PVC cable use is in decline, as shown by the withdrawal of the BS 6346 cable Standard and the development of a new Standard, BS857, Dr Jeremy Hodge tells us more.

For some time there has been specifier demand for a low smoke halogen free non-armoured power cable for use within buildings, where the armour protection afforded by traditional armoured cables is not fully justified. The new standard would be for a non-armoured XLPE insulated cable with a low smoke sheath, similar to PVC-sheathed cables made to a current standard, BS 7889.

A new Standard for low smoke cable – BS 8573

A new standard 'BS 8573 Electric cables – thermosetting insulated, non-armoured cables with a voltage of 600/1 000V, for fixed installations, having low emissions of smoke and corrosive when affected by fire', is currently in preparation with the British Standards Institution (BSI). The use of such cables is predicted to offer specifiers potential savings of weight, space and cost. These power cables could be used in places where, in case of fire damage, loss of human life and material assets must be prevented, but where mechanical protection is less important or provided by other means.
The same cable type with a PVC sheath is currently on the market, to BS 7889. This is a non-armoured XLPE insulated PVC sheathed cable commonly used within buildings for power distribution. This scheme will be extended to use the low smoke cable version once the standard is published. The BS 7889 standard will remain unchanged, although cables with PVC sheaths are becoming less commonly used in environments such as shopping centres, schools, hospitals and other public buildings where the preference is changing towards predominantly low smoke cables.

PVC in decline

Other PVC-containing standards are continuing to decline in use. In particular, standard BS 6346 – PVC insulated, PVC sheathed armoured cables for voltages of 600/1000 V and 1900/3300 V – has recently been withdrawn without a replacement being substituted. The modern alternative to PVC insulation is cross-linked polyethylene (XLPE), although PVC sheathing remains widely used.
The IEC standard IEC 60502-1 for low voltage power distribution cables is also available. This standard permits many options of construction, including armoured or unarmoured, PVC or low smoke materials, so buyers should be careful to specify exactly what cable they want when using this standard.


Common isssues found with power cables

Damage to armouring from poor handling of the cable during installation.
Splits in low smoke cable sheathing due to handling in either hot or freezing conditions, or over-bending the cable.
Some territories require fully coloured neutral and/or earth cores within a cable – BASEC will permit certified manufacturers to supply these.
The overall diameter of most power cables is not specified, so getting them to fit glands and fittings can be an issue at times – advise use of manufacturer's recommended accessories.

Other cable standards relevant to power cables

BS 5467 (XLPE insulation, PVC sheath), BS 6724 (XLPE insulation, low smoke halogen free sheath), BS 7846 (XLPE insulation, low smoke halogen free sheath, fire resistant) – mainly used buried in the ground, the low smoke version is used where the cable comes up into a building.
BS 7846 armoured power cables for fire resistance applications (e.g. supplies to fire safety systems). This standard was reviewed in 2009 and new, higher performance cable types added, for fire critical systems.
BS 7870 series of standards – used by power distribution utilities, includes split concentric cable types.

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