The Heat and Buried Cable Conundrum: A Method to Help Determine Underground Cable Ampacity

One of the most important factors affecting underground cable ampacity is the thermal resistivity of the soil. A soil's thermal resistivity varies with moisture content, and the heat generated by cables can cause the soil to dry, increasing its resistivity. The ability of the soil to maintain its thermal resistivity in the presence of a heat source is known as thermal stability. Since no soil has perfect stability, accounting for the fluctuating thermal resistivity of soil makes the cable ampacity calculations difficult. This article will examine the information available from standard soil tests and the information these tests may provide relating to the migration of moisture in the soil and the resulting changes in soil resistivity. Furthermore, we suggest a method for including this information in underground cable ampacity calculations.