Electrician Red Seal · Question
An electrician is troubleshooting a 480 V, three-phase squirrel cage induction motor that fails to start when energized. A voltmeter shows proper voltage at the motor terminals, and an ohmmeter reading across phases U-V, V-W, and W-U of the windings shows 0.8 ohms, 0.8 ohms, and infinity respectively. What is the most likely issue?
An 'infinity' reading on an ohmmeter between two phases (V-W in this case) indicates an open circuit in one of the motor windings. This prevents the motor from
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Question: An electrician is troubleshooting a 480 V, three-phase squirrel cage induction motor that fails to start when energized. A voltmeter shows proper voltage at the motor terminals, and an ohmmeter reading across phases U-V, V-W, and W-U of the windings shows 0.8 ohms, 0.8 ohms, and infinity respectively. What is the most likely issue?
Answer options:
- The motor is overloaded.
- There is a short circuit in one winding. ✅ One phase of the motor winding is open.
- The power factor correction capacitors are faulty.
Correct answer: One phase of the motor winding is open.
Explanation: An 'infinity' reading on an ohmmeter between two phases (V-W in this case) indicates an open circuit in one of the motor windings. This prevents the motor from establishing a rotating magnetic field and starting.
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