Soil resistivity depends on the content of electrolytes in the soil. Geological differences and seasonal variations on a site can be big.
In particular frozen soil and dry soil are very poor conductors:
- In frozen soil, position the ground electrode deep enough to reach non-frozen moist soil even during the winter or dry season. Do this if you need a low resistance to ground for electrical safety reasons.
- In very dry soil, add soil enhancing chemicals, also known as backfill compounds, around the ground electrode to raise the moisture level, lowering the resistance to ground.
For installation examples in different soil types, see Installing Ground Electrode.
| Type of Soil or Water | Resistivity (Ωm) | Usual Range (Ωm) |
|---|---|---|
| Sea Water | 2 | 0.1 … 10 |
| Clay | 40 | 8 … 70 |
| Ground well and spring water | 50 | 10 … 150 |
| Clay and sand mixtures | 100 | 4 … 300 |
| Shale, slates, sandstone, etc. | 120 | 10 … 1000 |
| Peat, loam and mud | 150 | 5 … 250 |
| Lake and brook water | 250 | 100 … 400 |
| Sand | 2000 | 200 … 3000 |
| Moraine gravel | 3000 | 40 … 10 000 |
| Ridge gravel | 15 000 | 3000 … 30 000 |
| Solid granite | 25 000 | 10 000 … 50 000 |
| Ice | 100 000 | 10 000 … 100 000 |
| Moisture Content (% of weight) | Resistivity of Clay Mixed with Sand (Ωm) |
|---|---|
| 0 | over 10 000 000 |
| 2.5 | 1500 |
| 5 | 430 |
| 10 | 185 |
| 15 | 105 |
| 20 | 63 |