FAT and SAT in engineering: understand Factory Acceptance Test and Site Acceptance Test, their differences, planning, evidence, retesting, integrated testing, and technical acceptance criteria.
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FAT and SAT are acceptance tests used to verify whether equipment, panels, automation systems, software, and engineering solutions meet defined requirements before acceptance. FAT means Factory Acceptance Test, and SAT means Site Acceptance Test.
The main difference is the timing and environment of verification. FAT takes place before shipment to the site, normally at the factory or in a controlled environment, to demonstrate compliance with specifications, functions, assembly, configuration, and documentation. SAT takes place after installation, in the actual environment, and verifies whether the solution continues to meet requirements when connected to the project’s infrastructure, power, networks, instrumentation, interfaces, and operating conditions.
In critical projects, FAT and SAT should not be treated as simple commercial demonstrations. They are engineering activities with scope, prerequisites, procedures, acceptance criteria, responsibilities, witnessing, evidence, deviation records, and retesting. IEC 62381:2024 specifically organizes FAT, FIT, SAT, and SIT for process-industry automation systems, while ABNT NBR IEC 62337:2020 places testing, records, punch lists, commissioning, performance, and acceptance within the delivery cycle.
When these elements are defined before execution, the test no longer answers only “did it work?” and instead answers a technically defensible question: was the requirement demonstrated, under the specified conditions, with sufficient evidence to support the next engineering decision?
FAT and SAT: What Are They and What Is the Difference?
In engineering, FAT and SAT are two different verification gates. FAT demonstrates, before shipment, that the supplied item was built, configured, and tested against the applicable specification. SAT demonstrates, after installation, that the same item operates correctly in its final environment and with its actual interfaces.
| Aspect | FAT — Factory Acceptance Test | SAT — Site Acceptance Test |
|---|---|---|
| Location | factory, workshop, laboratory, or controlled environment | final installation site |
| Timing | before shipment or release to the site | after assembly, connection, and site preparation |
| Objective | demonstrate compliance of the supply with agreed specifications and functions | demonstrate operation under actual infrastructure and integration conditions |
| Dependencies | simulations, test benches, loads, and potentially emulated interfaces | actual power, networks, utilities, instruments, signals, and systems |
| Typical output | FAT report, deviations, punch list, and release or hold for shipment | SAT report, deviations, retests, and recommendation for the next stage |
| Does not demonstrate by itself | performance in the final environment | all system integration or overall project performance |
IEC 62381:2024 expands this logic to four test types for process-industry automation systems: FAT (Factory Acceptance Test), FIT (Factory Integration Test), SAT (Site Acceptance Test), and SIT (Site Integration Test). The distinction is useful because it separates acceptance of the individual system from validation of integrations among systems, first in a controlled environment and then at the site.
Therefore, FAT does not replace SAT, and SAT does not replace integrated testing. Each test reduces a different set of uncertainties. In critical systems, equipment may pass FAT and still fail SAT because of installation, power supply, network, grounding, addressing, or site configuration; likewise, it may pass an isolated SAT and fail when subjected to integrated scenarios with other systems.
FAT and SAT produce defensible acceptance only when the criteria are defined before testing. If the procedure is created after the equipment is already complete, the project risks adapting the criterion to the result obtained. Structure requirements, evidence, and acceptance criteria before executing the tests →
Why are these tests critical before technical acceptance?
Technical acceptance represents a formal decision by the contracting party. Accepting a delivery without adequate testing may mean assuming risks that will only emerge during operation.
| Without structured testing | With FAT, SAT, and integrated testing |
|---|---|
| Delivery validated by perception | Delivery validated by evidence |
| Failures appear during operation | Failures are identified before acceptance |
| Pending items without traceability | Pending items recorded and classified |
| Subjective acceptance | Criteria-based acceptance |
| Conflict between contracting party and supplier | Clearer responsibilities |
| Difficulty demonstrating compliance | Test reports and records support the decision |
In critical environments, incomplete testing can cause unavailability, safety failures, performance loss, operational risk, maintenance difficulties, and continuity problems.
What is FAT?
FAT means Factory Acceptance Test. It is performed before equipment, panels, software, controllers, or solutions are shipped to the installation site.
The purpose of FAT is to verify whether the solution complies with the basic requirements, technical specifications, contracted configuration, functions, and defined criteria before it is sent to the site.
When should FAT be used?
