Design practical earthing for towers and sites. Adjust soil, rod length, and installation depth easily. Export reports fast, reduce risks, and meet standards confidently.
| Scenario | ρ (Ω·m) | L (m) | d (mm) | n | s (m) | Ring C (m) | Season | Target (Ω) |
|---|---|---|---|---|---|---|---|---|
| Moderate soil, four rods | 100 | 3.0 | 16 | 4 | 3.0 | 0 | 1.00 | 5 |
| High resistivity, add ring | 300 | 3.0 | 16 | 6 | 4.0 | 80 | 1.10 | 10 |
| Low resistivity, longer rods | 50 | 6.0 | 14 | 4 | 6.0 | 60 | 1.00 | 2 |
Single vertical rod
R1 = (ρ / (2πL)) × ( ln(4L / d) − 1 )
Multiple rods with spacing
Rrods ≈ R1 / ( n × η )
η is a utilization factor based on spacing ratio (s/L). Wider spacing increases η.
Optional ring electrode
Rring ≈ ρ / (2πa) × ( ln(8a / r) − 2 ), a = C/(2π), r = conductor radius
Parallel combination
1/Rcombined = 1/Rrods + 1/Rring
Adjustments
Rtotal = Rcombined × (1 − reduction%) × season_factor
Tower earthing limits touch and step voltages. Many projects specify 1–10 Ω depending on voltage class, soil, and utility criteria. Lower resistance reduces lightning surge impedance and improves equipment bonding performance. Consistent grounding also supports reliable protection device operation and minimizes nuisance trips on sensitive telecom power systems.
Soil resistivity ρ drives most uncertainty in calculations. Use a site survey method such as four-pin testing and note seasonal moisture. When ρ doubles, the calculated electrode resistance roughly doubles for the same geometry, so capturing representative layers is critical. If results vary by direction, average traverses and record test spacing.
For a vertical rod, resistance falls as length increases, following a logarithmic relationship with diameter. Multiple rods reduce resistance, but only when spaced adequately. The utilization factor η in this tool reflects diminishing returns when spacing s is small versus rod length L. As a rule, spacing near one to two times L performs better than tight clusters.
A buried ring conductor around the tower base adds a parallel current path and can stabilize performance. In the calculator, rod resistance and ring resistance combine in parallel, so the lower element dominates, and the benefit is strongest when both are comparable. Rings improve bonding around foundations when connected to ground leads.
Dry seasons, frozen ground, or backfill changes can increase resistance. The season factor applies a multiplier to reflect worst-case conditions, while the enhancement reduction field models improvement from conductive concrete, bentonite, or backfills. Review Rtotal against the target and compare GPR using the entered fault current. High GPR indicates greater risk for transferred potentials and may require more electrodes, grading, or bonding to metallic services. If the target is missed, increase rod length, add rods with larger spacing, or include a ring, then re-run. Export results and confirm with field testing.
Use the project specification or utility requirement first. Common targets range from about 1–10 Ω depending on voltage level, soil, lightning exposure, and equipment sensitivity. Always confirm with the authority having jurisdiction.
Prefer measured data from a site resistivity survey. If only estimates exist, use conservative higher values and apply a season factor for dry conditions. Resistivity often varies by depth, so multiple test spacings are helpful.
Mutual coupling between rods causes diminishing returns when rods are close together. The utilization factor η accounts for spacing relative to rod length. Increasing spacing often improves performance more than simply adding rods in a tight cluster.
Enable it when your design includes a buried ring conductor connected to the tower grounding system. Rings provide an additional parallel path and improve equipotential bonding around the foundation, especially when combined with multiple rods.
GPR is the approximate voltage rise of the grounding system during a fault: fault current (A) multiplied by grounding resistance (Ω). Higher GPR can increase touch and transferred potential risk, so mitigation may be required.
No. It provides screening estimates for planning and comparison. Final acceptance should be based on approved test methods after installation, including seasonal considerations and any soil enhancement stabilization time.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.