SATHYABAMA

INSTITUTE OF SCIENCE AND TECHNOLOGY

(DEEMED TO BE UNIVERSITY)
Accredited with ‘A++’ Grade by NAAC
Jeppiaar Nagar, Rajiv Gandhi Salai (OMR), Chennai – 600 119, Tamil Nadu. India

SEEB1203 – BASIC ELECTRICAL ENGINEERING

UNIT – I

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 UNIT – I
INTRODUCTION TO ELECTRICAL SYSTEMS

 Basic Elements Resistors, inductors and capacitors

 Domestic Wiring – Wiring Materials & Accessories

 Staircase Wiring

 Fluorescent Lamp

 Types of Earthing

 Benefits of Earthing
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 TYPES OF ELECTRICAL ELEMENTS
 The electric circuit elements can be broadly classified into

1. Active Elements
2. Passive Elements

 The elements that deliver power to a circuit are called active elements. Energy
sources like voltage sources or current sources are the examples of active elements.

 An element that absorbs electrical energy, and cannot supply energy to the circuit is
called a passive element. Examples of passive elements are resistor, inductor and
capacitor.

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 RESISTORS
• A resistor is a two-terminal electrical component that provides electrical resistance.
• There are two basic types of resistors as follows
1. Linear resistor
2. Non-linear resistor
 Linear resistors
The resistors whose values change with change in applied temperature and voltage are known as
linear resistors. There are two types of linear resistors

• Fixed resistors: These resistors have a specific value and these values cannot be changed.

• Variable resistors: These resistors do not have a specific value and the values can be changed
with the help of dial, knob, and screw. Examples rheostat and potentiometer.

 Non-linear resistors: The resistor values change according to the temperature and voltage applied
and
is not dependent on Ohm’s law. 4
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Resistance:
 Resistance may be defined as the property of a substance to oppose the flow
of current through it.
 It is represented by the letter R and the unit is ohm(Ω).
 It is measured by ohm meter. Mega ohms value is measured by using megger.
 According to ohms law
R = V/I
Laws of resistance:
The resistance of a conductor in a circuit depends upon the following:
• It depends upon the resistivity of the material used (ρ)
• The value of resistance directly proportional to the length of the conductor.
(R)
• It is inversely proportional to the area of cross section of the conductor.(A)
• Temperature of the conductor.
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 INDUCTORS
 An inductor is defined as a two-terminal passive electrical element that stores energy in the form of a
magnetic field when electric current flows through it. It is also called a coil, chokes, or reactor.

 It usually consists of a coil of conducting material, typically insulated copper, wrapped into an iron
core either of plastic or ferromagnetic material; thus, it is called an iron-core inductor.

 According’s to Faraday’s law of electromagnetic induction, when an electric current flowing through
an inductor or coil changes, the time-varying magnetic field produces an e.m.f or voltage in it. The
induced voltage or e.m.f. across an inductor is directly proportional to the rate of change of the electric
current flowing through the inductor.

 Inductance: Inductance is defined as the ratio of the induced voltage to the rate of change of
current causing it.

 Unit of Inductance is Henry

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 CAPACITORS
 A capacitor is a two-terminal electrical device that can store energy in the form of an electric charge. It consists of
two electrical conductors that are separated by a distance. The space between the conductors are filled by an
insulating material known as a dielectric such as vacuum , air, mica, paper, ceramic, aluminum etc..

 The ability of the capacitor to store charges is known as capacitance. Its unit is Farad

 The parallel plate capacitor consists of two parallel plates separated by a dielectric. When we connect a DC voltage
source across the capacitor, one plate is connected to the positive end (plate I) and the other to the negative end
(plate II). When the potential of the battery is applied across the capacitor, plate I become positive with respect to
plate II. The current tries to flow through the capacitor at the steady-state condition from its positive plate to its
negative plate. But it cannot flow due to the separation of the plates with an insulating material.
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 An electric field appears across the capacitor. The positive plate (plate I) accumulates positive charges from the
battery, and the negative plate (plate II) accumulates negative charges from the battery. After a point, the
capacitor holds the maximum amount of charge as per its capacitance with respect to this voltage. This time
span is called the charging time of the capacitor.

