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Necessity – different methods – pipe earthing and plate earthing – materials required - requirements of good earth electrode – neutral wire – difference between neutral wire and earth wire - connection with earth – value of earth resistance and factors on which it is dependent – points to be remembered while providing earth – ELCB system - Earthing of domestic fitting and appliances – Industrial Earthing – Substation Earthing.
Electricity today is playing an ever increasing role in the lives of everyone in the civilized world. Increased use of electricity has resulted in increased danger to human beings. Not only defects at consumer's premesis, but even at Supply Authority's premesis can electrocute a customer at his own premesis.Earthing protects humans from danger of electrocution.A lightening strike on a tall building can seriously injure the occupants or even completely demolish that building. Tall buildings or structures like towers are more prone to lightening strikes. Earthing tall structures protects them against lightening. Earthing provides return path for large number of electronic equipments or RF antennas etc. For example a 3phase star wound generator must have its neutral point at earth potential.Earthing is necessary for proper functioning of certain equipments.
What is earthing?
Earthing a tower/ equipment means connecting that tower /equipment to general mass of earth by means of an electrical conductor. Connection to earth is achieved by embedding a metal plate or rod or conductor in earth. This metal plate or rod or conductor is called as "Earth electrode". Effectiveness of the earthing connection made by embedding a metal plate in earth is quantified as "Earth Resistance". This earth resistance is measured in ohms.
Earth resistance consists of following components
a) Resistance of metal electrode
b) Contact resistance between electrode and soil
c) Resistance of soil away from electrode surface.
Need of good earthing:
Main Objectives of Earthing systems are: