This applicable for main earth grid connected with the transformer/return path The continuity resistance of the earth return path through the earth grid should be maintained as low as possible and in no case greater than Unless otherwise specified ,It is recommended that the value of any earth system resistance shall not be more than
#Bs 7430 earthing calculation code#
National Electric code (NEC) 2011, (IS SP30 Chapter 14 -India) Such a low resistance is only required for large substations, transmission lines, or generating stations. Resistances of less than 1 ohm may be obtained using a number of individual electrodes connected together. This is because the higher the ground resistance, higher would be noise interference in the systems.įor industrial plant substations and buildings and large commercial installations. But communication systems need very stringent limit, typically one ohm.Electrical Systems can work with earth resistance of 20 ohms, though generally 10 ohms is the specified Maximum limit.Different codes specifies the required value of earthing system. value of individual earthing pit resistance is not so important. Moisture content in soil plays a vital role in the soil resistivity. The value of earthing resistance varies on the Type of Soil, Soil characteristic, soil resistivity and the climatic condition.Total earthing resistance is the sum of the resistance of earth lead wires, Contact resistance between the surface of the earth electrode and the soil and The resistance of the body of the soil surrounding the earth electrode.System ground resistances can be reduce by the use of a number of individual electrodes connected together. Ideally a ground resistance should be of zero ohms but It is always greater than Zero.The resistance offered by the earth electrode to the flow of current into the ground is known as the earth resistance or resistance to earth.
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