- electrical or automation panels;
- control systems;
- software configured in a factory environment;
- custom equipment;
- integrated electronic-security solutions;
- supervisory, monitoring, or automation systems;
- critical equipment for which site rework would be expensive or time-consuming.
What should be verified during FAT?
| Item | Example verification |
|---|---|
| Compliance with specification | Technical requirements, models, capacities, and configurations |
| Assembly and workmanship | Identification, internal organization, fastening, and protection |
| Basic functions | Commands, alarms, screens, logic, and expected responses |
| Configuration | Parameters, addresses, firmware, licenses, and versions |
| Documentation | Drawings, bill of materials, manuals, and certificates |
| Pending-item record | Failed items, corrections, and need for retesting |
FAT does not replace SAT. It reduces risks before shipment but does not demonstrate that the solution will operate under actual installation conditions. For critical supplies, the procedure should also define hold points, witness points, release conditions, deviation treatment, and criteria for partial or full repetition of the test.
The best time to discover an assembly, logic, or configuration error is before shipment. A well-specified FAT reduces site rework and prevents the installation schedule from absorbing problems that could have been resolved at the supplier. Structure the testing and witnessing plan before the supply is released →
What is SAT?
SAT means Site Acceptance Test. It is performed at the installation site after assembly, energization, configuration, preliminary integration, and system preparation.
SAT verifies whether the solution operates in the actual environment, considering infrastructure, network, power, interfaces, physical conditions, communication, installation, and site operation.
When should SAT be used?
- after equipment installation at the site;
- after system configuration;
- before technical acceptance;
- before assisted operation;
- before final handover;
- when there are dependencies on local infrastructure;
- when performance depends on integration with existing systems.
What should be verified during SAT?
| Item | Example verification |
|---|---|
| Physical installation | Fastening, identification, infrastructure, and workmanship |
| Power and grounding | Power supply, protection, continuity, and safety conditions |
| Communication | Network, addressing, latency, connectivity, and protocols |
| Local functionality | Commands, alarms, sensors, actuators, and responses |
| Preliminary integration | Exchange of signals, events, and data with related systems |
| Site documentation | Reports, photographs, measurements, checklists, and pending items |
SAT is an essential stage for preventing the contracting party from accepting a solution that worked on a test bench but not under actual project conditions. To be technically useful, SAT should start from a controlled configuration and record the differences between the condition approved during FAT and the condition actually installed.
Passing FAT does not justify assuming that SAT will be satisfactory. Transportation, assembly, parameterization, local interfaces, power, network, and field changes may alter the system condition. Connect SAT, functional testing, and commissioning in a single readiness and acceptance sequence →
What are integrated tests?
Integrated tests verify the combined operation of systems, subsystems, interfaces, and operational scenarios. They are especially important in environments where an interface failure can compromise operation even when each system works correctly in isolation.
In critical systems, the value of integrated testing lies in verifying the chain of events: a condition occurs, one system detects it, another receives the information, automation responds, an alarm is recorded, a team is notified, and an operational action is performed.
| System or interface | Example integrated test |
|---|---|
| CCTV and access control | Access event triggers the associated camera view and recording |
| Detection and alarm | Critical event triggers alert, notification, and operational procedure |
| Automation and supervision | Equipment failure generates an alarm and programmed response |
| Critical power and HVAC | Power failure triggers contingency and verifies continuity of operation |
| Data center | Interaction among power, cooling, monitoring, and alarms |
| Electronic security | Integration among sensors, video, access control, and operations |
FAT, SAT, and integrated testing in commissioning
Commissioning is a systematic process of verification, testing, documentation, and validation. ASHRAE Guideline 0 defines the Commissioning Process as a quality-focused process for verifying and documenting that planned, designed, installed, tested, operated, and maintained systems meet the owner’s requirements.
The ACG Commissioning Guideline also reinforces the role of communication, coordination, installation verification, startup, functional testing, operations and maintenance training, and complete documentation.
Within this process, FAT, SAT, and integrated testing are verification instruments. They are not the entire commissioning process, but they form part of the practical basis for demonstrating that the delivery meets requirements.
| Stage | Relationship to commissioning |
|---|---|
| FAT | Reduces risk before shipment to the site |
| SAT | Validates installation and operation at the site |
| Functional tests | Verify specific functions defined in the design |
| Integrated tests | Validate interfaces and operational scenarios |
| Test reports | Document evidence for the acceptance decision |
| Punch list | Records pending items and required corrections |
How do these tests support technical acceptance?
