Electrician Red Seal · Question
When commissioning a new 230 V, single-phase motor, an electrician observes that the motor hums loudly but does not rotate. There is proper voltage at the terminals, and the shaft spins freely by hand. What is the most probable cause?
A single-phase motor requires an auxiliary (starting) winding, often with a capacitor, to create a rotating magnetic field for starting. If the motor hums but d
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Question: When commissioning a new 230 V, single-phase motor, an electrician observes that the motor hums loudly but does not rotate. There is proper voltage at the terminals, and the shaft spins freely by hand. What is the most probable cause?
Answer options:
- The motor bearings are seized. ✅ The starting winding or capacitor is faulty.
- The main winding has an open circuit.
- The supply voltage is too high.
Correct answer: The starting winding or capacitor is faulty.
Explanation: A single-phase motor requires an auxiliary (starting) winding, often with a capacitor, to create a rotating magnetic field for starting. If the motor hums but doesn't rotate and spins freely, it indicates the main winding is energized but the starting mechanism is not engaging, likely due to a faulty starting winding or capacitor.
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