Build stage 3
Commissioning levels L1 to L5
Commissioning is the third stage of a data center build. It proves that every piece of equipment and every system works the way the design says before servers go in. The work is split into five levels, and each one builds on the one before it.
By Czarina Tabayoyong, Founder, Critical Path Hiring. Former Amazon, AWS and Google recruiter.
Last reviewed · First published
Reviewed as terms, pay and markets change.
The five levels
L1 factory testing
Before major equipment ships, the owner's team and the commissioning agent watch the manufacturer test it at the factory. This covers generators, switchgear, UPS systems, transformers and chillers. Problems found here are fixed before the equipment reaches the site.
L2 installation checks
When equipment arrives, it is checked against the order and the drawings, then checked again once it is installed: nameplates, connections, clearances, labeling and damage. Most owners track this on checklists, and many use colored tags on the equipment to show which level it has passed. The tag colors differ from owner to owner.
L3 startup
Each piece of equipment is energized and started for the first time, usually by the manufacturer's field engineer with the contractor. Controls points are checked one by one against the BMS and EPMS. This is sometimes called pre-functional testing.
L4 functional testing
Each system is tested as a system against its sequences of operation: a UPS transferring to battery and back, a generator starting and taking load, a chilled water plant staging chillers up and down. Load banks stand in for the servers so systems run at real load. Every test follows a written script, and every failure goes on an issue log until it is fixed and retested.
L5 IST
All the systems are tested together under load, including a loss of utility power. The best-known test cuts utility power to the building and confirms the generators start, the UPS carries the load in between, the cooling keeps running and the monitoring systems report it all correctly. IST is the last gate before the owner accepts the building.
Leads by level
- Level 1: the commissioning agent and the owner's engineers witness; the manufacturer runs the test.
- Levels 2 and 3: the contractors and vendor field engineers do the work; the commissioning agent checks it and logs issues.
- Levels 4 and 5: the commissioning agent writes the scripts, directs the tests and signs off the results; contractors, controls technicians and vendors operate the equipment; the owner and operations staff witness.
The commissioning agent, or CxA, works for the owner. On large campuses the commissioning provider also staffs commissioning managers, mechanical and electrical commissioning engineers, controls specialists and technicians.
Hiring impact
Most open commissioning roles ask for people who have led L4 and L5, and fewer candidates have done that. Many resumes list IST because the person was on site during it. A candidate who led it can show the scripts they wrote, name the systems and the size of the load they tested, describe a failure they found during IST and explain how it was fixed. Electrical and mechanical commissioning are separate specialties, so screen for the discipline the project needs.
Screening questions
- Which levels did you lead, and which did you witness?
- Show me a script you wrote. What system was it for?
- Walk me through the last IST you ran. What failed, and what did you do?
- How much load did you test with, and how were the load banks set up?
- Who did you report to: the owner, the GC or the commissioning provider?
For the full question sets by discipline, see commissioning interview questions.
For when to open each search against the build schedule, see the hiring timeline by build stage.
Related
Commissioning pay ranges
Posted pay for commissioning engineers, managers and agents from public job postings, updated monthly.
Commissioning interview questions
Questions that separate people who have run L4 and L5 from people who have watched it.
Commissioning collision
Quarters when several tracked projects need commissioning crews at the same time.
Czarina Tabayoyong
Founder and principal recruiter, Critical Path Hiring. Czarina recruits commissioning, MEP, power and critical facilities people for data center builds. She previously recruited cloud and data center architecture talent at AWS Professional Services, and PMO and project delivery talent for hyperscale data center campuses in Texas and Virginia.
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