What may cause a single-phase motor to hum but not start?

A humming sound in a single-phase motor without it starting typically indicates that the motor is experiencing an issue with its rotor's ability to turn. The correct answer points to a locked rotor condition or a malfunctioning starting mechanism.

In single-phase motors, especially those that require a starting capacitor or have a starting winding, the initial phase of starting is crucial. If the rotor is locked or if the starting mechanism such as the capacitor is not functioning correctly, the motor can become energized and produce a hum as it attempts to start but cannot generate the necessary rotational motion.

This condition could arise from mechanical obstructions preventing the rotor from turning or from faults in the starting components that are designed to provide the initial torque required to start the motor. The humming sound results from the motor drawing current without the rotor moving, indicating that while electrical power is reaching the motor, something is preventing it from functioning as intended.

Other options might not directly explain the humming sound in conjunction with the failure to start. For instance, while an insufficient power supply could lead to suboptimal motor performance, it would not typically result solely in a humming noise without rotation. Similarly, excessive load on the motor usually leads to stalling rather than a distinct humming sound, and though a malfunction