Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Manonmaniam Sundaranar University,

Directorate of Distance & Continuing Education,

Tirunelveli - 627 012 Tamilnadu, India

OPEN AND DISTANCE LEARNING (ODL) PROGRAMMES

(FOR THOSE WHO JOINED THE PROGRAMMES FROM THE ACADEMIC YEAR 2023–2024)

M.Sc. Physics
Course Material
Home Electrical Installation
JSPH21
Prepared
By

Dr. Lavanya Raveendran

Department of Physics
Manonmaniam Sundaranar University
Tirunelveli - 12
Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

B.Sc. Physics I Year

HOME ELECTRICAL INSTALLATION

Syllabus

HOME ELECTRICAL INSTALLATION

Learning Objective: The students will get knowledge on electrical instruments,
installations and domestic wiring techniques with safety precautions and servicing.

UNITS COURSE DETAILS

SIMPLE ELECTRICAL CIRCUITS: charge, current, potential
difference, resistance – simple electrical circuits – DC ammeter,
voltmeter, ohmmeter – Ohm’s law – difference between DC and AC –
UNIT-I
advantages of AC over DC – electromagnetic induction - transformers
– inductors/chokes – capacitors/condensers – impedance – AC
ammeter, voltmeter –symbols and nomenclature
TRANSMISSION OF ELECTRICITY: production and transmission
of electricity – concept of power grid – Series and parallel connections

UNIT-II – technicalities of junctions and loops in circuits –transmission losses

(qualitative) – roles of step-up and step-down transformers – quality of
connecting wires – characteristics of single and multicore wires
ELECTRICAL WIRING: different types of switches – installation of
two way switch – role of sockets, plugs, sockets - installation of meters
– basic switch board – electrical bell – indicator – fixing of tube lights
UNIT-III and fans – heavy equipment like AC, fridge, washing machine, oven,
geyser, jet pumps – provisions for inverter – gauge specifications of
wires for various needs
POWER RATING AND POWER DELIVERED: conversion of
electrical energy in to different forms – work done by electrical energy
– power rating of electrical appliances – energy consumption –
UNIT-IV
electrical energy unit in kWh – calculation of EB bill – Joule’s heating
– useful energy and energy loss – single and three phase connections –
Measures to save electrical energy – energy audit

1
Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

SAFETY MEASURES: insulation for wires – colour specification for

mains, return and earth – Understanding of fuse and circuit breakers –
types of fuse: kit-kat, HRC, cartridge, MCB, ELCB – purpose of earth
UNIT-V
line – lighting arrestors – short circuiting and over loading – electrical
safety – tips to avoid electrical shock – first aid for electrical shock –
fire safety for electric current
1. Wiring a House: 5th Edition by Rex Cauldwell, (2014).
2. Black and Decker Advanced Home Wiring, 5th Edition: Backup Power -
Panel Upgrades - AFCI Protection - "Smart" Thermostats, by Editors of
TEXT BOOKS Cool Springs Press, (2018).
3. Complete Beginners Guide to Rough in Electrical Wiring: by Kevin
Ryan (2022).

2
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

UNIT I
SIMPLE ELECTRICAL CIRCUITS

CHARGE

Electric Charge is the basic property of the material that is responsible for

the electrostatic property of the material. Electric charge, which can be

positive or negative, occurs in discrete natural units and is neither created

nor destroyed.

Many fundamental, or subatomic, particles of matter have the property of

electric charge. For example, electrons have negative charge and protons

have positive charge, but neutrons have zero charge. The negative charge

of each electron is found by experiment to have the same magnitude,

which is also equal to that of the positive charge of each proton. Charge

thus exists in natural units equal to the charge of an electron or a proton, a

fundamental physical constant.

1. Magnitude: Electric charge exists in discrete quantities, and the

smallest unit of charge is the charge of an electron or proton, which

is approximately 1.6×10−19 coulombs (C). Charges can be positive or

negative. The charge of an electron is considered negative, while the

charge of a proton is considered positive.

2. Conservation: Electric charge is conserved in isolated systems. This

means that the total electric charge within a closed system remains

constant over time. In any process, the total amount of positive

charge must equal the total amount of negative charge.

3
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

3. Additivity: Electric charge is additive. The total charge of a system is

the algebraic sum of the charges of its constituents. For example, if

two objects carry charges of +3C and -2C respectively, the net

charge of the system is +1C.

4. Quantization: Electric charge comes in discrete packets. The charge

of any object is always an integer multiple of the elementary charge,

e, which is the charge of a single proton or electron.

5. Attraction and Repulsion: Charged objects exert forces on each

other according to Coulomb's law. Like charges repel each other,

while opposite charges attract each other. The magnitude of the

force is directly proportional to the product of the magnitudes of the

charges and inversely proportional to the square of the distance

between them.

6. Mobility: Electric charge can move through conductive materials,

such as metals or electrolytes, under the influence of an electric field.

This movement of charge is what constitutes an electric current.

Current

When charge is flowing in a circuit, current is said to exist. An electric

current is the physical phenomenon of the displacement or flow of an

electric charge, usually of electrons, by means of a conductive material. In

order for there to be an electric current, the electrons furthest from the

nucleus of an atom of a certain material must detach and circulate freely

through a conductor in an electrical circuit.

4
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Mathematically, current describes the rate at which charge flows through

a conductor.

The intensity of the electric current is determined by the amount of charge

passing through a conductor in a unit of time. The intensity is measured in

coulombs per second (C/s), which is equivalent to one ampere (A).

1. Direction: Electric current flows from the positive terminal to the

negative terminal in a circuit. This convention is opposite to the

actual movement of electrons, which flow from negative to positive.

2. Magnitude: The magnitude of electric current is measured in

amperes. One ampere is equivalent to the flow of one coulomb of

charge per second.

3. Resistance: The opposition to the flow of electric current in a

material is known as resistance. It is measured in ohms (Ω). Ohm's

law states that the current flowing through a conductor between two

points is directly proportional to the voltage across the two points

and inversely proportional to the resistance between them.

4. Voltage: Electric current flows in response to a potential difference, or

voltage, between two points in a circuit. Voltage is measured in volts

(V) and represents the energy per unit charge.

5. Power: The rate at which electric energy is transferred by an electric

circuit is known as electric power. It is measured in watts (W) and

can be calculated as the product of voltage and current (P = VI) or

as the square of current multiplied by resistance (P = I2R).

5
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

6. Conductivity: The ability of a material to conduct electric current is

termed as conductivity. Materials with high conductivity, such as

metals, allow electric current to flow easily, while insulators have low

conductivity, impeding the flow of current.

7. Temperature Dependence: The resistance of a material typically

increases with temperature. This property is used in devices like

thermistors and resistive heating elements.

Potential Difference

Electric potential difference is also known as voltage. The electric potential

difference is the work done per unit

charge to move a unit charge from one

point to another in an electric field. The

energy possessed by Electric charges is

known as electrical energy. A charge with

higher potential will have more potential energy, and a charge with lesser

potential will have less potential energy. The current always moves from

higher potential to lower potential. The difference in these energies per unit

charge is known as the electric potential difference. In order to create

electricity and the flow of current, a potential difference is always required,

which is maintained by a battery or a cell.

Electric Potential Difference Formula

Vxy= Vx – Vy = [Wx – Wy]/q

The SI Unit of Electrical potential difference is the same as the electric

potential, i.e, Voltage or Volts.

6
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Resistance

Electrical resistance is defined as the obstruction by the material in the

flowing of the current through the material. Thus, the higher the resistance

the lower the amount of current passes through it. it is the property of a

material that tells us about the flow of the current through the material.

The substances that easily conducts the electric current are called

conductors and they have very low electrical resistance, on the contrary,

the substance that does not easily conducts the electric current are called

insulators and they have very high resistance.

Georg Simon Ohm was a German physicist who gave a law which is known

as Ohm’s law. According to Ohm’s law, the current flowing through a

conductor is directly proportional to the potential difference across it.

V∝I

V = IR

Factors Affecting Resistance

There are various factors that affect the resistance of the conductor, these

factors are:

• Material of the Conductor

As resistance is the physical property of a material, different

materials can have different values of resistance. Conductors have

less resistance compared to semiconductors and insulators.

• Length of the Conductor

By the relation between resistance and resistivity, the resistance of

the conductor is directly proportional to the length of the conductor

7
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

i.e., the longer the length of the wire the more resistance it will offer in

the circuit.

• Cross-Sectional Area of the Conductor

As the relation between Specific Resistance or resistivity and

Resistance is given by R = (ρ×L)/A. In which, the resistance R of the

conductor and cross-sectional area A of the conductor are inversely

proportional to each other i.e., if one increases the other should

decrease if all other things remain constant. Thus, by increasing

cross sectional area of the conductor the resistance of it decreases.

• Temperature of the Conductor

The resistance of the conductor and temperature both are directly

proportional to each other i.e., as the temperature of the conductor

rises, its resistance increases due to variations in its resistivity.

Simple Electrical Circuits

A simple electric circuit can consist of a battery (or other energy source), a

light bulb (or other device that uses energy), and conducting wires that

connect the two terminals of the battery to the two ends of the light bulb. In

the scientific model for this kind of simple circuit, the moving charged

particles, which are already present in the wires and in the light bulb

filament, are electrons.

A simple electric circuit typically consists of a few basic components:

1. Power Source: This provides the energy for the circuit to operate. It

could be a battery, a generator, or a power supply from an outlet.

8
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

2. Conductors: These are materials that allow the flow of electric

current. Wires are the most common conductors used to connect the

various components of a circuit.

3. Load: The load is the component of the circuit that consumes

electrical energy to perform a task. It could be a light bulb, a motor,

or any other device that converts electrical energy into another form,

such as light, motion, or heat.

4. Switch: A switch is a device that can open or close a circuit,

controlling the flow of electricity. It can be manually operated or

automatically controlled.

Electrons are negatively charged. The battery pushes the electrons in the

circuit away from its negative

terminal and pulls them towards the

positive terminal. Any individual

electron only moves a short

distance. While the actual direction of the electron movement is from the

negative to the positive terminals of the battery, for historical reasons it is

usual to describe the direction of the current as being from the positive to

the negative terminal (the so-called ‘conventional current’).

The energy of a battery is stored as chemical energy. When it is connected

to a complete circuit, electrons move and energy is transferred from the

battery to the components of the circuit. Most energy is transferred to the

light globe (or other energy user) where it is transformed to heat and light

9
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

or some other form of energy. A very small amount is transformed into

heat in the connecting wires.

DC Ammeter

A DC ammeter is an instrument which is used to measure the amount of

DC current flowing in a circuit. The DC ammeter has a scale which

represents current in ampere. The instrument got its name ammeter from

ampere meter because it measures the amount of current in ampere.

For measuring large amounts of DC current, we

can use DC ammeters. In cases where the

current flowing in the circuit is very small, that is

in the range of milliampere or microampere,

then we should use an ammeter in that range.

