Steel Wire Armoured Cable: All you need to know
SWA Cable, abbreviation for Steel Wire Armoured Cable, is a hard-wearing power cable designed for the supply of mains power, or to quote most electricians a pain in the ar… neck. swa stripping tool
SPOILER ALERT: A solution for Electricians, Engineers, Contractors, Construction Managers, Project Managers and anyone dealing with SWA Cable at the end of this post (SWA Stripping Tool).
What is an SWA Cable?
SWA is a power and auxiliary control cable, designed for use in mains supply electricity. It is one of the various protected electrical links – including 11 kV Cable and 33 kV Cable. Found in underground systems and frameworks, cable networks, control systems, power networks, outdoor and indoor applications, and cable ducting.
Steel Wire Armoured Cable’s design features have mechanical protection, which explains its common use for external applications. The armour reduces any risk of pinching or damaging the cable, while the steel protects the armoured cable. SWA cables are heavy, which makes them extremely difficult to bend; therefore they are most suited to underground cabling or fixed to outdoor walls using cable cleats.
Other widely used terms for it are: Mains Cable, Armoured Cable, Booklet Armoured Cable and Power Cable. The name Power Cable though, applies to a large variety of links including 6381Y, 6491X, NYCY, NYY-J Cable.
(For our fellow Americans: replace Armoured with Armored)
Using Steel Wire Armoured Cable as Earthing
Using armour as the means of providing earthing/ grounding to the equipment supplied by the cable, is a subject of controversy within the electrical installation industry. This function is technically famous as circuit protective conductor or CPC.
Usually an additional core within the cable is the CPC (for example, using a three core cable instead of a 2-core one for line and neutral, and the armouring as the CPC) or an outside earth wire runs alongside the cable, serving as the CPC. The main concerns are:
- The relative conductivity of the armouring compared to the cores (which decreases as the size of the cable increases),
- Reliability and Health & Safety issues.
According to recent articles and research by authoritative sources, a detailed analysis of the practice concluded that, in most cases, the armouring is suitable to serve as the CPC under UK Wiring Regulations.
Construction of SWA Cables
The typical construction of a Steel Wire Armoured Cable includes:
- Conductor: Class 2 Plain Stranded Copper (Cu) Conductor, complying with BS EN 60228:2005.
- Insulation: Cross-Linked Polyethylene’s (XLPE) use as insulation in many power cables offers excellent electrical properties and water resistance. It also ensures that conductors and other metal substances do not come into contact with each other.
- Bedding: Polyvinyl Chloride’s (PVC) choice as bedding provides a protective boundary between inner and outer layers of the cable.
- Armouring: Steel Wire Armour (SWA) used for mechanical protection. That way the cable can withstand higher stresses, be buried directly and used in external or underground projects. The armouring usually connects to earth and can be used as the CPC (as above).
- Sheath: Polyvinyl Chloride (PVC) Sheath holds all the components together and provides additional protection from external damage.
Sheath Colour: Black (Carbon loaded for UV stability)
Voltage Rating: 600/100V
The construction of a Steel Wire Armoured Cable depends on the intended use. For example, when the power cable needs to be installed in a highly populated and /or enclosed public area, a Low Smoke Zero Halogen (LSZH) equivalent, called SWA BS 6724 Cable must be used (SWA Cable BS 6724 has LSZH bedding and a black LSZH sheath). All London Underground cables have to use LSZH sheathing after the fatalities due to toxic gas and smoke inhalation during the King’s Cross fire in London in 1987.
What do BS5467 and BS6724 stand for?
The use of terms BS5467 or BS6724 is very common when referring to Steel Wire Armoured Cable. These phrases mean that the SWA cable meets the corresponding British Standard requirements, for both construction and testing.
Steel wire armour is only used on multi core cables. Multi core swa cable, is a cable with two or more cores:
2-Core SWA Armoured Cable is live and neutral for Class II and Double Insulated appliances which do not need earth connection.
3-Core SWA Armoured Cables are live, neutral and earth, unlike 2-Core. Three core cable is for Class I or Single Insulated which must have earth connections.
4-Core SWA Armoured Cable are perfect for low voltage or low current signal applications. Made of 4 copper individual colour coordinated cables hence the name four core cable.
5-Core SWA Armoured Cable is most commonly used in low-voltage transmissions and uses a three-phase line with one zero line for the power supply.
7-Core SWA Armoured Cable’s main purpose is for low-voltage connections with a max of normal 50Vdc. Each core is from copper conductors within the steel armouring.
Single core (Aluminium Wire Armoured)
Steel wire armour is only suitable for use on multicore versions of the cable. When a cable has only one core, the use of aluminium wire armour (AWA) instead of steel wire is preferrable. This is because the aluminium is non-magnetic. In a single core cable, the current produces a magnetic field. This would induce an electric current in the steel wire, which could cause overheating.
Cutting & Stripping SWA Cable Easily & Safely
The increasing number of electricians’ injuries while working with SWA cable along with the updated Health and Safety Regulations that forced most major contractors to ban blades and cable knives on site, made the need for a new SWA stripping tool an urgency. The SACS Tool was a welcome breath of fresh air to tackle this issue while countering all the drawbacks of previous SWA cutters: