As long as I know the accepted methods for measuring the resistivity of electric grounding grids, once they are built, for any kind of building (in cities, at industrial level, transmission towers, etc) are:
- Fall of potential using 3 stakes (I have seen this method the most)
- Using a clamp-on tester and rods.
- All sort of, in my opinion, unreliable 'things' using normal testers and cooper bars.
Does anybody know about other methods which are accepted according to norms or at least reliable enough?