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.
