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SITARAMBHAI NARANJI PATEL INSTITUTE OF TECHNOLOGY & RESEARCH
CENTRE, UMRAKH
Course Contents
PART -1 (STUDY)
PART -2 (PRACTICAL EXERCISES)
SR
NO NAME OF STUDY PRACTICALS DATE SIGN
1. To Study of safety devices. / /
2. To Study type of earthing. / /
3. To Study the different type of wirings for House hold
Applications. / /
4. To study the working of table fan and ceiling fan.
/ /
5. To study the working of induction type energy meter / /
6. To study multi meter and perform difference functions of
it.
/ /
SR
NO NAME OF STUDY PRACTICALS DATE SIGN
1. To Study different electrical and electronics symbols.
/ /
2. Familiarization of electrical and electronics components and
study of measuring devices & PCB fabrication and soldering
practice.
/ /
3. study and perform the fluorescent tube light wiring. / /
4. To perform the Full wave circuit on breadboard and verify the
waveform on SCR.
/ /
5. To measure power & energy in 1- AC circuit. / /
6. To performs the wiring that control (A) Two lamps by two
separate switches (House Wiring)
(b) One lamp by two 2-way switches (Stair-case Wiring).
/ /
7. To determine power factor of RLC series circuit.
/ /
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SITARAMBHAI NARANJI PATEL INSTITUTE OF TECHNOLOGY & RESEARCH
CENTRE, UMRAKH
DOs and DONTs in Laboratory:
1. Understand the equipment to be tested and apparatus to be
used.
2. Select proper type (i.e. A. c. or D. C.) and range of meters.
3. Do not touch the live terminals.
4. Use suitable wires (type and size). 5. All the connection
should be tight.
1. Do not leave loose wires (i.e. wires not connected).
2. Get the connection checked before switching ON the
supply.
3. Never exceed the permissible values of current, voltage, and
/ or speed of any machine, apparatus, wire, load, etc.
4. Switch ON or OFF the load gradually and not suddenly.
5. Strictly observe the instructions given by the teacher/Lab
Instructor
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SITARAMBHAI NARANJI PATEL INSTITUTE OF TECHNOLOGY & RESEARCH
CENTRE, UMRAKH Page 1
General Workshop Rules
All students in the workshop are expected to adhere to the
following guidelines.
The students are supposed to come in proper workshop uniform
dress. Wearing shoes in
the workshop is compulsory.
Do not fool around in the lab: Take your lab work seriously and
behave appropriately in the laboratory. Be aware of your classmates
safety as well as your own at all times.
To successfully complete the experiments in one lab period, you
must come prepared to the laboratory. You must read the experiment
in advance and answer the pre-lab
questions.
Please treat the instruments with care, as they are very
expensive. Return the components to the correct bins when you are
finished with them.
Before leaving the lab, place the stools under the lab
bench.
Before leaving the lab, turn off the main power switch to the
lab bench.
Keep your work area neat and uncluttered- Have only books and
other materials that are
needed to conduct the experiment in the laboratory.
Experiment: The student works with a partner and they both take
the data on separate
notebooks. The lab instructor will look at the data and sign on
your notebook at the end of the experiment.
Any student missing a lab (not present in the lab) with no
proper or reasonable excuse will get a 0 grade on that specific lab
and will have his/her final letter grade reduced. Any student
missing two labs with no proper excuse will automatically get a
failing grade
(F).
This laboratory can be used by students during laboratory hours
only.
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SITARAMBHAI NARANJI PATEL INSTITUTE OF TECHNOLOGY & RESEARCH
CENTRE, UMRAKH Page 2
Electrical Safety Principles
When planning and performing work on electrical systems and
equipment, keep these principles in mind:
Understand the procedure completely before starting the
work.
Use good quality footwear/shoes in order to provide maximum
resistance.
Never energize any circuit unless you are sure that no one is
working on the circuit. Give electric supply to the wiring system
only after thorough verification.
Before replacing a blown fuse always remember to put the switch
off.
Do not touch switch boards, main switches, holder points etc
with wet hands.
Do not use broken switches, sockets or plug.
Use non-conductive tools whenever possible.
Before putting the plug pins in socket put off the plug switch
and disconnect the plug by pulling the plug pin and not by pulling
cable.
Take utmost care while handling lamps, lamp holders, switches
etc, because these materials are brittle.
Never drape electrical cords over heat sources
Before beginning work, tie back long hair, and roll up loose
sleeves.
Know the location and how to operate shut-off switches and/or
circuit breaker panels. Use these devices to shut off equipment in
the event of a fire or electrocution.
Dont over bend cables when pulling them through a bend in a
raceway, often a
Pressure or squeezing develops causing insulation damage.
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CENTRE, UMRAKH Page 3
Electrical engineering an over view
Some definitions
1. Electric current: - Rate of change of charge with respect to
time. (I=dq/dt). One ampere is the current produced when a pressure
of one volt is applied across a circuit having one ohm
resistance.
2. EMF: - EMF is electro motive force. Potential difference
between two points in a circuit is the electrical pressure
difference required to drive a current between them. Potential
difference may be termed as voltage.
3. Voltage of a torch battery is 1.5 V and that of automobile
battery is 12V. KSEB supply voltage for domestic installation is
240 V.
4. Electric power (watt):- Electric power, P = Voltage * current
* Power factor Unit of
electric power is watt (W)
5. Electric energy:-Unit of electric energy is KWh (Kilo Watt
hour) 1 unit energy = 1 KWh KSEB provides one KWh meter at every
Installation for measuring consumed energy.
6. Resistance is the property of a substance due to which it
opposes the flow of current
through it. Unit of resistance is ohm
7. Where I is the length of material & A is the area of
cross section
8. Effect of temperature on resistance:-When temperature
increases resistance of pure metals and Alloys increases when
temperature increases resistance of electrolyte,
insulators etc decrease.
9. Resistance in series:-Consider three resistors connected in
series, and then the total resistance of the circuit will be the
sum of the three resistors.
10. Ohms law:-Ohms law states that, the ratio of potential
difference between any two points in a conductor to the current
flowing between them is constant.
11. R = V /I Keeping temperature constant.
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CENTRE, UMRAKH Page 4
Study of Electric Power supply
Electricity:- Electricity is a form of energy. Electricity is
the flow of electrons. We get electricity,
which is a secondary energy source, from the conversion of other
sources of energy, like coal,
natural gas, oil, nuclear power, Hydel power and other natural
sources, which are called primary
sources.
Electric power supply system
AC&DC: DC or direct current is steady current. It never
changes its direction, and AC is
alternating in nature. AC voltage can be increased or decreased
with the help of transformers. By
using high voltage AC, we can drastically reduce the
transmission losses. AC can be converted
into DC easily but reverse is not so easy.
In India state electricity boards are the authorities to
generate and distribute electric
energy. Power plant generates electric power at a voltage of 11
KV. This power is transmitted by
increasing the voltage at different levels as 33 KV, 66KV, 110
KV, 220KVor 400 KV from
different substations. At load centers this voltage again
stepped down as 11 KV and a feeder
network is created. This feeder line energizes the 11KV/415V
step down transformer, and from
these transformers electric supply can be given to consumers at
240V and 415 V as single phase
or three phases.
All domestic and commercial consumers get electric energy from
the distribution network
of concerned electricity boards. Based on the power requirements
of consumers Electricity
Boards may give 3-phase connection (for high power) or single
phase connection (for low
power). In the three phase connections 4 wires are provided,
where as in single-phase connection
one phase and a neutral connection are provided to the
consumers. Phase to neutral voltage in
our country is 230 V and phase-to-phase voltage is 400 V of
frequency 50 Hz. Most of the
appliances work on single-phase supply. There are some motors,
which require three phase
supply.A KWh meter is provided at the consumer end for measuring
the electrical energy
consumed. KSEB introduces different tariffs for different
consumers, as per their connected load
and nature of connection.
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SITARAMBHAI NARANJI PATEL INSTITUTE OF TECHNOLOGY & RESEARCH
CENTRE, UMRAKH Page 5
PRACTICAL: 1
AIM: - STUDY OF SAFETY DEVICES. Date :- / /
Importance of safety devices
The safety features are inbuilt with electric power
distribution. The current is to flow
through the path it is expected to pass and should not take
another path through which it is not
expected to pass. Conductors made of copper or aluminum are
provided across the path for
carrying the current and insulators like PVC, paper or rubber
are provided across the path
through which the current is not expected to flow.
