One key determinant of a good earthing installation is the soil resistivity of the soil where the earth electrode is installed. If you are involved in earthing buildings and electrical installations, here is a list of the typical soil resistivity values for different types of soil that you might encounter:
| Type of Soil | Mean Value of Resistivity in Ωm |
|---|---|
| Swampy soil, bogs | 1 - 30 |
| Silt alluvium | 20 - 100 |
| Humus, leaf mould | 10 - 150 |
| Peat, turf | 5 - 100 |
| Soft clay | 50 |
| Marl and compacted clay | 100 - 200 |
| Jurassic marl | 30 - 40 |
| Clayey sand | 50 - 500 |
| Siliceous sand | 200 - 300 |
| Stoney ground | 1,500 - 3,000 |
| Grass-covered-stoney sub-soil | 300 - 500 |
| Chalky soil | 100 - 300 |
| Limestone | 1,000 - 5,000 |
| Fissured limestone | 500 - 1,000 |
| Schist, shale | 50 - 300 |
| Mica schist | 800 |
| Granite and sandstone | 1,500 - 10,000 |
| Modified granite and sandstone | 100 - 600 |
| Fertile soil, compacted damp fill | 50 |
| Arid soil, gravel, uncompacted non-uniform fill | 500 |
| Stoney soil, bare, dry sand, fissured rocks | 3,000 |