Short circuit rating of LT cables :
(i)The short circuit for aluminum cables is different for copper cables. Copper can withstand higher temperature than aluminum.
(ii)With the recent increase in kVA capacity of the power distribution system, the cables are expected to carry short circuit currents of higher magnitudes
(iii) If it is required that the cables should be predicted from higher temperature during short circuit, it is essential that the fuses should be designed to minimize the fault duration
(iv)HRC fuses are best suited for low tension power supply circuits, because of the following reasons
1. They limit the magnitude of short circuit current.
2. They minimize the fault duration time
(v)Under short circuit conditions the current flowing the cable is many times the full load value of current. The heat produced in the conductor is proportional to the square of the current.
(vi)The duration of short circuit is very small. The temperature attained under short circuit conditions is greater than the maximum permissible temperature for continuous rating
(vii)The short circuit is not defected by the condition of installation of the cable but it depends upon the maximum temperature attained by the cable under short circuit condition
(viii)The safe value of limiting temperature is usually taken as 120°C. for maximum continuos operating conductor temperature of 800 C and a permissible temperature rise of 500 C during short circuit.