A DC ammeter should always be connected in series with the circuit for

measuring DC current. In terms of a circuit diagram, the ammeter is

represented by a circle with the letter A. In this case, consider the following

circuit with a resistor R and a voltage source.

In order to measure the DC current, the DC ammeter should always be

connected in a series combination. Modern DC ammeters can come in

analog or digital forms, with digital ones offering more precision and often

additional features like data logging or connectivity options.

Voltmeter

The voltmeter is used to measure the electrical potential difference

between two points of an electrical circuit. It is used to measure both direct

and alternating electric current. A voltmeter is a current-controlled device,

10
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

which means it needs a current to function. To measure the potential

difference, the voltmeter is connected in parallel with the electrical circuit.

A voltmeter has high resistance so that it

consumes less current to function. That is why

the Current consumption by the voltmeter

doesn’t affect the circuit current. In the parallel

connection, the high resistance of the voltmeter

gives almost the same impedance as the impedance of the load

resistance. The voltage in the parallel circuit and the voltage between the

voltmeter and the load become the same. Thus, the voltmeter measures

the voltage of the electrical circuit. They are essential tools for electrical

testing and troubleshooting in various applications, from household

electronics to industrial machinery.

Ohmmeter

An ohmmeter can be defined as,

it is one kind of electronic device

mainly used for calculating

electrical resistance of a circuit,

and the unit of resistance is ohm.

Electrical resistance is a calculation of how much an object resists allowing

the flow of current through it. There are different types of meters available

with different sensitivity levels such as micro, mega and milli-ohmmeters.

The micro-ohmmeter is used for calculating very low resistances with high

precision at specific test currents, and this ohmmeter is used in bonding

contact applications.

11
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

The working principle of ohmmeter is, it comprises of a needle and two test

leads. The needle deflection can be controlled with the battery current.

Initially, the two test leads of the meter can be shorted together to

calculate the resistance of an electrical circuit. Once the two leads of the

meter are shorted, then the meter can be changed for appropriate action

in a fixed range. The needle comes back to the highest point on the meter

scale, and the current in the meter will be highest.

The classification of this meter can be done based on the application in

three types namely series type ohmmeter, shunt type ohmmeter, and

multi-range type ohmmeter.

Ohm’s Law

Ohm’s law states that the voltage across a conductor is directly

proportional to the current flowing through it,

provided all physical conditions and

temperatures remain constant.

Hence, according to Ohm’s Law, the current

flowing through the conductor is directly

proportional to the voltage across the circuit, i.e. V ∝ I. Thus, as Ohm’s Law

provides the basic relation between the voltage applied and current

through the conductor, it is considered as the basic law which helps us in

dealing electric circuit. Ohm’s Law states that the current follows a linear

relationship with voltage.

12
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Ohm’s Law is one of the fundamental laws of electrostatics which state

that, the voltage across any conductor is directly proportional to the

current flowing in that conductor. We can define this condition as,

V∝I

Removing the proportionality sign,

V = RI

where R is the proportionality constant and is called the Resistance of the

material. The resistance of the material is calculated as,

R = V/I

Resistance is measured in Ohms. It is denoted by the symbol Ω.

Ohm’s Law holds good when

physical conditions like

temperature and others are

constant. This is because of

the fact that the current

flowing through the circuit varies by changing the temperature. Therefore,

in such cases when physical factors like temperature come into play,

Ohm’s law violates. For example, in the case of a Light bulb, where

temperature increases when the current flowing through it rises. Here,

Ohm’s Law doesn’t follow.

Vector Form of Ohm’s Law

The relation between current and voltage is established by, Ohm’s law, and

its vector form is,

13
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

𝑗⃗ = 𝜎 𝐸⃗⃗

Where,

• 𝑗⃗ is Current Density vector,

• 𝐸⃗⃗ is Electric Field vector, and

• 𝜎 is conductivity of material.

Resistivity

The hindrance faced by the electrons while moving in any material is

called the resistivity of the material.

Let a resistor of a length of ‘l’ and the cross-sectional area of ‘A’ has a

resistance be R. Then we know,

Resistance is directly proportional to the length of the resistor, i.e. R ∝ l, . . .(1)

Resistance is inversely proportional to the cross-section area of the

resistor, i.e. R ∝ 1/A . . .(2)

combining eq. (1) and eq.(2)

R = ρl / A

Where ρ is the proportionality constant called coefficient of resistance or

resistivity.

Experimental Verification of Ohm’s Law

The key K is closed initially and the

rheostat is adjusted such that the

reading in ammeter A and voltmeter V

is minimum. The current is then

14
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

increased in the circuit by adjusting the rheostat, and the current at

various values of the rheostat and their respective voltage is recorded. Now

for different values of voltage(V) and current(I) and then calculate the

ratio of V/I. After calculating all the ratios of V/I for different values of

voltage and current, we notice that the value is almost constant. Now

plotting a graph of the current against the potential difference we get a

straight line. This shows that the current is directly proportional to the

potential difference and its slope is the resistance of the wire.

Difference between DC And AC

DC refers to Direct Current in which there is no change in the Direction of

Current flow. Hence, the major difference between AC and DC Current is

the electric current flows only in One Direction in a stable voltage in DC

Current. One of the major uses of DC is to charge batteries and supply

power for electrical devices. In the DC circuit, electrons emerge from the

negative side and move towards the positive side. The basic source of DC

is produced by photovoltaic cells, batteries, or electrochemical cells. Some

of the examples of DC include flashlights, mobile phone batteries, electric

vehicles, and more.

The term AC refers to Alternating Current in Physics, which is highly

preferred electric power for office, household equipment, and more. The

critical difference between Alternating Current and Direct Current lies in the

Direction in which electric charges flow. In AC, electrons continuously

change their Directions from forward to backward periodically. As

compared to DC Current, it’s easy to generate and transport AC across

15
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

large distances. Hence, Alternating Current is widely used in buildings,

powerhouses, and more.

16
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Advantages of AC Over DC

There are following advantages of alternating current over direct current

1. Long distance transmission can be done at high voltages, thereby

reducing the current, and consequently losses in transmission.

2. Generation of alternating current is easier, and so is transmission.

3. Generation and transmission can be at high voltages, so the fact that it

can be stepped up and down from level to other easily and efficiently.

4. Cable sizes for AC are quite lighter in the comparison of D.C.

5. Power loss in AC is less as compared to DC during transmission.

6. AC can be easily converted into DC.

7. Voltage at which power can be sent can be higher in AC. These levels

can be dangerous in DC.

Electromagnetic Induction

Electromagnetic induction is the production of electromotive force

otherwise known as voltage across an electrical conductor where the

magnetic field changes. For the discovery of induction, Micheal Faraday

was awarded this credit in 1831. Here, Faraday's law of induction was

described by Maxwell in mathematical terms. Take for example any

conductor and place it in a specific position. Here the process of

electromagnetic induction will let the conductor vary keeping the

magnetic field stationary.

Principle of Electromagnetic Induction states that the emf induced in a

loop due by a changing magnetic flux is equal to the rate of change of the

magnetic flux threading the loop. When it comes to the principle of

electromagnetic induction, it will enable the transformers, motors, electric

17
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

generators and other rechargeable items such as wireless communication

devices or electric toothbrushes to adopt the principle. Apart from that,

your rice cooker works by using induction. Now let's learn how induction

cooktops are heated by using induced current.

Faraday's Law is the equation that mathematically describes

electromagnetic induction. It

states that voltage (EMF) will be

induced when there is a change in

the magnetic environment of a

coiled wire. Many ways were

discovered by Faraday for this to

happen. For example: by changing

the magnetic field strength by moving a magnet over a coil of wire or by

moving a coil of wire through a magnetic field, etc. The voltage (EMF)

generated can be explained by the help of the following equation,

EMF=−NΔ(BA)Δt

Where, N is the number of turns in the wire. Δ(BA) is the difference in

magnetic flux. Δt is the difference in time. Faraday's methods found the

change in flux and can be expressed with the help of this equation. But

because of Lenz's Law, this equation is negative, as it requires the change

in magnetic flux to be reproduced in equal strength and the opposite

direction by the wire. For many electromagnetic applications around the

world, including cars, Faraday's Law is important. For example, in a car the

ignition system, the internal combustion engine takes only 12 volts from the

battery and ramps it up to 40000 volts. The use of magnetic flux through a

18
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

wire is stated by Faraday's Law of electromagnetic induction. The magnetic

flux is defined as:

Here ΦB is the magnetic flux

dA is the surface of the element

B is the magnetic field.

According to Faraday's Law of induction, when there is a change in the flux

through the surface, the wire coil obtains the electromagnetic force. The

rate of variation in magnetic flux, which is surrounded by the circuit, is

equal to the induced electromotive force in a closed circuit as per the Law.

With the help of Lenz's Law, the direction of the electromotive force is given.

It states that when an electric current is induced by changing the

magnetic field of a source, it will always create a counterforce opposing

the force induced in it. The Law explains such phenomena as

diamagnetism and the electrical properties of inductors.

With the help of variation in magnetic flux through the surface of a wire

loop, an EMF can be generated.

19
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• The magnetic field B variations.

• The wire loop is misshapen, and the surface Σ changes.

• The alignment of the surface dA changes

Transformers

Transformer is the simplest device that is used to transfer electrical energy

from one alternating-current circuit to another circuit or multiple circuits,

through the process of electromagnetic induction. A transformer works on

the principle of electromagnetic induction to step up or step down

voltage. Transformer either increases AC voltage (Step-up transformer) or

decreases AC voltage (Step-

down transformer). Transformer

which is normally utilized in the

transmission and distribution of

alternating current power is

fundamentally a voltage control

device. Transformer are used for a

wide range of purposes, including increasing the voltage from electric

generators to enable long-distance transmission of electricity and

decreasing the voltage of conventional power circuits to run low-voltage

devices like doorbells and toy electric trains.

A transformer is a static electrical device that transmits AC power from

one circuit to another at a constant frequency, but the voltage level may

be changed, implying the voltage can be increased or decreased

depending on the requirement.

20
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

There are primarily two types of transformers based on the operating

voltage. The following are some of them:

• Step-down Transformer: The primary voltage is converted to a lower

voltage across the secondary output using a step-down transformer.

The number of windings on the primary side of a step-down

transformer is more than on the secondary side. As a result, the

overall secondary-to-primary winding ratio will always be less than

one. Step-down transformer are used in electrical systems that

distribute electricity over long distances and operate at extremely

high voltages to ensure minimum loss and economical solutions.

Step-down transformer are used to change high-voltage into low-

voltage supply lines.

• Step-up Transformer: The secondary voltage of a step-up

transformer is raised from the low primary voltage. Because the

primary winding has fewer turns than the secondary winding in this

sort of transformer, the ratio of the primary to secondary winding will

be greater than one. Step-up transformer are frequently used in

electronics stabilizers, inverters, and other devices that convert low

21
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

voltage to a significantly higher voltage. A step-up transformer is

also used in the distribution of electrical power. For applications

connected to power distribution, high voltage is necessary. In the

grid, a step-up transformer is used to raise the voltage level prior to

distribution.

