Earthing resistance calculator
Calculate the resistance of a single rod, a line or a square of rods and compare the variants.
Earthing parameters
Choose the configuration and set the conditions.
Model of uniform soil and identical rods per BS 7430. The effect of the horizontal conductor on resistance is not included. The result is for preliminary calculations and must be checked in the design and by measurement. It does not confirm that the installation complies with standards.
Calculation method and assumptions
R = ρ / (2πL) · [ln(8L/d) − 1]
Rₙ = R / N · [1 + λρ / (2πRs)]
The diameter d is converted from millimetres to metres. For a square, the factor λ is chosen by the number of rods on one side; the total number is N = 4(n − 1). Spacing s is the distance between adjacent rods. Connecting conductor: (N − 1)s for a line and Ns for a square. Quantities of 1.5 m sections are rounded up.
With spacing shorter than the rod length and non-uniform soil layers, the result needs particular verification. We do not check step or touch voltages or current standard requirements.
Vertical earth rod arrangement: in line
- Date
- Arrangement
- In line
- Number of earth rods
- 4 pcs
- Rod length L
- 3.0 m
- Diameter d
- 14.2 mm
- Spacing s
- 3.0 m
- Soil resistivity ρ
- 100 Ω·m
- Connecting conductor
- 9.0 m (no allowance)
R = ρ / (2πL) · [ln(8L/d) − 1] · Rₙ = R / N · [1 + λρ / (2πRs)]. Preliminary calculation to BS 7430 for uniform soil; the result must be checked in the design and by measurement after installation. Diagrams are schematic, dimensions come from the parameters.
Bill of materials
In line, 4 pcs × 3.0 m. Quantities are a geometric suggestion; the designer enters prices from the distributor’s offer.
| Item | Catalogue no. | Quantity | Price / unit [PLN] | Value [PLN] |
|---|---|---|---|---|
| Forged earth rod 14.2 mm / 1.5 m | 8 pcs | – | – | |
| Copper-bonded tape (price per metre) | Selected per design | 14.0 m | – | – |
| Conductor to earth rod clamp | Selected per design | 4 pcs | – | – |
| Laying the tape | Labour | 14.0 m | – | – |
| Driving the rods | Labour | 12.0 m | – | – |
| No complete price | – | |||