Choosing a Low Voltage Switchgear
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.
Switchgear designs are drifting more towards safety and reliability. They are now made to withstand a higher short circuit rating capacity and superior mechanical strength to ensure optimum performance. Compliance to the latest IEC standards is compulsory for owners to adopt due to increasing regulatory requirements by utilities and authorities. The latest switchgear are required to be arc resistant to reduce the risk of an arc -flash hazard. Operators demand flexibility in termination of cables/busduct as well as convenience during maintenance. In addition, control and protection functions are required to be integrated for greater reliability. The M-Cube is a switchgear that has the solutions to all these requirements.
The IEC 61439 series replaces the old IEC 60439 standard series following dissatisfaction over the uses of the series which were lacking in several areas. The introduction of IEC 61439 was intended to be a positive step forward in enabling panel and system builders to produce assemblies that meet essential quality and safety standards demanded by customers. The new IEC standard comprises of 6 parts. Parts 1 and 2 were published in January 2009 and the rest are being developed and will be published at a later date.
Part 1 – Contains definitions and states the service conditions, construction requirements, technical characteristics and verification requirement for low-voltage switchgear and controlgear assemblies.
Part 2 – Defines the specific requirements of power switchgear controlgear assemblies, whereby rated voltage ≤1000 V a.c. or 1500 V d.c.
Design Verification (3 Different Methods)
- Satisfying design rules
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|
|10||Short-circuit withstand strength||10.11|
|11||Electromagnetic compatibility (EMC)||10.12|
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.
- 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
- Test methods extended and adapted
- Derivation is allowed for similar modules, with limitation being clearly listed
- Verification by calculation is limited to assemblies
- ≤ 630A for single compartments
- ≤1600A for multiple compartments
Other IEC Standards
IEC 529: Degree of Protection
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
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 into safety.
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.
The M-Cube is tested to IEC 61439, clause 10.2.2 (Severity Test A), which meets the requirement of IEC 60068-2-11 and IEC 60068-2-30. This ensures that our switchboards are resistant to corrosion caused by salt mist and damp heat.