Common use of Resistance to Earth Clause in Contracts

Resistance to Earth. The resistance of a grounding electrode is dependent on the: -- resistance of the electrode, -- contact resistance between the electrode and the soil, and -- resistance of the soil from the electrode surface outward as described by the geometry set up by the flow of current from the electrode to infinite earth. The first two resistances are negligible, and can be disregarded. The third resistance is larger and must be considered. Around a ground rod this resistance is the sum of the series resistances of virtual shells of earth, located progressively outward from the rod. The shell nearest the rod has the smallest circumferential area or cross section, so it has the highest resistance. Each successive shell has progressively larger areas, and thus, progressively lower resistances. For an 8-foot ground rod, the incremental increase in resistance decreases to nearly zero when the rods are spaced 16 feet apart. Therefore, when using multiple ground rods, the optimal spacing between rods should be double the length of the rod.

Resistance to Earth. The resistance of a grounding electrode is dependent on the: -- o resistance of the electrode, -- o contact resistance between the electrode and the soil, and -- o resistance of the soil from the electrode surface outward as described by the geometry set up by the flow of current from the electrode to infinite earth. The first two resistances are negligible, and can be disregarded. The third resistance is larger and must be considered. Around a ground rod this resistance is the sum of the series resistances of virtual shells of earth, located progressively outward from the rod. The shell nearest the rod has the smallest circumferential area or cross section, so it has the highest resistance. Each successive shell has progressively larger areas, and thus, progressively lower resistances. For an 8-foot ground rod, the incremental increase in resistance decreases to nearly zero when the rods are spaced 16 feet apart. Therefore, when using multiple ground rods, the optimal spacing between rods should be double the length of the rod.