Single Earth Rod Resistance Estimate
Estimate the resistance of a single vertical rod in uniform soil using the modified Dwight long-rod approximation and user-entered soil resistivity.
Result
Approximation note
Formula
Calculation logicFormula definitions and substituted values.
Diameter M
Rod diameter d (mm) / 1000
Rod diameter d (mm) / 1000Length-to-diameter ratio L/d
Driven rod length L (m) / Diameter M
Driven rod length L (m) / Diameter MLong-rod logarithmic term
ln(8 * Driven rod length L (m) / Diameter M) - 1
ln(8 * Driven rod length L (m) / Diameter M) - 1Estimated rod resistance (Ω)
Uniform soil resistivity (Ω·m) * Long-rod logarithmic term / (6.2831853071796 * Driven rod length L (m))
Uniform soil resistivity (Ω·m) * Long-rod logarithmic term / (6.2831853071796 * Driven rod length L (m))Approximation note
The rod is short relative to its diameter for this long-rod approximation; treat the result as outside the stated approximation range. if Length-to-diameter ratio L/d < 20; This is a uniform-soil single-rod estimate, not a measured or compliance result. otherwise
The rod is short relative to its diameter for this long-rod approximation; treat the result as outside the stated approximation range. if Length-to-diameter ratio L/d < 20; This is a uniform-soil single-rod estimate, not a measured or compliance result. otherwiseBefore relying on the result
- Comparing rod length and diameter during preliminary layout
- Estimating resistance from a measured soil resistivity
- Use the estimate only as a preliminary uniform-soil comparison; verify the site with an appropriate measurement and engineered design.
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