Emergency loading of buried cable with temperature-dependent conductor resistance

A constant current is applied to a buried cable for a sufficiently long time for steady-state conditions to be effectively reached. A constant emergency current is then applied for a specified time, at the end of which a specified conductor temperature is reached, the latter value being in excess of, or equal to, the maximum permissible value associated with sustained 100% rated current. Close upper and lower bounds for the constant emergency current are derived, taking into account the variation of the electrical resistivity of the conductor with temperature. It is shown that the neglect of the latter variation may lead to unsafe results.