Technical acceptance should be based on criteria, evidence, and traceability. FAT, SAT, and integrated testing provide an important part of this foundation.
A test report may indicate whether the delivery should be accepted, accepted with conditions, subjected to corrections, or technically rejected.
| Test result | Possible acceptance decision |
|---|---|
| All criteria met | Full technical acceptance |
| Noncritical pending items | Conditional acceptance with action plan |
| Critical pending items | Technical rejection or acceptance hold |
| Incomplete testing | Request for completion |
| Insufficient evidence | Do not recommend acceptance until regularized |
For this reason, acceptance criteria should be defined before testing, preferably in the Terms of Reference, basic design, contract, commissioning plan, or requirements matrix. A “partially satisfactory” result is manageable only when the project has already defined which deviations block progress, which may be accepted conditionally, who approves the exception, and within what period retesting must occur.
A recorded failure is not a closed failure. The deviation, corrective action, evidence of correction, and retest must remain linked until the formal acceptance decision. Use technical acceptance to control pending items, evidence, and the decision to accept, conditionally accept, or reject →
Which evidence should be recorded?
A test without evidence has limited value. To support a technical decision, evidence must be traceable, organized, and linked to acceptance criteria.
| Evidence type | Examples |
|---|---|
| Documentary | Test procedure, test plan, acceptance criteria, and signed records |
| Visual | Photographs, videos, screens, labels, installations, and field measurements |
| System | Logs, alarms, events, screenshots, software reports, and supervisory-system records |
| Technical | Measurements, tests, functional results, protocols, and certificates |
| Operational | Checklists, training, simulations, and assisted-operation records |
| Contractual | Scope, requirements, warranties, responsibilities, and accepted pending items |
How to build a test plan
A test plan should define what will be tested, how it will be tested, who will participate, which criteria will be used, and which evidence will be accepted.
| Test-plan element | Function |
|---|---|
| Objective | Explains what the test is intended to validate |
| Scope | Defines tested systems, subsystems, and interfaces |
| Prerequisites | Indicates conditions required before starting |
| Procedure | Describes the test step by step |
| Acceptance criteria | Defines what will be considered approved |
| Responsible parties | Identifies who executes, witnesses, approves, and records |
| Evidence | Defines mandatory records |
| Pending items | Establishes how they will be recorded and classified |
| Retest | Defines when and how a failure will be reassessed |
This plan should be connected to the RACI matrix, risk matrix, schedule, contract, and commissioning plan.
RACI matrix in FAT, SAT and integrated testing
Testing involves different parties: owner, supplier, integrator, operations, maintenance, designer, technical consultant, commissioning team and Owner’s Engineering. The RACI matrix helps define who performs the work, who approves it, who must be consulted and who must be informed.
| Activity | Owner | Supplier | Technical Consultant | Operations |
|---|---|---|---|---|
| Define test criteria | A | C | R | C |
| Perform FAT | I | R | C | I |
| Witness SAT | A | R | R | C |
| Validate integrated tests | A | R | R | C |
| Record evidence | I | R | R | I |
| Classify open items | A | C | R | C |
Risk matrix in testing
The risk matrix helps prioritize failures, open items and decisions after testing. Not every failure has the same impact. Some prevent acceptance; others may be managed as conditional open items.
| Identified failure | Associated risk | Criticality | Recommended action |
|---|---|---|---|
| Integration does not communicate a critical event | Operational failure during an emergency | Critical | Correct and retest before acceptance |
| Missing SAT report | Lack of compliance evidence | High | Perform a documented test |
| Incomplete labeling | Maintenance difficulty | Medium | Regularize before final handover |
| Incomplete manual | Impaired operation | High | Complete documentation |
| Integrated scenario failure | Risk of unavailability or inadequate response | Critical | Review configuration and retest |
Testing in critical systems: application examples
Critical systems require more rigorous testing because failures can affect safety, continuity, availability, operation or compliance.
