# Thickness of insulation to sheath

Insulation thickness between conductors and sheath used to calculate $T_1$ with following considerations:

• For multi-core cables, $t_1$ is up to the sheath and $t_2$ is between sheath and armour.
• A tape screen is considered equivalent to a sheath, so for single-core cables with a tape screen and no sheath and for multi-core cables with a common screen and no sheath, the screen serving is added to $t_2$.
• A wired screen is not relevant for the calculation.
• For multi-core cables with separate sheaths, the filler is part of $t_2$.

Type of screen/sheath of multi-core cables

• SS: with separate screen and separate sheaths
• SC: with separate screen and common sheath
• CC: with common screen and common sheath

Symbol
$t_1$
Unit
mm
Formulae
 $t_i+t_{scb}+t_{scs}+\frac{\Delta d_{sh}}{2}$ Single-core cables $t_i+t_{scb}+t_{scs}+\frac{\Delta d_{sh}}{2}$ Multi-core cables type SS $t_i+t_{scb}+t_{scs}+t_f+\frac{\Delta d_{sh}}{2}$ Multi-core cables type SC $t_i+t_f+t_{scb}+t_{scs}+\frac{\Delta d_{sh}}{2}$ Multi-core cables type CC $t_i+t_{scb}$ Pipe-type cables
Related
$\Delta d_{sh}$
$t_f$
$t_i$
$t_{scb}$
$t_{scs}$
Used in
$T_1$
$t_{1t}$