting torque is not critical. This type of motor operates by using a shaded area on the pole, creating a weak magnetic field that allows for rotation. While its design is straightforward and inexpensive, it limits the amount of torque it can generate when starting up. In comparison, other motor types listed generally produce higher starting torque. Permanent Split Capacitor (PSC) motors, for example, utilize a capacitor to improve starting torque and overall efficiency. Split-phase motors also feature a starting winding along with the main winding, which adds to their ability to generate more starting torque. Three-phase motors are designed for high-performance applications and are known for their excellent torque characteristics, including high starting torque, making them suitable for heavy-duty operations. Understanding the characteristics of these motor types is essential for selecting the appropriate motor for specific HVACR applications, particularly where starting torque requirements differ significantly.