Which condition could cause an AC electric motor to run too slowly?

Which condition could cause an AC electric motor to run too slowly?

• A. Lack of lubrication, defective wiring, or low applied voltage
• B. High ambient temperature
• C. Overlubricated bearings
• D. Incorrect rotor direction

Answer: (A)

AC motor speed under load is governed by how much torque the motor can develop to meet the mechanical demand. If the voltage is too low, the magnetic flux falls and the motor can’t produce full torque, so it can’t accelerate to near synchronous speed. Defective wiring reduces current, weakening the magnetic field and torque as well, leading to slower operation when the motor is loaded. Lack of lubrication increases friction in the bearings, effectively raising the load the motor must overcome, which also pushes it toward more slip and slower speed. Together, these conditions directly reduce torque or increase mechanical load, causing the motor to run slower than intended. High ambient temperature by itself doesn’t directly slow speed, overlubricated bearings add drag but are less likely to be the primary cause, and incorrect rotor direction would usually prevent normal operation or cause reverse rotation rather than just a slower forward run.

AC motor speed under load is governed by how much torque the motor can develop to meet the mechanical demand. If the voltage is too low, the magnetic flux falls and the motor can’t produce full torque, so it can’t accelerate to near synchronous speed. Defective wiring reduces current, weakening the magnetic field and torque as well, leading to slower operation when the motor is loaded. Lack of lubrication increases friction in the bearings, effectively raising the load the motor must overcome, which also pushes it toward more slip and slower speed. Together, these conditions directly reduce torque or increase mechanical load, causing the motor to run slower than intended.

High ambient temperature by itself doesn’t directly slow speed, overlubricated bearings add drag but are less likely to be the primary cause, and incorrect rotor direction would usually prevent normal operation or cause reverse rotation rather than just a slower forward run.