By Dovydas Kersys · Chapter 48 of 58 in Machine Commissioning.
Before you begin: Follow the machine documentation, risk assessment, site procedures and lockout/tagout requirements. Commissioning can expose personnel to electrical energy, stored pressure and unexpected motion. Never defeat a safety function merely to make a test easier. Examples and diagrams are generic and must be checked against the actual machine.
Power interruption tests prove what the machine remembers, what de-energizes, how controllers and HMIs restart, and whether motion can resume unexpectedly.
Commission the unexpected before production experiences it.
Why this matters during commissioning
Recovery faults often appear only after the commissioning team leaves because normal testing rarely includes deliberate power loss.
Commissioning procedure
- Start from defined machine states: idle, ready and running where safe.
- Interrupt selected power or communication in a controlled test.
- Verify outputs and actuators reach the intended safe state.
- Restore power and observe PLC, HMI, drives, networks and retained variables.
- Confirm the machine requires the correct reset/restart actions.
- Check sequence recovery and product tracking after restart.
Common failure patterns
- Maintained run command survives reboot.
- PLC restarts faster than remote I/O and generates nuisance faults.
- Servo absolute position lost or home status incorrect.
- HMI reconnects but displays stale status for several seconds.
Evidence to record
- Measured value and test point
- Expected value / expected state
- Observed value / observed state
- Pass/fail result and any deviation
- Name/date or responsible person where required
FIELD RULE: Power-loss testing is one of the best ways to expose hidden assumptions in machine logic.
Continue the series
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Adapted from Machine Commissioning for Maintenance and Automation Technicians, by Dovydas Kersys. © 2026 Dovydas Kersys. Featured cover image is an AI-generated editorial illustration.