Transformer Types based on Core Material

Different types of Transformers are used in the power and electronics

industries, depending on the core materials, which are

• Iron Core Transformer

• Ferrite Core Transformer

• Toroidal Core Transformer

• Air Core transformer

The fundamental principle of how the transformer functions are mutual

induction between the two coils or Faraday’s Law of Electromagnetic

Induction. Only alternating current can be used because mutual induction

between the two windings requires an alternating flux.

A transformer majorly consists of three parts:

Core

The transformer core serves as a support for the winding. Additionally, it

offers a magnetic flux flow channel with minimal resistance. As seen in the

image, the winding is looped around the core. To cut down on losses in a

transformer, it has a laminated soft iron core. Core composition is

determined by variables including operational voltage, current, and power,

22
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

among others. The core diameter is negatively correlated with iron losses

and directly correlated with copper losses.

Windings

The copper wires that are wound over the transformer core are known as

windings. Copper cables are used because Copper’s high conductivity

reduces transformer loss because resistance to current flow lowers as

conductivity rises. And copper’s high degree of ductility makes it possible

to produce incredibly thin wires out of it.

The two basic types of windings are. windings for the primary and

secondary coils. The primary winding is the group of winding turns that

receive supply current. The number of winding turns from which output is

derived is known as secondary winding. Insulation coating agents are used

to insulate the primary and secondary windings from one another.

Insulation Agents

Transformer require insulation to keep the windings apart and prevent

short circuits. This makes mutual induction easier. Transformer stability

and durability are influenced by insulation agents. In a transformer, the

following are employed as insulating mediums: Insulating fluid, tape, Paper,

and Lamination made of wood.

Tank

A transformer main tank serves two purposes:

• The core and the windings are protected from the elements, such as

rain and dust.

23
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• It functions as an oil container as well as a support for all other

transformer attachments.

Transformer Oil

The majority of the huge transformer are submerged in oil. The transformer

oil adds insulation between the conductors, improves heat dissipation

from the coils, and has fault-detecting capabilities. Transformer oil is

typically made of hydrocarbon mineral oil.

The induced emf or voltage (εs) in the secondary with Ns turns is then

calculated.

εs = –Ns x dϕ/dt ……(1)

In addition, the alternating flux generates a reverse emf in the main. This is

it.

εp = –Np x dϕ/dt ……(2)

And for an ideal transformer, εp=Vp

By approximation, if the secondary is an open circuit or the current drawn

from it is modest, εs=Vs.

The voltage across the secondary coil is Vs. As a result, Equations (1) and

(2) may be written as

Vs = –Ns x dϕ/dt ……(3)

Vp = –Np x dϕ/dt ……(4)

From Equations (3) and (4), we have

Vs / Vp = Ns / Np ……(5)

24
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

The above equation is known as Transformer Equation or Transformer

Formula.

The following three assumptions are used to get the previous relationship:

• The primary and secondary coils’ electrical resistances are

insignificant.

• The flux connectivity to both the primary and secondary coils is the

same, or very few fluxes escape from the core.

• The secondary current is insignificant.

Efficiency of Transformer

The efficiency of a transformer is also known as commercial efficiency. It is

represented by the letter ‘η’. The efficiency of a Transformer is described as

the ratio of output (in W or kW) to input (in W or kW).

Hence, the efficiency of transformer may be expressed as follows:

Efficiency (η) = (Power Output / Power Input)

The above equation can be used for an ideal transformer in which there

are no transformer losses and all input energy is transferred to the output.

As a result, the following equation is mostly used if transformer wastes are

taken into account and the efficiency of the transformer is evaluated

across the practical states.

Efficiency = ((Power O/P) / (Power O/P + Losses)) × 100%

or

25
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Efficiency = (Power i/p – Losses) / Power i/p × 100 = 1− (Losses/ i/p Power)

× 100

Energy Losses in a Transformer

We used an ideal transformer in the previous equations (without any

energy losses). However, some energy losses do occur in actual

transformer for the following reasons:

• Flux Leakage: Because some flux leaks from the core, not all flux

generated by the primary coil make it to the secondary coil. This

occurs as a result of the core’s inadequate design or the presence of

air holes in the core. It is possible to lower it by wrapping the primary

and secondary coils over each other. It can also be lowered if the

core is well-designed.

• Windings Resistance: Because the wire used for the windings has

some electrical resistance, energy is wasted as a result of the heat

generated in the windings. These are mitigated in high current, low

voltage windings by utilizing thick wire with a high conductive

substance.

• Eddy Currents: The alternating magnetic flux creates eddy currents

in the iron core, resulting in energy losses through heating. By using a

laminated core, the impact is decreased.

• Hysteresis Loss: In each AC cycle, the alternating magnetic field

reverses the magnetization of the core. The loss of energy in the core

occurs as heat owing to hysteresis loss, which is minimized by

employing a magnetic material with a low hysteresis loss.

26
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Application of Transformer

The following are some of the most common uses for transformer:

1. Increasing or reducing the voltage level in an AC circuit to ensure the

correct operation of the circuit’s various electrical components.

2. It stops DC from flowing from one circuit to another.

3. It separates two separate electric circuits.

4. Before transmission and distribution can take place, the voltage level

at the electric power plant must be increased.

Inductors/Chokes

Inductors are electrical components that create a magnetic field when an

electric current is passed through them. Inductors are most commonly

coil-like structures in electronic circuits that are mostly used to reduce or

control electrical spikes in a circuit. There are various types of inductors

including, Iron Core and Air Core Inductors. Its main functions include

controlling signals and storing energy.

Inductor is a passive electronic component which stores energy in the form

of a magnetic field. In

simple words, an inductor

consists of just a wire loop

or coil that is used to

control electric spikes by

temporarily storing energy and then releasing it back into the circuit

through an electromagnetic field.

27
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Inductance is directly proportional to the number of turns in the coil. It also

depends on other things such as the radius of the coil and the type of

material around which the coil is wound.

Inductor is made of a wire whose property is inductance, i.e. it opposes the

flow of current. The inductance of the wire increases when the number of

turns is increased. Inductance is represented by the alphabet ‘L’ and it is

measured in Henry. The formula of Inductance can be given by the ratio of

flux and the current in the circuit. It is represented as:

L = Φ/I

where,

• L is Inductance

• Φ is Flux

• I is Current

Unit of inductance is 1 henry (H). The unit is symbolized by the letter H. An

inductor be a passive electronic component that is more often used to

gain energy in form of magnetic field. This is a measure of amount of

energy stored in an inductor, which depends on the amount of inductance.

The voltage (V) across an inductor is directly proportional to the rate of

change of current (I) flowing through it:

V(t) = L dI(t)/dt

Where:

• V(t) is the inductive voltage at time t

28
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• L is the inductor inductance

• dI(t)/dt denotes the speed of change of current over time ‘t’

Construction of an inductor consists of a coil that is formed by twisting wire

into circles wrapped around a core and is used to store energy in a

magnetic field while electricity runs through it.

Different Types of Inductors

The different types of inductors include the following:

• Iron Core Inductor

• Coupled Inductor

• Air Core Inductor

• Iron Powder Inductor

• Variable Inductor

• Ferrite Core Inductor

• Choke

Choke

A choke inductor, more commonly called a “choke,” is an electrical

component used chiefly for choking off or blocking alternating current (AC)

while allowing direct current (DC) to pass with relatively little resistance.

This sort of inductor has a high impedance to AC signals, so it effectively

filters or isolates them from circuits.

Chokes are most commonly used in electronic circuits for filtering and

noise suppression as well as to separate AC and DC signals.

29
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Controlling Signals

Controlling signals is one of the primary functions of an inductor. It is used

to handle electric or digital signals to get specific results, like changing

frequency and filtering them.

The frequency of the current passing in an inductor plays a vital role in

controlling the signals within an inductor. It is helpful in blocking AC and

allows the DC to pass through it. This is possible because higher frequency

symbols are passed easily inside an inductor thus allowing DC currents to

pass through them easily.

Storing Energy

In an inductor, the core is used to store energy. Inductors store energy in

the form of magnetic fields. Energy storage is the process of adding and

maintaining power to a system or gadget for future use. This aids in

managing, balancing, and controlling the energy consumption of many

systems, including buildings and automobiles.

Capacitors/Condensers

The capacitor is an electric component that has the ability to store energy

in the form of electrical charges that creates a potential difference, which

is a static voltage, much like a small rechargeable battery. The most basic

design of a capacitor consists of two parallel conductors (Metallic plate),

separated with a dielectric material. When a voltage source is attached

across the capacitor, the capacitor plate gets charged up. The metallic

plate attached to the positive terminal will be positively charged, and the

plate attached to the negative terminal will be negatively charged.

30
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Types of Capacitors

Film Capacitors: Film capacitors are the ones that use plastic film as the

dielectric medium. They are available in nearly any value and voltages up

to 1500 volts. They range from 10% to 0.01% in any tolerance. Additionally,

film condensers arrive in a combination of shapes and case styles. There

are two types of film condensers, radial type lead, and axial type lead.

Ceramic Capacitors: Ceramic capacitors are the ones that use ceramic

as the dielectric material. It is used in high-frequency circuits such as

audio to RF. In ceramic capacitors, one can develop both high capacitance

and low capacitance by altering the thickness of the ceramic disc.

Electrolytic Capacitors: Electrolytic capacitors are the ones that use the

oxide layer as the dielectric material. It has a wide tolerance capacity.

There are mainly two types of electrolytic capacitors, tantalum, and

aluminum. They are available with working voltages of up to approximately

500V, but the maximum capacitance values are not available at high

voltage, and higher temperature units are available but are rare.

Variable Capacitor: Variable capacitors mostly use air as the dielectric

medium. A Variable Capacitor is one whose capacitance can be

mechanically adjusted several times. For example, this form of the

capacitor is used to set the resonance frequency in LC circuits to change

the radio to match impedance in antenna tuner devices.

The accumulation of charges in the conductors causes a potential

difference across the capacitor. The amount of charge accumulated is

called the charge holding capacity of the capacitor. This charge holding

31
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

capacity is what is known as capacitance. The accumulated charge in the

capacitor is directly proportional to the voltage developed across the

capacitor:

Q ∝V

Q = CV

C = Q/V

C is the constant of proportionality, also called the capacitance of a

capacitor. The unit of capacitance is Farad(F) - 1 coulomb per volt.

The value of capacitance depends upon the physical features, area of the

capacitor plates ‘A’, distance between the plates ‘d’, and the permittivity of

the dielectric medium ‘ε’.

C=ε×(A/d)

The energy is stored in joules and is equal to half of the capacitance times

the square of the capacitor’s voltage. E=1/2 (C×V2)

Factors affecting Capacitance

Surface Area: The surface area of the two plates affects the capacitance

value. Higher the value of the surface area, the higher the capacitance.

