General Construction of a Cable

The Fig. 1 shows the general construction of a cable. The cable shown is a single conductors underground cable. Its various parts are,

1- Conductor or core : This section consists of single conductor or more than one conductors. The conductors are also called cores. A cable with three conductors is called three core cable. The conductors used are aluminium or annealed copper. The conductors are stranded conductors in order to provide flexibility to the cable.

2- Insulation : Each conductors or core is covered by insulation of proper thickness. The commonly used insulating materials are varnished cambric, vulcanized bitumen and impregnated paper.

3- Metallic sheath : The insulated conductors are covered by lead sheath or aluminium sheath. This provides the mechanical protection but mainly restricts moisture and other gases to reach to the insulation.

4- Bedding : The metallic sheath is covered by by another layer called bedding. The bedding consists of paper tape compounded with a fibrous material like jute strands or hessian tape. The purpose of bedding is to protect the metallic sheath from corrosion and from mechanical injury resulting due to aemouring.

5- Armouring : This layer consists of the layer of galvanized steel wires which provide protection to the cable from the mechanical injury.

6- Serving : The last layer above the armouring is serving. It is a layer of fibrous material like jute cloth which protects the armouring from the atmospheric conditions.

Fig. 1 General construction of a cable