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Home / Technical Articles / 13 very important type tests of a low voltage switchgear carried out by the manufacturer

Type tests defined in IEC 61439

Certification of distribution assemblies is defined by international standard IEC 61439-1. This standard provides common rules that are recognized worldwide. Compliance with the standard is certified, depending on the country or market, by a declaration of the panel builder, the design office, the installer or the user.

13 most important type tests of a low voltage switchgear performed in a factory
13 most important type tests of a low voltage switchgear performed in a factory (photo credit: eksiton.ru)

Just to mention before going into test, that low voltage switchgear and controlgear assemblies (Un ≤ 1000 V AC) may be used at the origin of an electrical installation with:

  1. Low Voltage Main switchboard (transformer area)
  2. Low Voltage Main Distribution Board (technical area) and
  3. Sub Distribution boards
To avoid checks and tests that take a long time, are sometimes destructive, and above all too costly, the standard permits them to be reduced to the minimum, using ‘type tests’ carried out and guaranteed by the manufacturer.

Seven type tests are carried out officially on low voltage assemblies representative of the usual wiring configurations and equipment layouts. These assemblies are called ‘standard assemblies’. By definition, standard assemblies only contain layouts that have undergone type tests.

Table of contents:

They cover the following checks for type tests:

  1. Type tests:
    1. Temperature rise limits
    2. Dielectric properties
    3. Short-circuit resistance
    4. Effectiveness of the protective circuit
    5. Clearances and creepage distances
    6. Mechanical operation
    7. Degree of protection (IP)

And there are also six tests designed to check the construction quality are added to the above type tests in standard IEC 61439-1.

  1. Additional type tests:
    1. Resistance to mechanical impact
    2. Rust resistance
    3. Resistance to damp
    4. Resistance of insulating materials to heat
    5. Fire resistance
    6. Mechanical performance of assemblies and fixings

1. Type tests

1.1 Temperature rise limits

Verification in temperature rise limits test is one of the most critical in determining the reliability and long service capability of a low voltage assembly and must not be overlooked. Excessive temperatures result in premature ageing of components and insulation, and ultimately failure.

Current ratings of components are valid only when the temperature around them is within the limits specified by the component manufacturer.

When temperature rise verification is carried out by test, the manufacturer can select from three options to suit the design and the total time to be devoted to testing:


Option 1

The incoming circuit and at least one outgoing circuit of each rating are loaded to their rated current. If a circuit of each basic type is not included in the test, further tests are carried out until one outgoing circuit of each type has been included. This approach is suitable where a specific arrangement and design of assembly is to be verified with the minimum amount of testing.

As the outgoing circuits are tested with a diversity (loading) factor of unity, it does, however, result in a more onerous test than necessary for most applications.

IEC 61439 temperature rise test
Figure 1 – IEC 61439 temperature rise test

Option 2

Outgoing circuits are temperature rise tested individually to verify they are capable of carrying their rated current. The incoming circuit is then supplied to its rated current. This is distributed through as many outgoing circuits as practical, including one outgoing circuit of each basic type and in the most onerous configuration, with each circuit loaded to its rated current multiplied by the rated diversity (loading) factor.

Again, this test regime is only suitable for a specific arrangement and design of assembly, but it does better reflect the normal loading of an assembly.


Option 3

This alternative has been included to enable modular assembly systems to be fully verified. Horizontal busbars, vertical busbars and outgoing functional units are tested individually. The assembly as a whole is then verified as in Option 2.

Whilst this method of temperature rise testing involves a lot of testing, once it is completed it covers all the possible arrangements available in a flexible modular system, and avoids any concerns that may previously have arisen due to the specific arrangement supplied not being exactly as that tested.

Note that temperature rise tests are time consuming. A lot of time is required to connect all the circuits to be included in the test, balance the current and insert the thermocouples. Current is applied until conditions stabilize, usually around eight hours, and, in the final hours, temperatures are monitored, normally with thermocouples.

Critical areas for temperature measurement are covers, operating handles, busbars and joints, insulators, cable terminals, device and/or internal air temperatures.


