Effect of Temperature on Earth Resistance — The temperature coefficient of resistivity for soil is negative, but is negligible for temperatures above freezing point. At about 20°C, the resistivity change is about 9 percent per degree Celsius. Below 0°C the water in the soil begins to freeze and introduces a tremendous increase in the temperature coefficient, so that as the temperature becomes lower the resistivity rises enormously. It is, therefore, recommended that in areas where the temperature is expected to be quite low, the earth electrodes should be installed well below the frost line. Where winter seasons are severe, this may be about 2 metres below the surface, whereas in mild climates the frost may penetrate only a few centimeters or perhaps the ground may not freeze at all. Earth electrodes which are not driven below the first depth may have a very great variation in resistance throughout the seasons of the year. Even when driven below the frost line, there is some variation, because the upper soil, when frozen, presents a decided increase in soil resistivity and has the effect of shortening the active length of electrode in contact with soil of normal resistivity. We, at Atul Casting and Metal Works manufactures all earthing related products such as G.I Strips, G.I plates, G.I Rods, G.I Pipes, C.I covers, Cable Trays, G.I Wire, Manhole Covers and Route Markers for past 50 + Years in heart of New Delhi. Call us at +91 9873361672 for best deals