Under abnormal condition there can be failure of insulations and
current will flow
through the undesired path which can cause damage to equipments
and more important the safety
of the user. Sometimes the user may inadvertently touch a live
conductor and cause electric
shock. The circuit may also carry under short circuit condition
much more than normal value of
the current. The inbuilt safety features will isolate the faulty
circuit from the rest of the supply.
The very high currents caused by short circuit situation can
cause lots of damage to
electrical installation. Protective devices are needed to break
short-circuit and overload currents.
Circuit breakers and fuses are protective devices that control
the power going to a
particular route of wiring. In case of an overload or a short on
that circuit, the breaker or fuse
trips and automatically shuts off power to that circuit. Fuses
are the commonly used protection
devices to protect components like wires, transformers
electronics circuit modules against
overload. The general idea of the fuse is that it "burns fuse
link" when current gets higher than
it's rating and thus stops the current flowing.
Types of safety devices:-
Fuse Circuit breakers( MCB, MCCB & ELCB) Earthing.
Basically two types of protections are provided in the power
supply system of domestic consumers.
a. Protection from over current. b. Protection from leakage
current due to failure of insulation or
inadvertent contact with live conductors by the user.
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CENTRE, UMRAKH Page 6
Protection against electrocution
The use of exposed, substandard, badly wired, wrongly connected
or damaged equipment
as well as frayed or badly repaired cables reduces the safety of
an installation and increases the
risk of person receiving an electric shock.
Electrocution is a passage of current through human body, which
is dangerous. The flow
of current through human body effects vital functions.
a. Breathing b. Heartbeat
A correctly chosen RCCB can detect small currents flowing to
earth and reduces the risk
of electrocution. Effect of electric current through human body
has been well researched and
following chart summarizes the results: Human sensitivity to
electricity
500mA Immediate cardiac arrest resulting in death. 70-100mA
Cardiac fibillarillation; the heart begins beats at a steady 20-30
mA Muscle contraction can cause respiratory paralysis 10mA Muscle
contraction : the person remains stuck, to the conductor 1-10 mA
Prickling sensations
However, electrocution should not be viewed in terms of current
alone but in terms of
contact voltage. A person gets electrocuted by coming in contact
with an object that has a
different potential from his/her own. The difference in
potential causes the current to flow
through the body.
The human body has known limits: Under normal dry conditions,
voltage limit = 50V.
In damp surroundings, voltage limit = 25V
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CENTRE, UMRAKH Page 7
Over current and Short circuit
One type of situation that wiring needs to be protected against
is over current. The electrical
wiring is rated for certain maximum current. If you try to pull
more current through it, the wiring
will heat considerably. When the wiring heats too much, it will
cause the melting of cable
insulation, cause fire if there is something flammable near
cable and even melt the copper
conductors in the cable. So protection is needed to guarantee
that in case of something tries to
pull too much current through mains wiring, this cannot happen
for any long time until the fuse
blows and stops the current.
Many people are familiar with a "short circuit", which is a type
of fault that occurs when two
conductors of an electric circuit touch each other. The current
flow caused by a short circuit is
usually high and rapid and is quickly detected and halted by
conventional circuit protective
devices, such as fuses or circuit breakers. Ground faults are
one type of problem when the
insulation fails.
Protection against over current
Every electrical circuit shall be protected against over current
by suitable over current devices. These devices could be
1. Miniature Circuit Breaker (MCB) 2. Molded Case Circuit
Breaker(MCCB) 3. Semi enclosed rewirable fuses 4. High Rupturing
Capacity (HRC) fuses
Typical breaking capacities of protective devices are as
follows:
HRC fuses - 80 kA
MCB - 16 kA
Rewirable fuses - 1 to 4 kA
1) FUSES Fuse is a wire of short length having low melting point
which gives protection against excessive
current. This excessive current may be due to over load or short
circuit. Under normal working
condition the current flowing through the circuit is within safe
limit. But when some faults such
as short circuit occurs the current exceeds the safe limit
value, the fuse wire gets heated and
melts. This will cause breaking of the circuit. After one fusing
operation, fuse wire must be
rewired with the same size wire.
This basic guide will help you decide which fuse to fit to
ensure the safe use of your household appliances.
Appliances up to 700 Watts = 3 Amp fuse
Appliances between 700 and 1000 Watts = 5 Amp fuse
Appliances over 1000 Watts = 13 Amp fuse
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CENTRE, UMRAKH Page 8
COMMON FUSE TYPES
a) Rewirable fuse b) Cartridge fuse c) HRC fuse
a) Rewirable fuse:
This is the cheapest method for protecting a circuit from short
circuit. Wires of
different diameters made of lead and tin are used in the
circuit. When large current flows these
wires melts and disconnects the faulty circuit from the rest of
the supply.
There are different types of fuses. The usual type is the
rewirable type in which the
fuse wire is carried in a removable fuse link (Fig. a). The fuse
link is made of porcelain or other
suitable insulating material. The fuse carrier is push-fitted to
the fuse base to make the
connection through. An advantage of this type is that the blown
fuse wire can be replaced with
negligible cost. But there is a chance of selecting a wrong size
of fuse wire. Another
disadvantage with rewirable fuse is that it may sometimes lead
to fire hazards, when the fuse
wire blows.
Fig. (a) Re-wirable fuse
The semi enclosed rewirable fuses has the following
drawbacks:
It normally melts on 50 % to 100 % excessive overload. The
melting current
cannot be accurately predicted. It takes time to rewire the
fuse. Standard fuse wire should be always made available.
However it is the cheapest mode of protection from short
circuit.
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SITARAMBHAI NARANJI PATEL INSTITUTE OF TECHNOLOGY & RESEARCH
CENTRE, UMRAKH Page 9
b) Cartridge fuse
Cartridge fuse consists of a tube with metal end caps at both
ends
(Fig. b). The tube is usually made of glass with no filling
material.
The fuse wire is placed inside the tube, connected between the
end
caps. Since the tube is made of glass, the fuse element can be
easily
inspected for breakage. When the fuse is blown, the whole
cartridge
has to be replaced. The advantages of cartridge fuses are, quick
and
easy replacement and the fuse rating is marked on the end cap of
the
cartridge itself. Cartridge fuses are mainly: used in various
electrical
and electronic equipment.
(Fig. b Cartridge fuse)
c) High Rupturing Capacity Fuse (HRC)
This is a completely enclosed cartridge type of fuse. These
fuses are screwed or linked in
the circuit. Generally it is used in the high power circuits.
High Rupturing Capacity (HRC)
fuse consists of a porcelain tube! with metal end caps and
fixing tags (Fig. c). The fuse
element is held inside the tube between the end caps and the
tube is filled with silica sand or
granulated quartz. When the fuse element blows, the silica
inside the tube prevent the
formation of an arc, and thus avoids the possibility of fire
hazards. HRC fuse links are
available in a range of 10A to 800A.
The HRC fuse has the following advantages: It is very reliable.
It has an enclosed fuse wire, therefore no chance its arc doing any
damage to the surroundings. It has low temperature rise at rated
load. Maintenance free
The drawbacks are: It is costly. Take time to replace the
fuse.
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CENTRE, UMRAKH Page 10
2) CIRCUIT BREAKERS MCB and ELCB MCB is miniature circuit
breaker. It is automatic in action. When excessive current
passes
through the circuit, handle of MCB will moves down and thus
trips the circuit. After one such an
operation we can manually reset the supply by solving the fault
in that circuit. Thus rewiring
fault size fuse wire in the case of fuse can be avoided by using
MCBs.
ELCB is earth leakage circuit breaker. It protects the circuit
from any leakage of current. It
protects the circuit from lightning and thunder.
a) Miniature Circuit Breaker (MCB)
Miniature circuit breakers are compact devices used in
distribution boards for protection
against overload and short circuit show in fig a.. The overload
protection is achieved by a
thermal trip mechanism using a bimetallic strip. An
electromagnetic trip mechanism is also
incorporated for instantaneous tripping in the event of a short
circuit.
When there is a sudden increase in current due to a short
circuit, the circuit should open
immediately, but the bimetallic strip does not respond quickly.
In this case, the solenoid attracts
the plunger and thus triggers the trip mechanism. After clearing
the fault, the MCB can be
switched on manual. Fig a. Fig b. Fig b. shows the current path
in a typical miniature circuit breaker when it is in the 'on'
position. The current passes through a solenoid coil and a
bimetallic strip. When an overload
condition persists for a few seconds, the bimetallic strip bends
and triggers the trip mechanism.
