Element B of equivalent thermal circuit

In the case of cables in air, the transient temperature rise of conductor above outer surface is obtained by replacing $T_B$ by $(T_B+T_C)$.

Symbol
$T_{B}$
Unit
K.m/W
Formulae
$T_{2_{1}} q_{2_{1}} + T_{2_{2}} q_{2_{2}} + T_{4ii} q_{4} + q_{3} \left(T_{3} + T_{4i}\right)$long-term transients
$\frac{T_{1}}{2} + T_{2_{1}} q_{2_{1}} + T_{2_{2}} q_{2_{2}} + T_{4ii} q_{4} + q_{3} \left(T_{3} + T_{4i}\right)$short-term transients
$T_{B} + T_{C}$cables in air