What is a Factory Acceptance Test (FAT)?

A Factory Acceptance Test is done at the manufacturer’s facility before equipment is shipped. It’s a thorough check that all parts meet the agreed specifications. As one industry guide puts it, FAT “involves a series of tests and inspections… conducted by the manufacturer” to ensure the equipment meets design criteria before delivery. For example, engineers might run functional tests, stress runs, and safety checks on a generator or control panel under controlled conditions. They will examine drawings and documentation, verify calibrations, and simulate operating conditions as best as possible. Essentially, FAT is the factory saying “Yes, it works as promised.”

Who performs FAT? The vendor or OEM (Original Equipment Manufacturer) leads the FAT, often with quality engineers and sometimes with the customer or a third‐party witness present. A packaging-machine maker explains that FAT “takes place with the client present,” where the production team and project manager assist through testing. In the power and infrastructure world, FAT teams include factory test engineers, and customers may send engineers to witness tests. The goal is to catch and fix issues early. As one source notes, doing a proper FAT “[saves] effort, time and money,” because problems are easier to solve before shipping.

What FAT includes: A typical FAT covers functionality and performance. For a mechanical system, this might mean running motors, checking speeds or flow rates, and verifying safety interlocks. For an electrical substation, it could include energizing switchgear, checking breaker operations, and running control logic tests. FAT usually includes:

  • Functional tests: Does each feature work? (e.g. sensor trips, alarms, control loops)

  • Performance tests: Does it meet specs? (e.g. motor runs at rated speed, UPS delivers rated load)

  • Safety/interlock checks: Are failsafes working? (e.g. emergency stop, protection relays)

  • Documentation review: Verify manuals, wiring diagrams, data sheets.

  • Calibration checks: Ensure instruments and meters are in spec.

By the end of FAT, the equipment should be signed off as ready for shipment. “After completing the FAT, the owner… agrees with the vendor whether the system is ready to be shipped,” confirming all pre-shipment checks are done.

What is a Site Acceptance Test (SAT)?

A Site Acceptance Test takes place after FAT, once the equipment has been delivered and installed at the customer’s location. The SAT verifies that the installed system works correctly in its actual environment. In other words, even though everything passed in the factory, the team needs to make sure nothing broke in transit or went wrong during setup.

According to one operations guide: “A Site Acceptance Test… is performed directly at the customer’s site after a successful Factory Acceptance Test”. It makes sure the machine or plant is properly installed, configured, and “ready for operation”. The system is now hooked up to real utilities (power, network, chilled water, etc.), so SAT checks things FAT couldn’t fully test.

Who performs SAT? Typically the customer’s engineering/commissioning team works together with vendor or contractor field engineers during SAT. For example, equipment suppliers often send service reps to assist, while the owner’s technicians watch and learn. The goal is to simulate real operation: e.g. running the plant at load, integrating with control systems, and verifying safety in the live setup.

What SAT includes: SAT often covers integration and performance under real conditions. It may involve:

  • Integration and connectivity tests: Ensuring the new equipment talks correctly with existing systems (networks, SCADA, control room consoles, etc.). For instance, verifying a new substation communicates with the grid control center, or a data-center UPS properly connects to the building’s power and monitoring network.

  • Operational tests: Running the equipment under normal (and sometimes extreme) loads to see that it performs as expected. For a generator this might mean running it up to full load or “cranking” a turbine to its rated rpm.

  • Safety and interlock checks: Confirming emergency stops, alarms and shutdown systems work in the actual installed context.

  • Documentation and user training: Often SAT includes handing over final manuals and training on-site staff, so operators understand the equipment.

One guide notes SAT may involve simulating real-world scenarios “to ensure the equipment operates correctly within the customer’s specific environment”. In short, SAT is like turning the key in the ignition at the customer’s site – you check that it truly starts and runs in real life. Any problems found (say a calibration drifted or a network setting was wrong) are fixed on-site.

Key Differences at a Glance

  • Location & Timing: FAT is done at the factory (before shipping); SAT is done at the customer’s site (after installation).

  • Purpose: FAT checks that the built system meets all specs and works in a controlled environment. SAT checks that the same system works correctly in its actual installed environment.

  • Scope: FAT often uses simulators or emulators for external systems. SAT uses real services and loads. In FAT you might fake inputs (software simulations or test benches); in SAT you plug into actual utilities (power grid, water supply, etc.) and final control networks.

  • Who’s involved: FAT is led by the manufacturer’s engineers (and often witnessed by the customer’s reps). SAT is led by the project’s commissioning team (often the installing contractor or vendor field engineers with customer oversight).

  • Documentation: FAT typically has very detailed test protocols and paperwork (since it’s a controlled factory check). SAT paperwork is simpler – it focuses on final configurations and any on-site adjustments.