 When the battery is removed from the capacitor, the two plates hold a negative and positive charge for a certain
time. Thus, the capacitor acts as a source of electrical energy. If these plates are connected to a load, the current
flows to the load from Plate I to Plate II until all the charges are dissipated from both plates. This time span is
known as the discharging time of the capacitor.

 The greater the applied voltage the greater will be the charge stored on the plates of the capacitor. Likewise,
the smaller the applied voltage the smaller the charge.

We know that V is directly proportional to the electric charge.

Where,
Q - Charge, in Coulombs
C - Capacitance, in Farads
V - Voltage, in Volts 1
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 TYPES OF CAPACITORS
• Polarized Capacitors
Those capacitors which are having the specified positive and negative polarities, are called as
polarized capacitors. When these capacitors are used in the circuits, they should be connected in
perfect polarities.

• Non-Polarized Capacitors
The non-polarized capacitors are the ones that does not have specific positive and negative
polarities i.e. they can be connected in the circuits without considering that which lead is
connected to the positive and which one to the negative.

• Variable Capacitors
The variable capacitors are the ones whose capacitance value can altered either electrically or
mechanically. The variable capacitors consist of sets of stationary and movable plates. A shaft is
attached with the movable plates and by rotating the shaft, the capacitance value can be
altered.

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 WIRING MATERIALS AND ACCESSORIES
 Wiring Materials
• Electrical wire is made of materials like copper,
aluminium and silver. As silver is expensive,
mostly copper and aluminium are used in wiring.
• Materials are classified into two types according
to their properties:
– 1. Conducting materials
– 2. Insulating materials

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• Conducting Material
• (a) Copper
– Copper is a good conductor of electricity.
– It is used in wiring materials in cables.
– Its has low resistance and is used for conduction of
electricity at high, medium and low voltage.
– It is used in wiring and cable making.
• (b) Aluminium
– It is light weight and cheaper in comparison to copper.
– Therefore, this type of conducting material is mostly
used in electrical wiring.
– It is silvery–white in colour and it has a soft texture. It is
often used in wiring and making cable .
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• Insulating Materials
– Insulating materials are used for insulating
purpose.
– These types of materials are bad conductors of
current.
– For example rubber, paper, mica, wood, glass and
cotton.

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 Wiring
• a) Switch Accessories
• c) Ceiling Rose
– surface switch • d) Socket outlet
• 1. One-way switch
• e) Plug
• 2. Two-way switch
• 3. Intermediate switch • f) Main switch
– flush switch • g) Miniature Circuit
– bed switch Breaker
– pull or ceiling switch • h) PVC casing-
– push button switch capping wiring
• b) holders • i) Fuses
• j) Cables
• k) Junction Box 17
 Wiring
• (a) Switch Accessories
• A switch is used to make or break an electrical
circuit.
• It is used to switch ‘on’ or ‘off ’ the supply of
electricity to an appliance.
• There are various switches such as
– 1.surface switch
– 2.flush switch
– 3.bed switch
– 4.pull switch
– 5.push button switch 18
1.Surface switch:
• It is mounted on wooden boards fixed on the
surface of a wall.
• It is of three types
• 1. One-way switch
• 2. Two-way switch
• 3. Intermediate switch

