Ammeter, voltmeter, ohm meter (multi meter) megger, earth tester. Earthing.

1. Usage of meters
01
Name : Adithya Ballaji
Department : School of EEE, REVA UNIVERSITY

2. Introduction
• An ammeter (from Ampere Meter) is a measuring instrument used to
measure the current in a circuit.
• Electric currents are measured in amperes (A), hence the name.
Instruments used to measure smaller currents, in the milliampere or
microampere range, are designated as milliammeters or microammeters.
• By the late 19th century, improved instruments were designed which could
be mounted in any position and allowed accurate measurements in electric
power systems.
• It is generally represented by letter 'A' in a circle. Ammeters have very low
resistance and are always connected in series in any circuit.
• The current is the flow of electrons whose unit is ampere. Hence the
instrument which measures the flows of current in ampere is known as
ampere meter or ammeter.
2

3. • The ideal ammeter has zero internal resistance. But practically the
ammeter has small internal resistance. The measuring range of the ammeter
depends on the value of resistance.
• The ammeter is connected in series with the circuit so that the whole
electrons of measured current passes through the ammeter. The power loss
occurs in ammeter because of the measured current and their internal
resistance. The ammeter circuit has low resistance so that the small
voltage drop occurs in the circuit.
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4. Types of ammeter
4
• The resistance of the ammeter is kept low because of the two reasons.
• The whole measured current passes through the ammeter.
• The low voltage drop occurs across the ammeter.
• Types of Ammeter
• The classification of the ammeter depends on their design and the type of
current flows through the ammeter. The following are the types of an
ammeter regarding construction.
• Permanent moving coil ammeter - DC
• Moving iron ammeter – AC & DC
• Electro-dynamometer ammeter - AC & DC – efficient then PMMC & MI
• Rectifier type ammeter - AC
• By the current, the ammeter categorizes into two types.
• AC ammeter
• DC ammeter

5. 5
Ammeter Shunt
• Ammeter Shunt
• The high-value current directly passes through the ammeter which damages
their internal circuit. For removing this problem, the shunt resistance is
connected in parallel with the ammeter.
• If the large measured current passes through the circuit, the major portion
of the current passes through the shunt resistance. The shunt resistance will
not affect the working of the ammeter, i.e., the movement of the coil
remains same.

6. Effect of Temperature
6
• Effect of Temperature in Ammeter
• The ammeter is a sensitive device which is easily affected by the
surrounding temperature. The variation in temperature causes the error in
the reading. This can be reduced by swamping resistance. The resistance
having zero temperature coefficient is known as the swamping resistance. It
connects in series with the ammeter. The swamping resistance reduces the
effect of temperature on the meter.
• The ammeter has the inbuilt fuse which protects the ammeter from the
heavy current. If substantial current flows through the ammeter, the fuse
will break. The ammeter is not able to measure the current until the new
one does not replace the fuse.

7. 7
• Calibration of Ammeter
• The figure below shows the circuit for the calibration of the ammeter.
• The standard resistance is connected in series with the ammeter which is to
be calibrated. The potentiometer is used for measuring the voltage across
the standard resistor. The below mention formula determines the current
through the standard resistance. I =Vs/ S
• Where, Vs – voltage across the standard resistor as indicated by the
potentiometer. & S – resistance of standard resistor
• This method of calibration of the ammeter is very accurate because in this
method the value of standard resistance and the voltage across the
potentiometer is exactly known by the instrument.

8. 8
• Calibration of Voltmeter
• The circuit for the calibration of the voltmeter is shown in the figure below.
• The circuit requires two rheostats, one for controlling the voltage and
another for adjustment. The voltage ratio box is used to step-down the
voltage to a suitable value. The accurate value of the voltmeter is
determined by measuring the value of the voltage to the maximum possible
range of the potentiometer.
• The potentiometer measures the maximum possible value of voltages. The
negative and positive error occurs in the readings of the voltmeter if the
readings of the potentiometer and the voltmeter are not equal.

9. 9

10. 10
• Why do we use thick wires for connecting ammeters but thinner ones
for voltmeters?
• In ammeters, the cross sectional diameter of the wires must be large so that
it can carry large current. The current that you want to measure directly
flows into ammeter coz you have to connect them in series with load. But if
you use clamp ammeters, you won't need to use such thick wires.
In voltmeters, you don't need to use thin wires coz it just measure the
voltage. Since voltmeters connect in parallel with the load, the load current
will not flow in voltmeter circuit.

