6.5.2.1 Definition of soil resistivity

The specific earth resistivity (often referred to as specific soil resistivity) is a material constant that expresses how strongly a particular soil resists electric current. This parameter is of central importance when planning earthing systems, as it significantly determines the earthing resistance to be achieved.

The specific earth resistivity ρₑ indicates the resistance of a substantially homogeneous soil volume through which current flows. It can be imagined as the electrical resistance of a cube measuring 1 metre in length, through which, ideally, current flows between two opposite surfaces. The resistance of a specific material is measured in ohm metres (Ωm). Similar to the specific resistance of metals (also simply referred to as 'specific resistance' or resistivity), it expresses the extent to which a material – in this case, the soil – impedes the flow of an electrical charge.