Electrode Resistance Calculation:

Short Circuit Current Calculation and Protective Earth Conductor Selection

How to measure soil resistivity?
-Soil Resistivity is necessary when determining the design of the earthing system for new installations to meet your ground resistance requirements.
the resistivity of the soil affects earth resistance by many factors geographics, different soil depths, temperature, and moisture.
poor soil conditions can be overcome by increasing conductivity.
-To measure soil resistance four earth ground electrodes are positioned in the soil in a straight line, equidistant from one another.
The distance between earth ground electrodes should be at least three times greater than the electrode depth.
The megger generates a known current through the two outer ground electrodes and the drop in voltage potential is measured between the two inner ground electrodes.
Using Ohm's Law V=IR, the megger tester automatically calculates the soil resistance.