11. Application of ammeter
11
• Most well known and common use of ammeter is naturally direct
measurement of current, when connected in a circuit or branch of a circuit.
• Ammeter can be used for measurement of much higher current than its
rating, by use of shunt resistors, or by use of current transformers.
• Low current ammeter is used to measure voltages by connecting series
resistors. In this usage, even range of measurement can be changed by
using different series resistors for different ranges, and selection through
switches.
• Ammeter can also be used in digital form to control processes in industry.
• It is possible to use an ammeter with thermocouple to check and monitor
temperature.

12. Voltmeter
12
• A voltmeter, also known as a voltage meter, is an instrument used for
measuring the potential difference, or voltage, between two points in an
electrical or electronic circuit.
• Some voltmeters are intended for use in direct current (DC) circuits; others
are designed for alternating current (AC) circuits. Specialized voltmeters
can measure radio frequency (RF) voltage.
• A basic analog voltmeter consists of a sensitive galvanometer (current
meter) in series with a high resistance. The internal resistance of a
voltmeter must be high.
• Otherwise it will draw significant current, and thereby disturb the operation
of the circuit under test. The sensitivity of the galvanometer and the value
of the series resistance determine the range of voltages that the meter can
display.

13. Voltmeter
13
• A digital voltmeter shows voltage directly as numerals. Some of these
meters can determine voltage values to several significant figures. Practical
laboratory voltmeters have maximum ranges of 1000 to 3000 volts (V).
• Most commercially manufactured voltmeters have several scales,
increasing in powers of 10; for example, 0-1 V, 0-10 V, 0-100 V, and 0-
1000 V.

14. Voltmeter
14
• The main principle of voltmeter is that it must be connected in parallel in
which we want to measure the voltage. Parallel connection is used because
a voltmeter is constructed in such a way that it has a very high value of
resistance. So if that high resistance is connected in series than the current
flow will be almost zero which means the circuit has become open.
• If it is connected in parallel, than the load impedance comes parallel with
the high resistance of the voltmeter and hence the combination will give
almost the same the impedance that the load had.
• Also in parallel circuit we know that the voltage is same so the voltage
between the voltmeter and the load is almost same and hence voltmeter
measures the voltage.
For an ideal voltmeter, we have the resistance is to be infinity and hence the
current drawn to be zero so there will be no power loss in the instrument.
But this is not achievable practically as we cannot have a material which
has infinite resistance.

15. Voltmeter
15
• Classification or Types of Voltmeter
• According to the construction principle, we have different types of
voltmeters, they are mainly –
• Permanent Magnet Moving coil (PMMC) Voltmeter - DC
• Moving Iron (MI) Voltmeter – AC & DC
• Electro Dynamometer Type Voltmeter – AC & DC
• Rectifier Type Voltmeter - They are used for AC or DC measurements. For
DC measurement we have to connect a PMMC meter which measures
pulsating DC voltage which measures rectified voltage which is connected
across the bridge rectifier
• Electrostatic Type Voltmeter – AC & DC
• Digital Voltmeter (DVM) – AC & DC
• Depending on this types of measurement we do, we have-
• DC Voltmeter.
• AC Voltmeter.

16. Accuracy Class
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• The basic difference between accuracy class 1 and class 0.5 is the amount
of error which will be shown by meter with respect to running load.
• Suppose the current load of 40 Amp is connected with class 1 meter then
the meter will show the error of 1% i.e 0.4 amp, while with the class 0.5
meter it will be 0.5% i.e. 0.2 Amp.
• Class 1.5 = 1.5% error margin.
Class 2.5 = 2.5% error margin.

17. Ammeter and Voltmeter
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18. Ammeter and Voltmeter
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19. Ohm-meter
• An ohmmeter is an electrical instrument that measures electrical
resistance, the opposition to an electric current. Micro-ohmmeters is used
for low resistance measurements. Mega-ohmmeters (also a trademarked
device Megger) measure large values of resistance. The unit of
measurement for resistance is ohms (Ω).
• The OHMMETER is an instrument which measures resistance of a
quantity. Resistance in the electrical sense means the opposition offered by
a substance to the current flow in the device. Every device has a resistance,
it may be large or small and it increases with temperature for conductors,
however for semiconducting devices the reverse is true.
There are many types of ohmmeters available such as
• Series ohmmeter.
• Shunt ohmmeter.
• Multi range ohmmeter.
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20. Ohm-meter
20

21. Series - Ohm-meter
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22. Series - Ohm-meter
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• To mark the “0” reading on the scale, the terminals A and B are shorted, i.e.
the unknown resistance Rx= 0, maximum current flows in the circuit and
the zero adjustment resistance R2 is adjusted until the movement indicates
full scale current (Ifsd). The position of the pointer on the scale is then
marked “0” ohms.
• Similarly, to mark the “∞” reading on the scale, terminals A and B are
open, i.e. the unknown resistance Rx = ∞, no current flow in the circuit and
there is no deflection of the pointer. The position of the pointer on the scale,
is then marked as “∞” ohms.
• By connecting different known values of the unknown resistance to
terminals A and B, intermediate markings can be done on the scale. The
accuracy of the instrument can be checked by measuring different values of
standard resistance, i.e. the tolerance of the calibrated resistance, and noting
the readings.
• A major drawback in the series ohmmeter is the decrease in voltage of the
internal battery with time and age. Due to this, the full scale deflection
current drops and the meter does not read “0” when A and B are shorted.

23. Series - Ohm-meter
23
• The variable zero adjust resistor R2 across the movement is adjusted to
counteract the drop in battery voltage, thereby bringing the pointer back to
“0” ohms on the scale. It is also possible to adjust the full scale deflection
current without the shunt R2 in the circuit, by varying the value of R1 to
compensate for the voltage drop. Since this affects the calibration of the
scale, varying by R2 is much better solution.

24. Shunt - Ohm-meter
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25. Shunt - Ohm-meter
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• The second type of ohmmeter is the shunt ohmmeter, so called because the
meter movement is in parallel with the unknown resistance.
• Notice that a switch, S, is necessary to prevent current flow from the source
of emf when the ohmmeter is not in use.
• If the terminals of the shunt ohmmeter are shorted, Rx=0 Ω Rx=0 Ω and all
current is shunted away from the meter mechanism. However, when the
terminals are open, Rx=∞ and maximum current flows. As before, a control
is provided for the adjustment of full-scale deflection, but it is now an
infinity adjust (∞ adjust).
• As in the series-type ohmmeter, when the unknown resistance equals the
meter resistance, the meter reading is at half scale.
• In comparison to the series type, though, the shunt ohmmeter has a low
meter resistance, making it particularly useful for unknown resistances that
are relatively low.
• Regardless of the type of ohmmeter used, one must be certain that it is not
connected to an energized or active circuit

26. Multirange- Ohm-meter
26
• The Multi-range Ohmmeter circuit shown in Fig. below. To measure
resistance over a wide range of values, we need to extend the ohmmeter
ranges. This type of ohmmeter is called a multi-range ohmmeter,

27. Megger
27
• History of Megger
• The device is being used since 1889, popularity raised during 1920s since
long back device is same in its uses and purpose of testing, few real
improvements appeared in recent years with its design and quality of tester.
Now high-quality options are available which are easy to use and quite
safe.
• What is Megger?
• Insulation resistance IR quality of an electrical system degrades with time,
environment condition, i.e., temperature, humidity, moisture and dust
particles. It also gets impacted negatively due to the presence of electrical
and mechanical stress, so it’s become very necessary to check the IR
(Insulation resistance) of equipment at a constant regular interval to avoid
any measure fatal or electrical shock.

28. Uses of Megger
28
• The device enable us to measure electrical leakage in wire, results are very
reliable as we shall be passing electric current through device while we are
testing.
• The equipment basically uses for verifying the electrical insulation level of
any device such as motors, cables, generators, windings, etc.
• This is a very popular test being carried out since very long back. Not
necessary it shows us exact area of electrical puncture but shows the
amount of leakage current and level of moisture within electrical
equipment/winding/system.

29. Types of Megger
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• This can be separated into mainly two categories:-
• Electronic Type (Battery Operated)
• Manual Type (Hand Operated)
• But there is another types of megger which is motor operated type which
does not use battery to produce voltage it requires external source to rotate
a electrical motor which in turn rotates the generator of the megger.

30. Electronic Type Megger
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• Important parts:-
• Digital Display :- A digital display to show IR value in digital form.
• Wire Leads :- Two no. of wire leads for connecting megger with electrical
external system to be tested.
• Selection Switches :- Switches use to select electrical parameters ranges.
• Indicators :- To indicates various parameters status i.e. On-Off. For
Example Power, hold, Warning, etc.
• Note: – Above construction is not similar for every megger, it difference
appears manufacture to manufacture but basic construction and operation
are same for all.

31. Electronic Type Megger
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• Advantages of Electronic Type Megger
• Level of accuracy is very high.
• IR value is digital type, easy to read.
• One person can operate very easily.
• Works perfectly even at very congested space.
• Very handy and safe to use.
• Disadvantages of Electronic Type Megger
• Require an external source of energy to energies i.e. Dry cell.
• Costlier in market.

