FAT vs SAT for Data Center E-Houses: What Is the Difference?

Factory Acceptance Testing (FAT) checks a data center E-House and its specified equipment before shipment, usually at the manufacturing or assembly location. Site Acceptance Testing (SAT) checks the installed package at the project site, where connections, interfaces, and operating conditions can be verified. In short, FAT helps confirm that the supplied system matches agreed requirements before dispatch; SAT helps confirm that it works as intended after installation. Neither test replaces the other, and the exact scope should be defined in the project’s contract and commissioning plan.

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For buyers, the practical distinction is where each test happens and what it can prove. FAT can identify equipment, wiring, documentation, and functional issues before transport; SAT can reveal installation or integration issues that are not visible at the factory. We recommend agreeing on test procedures, responsibilities, and pass/fail criteria before production begins.

Quick Difference Summary

• FAT: Pre-shipment verification at the factory or assembly facility, using the agreed design documents and test procedures.
• SAT: Post-installation verification at the project site, including relevant site connections and interfaces with other systems.
• Shared purpose: Both provide documented evidence for project acceptance, but they address different stages and conditions.
• Important limit: Passing FAT does not prove that site installation, external cabling, or integration is correct.

What FAT Covers for a Data Center E-House

An E-House is a prefabricated electrical building or enclosure that can contain electrical distribution and control equipment. Its configuration varies by project, so the FAT scope should follow the approved drawings, equipment list, specifications, and purchase order rather than a generic checklist. Depending on the supplied scope, checks may cover physical condition, equipment identification, internal wiring, labeling, and document completeness.

Typical FAT checks

• Compare installed equipment and nameplate details against the approved equipment schedule.
• Inspect enclosure assembly, internal layout, cable routing, labeling, and accessible workmanship.
• Perform agreed electrical checks, such as continuity or insulation-resistance testing, where applicable to the design and procedure.
• Verify control logic, alarms, interlocks, or communication functions that can be tested with available factory interfaces or simulation.
• Record deviations, corrective actions, and the final status of each agreed test point.

FAT is most useful when the project team defines what “pass” means before witnessing starts. For example, a project may specify a 400 V AC, 50 Hz distribution system and require the FAT record to show the tested configuration against those design values. These figures are illustrative only; the actual voltage, frequency, and acceptance limits must come from the project’s approved documents.

What SAT Covers at the Project Site

SAT takes place after the E-House has been delivered, positioned, installed, and prepared for testing. The site team can check items that factory testing cannot fully establish, such as incoming and outgoing field connections, grounding and bonding interfaces, site-specific control wiring, and coordination with upstream or downstream equipment. Testing must follow the approved commissioning procedure and site safety controls.

Typical SAT checks

• Inspect the delivered E-House for transport or handling damage and confirm its installed position and orientation.
• Verify field cabling, terminations, grounding connections, and interfaces against approved site drawings.
• Confirm that relevant protection, control, and communication interfaces operate with connected equipment.
• Check agreed operating sequences under site conditions, using approved methods and authorized personnel.
• Document outstanding items, corrective work, retesting, and acceptance status.

SAT does not automatically mean energizing every circuit or operating the complete data center at full load. The safe and appropriate test scope depends on the design, project stage, available utilities, and commissioning plan. For instance, a plan might require a 30-minute observation of a defined operating sequence, but that duration is an example—not a universal FAT or SAT requirement.

FAT vs SAT: Comparison for Buyers

How the Two Tests Work Together

FAT and SAT are complementary acceptance stages, not competing alternatives. A well-planned FAT creates a clear record of the E-House configuration and any agreed factory test results. That record gives the site team a reference for checking what arrived and for identifying which issues are new, unresolved, or caused by installation and integration.

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To make the handover traceable, project teams can number each test point and connect it to a drawing, equipment tag, or procedure step. One practical example is to track 100% of the test points listed in the approved acceptance procedure as passed, failed, or not tested, with reasons recorded for exceptions. This is a documentation approach, not a universal acceptance rule; the contract defines the required scope and final acceptance conditions.

Example of a project-specific test value

If a control circuit is designed for 24 V DC, the FAT procedure may verify the relevant control functions using that specified supply, while the SAT procedure verifies the corresponding site connections and end-to-end signals. The 24 V DC value here is illustrative and should never be used in place of the actual approved design. Buyers should also agree how simulated inputs, unavailable site systems, and deferred tests will be recorded and closed.

Cost, Schedule, and Sourcing Considerations

FAT typically requires coordination before dispatch, including an agreed procedure, equipment readiness, witness arrangements, and a process for resolving deviations. SAT depends on site readiness, installation completion, access, safe work authorization, and the availability of connected systems. If either stage is planned late, it can create rework or delay acceptance, although the schedule impact depends on the project and the issue found.

For sourcing, clarify whether the quoted scope includes test documentation, buyer witnessing, repeat tests after corrective action, and support during site commissioning. Also establish who supplies test instruments, temporary utilities, simulation tools, and any external equipment needed for the procedure. These details help compare supplier offers on a like-for-like basis rather than price alone.

Common Buyer Mistakes

• Treating FAT as proof of site readiness: Factory tests cannot confirm every field connection or site interface.
• Using vague acceptance language: Terms such as “fully tested” are less useful than named procedures and measurable criteria.
• Leaving interfaces undefined: Identify which party is responsible for each cable, signal, communication link, and integrated test.
• Ignoring exceptions: Record not-tested items, open deviations, owners, and closure evidence rather than assuming they are accepted.
• Scheduling SAT before readiness: Confirm installation, utilities, permits, and required site equipment before booking testing.

Which Test Is Best for Your Project?

If your priority is verifying the supplied E-House before it leaves the factory, FAT is the relevant stage. If you need to confirm installation and operation with actual site systems, SAT is essential. For most projects that specify both stages, the stronger approach is to use FAT to verify the package and SAT to verify the installed system, with clear records linking the two.

Before placing an order, ask the supplier to review your acceptance requirements alongside the equipment scope, interface list, drawings, and delivery schedule. At Pushen, we recommend buyers define the FAT and SAT boundaries early, including witness points, pass/fail criteria, and responsibility for open items. Share your E-House specifications and project acceptance requirements with our team to discuss a test scope aligned with your procurement and commissioning plan.