Earthing System

1. Earthing
System
Prepared By
Trinayan Chetia

2. INTRODUCTIONTOGROUNDING
The primary goal of the grounding system throughout any
facility is SAFETY.
Grounding is implemented to ensure rapid clearing of faults
and to prevent hazardous voltage, which in turn reduce the
risks of fires and personnel injuries. Grounding serves the
primary functions of referencing the AC systems and
providing a means to ensure fault clearing.
99.5% survival threshold –
116 mA for one (1) second.
367 mA for zero point one (0.1)second.

3. A safe grounding design has two objectives:
1. To provide means to carry electric currents
into the earth under normal and fault
conditions without exceeding any operating
and equipment limits or adversely affecting
continuity of service.
2. To assure that a person in the vicinity of
grounded facilities is not exposed to the
danger of critical electric shock.

4. SIX (6) GROUNDING SYSTEMS IN USE
1. Equipmentgrounds,
2. Static grounds,
3. Systemsgrounds,
4. Maintenancegrounds,
5. Electronic grounds,
6. Lightninggrounds.

5. EQUIPMENT GROUNDS:
Equipment grounds: An equipment ground is the
physical connection to earth of non-current carrying
metal parts. This type grounding is done so that all
metal part of equipment that personnel can come into
contact with are always at or near zero (0) volts with
respect to ground. All metal parts must be
interconnected and grounded by a conductor in such
away as to ensure a path of lowest impedance for flow
of ground fault current. Typical items (equipment) to be
grounded are; electrical motor frames, outlet boxes,
breaker panels, metal conduit, support structures, cable
tray, to name a few.

6. STATIC GROUNDS:
A static ground is a connection made between
a piece of equipment and the earth for the
purpose of draining off static electricity charges
before a flash over potential is reached. This
type grounding system is utilized in dry materials
handling, flammable liquid pumps and delivery
equipment, plastic piping, and explosive storage
facilities.

7. SYSTEMGROUNDS:
A system ground refers to the point in an
electrical circuit that is connected to earth.
This connection point is typically at the
electrical neutral. The sole purpose of the
system ground is to protect equipment. This
type ground also provides a low impedance
path for fault currents improving ground fault
coordination. This ensures longer insulation
life of motors, transformers and other system
components

8. MAINTENANCEGROUNDS:
This type ground is utilized for safework
practices, and is a temporary ground.

9. ELECTRONICANDCOMPUTERGROUNDS:
Grounding for electronic equipment is a special
case in which the equipment ground and the
system ground are combined and applied in unity.
Electronic equipment grounding systems must not
only provide a means of stabilizing input voltage
levels, but also act as the zero (0) voltage
reference point. Grounding systems for the modern
electronics installation must be able to provide
effective grounding and bonding functions well into
the high frequency megahertz range.

10. LIGHTNING PROTECTION:
Lightning protection grounding requirements
are dependent upon the structure, equipment to
be protected, and the level of lightning
protection required of desired.

11. 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.

12. 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

13. 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 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

14. 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.

15. Methods of Earthing
• Conventional Earthing
• Maintenance Free Earthing

16. 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.

17. FIGURE:.
CONVENTIONAL
EARTHING

18. 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.

19. Maintenance Free Earthing(Contd.)
• LOW EARTH RESISTANCE: Highly
conductive. Carries high peak current
repeatedly.
• NO CORROSION:
• LONG LIFE.
• EASY INSTALLATION.

20. Methods of Conventional Earthing
1. Plate Earthing
2. Pipe Earthing
3. Rod Earthing
4. Strip Earthing
5. Earthing through Water Mains

21. Earthing Electrode
The resistance of a ground
electrode has 3 basic
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

22. 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
coke and salts for a minimum 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.

23. PLATE EARTHING

24. 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 electrod but the depth depend upon
the soil conditions, there is no hard and fast rule forthis.
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 earthingsystem.
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 ofearthing.

