Part 2 of the earthing series. One rod gives 33.5 Ω, four rods 9.1 Ω, a 10 m ring 6.3 Ω and a 20 m × 20 m mat 2.7 Ω. Why size beats everything else.
| Soil | Uniform, ρ = 100 Ω·m |
| Burial depth | 0.6 m for horizontal conductors |
Rods closer together than about twice their length share the same soil, so the resistance does not fall in proportion to the number of rods.
| Check | Requirement | Actual | Status |
|---|---|---|---|
| Single rod | — | 33.5 Ω | ✓ PASS |
| Four rods | — | 9.14 Ω | ✓ PASS |
| 10 m ring | — | 6.33 Ω | ✓ PASS |
| 20 m × 20 m mat | — | 2.73 Ω | ✓ PASS |
Key insight: Resistance of a grid is roughly ρ/(4r) for an equivalent disc of radius r. Doubling the area lowers resistance by about 30 %; doubling conductor size barely changes it.
Every input in this example is editable in the live calculator — no signup needed.
Open Earthing Grid Design (IEEE 80) calculator →Rods reach deeper, often wetter soil that stays stable through the seasons, and rods at the perimeter reduce step and touch voltages at the grid edge.
No. Touch and step voltages must also be checked — see Part 3.