The Equivalent thermal resistance of the soil per unit surface, representing convection, is equal to a value of 0.20 K.m²/W.Refer to CIGRE Guide 218 or Electra 125 'Calculation of the continuous rating of three core, rigid type, compressed gas insulated cables in still air and buried'.

Symbol
$\beta_{\mathrm{T}}$
Unit
W/K.m²
Used in
$d_{\mathrm{im}}$