Thickness of insulation to sheath

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

Type of screen/sheath of multi-core cables

Symbol
$t_{1}$
Unit
mm
Formulae
$\frac{\Delta d_{sh}}{2} + \frac{t}{2} + t_{scb} + t_{scs}$single-core cables with sheath
$\frac{t}{2} + t_{scb} + t_{scs}$single-core cables without sheath, no screen
$\frac{t}{2} + t_{scb}$other single-core cables
$\frac{\Delta d_{sh}}{2} + \frac{t}{2} + t_{scb} + t_{scs}$multi-core cables type SS with sheath
$\frac{t}{2} + t_{f} + t_{scb}$multi-core cables type CC with screen and no sheath
$\frac{\Delta d_{sh}}{2} + \frac{t}{2} + t_{f} + t_{scb} + t_{scs}$other multi-core cables
Related
$\Delta d_{sh}$