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• One-way switch: It is used to control single circuits and lamp
• Two-way switch: It is used to divert the flow of current to
either of two directions. The two-way switch can also be
used to control one lamp from two different places as in
the case of staircase wiring.
• Intermediate switch: This switch has four terminals and four
different connection position. The main function of this switch is to
control a lamp from three or more different places, along with
ordinary two-way switch. Generally this switch is used in double
stair case wiring or corridor wiring. This switch is also known as
four-way switch.
• 2) Flush switch: It used for decorative purpose . The switches are used where
good appearance is required. The switches are fixed in flush with the wall
and do not project out.These switches are also known as “Piano Type
Switches”. 20
• 3) Bed switch: As the name indicates, it is used to switch ‘on’ or ‘off’ the
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4)Pull switch: These switches are operated with
a single pull of the cord, for the on and off
position. These are also used in bedroom and
bathroom. These switches are fixed near the
ceiling and hence these are also known as
“Ceiling Switches”.
5)Push Button switch: These switches are used
to control the electric bell and indicating
lamps etc. When the push button is pressed,
the circuit is completed and the bell or lamp is
switched on. The supply to bell or lamp is
switched off as the push button is released.

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• (b) Holders
• It is used to hold the lamp required for lighting
purpose.
• May be of Bakelite or Brass exteriorwith
porcelain interior.
• Types
• 1. Pendant holder
• 2. Batten holder

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• (c) Ceiling rose
• These are fixed on walls near the ceiling. Normally these
are used to provide tapping to the pendent lamp holder,
ceiling fan and fluorescent tube etc through the flexible
wire.
• (d) Socket Outlet
• The sockets have insulated base with moulded base
having two or three or five terminal sleeves.
• The two terminal sleeves having same cross-section are
used to connect phase and neural wire where as the
third having greater cross-section is used to connect
with earth wire.
• These are made for 5 amps and 15 amps load.
• Two-pin sockets are also available, in which only phase
and neutral wires are connected. These are available in 5-
amp capacity.
• (e) plug
• The plugs are also having moulded three pins of 2
brass or any electrically conducting material. 5
• (f) Main switch
• As the name indicates that this switch is used to switch
“on or off” the main supply.
• In other words these switches are used to control the
whole supply
for a house, office and machine.
• In single-phase circuit I.C.D.P. main switches are
used,whereas in three-phase circuits I.C.T.P. main
switches are used to control the supply.
• 1) I.C.D.P. Switch: Iron Clad Double Pole main switch is
used in single-phase supply circuits. These are available
in 15 Amp, 30 Amp, 60 Amps and 100 amperes current
rating.
• 2) I.C.T.P Switch: Iron Clad Triple Pole main switches are
used to control the three phase supply circuit. These are
available in 15 Amp, 30 Amp, 60 Amp,100 Amp, 150 Amp
and 250 Amps current rating.
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• g)Miniature Circuit Breaker (MCB)
• A miniature circuit breaker is an electro-
mechanical safety device which operate
and disconnect the circuit supply, when
the current drawn from the circuit
increases to a pre- determined value.
• An MCB will normally operates at 1.25
times its rated current value.
• It can be reset, by simply lifting its
operational knob, where as the fuse has
to replace its fuse wire.

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• (h) PVC casing-capping wiring
• PVC capping is done in order to cover the wires. It
includes casing also.
• This casing-capping wiring is also known as open
wiring, as it is done outside the wall.
• (i) Fuses
• It is the most common and important type of
safety device used for domestic and commercial
installations.
• Used to isolate the circuit in the event of any
overload or fault.
• Fuse base is porcelain and fuse wire is made up of
copper or tin or lead.
• These cut-outs are made of porcelain in current
rating of 15 to 28
300 amperes..
• (j) Cables
• It consists of a conductor made of copper or aluminium
surrounded by insulation and a sheath.
• Cables used for domestic wiring
– Vulcanised Indian Rubber
– Poly Vinyl Chloride
– Tough Rubber Sheathed
– Cab Tyre Sheathed
– Lead Sheathed
– Weather Proof
• (k) Junction Box
• Used to join some conductors and provide different paths for
different conductors.

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 Types of
• Cleat Wiring
Wiring
• Batten Wiring
• Casing- caping
wiring
• Conduit wiring

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• Cleat wiring
– VIR conductors are supported in porcelain cleats.
– Procelain cleats are spaced every 60cm .
– VIR or PVC insulated wires are used as conductors
– This wiring is suitable for temporary installation where
cost in the main criteria but not the appearance.
– Advantage – Faults can be identified easily
– Disadvantage-
• maintaintance cost is high,
• lot of dust may collect over the wire,
• no protection from mechanical injury, fire or gas.

