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Electrician Red Seal · Question

A technician is troubleshooting a PLC-controlled conveyor system. The conveyor stop button is wired as a normally closed (NC) contact to a digital input module. When the button is pressed, the input status light on the PLC module remains ON. What is the most likely issue?

If the stop button is wired as an NC contact, pressing it should open the circuit and turn the input status light OFF. If the light remains ON, it indicates the

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Question: A technician is troubleshooting a PLC-controlled conveyor system. The conveyor stop button is wired as a normally closed (NC) contact to a digital input module. When the button is pressed, the input status light on the PLC module remains ON. What is the most likely issue?

Answer options: ✅ The stop button contact is stuck open.

  • There is a short circuit in the wiring to the input module.
  • The input module is faulty.
  • The stop button contact is stuck closed.

Correct answer: The stop button contact is stuck open.

Explanation: If the stop button is wired as an NC contact, pressing it should open the circuit and turn the input status light OFF. If the light remains ON, it indicates the circuit is still closed, meaning the contact is stuck open and not breaking the circuit as intended. A faulty input module or short circuit would likely result in different symptoms or the light being permanently OFF.

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