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Electric cables are normally installed on the assumption of a safe working life

Electric cables are normally installed on the assumption of a safe working life

of at least 20 years. Changes in the insulating material take place with the passing of time and these changes, which may eventually result in an electrical

breakdown, are accelerated at higher temperatures. Thus, if the working life is fixed, the limiting factor is the temperature at which the cable is required

to operate.

During operation, the temperature at which the cable will operate depends upon the ambient temperature and the heating effects of the current produced

due to the resistance of the cable conductors.

The heat dissipation of buried cables depends on the depth of laying, ground ambient temperature and its thermal resistivity, these being dependent on

their geographical location and the season of the year. Nearby cables would also affect the ground temperature. Cables in air reach steady operating

temperatures more quickly than similar cables underground and large cables take longer than small ones.

The heat may cause a change in the properties of an insulating material or in extreme cases, deformation may occur. It is important, therefore, to

realise that there is “a cable for the job”.