Design safer sites with clear grounding metrics. Compare layouts, depths, and rods. Validate touch and step limits against expected fault conditions today with confidence.
Sample inputs and typical outputs for quick checking.
| ρ (Ω·m) | ρs (Ω·m) | hs (m) | L×W (m) | Spacing (m) | h (m) | Ik,e (kA) | Sf | tf (s) | Rnet (Ω) | GPR (V) |
|---|---|---|---|---|---|---|---|---|---|---|
| 100 | 3000 | 0.10 | 60×40 | 5 / 5 | 0.6 | 10 | 0.30 | 0.5 | ≈0.90 | ≈3,200 |
| 200 | 2000 | 0.10 | 80×60 | 6 / 6 | 0.8 | 20 | 0.25 | 0.4 | ≈0.70 | ≈7,000 |
Values are indicative; your layout and current split may differ.
Rg = ρ [ 1/LT + 1/√(20A) · ( 1 + 1/(1 + h√(20/A)) ) ]
Cs = 1 − [0.09 · (1 − ρ/ρs)] / (2hs + 0.09)
Ta = (X/R) · 1/(2πf)
Df = √(1 + (Ta/tf)(1 − e^(−2tf/Ta)))
IG = (Ik,e · Sf) · Df
GPR = IG · Rnet
Etouch = (1000 + 1.5Csρs) · k/√tf
Estep = (1000 + 6Csρs) · k/√tf
Use k=0.116 for 50 kg or k=0.157 for 70 kg.
An earthing grid provides a low-impedance path for fault current and helps control voltage gradients on a worksite. During a fault, the grid may rise in potential relative to remote earth. This rise is the GPR, and it increases touch and step risk if surface voltages become excessive.
Soil resistivity (ρ) dominates grid resistance. Grid footprint (L×W), conductor spacing, and burial depth increase effective conductor length (LT) and improve soil contact. A perimeter ring adds length and helps reduce edge gradients.
Where possible, use measured resistivity and consider seasonal variation. Run low and high cases to understand how margins change.
The calculator converts earth-fault current (Ik,e) to grid current using a split factor (Sf) and a decrement factor (Df) derived from X/R, frequency, and clearing time (tf). Longer clearing times reduce tolerable limits and can tighten margins.
Example: ρ=100 Ω·m, ρs=3000 Ω·m, hs=0.10 m, L×W=60×40 m, spacing 5 m, depth 0.6 m, Ik,e=10 kA, Sf=0.30, tf=0.5 s. The tool estimates Rnet≈0.90 Ω and GPR≈3200 V, then compares GPR against tolerable touch and step limits for the selected body-weight basis. The report also shows Cs and Df so you can explain changes after adjusting surfacing or fault assumptions.
If the screening result shows REVIEW, reduce resistance and gradients by tightening spacing, increasing grid area, adding a perimeter ring, deepening burial where practical, or adding well-distributed rods. Confirm conductor sizing for thermal duty, then complete a detailed gradient study for final approval.
GPR is the grid’s voltage rise during a fault relative to remote earth. Higher GPR can increase touch and step risk unless surface gradients are controlled and limits are satisfied.
Soil resistivity affects grid resistance, while the surface layer influences how much voltage appears at the surface. Higher-resistivity surfacing can reduce body current for a given surface voltage.
Sf is the fraction of fault current that actually returns through the grid. The remainder may flow via neutrals, shield wires, nearby metallic paths, or remote earth depending on the system.
Rods can lower the combined resistance by providing deeper contact with soil layers. They are helpful when space is limited or when reducing resistance is needed without expanding the grid footprint.
PASS means GPR is below the calculated tolerable touch and step limits for the chosen assumptions. REVIEW means you should refine the design and perform a detailed study of surface gradients.
No. It provides a screening-level estimate. Detailed design usually evaluates mesh voltage, step voltage distribution, transfer potentials, soil layering, and conductor sizing using recognized methods.
Increasing grid area, reducing spacing, adding a perimeter ring, improving surface layer conditions, and shortening clearing time often improve margins. The best combination depends on site constraints and measured soil data.
Use results responsibly and confirm designs with standards always
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.