Dangers of substandard armoured cable
What happens when armoured cable gets damaged?
The purpose of Steel Wire Armoured (SWA) cable is that it is manufactured to have mechanical protection; the wire armour surrounding the cable is intended to prevent the electrical insulation and conductors becoming damaged.
Insufficient Mechanical Protection
When the Approved Cables Initiative issued a public warning about a defective 35mm2 four core SWA power cable imported from India, one of the many things wrong with the cable was that it had insufficient mechanical protection.
The problem was that the diameter of the steel wire used to form the cable’s armour was too small. These thin wires were unable to provide the required level of protection to the conductor making the cable vulnerable and a potential hazard.
Another problem was that the wire’s armour had not been galvanised effectively as was evident from the corrosion that had already started to occur with the armour, probably because of incomplete zinc coverage, leaving the steel wires unprotected.
Cable Corrosion
Corrosion is likely to further reduce its strength and make it more susceptible to mechanical damage from a civil contractor, for example, digging near buried cables. This is a major concern because steel wire armoured cables are often used for outdoor applications where the cable is buried directly in the ground.
Of equal concern was that the wire armour’s conductivity was insufficient. This will have been made worse by its corrosion. This is a potential problem where the armour is used as a means of providing earthing to equipment supplied by the cable, where the armour is used as the circuit protective conductor (CPC).
Fire Hazard
Additional issues with the cable were that the cross-sectional area of the copper conductor was below the 25mm2 but it was sold and marked as 35mm2; the conductor’s resistance also exceeded the specified maximum, both of which could result in the conductor running hot, damaging the insulation and becoming a fire hazard.
British Standards
The findings serve to illustrate precisely why everyone should purchase cables made by reputable manufacturers, such as Prysmian, sold by reputable wholesalers and distributors. Prysmian manufacturers cables which comply with all relevant British Standards including BS 5467 PVC SWA cable BS6724 where low smoke zero halogen cables are required and BS 7846 for fire resistant SWA cables such as FP600s.