A handy analogy: FAT is like test-driving or inspection before delivery, while SAT is like plugging in and powering up your new gadget at home. For example, imagine the process of buying a custom smartphone. The manufacturer would run a full check that all apps and sensors work (FAT) before shipping. Once you get it home and set it up with your Wi-Fi and SIM card, you power it on and test it in your normal use-case environment (SAT). FAT says “it’s working” in theory; SAT says “it’s working here”.

When and Why

FAT always comes first in the timeline. It typically happens after design and fabrication but before shipment. Once the equipment passes FAT, it’s shipped. After delivery and installation at the customer’s site, SAT is performed. A typical project workflow is:

  1. FAT (Factory): Equipment built and tested in factory. Issues fixed, paperwork signed.

  2. Shipment: Goods packed up and transported to site.

  3. Installation: Equipment physically installed at the project location (e.g. a power plant, building, or data center).

  4. SAT (Site): Installed equipment tested and tuned on site.

  5. Commissioning: Final commissioning or startup – the system is brought into service.

This step-by-step approach is widely used in industries everywhere. It’s sometimes called “FAT → Shipment → Installation → SAT → Commissioning.” For example, in Indian power projects, the buyer (like NTPC or a utilities company) will demand FAT for major equipment (turbines, transformers, switchgear) so they can verify them at the factory. After installation at the power plant, they run SATs (often dubbed “cold start” tests in the field) before the plant goes live. Similarly, a data center rollout may have rack and UPS manufacturers do FAT in their factories, then the on-site IT team does SAT once racks are set up and powered in the computer hall.

The purpose of this sequence is risk mitigation. Finding and fixing a fault at the factory is usually much easier and cheaper than after installation. In a blog on FAT/SAT, PQE Group notes that checking equipment at the supplier’s facility “saves time and costs” because “if something… goes wrong, it is easier to solve it” there than on site. In short: don’t ship it until you’re sure it works (FAT), and once it’s at the site, don’t start it until you’re sure it survived shipping and installation (SAT).

Real-World Examples

To make it concrete, here are a few scenarios:

  • Power Plants (India/global): A gas turbine or boiler is assembled and FAT-tested at the manufacturer’s works – they’ll spin it up, check control logic, safety shutoffs, etc. After shipping to the plant, engineers install it, connect it to grid and auxiliaries, then run an SAT (often as part of cold commissioning) to verify it synchronizes to the grid and runs under load.

  • Telecom/IT Infrastructure: Consider a telecom base station or fiber-optic network. Equipment like radio units or switches might be FAT tested at the factory (with simulated network load). Once installed on the tower or data center, the SAT would involve connecting to the actual network and verifying the signal strength, handover, and internet traffic flow.

  • Data Centers: A UPS (uninterruptible power supply) or a server rack might go through FAT in the factory (running mock loads, checking battery backups). After shipping and installation, SAT would test the UPS under the data center’s actual electrical load and check that all servers power on correctly.

  • Manufacturing Lines: For automated assembly lines, each robotic station or conveyor system is FAT-tested (ensuring each robot arm moves as programmed). After the line is built on the factory floor, SAT confirms that all stations communicate and the line runs end-to-end, producing a test part without errors.

  • Pharma/Medical (globally): In cleanrooms or labs, equipment undergoes FAT to meet regulatory standards. Then SAT confirms it still meets GMP/ISO conditions in the actual plant environment.


Throughout India’s industrial projects (power plants, refineries, cement plants, telecom rollouts, etc.), and globally as well, this two-step acceptance process is standard practice. It gives both parties confidence. As one industry article puts it, FAT lets customers “get familiar with electrical equipment before it arrives onsite”, while SAT validates “that the system is installed properly and is operational”.

Remember with an Analogy

A favorite analogy is test-driving a new car. At the factory level, imagine driving the new car on a private track (FAT): you check the engine, brakes, lights, and that everything works as per spec. Once it’s delivered to you, doing the SAT is like driving it on public roads for the first time – you verify it starts, that it handles hills and traffic (real conditions), and that all features (AC, radio, etc.) work with your personal settings.

Another analogy is a smartphone: FAT is the factory powering on a phone with diagnostics and checking each function. SAT is like when you bring that phone home and insert your SIM, log into Wi-Fi, and make sure calls, texts and apps work in your hands.

In each case, FAT catches factory-level issues (“Does the car operate by design?”) and SAT catches site-specific ones (“Does the car work in my city’s climate and on its roads?”).

In short: FAT happens first at the factory to prove quality before shipping. SAT happens next on site to prove the system actually runs in its final home. Together, they help ensure your big project will start up smoothly when it really counts.

Sources: FAT and SAT processes are standard in industry. The definitions and workflows above are drawn from industrial equipment vendors and consultants (e.g. DXP, Kneat, operations1, PQE, Gashor, CDA USA) who explain that FAT is done at the manufacturer and SAT at the customer site.

Written By 
Aash Gates
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