Fall of Potential Method
The receiver portion of the MiniIRes is completely separated from the transmission portion of the MiniRes. You can not damage the MiniRes by connecting the wrong terminals together There are at least three methods
for measuring the electrical resistance of an
The triangulation or “three
electrode” method has the disadvantage that small errors in measuring or in
positioning can generate large errors in the final answer. Two temporary
electrodes are driven in the ground to form a triangle with the existing electrode
as the third corner of the triangle. The temporary electrodes should be at
least 15 feet (5 meters) and preferably 25 feet (8 meters) meters away from the
electrode to be tested. Resistances are read between each of the pairs of
electrodes. The resistances of the three electrodes (a, b, and x) are
The Direct method is some times referred to as the two-terminal
method It is straight forward but
subject to many sources of error. On the MiniRes the
The “Fall of Potential “ method
is the most common method for measuring the electrical resistance of an First, be sure that the grounding electrode to be measured MUST be disconnected from the NEUTRAL connection during the grounding test. If the grounding electrode remains connected to NEUTRAL during your testing, the results will be erroneous Connect the If the electrodes are too close together, there will not be a level “plateau” in the graph. You must expand the array until you do have a “plateau”. The value should be taken where the graph is about 62% of the distance from the electrode being tested and the far (C-) electrode. If the ground electrode is not a single rod then the following would apply (the following is quoted from Brewer (1987)): - When the grounding system contains two or more electrodes along a straight line, the maximum dimension is the distance between the first and last electrode.
- The maximum dimension for a grounding system containing electrodes in a circular ring configuration is the diameter of the circle.
- The diagonal distance across a grounding system having a square or rectangular form is the maximum dimension.
- The maximum dimension for a grounding system containing electrodes in a star configuration is twice the length of a single branch.
For sites where the grounding electrode system has not been installed as yet, the most common method of obtaining the necessary parameters for the designer is the Wenner technique. It is explained in another section of this manual. There are also some ASTM standards that can be obtained directly from ASTM over the internet.
Brewer, Myron L., (1987), Measurement
of resistance to ground, Chapter 12. Practical Grounding, Theory and Design
(published by
Tagg, G.F. |

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