How do manual motor starters respond to voltage below a preset level?

Manual motor starters are designed to protect motors from conditions that could lead to inefficiencies or damage, such as low voltage situations. When the voltage drops below a preset level, the manual motor starter will open the contacts. This action disconnects the motor from the power supply, preventing it from operating under inadequate voltage conditions, which can lead to overheating, inefficient operation, or damage to the motor windings.

This protective feature is crucial because low voltage can cause an increase in motor current draw, resulting in excessive heat and potential burnout over time. By opening the contacts in response to low voltage, the starter ensures that the motor does not run under harmful conditions, thereby safeguarding its longevity and performance. Thus, option B accurately describes the behavior of manual motor starters in a low voltage scenario.