12 Apr MRU (series) – How to perform earth electrode measurements when the area is covered by concrete and probes cannot be entered into the ground?
If the earthing system is not interconnected underground (e.g. a ground ring), but is connected to other earthing elements (e.g. air terminals on the roof), then you can use the double clamp method available in MRU-120, MRU-200 and MPI-530 meters (no need to enter the probes into the ground). In case of a single earthing this method can be applied, when the earthing is connected to PE of network (results will be slightly overstated, but an error in this direction is acceptable). For single earthing, you can try the fault loop method – a loop in the circuit consisting of phase and tested earthing is measured, whereas the circuit is closed by the earth.
The results of earth resistance are overstated as they are increased by the values of the fault loop of the power supply circuit. However this method is susceptible to power network interferences and requires proper interpretation of results by the operator (too low value may indicate that the circuit was closed by a metal element).
When you want to apply the fault loop method for multiple ground ring, disconnect power supply to the tested object and then disconnect all control connections and equipotential connections.