Current becomes large enough. The magnetic operation is very
fast and is used for braking fault
currents.
In most cases of MCBs, both types are provided so that overload
currents and short circuit currents are handled with the same
degree. It should however be remembered that the
mechanical operation of opening the contacts takes a definite
minimum time, typically 20ms, so
that there can never be the possibility of truly instantaneous
operation.
In many installations, MCBs are preferred over fuses mainly
because there is no need of
rewiring the fuse wire or replacing the cartridge. MCBs are
available in a range of 0.5A to 63A
normal operating current and for the entire range, the, physical
dimensions are almost identical.
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The principle of operation of an MCB is based on the following
two principles.
i. Thermal operation ii. Magnetic operation
i. Thermal operation
In thermal operation, the extra heat produced by the high
current warms the bimetal strip.
This results in bending the bimetallic strip and trips the
operating contacts. The thermal
operation is slow. Hence, it is not suitable for speedy
disconnection required to clear fault
currents. However, it is ideal for operation in the event of
small but prolonged overload currents.
Thus, in general the thermal operation is suitable for opening
the circuit in the event of excessive
current due to the overloaded machines.
ii. Magnetic operation
The magnetic operation, on the other hand is suitable for
protection against high short
circuit currents. This magnetic operation is due to the magnetic
field set up by a coil carrying the
current, which attracts an iron part to trip the breaker when
the current becomes large enough.
The magnetic operation is very fast and is used for braking
fault currents.
In most cases of MCB' s, both types are provided so that
overload currents and short
circuit currents are handled with the same degree. It should
however be remembered that the
mechanical operation of opening the contacts takes a definite
minimum time, typically 20ms, so
that there can never be the possibility of truly instantaneous
operation.
In many installations, MCBs are preferred over fuses mainly
because there is no need of
rewiring the fuse wire or replacing the cartridge. MCBs are
available in a range of 0.5A to 63A
normal operating current and for the entire range, the, physical
dimensions are almost identical.
The major advantages of MCBs are
Instantaneous opening of the contact on short circuit faults Can
be designed to operate even for very small overload currents They
can be quickly reset by hand They cannot be reclosed if fault
persist
In many cases they preferred over fuses as there is no need to
rewire it.
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CENTRE, UMRAKH Page 12
b) Earth Leakage Circuit Breaker
The earth leakage circuit breaker (ELCB) is a protective device,
which will automatically
trip, when there is an earth leakage within the installation. It
is also known as residual
current circuit breaker (RCCB). It works on the current balance
principle. The main part is
a core consisting of three windings. Here one winding carries
the phase current, the other
winding carries the neutral current and the third winding to the
tripping circuit. Under
normal operating conditions the net flux in the core is zero as
such no emf induced in the
trip coil. However, when earth fault occurs, the phase and
neutral current varies, the net
flux in the core will be different and as such, emf is induced
in the trip coil and it is
energized. It then opens the circuit. The functioning of the
ELCB can be checked using a
switch.
RCD - Residual Current Device. This is a generic term for the
entire range of RCDs.
RCCB - Residual Current Circuit Breaker. This is basically a
mechanical switch with an RCD
function added to it. Its sole function is to provide protection
against earth fault currents.
RCBO- Residual Current Breaker with over current Protection.
This is basically an over current
circuit breaker (such as an MCB) with an RCD function added to
it. It has two functions.
Types of RCD
RCDs can be divided into two categories based on the means by
which they detect and respond
to earth fault currents. The two types are Voltage Independent
(VI) and Voltage Dependent
(VD). These are sometimes also referred to as electromechanical
and electronic types
respectively. The VI type uses the output energy from the CT to
activate a relay which in turn
activates a tripping mechanism causing the RCD to trip. The VD
type uses electronic circuitry to
detect the earth fault current and to activate a tripping
mechanism causing the RCD to trip. The
VI device derives its operating energy from the earth fault
current whereas the VD device
derives its operating energy from the mains supply.
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CENTRE, UMRAKH Page 13
PRACTICAL: 2
AIM: - TO STUDY OF EARTHING. Date :- / / What is earthing
/grounding?
Earthing or grounding is the term used for electrical connection
to the general mass of
earth. Equipment or a system is said to be 'earthed' when it is
effectively connected to the ground
with a conducting object. Earthing provides protection to
personal and equipment by ensuring
operation of the protective gear and isolation of faulty circuit
during:
1. Insulation failure 2. Accidental contact 3. Lightning
strike
Importance of earthing
Earthing is necessary for proper functioning of certain
equipments. Earthing is done also
for preventing the operating personal from hazardous shocks
caused by the damage of the
heating appliances. Consider an electric heater connected to the
supply using two-pin plug and
socket. If by some chance the heating element comes in contact
with the metallic body of the
heater, the body of the heater being a conducting material will
be at the same potential as the
heating coil. If a person comes and touches the body of the
heater, current will flow through his
body, which will result in an electric shock.
To avoid unnecessary accident, it is recommended that electric
heater be connected to a
3-pin socket using a 3-core cable. (Note: To see a three-core
cable, open a plug of an electric
iron. There will be three wires, red, blue and green. The green
wire connected to the body of the
iron is the earth wire) In this case the body of the electric
heater is connected to the green wire of
the cable, which is connected to the earth through the earth
terminal. Besides the body of the
electric heater, bodies of hot plates, kettles, toasters,
heaters, ovens, refrigerators, air
conditioners, coolers, electric irons etc could be earthed using
three pin plugs. The resistance of
the path to the earth terminal through the earth wire is very
low. Hence, even if the heating
element comes in contact with the metallic body and a human
being comes in contact with the
metallic body, major part of the current will flow only through
the earth wire (usually the green
wire in a 3 core cable). Moreover because of the low resistance
path, a large current will flow
through the phase wire and the fuse will blow off. For large
current to flow, earth resistance
should be low. To achieve this proper earthing has to be
done.
Earthing is classified as:
1) System earthing 2) Equipment earthing
System earthing: It is the earthing of neutrals of generating
stations and substations. It is employed to limit the voltage of
live conductors with respect to potential of general mass of earth.
This is necessary to prevent failure of insulation.
Equipment earthing: Is earthing of noncurrent carrying metal
parts of electrical equipments. As per Rules 33 and 61 of Indian
Electricity Rule 1956 non-current carrying metal parts
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must be earthed with two separate and distinct earth continuity
conductors to an efficient
earth electrode. However equipments with double insulation need
not be earthed
Some Definitions:
Earthing: A tower/ equipments connecting to the general mass of
earth by means of an electrical conductor.
Earth Electrode: Connection to earth is achieved by electrically
connecting a metal plate, rod or other conductors or an array of
conductors to the general mass of earth. This metal plate or rod or
conductor is called as "Earth electrode".
Earth lead: The conductor by which connection to earth is
made.
Earth loop impedance: The total resistance of earth path
including that of conductors, earth
wire, earth leads and earth electrodes at consumer end and
substation end.
Factors affecting the value of earth electrode resistance
1. Electrode material. 2. Electrode size. 3. Material and size
of earth wire. 4. Moisture content of soil. 5. Depth of electrode
of underground. 6. Quantity of dust and charcoal in earth pit.
Earth resistance consists of following components
1. Resistance of metal electrode 2. Contact resistance between
electrode and soil 3. Resistance of soil away from electrode
surface.
The resistance decreases with the presence of moisture and salt
in soil. To increase the
effectiveness of earth, the total earth resistance should be
reduced. Efforts should be made to
reduce the resistance contributed by each of above three
components.
Earth Electrodes
Earth electrodes can be following shapes
1. Driven Rods or pipes 2. Horizontal Wires 3. Four Pointed
Stars 4. Conductive Plates
A. Round Vertical Plates B. Square Vertical Plates
5. Buried Radial Wires 6. Spheres made of metal 7. Water
Pipes
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CENTRE, UMRAKH Page 15
Water pipe as earth electrode
As water pipes exist extensively and these are most of the time
embedded in earth, they
can make a good earth electrode. Such earthing is not
objectionable with alternating currents. But
with direct currents, the flow of fault currents in pipes
produces electrolysis and results in heavy
corrosion of pipes. This electrolysis process makes the water
also harmful to certain extent. If
water pipes are proposed to be used as earth electrode, then
only main water supply pipe should
be used as an electrode. The water supply main pipe should have
metal-to-metal joints between
its segments.
