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 :
- Varnished cambric
- Poly vinyl chloride ( PVC )
- Paper
- Cross linked polyethylene ( XLPE )
- 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.
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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