Distance: The distance between the plates affects the value of the

capacitance. Lower the value of distance, the higher the capacitance.

Dielectric Medium: The type of material separating the two plates called

"the dielectric." The higher the dielectric's permittivity, the higher the

capacitance value.

32
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Uses of a Capacitor

The capacitors have both electrical and electronic applications. They are

used for several things such as filters, energy storage systems, engine

starters, signal processing devices, etc. Capacitors are used for storing

energy, which can be used by the device for temporary power outages

whenever they need additional power. Capacitors are used for blocking DC

current after getting fully charged and yet allow the AC current to pass

through the circuit of a circuit. Capacitors are used as sensor for several

things like measuring humidity, fuel levels, mechanical strain,

etc. Capacitors can be used in a time-dependent circuit. This could be

connected to any LED or loudspeaker system, and it’s likely that any

flashing light/regular beeping uses a timing capacitor.

Impedance

Electrical impedance, measure of the total opposition that a circuit or a

part of a circuit presents to electric current. Impedance includes both

resistance and reactance. The resistance component arises from collisions

of the current-carrying charged particles with the internal structure of the

conductor. The reactance component is an additional opposition to the

movement of electric charge that arises from the changing magnetic and

electric fields in circuits carrying alternating current. Impedance reduces to

resistance in circuits carrying steady direct current.

The magnitude of the impedance Z of a circuit is equal to the maximum

value of the potential difference, or voltage, V (volts) across the circuit,

divided by the maximum value of the current I (amperes) through the

33
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

circuit, or simply Z = V/I. The unit of impedance, like that of resistance, is the

ohm. Depending on the nature of the reactance component of the

impedance (whether predominantly inductive or capacitive), the

alternating current either lags or leads the voltage. The reciprocal of the

impedance, 1/Z, is called the admittance and is expressed in terms of the

unit of conductance, the mho unit (ohm spelled backward).

Capacitive Reactance

When a capacitor is connected to a circuit with AC supply, there is no

simultaneous change in the capacitor voltage and capacitor current. The

potential difference across the capacitor is dependent on the AC power

supply. Below is the graph illustrating the change in current and potential

difference. The current is maximum when the potential difference is at zero.

The capacitive reactance for a capacitor with capacitance C connected in

the circuit along with AC power supply is given as:

XC =1/(2πfC)

Where,

• XC is the capacitive reactance

• f is the frequency of AC power supply

• C is the capacitance

Inductive Reactance

In inductive reactance, the current across an inductor change when

potential difference develops across it. The potential difference and rate of

change of current are proportional to each other.

34
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

The inductive reactance for an inductor with inductance L connected in the

circuit along with AC power supply is given as:

XL =2πfL

Where,

• XL is the inductive reactance

• L is the inductance of the inductor

• f is the frequency of the alternating current

In phasor terms, impedance Z is represented as a combination of

resistance R and reactance X as:

Z=R+jX

Where reactance X is a combination of Inductive XL and capacitive XC

X = XL + XC

Difference between Resistance and Reactance

Parameter Resistance Reactance

Variation of current Resistance is a property of Reactance is a property of

an electrical component an electrical component

which opposes the flow of which opposes the change

current in current

Power dissipation Resistance leads to power Reactance does not lead to

dissipation power dissipation

Denoted by Resistance is denoted by R Reactance is denoted by X

35
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

AC Ammeter, Voltmeter

AC electromechanical meter movements come in two basic

arrangements: those based on DC movement designs, and those

engineered specifically for AC use.

Permanent-magnet moving coil (PMMC)

meter movements will not work correctly

if directly connected to alternating

current, because the direction of needle

movement will change with each half-

cycle of the AC.

Permanent-magnet meter movements,

like permanent-magnet motors, are

devices whose motion depends on the

polarity of the applied voltage.

In order to use a DC-style meter movement such as the D’Arsonval design,

the alternating current must be rectified into DC.

This is most easily accomplished through the use of devices called diodes.

We saw diodes used in an example circuit demonstrating the creation of

harmonic frequencies from a distorted (or rectified) sine wave. Without

going into elaborate detail over how and why diodes work as they do, just

remember that they each act like a one-way valve for current to flow.

The arrowhead in each diode symbol points in the permitted direction of

current flow.

36
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Arranged in a bridge, four diodes will serve to steer AC through the meter

movement in a constant direction

throughout all portions of the AC cycle:

Another strategy for a practical AC

meter movement is to redesign the

movement without the inherent

polarity sensitivity of the DC types.

This means avoiding the use of

permanent magnets. Probably the

simplest design is to use a

nonmagnetized iron vane to move the

37
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

needle against spring tension, the vane being attracted toward a

stationary coil of wire energized by the AC quantity to be measured.

Electrostatic attraction between two metal plates separated by an air gap

is an alternative mechanism for generating a needle-moving force

proportional to applied voltage.

This works just as well for AC as it does for DC. The forces involved are very

small, much smaller than the magnetic attraction between an energized

coil and an iron vane, and as such these “electrostatic” meter movements

tend to be fragile and easily disturbed by physical movement.

But, for some high-voltage AC applications, the electrostatic movement is

an elegant technology.

If nothing else, this technology possesses the advantage of extremely high

input impedance, meaning that no current need be drawn from the circuit

under test. Also, electrostatic meter movements are capable of measuring

very high voltages without need for range resistors or other, external

apparatus.

38
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

When a sensitive meter movement needs to be re-ranged to function as

an AC voltmeter, series-connected “multiplier” resistors and/or resistive

voltage dividers may be employed just as in DC meter design.

Symbols and Nomenclature

39
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Unit II
TRANSMISSION OF ELECTRICITY

Production and Transmission of Electricity

There are three stages of electric power supply; generation, transmission

and distribution. Power plants are the most commonly used energy

conversion technology to create electricity from primary energy. Common

types of power plants include coal, nuclear, and hydro.

Electrical power generation is based on Faraday's law of mutual

electromagnetic induction. In an electrical circuit moving (for example

rotating) so that it cuts magnetic lines of force, an electromotive force

(emf) is generated that is proportional to the rate at which unit lines of

force are cut. The magnetic field is generated by direct current excitation

current in a primary circuit, produced by rectifying alternate current from a

subsidiary generator geared mechanically to the main alternator.

According to Lenz's law, the direction of the current set up in the subsidiary

circuit is such that electromagnetic interaction between the two circuits

tends to hinder the motion setting up the emf in the secondary circuit.

Most electricity is generated from power plants that utilize steam turbines

to convert mechanical (also called kinetic) energy into electrical energy.

The rotation of the turbine spins the rotor, a set of magnets or

electromagnets, inside the core of the stator, a coil of wires. This rotational

movement generates a changing electromagnetic field, or voltage, which

creates an electric current when run through a conductor. The electric

40
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

current can then be delivered from the plant via power lines to provide

electricity to homes and businesses.

Power plant output is measured in megawatts, and a megawatt (M.W.) is

one million watts. Electrical output, the amount of electricity generated,

varies depending on the size of a power plant. The average coal-fired plant

generates about 750MW of electricity.

The rotation of the turbines can be fueled from several sources including

wind, water, and heat.

Thermal power plants

Where does most electricity come from? Currently, most of the world’s

electricity is produced by thermal power plants that burn fossil fuels such

as coal, oil, or natural gas to heat water and produce steam. The steam

then drives a turbine connected to an electric generator, converting the

mechanical energy into electricity.

Hydroelectric power plants

These large power plants can use the energy from flowing or falling water

to drive a turbine connected to a generator. The kinetic energy of the

moving water is converted into mechanical energy in the turbine and then

into electrical energy in the generator.

Wind turbines

Wind turbines convert the kinetic energy in wind into electrical energy. As

the wind turns the blades of the turbine, the mechanical energy generated

drives an electric generator.

41
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Solar power plants

Solar power plants convert sunlight directly into electricity using

photovoltaic (PV) cells. When sunlight hits the PV cells, electrons are

knocked loose and flow through the cells, generating an electric current.

Nuclear power plants

In nuclear power plants, nuclear reactions release energy in the form of

heat, which is then used to produce steam from water. The steam drives a

turbine connected to an electric generator, converting the mechanical

energy into electricity.

Currently, nuclear power plants are powered by fission reactions (splitting

atoms), but scientists are working hard to generate consistent electricity

using fusion reactions (combining atoms).

Geothermal power plants

These power plants generate electricity by tapping into the Earth’s internal

heat. They use hot water or steam from the Earth’s interior to produce

electricity to drive a turbine connected to an electric generator.

Biomass power plants

Biomass power plants burn organic materials such as wood, agricultural

waste, and animal waste to produce steam. The steam drives a turbine

connected to an electric generator, which generates electricity by

converting the mechanical energy into electricity.

42
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Ocean energy

This includes both wave power, which uses the energy from waves to

generate electricity, and tidal power, which uses the energy from rising and

falling tides.

Transmission

After electrical power is generated, it is transmitted over distances using

transmission lines. Transmission lines are constructed between

transmission substations located at electric generating stations.

Transmission lines may be supported overhead on towers or they may be

underground. They are operated at high voltages. They send out large

amounts of electrical power and extend over considerable distances.

Electrical energy, after being produced at generating

stations (TPS, HPS, NPS, etc.) is transmitted to the consumers for utilization.

This is due to the fact that generating stations are usually situated away

from the load centers. The network that transmits and delivers power from

the producers to the consumers is called the transmission system. This

43
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

energy can be transmitted in AC or DC form. Traditionally, AC has been

used for years now, but HVDC (High Voltage DC) is rapidly gaining

popularity.

Single Line Diagram of AC Power Transmission System

A typical single line diagram that represents the flow of energy in a

given power system is shown below:

44
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Electric power is commonly (or usually) generated at 11 kV in generating

stations in India and Europe. While in some cases, generation voltage

might be higher or lower. Generating machines, to be used in power

stations, are available between 6 kV to 25 kV from some big

manufacturers. This generating voltage is then stepped up to 132kV, 220kV,

400kV or 765kV etc. Stepping up the voltage level depends upon the

distance at which power is to be transmitted. Longer the distance, higher

will be the voltage level. Stepping up of voltage is to reduce the I 2R losses

in transmitting the power (when voltage is stepped up, the current

reduces by a relative amount so that the power remains constant, and

hence I2R loss also reduces). This stage is called as primary transmission.

he voltage is the stepped down at a receiving station to 33kV or

66kV. Secondary transmission lines emerge from this receiving station to

connect substations located near load centers (cities etc.).

The voltage is stepped down again to 11kV at a substation. Large industrial

consumers can be supplied at 11kV directly from these substations. Also,

feeders emerge from these substations. This stage is called as primary

distribution.

Feeders are either overhead lines or underground cables which carry

power close to the load points (end consumers) up to a couple of

kilometers. Finally, the voltage is stepped down to 415 volts by a pole-

mounted distribution transformer and delivered to the distributors. End

consumers are supplied through a service mains line from distributors.

The secondary distribution system consists of feeders, distributors and

service mains.

