SHORT CIRCUIT CAPACITIES OF CABLES WITH SOLID INSULATION.

It happens frequently that the conductor size necessary for an installation is dictated by its ability to carry short circuit rather than sustained current. During a short circuit there is a sudden inrush of current for a few cycles followed by a steadier flow for a short period until the protection operates, normally between 0. 2 and 3 sec. During this period the current falls off slightly due to the increase of conductor resistance with temperature but for the calculation purposes it is assumed to remain steady. The short circuit ratings of the cables are analyzed.