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Electrician Red Seal · Question

An electrician is troubleshooting a PLC program where a motor starter is not engaging. The ladder logic rung for the motor control is: XIC Start_PB AND XIO Stop_PB OTE Motor_Starter. The Start_PB (Start Push Button) is wired as NO to input I:1/0, and Stop_PB (Stop Push Button) is wired as NC to input I:1/1. Both input lights on the PLC module are ON. What is preventing the Motor_Starter from engaging?

Given both input lights are ON: Start_PB (NO) being ON means it is pressed (making contact), providing a logical '1' for XIC Start_PB. Stop_PB (NC) being ON mea

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Question: An electrician is troubleshooting a PLC program where a motor starter is not engaging. The ladder logic rung for the motor control is: XIC Start_PB AND XIO Stop_PB OTE Motor_Starter. The Start_PB (Start Push Button) is wired as NO to input I:1/0, and Stop_PB (Stop Push Button) is wired as NC to input I:1/1. Both input lights on the PLC module are ON. What is preventing the Motor_Starter from engaging?

Answer options:

  • The Start_PB is not being pressed. ✅ The Stop_PB is currently being pressed.
  • The PLC input module for I:1/0 is faulty.
  • A wiring error to the Stop_PB causing the NC contact to appear open.

Correct answer: The Stop_PB is currently being pressed.

Explanation: Given both input lights are ON: Start_PB (NO) being ON means it is pressed (making contact), providing a logical '1' for XIC Start_PB. Stop_PB (NC) being ON means it is NOT pressed (its normally closed contact is closed), so XIO Stop_PB will evaluate to '0', preventing the rung from going true. If the Stop_PB were pressed, its contact would open, and its input light would be OFF, causing XIO Stop_PB to evaluate to '1'.

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