Electrical commissioning of an industrial plant verifies, from the service entrance to the last load, that the substation, switchgear, motors, drives, on-site generation and control systems work as designed before the process starts. It follows a downstream order: first the source, then distribution and finally the loads, and it is coordinated with the mechanical and instrumentation disciplines, which need power to commission their own systems.
What the electrical scope covers
In a new industrial plant or a large expansion, commissioning is split among disciplines: civil, mechanical, instrumentation and control, and electrical. The electrical side has to be ready first, because the others need power to test pumps, compressors, instruments and control systems.
Its scope runs from the service entrance to the last load:
- Main substation: incoming switchgear, transformers, protection and the connection to the utility.
- Medium- and low-voltage distribution: switchgear, main switchboards, MCCs and service panels.
- Loads: low- and medium-voltage motors, starters, variable frequency drives, capacitor banks, lighting and power outlets.
- On-site and backup generation: diesel gensets, cogeneration, solar and transfer schemes.
- Station service: DC systems, UPS and batteries.
- Control systems: integration of relays, meters and drives with the plant SCADA or DCS.
- Grounding and lightning protection.
The phases, as the process industry sees them
In industrial plants it is common to speak of pre-commissioning, commissioning and start-up. IEC 62337 organizes those phases and their milestones for the electrical, instrumentation and control systems of the process industry, between the end of construction and acceptance of the plant by the owner, and recognizes that construction and pre-commissioning can overlap by area. The difference between the three terms is in pre-commissioning, commissioning and start-up.
- 01Service entrance and substationPrimary tests, protection and energization with the utility
- 02DistributionSwitchgear, main switchboards and MCCs
- 03Uncoupled loadsNo-load motor runs, drives, direction of rotation
- 04Generation and transfersDiesel, cogeneration or solar with the internal network stable
- 05Control and processSignals to SCADA or DCS and start-up with the real load
The downstream order lets each level be energized from one already tested. Skipping it, for example energizing an MCC from a temporary generator because the substation is not ready, is possible but requires a specific protection and grounding plan for that condition.
What is tested in each system
| System | Main checks |
|---|---|
| Substation and transformers | Primary equipment tests, protection with secondary injection, energization coordinated with the utility |
| Switchgear and panels | Routine verification, insulation, functional tests, interlocks and trip settings |
| Medium-voltage motors | Insulation, polarization index, winding resistance, motor relay protection |
| Low-voltage motors and drives | Insulation, drive parameters, direction of rotation and no-load start |
| On-site generation | Generator protection, synchronizing, transfers and anti-islanding if it runs in parallel with the grid |
| Station service | Batteries, chargers, UPS and autonomy |
| Control | Point-to-point signal testing with SCADA or DCS, controls and interlocks between systems |
Low-voltage motor tests are described in electrical tests on low-voltage motors.
Interfaces with the other disciplines
Most delays in plant commissioning do not happen inside a discipline but at its boundaries:
- With mechanical. The motor is tested uncoupled; coupling, alignment and the run with the machine belong to mechanical, but direction of rotation and no-load current are electrical. Who gives the go-ahead for the first coupled start must be agreed.
- With instrumentation and control. Start permissives, emergency stops and the signals from the MCCs to the DCS are tested together. IEC 62382 covers loop checks, and IEC 62381 the FAT, SAT and site integration test (SIT) of automation systems.
- With the process. Starting large motors can sag the bus voltage and trip other equipment; it should be reviewed before the first start under load.
- With the utility. Energizing the service entrance has its own procedure and dates.
A common nonconformity log, with an owner per discipline, keeps an electrical punch item from blocking mechanical, or the other way around.
Expansions in an operating plant
When the job is an expansion, commissioning lives alongside production. The new switchgear or panels are tested cold while the rest stays energized, and their connection to the existing bus requires clearances, shutdown windows and often changes to the upstream protection, because the new circuit changes the load and the short-circuit level. The prudent course is to retest the protection that was modified, not only the new one.
Common mistakes
- Factory defaults in relays and drives. Incomer, transformer and motor relays must have the settings of the coordination study before energization. You can check selectivity between two relays with our free relay coordination tool.
- Starting motors without checking voltage dip or the starting sequence of large motors.
- On-site generation without transfer and anti-islanding tests on the real internal network.
- Drawings that do not reflect what was built, starting with the plant single-line diagram.
- Signals to the DCS tested only from the panel, without the field side.
The detailed plan depends on the type of plant, its process standards and the owner’s specification.
What is delivered
Test reports per piece of equipment, the settings loaded in each relay and drive compared with the study, verified signal lists, a closed nonconformity log, as-built drawings and the final report. Those reports are the baseline for the plant’s electrical maintenance.
We commission the electrical side of your plant
Our crew commissions substations, switchgear, motors and generation in industrial plants, and coordinates with mechanical, instrumentation and the utility, in Colombia, or elsewhere on request. Send us the plant single-line diagram.
Related guides
- Commissioning electrical panels and MCCs
- Cold and hot commissioning
- Electrical tests on low-voltage three-phase motors
- Low-voltage breaker testing: ACB and MCCB
- Substation commissioning: stages and tests
References
- IEC 62337:2012, Commissioning of electrical, instrumentation and control systems in the process industry – Specific phases and milestones.
- IEC 62381:2024, Automation systems in the process industry – Factory acceptance test (FAT), site acceptance test (SAT), and site integration test (SIT).
- IEC 62382:2024, Control systems in the process industry – Electrical and instrumentation loop check.
- ANSI/NETA ATS-2025 and ANSI/NETA ECS-2024.
- IEC 61439-1:2020 and IEC 62271-200.
Frequently asked questions
In what order is the electrical side of a plant commissioned?
Downstream: first the service entrance and main substation, then the distribution switchgear and panels, then the MCCs and service panels, and finally the loads, with the motors first uncoupled and then with the process. On-site generation is commissioned once the internal network is energized and tested.
What is the difference between electrical commissioning and plant start-up?
Electrical commissioning proves that the electrical system works, and it is a precondition for mechanical and instrumentation to commission their equipment. Start-up is the start of the production process with raw material, once every discipline has finished its commissioning.
Which documents should the electrical contractor deliver at the end?
Test reports per piece of equipment, the settings loaded in each relay and drive compared with the study, signal lists verified with the control system, a closed nonconformity log, as-built drawings and the final report.