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1. EARTHING

2. Objective of Earthing
•Connecting neutral point of the supply system or non
current carrying metal parts used in electrical distribution
system to the general mass of earth by wire of negligible
resistance .
•To ensure of immediate discharge of energy without
danger.
•Prime objective of earthing is to provide a zero potential
surface in and around and under the area where the
electrical equipment is installed or erected.
The current always passes through the path having low
resistance. If earth wire is not provided fault current
passes through human body.

3. Necessity of Earthing

4. Necessity Of Good Earthing
•To save human life from danger of electrical shock or
death by blowing a fuse i.e. To provide an alternative path
for the fault current to flow so that it will not endanger the
user.
•To protect buildings, machinery & appliances under fault
conditions
   ie. To ensure that all exposed conductive parts
do not reach a dangerous potential.
•To provide safe path to dissipate lightning and short circuit
currents.
•To provide stable platform for operation of sensitive
 
electronic equipments
   i.e. to maintain the voltage at any
part of an electrical system at a known value so as to
prevent over current or excessive voltage on the appliances
or equipment .
 
•To provide protection against static electricity from
 
friction
     

5. Qualities of good earthing
The quality of earthing you need depends upon your
application
•The qualities of a good earthing system are :
–Must be of low electrical resistance
–Must be of good corrosion resistance
–Must be able to dissipate high fault current repeatedly
  .

6. IS specifications regarding earthing
•An earthing electrode shall not be situated within a
distance of 1.5mts from the building whose
installation is being earthed.
•The crossection of earth continuity conductor
should not be less than 14 SWG.
•Resistance to earth: It should be low enough to
cause of flow of leakage current to make the
protective devices to operate.

7. Contd…
•The value of resistance to earth changes with
weather.
–As per IS standards the max permissible values of earth
resistances for various places are,
•For
–large power station- 0.5 Ω
–Major power station-1.0 Ω
–Small substation- 2.0 Ω
–In all other cases- 5.0 Ω

8. Contd…
•The value of resistance to earth changes with
weather.
–As per IS standards the max permissible values of earth
resistances for various places are,
•For
–large power station- 0.5 Ω
–Major power station-1.0 Ω
–Small substation- 2.0 Ω
–In all other cases- 5.0 Ω

9. Factors influencing earth
resistance
•The resistance of earth system depends on
–Condition of soil
–Temperature of soil
–Moisture content of soil
–Size and spacing of earth electrodes
–Depth at which the electrode is embedded
–Material of conductor
–Quality of coal, dust and charcoal in the earth
electrode pit.

10. PIPE EARTHING
•A galvanised steel and perforated pipe of
2.5mts(ordinary soil) and 40mm dia is placed upright
in a permanently wet soil.
•The pipe is tapered with the tapered casting at the
bottom.
•Charcoal and salt are filled in the pit alternately of
15cm layers for a distance of about 2mts.
•The pipe has 12mm dia holes drilled in it to facilitate
spreading of dampness and thereby decreasing soil
resistivity.

11. Contd..
•At the top cement concrete work is done to protect
the pipe from mechanical damage.
•A funnel with wire mesh is provided with the
concrete work. The funnel is connected to another
pipe which is connected to main earth GI pipe.
•Another GI pipe is taken from funnel to outside to
connect to the earth wire of not less than 8
SWG( small installations) should be used for earthing.
It should be carried in a pipe of 12.7mm dia at a
distance of 60 cm below the ground

14. PLATE EARTHING
•An earthing plate of Cu of dimensions 60 cm x 60 cm x 3
mm and GI of dimensions 60 cm x 60 cm x 6 mm is buried
in the ground with its face vertical at a depth of not less
than 3 mts from the ground level
•The earth plate is embedded in alternate layers of coke
and salt for a thickness of 15 cm.
•The electrode or plate is connected to GI pipe of 12.7mm
dia for connecting the earth wire to the earthplate.
•The earthwire is bolted on the Earth plate with bolt and
nut of the same material of that of earth plate.
•The pit filled with charcoal and salt is connected with a
pipe for carrying water fro the concrete work to the pit
where earth plate is kept to increase the dampness