Author: Mark Keogh, Schneider Electric Ireland In January 2009, a new standard was introduced by the International Electrotechnical Commission (IEC), which governs the safety and performance of electrical switchgear and controlgear assemblies. The new IEC 61439-1 and -2 are now the market standards for the construction of electrical LV switchboards. IEC 61439-1 and -2 fully satisfy the requirements of designers and end users with a new generation of LV switchboards, complying with safety of:

  • Persons and equipment;
  • Electrical availability; and
  • Long-term reliability and conformity.
To guarantee these essential values, the standard sets out a wide range of requirements. These include designing a ‘system’ to be compliant in all aspects. This includes checking interactions and consistency between switchgear and equipment as well as providing protection against electrical, mechanical and structural hazards, whilst making sure there is a simplified system of maintenance and upgradability of the low-voltage switchboard during its life cycle. [caption id="attachment_17482" align="aligncenter" width="990"]New Picture Responsibilities under IEC 61439-1 and -2[/caption] The Standard IEC 61439-1 and -2 clearly defines the type of verifications that must be conducted by and the responsibility of the various parties:
  • The manufacturer, having carried out the original design and the associated verification of an assembled system. They are responsible for the ‘design verifications’ listed by IEC 61439-1 and -2, including many electrical tests.
  • The panel builder is responsible for the ‘completed assembly’. They are responsible for ‘routine verifications’ on each panel produced, according to the standard. If they deviate from the instructions recommended by the original manufacturer, they are responsible to carry out design verifications again.
  • The end user should ask for a certified LV switchboard or a ‘tested assembly’. By systematically requesting routine verifications, they can ensure that the assembly selected is compliant with the new IEC 61439-1 and -2 standard.
  • The consultant specifies the needs and constraints for design, installation, operation and upgrading of the complete system. They check that its requirements have been fully integrated by the panel builder. However, depending on the application, the consultant may be the end-user or a design office.
There are a number of main functions/requirements of standard IEC61439, as outlined in the following tables.

Safety

  •  Voltage Stress Withstand Capability
Needs and design requirements Design verification Routine verification
Insulation to withstand long-term voltages, transients and temporary overvoltages shall be guaranteed through clearances, creepage distances and solid insulation.
  • Measurement of clearances and creepage distances
  • Power frequency dielectric test
  • Impulse withstand voltage test, when clearances are greater than specified values
  • Visual inspection of clearances (subject to design conditions and
 creepage distances)
  • Power frequency dielectric test
 
  • Current-Carrying Capability
Needs and design requirements Design verification Routine verification
Protect against harmful thermal effects by limiting excessive temperatures:
  • when any single circuit is continuously loaded to its rated current and
  • when any circuit is continuously loaded to its rated current multiplied by its rated diversity factor.
  • Temperature rise tests
  • Or, comparison with a tested reference design, under restrictive conditions
  • Or, under very restrictive conditions, calculations with safety margins (including 20% derating of devices)
  • Visual inspection
  • Random verification of tightness
 
  • Short-Circuit Withstand Capability
Needs and design requirements Design verification Routine verification
Withstand short-circuit thanks to short-circuit protection devices, short-circuit co-ordination and capability to withstand the stresses resulting from short-circuit currents in all conductors.
  • Short-circuit tests (Icc and Icw) of the main circuit, including the neutral conductor, and of the protection circuit
  • Or comparison with a tested reference design under restrictive conditions
  • Visual inspection
 
  • Protection Against Electric Shock
Needs and design requirements Design verification Routine verification
Hazardous live parts are not accessible (basic insulation protection) and accessible conductive parts are not hazardous for life (fault protection and continuity of protective equipotential bonding).
  • IP XXB test and verification of insulating materials
  • Mechanical operation tests
  • Verification of dielectric properties
  • Measurement of the resistance between each exposed conductive part and the PE terminal
  •  Short-circuit strength of the protection circuit
  • Visual inspection of basic fault protection devices and test were necessary on a regular basis.
  • Random verification of tightness of the protective circuit connections
 
  • Protection Against Fire or Explosion Hazard
Needs and design requirements Design verification Routine verification
Protect persons against the fire hazard: resistance to internal glowing faulty elements, through selection of materials and various design provisions.
  • Glow wire test
  • Special test according to IEC TR 61641, where specified
 None
 

