Before disconnecting a programming device, which precaution is recommended?

• A. Ensure the PLC is in a safe state (e.g., STOP)
• B. Disconnect while the PLC is RUN
• C. Remove all power from the entire plant
• D. Reprogram all devices simultaneously

Answer: (A)

The main idea is to put the PLC in a safe, non-operating state before disconnecting the programming tool. When the PLC is in STOP, outputs are held in safe values and the controller isn’t actively executing the program, so unplugging the programmer won’t cause unexpected actuator movement or changes in I/O. Disconnecting while the PLC is RUN can lead to abrupt or unpredictable behavior, potentially creating hazards or equipment damage. Powering down the entire plant is unnecessary and disruptive for simply updating or inspecting the PLC. Reprogramming all devices at once isn’t related to staying safe while disconnecting a programming tool. For best practice, confirm the PLC shows a safe STOP state and follow any site lockout/tagout procedures as needed.