FAT verifies manufacturing, configuration, protection and load performance in a controlled environment. SAT proves the set with the real room, fuel, exhaust, distribution, ATS and critical loads. Neither replaces the other.
Agree the FAT-SAT matrix, load points, records, witnessing and acceptance criteria before ordering. FAT removes factory-scope defects; SAT closes site-interface risk.
1. Understand what this decision changes
FAT verifies equipment within the supply scope
Identity, configuration, assembly, controls, protection, leaks, vibration, load performance and documents belong here.
SAT verifies connection to the real site
ATS, cables, grounding, fuel, ventilation, exhaust, remote data and real loads can only be proved after installation.
Acceptance needs predefined evidence
“Runs normally” does not replace calibrated readings, raw data, events, photos and signed records.
2. Inputs to confirm before procurement
Build the matrix from contract scope, single-line diagram and critical-load recovery objectives.
- Approved specification, configuration and drawings
- Operating duty and required load points
- ATS, distribution, paralleling and monitoring interfaces
- Site fuel, cooling, ventilation, exhaust and grounding
- Witnesses, instruments, criteria and corrective workflow
3. How the main options compare
| Option or parameter | Where it fits | What must be verified |
|---|---|---|
| Standard functional FAT | Conventional single sets with moderate project risk. | Identity, protection, controls, leaks and stated load points. |
| Project-witnessed FAT | Paralleling, critical facilities or complex configuration. | Project logic, communications, simulated failures and signed records. |
| Complete SAT and integrated drill | Systems that must prove utility-loss-to-load-recovery performance. | Interfaces, transfer timing, staged loading and safe abort. |
4. The most common decision errors
Common mistakes
- Calling a no-load start a complete FAT
- Canceling site load tests because FAT passed
- Testing without frozen configuration and criteria
- Closing defects verbally without retest evidence
The later a defect is found, the higher the site delay, outage-window and responsibility cost.
5. What the technical specification must state
The specification should state at least
- Each FAT and SAT item, owner and witness point
- Load percentage, duration, steps and tolerance
- Instrument accuracy, calibration and raw-data format
- Alarm, protection, interlock and failure simulations
- Nonconformance, correction, retest and sign-off
Test records should be part of the final documentation and match the delivered configuration revision.
6. How to verify and make the final decision
Verification and acceptance
- Cross-check serials, plates, BOM and approved drawings
- Record electrical and engine data at every load point
- Simulate alarms, shutdowns, communications and transfer failures
- Verify ATS timing and critical-load restoration on site
- Close every defect with retest evidence
Even simple projects need baseline FAT and SAT; complex projects add project logic and system drills.
The goal is not merely to run the engine but to prove contracted functions and the real backup mission with traceable evidence.