10.2.1 Thermal effects and thermal short-circuit strength

The thermal withstand capability (thermal short-circuit strength) of equipment is determined by the maximal permissible conductor temperature prior to the short- circuit, the duration of the short-circuit and the short-circuit current itself. The maximal permissible temperature of conductors under normal operating conditions and in the case of short-circuits, e.g., as per DIN VDE 0276, is summarised in Table 10.1. Figures are given for a short-circuit duration of T _k = 5 s. It is assumed that no heat transfer is taking place during the short-circuit duration (adiabatic heating). Skin- and proximity-effects are neglected, the specific caloric heat of the conductor and insulation is constant and the relation resistance-to-temperature is linear. Special consideration is to be taken for conductors in a.c. installations with cross-section above 600 mm ², as the skin-effect has to be taken into account. Additional requirements according to IEC 60986:1989 and IEC 60949:1988 for cables and isolated conductors are to be met.