Low Voltage Switchgear and Controlgear Assemblies: BS EN 60439-1: 1994 (IEC 439-1) Including Amendment No1: 1995

INTRODUCTION TO EIEMA

EIEMA the Electrical Installation Equipment Manufacturers’ Association, is an autonomous, incorporated Association of British manufacturers of electrical installation equipment. The Association’s roots date back to 1915 as a product section of BEAMA - The Federation of British Electrotechnical and Allied Manufacturers’ Association. EIEMA’s Low Voltage Distribution Switchboard Technical Committee consists of major UK manufacturing companies operating under the guidance and authority of the EIEMA Industrial Products Group supported by specialist central services for guidance on European Single Market, Quality Assurance, Legal and Health & Safety matters. EIEMA members actively participate in the work of numerous International, European and National standards committees. This provides the background and support to ensure safety and performance for the design, development and manufacture of its members’ products. The result is quality equipment of the highest standard throughout each group of the Association. Membership of EIEMA Low Voltage Distribution Switchboard Technical Committee is conditional upon compliance with, or a commitment to, achieving the stringent standards of quality to BS EN ISO 9001:1994.

INTRODUCTION

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 utilised 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.

2.1.1 Assembly: “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.

2.1.5 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’).

2.2.1 Section: “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.

2.2.2 Sub-Section: “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.

2.2.3 Compartment: “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. See also 2.4.5.

2.4.5 Enclosure: “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”.

2.4.10 Partition: “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. 2.4.11 Barrier: “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).

FUNDAMENTALS OF SEPARATION

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: a) PVC sleeving, wrapping or plastic coating of conductors. b) Insulated terminal shields or PVC ‘boots’. c) Rigid insulated barriers or partitions. d) Compartments formed from earthed metal. e) A device’s integral housing. Where a Specifier or User has a particular preference, this should be clearly stated at the enquiry stage.

SELECTING A FORM OF SEPARATION

In general, the price of an Assembly will increase with increased levels of separation and/or types of construction. Choosing the arrangement with the most internal barriers will not always lead to the most appropriate solution. Where specific requirements are not stated or identified, the manufacturer is likely to assume the most cost effective solution will satisfy the customer’s needs and offer it accordingly. To select the most suitable arrangement for each application, EIEMA members recommend the following points are considered:

• Site and position of the Switchboard.

• Maintenance requirements of the switchgear.

• Skill level of personnel having access to the Assembly

• Probability of requiring access to the terminals of a particular circuit with those adjacent live and still in service.

• Difficulty and/or inconvenience in isolating the complete Assembly.

• Price and benefits of the different forms.