Methodology: resistance, EPR and touch/step voltage formulae are from ENA EREC S34 Issue 2 (2018), Appendix B. Permissible touch/step voltage limits are from ENA TS 41-24 Issue 1 (2017), Tables 1 & 2. The primary electrode model (buried grid + rods around the periphery, Formula R6) has been validated against S34's own worked example (Section 6.1.1, Case Study 1).
Soil resistivity: S34 does not itself define how to turn Wenner readings into a resistivity model — the single-value and simplified two-layer options here are standard engineering estimates (IEEE 81 style), not full curve-matching software. Cross-check critical or complex sites against dedicated analysis.
Additional electrodes: extra tape runs, rings, or foundation/plate electrodes not part of the grid+rods system are combined via parallel resistance (Formula R10), which neglects proximity effects between closely-spaced electrodes.