Switchgear and MCC commissioning: tests and checks

Short answer

Commissioning an electrical panel or a motor control center (MCC) confirms that the assembly arrived as it left the factory, was installed and connected correctly, and works with the loads and the plant control system. It starts from the routine verification that IEC 61439 requires from the manufacturer, continues with the FAT and goes on site with inspection, insulation, protective circuit continuity, functional tests, interlocks and energization.

What panel commissioning is

An electrical panel or motor control center (MCC) is not a stand-alone piece of equipment: it distributes power to the plant loads, starts and protects the motors, transfers between sources and communicates with the control system. Its commissioning proves that the assembly arrived as it left the factory, that it was installed and connected correctly, and that it works with the real installation.

It takes place at three moments: the manufacturer’s routine verification, the factory acceptance test (FAT) witnessed by the client, and the site tests, which include the SAT and energization. Each one finds different errors and none replaces the others. The panel is one part of the electrical commissioning of an industrial plant.

This scope covers low-voltage main switchboards, MCCs, distribution and transfer panels in industrial plants and the station service panels of substations. The FAT and SAT of the protection, control and communications panels of a substation have their own scope.

The basis: IEC 61439

IEC 61439-1 sets the general rules for low-voltage assemblies up to 1,000 V AC or 1,500 V DC, and IEC 61439-2 the requirements for power switchgear and controlgear assemblies, including main switchboards and MCCs. In North America the equivalent product standards are UL 891 for switchboards, UL 845 for MCCs and IEEE C37.20.1 for metal-enclosed low-voltage power circuit breaker switchgear. IEC 61439 distinguishes two parties:

The original manufacturer verifies the design by test, by comparison with a reference design or by assessment: temperature rise, short-circuit withstand, dielectric properties, clearances, protective circuit and IP rating.
The assembly manufacturer, who builds the panel, carries out the routine verification of each unit: degree of protection, clearances and creepage distances, protection against electric shock and continuity of the protective circuit, incorporated components, internal connections, terminals, mechanical operation, dielectric properties, wiring and operation.

The routine test report is the first document to ask for when receiving the panel: it is the reference against which the site tests are compared.

The panel FAT

The FAT is the last chance to correct the panel in comfortable conditions, with drawings, spare parts and the manufacturer’s staff at hand. In general it covers:

Conformity with the approved drawings: layout, equipment, markings, nameplates and cable labels.
Inspection of power and control wiring, connection torques and forms of internal separation.
Dielectric or insulation test according to the manufacturer’s procedure.
Functional tests with auxiliary power: controls, indication, starters, transfers and electrical and mechanical interlocks.
Settings of the breaker trip units and motor protection relays according to the coordination study.
Communications with the control system, if the panel has them.

Commissioning a panel, from the factory to operation

01Routine verificationThe manufacturer tests each assembly per IEC 61439
02FATThe client witnesses drawings, wiring, functional tests and interlocks
03Receiving and inspectionTransport damage, installation and anchoring
04Cold testsInsulation, grounding, settings, functional tests with cables and motors
05Energization and loadVoltages, phase sequence, motor starts and thermography

Site tests

Receiving and installation

Inspection for transport damage, anchoring and leveling, joining of shipping sections and of the bus splices between them with their torque, connection of the panel ground to the grounding grid, and cable entry.

De-energized tests

Insulation resistance of the bus and power circuits, with sensitive electronic devices disconnected as the manufacturer instructs.
Continuity of the protective circuit for all metal parts.
Settings of breakers, motor relays and protection, compared with the study.
Outgoing cables and motors: insulation and connection to the right terminal.
Functional tests with auxiliaries: local and remote control, indication, starters, drives with the motor uncoupled when the process requires it, and transfers.
Interlocks: between incoming and tie breakers, of withdrawable units and of doors. Each interlock is proven to block what it should; see low-voltage breaker interlocking. You can build the case matrix with our free interlocking table tool.

Energization and on-load tests

Bus voltages and phase sequence, motor starts with direction of rotation, consistency of the measurements with the control system and, under load, thermography of connections and bus.

The first energization is done with the outgoing feeders open and the incomer protection active. The feeders are then closed in groups, the motors are started one by one and voltages, currents and alarms are recorded. In panels with automatic transfer, the final test uses the real sources: loss of the utility supply, generator start, transfer and retransfer.

Medium-voltage switchgear

Medium-voltage switchgear follows IEC 62271-200 (IEEE C37.20.2 for metal-clad switchgear in North America), and its commissioning adds its own tests: vacuum or SF6 breakers, instrument transformers, racking and grounding switch interlocks, and medium-voltage protection with secondary injection.

Common mistakes

Receiving the panel without the manufacturer’s routine test report.
Running the insulation test with drives, meters or power supplies connected.
Leaving factory defaults in the trip units, without the coordination study.
Testing the MCC with the motors uncoupled and never repeating with the real process.
Not checking direction of rotation before coupling pumps and compressors.

The test reports of each stage are filed in the commissioning dossier. The test list of a specific project depends on the type of panel, the client’s specification and the manufacturer.

We commission your panels

Our crew witnesses the FAT, performs the site tests and supports the energization of panels, MCCs and switchgear in industrial plants and substations, in Colombia, or elsewhere on request. Contact us about your project.

References

IEC 61439-1:2020, Low-voltage switchgear and controlgear assemblies – Part 1: General rules.
IEC 61439-2, Low-voltage switchgear and controlgear assemblies – Part 2: Power switchgear and controlgear assemblies.
IEC 62271-200, AC metal-enclosed switchgear and controlgear for rated voltages above 1 kV and up to and including 52 kV.
IEC 60947-6-1, transfer switching equipment.
IEC 62381:2024, Automation systems in the process industry – FAT, SAT and SIT.
UL 891, Switchboards; UL 845, Motor Control Centers.
ANSI/NETA ATS-2025.

Frequently asked questions

Which tests are done on an electrical panel before energizing it?

Inspection of assembly and torques, insulation resistance, continuity of the protective circuit, verification of breaker trip unit and relay settings, functional tests of controls, indication and interlocks, and a check of the communications with the control system. After energization, thermography under load.

Does the panel FAT replace the site tests?

No. The FAT proves the panel left the factory in good condition; the SAT and site commissioning verify that it was not damaged in transport, that it was correctly connected to cables, motors and control, and that it works with the real installation.

Which standard applies to testing a low-voltage panel?

IEC 61439-1 and -2 for low-voltage assemblies, which set the design verification by the original manufacturer and the routine verification of each assembly. In North America the product standards are UL 891 and UL 845, among others. Field tests usually follow ANSI/NETA ATS or the client's specification.