Construction of Electrical Cable

Construction of Electrical Underground Cable

Components of Cable 

1. Conductors
2. Insulation 
3. Metallic sheath 
4. Bedding 
5. Armouring (Mechanical protection)
6. Serving

(1) Conductors

• Conductors used for cables are generally made up of tinned copper or aluminium. To provide the sufficient flexibility conductors are used in stranded form.
• Cable may consists of one, two, three or four conductors depending upon the service required.

(2) Insulation 

• As the cable is laid underground conductor has to be provided with sufficient thickness of insulation.
• The type and thickness of insulation depends upon the voltage level.

• Insulating materials should provide the following properties :-

1. High insulation resistance to avoid leakage current.
2. High mechanical strength.
3. Non porous.
4. Chemically inert.
5. High dielectric strength.
6. Non inflammable.

• Following are the different materials used for cable insulation :-

1. Rubber.
2. V.I.R. i.e. Vulcanized India Rubber.
3. Impregnated paper.
4. P.V.C. i.e. Polyvinyl Chloride.
5. Varnished cambric.

(3) Metallic sheath

• As the cable is placed under ground , soil may present , moisture , gases and some other liquids.
• Therefore to protect the cable metallic sheath made up of lead or aluminium is provided over the insulation.

(4) Bedding

• To protect the metallic sheath from corrosion and some mechanical injury, bedding is provided.
• It is made up of some fibrous material such as jute or hessian tape.

(5) Armouring (Mechanical protection)

• Armouring is used to protect the cable from mechanical injury while handling.
• It consists of one or two layers of galvanised steel wire or steel tape.

(6) Serving

• Serving is provided to protect the armouring from atmospheric conditions.
• It is made up of some fibrous material like jute.