Three preliminary calculators
Enter your values below for an instant estimate. Each calculator shows the formula it uses, so you can check the working yourself.
Calculations run in your browser. Values are not sent to PrimeEarth; use the copy or download controls to keep a local summary.
Compare your rod options
Save up to three sets of calculator inputs and compare the estimates. Each row represents one separate rod in uniform soil, not rods connected as an array.
No options saved. Enter dimensions and soil resistivity above, then save your first option.
| Option | Length | Diameter | Soil ρ | Estimate | Action |
|---|
How this is calculated+
Model: uniform soil, one vertical rod with its top at ground surface. L and d are converted to metres. nVent electrode-design reference.
Rod dimensions should be selected for the electrode design, mechanical strength, corrosion environment and manufacturer/product specification. This calculator is a preliminary mathematical estimate, not a design approval.
This is a preliminary single-electrode estimate. Multi-rod arrays, mutual resistance between electrodes, and seasonal soil moisture variation are not accounted for — confirm with a fall-of-potential test on site.
How this is calculated+
Transformer short-circuit impedance is equipment-specific. The 4% value is only an illustrative calculator default; use the transformer nameplate or project data for an actual assessment.
The optional voltage-rise illustration uses separately supplied earth-system current Iₑ and resistance Rg. Three-phase fault current is not assumed to enter the earthing system. Obtain Iₑ from a qualified fault study accounting for return-path current division. This steady-state illustration excludes transient and impedance effects and does not assess step/touch safety. SEL grounding case study.
How this is calculated+
Increasing the spacing a samples soil behaviour over a greater effective depth. Soil profiles can vary with depth, so multiple spacings and engineering interpretation may be required for a full resistivity study.
Retain readings separately for each electrode spacing and test direction. Changes with spacing can indicate soil layering; do not average different spacings into one design value without engineering interpretation.
Preliminary engineering estimates only, provided for design guidance. Actual earthing performance depends on soil conditions, moisture, and seasonal variation — confirm with on-site testing before finalising an installation. Reference: IS 3043 (Code of Practice for Earthing).
Build a concise project brief
Use a short guided flow to organize your requirement before contacting our team.
Move the inputs. See the effect.
Explore how rod length and soil resistivity affect a mathematical estimate before using the detailed calculator.
33.5 Ω
Illustrative single-rod estimate: diameter 16 mm, top at ground surface, uniform soil. R = ρ/(2πL) × [ln(8L/d) − 1]. Multiple electrodes, layered soil and seasonal effects are excluded.
The curve shows why changing rod length has diminishing returns in this simplified model. A lower estimate alone does not establish safe disconnection or touch-voltage performance.