Steel Wire Armoured (SWA) Cable
Encyclopedia
Steel Wire Armoured Cable, commonly abbreviated as SWA, is a hard-wearing power cable
designed for the supply of mains electricity. It is one of a number of armoured electrical cables - which include 11kV Cable and 33kV Cable - and is found in underground systems, power networks and cable ducting.
The typical construction of an SWA Cable can be broken down as follows:
The PVC version of SWA Cable, described above, meets the requirements of both British Standard BS5467 and International Electrotechnical Commission
standard IEC 60502. It is known as SWA BS5467 Cable and it has a voltage rating of 600/1000V.
SWA Cable can be referred to more generally as Mains Cable, Armoured Cable, Power Cable and Booklet Armoured Cable. The name Power Cable, however, applies to a wide range of cables including 6381Y, NYCY, NYY-J and 6491X Cable.
, as the name suggests, is one where there are a number of different cores. When SWA Cable has only one core, aluminium wire armour (AWA) is used instead of steel wire. This is because the aluminium is non-magnetic. A magnetic field is produced by the current in a single core cable. This would induce an electric current in the steel wire, which could cause overheating.
(LSZH) equivalent, called SWA BS6724 Cable must be used. After the King’s Cross fire in London in 1987 it became mandatory to use LSZH sheathing on all London Underground cables - a number of the fatalities were due to toxic gas and smoke inhalation. As a result, LSZH cables are now recommended for use in highly populated enclosed public areas. This is because they emit non-toxic levels of Halogen and low levels of smoke when exposed to fire. SWA Cable BS6724 - which meets the requirements of British standard BS6724 - has LSZH bedding and a black LSZH sheath.
Power cable
A power cable is an assembly of two or more electrical conductors, usually held together with an overall sheath. The assembly is used for transmission of electrical power...
designed for the supply of mains electricity. It is one of a number of armoured electrical cables - which include 11kV Cable and 33kV Cable - and is found in underground systems, power networks and cable ducting.
The typical construction of an SWA Cable can be broken down as follows:
- Conductor: consists of plain stranded copper (cables are classified to indicate the degree of flexibility. Class 2 refers to rigid stranded copper conductors as stipulated by British Standard BS EN 60228:2005)
- Insulation: Cross-linked polyethylene (XLPE) is used in a number of power cables because it has good water resistance and excellent electrical properties. Insulation in cables ensures that conductors and other metal substances do not come into contact with each other.
- Bedding: Polyvinyl chloridePolyvinyl chloridePolyvinyl chloride, commonly abbreviated PVC, is a thermoplastic polymer. It is a vinyl polymer constructed of repeating vinyl groups having one hydrogen replaced by chloride. Polyvinyl chloride is the third most widely produced plastic, after polyethylene and polypropylene. PVC is widely used in...
(PVC) bedding is used to provide a protective boundary between inner and outer layers of the cable. - Armour: Steel wire armour provides mechanical protection, which means the cable can withstand higher stresses, be buried directly and used in external or underground projects. The armouring is normally connected to earth and can also be used as the circuit protective conductor ("earth wire") for the equipment supplied by cable.
- Sheath: a black PVC sheath holds all components of the cable together and provides additional protection from external stresses.
The PVC version of SWA Cable, described above, meets the requirements of both British Standard BS5467 and International Electrotechnical Commission
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...
standard IEC 60502. It is known as SWA BS5467 Cable and it has a voltage rating of 600/1000V.
SWA Cable can be referred to more generally as Mains Cable, Armoured Cable, Power Cable and Booklet Armoured Cable. The name Power Cable, however, applies to a wide range of cables including 6381Y, NYCY, NYY-J and 6491X Cable.
Aluminium Wire Armoured Cable
Steel Wire Armour is only used on multicore versions of the cable. A multicore cableMulticore cable
An audio multicore cable is a cable which contains from 4 to 64 individual audio cables inside a common outer jacket. Audio multicore cables are widely used whenever multiple audio signals, for example from a number of microphones, need to be conveyed between common locations...
, as the name suggests, is one where there are a number of different cores. When SWA Cable has only one core, aluminium wire armour (AWA) is used instead of steel wire. This is because the aluminium is non-magnetic. A magnetic field is produced by the current in a single core cable. This would induce an electric current in the steel wire, which could cause overheating.
Use of armour for earthing
The use of the armour as the means of providing earthing to the equipment supplied by the cable (a function technically known as the circuit protective conductor or CPC) is a matter of debate within the electrical installation industry. It is sometimes the case that an additional core within the cable is specified as the CPC (for instance, instead of using a two core cable for line and neutral and the armouring as the CPC, a three core cable is used) or an external earth wire is run alongside the cable to serve as the CPC. Primary concerns are the relative conductivity of the armouring compared to the cores (which reduces as the cable size increases) and reliability issues. Recent articles by authoritative sources have analysed the practice in detail and concluded that, for the majority of situations, the armouring is adequate to serve as the CPC under UK wiring regulations.SWA BS6724 Cable
The construction of an SWA Cable, however, does depend on the intended use of the cable. When the power cable needs to be installed in a public area, for example, a Low Smoke Zero HalogenLow Smoke Zero Halogen
Low smoke zero halogen or low smoke free of halogen is a material classification typically used for cable jacketing in the wire and cable industry. LSZH cable jacketing is composed of thermoplastic or thermoset compounds that emit limited smoke and no halogen when exposed to high sources of...
(LSZH) equivalent, called SWA BS6724 Cable must be used. After the King’s Cross fire in London in 1987 it became mandatory to use LSZH sheathing on all London Underground cables - a number of the fatalities were due to toxic gas and smoke inhalation. As a result, LSZH cables are now recommended for use in highly populated enclosed public areas. This is because they emit non-toxic levels of Halogen and low levels of smoke when exposed to fire. SWA Cable BS6724 - which meets the requirements of British standard BS6724 - has LSZH bedding and a black LSZH sheath.
See also
- CableCableA cable is two or more wires running side by side and bonded, twisted or braided together to form a single assembly. In mechanics cables, otherwise known as wire ropes, are used for lifting, hauling and towing or conveying force through tension. In electrical engineering cables are used to carry...
- Cross-linked polyethylene
- Electrical wiringElectrical wiringElectrical wiring in general refers to insulated conductors used to carry electricity, and associated devices. This article describes general aspects of electrical wiring as used to provide power in buildings and structures, commonly referred to as building wiring. This article is intended to...
- Polyvinyl chloridePolyvinyl chloridePolyvinyl chloride, commonly abbreviated PVC, is a thermoplastic polymer. It is a vinyl polymer constructed of repeating vinyl groups having one hydrogen replaced by chloride. Polyvinyl chloride is the third most widely produced plastic, after polyethylene and polypropylene. PVC is widely used in...
- Power cablePower cableA power cable is an assembly of two or more electrical conductors, usually held together with an overall sheath. The assembly is used for transmission of electrical power...
Further reading
- http://www.bs6724.co.uk/
- http://swacables.co.uk/