FAT vs. SAT - Factory Acceptance Test vs. Site Acceptance Test

Executive Summary

Factory Acceptance Test (FAT) and Site Acceptance Test (SAT) are two different acceptance stages used for industrial equipment, machinery, automation systems, electrical panels, control systems and integrated technical solutions.

FAT is performed at the manufacturer's or integrator's facility before shipment. It verifies that the equipment has been built, configured and tested against the agreed technical and functional requirements in a controlled environment.

SAT is performed after delivery, installation and site integration. It verifies that the equipment operates correctly in the actual customer environment, with the real utilities, interfaces, field devices, network connections, safety conditions and operating dependencies that cannot be fully reproduced at the factory.

This guide focuses on FAT and SAT as equipment-level acceptance gates. It deliberately stays separate from Supplier Audit, Pre-Shipment Inspection and First Article Inspection. A supplier audit evaluates the organization and its systems; PSI checks a finished shipment lot; FAI validates first-production characteristics. FAT and SAT validate the performance and readiness of a complete machine, system or technical package against an agreed acceptance protocol.

The strongest FAT/SAT programs define acceptance criteria before testing begins, separate factory-verifiable items from site-dependent items, document every result, control punch-list items and link final acceptance to clear evidence rather than subjective statements that the system 'looks ready'.

1. What Is a Factory Acceptance Test (FAT)?

FAT is a planned acceptance test performed before shipment at the manufacturer's, OEM's, panel builder's or system integrator's facility.

The buyer and supplier use an approved protocol to verify construction, configuration, functionality, documentation and agreed performance before the equipment leaves the controlled factory environment.

2. What Is a Site Acceptance Test (SAT)?

SAT is performed after the equipment has been delivered, installed and connected at the customer's site.

It verifies functions that depend on the real operating environment and confirms that installation, integration and site conditions have not introduced unacceptable problems.

3. FAT and SAT Are Not the Same Test Repeated Twice

Some checks may appear in both protocols, but the purpose changes.

FAT emphasizes supplier-controlled build and function before shipment. SAT emphasizes site installation and integration after delivery.

4. FAT/SAT vs. Supplier Audit

A supplier audit reviews the supplier's capability, systems, processes and controls.

FAT/SAT evaluates whether a specific machine or system meets the agreed acceptance criteria. A supplier may pass an audit and still produce a machine that fails FAT.

5. FAT/SAT vs. Pre-Shipment Inspection

Pre-shipment inspection typically uses product and shipment checks such as quantity, workmanship, packaging and selected functional tests.

FAT is usually deeper and protocol-driven for a specific engineered machine or system, with defined operating sequences, alarms, interlocks, software and performance criteria.

6. FAT/SAT vs. First Article Inspection

FAI verifies first-production characteristics against engineering requirements. FAT/SAT verifies assembled equipment or systems through functional and integration testing.

A component can pass FAI and still be installed incorrectly in a machine that later fails FAT or SAT.

7. Define Acceptance Philosophy in the Contract

FAT and SAT should be contractually anticipated before design and manufacturing are complete.

The contract or technical agreement should identify which tests are required, who attends, which results are binding and what happens after failure.

8. Build the FAT/SAT Responsibility Matrix

Acceptance testing is cross-functional.

The parties should know who prepares the protocol, executes tests, witnesses results, approves deviations and signs final acceptance.

9. Create the Acceptance Requirements Matrix

Every contractual or technical requirement should be mapped to a planned verification method.

The matrix prevents important requirements from disappearing between design documents, FAT and SAT.

10. Separate Factory-Verifiable and Site-Dependent Requirements

A good acceptance strategy avoids both extremes: trying to simulate everything at FAT and postponing too much to SAT.

The division should reflect what can be proven realistically at each stage.

11. Define FAT Readiness Criteria

FAT should start only when the supplier is genuinely ready.

Using buyer attendance as a troubleshooting session wastes time and weakens confidence.

• Equipment mechanically complete.
• Required wiring complete.
• Released software loaded.
• Internal supplier tests completed.
• Required instruments available and calibrated.
• Open design changes controlled.
• FAT protocol approved.
• Required documents ready.

