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

In a single phase induction motor, what determines the direction of rotation?

1. The voltage level

2. The speed of the rotor

3. The direction of current flow through the start winding

4. The size of the motor

The correct answer is: The direction of current flow through the start winding

The direction of rotation in a single-phase induction motor is determined by the direction of current flow through the start winding. When the motor is powered, current flowing through the start winding generates a magnetic field that interacts with the magnetic field produced by the main winding. The phase relationship between the currents in the start winding and the main winding creates a rotating magnetic field. Depending on which way this current flows, the resulting magnetic field will cause the rotor to turn in one direction or the other. When the current direction is reversed in the start winding, the rotating magnetic field also reverses, causing the motor to rotate in the opposite direction. This principle is essential for controlling the operational direction of the motor in various applications, making the correct understanding of current flow vital for installation and troubleshooting. The other aspects, such as voltage level, rotor speed, and size of the motor, do not directly affect the direction of rotation. Voltage levels can influence motor performance and torque but do not dictate which way the motor turns. Rotor speed is a result of the operation and is not a factor in initially determining the direction. The physical size of the motor may impact its power capacity and suitability for certain tasks but does not influence the rotational direction.