# Thermal resistivity of soil

The thermal resistivity of the soil has a significant impact on cable ampacity of buried cables, especially when directly buried without backfill. The lower the thermal resistivity, the higher the cable ampacity for the same conductor temperature $\theta_c$.

If the thermal resistivity of soil is unknown, the values from the reference operating conditions in IEC 60287-3-1 are recommended. Or else, the IEEE Standard 442 provides values for some materials and a paper by O.E. Gouda from 2010 lists values for some tested type of soils.

Symbol
$\rho_4$
Unit
K.m/W
Used in
$d_{im}$
$D_x$
$\delta_{soil}$
$\Delta \theta_{e,t}$
$\Delta \theta_{kp}$
$g_{dry}$
$R_{q22}$
$R_{q32}$
$T_{4d}$
$T_{4db}$
$T_{4iii}$
$T_{4w}$
$T_{4y}$
$T_e$