FAT, SAT and IST in Data Center Projects Explained
Three acronyms, three questions: does the equipment work, does it work as installed, and do the systems work together. Here is how they fit in sequence.
The three tests
| FAT | SAT | IST | |
|---|---|---|---|
| Where | Factory | Site | Site |
| Question | Does the equipment meet the specification? | Does it work as installed and connected? | Do the systems work together, including during failures? |
| Typical scope | One equipment item or assembly, such as switchgear or a UPS | The installed equipment and its connections | Whole-facility scenarios |
| Sign-off | Client or representative witnesses | Contractor, supplier and client or commissioning agent | Commissioning agent and client |
Why all three
Each finds faults the others cannot. FAT catches manufacturing and configuration problems before delivery, SAT catches installation and interface problems, and IST catches system-level behaviour such as sequencing and control logic. Skipping one pushes the fault to a later, more expensive stage.
Relation to the commissioning levels
FAT corresponds roughly to the first commissioning level, SAT to the installation and functional levels, and IST to the last. See commissioning levels explained.
Written by the Vision Matrix Institute editorial team. Worked examples use stated, illustrative assumptions; check them against your project data, the applicable standards and manufacturer datasheets before use.
Frequently Asked Questions
What is FAT in a data center project?
Factory acceptance testing is performed at the manufacturer's facility, usually witnessed by the client or their representative, to confirm the equipment meets the specification before it ships.
What is SAT?
Site acceptance testing is performed on site after installation to confirm the equipment works as installed and connected, including checks that could not be done at the factory.
What is IST?
Integrated systems testing verifies that all interdependent systems work together, including their response to simulated failures.
Is the order fixed?
Normally FAT comes first, then SAT, then integrated testing, but project plans define the exact sequence and overlap.
Want to learn this properly?
This topic is covered in depth in our Electrical Design – Data Center Specialist program.
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