A perfect electrical connection should be made between water
pipe & earth conductor.
Pipe should be cleaned thoroughly with emery paper. Earth
conductor also should be cleaned
thoroughly. The cleaned conductor should be wrapped 4 to 5 times
and ends clamped by nuts &
bolts. The earth resistance achieved by such an arrangement is
usually a fraction of an ohm. Low
resistance of such system is due to long length of water pipe
and the fact that it is mostly
embedded below earth. This method is mostly used for grounding
in telephone services.
Electrodes should be made of a metal, which has a high
conductivity. Normally copper is used.
The size of the electrode should be such, that it is able to
conduct the expected value of stray
equipments. For example a 3 phase star wound generator must have
its neutral point at earth
potential.
The salts commonly used for chemical treatment of soil are
1. Sodium Chloride 2. Calcium Chloride 3. Sodium Nitrate 4.
Magnesium Sulphate
Other factors, which affect the soil resistivity, are
1. Temperature of soil: the resistivity increases when
temperature falls below the freezing point. If the temperature
falls from 20degrees C to O degree C, soil resistivity goes up from
7200-ohm cm to 14000-ohm cm.
2. Moisture Content of Soil: Small changes in moisture content
seriously affect the resistivity. For example if the moisture
content changes from 25% to 30%, soil resistivity drops from
250000-ohm cms to 6400-ohm cm. It is important that earth
electrodes should be in contact
with moist soil. It should be ensured that the electrodes are
deep in soil and if possible below
the permanent water level.
3. Mechanical Composition of soil: finer the grading, lower the
resistance.
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Methods of placing earth electrodes in soil
1. Pipe Earthing:
Pipe earthing is done by permanently placing a pipe
in wet ground. The pipe can be made of steel, galvanized
iron or cast iron. Usually GI pipes having a length of 2.5m
and an internal diameter of 38mm are used. The pipe
should not be painted or coated with any non-conducting
material.
Fig. A (1) shows an illustration of a typical pipe
electrode. The pipe should be placed atleast 1.25m below
the ground level and it should be surrounded by alternate
layers of charcoal and salt for a distance of around 15 cm.
This is to maintain the moisture level and to obtain lower
earth resistance. The earth lead of sufficient gauge should
be firmly connected to the electrode and it should be
carried in a Gl pipe at a depth of 60cm below the ground
level. A funnel with a wire mesh should be provided to
pour water into the sump. Three or four bucket of water
should be poured in a few days particularly during summer
season. This is to keep the surroundings of the electrode
permanently moist.
Fig. A (1) Cross section of pipe earthing
2. Plate earthing
A typical illustration of plate earthing is
shown in Fig. E (2). The plate electrode should
have a minimum dimension of 600x600x3.15mm
for copper plate or 600x600x6.3mm for Gl plates.
The plate electrode should be placed at least 1.5m
below the ground level. The earth conductor is to
be securely connected to the plate by means of
bolts and nuts. The bolts and nuts should be of the
same material as that of the plate. The earth
conductor should be carried in a Gl pipe buried 60
cm below the ground level. The plate electrode
should be surrounded by a layer of charcoal to
reduce the earth resistance. A separate Gl pipe with
funnel and wire mesh attached is provided to pour
water into the sump.
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3. Strip earthing
For all places having a rocky soil
bed, this type of earthing is suitable. On
this system, wires or strips made of GI of
size 25 mm x 4 mm or made of copper of
size 25 mm x 1.6 mm are embedded 0.5
m, below the soil in the form of a network.
The length should not be less than 1.5 m
as per ISI specification. Detail are given in
figure below.
Effect of Soil Properties in Earthing
While it is not possible to change the fundamental nature
/properties of soil at a given
location, but local variations of soil conditions do occur even
in a small area. When a location for
making earthing pit has to be selected, preference should be
given to location, which is likely to
give minimum electrical resistance. In the list below, soils
have been arranged in ascending order
with regard to their electrical resistance.
Wet marshy lands, or lands containing ashes (Avg Resistivity
2400 ohm cms) Clay, loamy soil, arable land clay Clay & loam
mixed with varying proportion of gravel & sand (Avg
Resistivity
15,800 ohm cms) Damp & wet sands Dry sand Gravel &
Stones
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PRACTICAL: 3
AIM: To Study the different type of wirings for House hold
Applications. Date :- / /
Introduction
A network of wires connecting various accessories for
distribution of electrical energy from the
suppliers meter board to the numerous electrical energy
consuming devices such as lamps, fans and other domestic appliances
through controlling and safety devices is known as wiring system.
The suppliers service cable feeding an installation terminates in
what is usually called the
service fuses. In an ordinary house the service fuse is called
as service cutout. Such cutouts
including service meters remain the property of the supplier and
represent the furthest point of
the supplier responsibility. The point at which the consumer's
wiring is connected into cutout is
known as point of commencement of supply or consumer's
terminals. From consumer terminals
onwards the supply cables are entirely under the control of
consumer's and so laid out as per his
selection. A typical house wiring circuit is shown in fig. a
fig (a)
Systems of distribution of electrical energy
Since as per recommendations of ISI the maximum number of points
of lights, fans and socket-
outlet that can be connected in one circuit is 10 and the
maximum load that can be connected in
such a circuit is 800 watts, hence in case more load or more
points are required to be connected
to the supply system, then it is to be done by having more than
one circuit.
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In distribution board system, which is most commonly adopted for
distribution of electrical
energy in a building, the fuses of various circuits are grouped
together on a distribution board, sometimes simply known as fuse
board.
The two copper strips, known as bus-bars, fixed in a
distribution board of hard wood or metal
case are connected to the supply main through a linked switch so
that the installation can be
switched off as a whole from both the poles of supply if
required. A fuse is inserted in the + ve or
phase pole of each circuit so that each circuit is connected up
through its own particular fuse.
In large buildings, however, if only one distribution board were
used, some of the points would
be at a considerable distance from it and in such cases it is
advisable to employ sub-distribution
boards either to save cable or to prevent too great voltage drop
at the more distant points (lamps
or fans or other appliances). In such cases main distribution
board controls the circuit to each
sub-distribution board from which the sub-circuits are taken, as
shown in fig. a
The number of circuits and sub-circuits are decided as per
number of points to be wired and load
to be connected to the supply system. For determination of load
of an installation the following
ratings maybe assumed unless the values are known or
specified.
1. Fluorescent lamps 40 watts. 2. Incandescent lamps, fans, and
socket outlets 60 watts. 3. Power socket-outlets 1,000 watts. 4.
Exhaust fans as per capacity of exhaust fans.
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The Tree System
Another system of distribution of electrical energy in a
building is the tree system. In this
system smaller branches are taken from the main branch, as shown
in fig. b and the wiring
system resembles a tree. As each branch is taken off, a fuse is
inserted. This system used to be
employed in early days. Now-a-days it is no more adopted due to
the following draw-backs in
this system.
1. The voltage across all the lamps does not remain the same.
The lamps in the
last branch will have least voltage across them on account of
voltage drop in
leads.
2. A number of joints are involved in each circuit. 3. Fuses are
scattered. 4. In case of occurrence of fault all the joints have to
be located and if some of these
joints are concealed beneath floors or roof spaces, a lot of
difficulties are to be
faced. Sometimes a number of such joints are required to be
opened for testing
purposes, so damage is caused to installation, conductors and
building. Methods of wiring
There are two methods of wiring known as
1. joint box system (or Tee system) and 2. Loop-in system
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Joint Box or Tee System: In joint box system the connections to
the lamps are made through joints made in joint boxes by
means of suitable connectors or joint cutouts. In this method
though there is a saving in the
quantity of wire or cable required but the same is offset by the
extra cost of joint boxes. The
other disadvantage of T-connections is that the number of
T-connections made in a wiring
system results in weakness if not properly made. Now-a-days the
use of this system is limited to
temporary installations only, as its cost is low. 2. Loop- in-
system: This system is universally employed for connections of
various lamps or other appliances in
parallel. In this system when a connection is required at a
light or switch, the feed conductor is
looped-in by bringing it direct to the terminal and then
carrying it forward again to the next point
to be fed, as shown in fig. d. The switch and light feeds are
carried round the circuit in a series of
loops from one point to another until the last point on the
circuit is reached. The phase or line conductors are looped either
in switch board or box and neutral conductors are
looped either in switch board or from light or fan. Line or
phase should never be looped from light or fan.