32. Hand Operated Megger
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• Important parts:-
Analog display:- Analog display provided on front face of tester for IR
value recording.
Hand Crank:- Hand crank used to rotate helps to achieve desired RPM
required generate voltage which runs through electrical system.
Wire Leads:- Used same as in electronic tester i.e. For connecting tester
with electrical system.

33. Hand Operated Megger
33
• Advantages of Hand Operated Megger
• Still keeps important in such high-tech world as it’s an oldest method for IR
value determination.
• No external source required to operate.
• Cheaper available in market.
• Disadvantages of Hand Operated Megger
• At least 2 person required to operate i.e. one for rotation of crank other to
connect megger with electrical system to be tested.
• Accuracy is not up to the level as it’s varies with rotation of crank.
• Require very stable placement for operation which is a little hard to find at
working sites.
• Unstable placement of tester may impact the result of tester.
• Provides an analog display result.
• Require very high care and safety during use of the same.

34. Construction of Megger
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35. Construction of Megger
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• Deflecting and Control coil : Connected parallel to the generator, mounted
at right angle to each other and maintain polarities in such a way to
produced torque in opposite direction.
• Permanent Magnets : Produce magnetic field to deflect pointer with North-
South pole magnet.
• Pointer : One end of the pointer connected with coil another end deflects on
scale from infinity to zero.
• Scale : A scale is provided in front-top of the megger from range ‘zero’ to
‘infinity’, enable us to read the value.
• D.C generator or Battery connection : Testing voltage is produced by hand
operated DC generator for manual operated Megger. Battery / electronic
voltage charger is provided for automatic type Megger for same purpose.
• Pressure Coil Resistance and Current Coil Resistance : Protect instrument
from any damage because of low external electrical resistance under test.

36. Working Principle of Megger
36
• In hand operated megger electromagnetic induction effect is used to
produce the test voltage i.e. armature arranges to move in permanent
magnetic field or vice versa.
• Where as in electronic type megger battery are used to produce the testing
voltage.
• As the voltage increases in external circuit the deflection of pointer
increases and deflection of pointer decreases with a increases of current.
• Hence, resultant torque is directly proportional to voltage and inversely
proportional to current.
• When electrical circuit being tested is open, torque due to voltage coil will
be maximum and pointer shows ‘infinity’ means no shorting throughout the
circuit and has maximum resistance within the circuit under test.
• If there is short circuit pointer shows ‘zero’, which means ‘NO’ resistance
within circuit being tested.
• Work philosophy based on ohm-meter or ratio-meter. The deflection torque
is produced with megger tester due to the magnetic field produced by
voltage and current, similarly like ‘Ohm’s Law’.

37. Working Principle of Megger
37
• The torque of the megger varies in a ration with V/I, (Ohm’s Law:- V = IR
or R = V/I). Electrical resistance to be measured is connected across the
generator and in series with deflecting coil.
Produced torque shall be in opposite direction if current supplied to the
coil.
• High Resistance = No Current :- No current shall flow through deflecting
coil, if resistance is very high i.e. infinity position of pointer.
• Small Resistance = High Current :- If circuit measures small resistance
allows a high electric current to pass through deflecting coil, i.e. produced
torque make the pointer to set at ‘ZERO’.
• Intermediate Resistance = Varied Current :- If measured resistance is
intermediate, produced torque align or set the pointer between the range of
‘ZERO to INIFINITY’.

38. General Inspection of Megger
38
• Check for loose connections, defective insulation, and cleanliness
• Check meter stop and pointer for damage
• Check the carrying case for corrosion, foam fungus etc.
• Check for easy cranking arrangement for mechanical megger
• Check the foam rubber lining if fitted
• Check the battery level for digital megger
• Check all indicators are working fine
General Maintenance of Megger:
• Digital multimeter is provided with a fuse. Replace it if the megger is not
working
• Clean the surface from dust, dirt, grease fungus etc.
• Remove dust or dirt from terminals with a soft brush
• Clean the display using a soft cloth
• Clean the cables, meter glass, and the exterior
surface with a clean, soft cloth. Dampen the cloth with water if required

39. What Things to Record After a
Megger Test?
39
• When performing a megger test on machinery or equipment, following
things to be recorded:
• Name and location of the equipment/ wiring
• Date on which the test is performed
• The Insulation Resistance values of test results along with time
• Range, voltage, and serial number of the Megger instrument used
• The temperature of the apparatus during the time of IR test
• When doing IR test of bigger machines such as alternator, transformer etc.
wet and dry bulb temperatures and dew-point determinations to be noted
• Insulation resistance measurement corrected for temperature

40. Safety Caution
40
• Always remember to disconnect the machinery and equipment being tested
for insulation resistance as there is a possibility of voltages being induced
in apparatus under test or lines to which it is connected (because of
proximity to energized high voltage equipment). Use required PPEs such as
rubber gloves etc. when connecting the wire leads to test the apparatus for
performing the insulation resistance test.
• Some megger may be provided with a voltage scale to ensure the line to be
tested does not have any voltage for insulation testing.

