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.

Insulation

• 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

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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.

Bedding

• 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.

Armouring

• 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.

Serving

• 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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