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The advantages and disadvantages of loop-in system are as
follows;
Advantages
1. Joint boxes are not required. 2. In loop-in system no joint
is concealed beneath floor or in roof 3. spaces. As they are made
only at outlets so they are accessible for inspection
and opening out merely by removing the fitments concerned. Hence
fault location is easy.
Disadvantages:
1. Length of wire or cable required is more and voltage drops
and copper losses are,
therefore, more.
2. Looping-in switches and lamp holders is usually
difficult.
SYSTEMS OF WIRING
The types of internal wiring usually employed in our country
are:
1. Cleat wiring:
In this system of internal wiring the cables used are either VIR
or PVC type. The cables
are held by porcelain cleats about 6 mm above the walls or
ceiling. The cleats are made in two
halves, one base and the other cap. The base is grooved to
accommodate the cables and the cap is
put over it and whole of it is then screwed on wooden plugs
(gutties) previously cemented into
the wall or ceiling. Thus the cables are firmly griped between
the two halves of the cleats and
secured to the supporting wall or ceiling. The cleats used are
of different sizes and different types
in order to accommodate cables of various sizes and different
numbers of cables respectively.
The cleats are of three typesone groove, two grooves and three
grooves to accommodate one,
two, and three cables respectively.
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Advantages:
1. It is the cheapest system of internal wiring. 2. Its
installation and dismantlement is easy and quick. 3. Material is
recoverable after dismantlement. 4. Inspection, alterations and
additions can be easily made. 5. Skill required is little.
Disadvantages:
1. It is not good looking. 2. It is quite temporary and perishes
quickly. 3. The wires are exposed to mechanical injury.
4. The insulation catches dampness from the atmosphere and
common salt like substance
appears on the insulation which lowers the insulation resistance
and Causes leakage.
Hence this system of wiring cannot be used in damp places.
5. Oil and smoke are injurious to VIR insulation.
Fields of Application:
The wiring of this type is very suitable for temporary
installations in dry places. This is also acceptable where
appearance is not so important and cheapness is the main
consideration. This system is not suitable for use in domestic
premises.
2. Wooden Casing and Capping Wiring:
The cable used in this type of wiring is either VIR or PVC or
any other approved
insulated cables. The cables are carried through the wooden
casing enclosures. The casing
consists of V-shaped grooves (usually two to hold the cables of
opposite polarity in different
groves) and is covered at the top by means of rectangular strip
of wood, known as capping, of
same width as that of casing. The capping is screwed to the
casing by means of wooden screws
fixed at every 15 cm on the centre fillet. To protect the casing
against white ants first class
seasoned teak wood, varnished by shellac varnish is employed.
Two or three cables of same
polarity (either all phases or all neutrals) may be run in one
groove and in no case the cables of
opposite polarity should be run in the same groove. The casing
ia usually placed 3.2 mm apart
from the wall or ceiling by means of porcelain distance pieces
of thickness not less than 6.5 mm
in order to keep the casing dry at the back.
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3. CTS or TRS Wiring.
In this type of wiring the cables used may be single core, twin
core or three core TRS
cables with a circular oval shape. Usually single core cables
are preferred. TRS cables are
sufficiently chemical proof, water proof, steam proof but are
slightly affected by lubricating oils.
TRS eaoles are run on well seasoned, perfectly straight and well
varnished (on all four sides)
teak wood batten of thickness 10 mm at least. The width of the
batten depends upon the number
and size of cables to be carried by it. The battens are
available in width of
13,19,25,31,38,44,50,56,63,69 and 75 mm. The wooden battens are
secured to the walls or
ceiling by flat head wood screws to wood or other approved plugs
at an interval not exceeding 75
cm. The cables are held on the wooden batten by means of tinned
brass link clips already fixed
on the batten with brass pins and spaced at an interval of 10 cm
in case of horizontal runs and 15
cm in case of vertical runs. The wiring after erection is neatly
painted with two coats of oil-less
non-cracking paint as specified in IS 732 and so on.
Advantages
1. Its installation is easy and quick and saving in labor
largely compensate for the
extra cost of the cable.
2. Its life is long. 3. Within certain limits it is fire proof.
4. It can withstand the action of most chemicals such as acids and
alkalies. 5. It is cheaper than other types of wiring except cleat
wiring. 6. If the job is carried out with proper attention, it
gives a nice
appearance.
Disadvantages
1. Good workmanship is required to make a sound job in TRS
wiring. 2. This type of wiring cannot be recommended for use in
situations open to sun
or rain unless preventive steps are taken to preserve the
insulation of cables.
Fields of Application
The TRS wiring is suitable for low voltage installations and is
extensively used for lighting purposes everywhere i.e. in domestic,
commercial or industrial buildings except workshop where it is
liable to mechanical injury. This type of wiring is suitable in
situations where acids and alkalies are likely to be present.
4. Lead Sheathed Wiring
This type of wiring employs conductors insulated with VIR and is
covered with an outer
sheath of lead aluminum alloy containing about 95% lead. This
metal sheath gives protection to
the cable from mechanical injury, dampness and atmospheric
corrosion. The whole lead covering
is made electrically continuous and is connected to earth at the
point of entry to protect against
electrolytic action due to leaking current and to provide safety
against the sheath becoming a
live. The cables are run on wooden batten and fixed by means of
link clips as in TRS wiring. The
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great part of the cable employed is flat twin (the cable having
two insulated conductors side by
side covered with red and black tape respectively and under one
flat covering of lead alloy).
Three-core flat type cable is also used in certain cases as well
as single core cables under a
circular sheath of lead alloy
Advantages
1. It provides protection against mechanical injury better than
provided by 2. TRS wiring. 3. It is easy to fix and looks nice as
it can be run in building without damaging
decoration and can be painted to suit colour scheme of the
surroundings.
4. Its life is long if proper earth continuity is maintained
throughout. 5. It can be use din damp situations provided
protection against moisture effect
on the ends of the cable is given.
6. It can be used in situations exposed to rain and sun provided
no joint is exposed.
Disadvantages
1. It is costlier than TRS wiring. 2. It is not suitable for
places where chemical corrosion may occur. 3. In case of damage to
insulation the metal sheath becomes alive and gives shock, so as to
provide safety against electrical shock it is necessary that the
sheath is properly earthed
and an earth wire is run side by side with it and all pieces are
properly bounded or joined
together so that not a single cover is left unearthed.
4. Skilled labour and proper supervision is required. 5.
Fields of Application
This wiring system is suitable for low voltage (up to 250 volts)
installations. It may be
used in places exposed to sun and rain provided no joint is
exposed. It may also be used in damp
places with a suitable protective covering. It should not be
used in places where chemical
corrosion may occur.. This type of wiring is not very common in
use these days except for some
small installations and distribution boards etc.
5. Conduit Wiring
In this system of wiring steel tubes, known as conduits, are
installed on the surface of
walls by means of saddles or pipe hooks or buried under plaster
and VIR or PVC cables are
drawn into afterwards by means of a GI wire of size of about 18
SWG. In damp situations the
conduits can be spaced from the walls by means of small wooden
blocks fixed below the pipes at
regular intervals. In order to facilitate drawing of wires
numbers of inspection fittings are
provided along its length. The conduits should be electrically
and mechanically continuous and
connected to earth at some suitable point. The conduits used for
this purpose are of two types
namely (i) light gauge (or split type) conduit and heavy gauge
(or screwed type) conduit. Light
gauge or split conduit with a seam along its length is used for
cheap work. It is not water tight or
even damp proof and is not permitted on medium voltage (i.e. on
voltages higher than 250V).
Screwed conduit (solid drawn or with welded seam) is used for
all medium voltage (250 V or
600 V) circuits and in places where good mechanical protection
and absolute protection from
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moisture is desired. In general the finish of the conduit is
black stove-enamelled, there being a
smooth coating of enamel both on the inside and outside surface
of the tube. Galvanized conduit
is also employed, especially in damp situation when the conduit
is on the surface but under
ordinary conditions buried in walls it offers little, if any,
advantage over good enamelled
conduits.
Advantages
1. It provides protection against mechanical damage. 2. It
provides complete protection against fire due to short-circuits
etc. 3. The whole system is water proof. 4. Replacement and
alteration of defective wiring is easy. 5. Its life is long if the
work is properly executed. 6. It is shock proof also if earthing
and bonding is properly done.
