Distance along the cable route from the hottest point where longitudinal heat flux is negligible.

The distance $z_{max}$ is a function of the longitudinal thermal resistance of the conductors, the separation between the cable and the heat source and the heat generated by the crossing source. In the example in Annex A of standard IEC 60287-3-3 a value of 5 m is used. We calulate over a distance of 20 m.

Symbol
$z_{\mathrm{max}}$
Unit
m
Used in
$N_{\mathrm{X}}$