Commissioning Levels L0–L5

The levels

• L0 — Design review. Verifying the design against owner requirements before anything is built.
• L1 — Factory witness testing. Equipment tested at the manufacturer before it ships.
• L2 — Delivery and installation verification. Equipment arrives complete, undamaged, installed per spec.
• L3 — Pre-functional and startup. Individual components energized and started.
• L4 — Functional performance testing. Each system proven against its sequence of operation.
• L5 — Integrated systems testing. Everything tested together, including failure modes. The real test.

The three seats people confuse

• The third-party Commissioning Agent (CxA) works for the owner. Writes the scripts, witnesses, and signs.
• The GC-side commissioning manager or engineer makes sure systems are actually ready when the CxA arrives, and fixes what fails.
• The trade or vendor startup technician performs the work on their own equipment.

A consultant with fifteen years of CxA experience may have never carried a schedule, coordinated trades, or removed a roadblock in the field. That is not a knock on them — it is a different job, and it is the most common mis-hire we see on the GC side.

Screening questions that separate them

• Walk me through the L4 to L5 transition on your last project. What went wrong?
• Who did you report to, and who did the CxA report to?
• Have you written scripts, executed them, or both?
• Describe a test failure you owned start to finish.