Technical Information: LV Switchgears

TECHNICAL INFORMATIONS

Essential Guide to Selecting Reliable Low Voltage Switchgear for Optimal Safety

Technical Information

Choosing a Low Voltage Switchgear

01 What is Low Voltage Switchgear ?

Low voltage switchgear distributes power and protects equipment within a facility’s electrical system. Power is distributed through low voltage circuit breakers and faults are sensed in the system. The fault sensing equipment can open the necessary breaker(s) to clear the fault and maintain power to the rest of the facility.

Choosing a Low Voltage Switchgear

02 Switchgear trends

Switchgear designs are increasingly focused on safety, reliability, and compliance with the latest IEC standards to meet regulatory demands. Modern switchgear is built with higher short circuit capacity, mechanical strength, and arc resistance to reduce arc-flash risks. Operators also seek flexibility in cable termination, easy maintenance, and integrated control and protection for enhanced reliability. The M-Cube switchgear meets all these requirements.

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IEC 61439 series

The IEC 61439 series cover low-voltage switchgear and controlgear assemblies, including those used in connection with the generation, transmission, distribution, and conversion of electrical energy, as well as for controlling equipment consuming electrical energy.

Purpose:

The IEC 61439 series aims to:

Standardize rules and requirements for low-voltage switchgear and controlgear assemblies.
Ensure safety and performance of these assemblies.
Define the responsibilities of the original manufacturer (who designs the assembly system) and the assembly manufacturer (who is responsible for the final conformity of the switchboard).

Key Standards:

IEC 61439-1: Provides general rules for the IEC 61439 series, including general definitions, service conditions, construction requirements, technical characteristics, and verification requirements.

IEC 61439-2: Specifies requirements for low-voltage switchgear and controlgear assemblies for specific applications, such as those in ships, rail vehicles, or domestic applications.

Verifications

Design Verifications

There are 3 different methods of verification

Testing

Calculation/ measurement

Satisfying design rules

Routine Verifications

It is a checklist to ensure that all of our switchboards are being build in accordance to the IEC 61439 standards. A total of 12 clauses, 10.2- 10.13 have been verified by these methods under the IEC 61439 standard.

No.	Characteristics to be verified	Clauses
1	Strength of material and parts	10.2
2	Degree of protection of enclosures	10.3
3	Clearances and creepage distances	10.4
4	Protection against electric shock and integrity of protective circuits	10.5
5	Incorporation of switching devices and components	10.6
6	Internal electrical circuits and connections	10.7
7	Terminals for external conductors	10.8
8	Dielectric properties	10.9
9	Temperature-rise limits	10.10
10	Short-circuit withstand strength	10.11
11	Electromagnetic compatibility (EMC)	10.12
12	Mechanical operation	10.13

The fundamental change between the old and new standard is the elimination of type-tested assemblies (TTA) and partially type-tested assemblies (PTTA) in favour of the new design verification approach. This new approach was adopted to reflect current market and application requirements through a controlled and consistent approach.

Technical Change

Verification of mechanical
operations

Mechanical operating cycles increased to 200

Rated Diversity Factor

Each circuit requires a defined rating

Clearance verification

Safety factor of 50%

Neutral / PEN Cross Section

Raised to minimum of 50%

Verification of temperature
rise

IEC 61439 introduces stricter and more consistent temperature rise requirements, ensuring safer and more reliable switchgear assemblies.

Test methods extended and
adapted

IEC 61439 extended and refined testing methodologies to ensure real-world safety and reliability.
More flexible verification through Testing, Derivation, or Calculation, but PTTA is no longer allowed.
Temperature rise, short-circuit, dielectric, and EMC tests have stricter and clearer requirements.
Improved definition of rated current (InA) and performance conditions ensures consistency across designs.

Derivation is allowed for
similar modules, with
limitation being clearly listed

Manufacturers must justify derivations with engineering evidence.
Physical testing is preferred, especially if significant design variations exist.
IEC 61439 eliminates loopholes that existed in IEC 60439, ensuring better safety and performance.

Verification by calculation is
limited to assemblies

≤ 630A for single compartments
≤1600A for multiple compartments

Verification of mechanical operations

Mechanical operating cycles increased to 200

Rated Diversity Factor

Each circuit requires a defined rating

Clearance verification

Safety factor of 50%

Neutral / PEN Cross Section

Raised to minimum of 50%

Verification of temperature rise

IEC 61439 introduces stricter and more consistent temperature rise requirements, ensuring safer and more reliable switchgear assemblies.

Test methods extended and adapted

IEC 61439 extended and refined testing methodologies to ensure real-world safety and reliability.
More flexible verification through Testing, Derivation, or Calculation, but PTTA is no longer allowed.
Temperature rise, short-circuit, dielectric, and EMC tests have stricter and clearer requirements.
Improved definition of rated current (InA) and performance conditions ensures consistency across designs.

Derivation is allowed for similar modules, with limitation being
clearly listed

Manufacturers must justify derivations with engineering evidence.
Physical testing is preferred, especially if significant design variations exist.
IEC 61439 eliminates loopholes that existed in IEC 60439, ensuring better safety and performance.

Verification by calculation is limited to assemblies

≤ 630A for single compartments
≤1600A for multiple compartments

Standard

Other IEC Standard

IEC 529 outlines an international classification system for the sealing effectiveness of enclosures of electrical equipment against the intrusion into the equipment of foreign bodies (i.e., tools, dust, fingers) and moisture. This classification system utilises the letters ‘IP’ (Ingress Protection) followed by two digits. The first digit of the IP code indicates the degree that equipment is protected against solid bodies intruding into an enclosure. The second digit indicates the degree of protection of the equipment inside the enclosure against the harmful entry of various forms of moisture (e.g., dripping, spraying, submersion, etc.). Fuji SMBE’s M-Cube switchgear is designed specifically to IP 44.

A higher IP rating would result in poor ventilation of the switchboard and result in poor performance and de-rating of the components.
Therefore, the M-Cube is designed to IP 44 so as to balance safety and performance of the switchboard.

IEC Series

IEC 61641: Internal Arc Fault Containment

According to the IEC 61641 standard, a LV Switchgear and controlgear assembly shall:

Limit the risk of injuries/accidents for the personnel in case of an internal arc
Limit the damage of the switchboard to the section affected by the fault, thus allowing the non-affected part to be put in safely.

The M Cube assembly is mechanically capable of withstanding the electric arc because of its specially designed frames, hinges and joints along with internal segregation of up to form 4b to confine the arc.

IEC 60068-2-11: Resistance to Salt Mist

This standard compares resistance to deterioration from salt mist between specimens of similar construction. It may also be used to evaluate the quality and the uniformity of protective coatings.

IEC 60068-2-30: Resistance to Damp Heat

IEC 60068 determines the suitability of components, equipment or other articles for use, transportation and storage under conditions of high humidity – combined with cyclic temperature changes and, in general, producing condensation on the surface of the specimen. If the test is being used to verify the performance of a specimen whilst it is being transported or stored in packaging then the packaging will normally be fitted when the test conditions are being applied.