There are 3 combined elements that compose earth resistance:

1. Resistance of earth wire and the earth electrode
2. Contact resistance between the earth electrode and the ground
3. Ground resistance or better the earth resistivity intended as the characteristic of the earth.

Analyzing these 3 elements, the value of element

1. Is normally very small and it can be ignored, but of element
2. Varies depending on the material, shape and installed depth of the electrode. Meanwhile, the value of element
3. Has the greatest effect on the earth resistance value.

The soil composition, temperature and moisture content all have an impact on the earth resistivity. The schematic below shows the effect of soil composition, temperature and moisture on earth resistance.

As a general rule, it is recommended that an earth electrode is placed as deep as possible into the ground, ideally in humid soil, to lower the earth resistance to a minimum level. In addition, the electrode should be installed where there is a stable temperature regardless of seasons change, i.e. below the frost line.