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Home / Technical Articles / 3 most important routine tests for successful verification of a low voltage switchgear

Routine tests and checkings

Individual tests or routine verifications are intended to check the essential safety aspects of LV assemblies that could be affected by hazards during mounting or possible manufacturing faults. In principle, they must be carried out on all assemblies, either in the workshop or at the installation site.

3 most important routine tests for successful verification of a low voltage switchgear
3 most important routine tests for successful verification of a low voltage switchgear

If the assemblies are transported as dismantled units, it is preferable to carry out these tests after reassembly on site. All below tests must form the subject of an individual inspection report.

The certification of low voltage switchgear is defined by international standards IEC 61439-1, IEC 61439-2 and IEC 61439-3.

The individual tests comprise:

    1. Checking the insulation
      1. Measurement of the insulation resistance
      2. Dielectric test
    2. Checking the continuity of the protective circuits
      1. Test conditions
      2. Measurement of the continuity resistance
      3.  Checking the continuity with tester with signal
    3. Inspection and final check
      1. Conductors and wiring
      2. Checking wiring accessories
      3. Measures for protection against electric shocks
      4. Checking the clearances
      5. Checking the mounting distances
      6. Testing of electrical operation
      7. Testing of mechanical elements
      8. Checking degree of protection
      9. Checking of labels/marks and information
      10. Checking of information in the technical documentation

1. Checking The insulation

This check can be carried out using a dielectric test or by measuring the insulation resistance. The measurement of the insulation resistance must be considered as being in addition to checking the distances during the visual inspection of the assembly.

Inadequate distances cannot only be detected by the impulse voltage dielectric test.


1.1. Measurement of the insulation resistance

The insulation resistance must be measured with a megohmmeter (external or with standalone source) at a minimum voltage of 500 VDC. The LV switchgear being tested must be turned off and there must be no receiver devices connected and all the breaking devices must be in position I (ON).

The voltage is applied between each circuit and the exposed conductive part. It is possible to link all the poles: phases and neutral, except in TNC layout in which the pen conductor is considered to be linked to the exposed conductive part of the assembly.

Devices (measurement windings, instruments) which would not withstand the test voltage must have their supply terminals short-circuited.

Principle of measurement of insulation
Figure 1 – Principle of measurement of insulation

The minimum value measured must be according to standard IEC 61439-1 at least 1000 Ω/V with reference to the nominal voltage in relation to the earth of the circuit being tested.

In practice, a target value of at least 0.5 MΩ should be used for 230/400 V assemblies and at least 1 MΩ above that.

The measurement conditions can influence the results obtained. measurements should not be carried out temperatures below dewpoint (condensation will dampen the surfaces).

The insulation resistance decreases with the temperature. If repeated measurements have to be taken, the environmental conditions must be recorded. The period for which the voltage is applied also has a major influence, and measurement can be considered to consist of three sequences.

At the start of measurement, the device charges the capacitor which represents the installation in relation to earth and the leakage current is at its highest. At the end of this charge, the current stabilizes and is only due to the insulation resistance.

If the voltage continues to be applied, it will be noted that the resistance continues to increase slowly. This phenomenon is due to the decrease of the dielectric absorption current.

A measurement would require calculation of the ratio of the resistances (R) measured at 1 minute and 10 minutes. A value R10 min / R1 min > 2 indicates good insulation. In practice, the minimum value threshold is increased and the measurement time is decreased, but must not be less than 1 min.

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1.2 Dielectric test

Principle of the dielectric test
Figure 2 – Principle of the dielectric test

If the insulation resistance has not been measured, the dielectric test must be carried out according to the instructions or specifications connected with the assembly.

  1. Test at industrial frequency for a given insulation value Ui
  2. Impulse voltage test (1.2/50 µs wave) for a given Uimp value conditions applicable to both types of test
  3. The assembly being tested must be turned off and there must be no receiver devices connected.

