An underground cable essentially consists of one or more conductors converted with suitable insulation and surrounded by a protecting cover.Although several types of cables of available, the type of cable to be used will depend up on the working voltage and service requirements.In general, a cable must fulfil the following necessary requirements.The conductor used in cables should be stranded copper or aluminium of high conductivity.stranding is done so that conductor may become flexible and carry more current.
The conductor size should be such that the cable carries such that the desired load current without over heating and causes voltage drop within permissible limits.The cable must have proper thickness of insulation in order to have high thickness of safety and reliability at the voltage for which it is designed.The cable must be provided with suitable mechanical protection so that it may withstand the rough use in laying it.the material used in manufacture of cables should be such that there is complete chemical physical stability throughout.Construction of cables:Cores of conductor .A cable may have one or more than one core depending upon the type of service for which it is intended.The conductors are made of tinned copper or Al and are usually stranded in order to provide flexibility to the cable.
Insulation.Each core or conductor is provided with a suitable thickness of insulation, the thickness of layer depending up on the voltage withstood by the cable.The commonly used materials for insulation are impregnated paper,varnished cambric or rubber mineral compound.Metallic Sheath.In order to protect the cable from the moisture gases,or other damaging liquids in the soil and atmosphere,a metallic sheath of lead or aluminium is provided over the insulation.
The conductor size should be such that the cable carries such that the desired load current without over heating and causes voltage drop within permissible limits.The cable must have proper thickness of insulation in order to have high thickness of safety and reliability at the voltage for which it is designed.The cable must be provided with suitable mechanical protection so that it may withstand the rough use in laying it.the material used in manufacture of cables should be such that there is complete chemical physical stability throughout.Construction of cables:Cores of conductor .A cable may have one or more than one core depending upon the type of service for which it is intended.The conductors are made of tinned copper or Al and are usually stranded in order to provide flexibility to the cable.
Insulation.Each core or conductor is provided with a suitable thickness of insulation, the thickness of layer depending up on the voltage withstood by the cable.The commonly used materials for insulation are impregnated paper,varnished cambric or rubber mineral compound.Metallic Sheath.In order to protect the cable from the moisture gases,or other damaging liquids in the soil and atmosphere,a metallic sheath of lead or aluminium is provided over the insulation.
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