This article is about:
- Which methods of earth resistance are most commonly used?
There are two methods for earth measurements which are most frequently used, and also described
in Annex C of the installation test standard IEC/HD 60364-6 or the corresponding local equivalent standards.
The three wire (or 3-pole) method
This is the measurement with 2 earth spikes (auxiliary earth electrode and probe electrode).
The two earth spikes are placed at least 20 meters apart and away from the earth electrode to be measured so that they do not influence each other.
The earth electrode to be measured must be disconnected from the PEN before the measurement,
otherwise the EVU earth electrode will also be measured and a faulty earth electrode will not be detected!
The advantage of this method is that the measurement result shows the resistance of the earth electrode directly.
The two wire method (city method)
This method is used when earth spikes cannot be placed. This may be the case in a densely built-up area or areas with sealed surfaces.
A known earth electrode is required as a reference. The PEN (or the system earth electrode of the utility) is best suited for this,
as this is usually less than 0.1 to 0.5 Ohm and can therefore be disregarded.
For this measurement, the connection between the system earth electrode and the PEN must be disconnected.
The measurement result is the serial connection of the system earth electrode (RA) and the utility earth electrode.