What is an integrated systems test (IST)?

Where the IST sits in commissioning

Schneider Electric's commissioning paper (White Paper 148) gives the reason a separate integrated level exists. Vendor start-ups were each driven by a contract that operated in a vacuum, independent of the other components, and no contractual requirement existed for the products to perform in a fully integrated manner. Whole-site commissioning developed because standard start-up procedures kept failing to find system-wide weaknesses.

What the IST covers

The power part starts at the high-voltage service entrance and works forward through medium-voltage distribution, parallel switchgear, transfer switches, the emergency generator, the UPS system, the monitoring system and the distribution down to the racks. Lighting and life safety systems, including emergency power off (EPO), are tested too, and WP 148 adds a short-circuit study that checks every circuit breaker and ground fault trip setting. Cooling, fire suppression, physical security and the building and energy management systems are tested alongside, and each alarm is verified.

The method is the sequenced failure. WP 148 says every piece of equipment should be tested by failing it, then restarting it and returning it to stable operation. A failure in one component, such as a generator, is communicated to a related one, such as the air conditioning, so the second can act to limit downtime or be ready when power returns. The cycle runs on each component and on the whole integrated system, which means a complete power down and an automatic restart.

UPS scenarios and what to record

The table pairs the power events in the sources with the response each one describes. Aggreko's level 5 stages machinery failures and utility problems; WP 148 adds sequenced failures and a complete power down.

The UPS-level version of these steps, in Eaton's load bank method (a battery discharge of up to 4 minutes by opening the rectifier input, and three transfers to bypass and back), is covered under UPS load bank testing.

The UPS input window and walk-in are explained in UPS and generator. For the bypass paths themselves, see static and maintenance bypass.

Prerequisites

• Levels 1 to 4 complete (Aggreko); every subsystem tested to its manufacturer's start-up process, with the start-up results in the commissioning team's hands before commissioning starts (WP 148).
• A written test script: line by line procedures, communicated by the command center and executed by the testing team. The commissioning agent writes it, and the team rehearses it beforehand (WP 149).
• A command center to give permission for each next step, handle all communication and hold every contact and emergency number; on a small site, one person can fill the role (WP 148).
• Cooling, electrical and monitoring systems ready to run when the load banks arrive (WP 148).
• Heat loads in place: free-standing load banks sized for the halls, or rack-mounted loads at the server positions (Aggreko).
• A checklist of the expected inputs and outputs for each critical component in the test schedule (WP 149).
• Emergency operating procedures posted on each piece of equipment and at each EPO station (WP 149).
• A shift plan, so every tester has a backup who can step in (WP 149).

Pass criteria and the record

WP 148's script report sets the expected response beside the actual response for each line and designates each line pass or fail.

WP 148 lists three documents that commissioning should produce. The "as built" script report records what was tested and how, and gives a line by line account of each pass or fail, with the test procedure, expected response and actual response. The component error log, also called a failure mode effects analysis (FMEA), records each component that failed and how the failure affected equipment upstream and downstream. The trending report closes the job with an action plan and a validation statement from the commissioning agent.

WP 148's sample error log shows the kind of fault an IST catches. A UPS failed to support the load after switching from bypass back to normal operation, because the battery leads at the head of the string were disconnected. The corrective action was to have every battery lead checked and the test rerun.

Common errors

WP 149 collects ten errors that undermine commissioning. Six bear on an IST, three of them on the UPS directly:

• Outdated test procedures, such as testing a delta conversion UPS with procedures written for a double conversion UPS.
• A script that is unclear or never rehearsed, so it is misinterpreted, and steps are left incomplete.
• Only the UPS gets tested: large exterior resistive load banks wired to the UPS output leave the cooling system out. Resistive heating units installed in the racks let the UPS, emergency power and cooling be tested together.
• Battery charge run down. Each test that puts the UPS on battery reduces the runtime left for the next; WP 149's best practice is to allow sufficient recharge after a major power drain test.
• Fatigue. WP 149 calls it the principal cause of human error during commissioning, with staff logging 12 to 18 hour days; rotate shifts.
• A commissioning agent engaged late, and budget cuts that compress the test scope.

Why the power path gets the most attention

Power remains the leading cause of impactful outages in Uptime Institute's 2026 outage analysis, and failures involving UPS systems, transfer switches and generators dominate. The same report notes that grid failures should not cause a data center outage, yet transfers to generators sometimes fail. Uptime's Data Center Resiliency Survey 2026, cited in the report, finds that power-related issues caused more than one in five IT service outages reported over the past three years. Among power causes, UPS failures are cited most often, followed by transfer switch and generator issues.

Those are exactly the transfers an IST stages. For redundancy designs and the failures each one tolerates, see N+1 and 2N; for UPS work on a site preparing for commissioning, see UPS service for data centres.

After the IST

The yearly load bank simulation Aggreko recommends is covered under load bank procedure. WP 148 treats the commissioning record as the baseline for spotting changes and trends, and recommends bringing the commissioning agent back periodically or at major business events to review the integrated system. WP 149 adds a disciplined process to keep the documentation current. For the annual UPS test, see UPS load bank testing; for a new UPS, see installation and commissioning.