Commissioning Industrial Electrical Systems — From FAT to Energization
Key Takeaway
Commissioning is the structured process of verifying that every electrical component — from switchgear to the last instrument loop — works as designed before the facility goes live. This guide covers the commissioning sequence from factory acceptance testing (FAT) through site acceptance testing (SAT), energization, and operational handover.
What Commissioning Means in Industrial Electrical
Commissioning is not "turning it on." It is a documented, step-by-step verification that every installed component performs according to its design specification. For electrical systems this spans switchgear, transformers, motor feeders, VFDs, control panels, and instrument loops — each tested individually and then as an integrated system.
The Commissioning Sequence
Factory Acceptance Testing (FAT)
Before equipment ships to site, a FAT verifies that panels, switchgear, and control systems are built correctly. Electrical FAT typically includes:
- Visual inspection of wiring, labeling, and component placement against drawings
- Insulation resistance testing (megger) on all power and control circuits
- Point-to-point continuity checks on I/O wiring
- Functional testing — breaker operation, relay trip tests, VFD start/stop sequences
- Control logic simulation where PLC or DCS is included in the panel
Catching errors at FAT avoids costly field rework. A missing wire found in a climate-controlled shop costs 15 minutes; the same wire found at a remote wellsite costs a full day.
Site Acceptance Testing (SAT) and Pre-Energization
After equipment arrives and is installed, SAT verifies that nothing was damaged in transit and that field connections are correct. Pre-energization checks include:
- Megger testing on all installed cables (before termination to equipment)
- Torque verification on all power connections per manufacturer specs
- Grounding continuity — verify grounding electrode system resistance and bonding paths
- Breaker racking and operation verification
- Phase rotation check on three-phase feeders
- Visual inspection of conduit seals, cable entries, and hazardous-area fittings
Instrument Loop Commissioning
Every instrument loop must be verified from field device through the I/O card to the SCADA or DCS display. This includes signal injection at 0%, 50%, and 100% of range, alarm point verification, and control output testing (e.g., driving a control valve from 0–100% stroke from the PLC).
Energization and Load Testing
With all pre-checks complete, energization follows a controlled sequence — main breaker first, then distribution, then individual motor feeders. Each motor is bump-tested for correct rotation before coupling to the driven equipment. VFDs are ramped up under monitoring. Motor alignment and vibration baselines are recorded at this stage.
Integrated Systems Test and Handover
The final phase runs the entire facility through its operating scenarios — normal operation, emergency shutdown, power failure and recovery, alarm response. All test results are documented in a commissioning completion package that includes as-built drawings, test sheets, calibration records, and punch list closeout.
Who Does What During Commissioning
Commissioning requires coordination between electricians (power systems), I&E technicians (instrument loops), controls engineers (PLC and SCADA), and the owner's operations team. NFM Consulting's commissioning support provides all three technical disciplines in one team, reducing the hand-offs that typically slow down startup.
Frequently Asked Questions
Factory Acceptance Testing (FAT) happens at the manufacturer's shop before equipment ships — it verifies the build matches the design. Site Acceptance Testing (SAT) happens after equipment is installed at the project site — it verifies that nothing was damaged in transit and that all field connections are correct. Both are documented with test reports.
Megger (insulation resistance) testing identifies damaged cable insulation, moisture intrusion, or contamination before voltage is applied. Energizing a cable with compromised insulation can cause a short circuit, arc flash, or equipment damage. Megger testing is a standard pre-energization safety check per NETA and NFPA 70B.
Duration depends on facility size and complexity. A simple wellsite pad with one MCC and 20 instrument loops might take 3-5 days. A data center with redundant power paths, UPS systems, and hundreds of BMS points can take 4-8 weeks. The commissioning schedule should be planned during engineering, not estimated after construction.
A punch list is the documented list of items that do not pass commissioning testing and require correction. Each item includes the deficiency description, responsible party, priority (critical vs. non-critical), and resolution date. Commissioning is not complete until all critical punch list items are closed.
Yes. When the PLC controls engineer is testing outputs (starting motors, opening valves, energizing heaters), having the electrician on site allows immediate troubleshooting of wiring issues, breaker trips, or motor rotation problems. Without the electrician, every wiring issue becomes a schedule delay while waiting for the right person to arrive.