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• Batten Wiring
 These wiring are not suitable for outdoor ,they can be use for Damp
climate
 Single or doubleor threecore cables are used to be laid on straight
teak wooden batten.
 They are clipped on wooden battens With Brass clips(link or
joint )are
fixed on to walls or ceilings by flat head screws.
• Not suitable for outdoor
wiring
•Disadvantages:
Humidity, smoke, steam
Advantages:
• Easy installation etc directly affect on
• Cheap in material wires.
• Heavy wires are not
cost
• Appearance is recommended for this
better. wiring scheme.
• Only suitable for below
250 V.
• High risk of fire.
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• Wooden casing- capping wiring
– Used for residential buildings
– Consists of rectangular wooden blocks called casing, made
from first
class seasoned teak wood or any other wood free from any
defect.
– Has two grooves into which the wires are laid.
– Casing at the top is covered by means of capping which is
rectangular strip of wood of the same width as that of casing
and is screwed to it.
– Advantage:
• Sufficient mechanical protection is given to the cable.
– Disadvantage:
• High cost
• More risk of fire 33

•
• Conduit wiring
• VIR conductors run in metallic tubes are called
conduit wiring.
– Surface Conduit
• Wiring system with conduit on the surface of the wall
• In this wiring method, they make holes on the
surface of wall on equal
distances and conduit is installed then with the help of
plugs
– Concealed conduit
• Layout of the wiring done under the plaster of the wall of
the building
• It is the most popular, beautiful, stronger and common
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electrical wiring system nowadays.
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• Advantages of concealed wiring
– Safe
– Better appearance
– No risk of fire
– No risk of damage of cable
insulation
– Safe from humidity, smoke,
steam, etc.
– No risk
• Disadvantages of concealed
wiring
– Expensive
3
– Installation not easy 6
 Staircase
Wiring
• Staircase wiring is a common multi-way
switching or two-way light switching
connection;
• one light two switches wiring.
• Here one lamp is controlled by two switches
from two different positions.
• That is to operate the load from separate
positions such as above or below the staircase,
from inside or outside of a room, or as a two-way
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bed switch, etc
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39
 Fluorescent
•
Tubes
Works on the principle
discharge phenomena
of low pressure mercury vapour

• Converts ultra violet rays into visible rays with

the help of phosphor coated on the glass tube.
• Inner Parts
– Filament
– Phosphor coated tubes ( When mercury vapour
discharge takes place, the
UV rays is converted in to Visible rays with the help of
phosphor coating)
– Mercury vapour + Inert gas (Argon)
• Outer Parts
– Choke or Ballast 40
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• Switch is ON -full voltage comes across the lamp
and as
well as across the starter through the ballast.
• At that instant, no discharge happens.
• At that full voltage first the glow discharge is
established in the starter. This is because the
electrodes gap in the neon bulb of starter is much
lesser than that of the fluorescent lamp.
• Gas inside the starter gets ionized due to this full
voltage and heats the bimetallic strip----- causes to
bend the bimetallic strip to connect to the fixed
contact.
• Current starts flowing through the touched contacts
of the neon bulb of the starter --- Short circuited-
So less voltage across the neon bulb---no more gas
discharge ---hence the bimetallic strip gets cool
and breaks away from the fixed contact.
• Current gets interrupted --- a large voltage surge
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comes across the inductor(ballast) or choke.
• Surge voltage applied across the filament– heats
up the filament coil or electrode
• As the filament is oxide coated, a sufficient
amount of electrons is produced, and they rush
from the negative electrode or cathode to the
positive electrode or anode due to this strong
electric field.
• During the movement of free electrons, the
discharge process gets established.
– Free electrons are derived from the
electrodes, and they get accelerated by
the electric field applied.
– Kinetic energy of the free electrons is
converted into the excitation energy of the
gas atoms.
– The excitation energy of the gas atoms gets
converted into the radiation.
• The discharge of mercury atoms
produces ultraviolet radiation which
in turn excites the phosphor powder 43
 EARTHIN
 Earthing is the Process ofGconnecting metallic bodies of all the
electrical apparatus and equipment to the earth by a wire having
negligible resistance.