1.1.1 Temperature rise test on assemblies

This test checks that assemblies operate correctly under maximum operating conditions (current, number of devices, volume of enclosure). It is used to define the heat balance data for an average temperature rise of the air in assemblies of less than 30 K and a temperature rise of the terminals of less than 70 K.

Note that temperatures rises are given in Kelvin to differentiate them from temperatures given in °C.


1.1.2 Temperature rise test on busbars

The various currents given for all the bar and distribution systems have been checked under the most severe conditions, according to the degree of ventilation of the enclosure (IP ≤ 30 and IP > 30), so that the temperature rise of the busbars does not exceed 65 K.

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1.2 Dielectric properties

The dielectric tests check the insulation performance levels for the maximum operating voltage. They are carried out at the industrial frequency of 50 Hz and in the form of voltage waves simulating a lightning strike.

Impulse withstand voltage test performed on assemblies
Impulse withstand voltage test performed on assemblies (on photo: Tests in the impulse current laboratory by DEHN)

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1.3 Short-circuit resistance

The tests carried out ensure the resistance of busbars and their supports, breaking and protection devices and enclosures to thermal and electrodynamic stresses.

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1.4 Effectiveness of the protective circuit

The continuity of the protective circuit is a decisive factor for safety. It is checked in accordance with standard IEC 61439-1 at a test current of 25 A between the terminal connecting the protective conductors and all the exposed conductive parts.

The continuity of the protective circuit is also checked at a high fault current that could occur following accidental detachment of a conductor.

The protective circuits (conductors, terminals or collector bars), are sized and tested to withstand the maximum short-circuit thermal stress that could occur according to the current at the supply end of the assembly.

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1.5 Clearances and creepage distances

The methods for measuring creepage distances and clearances in standard IEC 60664-1 are repeated in full in appendix f of standard IEC 61439-1. The distances are measured between live parts with different polarities, and also between live parts and the exposed conductive parts.

When modular devices and equipment are installed in accordance with the specified conditions, the distances are observed for the insulation voltages of these devices. Experience has shown that the greatest risk is in the wiring.

Connections, bundles of conductors and busbars must be meticulously checked.

Unsuitable connectors, bolted connections, joints and metal supports can reduce the initially planned insulation values.

Clearances in air
Figure 3 – Clearances in air

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1.6 Checking mechanical operation

In accordance with the provisions of the standard, tests are carried out on parts and devices that are not subject to any specific requirements. Correct mechanical operation is checked by 50 operating cycles on drawout racks and faceplate fixings.

Testing drawout rack
Testing drawout rack

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1.7 Checking the degree of protection (IP)

The IP defines the ability to protect people and to prevent entry of solid objects (first number) and against liquids (second number). The additional letter indicates the protection against access to dangerous parts.

Table 1 – IP degrees of protection in accordance with standard IEC 60529

IP degrees of protection in accordance with standard IEC 60529
Table 1 – IP degrees of protection in accordance with standard IEC 60529

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2. Additional type tests

Defined by standard IEC 61439-3, six tests designed to check the construction quality are added to the seven type tests in standard IEC 61439-1.

They are applied to distribution panels whose incoming current is not more than 250 A at the supply end and which are to be installed in locations that are accessible to unqualified people (residential and commercial applications, public buildings, etc.).

They cover the following checks:

  1. Resistance to mechanical impact
  2. Rust resistance
  3. Resistance to damp
  4. Resistance of insulating materials to heat
  5. Fire resistance
  6. Mechanical performance of assemblies and fixings

2.1 Resistance to mechanical impact

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2.1.1 Spring hammer test

This test is carried out in accordance with IEC 60068-2-63 at a temperature of – 5°C with a spring hammer delivering an energy of 0.7 joule.


2.1.2 Pendulum impact test

Pendulum impact test is carried out in accordance with European standard EN 62262, this test determines the degree of impact protection (IK).

Pendulum impact test on the low voltage enclosure
Pendulum impact test on the low voltage enclosure

Table 2 – IK degrees of protection against mechanical impacts according to standard EN 50102

IK degrees of protection against mechanical impacts according to standard EN 50102
Table 2 – IK degrees of protection against mechanical impacts according to standard EN 50102

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2.2 Rust resistance

2.2.1 Ammonium chloride test

Ammonium chloride test checks that there is no rust present after 10 minutes’ immersion in a solution of ammonium chloride (according to IEC 61439-3).