Disadvantages
1. It is very costly system of wiring. 2. Its erection is not so
easy and requires time. 3. Experienced and highly skilled labour is
required for carrying out the job. 4. Internal condensation of
moisture may cause damage to the insulation
unless the system outlets are properly drained and
ventilated.
Fields of Application
As this system of wiring provides protection against fire,
mechanical damage and dampness so this is the only approved system
of wiring for:
1. Places where considerable dust or puff is present such as in
textile mills, saw mills, flour mills etc.
2. Damp situations. 3. In workshops for lighting and motor
wiring. 4. Places, where there is a possibility of fire hazards
such as in oil mills, varnish factories
etc.
5. Places, where important documents are kept such as a record
room. 6. Residential and public buildings, where the appearance is
the prime thing. The recessed
type conduit wiring is preferred for residential and public
buildings.
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CHOICE OF WIRING
The following factors should be considered before selecting a
particular type of wiring.
1. Safety: The first and foremost consideration is safety to a
person using electricity against leakage or shock. Where there is a
possibility of fire hazard, conduit wiring is used.
2. Mechanical Protection: The wiring must be protected from
mechanical damage during use.
3. Permanency: The wiring must not deteriorate unduly by action
of weather, fumes, dampness etc.
4. Appearance: The wiring should he good looking. 5. Durability:
The wiring must be durable. 6. Accessibility: In wiring system
there should be facilities for extension, renewal or
alterations.
7. Initial Cost: The wiring selected should suit the pocket of
the owner of the building. 8. Maintenance Cost: The wiring should
have, as far as possible, the lowest maintenance
cost.
9. The other factors, in addition to above, to be kept in view
while making the choice of wiring is load voltage to be employed,
type of building etc.
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Tools used in Electric Wiring
Some of the most commonly used tools are described below:
STUDY OF WIRING ACCESSORIES
Any device, associated with the wiring and electrical appliance
of an installation, such as a
switch, a fuse, a plug, a socket-outlet etc. is called the
wiring accessory. The cables, flexible
cords and various wiring accessories in common use are briefly
described below.
SR. NO
WIRING ACCESSORIES
SIZE USE
1. Combination Pliers 15,20,25 cms For holding, twisting or
cutting wires.
2. Round Nose Pliers or Flat Nose Pliers
10 cms For holding, twisting or joining the wires at narrow
places.
3. Side Cutting Pliers(side cutter)
20 cms Cutting wire at narrow or ordinary places and for
removing insulation.
4. Electrician Knife 10 cms It has two blades, one for removing
insulation of wires and other for cleaning the wires.
5. Electric Soldering iron 25,40,65,125 W To solder the joints
of wires and winding wires.
6. Cross peen Hammer 1/4 kg to 2 kg Used for fixing clip and
making gitties hole in wall.
7. Ball peen Hammer 1/4 kg to 2 kg Best suited for chipping on
teak wood batten, and riveting purpose in sheet metal works.
8. Tenon saw or Hand saw 30.5 cm & 40.5 cm
Used for cutting wooden boards, block casings etc.
9. Poker 10, 15 cm Used for making pilot holes for fixing wood
screw.
10. Hand drill 3,6,12 mm Used for making holes in wooden blocks
and boards.
11. Hacksaw 16,20,25,30 cms Used for cutting conduit G.I. pipes
or mild steel.
12. Measuring Tape 10,20 mm Used for measuring the
dimension of the wiring. It is
made of steel or cotton cloth.
13. Wire Stripper & Cutter
Used for removing insulation of PVC wires and available with
adjustable 22 SWG and onwards.
14. Files (Flat, round half) 3" to 4" To smooth the surface or
corners of any iron board etc.
15. Crimping Tool 1.5,2.5,6mm As soldering on Aluminum is
difficult, this plier is used to crimp the joint or lugs.
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Switches
A manually operated device used for closing and opening or for
changing the
connections of a circuit is known as a switch.
The switches used in internal wiring may be classified in
various ways. According to the
type of base material they are classified as porcelain or
bakelite switches. According to colour of
base they are either white or black or brown coloured switches.
According to operation required,
they are classified as one way, two-way, centre off, double pole
etc. switches.
1. One-way Switch
This type of switch consists of two terminals which can be
easily seen from the back side
of the switch as well, without removing the cover. The switch is
always connect* din series with the point (lamp, fan or
socket-outlet) to be controlled. 2. Two-way Switch
The switch of this type consists of four terminals, two of them
being short-circuited inside the switch. The switch of this type is
usually used for the stair-case wiring or circuits where one point
is to be controlled from two different places. 3. Two-way Centre
off Switch
The switch of this type is just like a two-way switch but having
three operations. In the
centre it becomes off. Such switches are used when two lamps are
to be operated alternately.
5. Double Pole Switch
This is a combination of two one-way switches, which can be
operated simultaneously as
ON-OFF terminals of both the switches, are connected together by
a handle made of bakelite.
Such switches are used as interlinked switches when the load
current is less than 5A and supply
voltage is under250V.Incaseeither of the voltage or current
exceeds the limits mentioned above
DPI C switch is used. 5. Push-button Switches
Such switches are used for controlling the electric bells. When
the knob is pressed, the circuit
is completed and the bell rings and as soon as the knob is left,
the circuit becomes open. 6. Table Lamp Switch
This is a small on-off switch which is commonly used in table
lamps.
7. Bed Switch
Such switches are used to switch off the table lamps or other
lamps while going to sleep
or making the lamp on while getting up at night. It is connected
in aeries with one of the two
flexible wires. The specialty with this switch is that
fluorescent material is applied to its knob so
that it may glow at night and can easily be seen in
darkness.
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Socket-Outlets
The socket-outlets are used to supply electrical connections
whenever required for electrical
appliances such as radios, table fans, table lamps, iron, stoves
etc. Socket-outlets are of two
types two pin type and three pin type. Two pin socket-outlets
have become obsolete now-a-
days. The three pin type socket-outlet has got three hollow
terminals in which three pin plugs can
easily be inserted but not loosely. Two holes being of same
size, are meant for making
connections to the flexible wire of the appliance and the third
hole, which is bigger
comparatively, is meant for earth connections. Thus three holes
or sleeves are for live, neutral
and earth connections. The three pin socket-outlets are also of
two types:
1. 5 A for table fans, table lamps, radios etc, and 2. 15 A for
power circuits as heater, stove, iron etc.
Three Pin Socket-Outlet Flush Mounting
Plugs
Plugs are used to take the supply from the socket-outlets for
electrical appliances such as
table lamp, table fan, heater etc. Similar to socket-outlets
plugs are also of two types namely two
pin and three pin. Two pin type plugs have become obsolete
now-a-days. Three pin type plugs
consist of three pins usually made from brass. To the two pins
which are thin and of same size,
flexible wires are connected and then covered up. To the third
pin, which is thicker
comparatively, earth wire from the electrical appliance is
connected. Similar to 3 pin-socket
outlets 3 pin plugs are also of two types5 A and 15 A. (see fig.
26.10)
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Lamp Holders
As the name indicates the function of lamp holder is to support
the lamp and also to connect it electrically. These are designed
for quick removal and replacement of the lamp. Lamp holders are of
many types. A few will be described here. Lamp-holders may be
either of brass or bakelite type with porcelain interior. Brass
holders are more durable but may give shock if connections are
poor. Though bakelite holders are not durable, but do not give
shock. 1.Pendant or Cored Grip Holders Such a lamp holder is used
when the lamp is to be suspended from the flexible cord. Such a
lamp
holder is hanged vertically downward from the ceiling with flu
flexible cord, one end of which
makes electrical connections with the ceiling rose and other
with the lamp holder and thus with
the lamp. Pendant Lamp Holder
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PRACTICAL: 4
Aim: - To study the working of table fan and ceiling fan. Date:
- / /
Theory:-
Fan is an essential home appliance nowadays and is available in
different style and facili-
ties. Generally used types are table fan and ceiling fan. We can
mount the ceiling fan on the
ceiling for providing wind to whole the room. As per IE rule the
minimum height from floor to
fan must be2.5 meter. Table fan can be places on tabletop or any
flat surface. But it has
minimum space limit compared to ceiling fan.
Construction
Main parts of a ceiling fan are 1. Winding 2. Capacitor & 3.
Regulator
Winding of the motor can be done manually or by automated
machine. Regulator may be
electronic type or resistance type. Electronic type regulator
has negligible power loss and
compact size. But in the case of resistance type, resistances
are connected in series with the
circuit; this may cause power loss as heat.
