This document contains basic details of 'Earthing', different types of earthing and Indian standards related to earthing.

1. Unit 6 -Earthing

2. Earthing
• The term Earthing means connecting the neutral point of
a supply system or non current carrying metal parts used
in electrical distribution system to the general mass of
earth by wire of negligible resistance in such manner that
at all times an immediate discharge of electrical energy
takes place without danger.
• This brings the body of the electrical equipment to zero
potential and thus will avoid electric shock to the
operator.
• The neutral of the 3phase four wire supply system is
also solidly earthed to ensure its potential to zero.

3. • Purpose of earthing
• A) to avoid electric shock to human body
• B) To avoid risk of fire due to earth leakage current
through unwanted path
• C) to ensure that no current carrying conductor rises
potential with respect to earth than its designed
insulation

4. Indian standard specifications
regarding earthing of electrical
installation
• Distance of earth from building: an earthing electrode shall
not be situated within a distance of 1.5 meters form the
building whose installation system is being earthed
• Size of earth continuity conductor : the conductor by means
of which the metal body of an equipment or appliance is
connected to the earth is known as earth continuity
conductor. the cross section of this conductor should not
be either less than 2.9mm2(14SWG) or half of the
installation conductor size
• Resistance of earth: resistance should be low enough

5. • Value of earth resistance changes with weather,
depends on moisture content of soil and maximum
during dry season
• Earth continuity inside an installation from the earth
plate to any point in the installation is 1ohm
• The earth wire and earth electrode will be of same
material
• The earth wire shall be taken through GI pipe of 12.7
mm of diameter for at least 30.5cm length above and
below ground surface to the earth electrode to protect
against mechanical damage

6. • The loop earth wires used shall not be either
less than 2.9mm2 or half of the size of the sub
circuit conductor
• The earthing electrode shall always be placed
in vertical position inside the earth or pit so
that it may be in contact with all different
earth layers
• What happens in case of failure of insulation
at one place?

7. What equipment is to be connected to
earth
• The neutral conductor of 3phase 4wire electrical
distribution system and middle conductor of
2phase 3wire DC supply system should be
earthed at generating station and at the sub
station by two separate and distinct earth
connections
• Metal frame of generators, motors and other
metallic parts of the equipment used for regulating
or controlling energy and all medium voltage
energy consuming apparatus

8. • All metal parts of electrical installation such as metal
conduits enclosing VIR or PVC cables, light fittings, iron
clad main switches, iron clad distribution boards etc
• 3pin lighting and power plug socket should be
permanently and efficiently earthed
• Fabricated steel transmission towers , tubular poles, rail
poles, concrete poles used in overhead trx line should be
earthed.

9. • The metal casing of portable apparatus should be earthed
• This covers electrical drill, soldering iron, hair driers, heaters refrigerators and
electrically operated equipment.
• Concentric cables :the external conductor of such cables should be earthed by
two separate and distinct connection with earth.
• On what basis would you select the earthing conductor?
• Electrical potential that it have to carry at time of short circuits
• High conductivity (copper)
• Sufficient diameter to carry fault current safely
• Galvanized iron (GI) so that it does not get rusty in adverse conditions and it
has buried into earth

10. • Earth electrode: Any wire or pipe or rod or metal
plate embedded in earth for the purpose of
making an effective electrical connections with
general mass of earth
• Earthing lead or main earthing conductor :the
wire which connects overhead earth wire or any
apparatus to be earthed to the earth electrode
• Sub main earthing conductor the earth wire
which runs between the main switch board to the
distribution board

11. ISI Specifications
• The cross section of earthing lead should not be less than half of
section of main supply conductor feeding the installation.
• The cross section of earthing lead should in any case such that it shall
never fuse out even under worst fault conditions
• The cross section of earthing lead should not be less than 161.3mm2
for main connection and 64.5mm2 for branch connections in large
installation
• Copper strip usually employed as a ring main connecting all apparatus
to earth
• Copper wire not less than 8SWG not more than 7/0.0915mm are used
for earthing in smaller installations

12. Precautions taken while installing
earth conductor
• There is not any possibility of its being damaged or cut accidently
• Earth conductor should be fixed to equipment with help of clamps
• The joints shall be made by soldering , brazing welding but for forged
diameter earth wires, clamps may be used for obtaining joints
• Every care should be taken that is electrically continuous
• The paint , enamel, corrosion and other non conducting materials
should be removed from the surface of the equipment to which
earthing is to be connected

13. Earth resistance depends on
• Condition of soil
• Moisture of soil
• Temperature of soil
• Depth of electrode
• Size and spacing of earth plates
• Metal of earth plate
• Quality of coal dust and charcoal in the earth
electrode pit

14. How earth resistance can be reduced
• Using number of earth electrodes inter
connected in parallel
• Using larger size of earth electrode
• Increasing the depth of pit for earthing system
• The area around earthing pipe is increased
and charcoal soaked in salt solution is filled in
pit

15. Earth pit should not be located
• Near pavements, roads and rail tracks
• Should not be located near building and
minimum distance from the wall to pit should not
be less than 1.5mt
• Metal fence
• Distance between two earth electrodes where
more than one electrode is required the plates
shall be separated from each other by not less
than 2.5mts and in case of rod or pipe not less
than 2 mts

16. Different types of earthing
• Earthing through water mains
• Wire or strip earthing
• Rod earthing
• Pipe earthing
• Plate earthing

17. Earthing through water mains
• Normally it is not advisable
• It must ensure that water pipe is of iron and
electrically continuous
• Care must be taken to limit the contact
Resistance to the minimum

18. Wire earthing or strip earthing
• Copper wires of 5swg or cross section not less than 25mm
wide and 1.6 mm thick used an earth wire
• If round conductor are used, their cross sectional area should
not be smaller than 3.0mm2
• The wire is buried in horizontal trenches of depth enough to
maintain earthing process

19. Rod earthing
• Soild rod of 12.5mm solid rods of copper , 19mm diameter of
GI or hollow GI pipe of diameter 25mm is driven vertically into
earth upto depth of 5 to6 diameters depending on depth of
moisture in earth.

20. Pipe earthing
• A pipe of diameter sufficient to carry the fault current
is selected
• The size of pipe which serves as an earth electrode
depends on
• A) Current to be carried
• B) Type of soil
• The GI pipe shall not be less than 38mm diameter and
2 meter long for ordinary soil (2.75mt for dry and
rocky)
• The pipe must be place in permanently wet ground.
The depth depends on condition of soil and
moisture(4.75 mt again depending upon moisture

22. Plate earthing
• The earthing is done by embedding GI or copper plate in the
earth sufficiently deep
• The size of the plate used should not be less than
60cm*60cm*6.36mm in GI case and 60cm*60cm*3.18mm in
case of copper
• A pit is dug about 4m deep and the earth electrode is placed
in such away that face is vertical
• The space around the plate is filled with charcoal and salt for
minimum thickness of 15cm. The electrode or plate is
connected to GI pipe of 12.7mm diameter for carrying GI
earth wire for connection to earth electrode.