Constant V for cables in ducts

According to standard IEC 60287-2-1 Ed.2.0

Symbol
$V_d$
Unit
K.m/W
Choices
MaterialValue
PE0.312
PP0.312
PVC0.312
WPE0.03
Metal1.4
Fibre0.83 (air)
0.91 (buried)
Earth0.28
Cem1.2 (air)
1.1 (buried)