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Why Earthing ?
Basic Electrical Engineering
Unit--05 Earthing and Electric
Unit “To protect persons using electric equipment from
electric shock”
Shock
Dr. Pritesh Mankad
Professor- Electrical Engg.,
BITS Educampus, Vadodara
What is Earthing ?
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.
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Purpose of Earthing Purpose of Earthing
• To save human life from danger of electrical shock or death • To provide stable platform for operation of
by blowing a fuse i.e. To provide an alternative path for the sensitive electronic equipments i.e. To maintain the voltage
fault current to flow so that it will not endanger the user at any part of an electrical system at a known value so as to
prevent over current or excessive voltage on the appliances or
• To protect buildings, machinery & appliances under fault equipment .
conditions ie. To ensure that all exposed conductive parts do
not reach a dangerous potential. • To provide protection against static electricity
from friction
• To provide safe path to dissipate lightning and short circuit
currents.
Methods of Earthing Earthing Electrode
The resistance of a ground
Plate Earthing electrode has 3 basic
components:
A) The resistance of the ground
Pipe Earthing electrode itself and the connections
to the electrode.
Rod Earthing B) The contact resistance of the
surrounding earth to the electrode.
C) The resistance of the surrounding
Strip Earthing body of earth around the ground
Electrode. It consist of three basic components:
Earthing through 1. Earth Wire
Water Mains 2. Connector
3. Electrode
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(1)Plate Earthing 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.
(2)Pipe 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 electrod 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.
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(3)ROD EARTHING (4)STRIP OR WIRE EARTHING
• In this system of earthing strip electrod of cross section not less
• In this system of earthing 12.5mm diameter solid rods of
than 25mm into 1.6mm of copper or 25mm * 4mm of GI or steel
copper 16mm diameter solid rod of GI or steel or hollow
are burried in horizontal trenches of minimum depth of 0.5m
section of 25mm GI pipe of length not less than 3 meters are
driven vertically into the earth • 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
• In order to increase the embeded length of electrod under the
used.
ground, which is some time necessary to reduce the earth
resistance to desired value more than one rod section are • The length of burried conductor shall be sufficient to give the
hammered one above the other. required earth resistance (about 0.5Ωto 1.5Ω)
• This system of earthing is suitable for area which are sandy in • It shall however be not less than 15 m
character .
• The electrod shall be as widely distributed as possible in a single
• This system of earthing is very cheap 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
Factors affecting earth resistance Electric Shock
• Material and size of earth electrode • When electric current passes through the human body, the
• Moisture content present in soil and soil temperature effect produced by it is called an electric shock
• Depth of earth electrode in soil
• Type of soil • 1mA- unpleasant tingling effect
• 1mA to 8mA strong effect, falling etc (Can’t let go currents)
• Above 100mA- fibrillation of the heart
• Above 200mA- Breathing may stop immediately
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Electric shock
• When a high voltage such as 13,800V is involved the
body is literally cooked and at times explodes
Safety precautions for Electrical appliances
• Check that earthing is there and its working
• Use standard quality three pin tips
• Use good quality earth wire
• Use ELCB
• Do not touch with wet hands
• Keep away from water/moisture
• Disconnect when not in use.
• Avoid loose connections
• Use rubber slippers when operating electric equipment.
