Single cables. Used throughout the industry, single cable comprise a central solid or stranded conductor which is given a single layer of insulation. The Insulation may be PVC, XLPE, LSF or some other specialist insulator depending on the application.Conductors are normally copper, although aluminium conductors used to be used.
Single cables require mechanical protection. They are commonly enclosed in conduit or trunking.
Steel Wire Armoured cable (SWA). Used for installation in underground, external or exposed situations, SWA cabling is probably the most common cable for mains distribution although it is extensively used in smaller sizes as well. It generally comprises central copper or aluminium conductors which are insulated usually with XLPE. The conductors are protected against damage by steel wires and the whole cable is sheathed in a protective plastic outer sheath. Available in all sizes and current ratings that are likely to be encountered within a normal building. Specialist SWA cables are available such as Paper Insulated Lead Sheathed (PILC) but are rarely used in building services.
Mineral Insulated Copper Clad Cable (MICC). (sometimes called MICS copper sheathed) This is a specialist cable that has copper inner conductors that are insulated with a mineral compound. The cable has an outer sheath of copper and can be further protected against the atmosphere by a outer plastic sheath. MICC is is available in Heavy & Light gauges. Sizes above 35mm˛ are usually single core cable. MICC is expensive to purchase and specialist skills are needed to install it. However, it is long lived, is smaller that an equivalent SWA cable and importantly is fire proof. Hence it can be used to serve emergency services where the cable is required to remain in use during fire conditions.
Twin & Earth Cable (T&E) - Possibly the cheapest and easiest wiring to install twin & earth cable comprises a central conductor (usually solid) which has PVC insulation. Two insulated conductors are combined with a third uninsulated conductor (used as a CPC) and all three are enclosed in an outer PVC sheath. Variants are available with additional cores (Triple & Earth).
Twin & Earth cable is used in the vast majority of domestic installations, as well as in budget commercial applications, and other installations where funds are limited.
It lacks the protection possessed by other forms of cable unless enclosed in conduit. T&E wiring can become messy in all but the simplest of wiring applications. Also, it can be hard to rewire (as opposed to singles in conduit).
T&E cable is not highly suitable for most industrial applications, neither can it be used where there is a requirement for LSF cable.
Flexible Cables. Used where a item of equipment is connected to an outlet or other termination. Flexible wiring is needed if it is likely that the equipment may move or vibrate in normal use. Many forms of flexible cable exist with many different forms of insulation. They all tend to have multistranded conductors and are all able to be flexed and bent without undue stress being placed on the conductor.
Trunking. A form of containment that having a hollow box shaped section, and available in linear lengths. Trunking is available in both PVC and steel. PVC trunking can range in size from 15x15mm up to 150x150mm or even bigger and is quick and easy to install. Steel trunking affords better protection but is harder to install. Steel trunking comes in sizes from 50x50mm up to 300x300 and above.
Trunking is particularly suitable for use with single cables where many circuits can be contained in a single trunking (subject to compliance with BS7671 segregation regulations). Twin & Earth cables can also be protected by trunking.
Conduit. Still by far the most common form of containment. Conduit comprises lengths of robust tube, available in set sizes 16mm, 20mm, 25mm & 32mm. Conduit is available in both PVC and Steel form. PVC conduit is available in light & heavy duty grades and is relatively easy to install, requiring basic tools & adhesive to install. Steel conduit affords better protection than PVC but requires specialist tools and knowledge to install. It is available in Black Enamel (painted) finish or Galvanised finish (for exterior applications). Properly installed steel conduit can be used as a CPC.
Conduit can be surface mounted or buried (flush) in walls. It is used extensively with single cables and Twin & Earth (for protection down walls ect.). Flexible conduit is not a direct variant of standard conduit, it is commonly formed from spiral arrangements of toughened PVC, steel or aluminium. The construction allows the conduit to be flexed and is normally used in short lengths to serve equipment and or items that may need to be moved.
Cable Tray. Cable tray is a form of steel traywork, available in linear lengths which is used in industrial and commercial situations as a support for cables which are installed in free air (such as SWA and MICC cables) Cable tray is normally available in sizes between 50mm wide and 900mm wide, in a range of gauges light, medium & heavy duty. It is usually supplied galvanised, although special finishes such as power coating are sometimes used.
In recent years, plastic based alternatives have been developed.
Cable Basket - Cable basket is a variant of cable tray. It comprises a basket like linear wire system which, although not a structurally strong as cable tray, is lighter and easier to install. It is commonly used for support of light cabling such as data & telephone wiring and has seen great increases in use with the advent of structured cabling systems.
Floor trunking. A form of trunking that is specially adapted for installation within floor voids, or screeds. It commonly has two or more compartments enabling segregation and hence is used for 240V services as well as data and telecommunication systems. It is often fitted with custom floorboxes. Space restrictions can mean limited room in floor trunking and the number of cables able to be installed can present problems
Powertrack. A specialist form of trunking that contains busbars. This system is far smaller than the busbar distribution systems used in mains distribution. It is commonly rated at no more than 63A and is installed in floor or ceiling voids. Take off sockets are installed at regular intervals to allow the "Plugging in" of floorboxes, sockets and other equipment. Variants are available with clean earth facilities. This type containment is common in office premises as well as industrial situations.
Perimeter trunking systems - Another trunking variant, this type of trunking is manufactured in various forms, normally with two or more compartments. It can be obtained in the form of dado trunking, skirting trunking or even cornice trunking. Available in PVC, aluminium or steel (powered coated or painted) perimeter trunking systems are a popular choice in open plan office, general offices and similar areas.
Floor boxes - Commonly installed in conjunction with floor trunking systems or powertrack systems. Recessed floor boxes can be installed into a cavity floor or screeded floor. They comprise one or more compartments and accessory boxes which can be used to terminate many different services at one box. This enables users to plug in 240V power, data and telephones etc. at the same position, maybe under a desk. Common in open plan office developments.
Modular systems - This phrase covers a wide range of various types of system, all of which are modular in their use and installation. Includes pre-wired conduits and trunking as well as modern systems which are wired on a "spider" system using pre-cut lengths of prewired flexible conduit or other flexible wiring. These systems have the great advantage of speed and ease of installation. They are popular in office type installations where large numbers of recessed fluorescent luminaires may be installed.
