Evaluation of Soil Thermal Characteristics

In 1962, the Association of Edison Illuminating Companies and the Insulator Power Cable Engineers Association sanctioned 10°C higher conductor temperatures for use in rating calculations by utilities having thorough knowledge of the thermal characteristics of the soil in which a particular cable is to be installed. A 2-stage sampling scheme is described for obtaining such knowledge with a minimum amount of time and effort. The first stage consists of a qualitative identification of the types of soil which occur throughout the cable route. The second stage comprises a series of tests on a prescribed number of soil samples. This procedure yields an upper value of soil thermal resistivity for a given percentile of the soil at a specific confidence level.