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).

Symbol
$t_{\mathrm{1t}}$
Unit
mm
Formulae
$t_{\mathrm{1}}$single-core cables and multi-core cables type SS
$D_{\mathrm{1}} - d_{\mathrm{ct}} - t_{\mathrm{sc}}$multi-core cables type SC
$D_{\mathrm{1}} - d_{\mathrm{ct}}$type CC with tape screen and no sheath
$D_{\mathrm{it}} - d_{\mathrm{ct}}$other multi-core cables type CC
Related
$D_{\mathrm{1}}$
$D_{\mathrm{it}}$
$t_{\mathrm{sc}}$