25. PIPE EARTHING

26. • 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
ROD EARTHING

27. • 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
STRIP OR WIRE EARTHING

28. • 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 Earthing Pit

29. • Step C :
• 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 Earth pit

30. • Step D :
• 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 Earth Pit

31. • 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 Earthing Pit

32. • 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 Earth Pit

33. • Step F :
• 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.
Procedure for filling up New Earth Pit

34. • 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 Equipment, Distribution Transformer
Centres, L.T. Distribution System Equipment

35. 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.
Standard Pipe & Plate Type Earthing Design for the 11
Kv. System Equipments, Distribution Transformer
Centers, L.T. Distribution System Equipments

36. • 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
Typical arrangement for Pipe electrode earthing
pit (Bore Type)

37. 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

38. Classification of Systems Based on Types of
System Earthing
Internationally, it has been agreed to classify the earthing systems as TN System, TT
System and IT System.They are:
a) TN system — has one or more points of the source of energy directly earthed,
and the exposed and extraneous conductive parts of the installation are
connected by means of protective conductors to the earthed point(s) of the
source, that is, there is a metallic path for earth fault currents to flow from the
installation to the earthed point(s) of the source. TN systems are further sub-
divided into TN-C, TN-S and TN-C-S systems.
b) TT system — has one or more points of the source of energy directly earthed
and the exposed and extraneous conductive parts of the installation are
connected to a local earth electrode or electrodes are electrically independent
of the source earth(s).
c) IT system — has the source either unearthed or earthed through a high
impedance and the exposed conductive parts of the installation are connected
to electrically independent earth electrodes.

39. IECNOMENCLATURE
 The first letter indicates the connection between earth
and the power-supply equipment (generator or
transformer):
 T : direct connection of a point with earth
 I : no point is connected with earth (isolation), except
perhaps via a high impedance.
 The second letter indicates the connection between
earth
and the electrical device being supplied:
T : direct connection with earth, independent of any other
earth connection in the supply system
N : connection to earth via the supply network

40. TN NETWORK

41. TTNETWORK
• 415 V Three phase industrial supply having 3 ~ and 1 ~ loads.
• All exposed conductive parts of the installation are connected to an earth electrode which is electrically
independent of the source earth.
• Single phase TT system not present in India.

42. ITNETWORK

43. It is also recognized that, in practice, a system may be an admixture
of type for the purposes of this code, earthing systems are designated
as follows:-
a) TN-S System (for 240 V single phase domestic/ commercial supply) —
Systems where there are separate neutral and protective conductors
throughout the system. A system where the metallic path between the
installation and the source of energy is the sheath and armouring of the
supply cable
• The protective conductor (PE) is the metallic covering (armour or load sheath of the cable supplying the
installation or a separate conductor).
• All exposed conductive parts of an installation are connected to this protective conductor via main earthing
terminal of the installation.

44. b) Indian TN-S System (for 415 V three-phase domestic
commercial supply) — An independent earth electrode
within the consumer's premises is necessary
ERATH
415 V Three phase Domestic/Commercial supply having 3 ~ and 1 ~ loads.
All exposed conductive parts of the installation are connected to protective conductor via the main earthing
terminal of the installation. An independent earth electrode within the consumer's premises is necessary.

45. c) Indian TN C-System — The neutral and protective functons are
combined in a single conuductor throughout the system (for example
earthed concentric wiring).
All exposed conductive parts are connected to the PEN conductor. For 3 ~ consumer,
local earth electrode has to be provided in addition.

46. d) TN-C-S System — The neutral and protective functions are
combined in a single conductor but only in part of the system.
CombinedPEN conductor from transformer to building distribution point,
but separate PE and N conductors in fixed indoor wiring and flexible
power cords.
• The usual form of a TN-C-S system is as
shown, where the supply is TN-C and the
arrangement in the installations in TN-S.
• This type of distribution is known also as
Protective Multiple Earthing and the PEN
conductor is referred to as the combined
neutral and earth (CNE) Conductor.
• The supply system PEN conductor is
earthed at several points and an earth
electrode may be necessary at or near a
consumer's installation.
• All exposed conductive parts of an
installation are connected to the PEN
conductor via the main earthing terminal
and the neutral terminal, these terminals
being linked together.
• The protective neutral bonding (PNB) is a
variant of TN-C-S with single point
earthing.

47. T-TN-S System (for 6•6/11 kV three-phase bulk supply) — The consumers
installation, a TN-S system receiving power at a captive substation through a delta
connected transformer primary

48. Reference:-
# IEC
# IS 3043 (1987): Code of practice for earthing [ETD 20: Electrical Installation]
# CEA