Before proceeding with the manufacture of the cable which may involve the laying together of many smaller cables, it is necessary that the insulation should be thoroughly tested. All tests are made in a separate test room at a distance from the water tanks, Any faults which develop must be rectified, or if this is impossible, the cable is destroyed.
The majority of cables from the smal] flexibles to the largest sizes of mains are protected with a braiding which is manufactured in exactly-a similar manner to a stocking. The wire passing through the centre of the knitting machine emerges with the stocking in position. The manufacture flexible cable such as one sees in every day use involves almost as much machinery as the -manufacture of the heaviest of mains.
When cables are to be buried underground they are usually protected from damage by armour ing with steel tapes or steel wire.
In many cases it is necessary to protect the insulation of the cable from damage by water by a lead covering under the armouring. The cable is passed through a machine containing molten lead which is squeezed in, the shape of a tube over the cable under hydraulic pressure.. The thickness. of this lead coating must be very carefully gauged in order that it is not too tight on the cable, in which case it might split, or too loose to allow the moisture to enter the cable with the air. Steel wire armour ing is done either by two layers of steel tape or by one or more layers of steel wire each layer of steel wire being wound in opposite directions.
Between the armour ing and the lead, the cable must be protected by a covering of jute or other, similar material which is impregnated with tar or bitumen as a preservative for the fabric, or on the other hand the fabric must be impregnated with fire-proofing compound.
ables which consist of more than one core require special preparation in the laying up of the various cores into a solid cable before it receives its covering of lead or rubber, There are numerous operations involved in the measuring and cutting to exact lengths and mak-~ ing up into small coils and winding on the big drums for despatch from the factory.
Text read from the printed page and cleaned; old type leaves the occasional error.