The test voltage must be applied according to the following sequence:

  1. Between each pole of each circuit (power, control, auxiliaries) and the exposed conductive part of the assembly.
  2. Between each pole of the main circuit and the other poles (between each phase and between each phase and neutral).
  3. Between each circuit if they are not electrically connected (for example, separate control circuit or SELV and main circuit)
  4. Between protective circuit and exposed conductive part for class ii assemblies
  5. Between drawn-out or separate parts for the isolation breaking function

IMPORTANT NOTES! – Devices that could be damaged by the application of voltage (measurement or detection devices, electronic releases) must have one of their terminals disconnected and isolated.

Interference suppression capacitors must not be disconnected.

Dielectric test at power frequency
Figure 3 – Dielectric test at power frequency
Test at industrial frequency

The voltage is applied for at least 1 second. There must be no breakdown or flashover.

Table 1 – Test at industrial frequency

 Insulation voltage Ui (V) Test voltage (V)
 Ui < 60 1000
 60 < Ui ≤ 300 2000
 300 < Ui ≤ 690 2500
 690 < Ui ≤ 800 3000
 800 < Ui ≤ 1000 3500

Voltage impulse test

The voltage is applied three times for each polarity at intervals of at least 1 s. The value applied corresponds to the Uimp value increased by the correction associated to the altitude of the location

Table 2 – Voltage impulse test

Given impulse voltage
Uimp (kV)
Test voltage (kV)
Se level 200 m 500 m 1000 m 2000 m
2.5 2.9 2.8 2.8 2.7 2.5
4 4.5 4.8 4.7 4.4 4
6 7.4 7.2 7 6.7 6
8 9.8 9.6 9.3 9 8
12 14.8 14.8 14 13.3 12

The high voltage testing technique requires basic safety precautions (marking out of the test area, wearing of insulated gloves, qualified staff), as well as the precautions associated with the test itself:

Safety Precaution #1 – Avoid switching overvoltages by starting the test at 0 v and returning to 0 v before switching off the high voltage.

Safety Precaution #2 – The period of the individual acceptance test in standard IEC 61439-1 must be deliberately limited (1 s) to avoid any damage that could prejudice future use. Using this approach will limit the trip threshold to a few milliamperes.

It must not be considered that this test checks the intrinsic properties of the insulating materials. It is only the clearances that are validated.

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2. Checking the continuity of the protective circuits

The structural provisions of the new assembly must directly provide continuity of the exposed conductive parts!

It is however necessary to check that all the exposed conductive parts are effectively connected to the protective conductor of the assembly and that all the protective circuits are correctly interconnected via by the main terminal (or protective conductor collector).

Principle of measurement of the continuity resistance
Figure 4 – Principle of measurement of the continuity resistance

2.1. Test conditions

  1. Measurement can be carried out in DC or AC
  2. The test voltage can be between 6 and 24 V
  3. One of the poles of the test source must be connected to the main terminal of the protective conductors, and the other (test key or test tongs) must be connected to the various elements.

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2.2. Measurement of the continuity resistance

It is recommended that the following standard values are applied:

  • Test current: 25 A
  • Application time: 1 min
  • Maximum resistance: 50 MΩ

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2.3. Checking the continuity with tester with signal

This procedure is not standardized. It is simply used to check that there is continuity, but does not assume its value. If it is applied, it must be accompanied by an increased visual check of each connection and element in the protective circuit.

For Class I assemblies, this visual check covers the actual continuity between the exposed conductive parts, and between the exposed conductive parts and the protective conductor. For checking this link, the continuity is measured at 25 A. The resistance must not exceed 50 MΩ.

The method used, measurement or checking, will be recorded on the individual inspection report. if other methods are used, for example those in standard EN 60204-1 (measurement of the voltage drop at 10 A), they must be specified.

Connecting exposed conductive parts
Figure 5 – Connecting exposed conductive parts

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3. Final inspection of the assembly (visual check)

This operation includes the visual inspections that must be carried out:

  1. Inspection of the mechanical elements: operation of locking systems, drawing out systems, closures, tightening torques, etc.
  2. Inspection of the wiring: cable entries, tightening of terminals, marking, etc.
  3. Lables/marks and information on the assembly: nameplates, etc.
  4. Technical information provided
  5. Compliance with the degree of protection
  6. Checking the mounting distances
  7. Electrical operating tests
  8. Provisions for transport and handling (if necessary).

