Step & Touch Voltage (Limits)

Compute permissible step and touch voltage limits using IEEE Std 80 simplified equations for surface layer resistivity ρ_s and clearing time.
Method (simplified): E_step,perm ≈ (1000 + 6ρ_s)·√t ; E_touch,perm ≈ (116 + 0.7ρ_s)·√t (V).
Note: This returns limits only; grid design (GPR, mesh/step) requires geometry & fault current.