12. Use a Formal FAT Protocol

The FAT protocol should define test steps, expected results, evidence and acceptance status.

A protocol turns a demonstration into an auditable test.

13. Verify Equipment Identity and Build

Before functional testing, confirm that the equipment presented at FAT is the equipment ordered.

Check serial numbers, model, major components, drawings, options and agreed revisions.

14. Verify Mechanical Completion at FAT

Mechanical checks should confirm that the equipment is complete enough for safe functional testing and shipment.

The exact scope depends on the machine or system.

15. Verify Electrical Construction

Electrical FAT can include checks of wiring, protection, labeling, terminals, grounding and component installation against released drawings.

16. Verify Software and Firmware Baselines

Software is part of the acceptance baseline.

Record PLC, HMI, controller, drive, firmware or application versions so the tested configuration can be reconstructed later.

17. Test Normal Operating Sequences

FAT should prove the defined operating sequences, not only that individual components can switch on.

Test automatic and manual modes where relevant, including start-up, normal operation, stop and reset behavior.

18. Test Alarms and Fault Handling

A system should behave correctly when something goes wrong.

Alarm testing should verify detection, indication, response, reset conditions and any required logging.

19. Test Interlocks and Safety Logic

Safety and protective interlocks should be tested according to the agreed scope and applicable responsibilities.

Site-dependent safety functions may require final SAT validation even when internal logic is checked during FAT.

20. Test Human-Machine Interfaces

HMI testing should check operator controls, status display, alarm messages, permissions, language and navigation relevant to the agreed requirements.

• Correct equipment status.
• Correct buttons / commands.
• Alarm wording and priorities.
• User access levels.
• Setpoint limits.
• Language / units where specified.

21. Test Communication Interfaces

Where the equipment communicates with other systems, FAT can simulate interfaces and SAT can validate the actual network or field connection.

22. Verify Instrumentation and I/O

Input/output testing confirms that signals are interpreted correctly.

Factory I/O may be simulated; SAT should validate field wiring and real device behavior where applicable.

23. Perform Performance Tests Where Contractually Required

Some equipment must demonstrate throughput, accuracy, energy use, response time, cycle time or another measurable performance target.

The test method and operating conditions should be agreed in advance.

24. Control Test Instruments and Temporary Equipment

Acceptance results may depend on instruments, simulators or temporary loads.

Identify critical test equipment and calibration where measurement validity matters.

25. Verify FAT Documentation Package

FAT should confirm that required project documentation is sufficiently complete for shipment and installation.

The exact documentation list should be defined by contract.

26. Record FAT Punch-List Items

Not every open item necessarily blocks shipment, but every item should be classified and owned.

The acceptance protocol should define which punch items are shipment-blocking and which may be closed later.

27. Define FAT Pass, Conditional Pass and Fail

The final FAT status should follow pre-agreed logic.

A conditional pass is useful only if the remaining items are explicitly documented and do not undermine safe shipment or later installation.

28. Control FAT Retesting

After a failed FAT item, the supplier should correct the cause and repeat the affected test.

Broader retesting may be necessary when the correction changes software, hardware or other interconnected functions.

29. Freeze the FAT-Approved Configuration

The tested configuration should become a controlled baseline before shipment.

Unauthorized changes after FAT can invalidate the acceptance evidence.

30. Prepare Equipment for Shipment Without Losing the Baseline

Dismantling, transport locks, cable disconnection and shipping preparation can change the equipment state.

The supplier should document items that must be restored or verified during site installation.

• Transport locks and supports.
• Disconnected cables / plugs.
• Removed assemblies.
• Site-reassembly instructions.
• Sensitive alignment points.
• Configuration backups before shipment.

31. Define SAT Entry Criteria

SAT should not begin simply because the equipment arrived.

The site should be ready enough for a valid integrated test.

• Equipment installed and mechanically complete.
• Required utilities available.
• Site wiring completed.
• External interfaces available.
• Approved software baseline restored.
• Installation checks complete.
• Safety prerequisites met.
• SAT protocol approved.

32. Verify Installation Before SAT Function Testing

First confirm that transport, installation and site assembly did not introduce defects.

Installation verification can include level, alignment, connections, cable termination, grounding, piping, orientation and environmental conditions.

