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Home / Technical Articles / Forms of Separation (1) – Introduction

Protection and limitation

Standard BS EN 60439 Part 1, describes a system for classifying the various forms of separation to be provided principally for:

  • protection against contact with live parts belonging to the adjacent functional units.
  • limitation of the probability of initiating arc faults.
  • protection against the passage of solid foreign bodies from one unit of an Assembly to an adjacent unit.

Even though the Standard has now been revised with a UK National Annex to provide a wider scope of forms, it still does not give detailed advice on how to achieve these aims.

Manufacturers of switchboard assemblies employ many variations of design to meet this protection and any other additional market requirements. The means utilized to achieve these conditions may be partitions or barriers of metallic or non-metallic material. The partitions or barriers may provide individual separate compartments or alternatively, barriered sub-sections.

Greater clarification has been included within this guide by providing some basic definitions of the terms used and explaining some of the various methods employed by manufacturers to meet the required degree of separation. In general, the cost of an Assembly increases with enhanced levels of separation, but choosing the most expensive arrangement will not necessarily lead to the most appropriate solution.

Useful Definitions

The Standard includes definitions relating to Assemblies. Those particularly relevant to the separation of Assemblies include the following. The same clause numbering has been used to aid cross reference to the Standard.


A combination of one or more low-voltage switching devices together with associated control, measuring, signalling, protective, regulating equipment, etc., completely assembled under the responsibility of the manufacturer with all the internal electrical and mechanical interconnections and structural parts.

This includes floor standing or wall mounting distribution switchboards, panelboards, and motor control centres using electromechanical and/or electronic components. It does however specifically exclude individual devices and self-contained components which control a single circuit i.e., wall mounted starters and fuse switches.

Functional Unit

A part of an assembly comprising all the electrical and mechanical elements that contribute to the fulfilment of the same function.

Essentially this is all parts necessary to form a complete incoming or outgoing circuit. It includes all the main current carrying equipment, including cable terminals, and control devices within the assembly, that are necessary to form the complete circuit. It excludes the connections from the unit to the busbars (busbar connections) and any insulation or shrouding with which they may be provided with.

(Generally such connections have a short-circuit rating to match the rated current and short-circuit characteristics of the functional unit and historically were referred to as ‘fault free zones’).


A constructional unit of an assembly between two successive vertical delineations.

Usually considered to be a single full height column containing one or more functional units. Generally several columns are required to complete an Assembly


A constructional unit of an assembly between two successive horizontal delineations within a section.

Abstract in nature. The area or space within a column identified and bounded by two adjacent and horizontal constructional members e.g., cross members or shelves.


A section or sub-section enclosed except for openings necessary for interconnection, control or ventilation.

An enclosed area or space within an Assembly. Also includes a product complete with its own integral housing (MCB, MCCB, Moulded Switch, ACB) if protection to IP2X is assured.


A part providing protection of equipment against certain external influences and in any direction, protection against direct contact to a degree of protection of at least IP2X


A part of the enclosure of a compartment separating it from other compartments.

A component used to form the top, bottom, sides, front or back of a compartment or enclosure and which can be manufactured from metal or an appropriate plastic material.


A part providing protection against direct contact from any usual direction of access (minimum IP2X) and against arcs from switching devices and the like, if any.

Prevents finger contact with live parts and/or protects operators from emissions from switching devices. It can take the form of insulating material in direct contact with the live part, e.g., heat shrink sleeving on a busbar.

Alternatively it can take the form of rigid insulation or an earthed metal screen appropriately positioned relative to the live part(s).

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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. Dre
    Apr 17, 2014

    Hi Edvard,

    I am interested in learning autocad designing for MV/LV circuits. can you guide me on that?

  2. tekenab
    Sep 13, 2013

    I just join this organization as subscription for articles and all that…. However, this site is super, well done professionals. I hope to add my articles on this site one day. Thank Edvard and co.

    • Edvard
      Sep 13, 2013

      Thanks man! You welcome to contribute in any way!!

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