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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 lightingsystems 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 broadlymeasures the amount of copper present. BASEC has issued a number of warnings to the

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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 testsTo 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 bunsenburner 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 atwww.basec.org.ukor you can contact BASEC directly on 01908 267300

http://www.basec.org.uk/http://www.basec.org.uk/http://www.basec.org.uk/