Estimates the resistance-to-earth of a single circular buried bare-conductor ground ring (a common perimeter electrode for equipment pads, substations, and tower bases) from soil resistivity, ring geometry and burial depth, and screens the result against a user-settable target resistance.
Standards followed
BS 7430:2011 §11.2.5 — single-ring electrode resistance formula
What it can do
- Single-ring resistance-to-earth from soil resistivity, overall ring diameter, conductor diameter and burial depth.
- Grading band (LOW/NORMAL/HIGH/VERY HIGH) and pass/fail against a user-settable target resistance.
- Uses the identical formula already verified in the Earthing Grid Design calculator's BS 7430 ring-sizing path.
Example problem
ρ=100 Ω·m, 10m ring diameter, 10mm conductor diameter (5mm radius), 0.6m burial depth.
- R = (ρ/2π²D) × (ln(8D/a) + ln(2D/h) − 2)
- R = (100/(2π²×10)) × (ln(8×10/0.005) + ln(2×10/0.6) − 2) = 0.5066 × (9.680 + 3.507 − 2) = 0.5066 × 11.187 ≈ 5.67 Ω
≈5.67 Ω — LOW band, well within the 25Ω rule-of-thumb target.
Ring resistance is very sensitive to soil resistivity, which varies with moisture and season — a measured fall-of-potential test result should always take precedence over a calculated estimate for final acceptance.