2.2.2 Salt spray test

Salt spray test, carried out in accordance with IEC 60068-2-11, ensures more than 168 hours’ resistance to salt spray on enclosures.

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2.3 Resistance to damp

Resistance to damp test, carried out in accordance with standard IEC 60068-2-3, checks that the insulation characteristics of the enclosure, busbars and conductor supports are not affected after 4 hours’ exposure in a steam chest (40°C at 95% relative humidity).

The insulation used has a tracking current resistance of at least 400 V, which means it is not very sensitive to damp (group I and group II according to IEC 60664-1).

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2.4 Resistance of insulating materials to heat

2.4.1 Test involving 168 hours’ exposure at 70°c

After 168 hours’ exposure at 70°C, in accordance with standard IEC 61439-3, the assemblies tested do not show any damage likely to affect their use.


2.4.2 Ball impact test

Ball impact test is carried out on the materials themselves to check that there is no warm creep. After exposure to the test temperature of 125°C for parts that hold live parts in place and 70°C for the others, the measured impression of the ball must not exceed 2 mm.

Ball impact test
Ball impact test

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2.5 Fire resistance

The glow wire test in standard IEC 60695-2-1 checks the fire behaviour of the materials and their ability to extinguish themselves (self-extinguishing ability). The test temperature is 960°C for the parts that hold live parts in place, and 650°C for other parts.

Extinguishing must take place in less than 30 seconds. All elements that make up LV assemblies comply with this requirement.


Glow wire tester for IEC60695-2-10

The testing device (model ZLT GTR) is designed to carry out fire hazard testing on electrotechnical products in accordance with the provisions of International standards.

The control unit is supplied with all the controls and metering necessary to accurately set the temperature of the glow wire. The wire current is continuously variable by means of the panel mounted controller and is monitored by the built in ammeter. A digital temperature indicator is fitted which, in conjunction with the thermocouple supplied, accurately measures the glow wire temperature.

The electrical circuit of the control unit is fully protected by fuses and a miniature circuit breaker and incorporates mains on off switching and push button control of the output current. Self contained cabinet with large viewing window and dark colored interior.


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2.6 Mechanical performance of assemblies and fixings

The test consists of tightening screws and nuts up to the torque required by standard IEC 61439-3 and then loosening them: five times for metal screws and nuts and ten times for those made of insulating materials.

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Sources:

  1. Enclosures and assembly certification by Legrand
  2. Ganbica technical guide – A guide to the requirements of BS EN 61439-1  and BS EN 61439-2
  3. Low voltage switchgear and controlgear assemblies in line with IEC 61439 by Hager
  4. Temperature rise tests in IEC 61439 x IEC 60439 (need to repeat tests?) by Sergio Feitoza Costa 

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author-pic

Edvard Csanyi

Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry facilities. Professional in AutoCAD programming.

10 Comments


  1. chola
    Nov 11, 2019

    What can happen if you connect earth to neutral which is not producing to 230v but 165v and when connecting line voltage to earth it is giving 240v.


  2. Ashok
    Nov 08, 2019

    Nice article


  3. Chandra Shekhar
    Nov 08, 2019

    Thank you for great explanation


  4. RR
    Nov 08, 2019

    Good explanation of type test with important test parameters.


  5. Ali
    Nov 07, 2019

    Thanks for your best data


  6. Ellezer G. Casiño
    Nov 07, 2019

    Dear Engr. Edvard,

    I hope to have a pdf file on this edition. It is very relevant for my job as an electrical professor and as an engineer too.

    Respectfully yours,

    Engr. Casiño


  7. Miles
    Nov 07, 2019

    Great high level switchboard testing summary, thanks for sharing!


  8. Say Leong LIM
    Nov 07, 2019

    This article is good; however it needs to talk about design verification which consists of three category. Type test is no longer used in IEC 61439, except for a footnote. Instead, verification by test should be the way that IEC 61439 is all about.


  9. veerendra
    Nov 06, 2019

    Informations are real medicine for healthy thinking.Many thanks.


  10. VB hemadri
    Nov 06, 2019

    Very useful information shared and very thankful to information, and sharing knowledge.

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