The efficiency of thermal resistivity within soil and backfill materials is governed by a myriad of influential factors.

Several factors influence the thermal resistivity of soil and backfill materials, most notably mineralogy, density, moisture content, and porosity. These factors greatly affect the ability to conduct heat away from the heat source (total losses of the energized power cables). Thermal resistivity, sometimes referred to as ‘thermal Rho,’ is expressed as °C-cm/W or K·m/W.

Geotherm performs thermal resistivity testing utilizing IEEE 442-2017 (as well as ASTM D5334-14): Guide for Thermal Resistivity Measurements of Soils and Backfill Materials. This guide was written for, and by, cable engineers for its specific application to underground and submarine power cable ratings. The findings have a significant impact on system design, not only on cost and efficiency but also on life expectancy. These are huge and long-term investments.

Understanding the thermal properties of the materials used in underground power systems (external thermal circuit) is crucial for cost-effective design. This applies not only to the native soil but, more importantly, to the concrete and/or backfill envelope around the cables to properly determine the size of the cable.