Industrial Cables

‘Industrial cables’ are defined as those power circuit cables which are installed on the customer side of the electricity supply point, but which do not fall into the category of ‘wiring cables’.

Generally, these cables are rated 0.6/1 kV or above. They are robust in construction and are available in a wide range of sizes. They can be used for distribution of power around a large industrial site or for final radial feeders to individual items of plant.

Feeder cables might be fixed or in cases, such as coal-face cutting machines and mobile cranes they may be flexible trailing or reeling cables.

Related: Wiring Cables

Many industrial cables are supplied to customers’ individual specifications and since these are not of general interest they are not described here. The following sections focus on types that are manufactured to national standards and which are supplied through cable distributors and wholesalers for general use.

Paper-Insulated Cables:

For ratings between 0.6/1 kV and 19/33 kV, paper-insulated cables for fixed installations were supplied in the UK to BS 480, and then to BS 6480 following metrication in 1969.

These cables comprise copper or aluminium phase conductors insulated with lapped paper tapes, impregnated with MIND compound and sheathed with lead or lead alloy. For mechanical protection, they were finished with armouring of steel tapes or steel wire and a covering of bitumenized hessian tapes or an extruded PVC oversheath.

The 3-core cables of this type with SWA have been preferred for most applications and these have become known as Paper-Insulated Lead-Covered Steel Wire Armoured

(PILCSWA) cables. Single-core cables to BS 6480 do not have armouring; this is partly because the special installation conditions leading to the selection of single-core do not demand such protection and partly because non-magnetic armouring, such as aluminium would be needed to avoid eddy current losses in the armour. These single-core cables are known as Paper-Insulated Lead Covered (PILC).

It has already been observed that paper-insulated cables are now seldom specified for industrial use, but BS 6480 remains an active standard.

Polymeric Cables for Fixed Installations:

The XLPE-insulated cables manufactured to BS 5467 are generally specified for 230/400 V and 1.9/3.3kV LV industrial distribution circuits. These cables have superseded the equivalent PVC-insulated cables to BS 6346 because of their higher current rating, higher short-circuit rating and better availability.

For MV applications in the range, 3.8/6.6 kV to 19/33 kV, XLPE-insulated wire armoured cables to BS 6622 are usually specified.

Multi-core LV and MV cables are normally steel wire armoured. This armouring not only provides protection against impact damage for these generally bulky and exposed cables, but it is also capable of carrying very large earth fault currents and provides a very effective earth connection.

Single-core cables are generally unarmoured, although aluminium wire armoured versions are available. Single-core cables are usually installed where high currents are present (for instance in power stations) and where special precautions will be taken to avoid impact damage.

For LV circuits of this type, the most economical approach is to use unarmoured cable with a separate earth conductor, rather than to connect in parallel the aluminium wire armour of several single-core cables.

For MV applications, each unarmoured cable has a screen of copper wires which would together provide an effective earth connection.

Even in the harsh environment of coal mines, XLPE-insulated types are now offered as an alternative to the traditional PVC- and EPR-insulated cables used at LV and MV, respectively. In this application, the cables are always multi-core types having a single or double layer of SWA.

The armour has to have a specified minimum conductance because of the special safety requirements associated with earth faults and this demands the substitution of some steel wires by copper wires for certain cable sizes.

Where LSF fire performance is needed, LV wire-armored cables to BS 6724 are the established choice. These cables are identical in construction and properties to those made to BS 5467 except for the LSF grade of sheathing material and the associated fire performance. Cables meeting all the requirements of BS 6724 and, in

addition, having a measure of fire resistance such that they continue to function in a fire are standardized in BS 7846, further details of which are given in section 9.3.3.

Similarly, BS 7835 for MV wire-armoured cable, which is identical to BS 6622 apart from the LSF sheath and fire performance, was issued in 1996 and revised in 2000.

The only other type of standardized cable used for fixed industrial circuits is multi-core control cable, often referred to as the auxiliary cable. Such cable is used to control industrial plant, including equipment in power stations. It is generally wirearmoured and rated 0.6/1 kV.

Cables of this type are available with between 5 and 48 cores. The constructions are similar to 0.6/1 kV power cables and they are manufactured and supplied to the same standards (BS 5467, BS 6346 and BS 6724, as appropriate).

Polymeric Cables for Flexible Connections:

Flexible connections for both multi-core power cables and multi-core control cables are often required in industrial locations. The flexing duty varies substantially from application to application. At one extreme a cable may need to be only flexible enough to allow the connected equipment to be moved occasionally for maintenance.

At the other extreme the cable may be needed to supply a mobile crane from a cable reel or a coal-face cutter from cable-handling gear.

Elastomeric-insulated and sheathed cable are used for all such applications. This may have flexible stranded conductors (known as ‘class 5’) or highly flexible stranded conductors (known as ‘class 6’). Where metallic protection or screening is needed, this comprises a braid of fine steel or copper wires.

For many flexible applications, the cable is required to have resistance to various chemicals and oils. Although flexible cables will normally be operated on a 230/400 V supply, it is normal to use 450/750 V rated cables for maximum safety and integrity.

A number of cable types have been standardized in order to meet the range of performance requirements and the specification for these is incorporated into BS 6500. Guidance on the use of the cables is provided in this standard and further information is available in BS 7540.

Source: Newnes – Electrical Power Engineers