Ground Grid Analysis - CableTrayRoute

Method & Assumptions

Ground grid analysis follows IEEE 80-2013, IEEE Guide for Safety in AC Substation Grounding. The tool evaluates a rectangular grid of horizontal conductors buried at uniform depth.

Grid resistance uses Sverak, IEEE 80-2013 Eq. 57.

Rg = rho/L + rho/sqrt(20A) * (1 + 1/(1 + h*sqrt(20/A)))

Mesh voltage is evaluated per IEEE 80-2013 Eq. 86.

Em = rho * Ig * Km * Ki / L

Step voltage is evaluated per IEEE 80-2013 Eq. 92.

Es = rho * Ig * Ks * Ki / L

Ground potential rise:

GPR = Ig * Rg

Surface layer reduction factor Cs accounts for high-resistivity surface material such as crushed stone.

Citations: IEEE 80-2013, IEEE 81-2012. See also: Arc Flash, Short Circuit.

Inputs

Study Setup

5 sections

Unit System

Soil Parameters

rho - Soil resistivity (ohm-m)

Measured by Wenner four-pin method (IEEE 81). Typical values: sand 200-2000, clay 10-100, rock 1000-10000 ohm-m. Use the lowest seasonal value for conservative design.

Grid Geometry

Grid length L_x (ft)

Length of the grid in the x-direction.

Grid width L_y (ft)

Width of the grid in the y-direction.

n_x - Conductors parallel to x-axis

Number of horizontal runs. Spacing = L_y / (n_x - 1).

n_y - Conductors parallel to y-axis

Number of vertical runs. Spacing = L_x / (n_y - 1).

h - Burial depth (ft)

Depth of grid conductors below grade. IEEE 80 commonly uses about 0.5 m (1.5 ft).

d - Conductor diameter (in)

Diameter of buried conductor. 2/0 AWG Cu approx. 0.418 in, 4/0 AWG approx. 0.528 in.

Include perimeter / corner ground rods

Includes rods tied to the grid for correction factors and effective buried length.

Interstitial rod spacing in x-direction (ft, 0 = corners only)

Target spacing between rod columns along L_x. Rods snap to conductor intersections.

Interstitial rod spacing in y-direction (ft, 0 = corners only)

Target spacing between rod rows along L_y. Set x and y spacing to place interior rods.

Enable ground rods to activate interstitial rod spacing.

Electrical Parameters

I_g - Maximum grid current (A)

Maximum symmetrical grid current = split factor times 3I0. Obtain from the Short Circuit study.

t_f - Fault clearing time (s)

Duration before the protective device clears. Typical primary relay plus breaker clearing is 0.1-0.5 s.

Body weight for tolerable voltage limits

IEEE 80-2013 provides limits for 50 kg and 70 kg body weights.

Surface Layer (optional)

A high-resistivity surface material, such as 3-6 in crushed stone, raises tolerable touch and step voltages.

rho_s - Surface layer resistivity (ohm-m, 0 = none)

Crushed granite: 2000-5000 ohm-m; asphalt: 10000-2000000 ohm-m. Leave 0 if no surface layer.

h_s - Surface layer thickness (in, 0 = none)

Typical crushed stone layer: 4-6 in (0.1-0.2 m).

The map updates live. The dashboard updates after analysis.

Touch Voltage -- Run analysis for Em / Etouch

Step Voltage -- Run analysis for Es / Estep

GPR -- Transferred-voltage review appears here

Grid Resistance -- Calculated from grid area and buried length

Interactive Map

Ground Grid Safety Map

Visual preview updates as you edit grid dimensions and conductor counts.

Show voltage-risk overlay Overlay opacity

Overlay is estimated from conductor spacing. Run analysis to scale overlay by IEEE 80 results.

Plan View

Elevation / Cutaway

Design Coach

Recommended Actions

Run analysis to receive ranked design actions.

What The Checks Mean

Voltage Safety Context

Mesh voltage is the touch-voltage proxy for a person touching grounded equipment inside the grid.

Step voltage evaluates the voltage between a person's feet near the grid surface.

GPR is grid current multiplied by grid resistance; high GPR can create transferred-voltage hazards beyond the grid.

Two-Layer Soil Model Fitting

Enter Wenner four-electrode apparent resistivity measurements (ANSI/ASTM G57). Requires at least 3 measurements. The tool fits rho₁, rho₂, and h using Sunde's image method with Nelder-Mead optimisation.

#	Electrode spacing a (m)	Apparent resistivity ρ_a (Ω·m)	Delete row

Irregular (Polygon) Grid

Define the grid boundary as a polygon and set mesh spacing. Conductor scan-line fill is computed automatically. IEEE 80 screening is then applied to the polygon area and perimeter (approximation — see study basis for limitations).

Polygon Vertices

#	X (m)	Y (m)	Delete

Mesh & Electrical Parameters

Mesh spacing X (m)

Mesh spacing Y (m)

Burial depth (m)

Conductor diameter (m)

Soil resistivity (Ω·m)

Max grid current I_g (A)

Fault duration (s)

Body weight

Grid Preview

Inspection Point Risk Assessment

Add named inspection points (equipment locations, fence posts, gate handles, etc.) and review touch and step voltage margins. Hazard Map must be generated first.

Label	X (m)	Y (m)	Touch V	Step V	Touch margin	Step margin	Risk	Delete
Generate Hazard Map to populate automatic risk points, or add inspection points manually.

Ground Grid / Substation Grounding Analysis