 The process of transferring the immediate discharge of the

electrical energy directly to the earth by the help of the low
resistance wire is known as the electrical earthing.

 copper wires are generally used as earthing lead, copper strips are
preferred for high installation as it can carry higher values of fault
current due to its wider area.
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EARTHIN
G

45
EARTHIN
G

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 IMPORTANCE OF
EARTHING
The earthing is essential because of the following reasons

 The earthing protects the personnel from the short

circuit current.
 The earthing provides the easiest path to the flow of short
circuit current even after the failure of the insulation.
 The earthing protects the apparatus and personnel from the
high voltage surges and lightning discharge.

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 Why is an Earthing
Necessary?
 It keeps people safe by preventing electric shocks

 It prevents damage to electrical appliances and devices by

preventing excessive current from running through the
circuit

 It prevents the risk of fire hazards that could otherwise be

caused by the current leakage
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 Basic needs of
 To Earthing
protect human lives as well as provide safety to
electrical devices and appliances from leakage current.
 To keep voltage as constant in the healthy phase (If fault
occurs on any one phase).
 To Protect Electric system and buildings form lighting.
 To serve as a return conductor in electric traction system
and communication.
 To avoid the risk of fire in electrical installation systems.

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 TYPES OF
Plate EarthingEARTHING
Pipe Earthing
Rod Earthing
Wire Earthing

Pipe Earthing and Plate Earthing are considered to

be the best as they have low value of Earth
resistance.

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PIPE
EARTHING

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 PIPE
 EARTHING
A galvanized steel 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 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).
 Alternate layers of Charcoal Powder and salt are arranged 15cm
around the pipe
. The Charcoal Powder and salt decrease the earth resistance. They
increase
the dampness and moisture.
 Earth Pipe is covered with cement concrete for protection from
Mechanical damage.
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PLATE
EARTHING

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 PLATE
 In this method ofEARTHING
Earthing, earth plate is provided at the
bottom of the earth rod in addition to the arrangement done
in pipe earthing.
 In plate earthing system, a plate made up of copper with
dimensions 60cm x 60cm x 3.18mm (i.e. 2ft x 2ft x 1/8 in) or
galvanized iron (GI) of dimensions 60cm x 60cm x 6.35 mm
(2ft x 2ft x ¼ in) is buried vertical in the earth (earth pit) which
should not be less than 3m (10ft) from the ground level.
 Charcoal Layers are placed immediately after the plate.

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 ROD EARTHING
• In this system of earthing 12.5mm diameter solid rods of copper
16mm diameter solid rod of GI or steel or hollow section of
25mm GI pipe of length not less than 3 meters are driven
vertically into the earth
• In order to increase the embeded length of electrode under
the ground, which is some time necessary to reduce the earth
resistance to desired value more than one rod section are
hammered one above the other.
• This system of earthing is suitable for area which are sandy in
character .
• This system of earthing is very cheap 55
 STRIP OR WIRE EARTHING
• In this system of earthing strip electrode of cross section not less
than 25mm into 1.6mm of copper or 25mm * 4mm of GI or steel
are burried in horizontal trenches of minimum depth of 0.5m
• If round conductor are used their cross sectional area shall not be
smaller than three if copper is used and 6mm2 if GI or steel is
used.
• The length of buried conductor shall be sufficient to give the
required earth resistance (about 0.5Ωto 1.5Ω). It shall however be
not less than 15 m
• The electrode shall be as widely distributed as possible in a
single straight or circular trenches radiating from a point
• This type of earthing is used in rocky soil earth bed because at56
THANK YOU

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