For calculation of the cyclic and emergency current rating of cables acc. IEC 60853, the multi-core cable is replaced by an equivalent single-core construction dissipating the same total conductor losses. The space between the equivalent single-core conductor and the sheath is considered to be completely occuied by insulation (for oil-filled cables, this space is filled partly by the total volume of oil in the ducts and the remainder is oil-impregnated paper).

$T_{\mathrm{1t}}$

K.m/W

$\frac{\rho_{\mathrm{i}}}{2 \pi} \ln{\left (1 + \frac{2 t_{\mathrm{1t}}}{d_{\mathrm{ct}}} \right )}$

$\pi$

$\rho_{\mathrm{i}}$

$t_{\mathrm{1t}}$

$Q_{\mathrm{B_{\mathrm{s}}}}$

$T_{\mathrm{A}}$

$T_{\mathrm{tot}}$