Military Handbook 419 (MIL-HDBK-419A) contains reference tables and formulae for the resistance of various patterns of rods and wires buried in soil of known resistivity. Sometimes the conductivity, the reciprocal of the resistivity, is quoted instead.Ī wide range of typical soil resistivity values can be found in literature. The SI unit of resistivity is the Ohm-meter (Ω-m) in the United States the Ohm-centimeter (Ω-cm) is often used instead. Exceptional values: from 1000 up to 10000 (Ω-m).The soil resistivity value is subject to great variation, due to moisture, temperature and chemical content. In general there is some value above which the impedance of the earth connection must not rise, and some maximum step voltage which must not be exceeded to avoid endangering people and livestock. In single wire earth return power transmission systems, the earth itself is used as the path of conduction from the end customers (the power consumers) back to the transmission facility. In most substations the earth is used to conduct fault current when there are ground faults on the system. It can also be a useful measure in agriculture as a proxy measurement for moisture content. It was formerly important in earth-return telegraphy. It is needed for design of grounding (earthing) electrodes for substations and High-voltage direct current transmission systems. An understanding of the soil resistivity and how it varies with depth in the soil is necessary to design the grounding system in an electrical substation, or for lightning conductors. It is a very important parameter for finding the best location of a transmitter working on low frequiencies (VLF, LF, MF and lower shortwave) as such radio stations usually use ground as counterpole. It is a critical factor in design of systems that rely on passing current through the Earth's surface. Soil resistivity is a measure of how much the soil resists or conducts electric current.
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