IEC 61439

Low-Voltage Switchgear and Controlgear Assemblies

IEC 61439 covers the design verification and routine testing of low-voltage switchgear and controlgear assemblies — motor control centres (MCCs), distribution boards, power distribution units (PDUs) and control panels. It replaced IEC 60439 and introduced mandatory design verification with defined test-based, calculation-based or comparison-based methods.

Body: IEC
Family: Electrical Equipment
First published: 2009
Latest revision: Various (per part, 2011–2021)
Status: current
Access: Paid (IEC webstore — price per part)

Document structure

IEC 61439-1

General rules

Defines the framework — terminology, service conditions, constructional requirements, design verification methods (test, calculation, comparison to reference design) and routine verification. The master part applicable to all assemblies.

IEC 61439-2

Power switchgear and controlgear assemblies (PSCGA)

Applies to distribution boards and MCCs in power distribution. The most widely used part in industrial plant electrical engineering — covers busbars, compartments, form of separation, IP ratings and short-circuit withstand.

IEC 61439-3

Distribution boards intended to be operated by ordinary persons (DBO)

Final distribution boards in buildings and light commercial premises. Equivalent to the former IEC 60439-3.

IEC 61439-4

Particular requirements for assemblies for construction sites (ACS)

Portable and semi-fixed assemblies for use on building sites — weatherproof, impact resistant, with RCD (residual current device) protection.

IEC 61439-5

Assemblies for power distribution in public networks

Secondary distribution cabinets and enclosures for public utility power networks — ring main units, compact secondary substations.

IEC 61439-6

Busbar trunking systems (BTS)

Requirements for busbar trunking — rising busbars in multi-storey buildings and horizontal power distribution in industrial plants and data centres.

Key concepts

Design verification: IEC 61439-1 requires that every assembly design is verified — either by prototype testing (most rigorous), by calculation (e.g., thermal and short-circuit), or by comparison with a reference design already tested. Design verification is the responsibility of the Original Equipment Manufacturer (OEM), not the panel builder using a system.
Routine verification: Tests carried out on every completed assembly before delivery — includes wiring check, dielectric test, insulation resistance, protective circuit continuity. Not the same as design verification. Routine tests are mandatory for every unit.
Form of separation: Defines how busbars and functional units are physically separated within an assembly. Form 1 = no separation; Form 2 = busbars separated from functional units; Form 3 = functional units separated from each other; Form 4 = terminals separated from functional units. Form 3b and 4b are standard for industrial MCCs.
Rated short-time withstand current (Icw)(Icw): The RMS current an assembly can carry for a defined duration (typically 1 second) without damage. Must be ≥ the prospective short-circuit current at the busbar — the critical parameter for coordinating panel rating with upstream protection.
Rated peak withstand current (Ipk)(Ipk): The peak (instantaneous) current the assembly can withstand. Related to Icw by a factor n (typically 1.5–2.2 depending on power factor). Must be verified against the asymmetric fault current at the panel supply point.
Internal arc classification (IAC)(IAC): Optional classification for assemblies designed to contain and direct the pressure wave from an internal arc fault. Relevant for high-power MCCs and primary switchboards where operator safety during fault is critical (IEC 62271-200 covers MV equivalent).

Notes & guidance

Overview

IEC 61439 is the standard for assembled low-voltage switchgear and controlgear — the motor control centres, distribution boards and switchboards that form the electrical backbone of every industrial plant. It replaced IEC 60439 and tightened the rules around design verification, distinguishing clearly between:

Original Equipment Manufacturer (OEM): designs and verifies the assembly system (e.g., ABB MNS, Schneider Okken)
Panel builder: assembles a specific installation using a verified system

Design Verification vs Routine Verification

Aspect	Design verification	Routine verification
When	Once per design / system	Every unit before delivery
Who	OEM (system supplier)	Panel builder / manufacturer
How	Test, calculation or comparison	Wiring check, dielectric, insulation
Purpose	Prove the design is safe	Prove this unit is correctly built

Panel builders using OEM-verified systems can inherit the design verification — they do not need to retest every bespoke panel build, provided they follow the OEM’s verified design rules.

Form of Separation — MCC Selection

Form	Separation provided	Typical use
Form 1	None	Light commercial boards
Form 2b	Busbars from units + terminals	Secondary distribution
Form 3b	Units from each other	Process plant MCCs
Form 4b	Terminals from units	High-availability MCCs

Form 4b is the standard for process plant and offshore MCCs where maintenance access to one feeder must not expose live terminals of adjacent feeders.

Key Design Checks

Verify Icw ≥ Isc at panel busbars (coordination with upstream protection)
Check thermal current rating of busbars at rated load + ambient temperature
Confirm IP rating matches the installation environment (IEC 60529)
For ATEX locations: the assembly itself must comply with IEC 60079-0 Ex e or Ex d
For arc flash mitigation: specify IAC rating and verify with arc flash study

Applicable industries

process
manufacturing
energy
oil-and-gas
water-treatment
mining
data-centres