Conditions for Current Carrying Capacity of Power Cable

Conditions for Current Carrying Capacity of Power Cable

The tabulated current ratings are designed by the conditions as below :

Current carrying capacity is defined as the amperage a conductor can carry before melting either the conductor or the insulation. Cables are mainly designed as per requirement. Power cables are mainly used for power transmission and distribution purpose. It is an assembly of one or more individually insulated electrical conductors, usually held together with an overall sheath.

Consider one circuit of three phase load to make sense.
Load factor = 1.0

Maximum operating conductor temperature :
70 degree Celsius ( PVC insulation ) and 90 degree Celsius ( XLPE insulation );
No other heat sources installed near the group of cables.


Cable laying :


 in air          : 
  • Ambient temperature
  • The cable have to protected against heat radiation of the sun as well as sufficiently large and ventilated rooms whose temperature is not perceptibly increased by the heat dissipating from the loaded cable.
in ground :
  • Soil temperature: 30 degree Celsius
  • Depth of laying: 70 cm
  • Specific thermal resistivity of soil: 100 degree C.m/watt
If the actual installed conditions are different from the above mentioned condition, the tabulated current ratings should be multiplied by the appropriate derating factors as shown below:




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