In table fan one permanent split capacitor run (PSC) motor is
the heart of a fan. This motor
consists of two windings one as starting winding and other as
running winding. Starting winding
of this motor has high resistance and low reactance but running
winding has low resistance and
high reactance. One capacitor is connected in series with the
starting winding and whole of this
circuit is put in parallel across running winding. In the case
of ceiling fan these two windings are
placed in stator in the inner side of the fan. Rotor has no
winding; it is the outer body of the fan.
Ceiling fan motor operates just in opposite manner as compared
to general motor. That is actual
rotor of the motor is blocked and the stator is free to rotate.
So ceiling fan runs in anticlockwise
direction. At the same time table fan motor is operated as
normal case and so it runs in clockwise
direction. Capacitor connected in series with the starting
winding should be value 2.5 micro
farad. Pyranel insulated foil paper capacitor is using for this
purpose. It helps to provide a split
phase effect from single phase AC supply.
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SERVICING
Problems and solutions normally occurring in fans are as
follows
1. Fan is not working when supply is given o Check the supply at
the consuming end. o Dismantle the fan from ceiling and remove the
cover. Check the
windings, if it is burnt rewind it with proper gauge copper
wire.
o Number of turns must be equal to the previous winding, because
it may affect the speed of the fan. If starting winding is burnt,
it alone can be replaced but in the
case of running winding we want change these two sets of
windings.
2. Fan is not starting and will work when push to start
o Check the voltage at the consuming end o Dismantle the
capacitor from fan and connect it to AC supply for 30 sec. Then
disconnect and short circuit the capacitor terminals. At that
time we can hear
one spot sound if it working, otherwise it can be replaced by
new one.
o Check the bearing of the motor; if it is dirty grease may be
applied. o Induction type single phase energy meter
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PRACTICAL: 5 Aim: - To study the working of induction type
energy meter. Date: - / / Induction type instruments are used only
for a.c measurements. These instruments can be
used either as ammeter, voltmeter or wattmeter. However, the
induction principle finds its widest
application as an energy meter. Induction type single-phase
energy meter is used invariably to
measure the energy consumption in any a.c circuit in a
prescribed period where supply voltage
and frequency are constant. Energy meter is an integrating
instrument which measures the total
quantity of electrical energy supplied to the circuit in a given
period.
Principle:
The basic principle of induction type energy meter is
electromagnetic induction. When
alternating current flows through two suitably located coils
(current coil and potential coil)
produces rotating magnetic field which is cut by the metallic
disc suspended near to the coils,
Thus an e.m.f is induced in the disc which circulates eddy
currents in it. By the interaction of
rotating magnetic field and eddy currents, torque is developed
and causes the disc to rotate.
Construction
An induction type single phase energy meters, as shown in fig.
has the following main parts of
the operating mechanism. Driving system
Moving System
Braking System Recording mechanism
Driving System:- The driving system of the meter consists of two
electromagnets,
1. Series magnet 2. shunt magnet
1. Series magnet:
It consists of a number of U- shaped laminations of silicon
steel together to form a core. A
core of thick wire having a few turns is wound on both the legs
of U-shaped magnet as shown
in fig. This coil is connected in series with load. Thus it is
excited by the circuit current I and is
known as current coil. This magnet is placed below the aluminium
disc and produces the
magnetic field se proportional to and in phase with the line
current I.
2. Shunt Magnet
It consist of a number of M-shaped laminations of silicon steel
assembled together to form a
core. A coil of thin wire having large number of turns is
wounded on the central limb of the
magnet as shown m above: Fig. The coil is connected across the
load. Thus it is excited by the
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current proportional to the supply voltage and is known as,
potential or pressure coil. This
magnet is placed above the aluminium disc.
In order to obtain deflecting torque, current in the pressure
coil must lag behind the supply
voltage by 90. For this the copper shading band (Short
circuiting copper ring) is provided on the
central limb of the shunt magnet. The phase difference of 90 is
obtained by adjusting the
position of this shading band. The shading band acts as Short
circuited transformer secondary.
Since its resistance Is negligibly small as compared to its
inductance, therefore current
circulating in the shading band lags behind the supply voltage
nearly by 90. Thus the shunt
magnet produced a field sh proportional to applied voltage. This
field is in phase with the
current flowing through the pressure coil Ip but is in
quadrature with the applied voltage.
Moving System:
It consists of a light aluminum disc mounted on a vertical
spindle. The aluminium disc is
positioned in the air gap between series and shunt magnets, The
spindle is supported by a cup
shaped jewelled bearing at the bottom end and has a spring jewel
bearing at the top end. Since
there is no control spring the disc makes continous rotation
under the action of deflecting torque.
Braking system:
A permanent magnet positioned near the edge of the aluminium
disc as showin the Fig.
forms the braking system. When the aluminium disc moves in the
field of the braking magnet,
flux is cat and currents are induced in the disc. The direction
of induced current is such that it
opposes the rotation (lenz's law). Thus braking torque is
produced. Since the induced current is
proportional to the speed of the disc (N) therefore braking
torque (T ) is proportional to the disc
speed (ie) T. x N.
The position of braking magnet is adjustable and therefore,
braking torque can be
adjusted by shifting the magnet to different radial positions.
If the braking magnet is moved
towards the centre of the disc, flux cut the disc is less which
reduces the induced current and thus
the braking torque is reduced. Hence by the inward movement of
the magnet, braking torque
decreases but the speed of the disc increases and
vice-versa.
The function of recording or registering mechanism is to record
continuosly a number on
the dial which is proportional to the revolutions made by the
moving system. The number of
revolutions of the disc is a measure of the electrical energy
passing through the meter.
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Working:
When the energy meter is connected in the circuit, the current
coil carries the load current
and pressure coil carries the current proportional to the supply
voltage. The magnetic field
produced by the series magnet (series coil) is in phase with the
line current and magnetic field
produced by the shunt magnet (pressure coil) is in quadrature
with the applied voltage (since the
coil is highly inductive). Thus a phase difference exists
between the fluxes produced by the two
coils. This set up a rotating field which interacts with the
disc and produces a driving torque and
thus, disc starts rotating. The number of revolutions made by
the disc depends upon the energy
passing through the meter. The spindle is geared to the
recording mechanism so that electrical
energy consumed in the circuit is directly registered in
kWh.
The speed of the disc is adjusted by adjusting the position of
the braking magnet. For
example, if the energy meter registers less energy than the
energy actually consumed in the
circuit. Then, the speed of the disc has to be increased which
is obtained by shifting the braking
magnet nearer to the centre of the disc and vice-versa.
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Electric lamps
The first ever practical model of the incandescent lamp was
invented in 1879. Since then,
there has been series of developments in the area of light
source and lighting technology. The
first incandescent lamp was made with a carbon filament with a
useful light output of only three
lumens per watt. A long time has gone by since then and today
there are about 200 thousand
different types of demands keeping in view the wattage, size,
applications, etc. It includes about
40,000 types of incandescent lamps alone. Lamp differ from each
other in terms of luminous
flux, light, the colour of the light, their colour rendering
characteristics, size and energy
consumption. Broadly, different types of lamps can be classified
as follows:
1. Incandescent lamp (GLS) 2. Fluorescent lamps (FTL) 3. High
Pressure Mercury Vapour lamps (HPMVL) 4. Halogen lamps 5. High
Pressure Sodium Vapour Lamps (HPSVL) 6. Low Pressure Sodium Vapour
lamps (LPSVL) 7. Metal Halide lamps 8. Mercury Blended lamps 9.
Compact Fluorescent lamps
1. Incandescent Lamps:- Incandescent lamp has a history of over
a century. The design of the lamp has changed many
times, but still it remains to be the most popular type due to
its simple construction, easy
replacement and cheap cost. Incandescent lamps are available in
wattage rating upto 1500W.
Construction
Fig.a illustrates the construction of a general lighting service
(GLS) lamp. Incandescent
lamps work on the principle that visible light and infrared
radiation are emitted as a result of
heating of the filament wire by a current passing through it.
These emissions become noticeable
above 500C. Tungsten is usually used as the filament material
since it has high melting point.
The diameter of the filament wire is determined by the operating
current and the length of the
filament by the operating voltage. For normal voltages, the
length will be too much and a coiled
coil arrangement is adopted to accommodate the long filament
wire. The filament is mounted on
leads that carry the current.
