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IEEE 80 recommends Substation ground resistance below 1-5 ohms for large installations, while IEC 60364 allows up to 10 ohms for many LV systems. A 1-ohm target is standard for MV substations; the calculator sizes the number of rods to meet your target.

Rod count depends on soil resistivity and target resistance. In 100 ohm-m soil, a single 2.4 m rod gives roughly 35-40 ohms; reaching 10 ohms needs 4-5 rods spaced 2.4 m apart, and 1 ohm needs 40-50 rods (or a grid). The calculator computes the single-rod resistance and the count for the target.

Soil resistivity varies from ~10 ohm-m (wet clay) to 1000+ ohm-m (dry rock). Higher resistivity means more rods or a larger grid for the same resistance. Sandy or rocky sites often need chemical treatment or deep-driven rods. The calculator takes soil resistivity as input and sizes the electrode accordingly.

Rods placed closer than their length interfere, raising the combined resistance. Spacing rods at least one rod length apart (typically 2.4 m) gives nearly independent rods and the full benefit. Closer spacing wastes material. The calculator applies the standard spacing rule.

Earth resistance is the electrode-to-earth impedance; touch and step voltages are the voltages a person can experience during a fault, which depend on the surface layer and grid geometry, not just resistance. IEEE 80 limits touch voltage to ~50-100 V depending on fault duration. The calculator sizes for resistance; full touch/step study needs IEEE 80 grid analysis.