Electrical Enclosures
Why they’re needed and how to use them
BS 7671 dictates that all electrical connections, other than those in a protective conductor, but including connections in extra–low voltage circuits, must be contained within an enclosure meeting certain requirements.
Here is a breakdown of guidelines:
Means of enclosure:
Electrical connections in a live conductor or a PEN conductor must be contained in one or more of the following (with the first two being most common):
- A suitable British standard–compliant accessory, such as a lighting switch or socket outlet.
- A British standard–compliant equipment enclosure, e.g. a box forming part of a conduit system.
- A suitable enclosure which complies with relevant glow–wire test requirements of BS 6458–2.1
- An enclosure formed or completed with building which is non–combustible when tested to BS 476–4.
- An enclosure formed or completed by part of the building structure, having the ignitability characteristic “P”, as detailed in BS 476–5.
Outside enclosures:
Should be selected and installed so that they provide adequate protection against mechanical damage, such as impact, temperature and water.
Cable cores and non–sheathed cables:
Cores of sheathed cables which have had the sheath removed, and non–sheathed cables at the termination of a conduit, trunking or ducting, must be enclosed.
Protection against direct contact:
- Under BS 7671, enclosures that are used to provide people and livestock with protection against direct contact must provide a degree of protection of IP2X or IPXXB (protection against access to live parts with a finger); and where a horizontal top surface is accessible, it must be IP4X protected against access to live parts with a 1mm diameter wire.
- It should only be possible to open the enclosure with a tool or key, unless an alternative is possible — for permissible alternatives check Regulation 421–03–04.
Extra–low voltage connections:
These are subject to requirements in exactly the same way as higher voltage ones — faulty connections in low voltage can deteriorate more rapidly during overheating due to the fact that currents are higher when voltage is lower.
Equipment:
- ELV equipment — care should be taken when selecting ELV products as some do not provide a means of termination enclosure.
- Backless equipment — such as with light fittings where connections will not fit into a standard box — requires care to be taken to meet regulations for enclosing the connections.
- If building material is used to complete the enclosure then it must be suitable and comply with BS 7671, for example concrete and plasterboard. For material which is not suitable an electrical black–box should be used to screen the connection from the material.
- Non–metallic moulded enclosures provide excellent protection and performance, for example, Glass Reinforced Plastic (GRP) enclosures are strong, lightweight, easier to handle and non–conductive.
Metal capping embedded in walls
In order to avoid damage to cables, for instance from a trowel, with a non–metallic sheath on walls that are to be plastered, metallic capping should be used to keep the cables securely in place. It does not have to be earthed providing it is installed according to the relevant regulations in BS 7671, however any sharp edges on the capping must be removed to prevent damage to the cables.
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