Earthing : Uses and Prev ention
Earthing is a very common phenomena in which we connect inclusion body of devices are any part of electric system with Earth. we know very well that Earth is a very big capacitor and any amount of charge can be withdrawn from it. in electrical system we basically absorb excess amount of charge in ground. Of course, we will learn earthing uses for safety and prevention.
uses of earthing :
letter start from our electric connection from electric pole. We must have seen four wires coming out of transformer. for domestic purpose we use all of them, there are three phases with colour code red , yellow and blue. fourth wire is used for neutral. there is a fifth wire by which we connect earthing in system. earthing is also used for grounding protective equipment in High Voltage system also. lightning arrester, neutral, outer body of Transformer, generator etc. are connected with earthing along with double wire .
Indian standard for earthing
IS: 3043 Code for Earthing Practice says that all medium voltage equipments should we Earthed with double wires. so that earthing purpose of saving equipment and human personal can we obtained. for example we should use 6 SWG wire for 10 HP motor and 14 SWG wire for 2 HP motor. So, so we can definitely use 6 SWG wire for all domestic purposes and we generally use this Thumb Rule.
what is safest earthing value ? what is exact limit ? we commonly face this issue in electrical connection. Actually there is no pre-define threshold limit for earthing. But according to NFPA and IEEE, earthing value must below than 5 mega ohm. So we can state that earthing station having impedance value less than 5 mega ohm is safe for equipment and personnel.
But definitely, it is not true in all cases like wise in case of high frequency equipment. However, to increase effectiveness of earthing, we should use earth grid & earth station. More than one earthing is connected in parallel to lower impedance value because of parallel connection of resistance.
For plate earthing, 600mm X 600mm X 6.5mm3 GI plate is used for construction of earth pit. At first, we dig a pit of 03 meter depending on earth soil resistivity. We use alternative multiple layers of coal and Common solt. Mutiple layers are used for increasing reliability and effectiveness of earthing. It also help for maintaining sustainability of earthing during change of weather. GI strips of thickness 32 mm or 25 mm is used according to installed euipments.
In fact, Copper earthing is recommended with 600 mm X 600mm X 3.2 mm. But copper is less resistant to weather and moisture. Copper is costlier than GI, that is why in general we use GI in electrical design.
However, in case of area where earth resistance is less than plate earthing (Like Hard rock area), pipe earthing should be used. Pipe diameter should be 2.5” (2.5 inch).
Prevention and safety
By using earthing we can get below benefits :-
- ELCB is used with help of earthing for human safety in domestic wiring.
- Earthing is used for apparatus safety during faults.
- Earthing is connected to establish neutral for any unbalanced current.
- Lighting arrester is connected with earth for protection of HT lines on pole and high rise buildings.
- earth is used as a conductor in tele-communication lines which saves a lot of amount.
- Guarding conductors is connected to earthing and helps in case of break of transmission lines.
- In electrical circuit earthing is used as “sink” for prevention.