41. Insulation Test
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42. Insulation Test
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43. Earth Tester
43
• The instrument used for measuring the resistance of the earth is known
as earth tester.
• All the equipment of the power system is connected to the earth through
the earth electrode.
• The earth protects the equipment and personnel from the fault current. The
resistance of the earth is very low.
• The fault current through the earth electrode passes to the earth. Thus,
protects the system from damage.
• The earth electrodes control the high potential of the equipment which is
caused by the high lightning surges and the voltage spikes.
• The neutral of the three-phase circuit is also connected to the earth
electrodes for their protection.
• Before providing the earthing to the equipment, it is essential to determine
the resistance of that particular area from where the earthen pit can be dug.
• The earth should have low resistance so that the fault current easily passes
to the earth. The resistance of the earth is determined by the help of earth
tester instrument.

44. Earth Tester
44
• There is no written standard on what should be the earthing pit resistance
value. There are several norms which are accepted.
• Indian Standard mentions creating a grid of numerous earthings to achieve
a resistance of 1 ohm or less. However, nothing is mentioned pertaining to
value for individual pits.
• The exact reason for the same is that it totally depends on the soil
conditions.
• The following factors affect the resistivity of the soil:
• Type of soil- rocky soil/marsh/ morrum filled/ land fill etc will have higher
resistivity
• Moisture content plays a bigger role in ascertaining the resistivity of the
soil
• The size and uniformity of grains also play an important role in
determining the resistivity.
• Considering the above parameters, the resistivity will vary from location to
location.

45. Earth Tester
45
• There is not one standard ground resistance threshold that is recognized by
all agencies.
• However, the NFPA and IEEE have recommended a ground resistance
value of 5.0 ohms or less.
• The NEC has stated to “Make sure that system impedance to ground is less
than 25 ohms specified in NEC 250.56.
• it could be 5 ohms for domestic installations and one ohm or less for power
stations.

46. Need for earth tester
46
• Poor grounding contributes to downtime but a lack of good grounding
is also dangerous and increases the risk of equipment failure.
• Over time, corrosive soils with high moisture and salt content and high
temperatures can degrade ground rods and their connections. So, although
the ground system had low earth ground resistance values when initially
installed, the resistance of the grounding system can increase if the ground
rods are corroded.
• Grounding testers are indispensable troubleshooting tools to help you
maintain uptime. It is recommended that all grounds and ground
connections be checked at least annually as a part of your normal predictive
maintenance plan. Should an increase in resistance of more than 20% be
measured during these periodic checks, the technician should investigate
the source of the problem and make the correction to lower the resistance
by replacing or adding ground rods to the ground system.

47. Need for earth tester
47
• The US National Fire Protection Agency (NFPA) and Institute of Electrical
and Electronics Engineers (IEEE) recommend a ground resistance value of
5 or less. The goal in ground resistance is to achieve the lowest ground
resistance value possible that makes sense economically and physically.
• What affects the grounding resistance?
• Four variables affect the ground resistance of a ground system: length or
depth of the ground electrode; the diameter of the ground electrode; the
number of ground electrodes and ground system design.
• Length/depth of the ground electrode
• Driving ground electrodes deeper is a very effective way to lower ground
resistance. Soil is not consistent in its resistivity and can be unpredictable.
The resistance level can generally be reduced by an additional 40% by
doubling the length of the ground electrode. It is sometimes impossible to
drive ground rods deeper – in areas composed of rock, for instance. In these
cases, alternative methods including grounding cement are viable.

48. What affects the grounding resistance?
48
• Diameter of the ground electrode
• Increasing the diameter of the ground electrode has very little effect in
lowering the resistance. For example, you could double the diameter of a
ground electrode and your resistance would only decrease by 10%.
• Number of ground electrodes
• Using multiple ground electrodes provides another way to lower ground
resistance. More than one electrode is driven into the ground and connected
in parallel to lower the resistance. For additional electrodes to be effective,
the spacing of additional rods must be at least equal to the depth of the
driven rod.

49. various ground resistances which can be
used as a rule of thumb.
49

50. Measuring soil resistance
50
• Measuring soil resistance
• To test soil resistivity, connect the ground tester as shown in Fig. below.
Four earth ground stakes are positioned in the soil in a straight line,
equidistant from one another.
• The distance between earth ground stakes should be at least three times
greater than the stake depth.
• The Fluke1625 earth ground tester generates a known current through the
two outer ground stakes and the drop in voltage potential is measured
between the two inner ground stakes.
• The tester automatically calculates the soil resistance using Ohm’s Law
(V=IR).

