PLC commissioning checklist: prove the machine one boundary at a time

Confirm the approved electrical drawings, I/O list, cause-and-effect, sequence description, safety requirements, software revision and device manuals. Mark unresolved design changes before energisation. A checklist cannot compensate for testing against the wrong revision.

Define who controls the work area, what may move, which energy sources are isolated and how temporary forces or bypasses will be logged and removed. Safety functions require their own validation plan and competent personnel; ordinary PLC functional testing does not certify them.

Inspect protection, earthing, segregation, terminals, labels, module positions, supply polarity and field-device ratings before power. Power the control supply without enabling motion where the design permits it. Record supply voltage at the source and at representative loads, then check CPU, I/O and network diagnostics.

Resolve unexpected faults before downloading or forcing around them. A wrong module, earth fault or undervoltage supply becomes harder to see after the application starts producing additional alarms.

For every discrete input, operate the real field device and confirm terminal voltage, input LED, raw PLC tag and HMI indication agree. Test both states. For outputs, isolate the load or use the approved test mode, command the channel and confirm the interface and feedback. Do not equate an output LED with a moving actuator.

For analog loops record zero, mid-scale and full-scale evidence, raw counts, engineering units, range and alarm behavior. For smart devices confirm identity, units, quality/status and parameter ownership. Remove every force immediately after its recorded test.

Begin with manual functions and one actuator at a time. Then prove permissives and interlocks, start/stop behavior, mode transitions and automatic sequences at reduced risk. Test each important fault deliberately: remove a permissive, break feedback, lose communication, trip an overload or create an out-of-range analog value using the approved method.

A sequence has not passed until it enters the safe defined state, gives an actionable alarm, prevents an unsafe restart and recovers through the documented operator action. Power-cycle and warm-restart behavior should be tested where the risk assessment allows it.

Save final controller, HMI, drive and network configurations with hashes or revision identifiers. Update as-built drawings, I/O checks, setpoints, alarm list, outstanding defects and temporary-change register. Demonstrate normal operation and recovery to the operator and maintenance owner.

The printable list below is intentionally vendor-neutral. Add model-specific checks from the current manufacturer documentation and site standards. Use the free wiring micro-lab to rehearse the point-to-point mindset before working on real equipment.