The “earth resistivity” is a fundamental parameter that influences an electrode system’s earth resistance expressed ohm-centimetre. But it is not appropriate to calculate the actual value of surface resistivity to test the resistance of the electrode earth.
Measurements of earth resistivity can be used for geophysical prospecting conveniently — to find ore sources, clays, and water-bearing gravel under the surface of the earth.
You can also use the metric to assess depth of bed rock and glacial drift density. Earth resistivity tests are also useful in finding the best location and depth for electrodes with low resistance.
These experiments were conducted, for example, in the construction of a new electrical unit; a generating station, substation, transmission tower, or central office telephone.
Finally, earth resistivity can be used to indicate the degree of corrosion expected in water, oil, gas, gas, etc. underground pipelines
In general, corrosion tends to increase in spots where the resistivity values are low. A good guide to installing cathodic protection is this same type of information.
Factors That Can Change Your Minimum Earth Resistance
First, however, consider three factors that may alter the specifications of the earth’s electrode from year to year: a plant or other electrical facility may grow in size.
Also, larger and larger new plants are still being built. These variations in the Earth’s electrode create different needs. What used to be a suitably low resistance to earth can become an obsolete “norm.”
The problems of electrical noise are magnified as facilities add more modern sensitive computer-controlled equipment. Older equipment can cause daily problems with new equipment due to noise that would not have an effect on crude.
As more nonmetallic pipes and conduits are installed underground, such installations become less and less dependable as effective, low-resistance ground connections.
The water table is gradually falling in many places. Earth electrode systems that were previously effective in a year or so may end up highly resistant in dry earth.
Such considerations underline the value of an active, daily Earth-resistance testing program. Only when built, it is not enough to test the earth’s resistance