Factory acceptance test checklist for PLC control panels

Before any power goes on, compare the panel with the released drawings, check the enclosure rating and cable entries, then read part codes against the BOM.

Sample wire numbers, ferrules and terminal labels, then inspect crimps and torque marks on power terminals, where a loose lug on a main breaker overheats under load. Easy to miss. Shut doors hide loose lugs.

Have the paperwork ready, meaning schematics at the correct revision, the I/O list and the programme backup, all laid out on the test bench before the first reading. A test that starts without the right drawing revision wastes the witness’s day, so confirm every document is present before anyone opens a meter.

Measure earth continuity between the main earth bar and each exposed metal part, including the door, back plate and gland plate, recording every reading against the instrument used.

Run the insulation resistance test between live conductors and earth after you disconnect or protect the PLC power supply and analogue cards, since the megger voltage can damage them. Note the test voltage on the sheet.

Write the result, not a tick. A tick tells the customer’s auditor nothing about whether the value sat close to the limit, and the auditor may ask for the numbers a year later.

Power up in stages. Check the incoming supply, then the control supply, then the PLC, and read the diagnostic buffer, since a module can show green while logging a configuration warning. Fault lights mean stop.

Go point by point through the I/O list, forcing each input with a switch until it changes in the programme, then drive each output and watch its relay.

Analogue channels need a signal source, so inject low, middle and high values and read the scaled result on the HMI to confirm the range matches the transmitter datasheet.

Safety circuits deserve their own pass. Test each emergency stop and confirm the contactors drop out, then test the door interlocks, light curtain inputs and the safety relay reset, skipping none of them. Press each emergency stop while the drives are running, because a stop that works on an idle panel proves little about the loaded machine.

Try to break them. A reset held down while a stop is pressed should restart nothing, and one channel pulled from a dual channel input must fault the safety relay. Perfect-day circuits are not safe.

Record who ran each test and what the result was, because an inspector asks for safety records first after an incident and will read them as a stranger. Exact entries protect you.

Every failed point gets a line in the deviation list, noting the fault, the fix, who fixed it and the retest result. Never erase a failure. Retest each failed point only after the fix is dated and initialled by the person who made it, so the sheet shows the whole story from fault to clearance.

When the list is clear, the customer’s witness and your quality lead sign the sheet, and you attach readings, the I/O sheet and programme backup as one pack.

Turn this list into a printable sheet with columns for expected, actual and initials, run it on the next panel off the line, and refine it afterwards.