Earthing
PMG Engineering
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Earthing is arrangement by which an electrical installation is connected to means of earthing. This is usually for safety purposes although sometimes also for functional purposes, for example in case telegraph lines which use earth as conductor to save cost of retrurn wire over a long circuit. If there is fault in electrical installation, a person could get an electric shock by touching a live metal part because electericity uses the body as path to earth. Earthing provides an alternate path for fault current to flow of earth. It can be seen in power system networks, industries, domestic homes, commercial buildings. ?
In this below diagram, we can easily see that euipment body leakage current leakage from equipment body, pass to a human body as there is no grounding of euipment or device. This increases the risk of electrical shock. Hence earthing play an immense important role in industries, commercial building, home etc.
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????????????????????????????????????????????????Electrical system without earthing
In this below diagram, with grounding of eqipment, the whole leakage of current in equipment? body passes through low resistance path called ground wire so there is a negligible chance of electrical shock.??????????????????????
Electrical system with earthing
There are variuos types of earthing is done like rod earthing, strip earthing, plate earthing, pipe earthing and earthing through water mains but pipe and plate earthing is preferred so much.
?It is done by number of joinining of rod through copper conductor and it reduces overall grounding resistance of system. Such type of earthing helps to limiting the potential. This type of earthing used in where there is a high fault current is to be experinced. While designing this system following points must consider.
?In this earthing, we may use wire, rod, pipe and inserted verically or horizontally into ground and In distribution system there is rod of nearly 1m is used and inserted vertically into ground but in generating substations there is earthing mat is used rathan than this.
This type of earthing is mostly used and this is considered best method as comared to other type of earthing for same soil condition. In this earthing, the galvanized steel or perforated pipe of approved length and diameter depend upon types of soil and current carried by that rod is placed upright in wet soil as shown in figurenormally size of pipe is of 40mm diameter and 2.5m in length for ordinary soil but for dry soil length may increase. When there is summer then moisture of soil decrease which cause increase in ground resistance some arrangement of water is done for water accesible or 3 or 4 buckets of water is put into a pipe which is connected to soil pit. In soil pit, there is mixed of charcoal and salt around the pipe to reduce the effective resistance of soil.?
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In this earthing, either copper plate of 60cm×60cm×3m?or galvanized iron rod of 60 cm× 60 cm×6mm is buried in ground with it face vertically to ground and depth is not less than 3m from ground level. The ground wire connected to copper plate through nut or bolt. Copper wire is not used mostly because of high costing. The layer of soil and coke is placed in soil pit.
In this type of grounding, the copper or GI wire is connected to water mains through water pipe and water pipe is directly connected to earth as shown in fig. when the fault condition occurs the whole leakage current passes through water steel pipe and e
rthed.
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