33. Verify Site Utilities

SAT uses real utilities, so actual conditions should be measured or confirmed against equipment requirements.

Marginal site utilities can cause failures that did not appear during FAT.

34. Validate Real Field Devices and Interfaces

SAT should replace factory simulation with actual field equipment wherever the project scope requires it.

This is one of the main reasons SAT exists.

35. Perform Site I/O and Loop Checks

Field wiring errors can be introduced during installation even when FAT was perfect.

SAT should verify relevant loops from field device to control system and back to the physical output.

36. Re-Test Safety Functions in the Site Context

Safety behavior that depends on site wiring, external equipment or physical zones should be validated after installation according to the applicable safety plan.

37. Perform Integrated Operating Tests

SAT should demonstrate that the system works with the surrounding plant or project environment.

This may involve upstream/downstream equipment, databases, utilities, field devices or operator workflows.

38. Test Site-Specific Performance

If final contractual performance depends on the real site, the decisive performance test may belong at SAT.

Factory performance results should not be presented as proof of site performance when real process conditions are materially different.

39. Verify Training and Handover Readiness

SAT often occurs near operational handover.

The buyer should confirm whether required operator and maintenance training, manuals, backups and spare-parts information are complete.

40. Create the SAT Punch List

Open site issues should be recorded separately from FAT history.

Each SAT punch item should state the issue, owner, priority, action and closure evidence.

41. Define Final SAT Acceptance

Final acceptance should be based on the agreed SAT criteria and punch-list rules.

If commercial handover, warranty start or retention release depends on SAT, those triggers should be clear and documented.

42. Control Changes Between FAT and SAT

Equipment often changes between factory test and site test because of transport, installation or engineering updates.

Every change should be logged and its effect on the FAT baseline assessed.

43. Use Remote FAT Carefully

Remote FAT can reduce travel and support international projects, but it requires strong evidence and preparation.

The buyer should define camera coverage, live data access, document sharing, witness interaction and how measurements will be verified.

44. Decide When Independent Witnessing Is Appropriate

Third-party or consultant witnessing can be useful when the buyer lacks local resources, contract requirements demand independence or the equipment is high-value and complex.

The witness still needs a clear approved protocol; independence does not replace technical clarity.

• Define witness authority.
• Confirm technical competence.
• Use the buyer-approved acceptance protocol.
• Clarify whether the witness can accept deviations.
• Retain signed evidence.

45. Manage FAT/SAT Deviations Formally

A deviation from the agreed requirement should remain visible.

The supplier should not redefine the acceptance criterion during the test simply because the system behaves differently than expected.

46. Maintain FAT/SAT Evidence as Project Records

Acceptance records should remain traceable after handover.

They can support warranty investigations, future modifications, repeat systems and dispute resolution.

• Approved protocols.
• Signed test sheets.
• Software / firmware versions.
• Photographs or data where relevant.
• Punch lists and closure evidence.
• Deviation approvals.
• Acceptance certificates.

47. FAT/SAT KPI Dashboard

48. Common FAT/SAT Mistakes

• Writing the protocol after the machine is already complete.
• Starting witnessed FAT before supplier internal testing is finished.
• Using demonstrations instead of measurable pass/fail criteria.
• Postponing factory-testable failures to SAT.
• Failing to record software and firmware versions.
• Allowing post-FAT changes without impact review.
• Starting SAT before site utilities and interfaces are ready.
• Assuming a FAT pass guarantees site integration.
• Mixing legal safety validation with ordinary commercial acceptance without clear responsibility.
• Using 'accepted with comments' without a controlled punch list.
• Closing punch items without retest evidence.
• Linking payment to acceptance without defining the acceptance mechanism in advance.

49. FAT/SAT Readiness Scorecard

50. 30-Day FAT/SAT Planning Framework

51. Practical Example: Industrial Automation System

A manufacturer supplied an automated inspection and conveyor system to a new production plant.

The contract required FAT before shipment and SAT after installation. During FAT, the supplier demonstrated the full automatic sequence using simulated sensors and test products. The test also verified alarms, motor protection, HMI screens, internal I/O, PLC software version and throughput under factory conditions.

