Earthing

Concept of Earthing Systems

All the people living or working in residential,
commercial and industrial installations, particularly
the operators and personnel who are in close
operation and contact with electrical systems and
machineries, should essentially be protected against
possible electrification. To achieve this
protection, earthing system of an installation is
defined, designed and installed according to the
standard requirements.
 What Is Earthing
The process of transferring the immediate discharge of
the electrical energy directly to the earth by the help
of the low resistance wire is known as the electrical
earthing. The electrical earthing is done by connecting
the non-current carrying part of the equipment or
neutral of supply system to the ground.
 What Is Earthing
Mostly, the galvanised iron is used for the earthing. The earthing
provides the simple path to the leakage current. The shortcircuit
current of the equipment passes to the earth which has zero potential.
Thus, protects the system and equipment from damage.
• Provide an alternative path for the fault current
to flow so that it will not endanger the user
• Ensure that all exposed conductive parts do not
reach a dangerous potential
• 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.
 Good Earthing Means
Good Earthing must have low impedance
enough to ensure that sufficient current can
flow through the safety device so that it
disconnects the supply ( <0.4 sec ). Fault
current is much more than the full load current
of the circuit which melts the fuse. Hence, the
appliance is disconnected automatically from
the supply mains.
 Qualities Of Good Earthing
• Must be of low electrical resistance
• Must be of good corrosion resistance
• Must be able to dissipate high fault current
repeatedly
 Purpose of 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 i.e. 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
 Electric shock
• An electric shock (electrocution)occurs when two portion of
a person’s body come in contact with electrical conductors
of a circuit which is at different potentials, thus producing a
potential difference across the body.
• The human body does have resistance and when the body is
connected between two conductors at different potential a
circuit is formed through the body and current will flow
• When the human body comes in contact with only one
conductor, a circuit is not formed and nothing happens.
When the human body comes in contact with circuit
conductors, no matter what the voltage is there is
potential for harm.
 Electric shock
• The higher the potential difference the more
the damage. The effect of an electric shock is a
function of what parts of body come in contact
with each conductor, the resistance of each
contact point the surface resistance of the body
at the contact as well as other factor.
• When the electrical contact is such that the
circuit path through the body is across the
heart, you have the greatest potential for death.
 Electric shock
• The human body’s resistance varies from as low as
500ohms to as high as 600,000 ohms. As the skin
become moist the contact resistance drop. If the skin
is moist due to sweat that contain salt the resistance
drop further
• Fig 1 illustrates the amount of current that can flow
through human body at three different potential
differences across the body also shown is the effect
of different current level both AC and DC the
ultimate effect is fibrillation which cause the heart to
stop and result in death.
 Electric shock
• When a high voltage such as 13,800V is
involved the body is literally cooked and at
times explodes
 Short circuit
• To analyze how an electrical shock occurs and
how grounding is applied you need to look at the
circuit involved.
• Fig illustrates the basic circuit that consist of a
source, a transformer or generator for all AC
circuits, circuit protection, conductors(R1s), and a
load (RL).
 Short circuit

• A short circuit is any unintended connection across the

circuit conductors between the power source and the load
 Equipment Earthing
• In case of insulation failure, the primary object
of connecting all the above points and
apparatus to earth is to release the charge
accumulated on them immediately to earth so
that the person coming in contact may not
experience electric shock.
 Equipment Earthing(Cont.)
The other object is that a heavy current when
flows through the circuit that operates the
protective devices that is fuse or CB, which
open the circuit
 Max. Value of Earth Resistance
to be achieved
Equipment to be Earthed Max. Value of Earth Resistance to be
achieved in Ohms
Large Power Stations 0.5
Major Substations 1.0
Small Substations 2.0
Factories Substations 1.0
Lattice Steel Tower 3.0
Industrial Machine and Equipment 0.5

* The Earth Resistance depends upon the moisture content in

the soil.
 Methods of Earthing
• Conventional Earthing
• Maintenance Free Earthing
 Conventional Earthing
• The Conventional system of Earthing calls for
digging of a large pit into which a GI pipe or a
copper plate is positioned in the middle layers
of charcoal and salt.
• It requires maintenance and pouring of water
at regular interval.
FIGURE:.

CONVENTIONAL
EARTHING
 Maintenance Free Earthing
• It is a new type of earthing system which is
Readymade, standardized and scientifically developed.
Its Benefits are
• MAINTENANCE FREE: No need to pour water at
regular interval- except in sandy soil.
• CONSISTENCY: Maintain stable and consistent
earth resistance around the year.
• MORE SURFACE AREA: The conductive compound
creates a conductive zone, which provides the increased
surface area for peak current dissipation. And also get
stable reference point.
Maintenance Free Earthing(Contd.)

• LOW EARTH RESISTANCE:

