Grid resistance (Sverak's simplified equation) and a screening check of ground potential rise against IEEE 80 tolerable touch voltage. Single-layer soil model — a preliminary study, not a substitute for a full two-layer design. Defaults include a crushed-rock surface layer, standard practice at real substations since bare soil rarely passes this check at all.
Verified against published standard
Grid & Soil
Total conductor length includes grid conductors AND any ground rods. Grid area is the plan area enclosed by the outer conductors.
Fault & Safety
Enter grid and soil data.
About This Calculation
A substation or plant grounding grid has one job during a fault: keep the voltage a person could touch (or step across) below what the human body can safely withstand for the time it takes protection to clear the fault. This calculator uses the IEEE 80 Sverak equation for grid resistance and the standard IEEE 80 tolerable touch/step voltage equations, for a single-layer (uniform) soil model — a real design with genuinely non-uniform soil needs the full two-layer method or dedicated software, but the single-layer method is a legitimate, widely-used screening-level check.
Frequently Asked Questions
Why does the default example use a crushed-rock surface layer?
Because bare soil essentially never passes this safety check at any realistic fault current — that’s exactly why real substations almost universally spec a high-resistivity surface layer (crushed rock, asphalt) under the areas people walk, which meaningfully raises the tolerable touch voltage by limiting current through a person’s feet.
What is Ground Potential Rise (GPR), and why is it compared to the tolerable touch voltage?
GPR is the voltage the entire grid rises to relative to remote earth during a fault (fault current × grid resistance). Comparing GPR to the tolerable touch voltage is a CONSERVATIVE screening check — actual touch voltage at the grid’s center is normally lower than GPR, but can approach it near the grid’s perimeter, so this comparison errs on the safe side rather than claiming the precision of the full mesh-voltage calculation.
Why does body weight (50 kg vs 70 kg) change the tolerable voltage?
IEEE 80’s tolerable voltage equations are based on the energy a human body can safely absorb, which the standard tabulates separately for 50 kg and 70 kg body weights — a heavier body is calculated to tolerate a higher voltage for the same fault duration.
What does this calculator NOT cover that a full grounding study would?
Two-layer (non-uniform) soil resistivity data, the complete IEEE 80 Annex B mesh and step voltage procedure across the whole grid geometry, and non-uniform current distribution around the grid perimeter — all genuinely needed for a final substation grounding design, typically done with dedicated grounding-analysis software.