BASEC News

BASEC's Top Five Cable Problems

03/05/11
Dr Jeremy Hodge, Chief Executive of the British Approvals Service for Cables (BASEC) discusses the top five problems electrical contractors ask about with electrical cables and offers advice on what to do if a problem is identified.
Dr Jeremy Hodge, Chief Executive of the British Approvals Service for Cables (BASEC) discusses the top five problems electrical contractors ask about with electrical cables and offers advice on what to do if a problem is identified.
Cable damaged during installation
Armoured cables are intended for use in tough environments such as burial, but they can be damaged during installation. The highest risk is during the process of pulling cable into buildings, particularly over complex routes. The external cable sheath can be scored by a sharp edge such as a cable tray end or even a screw or bolt, and leave a longitudinal groove that can result in later splitting of the sheath. Installers should check for sharp edges before pulling cable. Pulling in cable from a central point, in two directions, can sometimes result in twists or kinks in the cable, and this can result in bulging or displaced armour wires.  Installers should take care not to introduce twists or kinks into cable as it comes from the drum, particularly as it passes around rollers. Installers should take notice of the minimum bend radius of cable recommended by the manufacturer, both in the installation process and in cable tray design and layout. Finally, the un-terminated ends of armoured cables should be protected by end caps until terminated.
Conductor resistance
BASEC has issued a number of warnings to the electrical trade of cables that, when tested through BASEC’s independent testing laboratory, indicate excessive conductor resistance. Some conductors have been found to have up to two standard sizes smaller than that marked on the cables, which could result in overloading and overheating in use. End users are encouraged to check purchase documentation, design specifications and test their installation to ensure that the applied loading and earthing are acceptable. Findings should then be recorded in documentation. For peace of mind, look for the BASEC mark on the cable sheath, and on the drum or reel which proves it has been independently tested.
 
Failing smoke for fire test
To describe a cable as ‘LSHF’ (Low Smoke Halogen Free), it must pass two tests: (a) a smoke cube test, which sets a maximum accumulated smoke density produced when burning the cable with a standard fire, and (b) a corrosive and acid gas test where the cable materials are roasted and must give off a maximum of 0.5% acid gas. These tests are both specified in cable standards which include the description ‘having low emission of smoke and corrosive gases when affected by fire’. Cables made from PVC or similar halogenated materials are unlikely to pass these tests. In terms of market practice more people are specifying and using LSHF cables.  However this does not mean that these cables are fire resistant. For example for fire-fighting lifts and smoke extraction systems, robust fire resistant cables are needed to continue to work in a fire. For this you need special fire resistant cables such as BS 7846 armoured cable or mineral cable to BS EN (IEC) 60702-1.
Strippability
Sometimes due to a manufacturing fault, cables are found to be unstrippable. Installers should check their cable is strippable before first fix installation. If cable has been laid and plastering or decoration has been completed, when the installer comes to fit accessories at second fix and the cable cannot be stripped easily, there can be serious difficulties which will cost the installer both time and money. Strippability can be readily checked by feeling the free end of each reel of cable with a fingernail to check if the sheath and bedding can be lifted away from the cores. If it will not come away from the cores easily, then normal stripping of the cable should be attempted. If it is difficult to strip without damaging the insulation material, affected cable should be returned to the supplier.
Markings
Often it is not until cables are installed and tested that a problem is discovered and by then it can be too late to avoid the enormous cost of rectifying the situation. Contractors should ensure that the cable supplied by the distributor or wholesaler is the correctly specified cable and check the markings on the cable sheath - not just the packaging. When assessing cable markings look in particular for a recognisable or known manufacturer’s identification, so if there is a problem it will help in tracing the cable back through the supply chain. Without a manufacturer’s stamp it is nearly impossible to trace the cable, therefore never accept cable with no origin markings. For peace of mind, you should also insist on an independent third-party approved cable with marking such as BASEC, HAR or equivalent. It is also important to specify on your order the British or European standard number the cable should conform to.
For more information please visit: www.basec.org.uk, email: technical@basec.org.uk or call (01908) 267300
 
 
 
 
 
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