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 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 purposes. It is an assembly of one or more individually insulated electrical conductors, usually held together with an overall sheath.

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

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

Cable laying :
Cables may lay in the air or on the ground. Cable laying in the air means cables will be placed on a cable tray. Cabl laying in the ground means cable will be laid into the ground using a cable trench or direct burid into the ground.

 Cables In Air : 
  • Ambient temperature
  • The cable has to protect 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.
Cables In-Ground :
  • Soil temperature: 30 degrees Celsius
  • Depth of laying: 70 cm
  • Specific thermal resistivity of soil: 100 degrees 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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