What condition occurs when a motor is loaded so heavily that the motor shaft cannot turn?

• A. Overload Condition
• B. Locked Rotor
• C. Stall Condition
• D. Short Circuit

Answer: (B)

When a motor is loaded to the point where the motor shaft cannot turn, the condition referred to is called "Locked Rotor." This situation occurs when the rotor is unable to rotate due to excessive mechanical load or resistance that exceeds the motor's capacity to overcome. In this state, the motor draws a high current because it tries to start and perform work, but is unable to do so, leading to a situation where the rotor is effectively "locked" in place.

This condition can result in various issues, including overheating of the motor and potential damage if not addressed. It is important for engineers and technicians to recognize this condition to prevent damage to the motor and to ensure safe operation.

While "Overload Condition" may seem related, it generally refers to a state where the motor is under excessive load but can still turn, albeit at a reduced speed. A "Stall Condition" is similar but typically refers to an operating motor that slows to the point of stopping due to load without the rotor being locked. "Short Circuit" indicates a fault condition where electrical paths are unintentionally connected, which is different from the mechanical constraint described in this scenario.