51. Measuring soil resistance
51

52. Measuring soil resistance
52
• Wenner Method
• Fall of Potential method
• Schlumberger method

53. Difference Between Grounding and
Earthing
53
• One of the major difference between the grounding and the earthing is that
in grounding, the current carrying part is connected to the ground whereas
in earthing the non-current carrying parts is connected to ground.
• Definition of Grounding
• In grounding, the current carrying parts are directly connected to the
ground. The grounding provides the return path for the leakage current and
hence protect the power system equipment from damage.
• When the fault occurs in the equipment, the current in all the three phases
of the equipment become unbalanced. The grounding discharges the fault
current to the ground and hence makes the system balance

54. Difference Between Grounding and
Earthing
54
• The grounding has several advantages like it eliminates the surge voltage
and also discharge the over voltage to the ground. The grounding provides
the great safety to the equipment and improves the service reliability.

55. Definition of Earthing
55
• The ‘earthing’ means the connection of non-current carrying part of the
equipment to the earth. When the fault occurs in the system, then the
potential of the non-current part of the equipment raises, and when
any human or stray animal touch the body of the equipment, then they may
get shocked.
• The earthing discharges the leakage current to the earth and hence avoid the
personnel from the electric shock. It also protects the equipment from
lightning strokes and provides the discharge path for the surge arrester, gap
and other devices.
• The earthing is achieved by connecting the parts of the installation to the
earth by using the earth conductor or earth electrode in intimate contact
with the soil placed with some distance below the ground level.

56. Definition of Earthing
56

57. Comparison Chart
57

58. Key Differences Between Grounding and Earthing
58
• The earthing is defined as the connection of the non-current carrying part
like the body of the equipment or enclosure to earth. In grounding the
current carrying part like neutral of the transformer is directly connected to
the ground.
• For grounding, the black colour wire is used, and for earthing the green
colour, the wire is used.
• The grounding balanced the unbalanced load whereas the earthing protect
the equipment and human from an electrical shock.
• The grounding wire is placed between the neutral of the equipment and the
earth whereas in earthing the earth electrode is placed between the
equipment body and the earth pit which is placed under the ground.
• In grounding the equipment is not physically connected to the ground, and
the current is not zero on the ground, whereas in earthing the system is
physically connected to the ground and it is at zero potential.

59. Key Differences Between Grounding and Earthing
59
• The grounding gives the path to an unwanted current and hence protects the
electrical equipment from damage, whereas the earthing decrease the high
potential of electrical equipment which is caused by a fault and thus
protects the human body from the electrical shock.
• The grounding is classified into three types. They are the solid grounding,
resistance grounding and reactance grounding. Earthing can be done in five
ways. The different methods of earthing are the pipe earthing, plate
earthing, rod earthing, earthing through tap and strip earthing.

60. Specifications for Earth Electrodes
60
• The earthing electrode should not be placed near the building whose
installation system is earthed more than 1.5 m away.
• The resistance of the earth wire should not be more than 1 ohm.
• The wire use for electrode and circuit should be made up of the same
material.
• The electrodes should be placed in vertical position so that it can touch the
layers of the earth.
• The size of the conductor should not be less than 2.6 mm2 or half of the
wire used for electrical wiring. Bare copper wire is used for earthing and
grounding. Green 6 THHN (Thermoplastic high heat neutral coating wire)
and gauged copper wire of different sizes like 2,4,6,8 etc. are also used for
earthing and grounding.

61. Neutral Point
61
• Neutral is a circuit conductor that normally carries current back to the
source. A neutral is that wire which carries back current to source via
ground, this is our usually assumption and it's logically correct.
• A neutral usually represents a reference point in electrical distribution
system which carries current during normal operation but carries fault
current to ground during faults.
• A neutral can be called ground but a ground can never be neutral.
• Due to increase of using non linear loads like TV, Refrigerator etc
nowadays demand of neutral wire is increased. When any insulation
breakdown occurs then ground is useful for taking that fault current to
ground.
• The purpose of neutral wire is for return path while the purpose for
ground wire is to provide operator safety.
• In all electrical service panel ground and neutral wire are connected
together otherwise if not connected then there will be risk for operator
safety.