45
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Different Types of Transmission Systems

1. Single phase AC system

2. Two phase AC system

3. Three phase AC system

4. DC system

Electric power transmission can also be carried out using underground

cables. But, construction of an underground transmission line generally

costs 4 to 10 times than an equivalent distance overhead line. However, it is

to be noted that, the cost of constructing underground transmission

lines highly depends upon the local environment. Also, the cost of

conductor material required is one of the most considerable charges in a

transmission system. Since conductor cost is a major part of the total cost,

it has to be taken into consideration while designing. The choice of

transmission system is made by keeping in mind various factors such as

reliability, efficiency and economy. Usually, overhead transmission system

is used.

Main Elements of a Transmission Line

Due to the economic considerations, three-phase three-wire overhead

system is widely used for electric power transmission. Following are the

main elements of a typical power system.

▪ Conductors: three for a single circuit line and six for a double circuit

line. Conductors must be of proper size (i.e. cross-sectional area).

This depends upon its current capacity. Usually, ACSR (Aluminium-

core Steel-reinforced) conductors are used.

46
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

▪ Transformers: Step-up transformers are used for stepping up the

voltage level and step-down transformers are used for stepping it

down. Transformers permit power to be transmitted at higher

efficiency.

▪ Line insulators: to mechanically support the line conductors while

electrically isolating them from the support towers.

▪ Support towers: to support the line conductors suspending in the air

overhead.

▪ Protective devices: to protect the transmission system and to

ensure reliable operation. These include ground wires, lightening

arrestors, circuit breakers, relays etc.

▪ Voltage regulators: to keep the voltage within permissible limits at

the receiving end.

Concept of Power Grid

Electricity grid consists of four major components.

Individual generators

Variety of facilities generate electricity, including coal and natural gas

power plants, hydroelectric dams, nuclear power plants, wind turbines, and

solar panels.

Transmission lines

Transmission lines are necessary to carry high-voltage electricity over long

distances and connect electricity generators with consumers.

47
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Distribution

The distribution network is simply the system of wires that picks up where

the transmission lines leave off. These networks start at the transformers

and end with homes, schools, and businesses. The transmission grid

comes to an end when electricity finally gets to the consumer.

Grid

The electricity grid has grown and changed immensely since its origins in

the early 1880s, when energy systems were small and localized. During this

time, two different types of electricity systems were being developed: the

DC, or direct current, system, and the AC, or alternating current, system.

Despite a campaign by Thomas Edison to promote the direct current

system, businessman George Westinghouse and inventor Nikola Tesla won

the support of electric companies for the alternating current system, which

had the distinct advantage of allowing high voltages to be carried long

distances and then transformed into lower voltages for customer use.

Distribution grid refers to the final stage of the electrical grid which

distributes electricity to homes, industry, and other end users. Distribution

both delivers the electric power to every user on the grid and once

delivered, it also reduces power to safe customer-usable levels. The

transformers used for distribution can be seen on poles for overhead lines,

or on the ground for underground lines, called pads.

Distribution stations are either built within buildings or outdoors, but always

in an enclosed area. The design of these stations depends on economic,

environmental, legal and social factors.

48
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

The electricity grid is a dynamic system. It has changed and evolved

rapidly over the last century to accommodate new technologies, increases

in electricity demand, and a growing need for reliable, diverse sources of

electricity.

As technology changes and better options become available, significant

improvements could be made to the electricity grid.

For example, energy storage technologies could allow electricity to be

stored for use when demand for electricity peaks or increases rapidly,

increasing efficiency and reliability.

The interconnected and complex nature of the electricity grid delivers

several benefits, including:

• Reliability: Since the grid is an enormous network, electricity can be

deployed to the right places across large regions of the country. The

large transmission network allows grid operators to deal with

anticipated and unanticipated losses, while still meeting electricity

demand.

• Flexibility: The electricity grid allows a power system to use a

diversity of resources, even if they are located far away from where

the power is needed. For example, wind turbines must be built where

the wind is the strongest; the grid allows for this electricity to be

transmitted to distant cities.

• Economic competition: Because the grid allows multiple generators

and power plants to provide electricity to consumers, different

generators compete with each other to provide electricity at the

49
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

cheapest price. The grid also serves as a form of insurance –

competition on the grid protects customers against fluctuations in

fuel prices.

Series and Parallel Connections

A series circuit is a circuit in which resistors or loads are connected end to

end so that the circuit will have only one path through which electric

current flows. Thus, when a number of resistors are connected in series, the

50
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

effective resistance (total resistance in the circuit) is gotten by adding the

individual resistance algebraically. That is to say, if we have resistors with

resistance R1, R2, R3 …Rn connected in series, then;

Reff = RT = R1 + R2 + R3 + …Rn.

In series connections, the same current flows across all the branches of the

circuits, but different voltage across it thus making the resistors to have

different voltage across them. Each resistor or load will experience a

voltage drop. The applied voltage is equal to the sum of the voltage

drop across the different parts of the circuit. Voltage drop is proportional to

the resistance current being the same throughout the circuit. When loads

are connected in series, the loads will tend to have a common switch. This

kind of connection is employed in school halls, street lights.

With simple parallel circuits, all components are connected between the

same two sets of electrically common points, creating multiple paths for

the current to flow from one end of the battery to the other:

Series circuit connections are common and greatly employed in electrical

equipment. The tube filaments in small radios are usually in series. Current

51
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

controlling devices are always connected in series with the device that

they protect. Fuses are connected in series with the device they protect,

Automatic house-heating equipment has a thermostat, electromagnetic

coils, and safety cut-outs connected in series with a voltage source etc.

Rules regarding Series Circuits:

• Voltage drops add to equal total voltage.

• All components share the same (equal) current.

• Resistances add to equal total resistance.

Advantages of Series Connection

• Less size of wire cable is required in series wiring.

• We use to protect the circuit to connect fuse & circuit breakers in series

with other appliances.

• Series circuit don’t get overhead easily due to high resistance when

more load added in the circuit.

• The lifespan of battery in series circuit is more as compared to

parallel.

• It is most simple method of electrical wiring and fault can be easily

detect and repair as compared to parallel or series-parallel wiring.

Disadvantages of Series Circuit

• The break in the wire, failure or removal of any single lamp will break

the circuit and cause all of the others to stop working as there is only

one single path of current to flow in the circuit.

52
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• If more lamps are added in series lighting circuit, they will all be

reduced in brightness. because voltage are shared in series circuit. If

we add more loads in series circuit, the over voltage drop is

increases which is not a good sign for electrical appliances

protection.

• Series Wiring is “ALL or NONE” type wiring means all the appliances

will work at once or all of them will disconnect if fault occurs at any

one of the connected devices in series circuit.

• High supply voltage is needed if we need to add more load (light

bulbs, electric heaters, air conditioner etc.) in the series circuit. For

example, If five, 220V Lamps are to be connected in Series, then

Supply Voltage would have to be: 5 x 220V = 1.1kV.

• The overall series circuit resistance increases (and current

decreases) when more load added in the circuit.

• According to future need, only those electrical appliances should be

added in the current series circuit if they have the same current

rating as current are same at each point in series circuit. However,

we know that electrical appliances and devices i.e. light bulbs, fan,

heater, air conditioner etc have different current rating, therefore,

they cannot be connected in series circuit for smooth and efficient

operation.

Parallel Circuits:

Resistors, loads are said to be connected in parallel when the end of each

of the resistors or loads have a common point or junction and the other

53
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

ends are also connected to a common point or junction. Such circuits are

known as parallel circuits.

Unlike the series circuit connection, when finding the total (effective)

resistance in a parallel circuit, the reciprocal of the individual resistance is

taken. Thus, when a number of resistances are connected in parallel, the

reciprocal of the effective resistance is given by the arithmetic or algebraic

sum of the reciprocal of the individual resistance.

1/Reff or 1/RT = 1/R1 + 1/R2 + 1/R3 …1/Rn.

Parallel circuit connection have the same voltage flowing across all

the branches of the circuits. Different resistors have their individual

currents.

Advantages of Parallel Circuit

• Each connected electrical device and appliance are independent

from others. This way, switching ON / OFF a device won’t affect the

other appliances and their operation.

54
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• In case of break in the cable or removal of any lamp will not break

the all circuits and connected loads, in other words, other

lights/lamps and electrical appliances will still work smoothly.

• If more lamps are added in the parallel lighting circuits, they will not

be reduced in brightness (as it happens only in series lightning

circuits). Because voltage is same at each point in a parallel circuit.

In short, they get the same voltage as the source voltage.

• It is possible to add more light fixture and load points in parallel

circuits according to future need as far as the circuit is not

overloaded.

• Adding additional devices and components wont increase the

resistance but will decrease the overall resistance of the circuit

especially when high current rating devices are used such as air

conditioner and electric heaters.

• parallel wiring is more reliable, safe and simple to use.

Disadvantages of Parallel Connections

• More size of cable and wire is used in parallel lighting wiring circuit.

• More current needed when additional light bulb added in the parallel

circuit.

• Battery runs out quicker for DC installation.

• The parallel wiring design is more complex as compare to series

wiring.

Rules regarding Parallel Circuits:

55
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• All components share the same (equal) voltage.

• Branch currents add to equal total current.

• Resistances diminish to equal total resistance.

Series - Parallel Circuits

As the circuit is combination of series and parallel, We can not simplify the

current, voltage, resistance and power by simple Ohm’s Law. We have to

apply different theorems like Norton’s, Thevenin’s, maximum power transfer

theorem etc. or will simplify the circuit in basic series and parallel circuits to

find all those quantities.

Most common of household wiring installation nowadays using this wiring

method.

This circuit is neither simple series nor simple parallel. Rather, it contains

elements of both. The current exits the bottom of the battery splits up to

travel through R3 and R4, rejoins, then splits up again to travel through

R1 and R2, then rejoin again to return to the top of the battery.

Main differences between series and parallel connections

56
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

S No. Series Circuit Parallel Circuit

Current (I) Currents are same in each point in Currents are additive in

series circuit: parallel circuit:

I1 = I2 = I3 =…. In I1 + I2 + I3 +…. In
Voltage (V) Voltages are additive in series Voltages are same in each

circuit: point in parallel circuit:

V1 + V2 + V3 +…. Vn V1 = V2 = V3 =…. Vn
Resistance (R) Resistances are additive in Series Resistances are divided

& to Find (R) Circuit: when more load added in

R1 + R2 + R3 + …Rn = Reff = RT the circuit.