Standard IEC 61439-1 defines a non-exhaustive of requirements that must be dealt with specifically: climates, ip, accessibility, etc. These must form the subject of an agreement between the manufacturer and the user

Final inspection ensures the safety of the LV switchgear in accordance with good professional practice.

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3.1. Conductors and wiring

The following items must be checked:

  1. Compliance with the wiring diagram
  2. Cross-section of conductors
  3. Labeling/marking of the circuits (power, control, data)
  4. Identification of the conductors (colour, alphanumeric code)
  5. Marking of poles
  6. Identification of the load circuits (outgoing cables)
  7. Maintenance of the conductors
  8. Distance from sharp edges (sheet metal edges)
  9. Treatment of conductors not protected against short-circuits (steady circuits, measurements)
  10. Flexible links, clearance of conductors from removable parts (drawers, doors)
  11. Entry of conductors into the enclosure (seal, mechanical protection, no stresses)
  12. Layout of the busbars (mechanical hold, distances between supports, bolted connectors).

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3.2 Checking wiring accessories

The following items must be checked:

  1. Compliance of devices with the specified models (rating, type, breaking capacity, operating curves)
  2. Obtaining breaking capacity by combining devices (if necessary)
  3. Discrimination on specified circuits
  4. Nameplates and marks
  5. Positioning of connections (tightening, partitions, terminal covers)
  6. Crimping of lugs.

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3.3. Measures for protection against electric shocks

The main protection of enclosed distribution assemblies against electric shocks is provided by a metal or insulated casing (cabinets or enclosures). In addition, each assembly must have a protective conductor for easy automatic cut-off off the power supply if a fault occurs inside the assembly or on the external circuits supplied via the assembly.

This protective conductor must be able to withstand the short-circuit stresses which may occur where the assembly is installed.

All the metal conductive parts of the assembly must be connected together and to the protective conductor.

LV assembly enclosure must provide continuity of the exposed conductive parts
Figure 6 – LV assembly enclosure must provide continuity of the exposed conductive parts
3.3.1 Protection against direct contact

The following items must be checked:

  1. Presence of faceplates providing a degree of at least 2x or xxB
  2. Presence of screens (recommended) providing a degree of at least xxa
  3. Forms of internal separation (if required)
  4. Presence of “live” warning labels.

3.3.2 Protection against indirect contact

Class I – Visual checking of the electrical connection of the chassis and structure of the assembly and the accessible metal parts:

  1. Presence of equipotential links on elements that are accessible (panels, doors) or can be drawn out
  2. Cross-section of equipotential links according to the power of the installed equipment
  3. Connection of protective conductors to the device terminals if provided
  4. Cross-section of protective conductors and main terminal.

NOTE: These provisions are checked by measuring the continuity (individual tests).

Class II – Visual checking of the provisions specific to class II:

  1. Holding of conductors in the event of detachment
  2. Insulation of the exposed conductive parts and the protective conductors
  3. Non-connection of the exposed conductive parts to the protective conductor
  4. Routing of the conductors in ducting, or on isolating supports or use of class ii conductors
  5. Reservation and identification of the areas treated as class II
  6. Presence of the symbol o and warnings
  7. No metal parts passing through the enclosure
  8. Insulation of the wall fixings.

NOTE: These provisions are checked by measuring the insulation or using a dielectric test (individual test).

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3.4 Checking the clearances

The following items must be checked:

  1. Distances from the device connections (lugs, terminals for cable lugs, etc.) to the nearby exposed conductive parts (chassis, plate).
  2. Bolted connection and connection on the bars: distance between bars and with the exposed conductive part.
Distances in the air
Figure 7 – Distances in the air

Regarding distances from the device connections in the air, these represent the shortest distance between two conductive parts. If there is a breakdown that disrupts the air, the electric arc will follow this path. ribs or partitions can increase the distances in the air.

The distances in the air are sized according the Uimp voltage given for the assembly.

Table 3 – Minimum clearances (mm)

Impulse voltage
Uimp (kV)
Minimum clearences (mm)
Between live parts
with different polarity
(P, N, bonding)
Between live parts and bonding with double or reinforced insulation
4 3 5.5
6 5.5 8
8 8 14
12 14 18

Regarding creepage distances, they represent the shortest distance along the surface of the insulating materials between two conductive parts. They depend on the properties of the insulating materials themselves and the degree of pollution.

