Challenge #10 · motor-controls
It Won't Shut Off
A pump keeps running. The operator hit STOP, the HMI says it's commanded off, but the pump keeps pumping. Nobody can stop it from the panel. (That's a safety problem. LOTO upstream.)
① Run your checks
② Make the call
③ Explain your reasoning optional
A strong answer covers:
- What you did: confirmed the command is off (PLC output 0V) and the coil is de-energized (0V), then checked the main contacts / motor power.
- The reason: the controls released it, but the main contacts are still closed and the motor is still powered, so the contacts are stuck.
- Determined outcome: the contactor's main contacts welded; a dead coil can't open fused contacts. It's a safety issue, kill it upstream (LOTO) and replace the contactor; the logic is fine.