Aug 17, 2026
FAT Before Shipment: How a Factory Acceptance Test Cuts Control Panel Startup Failures
A Factory Acceptance Test (FAT) runs your control panel against real I/O before it leaves the supplier. Here is what to require in a FAT, and why it is the cheapest insurance against site startup fail
Why a FAT matters more than most buyers realize
When you source a control panel from a China supplier, the real risk is not the build — it is what happens on site, three weeks later, when the panel will not talk to the motor. A Factory Acceptance Test (FAT) is the one checkpoint that catches those failures before the panel is crated.
The short answer: a FAT simulates your actual field conditions in the supplier's workshop using mocked I/O and a load bank, so a faulty relay, wrong PLC address, or reversed interlock shows up on a bench instead of on your factory floor. Buyers who skip it trade a one-day test for a multi-day site shutdown.
What a FAT actually checks
A proper FAT is not "we powered it on and the light blinked." It is a documented, repeatable procedure. For a typical control panel sourcing project, require these five checks:
1. I/O force test on every point
Every digital input, digital output, analog input and analog output is forced and verified against the wiring schedule. If a proximity switch is mapped to the wrong PLC address, you see it here — not when the line jams.
2. Logic and interlock simulation
The supplier runs the PLC program through its normal and fault sequences: start, stop, emergency stop, permissive interlocks, and alarm states. A common failure we catch: an emergency-stop that kills the drive but not the auxiliary contactor.
3. Load and thermal test
Outputs are loaded to their rated current (or a representative load bank) and the thermal behavior is observed. Undersized wiring or a mis-specced contactor heats up under load — visible in a FAT, invisible on a bench "power-on."
4. Communications check
If the panel talks to a VFD, HMI, or upstream SCADA, the FAT verifies the protocol (Modbus RTU/TCP, Profinet, EtherNet/IP) and the actual register map. Most "communication problem during commissioning" tickets trace back to a register mismatch a FAT would have caught.
5. Documentation pack
The FAT should produce a signed report: as-found / as-left values, the I/O map used, and the firmware versions. This pack is what your site electrician opens at 2 a.m. when something will not start.
How we run FAT for sourced panels
As a sourcing partner, we do not build the panel in our own factory — we coordinate the build across vetted China workshops and own the FAT step. The pattern that works:
- Mock the field. We build a breakout box that simulates your sensors and actuators, so the program runs against realistic signals instead of open wires.
- Run it warm. The panel runs under load for a sustained period, not a five-minute blink test.
- You watch it. For critical projects we stream the FAT or share the recorded run, so there is no "trust us" gap.
This is why a FAT before shipment is the single highest-leverage step to reduce startup failure risk on a sourced control panel.
FAT vs SAT: where each earns its keep
A Site Acceptance Test (SAT) still matters — it confirms installation, cable runs, and field device wiring on your side. But SAT happens after shipping and after crane time is booked. A failure found at SAT costs crane, labor, and schedule. A failure found at FAT costs a rework day at the supplier. The economics are not close.
Common FAT mistakes buyers make
- Accepting a "visual inspection" as a FAT. If there is no I/O simulation and no report, it was not a FAT.
- No agreed test plan. The supplier tests what is easy. You should supply the sequence and the I/O map up front.
- Skipping the load test. A panel can pass a no-load logic run and still fail the first time a contactor pulls real current.
FAQ
Do I need a FAT for a simple panel?
If the panel has a PLC, a VFD, or any interlock, yes. For a passive junction or a basic start-stop with no logic, a visual and continuity check is enough.
Who pays for the FAT?
It is part of the build scope. A serious supplier includes it; if a quote excludes it, that is a cost you will pay later as downtime.
How long does a FAT take?
A small panel: half a day. A multi-bay line control panel: one to two days including rework if something fails.
Can I attend the FAT remotely?
Yes. We share the live run and the recorded test for most projects, so you do not need to fly to the workshop.
What if the FAT fails?
That is the point. The panel is reworked at the supplier and re-tested before shipment. You pay for a bench day, not a site shutdown.
Engineering takeaway
A FAT moves failure from your site (expensive, visible, schedule-killing) to the supplier's bench (cheap, quiet, fixable). For any sourced control panel with logic or comms, require a documented I/O-force test, a load test, and a signed report — and treat anything less as not-tested.
Related guides
Send us your panel spec
Tell us the PLC brand, I/O count, and field devices, and we will scope a sourced panel with a FAT built into the price — not bolted on after. Submit your requirements.