# Thickness of insulation to sheath, transient

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