Work out earthing resistance instantly with clear inputs, formula shown and shareable results.
For a driven rod, resistance is (rho / 2 pi L)(ln(8L/d) - 1). Length matters far more than diameter because it appears outside the logarithm, so doubling rod length nearly halves resistance while doubling diameter barely helps. Parallel rods must be spaced at least their own length apart to avoid overlapping resistance shells.
Rod electrode resistance
R = (rho / (2 pi L)) x (ln(8L/d) - 1); parallel rods give less than proportional benefit
Electrical results are planning estimates only. Verify against the applicable wiring rules (IEC 60364, BS 7671, NEC or local code) and have all installation work designed and checked by a qualified electrician.
It appears only inside a logarithm, so doubling it reduces resistance by a few percent. Driving deeper or adding rods is far more effective.
Adjacent rods share the same soil volume, so their resistance areas overlap. Spacing them at least one rod length apart limits the loss to around 20-25%.