Relates to the ability of the soil, in which the cable is installed, to conduct heat energy away from the cable.

The rating factor C_s is applied in cable sizing calculations to account for different soil thermal resistivities.

For cables with Installation Methods 70 to 73, the values of C_s are found in BS7671:2018, Table4B3.

For methods using BICC data C_s has a value of 1.0 for a resistivity of 1.2 K.m/W. For higher resistivities the value of the rating factor will be less than 1,and greater than one for lower resistivities.