Earthing



What is earthing?

A connection to the general mass of earth by means of an earth electrode i.e. a metal plate, pipe or other conductor electrically connected to the general mass of the earth.


Object of earthing

The earthing system is of supreme importance for protective purposes in both electricity supply and utilization. Apart from the employment of earthing in power system to limit the potentials of live conduits with respect to earth, the primary purpose of earthing is to prevent a dangerous potential occurring on part of the electrical installation or equipments that are not normally alive.

It is essential, therefore, that the earthing should be carried out in an efficient and permanent manner in order that risk attended upon the use of electricity wherever breakdowns occur may be eliminated. Proper low resistance earthing forms the corner stone of the usual protective measures against electric shock.


Aspects of Design

While designing an earthing system the following points for attaining desired value of earth resistance shall be borne in mind.

It must have sufficiently low resistance at any time of the year to pass enough current to operate the protective gear under faulty conditions.

It must carry the fault current for a sufficient time to operate the protective gear and as such it must have adequate carrying capacity.

The voltage gradient on the surface of the ground around the electrode must not be dangerously steep.


The electrode its connection must have high resistance to soil and atmospheric corrosion.