Earth Electrodes

Earth electrodes can be following shapes
a) Driven Rods or pipes

b) Horizontal Wires

c) Four Pointed Stars

d) Conductive Plates

i) Round Vertical Plates

ii) Square Vertical Plates

e) Buried Radial Wires

f) Spheres made of metal

g) Water PipesAs water pipes exist extensively and these are most of the time embedded in earth, they can make a good earth electrode.Such earthing is not objectionable with alternating currents. But with direct currents, the flow of fault currents in pipes produces electrolysis and results in heavy corrosion of pipes. This electrolysis process makes the water also harmful to certain extent.If water pipes are proposed to be used as earth electrode, then only main water supply pipe should be used as an electrode. The water supply main pipe should have metal to metal joints between its segments.A perfect electrical connection should be made between water pipe & earth conductor.Pipe should be cleaned throughly with emery paper. Earth conductor also should be cleaned throughly.The cleaned conductor should be wrapped 4 to 5 times and ends clamped by nuts & bolts.The earth resistance achieved by such an arrangement is usually a fraction of an ohm. Low resistance of such syestem is due to long length of water pipe and the fact that it is mostly embedded below earth. This method is mostly used for grounding in telephone services.Electrodes should be made of a metal, which has a high conductivity. Normally copper is used.The size of the electrode should be such, that it is able to conduct the expected value of stray current for expected duration of stray current.The resistance of electrode should not increase with time. It should have high resistance to soil & atmospheric corrosion.More the surface area of electrode in contact with soil, lesser will be its resistance to conduct the electricity to earth.90% of the total resistance offered by soil is situated within an area, the radius of which is roughly equal to the length of the electrode. When multiple electrodes are used for earthing, electrodes should be spaced far enough away from each other so as not to overlap the resistance areas of their neighbours. When a number of electrodes are used all the electrodes should be of same material. With Electrodes having spacings equal to approximately twice the length of each electrode , each additional rod introduces a new area of unused soil and the resistance is reduced by an amount which is almost inversely proportional to the number of rods installed.The depth of electrode also effects the efficacy of earthing, because at greater depths, the soil resistance is normally low