Effective Thermal Resistivity for Power Cables Buried in Thermal Backfill

Existing methods for calculating cable ampacities assume that buried cables are surrounded by a single, homogeneous material. These ampacity programs have limited application when a thermal backfill material is used to increase the current carrying capability of underground cables. This paper presents a method of calculating an effective thermal resistivity for any combination of backfill materials that are placed adjacent to the cable. Results are presented for a rectangular region of backfill covered by a protection layer. The concept of an effective thermal resistivity can extend the use of existing ampacity programs to cases involving non-homogeneous soil layers.