Earthing

Agenda THINK
SAFETY

• What Is Earthing
• Purpose of Earthing
• Electric shock
• Types of Earthing
• The advantages of earthing
• The disadvantages of earthing
What is earthing THINK
SAFETY
 The process of connecting metallic bodies of all the
electrical apparatus and equipment to huge mass of earth
by a wire having negligible resistance is called Earthing.
Purpose of Earthing
THINK
•To save human life from danger of electrical shock or death by blowing a
SAFETY
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.
 THINK
Electric shock SAFETY

When a high voltage such as

Pipe Earthing

Rod Earthing

Strip Earthing

Earthing through
Watr Mains
 Earthing electrode
The resistance of a ground THINK
electrode has 3 basic
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components:
A) The resistance of the ground
electrode itself and the connections
to the electrode.
B) The contact resistance of the
surrounding earth to the electrode.
C) The resistance of the surrounding
body of earth around the ground
Electrode. It consist of three basic components:
1. Earth Wire
2. Connector
3. Electrode
 Plate earthing
• In this type of earthing plate either of copper or THINK
of G.I. is buried into the ground at a depth of
SAFETY
not less than 3 meter from the ground level.
• The earth plate is embedded in alternative
l aye r o f c o ke a nd sa l t s f o r a m i ni m um
thickness of about 15cm.
• The earth wire(copper wire for copper plate
earthing and G.I. wire for G.I. plate earthing) is
securely bolted to an earth plate with the help
of bolt nut and washer made of copper, in case
of copper plate earthing and of G.I. in case of
G.I. plate earthing.
Plate earthing
THINK
SAFETY
 Pipe earthing
• Pipe earthing is best form of earthing and it is cheap also in this
system of earthing a GI pipe of 38 mm dia and 2meters length is THINK
embedded vertically in ground to work as earth electrod but the
depth depend upon the soil conditions, there is no hard and fast SAFETY
rule for this.
• But the wire is embedded upto the wet soil.
• The earth wire are fastened to the top section of the pipe with nut
and bolts.
• The pit area arround the GI pipe f illed with salt and coal mixture
for improving the soil conditions and ef ficiency of the earthing
system.
• It can take heavy leakage current for the same electrode size in
comparison to plate earthing.
• The earth wire connection with GI pipes being above the ground
level can be checked for carrying out continuity test as and when
desired, while in plate earthing it is difficult.
• In summmer season to have an effective earthing three or four
bucket of water is put through the funnel for better continuity of
earthing.
Pipe earthing
THINK
SAFETY
 Rod earthing
• In this system of earthing 12.5mm diameter solid rods of THINK
copper 16mm diameter solid rod of GI or steel or hollow
section of 25mm GI pipe of length not less than 3 meters SAFETY
are driven vertically into the earth
• In order to increase the embeded length of electrod
under the ground, which is some time necessary to
reduce the earth resistance to desired value more than
one rod section are hammered one above the other.
• This system of earthing is suitable for area which are
sandy in character .
• This system of earthing is very cheap
 Strip or wire earthing
• In this system of earthing strip electrod of cross section not less than 25mm into THINK
1.6mm of copper or 25mm * 4mm of GI or steel are burried in horizontal trenches
of minimum depth of 0.5m SAFETY
• If round conductor are used their cross sectional area shall not be smaller than
three if copper is used and 6mm2 if GI or steel is used.
• The length of burried conductor shall be sufficient to give the required earth
resistance (about 0.5Ωto 1.5Ω)
• It shall however be not less than 15 m
• The electrod shall be as widely distributed as possible in a single straight or circular
trenches radiating from a point
• This type of earthing is used in rockey soil earth bed because at such places
excavation work for plate earthing is difficult
 Advantages of earthing
1. The whole electrical system is tied to the potential of the general THINK
mass of earth and cannot 'float' at another potential. For example, we
can be fairly certain that the neutral of our supply is at, or near, zero SAFETY
volts (earth potential) and that the phase conductors of our standard
supply differ from earth by 240 volts.
2. By connecting earth to metalwork not intended to carry current (an
extraneous conductive part or a an exposed conductive part) by using
a protective conductor, a path is provided for fault current which can be
detected and, if necessary, broken. The path for this fault current is
shown in .
 Dis-advantages of earthing
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1. Cost: the provision of a complete system of protective conductors, earth electrodes, etc. is
very expensive. SAFETY
2. Possible safety hazard: It has been argued that complete isolation from earth will prevent
shock due to indirect contact because there is no path for the shock current to return to the
circuit if the supply earth connection is not made. This approach, however, ignores the
presence of earth leakage resistance (due to imperfect insulation) and phase-to-earth
capacitance (the insulation behaves as a dielectric). In many situations the combined
impedance due to insulation resistance and earth capacitive reactance is low enough to allow
a significant shock current.
Thank You