1/RT = 1/R1 + 1/R2 + 1/R3 …1/Rn

or
I = G1 + G2 + G3 + … Gn
To Find Current I = V1/R1 = V2/R2 = V3/R3 = Vn/Rn I = V1/R1 + V2/R2 + V3/R3 +

(I) Vn/Rn

To Find Voltage V = I1R1 + I2R2 + I3R3 + … InRn V = I1R1 = I2R2 = I3R3 = … InRn

(V)

To Find Electric P = I2R1 + I2R2 + … I2Rn P = V2/R1 + V2/R2 + … V2/Rn

Power (P) or or
P = V12/R1 + V22/R2 + … Vn2/Rn P = I12R1 + I22R2 + … In2Rn
Paths of flow of Only one path Two or more paths

Electric Current

Brightness of Dimmer if added more bulbs (P = V x Brighter due to same

Bulb I) voltages

If breaks occur Whole circuit is useless The rest of the circuit will still

in the circuit work

Battery Status Battery Discharge slowly (Ah Rating Battery Discharge Quickly

of Battery) (Battery Ah Time & Currents)

57
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Applications Used to protect the circuit while Used in most of household

connecting fuses and circuit electrical wiring installations

breakers in series with the

connected appliances

Technicalities of Junctions and Loops in Circuits

Circuit comes from the word circle. A circuit is a collection of real

components, power sources, and signal sources, all connected so current

can flow in a complete circle.

Closed circuit – A circuit is closed if the circle is complete, if all currents

have a path back to where they came from.

Open circuit – A circuit is open if the circle is not complete, if there is a gap

or opening in the path.

Short circuit – A short happens when a path of low resistance is

connected (usually by mistake) to a component. The resistor shown below

is the intended path for current, and the curved wire going around it is the

short. Current is diverted away from its intended path,

sometimes with damaging results. The wire shorts out the

resistor by providing a low-resistance path for current

(probably not what the designer intended).

Make or Break – You make a circuit by closing the current path, such as

when you close a switch. Breaking a circuit is the opposite. Opening a

switch breaks the circuit.

58
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Elements – The term elements means

"components and sources."

Symbols – Elements are represented in

schematics by symbols.

Lines – Connections between elements are drawn as lines, which we often

think of as "wires". On a schematic, these lines represent perfect

conductors with zero resistance. Every component or source terminal

touched by a line is at the same voltage.

Dots – Connections between lines can be indicated by dots. Dots are an

unambiguous indication that lines are connected.

Node – A junction where or more elements connect is called a node.

59
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Since lines on a schematic represent perfect zero-resistance conductors,

there is no rule that says lines from multiple elements are required to meet

in a single point junction. We can draw the same node as

a distributed node like the one in the schematic below. These two

representations of the node mean exactly the same thing.

Branch – Branches are the connections between nodes.

Loop – A loop is any closed path going through circuit elements. a loop

can visit (pass through) a node only one time. It is ok if loops overlap or

contain other loops.

Mesh – A mesh is a loop that has no other loops inside it.

Ground – The reference node is often referred to as ground.

60
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Transmission Losses (Qualitative)

When electrical currents travel on a network, some energy is dissipated in

the form of heat, and is “lost” due to the electrical resistance in the network.

This energy is known as network losses. The transmission network is the

high voltage network which carries electricity from generation to the

distribution network, or to large electrical users which are directly

connected to the transmission network. The places where the transmission

and distribution networks connect are called grid supply points1 (GSP).

Distribution losses happen between a GSP and a household.

Due to network losses, generators must produce more energy to ensure

that demand users receive all the energy they need. Rules are in place to

make sure that the cost of transmission losses is recovered from all

transmission network users in their transmission network charges.

The three main types of losses in transmission lines are:

1. Resistive

2. Capacitive

3. Inductive

Most conductors, like power lines, are not perfect. This means that when

power travels down cables, some of it is lost. Typically, electrical cables

carrying higher voltages incur less line losses. This can be understood

better by considering the formula for power: Power = current x voltage.

61
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Resistive, capacitive and inductive line losses do not only occur in high-

voltage transmission, but also in low and medium voltage scenarios. All

three of these types of line losses are caused, in part, by heat loss from

power being impeded along power lines. Alternating current (AC) power

suffers from all three of these line losses, regardless of voltage, and direct

current (DC) power only suffers from some types of resistive power losses.

AC power is compatible with transformers, it’s more easy and cost effective

to step AC voltages up or down, as well as isolate power for safety. This

makes the infrastructure to transmit AC power generally cheaper, and

that’s why transmission systems are usually high-voltage AC. High-voltage

AC is usually what power grids are transmitting, DC power is more often

associated with low-voltage distribution.

A lower voltage also implies a higher current, and a higher current

produces more heat and energy losses. So, if we compare a high-voltage

AC transmission system to a low-voltage DC distribution system, the high-

voltage AC transmission is more efficient. This is essentially where the

misconception that DC power is less efficient came from: because people

associate DC power with lower voltages, they might assume DC power is

just less efficient.

However, if we were to compare AC and DC distribution at the same

voltage level (high or low), AC power would suffer from all three types of

line losses, while DC power would only suffer from certain types of resistive

power losses, making AC power ultimately less efficient at all voltage

levels.

62
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Resistive Line Losses

Resistive power loss is when electrical power is lost due to the resistance of

a conductor, like a power line. There are no perfect conductors, except for

superconductors. Aside from those, all conductors have a bit of electrical

resistance.

This is why, when either type of electricity meets any resistance, electrical

power is converted into thermal power (or heat). Thus, energy is lost in the

form of heat.

Capacitive Line Losses

Capacitive losses only occur in AC circuits, not DC circuits, and are a type

of reactive power loss. Like resistive power losses, reactive power losses

come in the form of heat.

When two conductors run parallel to each other, they create a

“capacitance” with each other, especially if they’re close together. So, with

this in mind, consider these two conductors: power lines and the earth.

Every electrical cable has a “parasitic capacitance” with the earth.

“Parasitic”, in this context, means something unwanted, like a parasite.

As for capacitance, capacitance occurs when two conductors are close

enough together that they can store energy in an electric field. In the case

of power transmission, capacitance occurs between the earth and power

lines (our two conductors).

When energy is stored in an electric field, there is some loss of power,

which is known as capacitive line loss. Capacitive effects don’t occur in DC

circuits because the voltage of a DC circuit is steady.

63
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Inductive Line Losses

Inductive line losses are the third type of line loss experienced by AC

circuits, including power lines. Inductive losses are essentially power losses

that occur when a magnetic field is built and collapsed repeatedly, on a

wire.

To explain this further, an inductor is an electrical component that stores

energy in a magnetic field. When AC power alternates, it charges up a

parasitic inductor (created by the wire), creating a magnetic field that

collapses and changes direction repeatedly. When power is stored in these

magnetic fields, it doesn’t make it to power loads, which makes it a type of

line loss. Additionally, each time these parasitic inductors charge up and

down, power is lost in the form of heat. The lost power that’s stored up in

these magnetic fields and lost in the form of heat, is considered an

inductive line loss.

Direct current (DC) power doesn’t have an alternating frequency, so its

voltage is steady. This means it doesn’t charge a parasitic inductor up and

down repeatedly, like AC power, and so it doesn’t incur inductive power

losses.

Roles Of Step-Up and Step-Down Transformers

A transformer is a passive component that transfers electrical energy

among AC circuits. There is a part called the core in a transformer in which

any fluctuating current gives rise to magnetic flux, thereby inducing an

electromotive force around the core. More importantly, the transformers

are widely used to change the levels of AC voltage and for this application,

64
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

they are categorized into two types that are namely step up and step

down transformers. Sometimes, there are power losses along many power

distribution lines due to fluctuation in wire resistances. To prevent such

problems, we put forth a transformer that can control the output voltage

thereby overcoming the fluctuations. This is why step up and step-down

transformers are used. Let us dive deeper into it.

A step-up transformer is a device which makes long-distance

transmission of electrical energy economically efficient; it converts low

voltage AC into high voltage AC, which decreases the loss of energy during

transmission. In the process of voltage conversion, the output current is

decreased so that the input and output power of the system would be

equal. Step-up transformers are mostly used in electrical equipment to

create a balance between the low input voltage and required high voltage

such as microwave ovens, inverters, stabilizers, and so on.

Step-Down Transformer: The type of transformer having output voltage

less than the input voltage is called a step-down transformer. It converts

high voltage AC into low voltage AC, keeping the input and output power

the same. High voltage AC running in the transmission lines is converted

into the Low Voltage AC by step down transformer for the successful

operation of our home appliances. For example, the doorbell operates at

16V, while our power circuit carries 230V – 110V, so this balance between

input and output voltage is managed by a step-down transformer; it

reduces the voltage from 220V to 16V.

The major construction revolves around the two parts, the core and the

windings.

65
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Core: A transformer consists of a soft iron core and two inductive windings.

The core is made up of soft iron with a collection of laminated metal sheets

to facilitate the windings; laminated metal sheets are used to reduce the

eddy current loss.

Windings: It has two windings primary and secondary winding; primary

winding is connected to the input and secondary winding is connected to

the output. Proper insulation is provided between both the coils and

between the coil and core. Here is the image of the primary and

secondary winding of a step-up transformer.

In a step-up transformer, the number of turns in secondary windings is

greater than in primary windings, therefore it steps up the voltage, i.e.,

converts a primary voltage into a high secondary voltage. Meanwhile, in

step down transformers, the number of turns in the primary winding is

greater than in the secondary winding. Therefore, it converts the voltage in

a primary coil into a low secondary voltage.

66
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Step up and step-down transformers work on the principle of mutual

induction. According to this, the changing current in one coil induces EMF in

the other coil. Alternating current flows in one direction, stops reversing its

direction, and then again flows in another direction. Alternating current

flowing in the primary coil will create a varying magnetic field in the core of

the transformer that in turn produces the alternating current in the

secondary coil. Depending on the number of turns in the primary and

secondary coil, the voltage is either stepped up or down.

In the step-down transformer, the number of turns is greater in the primary

coil than in the secondary coil, so the output value will be lesser than the

input and it converts high voltage AC into low voltage AC. In the step-up

transformer, the number of turns in the secondary coil is greater than the

primary coil and it converts low voltage AC into high voltage AC. The

number of turns in coils, current and voltage can be related by the

equation below

Where Vs and Vp are the voltages of the secondary and the primary

winding of the transformer respectively. Ns and Np are the numbers of

67
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

turns of the secondary and the primary windings. Is and Ip are the currents

induced in the windings.

Step up and step down transformers neither create nor destroy the

electrical power. The input and output power remain the same by

changing the voltage and current at the primary and secondary coils.

Difference Between Step Up and Step Down Transformers

There are applications of step-up and step-down transformers which we

can witness in our daily life. A Step-up transformer would be applicable in

power transmission, microwave ovens, inverters, and so forth. Whereas a

step-down transformer is used in power distribution, electrical devices

such as bells, mobile chargers etc.

Step up and step-down transformers are used to create a balance

between the supply and required voltage in electrical appliances. Step-up

transformers are mainly used to reduce the loss of electrical energy during

transmission, while step-down transformers are used to distribute the high

68
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

supply voltage to the devices using low voltage for their operation. Step up

and step-down transformers do not create or destroy the electrical energy,

but only convert it.