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(Fig.a Incandescent lamp construction)
To reduce the effect of vibration, additional filament supports
are also employed. The
filament assembly is usually housed in a pear shaped glass bulb.
The bulb diameter for 25W,
40W, 60W and 100W coiled coil type lamps is 60 mm. The size of
the bulb is decided by the
maximum limit for cap temperature. For the same wattage if the
bulb size is reduced, the cap
temperature will increase and eventually result in failure of
mounting accessories.
Inside the lamp it may be vacuum or a filling of inert gas like
argon or krypton with a
small percentage of nitrogen. The choice between vacuum and gas
filling is made after
considering the following factors. Vacuum reduces heat loss and
therefore helps to get the
highest temperature of the filament and hence more light output.
But it also increases the
evaporation rate of tungsten, reducing its life. Filling with an
inert gas reduces evaporation of the
filament material, but conducts heat away from the filament,
reducing the temperature and the
light output. Generally vacuum is used for low wattage lamps
(15W or below) and gas filling for
higher power lamps.
Performance
Incandescent lamp is the most widely used lamp because of its
cheap cost and simple
usage. It is available in a wide range of voltage and wattage
ratings and do not require any
additional accessories for starting or normal operation. They
have excellent colour rendering
index and are used as automobile lamps, panel lamps etc. in
addition to general lighting
purposes.
The major disadvantage of the incandescent lamp is its low
efficacy. A typical 40W lamp
may have an efficacy of around 10 lumens/watt only. Compared to
other types
of lamps, the life is also less - around 1000 hours.
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2. Fluorescent Lamps
Fluorescent lamp is the most widely used discharge lamp. It is
an energy
efficient lamp available in low and medium wattage range making
it suitable for
domestic and commercial lighting purposes.
Construction
The construction of a standard fluorescent lamp is shown in Fig.
It consists of a glass
tube of around 36 mm diameter and a length of 1200 mm. The inner
surface of the tube is coated
with a fluorescent powder - usually phosphor coating. Tungsten
wire electrodes with bi-pin cap
are provided at both ends. There is an electrode shield around
each electrode to reduce the
blackening of the tubes due to deposition of evaporated
tungsten. The tube is filled with an inert
gas such as argon to a pressure of 1.5 to 5 mm of mercury. A
small drop-let of mercury is also
introduced into the tube. During normal operation this mercury
vaporizes and helps to maintain
the discharge.
Operation
Fluorescent lamps are designed for switch start operation. A
typical switch start circuit is
shown in Fig. The starter consists of two bimetallic contacts,
housed in a small glass bulb filled
with a noble gas at low pressure. The contacts are positioned
with a narrow separation between
them. When the normal voltage is applied, it creates a glow
discharge between the bimetallic
contacts and due to heating they bend towards each other. The
contacts touch each other for one
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or two seconds and the current path is completed through the
inductive ballast and the filament
electrodes. These current results in preheating the electrodes.
As the bimetallic contacts touch,
the glow discharge stops and now the contacts cool down and
leave apart to open the circuit. The
sudden break of current will induce a high voltage (600-1500V)
in the ballast and is applied
across -the tube, which in turn trigger the discharge through
the tube. The capacitor, which is
connected across the starter contact, is provided to reduce the
radio interference due to switching
operations. The starter has no function once the lamp is
started.
Like other discharge lamps, fluorescent lamps are also having a
negative temperature
coefficient of resistance. This means the resistance of the tube
decreases when temperature is
increased, resulting in increase of current. Therefore the
ballast is essential during normal
operation also to regulate the lamp current. When the ballast is
connected in series with the
circuit, it regulates the lamp current. The capacitor across the
supply line is for power factor
improvement.
When there is a discharge through the lamp, it produces
radiations mainly in the
ultraviolet region. This radiation is converted to visible
radiation by the phosphor coating on the
inner side of the glass tube.
Performance
The luminous efficiency of the fluorescent lamp is around 75
lumens/watt, which is much
higher than incandescent lamps. The colour rendering index of
this lamp is in the rage of 50-60
and this is sufficient for normal domestic or commercial
lighting. Fluorescent tamps have an
expected life varying from 6000 to 20000 hours. One disadvantage
with this lamp is that the
power factor of the circuit is low (around 0.5), but this
problem can be solved to some extent by
connecting a capacitor across the supply.
Compact Fluorescent Lamps
Compact Fluorescent Lamps (CFLs) are now becoming
very popular. It is a smaller type fluorescent lamp that is
even
more energy efficient. CFLs are available in wattage ratings
of
5W, 7W, 9W, 11W, 13W, 18W, 23W etc. and usually they come
with an adapter having a cap similar to the incandescent
lamp
cap so that the lamp can directly be fixed into an ordinary
lamp
holder. The adapter contains necessary circuits for startup
and
normal operation of the lamp. The principle of operation is
very
similar to ordinary fluorescent lamps, but uses a thin tube.
The
tube may be U shaped or having multiple folds. The light
output
of an 11W CFL is equivalent to that of a 60W incandescent
lamp. This means the energy saving by the use of CFLs is
enormous.
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PRACTICAL: 6
AIM: To study multi meter and perform difference functions of
it. Date: - / /
THEORY:-
A multi meter is an instrument designed to measure two or more
electrical quantities such
as voltage , current & resistance. Basically two types of
multi meters are used: analog & digital.
Now a days mostly digital multi meters are preferred. In
addition with above quantities advance
digital multi meters are used for checking diode, transistor as
well as capacitance measurement.
CONSTRUCTION:-
It consists of moving coil instrument, a no of ammeter shunts,
voltmeter multipliers,
rectifier and selector switches all in single casing. Selection
of particular mode of measurement
required ( i.e. D.C. or A.C. )is effected by function selector
switch & range selector switch can
be set to give a choice of several ranges of current, voltage
& resistance. A suitable protection is
provided to the meter movement against possible overload during
its use.
OPERATION :-
Circuit diagram shows basic circuitry of multimeter for the
measurement of different
electrical quantities. A multiplier provides a high voltage
range while shunt resistance provides
higher current range. A series rectifier make the measurement of
A.C. voltage possible with the
same D.C. meter movement. Thus the same scales are used for both
A.C. & D.C. current &
voltage. For resistance measurement a set of voltage from an
internal battery is applied across the
resistance & resulting current is measured. By Ohms law,
this current being inversely proportional to the resistance, scale
is calibrated to give directly resistance in ohms to use. The
resistance scale is exactly reverse of the current scale i.e.
full scale deflection of pointer
corresponds to maximum current in the range but on the
resistance scale it corresponds to zero
resistance.
Even through the total ckt of multimeter is complex fig. A to
fig. D shows separately the
simplified ckt diagram of different sections of typical
multimeter ckt. Used for various
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measurements. This fig. Is more or less self explanatory.
PROCEDURE :
1. Measure unknown D. C. voltage , A. C. voltage by connecting
multimeter across the ckt. 2. Measure D.C. current and A.C. current
by connecting multimeter in series with ckt. 3. Measure resistance
and capacitance directly with out connecting supply. 4. Check
Transistor & diode on multimeter.
OBSERVATIONS :
1. Value of unknown resistance = R = __________ohms. 2. Value of
voltage across D.C. supply =V1 =___________Volts 3. Value of
voltage across A.C. supply = V2 =___________Volt 4. Value of
unknown capacitor = C = ____________farad. 5. Value of A.C. current
in the ckt = I1 = __________Amps. 6. Value of D.C. current in the
ckt = I2 = __________Amps
APPLICATIONS :
Being portable and compact instrument, multimeters are widely
used in fields, shops &
laboratories to measure a wide range of D.C. Voltage &
currents. A. C. voltage & currents,
resistance and capacitance measurements. It is also used to
check continuity of conductors and
windings.
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PRACTICAL:-1 DATE:-
Aim: To Study different electrical and electronics symbols.
Component name Symbol Symbol
Electrical Wire
Connected Wires
Not Connected Wires
SPST Toggle Switch
SPDT Toggle Switch
Pushbutton Switch
(N.O)
Pushbutton Switch
(N.C)
Earth Ground
Chassis Ground
Digital / Common
Ground
Resistor (IEEE)
Resistor (IEC)
Potentiometer (IEEE)
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Potentiometer (IEC)
Variable Resistor /
Rheostat (IEEE)
Variable Resistor /
Rheostat (IEC)
Trimmer Resistor
Thermistor
Capacitor
Capacitor
Polarized Capacitor