62. Grounding
62

63. 63

64. Neutral in three phase system
64
• Three phase transmission system: A three phase supply is usually a three
wire system in the transmission side.
• A transmission system doesn't have any load connected to it directly. The
power flowing in a transmission system is unusable. It is usually rated at 11
kV, 33 kV, 132 kV, 400 kV, 765 kV, etc.
• In a three phase system, each phase is displaced from the next phase or the
previous phase by an angle of 120 degrees.
• This means that while one line acts as a forward path for current, the other
two lines can act as return paths. To explain in detail about forward and
return paths, let me tell you a simple example.

65. Neutral in three phase system
65
• The line connecting the positive end of the DC power source to the resistor
is the forward path, and the line connecting the resistor to the negative
terminal is the return path for the current.
• Now that we have cleared the concept of forward and return paths, let me
explain why the three phase system can use one line as a forward path and
other two lines as return path at any given instant.

66. Neutral in three phase system
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• In the above waveform, you will notice the three phases being shown on
the same reference line.
• Let us start at 0 degrees. Notice that blue and black are positive while red is
negative?
• It means that while the blue and black phases are acting as forward paths,
the red phase acts as a return path.
• After 30 degrees, you will notice that black phase has the largest
magnitude among the three phases. Hence it acts as a forward path, and the
other two phases act as return paths.
• Blue's magnitude is declining and red's magnitude is building up, which
means that after a while, at 60 degrees, blue will act as a return path for
black and red.
• This continues for the entire cycle. Now, all the three lines are utilized
equally in transmitting the power to the distribution system.

67. Neutral in three phase system
67
• Three phase distribution system: In the distribution system, the bulk
power is distributed among the consumers.
• This bulk power cannot be used at the voltage range of 11 to 765 kV, so it
has to be stepped down to a usable voltage range. The three phase line-to-
line voltage is 415 V in the consumer end.
• The line-to-ground voltage is 240 V. All our household appliances are rated
for 240 volts.
• This means that we cannot use the power from the distribution system by a
three wire system. By connecting a load between two phases, you are
applying a potential difference of 415 volts across it, and not 240 volts.
• To use the same system at 240 volts, we need another wire called neutral

68. Neutral in three phase system
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• Three phase four wire system:(3 phases and 1 neutral): The distribution
substation has a delta-star transformer if the transmission system was in
delta, which it usually is.
• The delta system is converted to a star system, and the neutral point is used
to lay another line, which is called the neutral line.
• Now each phase along with one neutral line can be utilized as a single
phase system.
• In the three wire transmission system, we have seen that the other two
phases act as return paths while one phase acts as a forward path. In case of
a four wire system, the current from one phase does not enter the other two
phases.
• It returns to the substation through the neutral wire. This means that any
phase can be loaded irrespective of the other two phases.

69. Why Earthing is Required?
69
• The main intention of electrical earthing is to keep away from the danger of
electric shock due to the outflow of current through the not preferred path
as well as to make sure that the potential of a conductor does not increase
with respect to the ground than its planned insulation.
• When the metallic element of electrical machines approaches in contact by
an existing wire, due to a breakdown of fixing the cable, the metal turn into
charged and static charge collect on it. If someone contacts such an electric
metal, then the outcome is a severe electric shock.
• So finally we can conclude that life is random, and one should always get
ready for unexpected circumstances
• So buildings and electric appliances have to be grounded to transfer the
electric charge directly to the ground. The main benefits of grounding
include protection from overvoltage, stabilization of voltage, and
prevention from injury, damage, and death.

70. Components used in Electrical Earthing System
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• The main components used in earthing system mainly include earth cable,
earthing joint (earthing lead), and earth plate, earth rod
• Earth Cable
• The conductor is used to connect metallic parts of an electrical system like
plug sockets, metallic shells, fuses, distribution boxes. Metallic parts of
motors, transformers, generators, etc. the range of these conductors depend
on the earth cable size used in the wiring circuit. The earth wire in the
cross-sectional area must be less than the solid wire used in the electrical
wiring system.
• In general, the copper wire utilized, Minimum size of earth wire for light
circuit is 1 mm square for copper and 1.5 mm square for aluminum. All
conductors should be made of copper. They should have a cross section less
than 0.0020 sq. inches, nominal area (3/0.029 inches) and every conductor
should be stranded. In some situations, copper strips are used instead of a
bare copper conductor.

71. Components used in Electrical Earthing System
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• Earthing Joint
• The ‘ground electrode’ as well as conductors fixing to the ‘ground
continuity conductor’ is called earthing joint (earthing lead).
• The tip where the earthing joint connects the ground continuity conductor
is known as connecting end.
• The lead of the ground must be low size, straight, & should include a
minimum amount of joints. Although copper wires are usually used as
grounding leads; whereas copper strips are selected for high fitting because
it carries high fault current values due to its broad region.