Quality of Connecting Wires

Wires come in many forms and are made from many materials. two

important points:

-Electricity in long wires used in transmission behaves very differently than

in short wires used in design of devices

-The use of wires in AC circuits brings on all sorts of problems like skin

effect and proximity effects.

1.) Behavior of electricity in wires: Resistance and Impedance

AC Power:

In AC power current likes to travel near the surface of a wire (skin

effect). AC power in a wire also causes a magnetic field to form around it

(inductance). This field effects other nearby wires (such as in a winding)

causing proximity effect. All of these properties must be dealt with when

designing an AC circuit.

DC Power:

In DC power current travels through the whole of a wire.

Size of the conductor and material (AC and DC power):

Electricity travels more easily in highly conductive elements like copper,

silver or gold, the less conductive the material, the larger the diameter has

to be to carry the same current load.

69
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Quality of Material: Impurities and Crystals:

Most materials have impurities. In copper the oxygen content and other

materials in the copper effect the conductivity, so copper which will be

made into an electrical wire is alloyed differently than copper which on it's

way to becoming plumbing.

Metals are crystalline. Monocrystalline copper or aluminum has better

conductivity than polycrystalline metals, however large crystal copper is

very expensive to produce and only used in high performance

applications.

Resistivity:

Resistance in a wire the describes the excitation of electrons in the wire's

conductor material. This excitation results in the creation of heat, and loss

of efficiency. Using DC power people couldn't send power for a long

distance without using wide-diameter copper wires due to resistance over

distance. This made DC power not cost effective and allowed for the

growth of AC power.

Measurement Tools:

Ohms Law is used to calculate how much resistance a given wire will have.

This tells us how much energy we will lose over distance.

I = V / R Amps = Volts divided by Resistance

Formulas for Resistance and Conductance:

Resistance = resistivity / cross sectional area

Conductance = 1 / Resistance

70
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Creation of heat in a wire is normally a sign of wasted energy, however in a

tungsten or tantalum wire the heat makes the wire glow and produce light

which may be desired. Tungsten is used to make filaments because it has

a very high melting point. The wire can get very hot and glow brightly

without melting. Tungsten would be very bad for power transmission since

most of the energy put through is lost in the form of heat and light.

In power transmission we look for the lowest resistivity possible, we want to

transmit power over long distances without losing energy through

heat. We measure resistance in a wire by ohms per 1000 feet or

meters. The longer electricity has to travel, the more energy it loses.

One great solution to power transmission is superconductors. As a metal

becomes super cold (approaching absolute zero) it obtains a conductivity

of infinity. At a certain point there is no resistivity at all. There have been

experimental superconductive high voltage lines which were able to

transmit power with almost no losses, however the technology is not

developed enough to be cost effective.

Magnetic Fields (inductance and impedance):

Every wire used to transmit AC power creates a magnetic field while

current flows through it. The magnetic field is visualized by concentric

rings around the cross section of the wire, each ring closer to the wire has a

stronger magnetic power. Magnetic fields are useful for making very strong

magnets (when in a coil) i.e. making motors and generators, however

these magnetic fields are unwanted in power transmission lines.

While resistivity of a wire can impedes the flow of current and make heat,

71
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

the inductance of a wire/transmission line can also impede the flow of

current but this impedance does not create heat since the energy is 'lost' in

creating a magnetic field rather than exciting electrons in the material. This

impedance is called Reactive impedance in AC Circuits. We used the word

'lost' however the power is not truly lost, it is used to create the magnetic

field and it returns when the magnetic field collapses.

2.) Skin Effect:

In AC power electrons like to flow on the outside of

a wire. This is because the changing of current

back and forth causes eddy currents that result in

current crowding toward the surface.

Skin Depth

Skin depth is a fixed number for given frequency, resistivity and permittivity.

The higher the frequency of AC power in system, the more current is

compressed on the outside of the wire, so a wire that is used at 60 Hz at a

given voltage will not be ok at 200 MHz.

3.) Types of Wire:

Here are the factors for determining wire design:

-Durability (ability to flex repeatedly or be subject to crushing weights)

-Voltage and Current level

-Suspension strength (ability to hold its own weight over long spans

between support)

-Underground or underwater

-Temperature of operation (like superconducting wire)

72
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

-Cost

4.) Wire Materials:

The most common material for electrical wire is copper and aluminum,

these are not the best conductors however they are abundant and low

cost. Gold is also used in applications because it is corrosion

resistant. Gold is used in automobile airbag electronics to guarantee that

the device will function many years later despite exposure to harmful

elements. Gold is usually used in contact areas because this point in the

system is more exposed to corrosion and has more potential for

oxidization.

Aluminum wrapped around a steel

center wire is used in power

transmission because the aluminum is

cheaper than copper and doesn't

corrode. The steel center is used simply

for strength, to hold the wire over long

spans. Above is a typical ACSR cable used in overhead powerlines around

the world.

4.) WIRE INSULATION:

Left: To make an efficient motor or generator windings have to be packed

tight together, minimizing air spaces. Wire used in motors and generators

is generally coated in enamel to allow the windings to be packed tight

together. Traditional rubber or polymer insulation would make the wire

73
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

diameter thicker; this is one reason why old electric motors were bigger

and heavier than modern motors of the same horsepower.

Characteristics of Single and Multicore Wires

Single-core cable

A solitary metallic conductor is characteristic of the design of cables that

are referred to as having a single core. A protective insulating coating is

wrapped over the conductor, which is commonly made of copper or

aluminum, so that the level of safety may be increased. When it comes to

the effective transmission of high voltage electricity, single-core cables are

among the best options available.

These cables can carry substantial current loads without producing an

excessive amount of heat, and they have that capability. Because of their

low resistance and capacity to endure metal fatigue, single-core cables

are renowned for their excellent durability and flexibility. This is due to the

fact that these cables can tolerate metal fatigue. Their very low levels of

resistance in comparison to those of other people are likely the root cause

of this phenomena. Nevertheless, the usage of single-core cables is

subject to a number of constraints that must be taken into consideration.

When compared to managing multi-core cables, the management of

bigger and heavier conductors involves a greater number of obstacles and

results in higher financial expenditures. In addition, the installation of these

components as well as their interface with one another calls for the

utilization of specific terminals and connections, which presents the

possibility of a difficulty.

74
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

When it comes to single-core cables is the possibility that they may

produce powerful magnetic fields. Magnetic fields like this have the ability

to affect the functioning of electrical equipment that are in close proximity

to them by causing electromagnetic interference.

Multi-core cable

Multi-core cables are known for their capacity to house multiple metal

conductors within a single cable structure. The conductors are commonly

twisted in a helical pattern, ensuring electrical isolation from each other

and the outer layer. The advantages of multi-core cables for low voltage

control or communication systems lie in their ability to efficiently transfer

multiple signals or data streams simultaneously.

Multi-core cables offer cost-effective and easy handling benefits over

single-core cables. This is because they use thinner and lighter conductors,

leading to improved efficiency and manageability. One key benefit of

utilizing multi-core cables is their capacity to reduce magnetic fields and

inductive reactance in the circuit. The cancellation of each conductor’s

effects is achieved through the twisted topology of the cables, resulting in

optimized performance. Multi-core cables have lower reliability and

flexibility compared to single-core cables due to their increased

resistance. This can increase the risk of short circuits and electrical

damage. Elevated stress and temperature can negatively affect the

performance and longevity of these cables, making them more vulnerable

to these factors. In addition, the challenges of securely attaching all

individual strands make the process of soldering or crimping connectors

for multi-core cables more complex.

75
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Unit III
ELECTRICAL WIRING

Different types of switches

A Switch is a device which is designed to interrupt the current flow in a

circuit. In simple words, a Switch can make or break an electrical circuit.

Every electrical and electronics application uses at least one switch to

perform ON and OFF operation of the device.

So, switches are a part of the control system and without it, control

operation cannot be achieved. A switch can perform two functions, namely

fully ON (by closing its contacts) or fully OFF (by opening its contacts).

When the contacts of a switch are closed, the switch creates a closed path

for the current to flow and hence load consumes the power from source.

When the contacts of a switch are open, no power will be consumed by the

load.

Another important function of a Switch is to divert the flow of electric

current in a circuit. Consider the following circuit. When the switch is in

position A, the lamp 1 turns ON and while it is in position B, lamp 2 turns ON.

76
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

There are numerous applications of switch, found in wide variety of fields

such as homes, automobiles, industrial, military, aerospace and so on. In

home and office applications, we use simple rocker switches to turn ON

and OFF appliances like lights, computers, fans etc. In some applications,

multi way switching is employed (like building wiring), where two or more

switches are connected to control an electrical load from more than one

location, like a Two-Way Switch, for example.

Types of Switches

Basically, Switches can be of two types. They are:

• Mechanical

• Electronic

Mechanical Switches are physical switches, which must be activated

physically, by moving, pressing, releasing, or touching its contacts.

Electronic Switches, on the other hand, do not require any physical contact

in order to control a circuit. These are activated by semiconductor action.

Mechanical Switches

Mechanical switches can be classified into different types based on

several factors such as method of actuation (manual, limit and process

switches), number of contacts (single contact and multi contact switches),

number of poles and throws (SPST, DPDT, SPDT, etc.), operation and

construction (push button, toggle, rotary, joystick, etc.), based on state

(momentary and locked switches), etc.

77
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Based on the number of poles and throws, switches are classified into

following types. The pole represents the number of individual power circuits

that can be switched. Most of the switches are designed have one, two or

three poles and are designated as single pole, double pole and triple pole.

The number of throws represents the number of states to which current

can pass through the switch. Most of the switches are designed to have

either one or two throws, which are designated as single throw and double

throw switches.

Single Pole Single Throw Switch (SPST)

• This is the basic ON and OFF switch consisting

of one input contact and one output contact.

• It switches a single circuit and it can either

make (ON) or break (OFF) the load.

• The contacts of SPST can be either normally

open or normally closed configurations.

Single Pole Double Throw Switch (SPDT)

• This switch has three terminals: one is input

contact and remaining two are output

contacts.

• This means it consist two ON positions and

one-OFF position.

• In most of the circuits, these switches are used as changeover to

connect the input between two choices of outputs.

78
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• The contact which is connected to the input by default is referred as

normally closed contact and contact which will be connected during

ON operation is a normally open contact.

Double Pole Single Throw Switch (DPST)

• This switch consists of four terminals: two input contacts and two

output contacts.

• It behaves like a two separate SPST configurations,

operating at the same time.

• It has only one ON position, but it can actuate the two contacts

simultaneously, such that each input contact will be connected to its

corresponding output contact.

• In OFF position both

switches are at open

state.

• This type of switches is

used for controlling two different circuits at a time.

• Also, the contacts of this switch may be either normally open or

normally closed configurations.

Double Pole Double Throw Switch (DPDT)

• This is a dual ON/OFF switch consisting of

two ON positions.

• It has six terminals, two are input contacts

and remaining four are the output contacts.

79
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• It behaves like a two separate SPDT

configuration, operating at the same time.