| Critical system | Recommended tests |
|---|---|
| Access control | SAT, functional testing, integration testing with CFTV and alarms |
| CFTV/VMS | Recording, live view, search, event and integration testing |
| Detection and alarm | Functional testing, alarm scenario, notification and operational response |
| Data center | Integrated testing of power, cooling, monitoring and alarms |
| Automation and supervision | Logic, event, communication and simulated-failure testing |
| Cabling and networks | Certification, connectivity, performance and As-Built documentation |
| Critical power | Transfer, autonomy, contingency, alarms and measurements |
Common mistakes in FAT, SAT and integrated testing
| Mistake | Consequence |
|---|---|
| Testing without acceptance criteria | Subjective discussion about approval |
| Not recording evidence | Difficulty supporting technical acceptance |
| Performing an incomplete SAT | Failures emerge during operation |
| Not testing integrations | Systems work independently but fail together |
| Not involving operations | The technical delivery may be impractical to operate |
| Not classifying open items | Critical items may be treated as minor details |
| Not planning retesting | Corrections are not verified |
| Accepting without final documentation | Maintenance and support are compromised |
How PMBOK 8 supports FAT, SAT and integrated testing
PMBOK 8 supports the management of these tests by reinforcing governance, scope, quality, risks, stakeholders, resources, value focus, tailoring and procurement.
| PMBOK 8 element | Application to testing |
|---|---|
| Governance Performance Domain | Defines how acceptance and escalation decisions will be made |
| Scope Performance Domain | Links tests to requirements, deliverables and acceptance criteria |
| Risk Performance Domain | Classifies failures, open items and operational risks |
| Stakeholders Performance Domain | Defines who participates, approves, is consulted and is informed |
| Resources Performance Domain | Organizes teams, suppliers, operations and specialists |
| Procurement Appendix | Connects testing to contracting, suppliers and responsibilities |
| Tailoring | Adapts the level of testing to the size and criticality of the system |
How consulting engineering supports testing and acceptance
Consulting engineering can support the owner before, during and after testing. Before FAT, the quality of the event depends on a consistent Vendor Inspection and an ITP/PIT that defines intervention points, criteria and records. After installation, SAT and integrated testing become part of the commissioning journey. This support is especially important when the owner needs independent analysis to validate deliverables, classify open items and decide on acceptance.
The scope may include:
- definition of test criteria;
- preparation or review of the test plan;
- witnessing FAT and SAT;
- validation of integrated tests;
- evidence analysis;
- classification of open items;
- post-test risk matrix;
- technical acceptance opinion;
- support for assisted operation;
- recommendation for acceptance, conditional acceptance or technical rejection.
In complex projects, this support may also be provided within an Owner’s Engineering engagement. The value of independent involvement lies in preserving traceability between specification, procedure, witnessing, result, deviation, retest and acceptance without replacing the responsibility of the manufacturer or contractor.
Witnessing a test does not mean assuming the supplier’s responsibility. Owner’s Engineering acts to protect the owner’s requirements and acceptance criteria, technically documenting what was demonstrated and what remains open. Structure independent witnessing of FAT, SAT and integrated testing on behalf of the owner →
Practical checklist for FAT, SAT and integrated testing
| Question | Status | Note |
|---|---|---|
| Have the acceptance criteria been defined? | Yes / No / Partial | They must be linked to the scope and requirements |
| Is there an approved test plan? | Yes / No / Partial | It must define the procedure, responsibilities and evidence |
| Have the prerequisites been met? | Yes / No / Partial | Installation, power, network, configuration and documentation |
| Was FAT recorded when applicable? | Yes / No / Partial | Reduces risk before shipment to site |
| Was SAT performed on site? | Yes / No / Partial | Validates operation under real conditions |
| Were integrated tests performed? | Yes / No / Partial | Validates interfaces and operational scenarios |
| Was the evidence attached? | Yes / No / Partial | Reports, photos, logs, measurements and screenshots |
| Were open items classified? | Yes / No / Partial | Separate critical, high, medium and low items |
| Is there a retest plan? | Yes / No / Partial | Corrections need to be verified |
| Is the acceptance recommendation clear? | Yes / No / Partial | Accept, condition, supplement or reject |
FAT and SAT as engineering gates, not delivery formalities
FAT and SAT deliver the greatest value when they are treated as decision gates. FAT should determine whether the supply can be released for shipment or site work; SAT should determine whether the installed condition has been sufficiently demonstrated to proceed to functional testing, integrated testing, commissioning or the acceptance milestone defined for the project.
This logic requires a continuous traceability chain: requirement → procedure → test condition → result → evidence → deviation → correction → retest → decision. A simple “approved” record loses strength when it is impossible to reconstruct which requirement the test was performed against, which configuration was used and who had authority to witness or accept it.
