Integrated systems testing and the five commissioning levels

Integrated systems testing (IST) is the commissioning stage that proves a data centre works as one facility, not as a set of separately tested machines. Uptime Institute describes Level 5 as confirming that each system and the whole facility perform as designed (Uptime Institute Journal, May 2015). That includes capacities, isolation and response to faults.

What are the five levels of data centre commissioning?

Each level tests a larger unit than the one before. Several organisations publish their own definitions, so boundaries vary between projects (Uptime Institute Journal, May 2015).

Levels 1–3 run during construction under the commissioning authority (CxA): factory witness tests repeated on site, post-installation checks, then start-up and functional checks. Level 4 load tests systems one at a time. Generator, UPS and battery load bank runs of at least eight hours are recommended, and up to 24 hours is best practice (Uptime Institute Journal, May 2015).

What happens during integrated systems testing?

At Level 5 the whole site is tested on utility power and on generator power. Fire detection and suppression stay active rather than bypassed (Uptime Institute Journal, May 2015).

Building services guidance describes IST as testing all systems together, often on emergency power or during fire alarm events (Consulting-Specifying Engineer, May 2022). A typical first test opens the main service breakers to simulate a whole-building power loss. The same article says most surprises surface at the transfer to emergency power and the transfer back.

Outage data points at the same plant. Among power-related IT service outages, Uptime Institute's 2026 research cites UPS failures in 39% of cases, transfer switches in 34% and generators in 28% (Uptime Institute, Jul 2026).

Who prepares and witnesses each level?

The US General Services Administration calls independent third-party commissioning industry best practice, because contractors otherwise verify their own work (GSA, Sep 2020). Its guide also requires specifications to name who writes, directs, conducts and documents each functional test.

The table draws on the Uptime Institute Journal guidance cited above. Contracts can move responsibilities, so check the project's roles and responsibilities matrix.

Level	What is tested	Who prepares it	Who else takes part	Hiring decision it drives
Level 1	Factory witness tests of major plant, repeated on site	OEM writes the test procedure	Commissioning team approves and witnesses	Owner-side commissioning lead in post before the first factory visit
Level 2	Post-installation checks against record drawings	Contractors, with the CxA	Whole commissioning team reviews	Contractor commissioning engineers per discipline
Level 3	Start-up and functional checks of each item	OEMs, with the CxA	CxA oversees	OEM service engineers booked for site
Level 4	Load bank tests of generators, UPS and batteries	CxA writes scripts with the operations team	OEM technicians on site	Operations leads hired before scripts are written
Level 5	Whole facility on utility and generator power, fire systems live	CxA writes scripts with the operations team	Commissioning team, contractors and OEM technicians across the site	Full test-window headcount, including controls and electrical specialists

Why integrated systems testing matters when hiring

IST fixes the hiring calendar. The operations team helps the CxA write the Level 4 and Level 5 scripts during construction (Uptime Institute Journal, May 2015). An operations lead hired at handover misses that work and the training it gives.

The test window is also labour-intensive. IST takes heavy planning and manpower from the owner's operations team, the contractor and subcontractors (Consulting-Specifying Engineer, May 2022).

Electrical is the joint-largest skills gap in Uptime Institute's 2026 survey, at 38% (Uptime Institute, Jul 2026). Ask candidates which levels they have run, on what plant, and which integrated test failed.

Line up commissioning and controls hires well before IST starts. Workfully is an AI-native recruiting company. AI agents match each role to recruiters with proven data centre placements in that market, and several recruiters work each role in parallel from day one (Workfully for data centres).