A three-core cable is represented as an equivalent single-core cable for long-term transients with duration $<PQ$.However, for very short transients with duration $<TQ$ where $TQ$ refers to a single core, the mutual heating of the cores is neglected, and a three-core cable is treated as a single-core cable with the dimensions corresponding to the one core. For durations between these two limits, the transient is assumed to be given by a straight line interpolation in a diagram with axes of linear temperature rise and logarithmic times.

Symbol
$T_{\mathrm{A}}$
Unit
K.m/W
Formulae
$T_{\mathrm{1t}}$long-term transients
$\frac{T_{\mathrm{1t}}}{2 n_{\mathrm{c}}}$short-term transients
Related
$n_{\mathrm{c}}$
Used in
$\alpha_{\mathrm{t}}$
$\delta \theta_{\mathrm{c}}$
$k_{\mathrm{t}}$
$T_{\mathrm{a0}}$
$T_{\mathrm{b0}}$