Earth resistance is the opposition to the flow of current between a ground electrode and the earth mass.The resistance is measured in ohms.By injecting a known current magnitude, the voltage drop across the earth mass and the electrode is measured and the resistance is calculated and displayed by the measuring device using the ohms law.
Measurement methods include, the three point, four point and clamping method.The resistance results are affected by the soil type, moisture content ,length of the electrodes, spacing of electrodes and the soil temperature.
Poor earth measurement results can be improved through the use of longer earth electrodes, additional of parallel electrodes and use of earth enhancement compound.