General Construction of a Cable

General Construction of a Cable

The Fig. 6.3.1 shows the general construction of a cable. The cable shown is single conductor underground cable. Its various parts are,

1. Conductor or core : This section consists of single conductor or more than one conductor. 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 conductor 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 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 armouring.

5. Armouring : This layer consists of the layers 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.

Review Question

1. Draw the cross sectional view of a single core cable and explain its construction.