72. Components used in Electrical Earthing System
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• Earth Plate
• The last part of the electrical grounding system which is hidden
underground and linked to the lead of grounding is known as the earth
plate.
• Earth electrode is a pipe, plate or metallic rod, or plate; which has
extremely low resistance for carrying the fault current to the ground safely.
• It can be of iron or copper rod and must be placed in wet earth and in case
the moisture content of earth is low then put some water in the earth plate.
• The earth plate is always placed in the vertical, and coat with salt and
charcoal lime around the earth plate.
• This helps in protecting the earth plate as well as in maintains ground
moisture around the earth plate. The earth plate must be placed four meters
long for the better earthing.

73. Types of Electrical Earthing Systems
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• The process of Earthing or electrical grounding can be done in several
ways like wiring in factories, housing, other machines, and electrical
equipment. The different types of electrical earthing systems include the
following.
• Plate Earthing System
• In this type of system, a plate is made up of copper or GI (galvanized iron)
which are placed vertically in the ground pit less than 3meters from the
earth. For a better electrical grounding system, one should maintain the
earth moisture condition around the plate earthing system.

74. Types of Electrical Earthing Systems
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• Pipe Earthing System
• A galvanized steel based pipe is placed vertically in a wet is known as pipe
earthing, and it is the most common type of earthing system. The pipe size
mainly depends on the soil type and magnitude of current. Usually, for the
ordinary soil, the pipe dimension should be 1.5 inches in diameter and
9feets in length. For rocky or dry soil, the pipe diameter should be greater
than the ordinary soil pipe. The soil moisture will decide the pipe’s length
to be placed in the earth. The pipe earthing diagram is shown below:

75. Types of Electrical Earthing Systems
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• Rod Earthing System
• This type of earthing system is similar to pipe earthing system. A copper
rod with galvanized steel pipe is placed upright in the ground physically or
using a hammer. The embedded electrodes lengths in the earth decrease the
resistance of earth to a preferred value.

76. Plate Earthing
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• Earthing is a series of connections into the ground for electrical safety. The
earthing terminal is the main component in the system.
• Putting it in a simple layman's language, earthing terminal is connected to
any electrical set up, whether DG Set, transformer, motor, control panel as
to effectively disseminate rising fault current safely to the ground. This also
applies to current generated due to lightning occurrences.
• There are various materials used as earthing terminal. One of them is metal
plates usually made of Copper, but not restricted to Galvanized Iron,
Copper Bonded material, and other conductive alloys.

77. Plate Earthing
77
• The earthing plate is placed deep into a pit (usually dug up to 2-3 meters),
along with Coal (absorbs and retains moisture) and Salt (creates ionic
solution for faster dissipation of current). The plate is connected via Copper
conductor, or GI Conductor or concealed copper cable to the respective
electrical set-up. A funnel is attached to add water at regular intervals.
• This is the conventional way of earthing. In this a plate of copper or zinc of
suitable size ie 1x1 ft ; 2x2ft is placed in the earthpit at the depth of
minimum 15ft (water level) and the pit is filled with coal & salt 100kg min.
The plate is connected with GI strip of suitable size. now-a-days
maintenence free chemical earthing electrodes are used as it covers all the
demerits of plate earthing.

78. 78
• Advantages:
• - Tried and tested method for earthing
• - Economic and easily available
• Disadvantages:
• - Salts get washed away during rains or water flow
• - Plate gets corroded and thus has a short life span
• - Due to high current flow, coal may burn and get reduced into ash, thus
creating resistance instead of being conductive
• - Regular addition of water is must.
• Plate earthing is nowadays being replaced by Advance Maintenance Free
Earthing (pipe in pipe/ Strip in pipe/ Solid Copper Bonded Earthing Rods)

79. 79

80. 80
• Pipe Earthing:
• A galvanized steel and a perforated pipe of approved length and diameter is
placed vertically in a wet soil in this kind of system of earthing. It is the
most common system of earthing.
• The size of pipe to use depends on the magnitude of current and the type of
soil. The dimension of the pipe is usually 40mm (1.5in) in diameter and
2.75m (9ft) in length for ordinary soil or greater for dry and rocky soil. The
moisture of the soil will determine the length of the pipe to be buried but
usually it should be 4.75m (15.5ft).

81. 81

82. 82
• Rod Earthing
• It is the same method as pipe earthing. A copper rod of 12.5mm (1/2 inch)
diameter or 16mm (0.6in) diameter of galvanized steel or hollow section
25mm (1inch) of GI pipe of length above 2.5m (8.2 ft) are buried upright in
the earth manually or with the help of a pneumatic hammer. The length of
embedded electrodes in the soil reduces earth resistance to a desired value.