Creepage distances
Figure 8 – Creepage distances

Degree of pollution X mm
(standard value)
2 1
3 1.5

Grooves and ribs can increase the creepage distance as long as they are large enough not to retain water.

In practice and for the elements concerned, which are mainly connected with mounting, only grooves at least 2 mm wide and deep should be taken into account.

The creepage distances are sized according to the insulation voltage Ui given for the assembly.

Table 4 – Minimum creepage distances in mm

Insulation voltage
Ui (V)
Minimum creepage distances in mm
(material group II, RC>4000)
Between live parts
with different polarity
(P, n, bonding)
Between live parts and bonding with double or reinforced insulation
Degree of polution 2 3 2 3
250 1.8 3.6 3.6 7.1
400 2.8 5.5 5.6 11
630/690 4.5 9 9 18
800 5.6 11 11 22
1000 7.1 14 14 28

The required clearance values between live parts when there is double or reinforced insulation are based on standard IEC 60664-1 “Insulation coordination for equipment within low-voltage systems”:

  1. The distances in the air are determined for the impulse voltage immediately above the value given for voltage Ui
  2. The creepage distances are determined for a voltage value corresponding to double the given insulation voltage Ui. The double or reinforced insulation values must be applied upstream of the devices providing effective protection of people against indirect contact: Residual current devices in TT system, short-circuit protection devices in IT and TN systems.

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3.5 Checking the mounting distances

Unlike clearances (distances in the air and creepage distances explained above) which are defined by the design of the devices, mounting distances are determined by the precautions taken at the installation stage (bolts between bars, custom supports, positions of lugs, etc.).

The following minimum distances must be complied with for assemblies at 400 V:

  • 10 mm between unprotected live parts with different polarity
  • 20 mm between unprotected live parts and exposed conductive parts (chassis, enclosure)

This distance is increased to 100 mm if the enclosure does not have a protection level of at least xxB.

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3.6 Testing of electrical operation

If required by the complexity of the assembly, an operating test may be necessary. The location (workshop or site) must be defined by agreement between the parties, as well as the test conditions:

  1. Circuits tested
  2. Number points connected
  3. Lock positions
  4. Sequencing of commands
  5. Current measurement
  6. Phase balancing
  7. Tests of residual current devices (RCDs)
  8. Measuring devices

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3.7 Testing of mechanical elements

The correct operation of the mechanical control devices, interlocks and locking devices, including those associated with
removable parts, must be checked.

This verification test does not have to be carried out on the devices (for example draw-out circuit breaker) of an LV assembly that has previously undergone type tests in accordance with their applicable product standard unless their mechanical operation has been modified by their mounting.

For devices which require verification by a test, the satisfactory mechanical operation must be checked after installation. 200 operating cycles must be carried out. The operation of the mechanical interlocks associated with these movements must be checked at the same time.

The correct mechanical operation of the doors and faceplates mounted on hinges must be checked, as well as the mechanical control components, interlocks and locking devices, including those associated with removable parts.

The following items must be properly checked:

  1. Locking and immobilisation
  2. Operation and closing of doors
  3. Presence of keys
  4. Coordination between locking and door of the room
  5. Draw-out and plug-in devices
  6. Mechanical safety of inverters
  7. Lifting devices (rings, brackets)
  8. Tightening torques

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3.8. Checking degree of protection

The degree of protection of LV assembly defines its capacity to protect people from direct contact with live parts and to prevent the entry of solid objects or liquids. It is specified by the IP code in accordance with the tests described in standard IEC 60529.

The IP code required for an assembly in an enclosure depends on its installation conditions and the external influences to which it is subjected.

In all cases it must be at least IP 2X. The degree of protection of an open assembly must be at least IP XXB

The following items must be performed and checked to confirm the given degree of protection:

  1. Maintenance of the degree of protection at the cable entries
  2. Links between assembled modules
  3. Sealing of doors, panels, openings
  4. Dust protection appropriate to the surrounding environment
  5. Protection of the ventilation or cooling devices
  6. Degree of accessibility to the energized internal parts (accessibility to informed people).

