Electrician Red Seal · Question
A technician is troubleshooting a three-phase motor control circuit that uses a magnetic starter. The motor fails to start when the START button is pressed. All overloads are reset, and the control transformer primary has 600 V AC. When measuring the control circuit voltage just after the stop button and before the start button, the technician reads 0 V AC. What is the most likely cause of this issue?
If the voltage just after the stop button is 0 V, it indicates an open circuit before that point in the control circuit. A blown fuse upstream (before the STOP
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Question: A technician is troubleshooting a three-phase motor control circuit that uses a magnetic starter. The motor fails to start when the START button is pressed. All overloads are reset, and the control transformer primary has 600 V AC. When measuring the control circuit voltage just after the stop button and before the start button, the technician reads 0 V AC. What is the most likely cause of this issue?
Answer options: ✅ A blown fuse in the control circuit before the STOP button.
- A faulty START button that is not making contact.
- An open coil in the motor starter.
- A short circuit in the motor starter holding contacts.
Correct answer: A blown fuse in the control circuit before the STOP button.
Explanation: If the voltage just after the stop button is 0 V, it indicates an open circuit before that point in the control circuit. A blown fuse upstream (before the STOP button) would interrupt the power supply to the rest of the control circuit.
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