Getting Down to Earth 21Resistance to earth can vary with changes in climate and temperature. Such changes can be considerable. An earth electrode that was good (low-resistance) when installed may not stay that way; to be sure, you must check it periodically.We cannot tell you what your maximum earth resistance should be. For specific systems in definite locations, specifications are often set. Some call for 5 Ω maximum; others accept no more than 3 Ω. In certain cases, resistances as low as a small fraction of an ohm are required.Nature of an Earth ElectrodeResistance to current through an earth electrode actually has three components (Fig. 9):1. Resistance of the electrode itself and connections to it.2. Contact resistance between the electrode and the soil adjacent to it.3. Resistance of the surrounding earth.The Megger DET2 Series of testers offer additional features for testing in a high-noise environment