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3.9. Checking of labels/marks and information

Check the presence of a visible nameplate containing at least:

  1. The name of the manufacturer of the assembly (or its trademark)
  2. The name of the type of assembly or information giving the corresponding technical details
The connection points of the equipotential links provided are marked with the (earth) symbol
Figure 9 – The connection points of the equipotential links provided are marked with the (earth) symbol

The phases must at least be marked N, L1, L2, L 3, at the ends and at the connection points
Figure 10 – The phases must at least be marked N, L1, L2, L 3, at the ends and at the connection points

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3.10. Checking of information in the technical documentation

The following information must be included on the nameplate or in the technical documentation.

  1. Reference to standard IEC 61439-1
  2. The current type and frequency
  3. The rated insulation voltages (Ui) and rated operating voltages (Ue) if they are different
  4. The rated impulse withstand voltages (Uimp) if they are indicated
  5. The voltages of the auxiliary circuits if necessary
  6. The operating limits
  7. The rated current (in amperes) of each circuit
  8. The resistance to short-circuit currents:
    • Prospective rms current at the supply end of the assembly (in kA),
    • Short-time withstand current (lcw in kA) and
    • Permitted peak current (Ipk in kA)
  9. The IP degree of protection
  10. The class i or class ii measures to protect people
  11. The connection of functional units (fixed, with front terminals, with rear terminals, draw-out, plug-in)
  12. The form of internal separation
  13. The operating conditions if they are different from the usual conditions (corrosive, tropical, dusty atmosphere)
  14. The type of neutral earthing system
  15. The dimensions (height x width x depth)
  16. The exposed conductive parts

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Bonus – Routine test reports (PDF)

Download few templates of routine test report in form of an active PDF (2.0MB, ZIP)

Download templates

Sources:

  1. Enclosures and assembly certification by Legrand
  2. Construction and certification of assemblies in accordance with IEC 61439-1 & 2

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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.

5 Comments


  1. E vasanth kumar
    May 26, 2019

    How to develop my skills in switchgear and systems from basic help me plz


  2. Celso Simon
    May 10, 2019

    Excuse me but I do not know much English but I loved the article. It is very complete. I worked in the years from 1989 to 1994 in Siemens of Venezuela in the area of ​​testing of medium voltage, low voltage and control boards.


  3. Che Kuan Yau
    May 09, 2019

    Good reference, but to be used with great caution. There are far too many very serious mistakes or typographical errors. Also take note that reference IEC 60439 has been replaced by IEC 61439 since year 2014; even though the latter publications state the same requirements.

    In para 1.1
    a) ” The minimum value measured must be (according to standard IEC 60439-1) 1000 Ω/v with reference to the nominal voltage in relation to the earth of the circuit being tested.”
    It is a serious mistake to state that ” ..The minimum value measured must be ….” It should mean to be ” The minimum value measured shall be not lower than …..”
    b) ” In practice, a target value of at least 0.5 mΩ should be used for 230/400 V assemblies and at least 1 mΩ above that. ”
    Another very serious typographical error. ” …. at least 0.5 mΩ … and ….at least 1 mΩ above….” The symbol ” m” for milli is an error . It should be “M” for mega.
    c) “…there must be no receiver devices connected …” I am unable to recall the term “receiver devices” in any IEC publications.

    Strongly suggest the author to vet through it thoroughly.

    Your sincerely

    • Edvard
      Edvard
      May 09, 2019

      Thank you Che Kuan Yau for the valuable comment, I appreciete it.

      Yes, there were both standards IEC 60349 and IEC 61439 mentioned, that was a mistake. Regarding a) I added ‘at least 1000 Ω/V’ as it should be and exactly what you stated. Regarding b), it’s a typo, mΩs are of course MΩs. And under c), the term ‘receivers’ although unusual, is a common word used for all connected devices in an assembly (CTs, Vts etc.) that might burn during testing if remain connected. We can call it and ‘connected devices’.


  4. Vilas Deshpande
    May 08, 2019

    Like it.

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