Overload rating :
In practice, the load is not continuous load and a large load may have the carried only for a comparatively short period of time.
Hence, in the case of cables, it is reasonable to consider that a greater load than that based on steady state theory can be transmitted without exceeding the permissible limit of temperature.
The overload rating will depends on the overload, duration of the overload the short time temperature rating of the insulation.
Following are the overload rating of cables:
(i)All the cables have excellent overload capacity, nearly 50% of rated value.
(ii)It can overload for 3 to 4 hrs.
(iii)Cables layed in air ducts on trays can safely be overload upto 13 times their rating for 4 hrs provided that the protective system used fuses designed to operate at 50% overload.
(iv)The cable layed in ground can be safely overload upto 13 times of their rated capacity for 4 hrs. But it is essential that the protective system is designed to operate above 30% overload
