BASEC News

Cable Types and Test Methods

20/03/12
BASEC is a specialist certification body for cables, working in the UK and around the world with reputable cable manufacturers. Gaining BASEC product approval for a cable is a prestigious mark of quality for a cable manufacturer.

Electrical power and wiring cables, data and signal cables and ancillary products are rigorously tested to meet necessary and appropriate standards through detailed examination of manufacturers' production processes and controls, full initial type testing and regular surveillance testing.  BASEC can in principal certify any type of cable, including bespoke and novel designs.

The technical specifications for cables are set out in standards at British, European and international level, supplemented in many cases by industry, application or company specific specifications. In addition to the construction and materials requirements (for example the types of plastics to use) these documents also specify the testing that needs to be applied in order to demonstrate and verify compliance. Most cables require between 30 and 60 different tests and examinations.

Common cable types:

Building wiring and flexible cables

BS 6004
- This is the main standard for PVC wire and cable commonly used in final circuits in buildings. There are 11 separate construction types set out in Tables, including the familiar ‘flat twin and earth’ ‘meter tails’, ‘conduit wire’ and other types.

BS 7211
- This standard offers Low Smoke Halogen Free (LSHF) versions of many of the types of wire and cable found in BS 6004. There are nine separate construction types set out in Tables.

BS 6231
- This is the primary British standard for single core instrument wire and includes the higher temperature rated type known commercially as ‘tri-rated’. This means it can simultaneously comply with the British, American (UL) and Canadian (CSA) standards.

BS 6500 - This is the main British Standard for flexible cables. It incorporates a number of construction types of various materials, many of which are harmonised with European standards and are within the HAR scheme.

BS 8436
- This is installation cable for use in final circuits, with an integral earthed screen and LSHF sheath. It is intended for use at shallow depths in partitions and related applications. It is nail penetration tested in conjunction with an RCD to meet Wiring Regulations requirements.

Armoured and special cables

BS 5467
- These are armoured power cables with XLPE or EPR insulation and PVC sheathing. They are used in many construction, commercial and industrial applications.  Two, three, four, five and multi-core versions are available.

BS 6724
- These are armoured power cables with XLPE or EPR insulation and LSHF sheathing, commonly used where public access is a factor.  Two, three, four, five and multi-core versions are available.

BS 7846
- These are fire resisting armoured power cables with XLPE or EPR insulation and LSHF sheathing and enhanced circuit integrity properties. Two, three, four, and five core versions are available.

BS 7629-1
- Commonly used with fire alarm systems to BS 5839-1 and emergency lighting systems to BS 5266-1, this is a widely used type of ‘soft skin’, fire resistant screened cables. They have low emission of smoke and corrosive gases when affected by fire.

BS EN 60702-1 (IEC 60702-1)
- Often used in emergency systems, this is an internationally harmonised standard for mineral insulated cables. They have high fire resistance and properties designed to survive fires.

Examples of tests on cables


Conductor resistance

This test measures the amount of electricity that a cable can safely transmit, and broadly measures the amount of copper present. 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.

Smoke tests
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.

Fire performance
Some cables are used in specialist fire systems and have to withstand a fire for two hours or more. Fire tests on cables vary considerably, but all cables are subjected to the ‘bunsen burner’ test and others are expected to continue working for many hours while being subjected to hot gas flames, water spray and hammering.

Strippability
Sometimes due to a manufacturing fault, cables are found to be unstrippable. 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.

Tensile strength
The plastic materials used for insulation and sheathing the cable must be pliable enough for the cable to be bent easily, but not too much that it easily stretches.  It must also not be too brittle that it cracks.  These materials are also artificially aged so that the likely performance of the materials in twenty of more years time can be assessed.

Heat and Cold
Cables are used in a wide variety of environments, so several tests assess their performance in very hot and very cold conditions, to check whether the insulation and sheathing material melts or cracks and hence ensuring safety.


Further information about BASEC and advice on faulty cables is available at www.basec.org.uk or you can contact BASEC directly on 01908 267300

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