Highly conductive. Carries high peak
current repeatedly.
• NO CORROSION:
• LONG LIFE.
• EASY INSTALLATION.
 Methods of Conventional Earthing
1. Plate Earthing
2. Pipe Earthing
3. Rod Earthing
4. Strip Earthing
5. Earthing through Water
Mains
 Earthing Electrode
A)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 of
G.I. is buried into the ground at a depth of not less
than 3 meter from the ground level.
• The earth plate is embedded in alternative layer of
charcoal and salts for a minimum thickness of about
15cm.
• The earth Wire (copper wire for copper
earthing andplate
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
 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 embedded
vertically in ground to work as earth electrode but the depth depend upon
the soil conditions, there is no hard and fast 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 filled with salt and coal mixture for
improving the soil conditions and efficiency 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
 ROD
• EARTHING
In this system of earthing 12.5mm diameter solid rods of
copper 16mm diameter solid rod of GI or steel or hollow
section of 25mm GI pipe of length not less than 3 meters
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 1.6mm of copper or 25mm * 4mm of GI or steel
are burried in horizontal trenches of minimum depth of 0.5m
• 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
Procedure for filling up New
Earthing Pit
• Step A :
• Excavate the earthing pit size 2000 X 2000 X
2500 mm depth. Sprinkle sufficient quantity
of water in the bottom and surrounding walls
to become wetty only.
• Fill up the bottom layer of the pit up to 250
mm height from the bottom by mixture black
soft soil + salt + wooden charcoal pieces. (Fig.
I)
• Step B :
• Prepare the electrode assembly as per Sr. No. -
3 of the drawing and rest the entire Assembly
in the pit as shown in (Fig. II)
 Procedure for filling up New
• Step C : Earthing Pit
• Collect thin C.R.C. sheet approx 18 to 20 SWG having size
500 mm width 3.5 meter length approx. (Please make joints
of three to four pieces to achieve requirement of 3.5 meter
length (Fig. III-a)
• Prepare the Cylindrical Ring from the above sheet by bending
both ends & joining each other. The diameter "D" of the
cylindrical ring shall arrive approx. 1000 mm and height shall
be 500 mm. Collect two pieces of scrap G.I. wire of approx. 8-
SWG and prepare two lifting round handles (Hooks) on upper
side of the cylindrical ring to facilitate the lifting of the
Cylindrical Ring. (Fig. III-b)
• Now wear this cylindrical ring to the electrode pipe of the
electrode assembly such a way that the electrode pipe
remains in the centre of the cylindrical ring. (Fig III-c)
 Procedure for filling up New
• Step D :
Earthing Pit
• Fill up the inner part of the Cylindrical Ring with
Mixture - I ( Homogeneous mixture of Black Soft
Soil.
• The remaining part i.e. the Gap between walls of the
pit and outer periphery of the Cylindrical Ring by
Mixture - II. After completing filling work of both
the mixtures up to 500 mm height, proper ramming
and watering is to be done. (Fig. IV)
Procedure for filling up New
Earthing Pit
• Step E :
• There after lift the Cylindrical ring
by help of two lifting handles
(hooks) and again rest it on the
layer for carrying out filling of 2nd
layer cycle. Again fill up the inner
cylindrical part of the ring by
Mixture - I and outer gap between
walls of the pit & outer Cylindrical
periphery by Mixture - II up to
height of the Cylinder (i.e. 500
mm) (Fig. V)
 Procedure for filling up New
• Step E :
Earthing Pit
• There after lift the Cylindrical ring by help of two
lifting handles (hooks) and again rest it on the layer
for carrying out filling of 2nd layer cycle. Again fill
up the inner cylindrical part of the ring by Mixture - I
and outer gap between walls of the pit & outer
Cylindrical periphery by Mixture - II up to height of
the Cylinder (i.e. 500 mm) (Fig. V)
 Procedure for filling up New
• Step F :
Earthing Pit
• Lift the cylindrical ring by lifting handles (hooks) after
proper ramming and watering. Now again place the
cylindrical ring on upper layer and arrange 3rd cycle,
subsequently complete the filling of entire pit. Please see that
water content is minimum 20 %
• Fill up upper layer of the pit by crushed rock pieces (Gravel)
size 50 X 35 mm. 1 CMT. approx. to provide insulating
layer to person moving side by the pit, and to prevent reptile
movements subsequently causing hazards.
Standard Pipe & Plate Type Earthing Design for the
11 Kv. System Equipments, Distribution
Transformer Centers, L.T. Distribution System
Equipments
• Design Details :
1. Earthing Pit : Size 1000 X 1000 X 1800 mm
Depth.M.S. / C.I. Plate : 500 X 500 X 8 mm
Thick.
2. Electrode Assembly : 40 mm Ø GI / CI
Perforated pipe duly fitted or welded with base
plate and 50 X 6 mm flat termination taken on
top for equipment earthing as shown in drawing.
Standard Pipe & Plate Type Earthing Design for
the 11 Kv. System Equipments, Distribution
Transformer Centers, L.T. Distribution System
Equipments
4. Mixture - I : Homogeneous mixture of
black soft soil 0.3 CMT. approx.
5. Mixture - II : Homogeneous mixture of
common salt 25 Kgs. + wood charcoal
pieces 25 Kgs. + Black soft soil 1 CMT.
Approx.
6. Crushed Rock pieces Gravel Size 50 X
35 mm
0.1 CMT. Approx.
7. Arrangement for earthing lead
terminations from equipment body, and
connection for main earthing Grid.
 Typical arrangement for Pipe
electrode earthing pit (Bore
Type) • Design Details :
1. 75 mm thick RCC Cover.
2. 300 mm Ø 6000 mm deep (Approx.
20 ft.) bore in the earth.
3. 65 mm Ø 6000 mm long (Approx 20 ft.)
G.I. pipe electrode. Forged at the top up
to 75 mm length and 12 mm hole
provided for taking earthing connection.
4. A homogeneous mixture of 50 kgs.
wooden coal pieces + 50 kgs. common
salt
5. Water pouring purpose at the time of
routine maintenance
 Applications
• Telecommunication
• Transmission
• Substations & Power Generations
• Transformer Neutral earthing
• Lightning Arrestor Earthing
• Equipment Body Earthing
• Water Treatment Plants
• Heavy Industries
• College, Hospitals, Banks
• Residential Building