IEC 62381:2024 reinforces the need to clearly establish the scope, responsibilities and activities for FAT, FIT, SAT and SIT for automation systems. ABNT NBR IEC 62337:2020, in turn, places verifications, reports, punch lists, retests, commissioning, performance and acceptance within a sequence of milestones. Together, these references help prevent acceptance testing from being reduced to a demonstration without criteria.
For the owner, the practical consequence is direct: accepting equipment or a system should result from sufficient evidence, not schedule pressure or a perception that it works. The more critical the asset, the more important it is to define criteria, witnessing, tolerances, documentation, exceptions and retest conditions in advance.
Technical references
[1] INTERNATIONAL ELECTROTECHNICAL COMMISSION. IEC 62381:2024 — Automation systems in the process industry — Factory acceptance test (FAT), site acceptance test (SAT), and site integration test (SIT). The 2024 edition defines requirements and checklists for FAT, FIT, SAT and SIT and the allocation of responsibilities between the parties. Official reference: IEC 62381:2024 — IEC Webstore.
[2] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS. ABNT NBR IEC 62337:2020 — Comissionamento de sistemas elétricos, de instrumentação e de controle de processos industriais — Fases e marcos específicos. The Brazilian standard adopts IEC 62337:2012 and structures completion, pre-commissioning, commissioning, performance testing and acceptance. Official international reference: IEC 62337:2012 — IEC Webstore.
[3] INTERNATIONAL ELECTROTECHNICAL COMMISSION. IEC 62382:2024 — Control systems in the process industry — Electrical and instrumentation loop check. Complementary reference for loop-check procedures and specifications between completion of loop construction and the start of cold commissioning. Available at: IEC 62382:2024 — IEC Webstore.
[4] ASHRAE. Guideline 0-2019 — The Commissioning Process. Reference for a commissioning process oriented to owner requirements, acceptance criteria, documentation and training throughout the project life cycle. Official information: ASHRAE — Standards and Guidelines.
Frequently asked questions
FAT stands for Factory Acceptance Test. It is the acceptance test performed before shipment to site, normally at the factory or in a controlled environment, to verify whether the equipment, panel, software or system meets the specifications, functionalities and criteria defined for the supply.
SAT stands for Site Acceptance Test. It is the acceptance test performed at the final installation site to verify operation under the project’s real infrastructure, power, network, interface, configuration and operating conditions.
FAT takes place before shipment and verifies the supply in a controlled environment. SAT takes place after installation and verifies the solution in the real environment. FAT reduces manufacturing and configuration risks; SAT verifies the effects of installation, infrastructure, interfaces and local conditions.
No. Equipment may pass FAT and still present problems after transportation, installation, connection, parameterization or integration. SAT verifies the installed condition and, when applicable, should be complemented by functional and integrated tests.
In IEC 62381:2024, FAT is Factory Acceptance Test, FIT is Factory Integration Test, SAT is Site Acceptance Test and SIT is Site Integration Test. The sequence distinguishes acceptance of individual systems from validation of integrations, first at the factory and then at the installation site.
The plan should define scope, test object, reference documents and revisions, prerequisites, procedure, test cases, acceptance criteria, responsibilities, hold points and witness points when applicable, instruments, evidence, deviation handling and retest rules.
The failure should be recorded as a deviation or open item, linked to the requirement and test case, classified by impact, corrected by the responsible party and retested. Release to the next stage must follow the criteria previously defined for blocking and conditional items.
FAT and SAT are verification tools that may be part of the commissioning strategy, but they do not constitute the entire process. Commissioning also addresses readiness, functions, interfaces, operation, performance, documentation, open items and criteria for moving between project milestones.
Complementary technical materials
Related solutions
- Requirements, Evidence and Acceptance Criteria Management
- Open Items, RFIs and Nonconformities Management
- Process, Workflow and Technical Approval Management
- Project, Program and Portfolio Governance
Related services
- Equipment Commissioning
- Technical Procurement
- Owner’s Engineering
- Technical Support for Construction and Contract Supervision
- Technical Acceptance of Engineering Works and Services
Main content on the topic
- Manufacturing Inspection and Vendor Inspection
- Inspection and Test Plan (PIT/ITP)
- Hold Point, Witness Point and Review Point
- Engineering Acceptance Criteria
- QA/QC in Engineering Construction
- Nonconformity Report (RNC/NCR)
- Construction Data Book