Continuity of service

  •  Maintenance and Modification Capability
Needs and design requirements Design verification Routine verification
Capability to preserve continuity of supply without impairing safety during assembly maintenance or modificationThorough basic and fault protection and optional removableparts
  • IP tests
  • Mechanical operation tests
(especially for removable parts)
  • Effectiveness of mechanical actuating elements
  • Check protection of persons against electric shocks
 
  •  Electro-Magnetic Compatibility
Needs and design requirements Design verification Routine verification
Proper functionality of equipment and avoid generation of EMC disturbances through incorporation of electronic devices complying with the relevant EMC standard, and their correct installation.
  • EMC tests according to product standards or generic EMC standards
 None

Compliance with end-user requirements

  • Capability to operate the electrical installation
Needs and design requirements Design verification Routine verification
Properly function, according to:
  •  The electrical diagram and the specifications (voltages, co-ordination, etc.) by selecting, installing and wiring the appropriate switching devices.
  •  The specified operating facilities (access to man-machine interfaces, etc) through accessibility and identification.
  • By inspection
  • Impulse withstand voltage test of isolating distance for optional withdrawable units
  • Visual inspection
  • Effectiveness of mechanical
actuating elements and function test (where relevant)
 
  • Capability to be installed on site
Needs and design requirements Design verification Routine verification
Withstand handling, transport, storage and installation constraints, and be capable to be erected and connected through selection or design of the enclosure and the external terminals, and by means of provisions and documentation.
  • By inspection
  • Lifting test, taken from
  • IEC 62208
  • Number, type and
  • identification of terminals for external
conductors
 
  • Protection of the assembly against environmental conditions
Needs and design requirements Design verification Routine verification
Protect the assembly against mechanical and atmosphericconditions through selection of materials and various design
  • IP test
  • IK test
  • Corrosion test
  • > UV test (outdoor only)
 None

Differences between IEC60439 and IEC61439

[caption id="attachment_17485" align="aligncenter" width="795"]New Picture Main differences between IEC60439 and IEC61439[/caption] There are some significant technical changes compared with IEC 60439-1, which is a pure 'general rules' standard to be referred to by subsidiary product parts of the IEC 61439 series. The product standard replacing IEC 60439-1 is IEC 61439-2; the discrimination between type-tested assemblies (TTA) and partially type-tested assemblies (PTTA) is eliminated by the new verification approach. These different but equivalent types of verification of requirements have been introduced:
  • Verification by testing, verification by calculation/measurement, or verification by satisfying design rules;
  • The requirements regarding temperature rise have been clarified;
  • The rated diversity factor (RDF) is covered in more detail; and
  • Requirements from the standard for empty enclosures for assemblies (IEC 62208) have been incorporated.
In addition, the new standard's whole structure has been aligned with its new function as 'general rules' standard. However, when a dated reference to IEC 60439-1 is made in another Part of the IEC 60439 series of assembly standards not yet transferred into the new IEC 61439 series, the superseded IEC 60439-1 still applies. More specifically, IEC 61439-1 compares to the previous edition, IEC 60439-1, in that the discrimination between type-tested assemblies (TTA) and partially type-tested assemblies (PTTA) is done away with by the verification approach – as already stated. Also, three different, but equivalent types of verification of requirements have been introduced. These are:
  • Verification by testing;
  • Verification by calculation/measurement; and
  • Verification by satisfying design rules.
In addition to proper testing, IEC 61439 specifies how calculations and design rules can be used to prove that the product family complies with the specified short circuit ratings and the temperature rise limits as stated by the standard. This is ideal for testing assemblies made up of several variants. Compliance with the new standard is compulsory. The IEC 60439-1 has been totally replaced by the IEC61439-1 and IEC 61439-2 (including the five-year overlapping period) and it was totally withdrawn in January 2014. This article is a summary of the IEC61439-1 and -2 standard and is designed for information purposes only. For more in-depth detail, please refer to the actual standard documents or contact the ETCI TC4 Technical committee. Alternatively, you can send an e-mail to mark_keogh@schneiderelectric.com requesting more information.