This Substation Earthing spreadsheet from 3D-LABS follows IEC 60479-1 and gives instant, checkable results for practising engineers — no manual derivation required.
This spreadsheet designs substation grounding (earthing) mats per IEEE Std 80-2013 (IEEE Guide for Safety in AC Substation Grounding). It calculates tolerable touch voltage, step voltage, mesh voltage, and grid resistance, then iterates grid conductor spacing and burial depth to meet IEEE 80 safety criteria — a mandatory calculation for all HV/EHV substations above 69 kV.
What standard does this calculation follow?
IEEE Std 80-2013 (IEEE Guide for Safety in AC Substation Grounding), IEC 60479-1:2016 (Effects of current on the human body) for body current limits, IEEE Std 81-2012 (Guide for Measuring Earth Resistivity), and IS 3043:2018 (Code of Practice for Earthing, BIS India).
What formula is used?
Tolerable step voltage: Es = (1000 + 6Cs × ρs) × 0.116/√ts (for 50 kg body, 50 Hz per IEEE 80 Eq. 32). Mesh voltage: Em = ρ × Km × Ki × IG / Lm, where Km = geometric spacing factor, Ki = irregularity factor, IG = symmetrical ground fault current (A), Lm = total length of buried conductor (m).
Frequently Asked Questions
What is the IEEE 80 formula for tolerable touch voltage in a substation?
Per IEEE Std 80-2013 Eq. 33: Et = (1000 + 1.5Cs × ρs) × 0.116/√ts for a 50 kg body at 50 Hz, where Cs = surface layer derating factor (accounts for crushed rock layer), ρs = surface layer resistivity (Ω·m), ts = fault clearing time (seconds). For crushed granite (ρs = 3000 Ω·m), 100ms clearing: Et ≈ (1000 + 4500) × 0.367 = 2,015 V.
What surface material reduces touch voltage hazard in substations?
Crushed rock (granite gravel, ρs = 2,000–7,000 Ω·m at 100mm depth) dramatically reduces step and touch hazard. The IEEE 80 surface layer derating factor Cs = 1 – [0.09(1-ρ/ρs)] / [2hs + 0.09], where hs = layer depth (m). A 150 mm crushed granite layer (ρs = 5,000 Ω·m over soil ρ = 100 Ω·m) increases tolerable touch voltage by 3–5×.
What inputs are required for an IEEE 80 substation earthing design?
Required: soil resistivity ρ (Ω·m, measured per IEEE 81-2012 Wenner 4-pin method), symmetrical ground fault current 3I0 (kA), fault clearing time ts (seconds), substation area (m²), grid conductor material (copper, stranded steel), burial depth h (m), and surface layer resistivity ρs (Ω·m).
What’s Included
An instant Excel download with the complete formula set, a worked numerical example, and reference to the governing standard — ready to adapt to your own project inputs.