The FAT identified two blocking issues: an emergency-stop reset sequence did not match the approved functional specification, and the data interface generated duplicate records under one fault condition. Both were corrected and regression-tested before shipment.

At the customer site, the equipment was installed and connected to the real line, plant network and upstream/downstream machines. SAT then exposed a different problem: one site sensor had been wired to the wrong input and a network-security setting blocked communication with the customer's production database.

Those issues could not have been meaningfully proven during factory testing because they depended on the real installation environment.

After correction, the integrated line completed the agreed site performance test and the remaining minor documentation items were placed on a controlled punch list.

FAT prevented known equipment defects from being shipped. SAT confirmed that the accepted factory system also worked after transport, installation and integration into the customer's real plant.

52. Complete FAT/SAT Checklist

• Define FAT and SAT requirements before manufacturing begins.
• Map every acceptance requirement to FAT, SAT or another verification stage.
• Define buyer, supplier and witness responsibilities.
• Approve FAT/SAT protocols before testing.
• Confirm FAT readiness before buyer attendance.
• Verify equipment identity and build configuration.
• Record software, firmware and parameter versions.
• Test normal operating sequences.
• Test alarms, faults and interlocks.
• Test required safety logic within the defined acceptance scope.
• Test HMI and communications.
• Verify I/O and instrumentation.
• Perform measurable performance tests where required.
• Verify required documentation.
• Classify FAT punch-list items and shipment blockers.
• Retest corrected functions.
• Freeze the FAT-approved baseline.
• Log every post-FAT change.
• Confirm SAT site readiness and utilities.
• Verify installation and field wiring.
• Replace simulations with actual site interfaces.
• Perform site I/O / loop checks.
• Re-test site-dependent safety functions.
• Perform integrated operating and site-performance tests.
• Confirm training and handover documentation.
• Control SAT punch-list closure.
• Link commercial acceptance only to clearly defined criteria.
• Retain signed FAT/SAT evidence and acceptance records.

53. Frequently Asked Questions

What is the difference between FAT and SAT?

FAT is performed before shipment at the supplier or integrator facility; SAT is performed after installation at the actual customer site.

Does a FAT pass mean SAT will automatically pass?

No. Transport, installation, utilities, field wiring and real interfaces can create site-specific failures.

Is FAT the same as pre-shipment inspection?

No. FAT is typically a detailed acceptance protocol for a specific engineered machine or system; PSI is a finished-shipment conformity inspection.

Is SAT just a repeat of FAT?

No. Some functions may be repeated, but SAT should emphasize actual installation, site utilities, field devices and integrated operation.

Who writes the FAT protocol?

Often the supplier drafts it, but the buyer should review and approve it before testing.

Should FAT be linked to payment?

It can be, if the contract clearly defines the acceptance criteria, witnessing, retest rules and payment milestone.

What is a FAT punch list?

A controlled list of open issues identified during FAT, with category, owner, due date and closure evidence.

What happens if software changes after FAT?

The change should be version-controlled, impact-assessed and retested where it can affect accepted functionality.

Can FAT be done remotely?

Yes for suitable projects, provided live visibility, evidence, witness control and protocol requirements are strong enough.

What should SAT verify?

Installation, utilities, field I/O, actual interfaces, site-dependent safety, integrated operation and any performance criteria that depend on the real environment.

Can XibUp help connect buyers with equipment manufacturers and integrators?

XibUp can support discovery and networking with manufacturers, integrators, suppliers and industrial buyers. FAT/SAT acceptance remains a project-specific technical and contractual responsibility between the parties.

Conclusion

FAT and SAT create two distinct evidence gates in engineered equipment projects.

FAT verifies that the supplier has built and configured the equipment correctly before shipment. SAT verifies that the delivered equipment also works after installation with the customer's real utilities, field devices, networks, surrounding systems and operating conditions.

The strongest acceptance process separates those responsibilities clearly, uses measurable protocols, controls configuration changes and refuses to treat demonstrations, punch lists or informal comments as substitutes for objective acceptance evidence.

Related Guides

• First Article Inspection (FAI) Guide
• Pre-Shipment Inspection Guide
• Supplier Audit Checklist
• Supplier Quality Agreement Guide
• Supplier Change Control and Product Change Notification (PCN) Guide