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Home / Technical Articles / Forms of Separation (2) – Fundamentals

Separation of an assembly elements

In accordance with the Standard, separation of the various elements of an Assembly: busbars, functional units, terminals, can be claimed providing one or more of the following criteria are met:

1. “Protection against contact with live parts belonging to adjacent functional units. The degree of protection shall be at least IP2X or IPXXB”

As a minimum, finger contact with live parts in adjacent functional units is prevented. With Assemblies supplied by EIEMA Member Companies this is extended to include protection against finger contact between: functional units, adjacent busbars and busbar connections, and terminals as required for the particular form of separation being considered.

The requirement is proven with the standard test finger.

2. “Limitation of the probability of initiating arcing faults”

Note: A second amendment to IEC 439-1 is presently being considered. This effectively removes this requirement from the Standard, since no common repeatable method of testing could be arrived at internationally.

EIEMA Members meet this non specific and probabilistic requirement by; good design practices and ensuring, usually by type test, the operation of switching and short circuit protective devices does not adversely affect adjacent functional units or busbars.

3. “Protection against the passage of solid foreign bodies from one unit of an Assembly to an adjacent unit. The degree of protection shall be at least IP2X”

The minimum requirement is proven by the standard test finger not being able to touch live parts in adjacent units and a 12mm ball not being able to pass between units. In practice a higher degree of protection may be required for horizontal partitions to prevent small objects from falling between compartments and should be identified in the contract specification.

These three fundamental criteria are interrelated. EIEMA Member Companies will therefore ensure all three are fully met in respect of the particular form of separation offered.

Achieving Separation

The fundamental requirements in the Standard are performance criteria and not constructional details on how separation should be achieved. There is a requirement that Assemblies are divided by means of partitions or barriers (metallic or non-metallic) into separate compartments or barriered sub-sections, but not for example:

  • each functional unit to be in its own compartment;
  • partitions and barriers to be manufactured from earthed metal, etc.

Separation can be achieved in several ways. Depending on a particular application and the requirements for maintenance, this may include:

  1. PVC sleeving, wrapping or plastic coating of conductors.
  2. Insulated terminal shields or PVC ‘boots’.
  3. Rigid insulated barriers or partitions.
  4. Compartments formed from earthed metal.
  5. A device’s integral housing.

Where a Specifier or User has a particular preference, this should be clearly stated at the enquiry stage.

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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.


  1. pankaj mishra
    Jul 11, 2015

    Want a traning

  2. John Lovel
    May 28, 2014

    Edvard thanks alot

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