Grounding Grid Design

Calculate grid parameters per IEEE Std 80-2013.

Typical: 10-1000 ohm-m
Crushed rock: 2500-10000
8ft rods at grid perimeter

Typical Soil Resistivity Values

Soil Type Resistivity (ohm-m)
Sea water0.1 - 1
Clay, wet5 - 20
Loam, moist20 - 100
Sand, wet50 - 200
Sand, dry200 - 3000
Gravel300 - 5000
Rock1000 - 100000

IEEE 80 Design Principles

Tolerable Voltages (50kg person)

E_touch = (1000 + 1.5 × Cs × ρs) × 0.116 / √ts
E_step = (1000 + 6 × Cs × ρs) × 0.116 / √ts

Design Criteria

  • E_touch (calc) ≤ E_touch (tolerable)
  • E_step (calc) ≤ E_step (tolerable)
  • Conductor must withstand fault current
  • Surface layer reduces body current
  • Ground rods reduce resistance