16 www.megger.comSECTION IIMeasuring Earth Resistance for Electrical Grounding SystemsThe simplest and somewhat misleading idea of a good ground for an electrical system is a section of iron pipe driven into the earth with a wire conductor connected from the pipe to the electrical circuit (Fig. 6). This may, or may not, be a suitable low resistance path for electric current to protect personnel and equipment.Lightning RodPlant ElectricWiringElectricMotorElectricWireEarthEarth Electrode(Pipe driven into ground)Fig. 6: A simplified grounding system in an industrial plantA practical earth electrode that provides a low ground resistance is not always easy to obtain. But from experience gained by others you can learn how to set up a reliable system and how to check the resistance value with reasonable accuracy. As you will see, earth resistivity (refer to Section I) has an important bearing on electrode resistance, as does the depth, size and shape of the electrode.The principles and methods of earth resistance testing covered in this section apply to lightning arrester installations as well as to other systems that require low resistance ground connections. Such tests are made in power-generating stations, electrical-distribution systems, industrial plants, and telecommunication systems.
