Construction of Cable

The cable consists of following main parts.

Core of Cable

  • The core of the cable is made of aluminum / copper. 
  • It is lies in the center part of cable. 
  • However the number of core depends upon the type of cable either single phase or three phases. 
  • There are three core of three phase supply system and four core for three phases , four wire system. 
  • The 3.5 core cable means that the cross section of neutral / fourth cable is one half that of main core.


  • The core is provided with insulation and the thickness of insulation depends upon operating voltage of the cable. 
  • There are following materials used for cable insulation : 
  1. Varnished cambric
  2. Poly vinyl chloride ( PVC )
  3. Paper
  4. Cross linked polyethylene ( XLPE )
  5. Vulcanized bitumen

Metallic sheath

  • The insulating material is protected by moisture, gases and other harmful liquid in a soil by metallic sheath. 
  • It is provided over the insulation. 
  • It protects the insulation against mechanical damage. 
  • It is made of lead / lead alloy. 
  • The aluminium is also used as metallic sheath because of higher mechanical strength, less cost and low weight as compared to lead sheath.


  • The mechanical sheath is made of metal therefore it has possibility of corrosion and mechanical injury. 
  • The bedding is made of fibrous material like jute / hessian tape and protects the cable from corrosion and mechanical injury.


  • When cable is handling and laying in the underground, it is protected from mechanical injury by armouring. 
  • It consists of two / three layers of steel wire / steel tape.


  • It is outer most layer of the cable. 
  • It is used over the armouring. 
  • The function of serving is to protect armouring against atmospheric conditions.
Finally, the inner most layer to outer most layer of cable is
  • Core
  • Insulation
  • Metallic sheath
  • Bedding
  • Armouring
  • Serving
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