Factory Acceptance Test Checklist for PLC Panels

A factory acceptance test checklist for a PLC control panel is the ordered list of checks a builder runs and signs before shipping: de-energised checks first, then PLC checks, then staged power, then function tests, fault injection and a sign-off pack. The order matters because you never power a panel you have not checked dead. This guide gives the order, the records to keep and the difference between FAT and SAT. All limits come from your project specification and standards, not from us.

What a factory acceptance test is

A factory acceptance test (FAT) is a structured verification at the builder's premises, before the panel ships, that the build, the wiring, the program and the I/O match the specification. One vendor guide that we read describes it that way, and its phases are the backbone of the order below. Because it is a single vendor's article, treat its numbers as that author's choices and check your own spec.

The test is the moment a customer says "yes, this is what we ordered". Fixing a fault in a workshop is cheaper and quicker than fixing it on site with other trades waiting, which is why FAT is worth doing well.

The RealPars video above shows the first part of a FAT, powering the control panel.

The checklist, phase by phase

Phase 1: de-energised checks on the build

Nothing is powered. This is also where you practise safe working, so lock off any supply that is connected and prove dead before touching terminals; the steps are in our guide to the safe isolation procedure.

• Visual check against the drawings and the bill of materials: right devices, right ratings, right labels.
• Terminal and wire numbering against the schematic.
• Terminal tightness and wire condition.
• Continuity of every circuit and of protective earth bonding.
• Insulation resistance tests where the spec calls for them, with the instrument, the test voltage and the reading recorded. Do this only with the panel isolated, proved dead and the sensitive electronics disconnected as your procedure says.

In EDWartens Lab, the insulation tester can only be used on a locked-out, proven-dead panel, at 500 V or 1000 V. That mirrors the real rule.

Phase 2: PLC checks before power

• Modules seated in the right slots and labelled.
• Program revision and firmware checked against the approved revision, and the backup saved.
• I/O list prepared, with every input and output assigned.
• Force or simulate inputs to prepare the I/O test.

Phase 3: staged energisation

Power goes on in steps so that a fault shows early and small. The vendor guide describes closing the main isolator, then the control supply, then breakers one by one, checking voltages at each stage against tolerances in your spec. Everyone stands clear, the panel door is shut where the design requires it, and a competent person does the work. OSHA's rules on verification, and HSE's preference for dead working, are why Phases 1 and 2 come first.

Phase 4: functional and cause-and-effect tests

Now the panel behaves. For each input, check the PLC sees it. For each output, check it operates the right device. For each sequence, check the order and the timing. A cause-and-effect matrix, where each row is a cause and each column an effect, keeps this tidy and makes sign-off easy.

Phase 5: fault injection

Prove the panel fails safely. Typical faults the vendor guide lists are a wire break, a short, an overload, phase loss, an interrupted emergency stop chain and loss of communications. For each fault, write the expected response, inject it, and record what happened. A panel that only works when everything is perfect is not accepted.

Phase 6: sign-off pack and punch list

Close with the record. The next section lists what goes in it.

Who does what during a FAT

Agree the roles and the test sheets before the test day. Surprises on the day, such as a missing revision or a missing witness, cost time and credibility. Where the customer asks for changes during the test, log them as variations on the punch list so that the signed record still matches what was built.

Sign-off records to keep

A FAT that is not written down has not happened. The record pack is the product.

Sign-off is by the builder's test engineer and the customer or a representative, who witnesses and accepts. Open points go on a punch list, with owners and dates. The contract decides who can accept and what can be closed after shipping, so confirm that before the test.

Instrument records matter more than people expect. If a reading is challenged later, a calibration date and serial number show the meter could be trusted. Fluke, in a pump-panel case, also suggests re-scanning with a thermal camera after a repair as a complementary check on energised work.

FAT vs SAT

A FAT proves the build and the program in the workshop. A site acceptance test (SAT) proves the installed system works with the real machine, real field devices and real process. A good FAT shortens the SAT, because the same logic, I/O and interlocks have already passed once. We label this a general industry description rather than a figure from a standard; your contract may define both tests differently.

Common reasons a FAT overruns

• The program on the PLC is not the approved revision.
• The I/O list and the drawings disagree, so tests cannot be ticked.
• Test instruments arrive without calibration records.
• Nobody agreed what happens to a failed test, so the argument takes the afternoon.
• The panel is energised before the dead checks are signed.

Each of these is a planning fault, not an engineering one, and each is avoided by agreeing the checklist early.

Standards and limits

IEC 60204-1 covers the electrical equipment of machines from the supply connection onwards. The IEC webstore lists its 6th edition of 2016 consolidated with Amendment 1 of 2021. Another assembly standard, IEC 61439-1, is cited by the vendor guide, but we did not open it, so check it directly if your contract uses it. Check the current editions, because they change.

Test voltages, minimum insulation resistance and voltage tolerances are numbers that come from your standard and project specification. Do not copy a figure from a blog, including this one.

Practise a FAT in the lab

Every job in EDWartens Lab ends in a numbered FAT that runs automatically. In the PLC lab you pass it with a program; in the Panel Lab you pass it after you lock out, prove dead, wire from the schematic and restore power. When you pass, you can download the FAT report as a PDF, and a paid review and signature by a Wartens engineer is available if you want one. The companies in the work orders are fictional, and the lab is a simulation, so it teaches the order and the habit rather than the real hazard.

Try it at lab.edwartens.com or the public pages under /project-sim. It is free with a free EDWartens account, and optional practice in the Free PLC Programming Internship, which is free to join and fully online. It is training, not employment.

Our free courses on control panel design and building, electrical and instrumentation QA/QC inspection, PLC and electrical troubleshooting and Siemens TIA Portal commissioning, simulation and troubleshooting cover the skills behind each phase. For careers, read how to become a commissioning engineer and our post on the electrical QA/QC engineer. Use the FAT report as evidence in a portfolio from course projects. An optional certificate of completion is a paid add-on that anyone can verify at edwartens.com/verification.

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