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 return 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 electricity 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 equipment body leakage current leakage from equipment body, pass to a human body as there is no grounding of equipment or device. This increases the risk of electrical shock. Hence earthing play an immense important role in industries, commercial building, home etc.
Electrical system without earthing
In this below diagram, with grounding of equipment, 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
Method of earthing
There are various 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.
- Earthing mat
It is done by number of joining 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 experienced. While designing this system following points must consider.
- Earthing electrode
In this earthing, we may use wire, rod, pipe and inserted vertically 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 rather than Earthing electrode.
- Pipe earthing
This type of earthing is mostly used and this is considered best method as compared 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 figure. Normally 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 accessible 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.
- Plate earthing
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.
- Earthing through water mains
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 earthed.