Vertical ground-rod resistance equations
A uniform-soil approximation estimates one rod before applying a generic multiple-rod spacing efficiency.
R1 = ρ/(2πL) × [ln(4L/d) − 1]Rn ≈ R1/(n × ηspacing)where:
- ρ
- Uniform soil resistivity[Ω·m]
- L
- Buried rod length[m]
- d
- Rod diameter[m]
- ηspacing
- Generic rod-array efficiency
Field measurement and layered-soil analysis govern final grounding performance.
How to use the Grounding Resistance Calculator
Estimate single vertical ground-rod resistance and a preliminary multiple-rod result from soil resistivity, rod length, diameter, count, and spacing. Start by choosing the operating mode, then enter values from nameplates, measurements, or project documents in the units shown. The result updates immediately and keeps intermediate quantities visible for review.
- Confirm the system and calculation mode.
- Enter measured or manufacturer-rated values.
- Review the primary result and intermediate metrics.
- Continue with the related protection or equipment-selection checks.
Calculation method and validation
The equations and symbol definitions above show the complete calculation basis. Inputs are checked before calculation so zero, negative, incompatible, or physically impossible combinations are flagged instead of silently producing a misleading result.
How to interpret the result
Use the main result as a starting value and read every supporting metric. Uniform homogeneous soil Vertical rods with length much greater than diameter Generic spacing-efficiency screen A passing or recommended result means the entered mathematical conditions are satisfied; it does not certify the complete installation or a particular product combination.
- Uniform homogeneous soil
- Vertical rods with length much greater than diameter
- Generic spacing-efficiency screen
Selection limits and next checks
Preliminary engineering estimate only. Verify the final design against the current applicable standard, local rules, manufacturer data, and project conditions. Layered soil, moisture, seasonal change, buried conductors, foundations, and nearby electrodes can dominate the result. Final grounding resistance must be measured using an accepted test method. Compare the output with the current applicable standard, local rules, exact VIOX product datasheet, environmental conditions, protection coordination, and the engineer's project requirements before procurement or installation.
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Assumptions
- Uniform homogeneous soil
- Vertical rods with length much greater than diameter
- Generic spacing-efficiency screen
Important Warnings
- Preliminary engineering estimate only. Verify the final design against the current applicable standard, local rules, manufacturer data, and project conditions.
- Layered soil, moisture, seasonal change, buried conductors, foundations, and nearby electrodes can dominate the result.
- Final grounding resistance must be measured using an accepted test method.