• Two input contacts are connected to the one

set of output contacts in one position and in

another position, input contacts are

connected to the other set of output contacts.

Push Button Switch

• It is a momentary contact switch that makes or breaks connection

as long as pressure is applied (or when the button is pushed).

• Generally, this pressure is supplied by a

button pressed by someone’s finger.

• This button returns its normal position,

once the pressure is removed.

• The internal spring mechanism operates these two states (pressed

and released) of a push button.

• It consists of stationary and movable contacts, of which stationary

contacts are connected in series with the circuit to be switched while

movable contacts are attached with a push button.

• Push buttons are majorly classified into normally open, normally

closed and double acting push buttons as shown in the above figure.

• Double acting push buttons are generally used for controlling two

electrical circuits.

80
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Temperature Switches

• The most common heat sensing element is the bimetallic strip that

operates on the principle of thermal expansion.

• The bimetallic strips are made with two

dissimilar metals (that are having different

thermal expansion rates) and are bonded with each other.

• The switch contacts are operated when the temperature causes the

strip to bend or wrap. Another method of operating the temperature

switch is to use mercury glass tube.

• When the bulb is heated, mercury in the tube will expand and then

generates pressure to operate the contacts.

Electronic Switches

The electronic switches are generally called as Solid State switches

because there are no physical moving parts and hence no physical

contacts. Most of the appliances are controlled by semiconductor switches

such as motor drives and HVAC equipment.

Bipolar Transistors

A transistor either allows the current to pass or it

blocks the current as similar to working of normal

switch.

In switching circuits, transistor operates in cut-off

mode for OFF or current blocking condition and in

saturation mode for ON condition. The active region of

81
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

the transistor is not used for switching applications.

Both NPN and PNP transistors are operated or switched ON when a

sufficient base current is supplied to it. When a small current flows though

the base terminal supplied by a driving circuit (connected between the

base and emitter), it causes the transistor to turn ON the collector-emitter

path.

And it is turned OFF when the base current is removed and base voltage is

reduced to a slight negative value. Even though it utilizes small base

current, it is capable of carrying much higher currents through the

collector- emitter path.

Installation of two-way switch

2 Way Switch. It is also called as a Staircase Switch, as you can control a

single load, a light bulb for example, from two different places, like either

ends of a staircase.

It is a standard single pole double throw switch with three terminals.

The three terminals are usually named COM, L1 and L2, but sometimes the

terms COM, 1 Way and 2 Way are also used. In one position, the COM and L1

terminals are connected, while in the second position, the COM and L2

terminals are connected.

This type of connection is typically called a “Break before make” design, as

the first connection has to be broken before making the second

connection. This is in contrast to a regular two terminal switch, which is just

a make-or-break device.

82
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

The following image shows the front and back

view of a typical household two-way switch.

wiring uses a couple of Two-Way Light Switches

with a three wire control (3 Wire Control). The following is the simple

schematic of a three-wire 2-Way Switch wiring.

You can observe in the schematic that both the COM terminals are

connected together. The L1 terminals of both the switches are connected to

line (or phase or live) of the AC Supply.

The L2 terminals of both the switches are connected to one terminal of the

light bulb, while the other terminal of the light bulb is connected to the

neutral of the AC power supply.

In the default state shown in the above image, the light is off. If either of the

switches is toggled, the light turns on. To turn off the light, you can toggle

any switch.

For example, in the above state, the COM terminals of both the switches

are connected to respective L1 terminals. Now, if we toggle Switch 1 i.e., COM

83
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

of Switch 1 is now connected to its L2 terminal, then there is a path to

complete the circuit and the light turns on.

To turn off the light, we can toggle either Switch 1 or Switch 2 as any

toggling action will break the flow of current to the light. So, considering all

the possibilities, the light is on in two cases:

• COM of Switch 1 is connected to L1 and COM of Switch is connected to

L2.

• COM of Switch 1 is connected to L2 and COM of Switch is connected

to L1.

If we compare this setup with digital electronics, then this is similar to an

Ex-OR Gate, where the status of the light (ON or OFF) depends on the status

of the COM terminals of both the switches connected to respective L1 and

L2 terminals.

The following table shows the truth table for Standard Wiring i.e., 3-Wire

Control of Two-Way Switch, where the output (status of the light) depends

on what terminal (L1 or L2) is connected to the COM terminal.

Switch 1 COM Switch 2 COM

Status of Light
(connected to) (connected to)

L1 L1 OFF

L1 L2 ON

L2 L1 ON

L2 L2 OFF

This method is recommended as both the line and neutral wires come

from the same lighting circuit (or breaker) even though it uses more wire.
84
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Role of sockets, plugs, sockets

Electrical plugs and socket-outlets differ in voltage and current rating,

shape, size and type of connectors. The types used in each country are set

by national standards. Generally, the plug is the movable connector

attached to an electrically operated device's power cord, and the socket-

outlet is fixed on equipment or a

building structure. The plug has

protruding prongs, or pins that fit

into matching slots or holes in the

socket-outlet. A socket is also

called a receptacle, outlet, or power point. It is enclosed in a cover. Design

features of plugs and socket-outlets have gradually developed to reduce

the risk of electric shock and fire.

Safety measures may include

• Pin and slot dimensions and layout that permit only proper insertion of

plug into socket-outlet

• Earth pins longer than power pins so the device becomes earthed before

power is connected.

• Electrical insulation of the pin shanks was added as an additional feature

to reduce live contact exposure when a plug is partially inserted in a

socket-outlet.

• Shutters that open only for the correct plug prevent foreign objects from

coming into contact with live slots.

85
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Commonly used Electrical Plugs: The two pin plug is also called the Euro

plug. It has two round pins. It can be inserted in either way into the socket.

The three-pin plug is rated at 6A / 250V or 16A/ 250 V. It has three round

pins in a triangular pattern. The earth terminal is slightly larger and longer

than the live and neutral terminals. Socket Outlets Socket outlets, or electric

receptacles, help provide direct access to an electric power source. They

are designed to feed power to most electrically-run equipment from a

series of small 2 boxes that are wired directly to an electrical panel or other

power source. Socket outlets are commonplace in most homes and

businesses, as they provide both easy and direct access to electrical

power from various points. A socket outlet’s design may vary depending on

the electrical current, the country of origin, and the type of equipment or

plug it must accept. Due to these variances, not all electrical outlets and

electric-run components are mutually compatible.

Damaged plugs, sockets and flexible cables can cause electric shocks,

burns and fires.

• Check the plug and socket for burn marks, sounds of ‘arcing’ (buzzing or

crackling), fuses blowing, circuit-breakers tripping or whether it feels hot.

• Remove plugs from sockets carefully. Pulling out a plug by the cable puts

a strain on it, and could damage the contact between the plug and the

socket. This could result in the plug overheating, its wires becoming loose

or an electric shock (if the earth wire is disconnected).

• Only use plugs with the ISI mark

86
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• Always replace damaged cables immediately. Touching exposed live

wires may give you an electric shock.

One way to avoid this is to install tamper-resistant electrical socket outlets

ie., with shutters. Many new homes already come equipped with them, and

we can upgrade socket outlets in older homes to these new receptacles.

Installation of meters

An electric meter, or energy meter, is a device that measures the amount

of electric energy consumed by a building, tenant space, or electrically

powered equipment.

The meter which is used for measuring the energy utilises by the electric

load is known as the energy meter. The energy is the total power

consumed and utilised by the load at a particular interval of time. It is used

in domestic and industrial AC circuit for measuring the power

consumption. The meter is less expensive and accurate.

Construction of Energy Meter

The construction of the single-

phase energy meter is shown in the

figure.

The energy meter has four main

parts. They are the

1. Driving System

2. Moving System

3. Braking System

4. Registering System
87
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

1. Driving System – The electromagnet is the main component of the

driving system. It is the temporary magnet which is excited by the current

flow through their coil. The core of the electromagnet is made up of silicon

steel lamination. The driving system has two electromagnets. The upper

one is called the shunt electromagnet, and the lower one is called series

electromagnet.

The series electromagnet is excited by the load current flow through the

current coil. The coil of the shunt electromagnet is directly connected with

the supply and hence carry the current proportional to the shunt voltage.

This coil is called the pressure coil.

The centre limb of the magnet has the copper band. These bands are

adjustable. The main function of the copper band is to align the flux

produced by the shunt magnet in such a way that it is exactly

perpendicular to the supplied voltage.

2. Moving System – The moving system is the aluminium disc mounted on

the shaft of the alloy. The disc is placed in the air gap of the two

electromagnets. The eddy current is induced in the disc because of the

change of the magnetic field. This eddy current is cut by the magnetic flux.

The interaction of the flux and the disc induces the deflecting torque.

When the devices consume power, the aluminium disc starts rotating, and

after some number of rotations, the disc displays the unit used by the load.

The number of rotations of the disc is counted at particular interval of time.

The disc measured the power consumption in kilowatt hours.

88
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

3. Braking system – The permanent magnet is used for reducing the

rotation of the aluminium disc. The aluminium disc induces the eddy

current because of their rotation. The eddy current cut the magnetic flux of

the permanent magnet and hence produces the braking torque.

This braking torque opposes the movement of the disc, thus reduces their

speed. The permanent magnet is adjustable due to which the braking

torque is also adjusted by shifting the magnet to the other radial position.

4. Registration (Counting Mechanism) – The main function of the

registration or counting mechanism is to record the number of rotations of

the aluminium disc. Their rotation is directly proportional to the energy

consumed by the loads in the kilowatt hour.

The rotation of the disc is transmitted to

the pointers of the different dial for

recording the different readings. The

reading in kWh is obtained by multiply the

number of rotations of the disc with the

meter constant.

Working of the Energy Meter

The energy meter has the aluminium disc whose rotation determines the

power consumption of the load. The disc is placed between the air gap of

the series and shunt electromagnet. The shunt magnet has the pressure

coil, and the series magnet has the current coil.

The pressure coil creates the magnetic field because of the supply voltage,

and the current coil produces it because of the current.

89
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

The field induces by the voltage coil is lagging by 90º on the magnetic field

of the current coil because of which eddy current induced in the disc. The

interaction of the eddy current and the magnetic field causes torque,

which exerts a force on the disc. Thus, the disc starts rotating.

The force on the disc is proportional to the current and voltage of the coil.

The permanent magnet controls Their rotation. The permanent magnet

opposes the movement of the disc and equalises it on the power

consumption. The cyclometer counts the rotation of the disc.

Theory of Energy Meter

The pressure coil has the number of turns which makes it more inductive.

The reluctance path of their magnetic circuit is very less because of the

small length air gap. The current Ip flows through the pressure coil because

of the supply voltage, and it lags by 90º.

The current produces the two flux linkages which is again divided into two.

The major portion of the flux Φp1 passes through the side gap because of

low reluctance. The flux Φp2 goes through the disc and induces the driving

torque which rotates the aluminium disc.

The flux Φp is proportional to the applied voltage, and it is lagged by an

angle of 90º. The flux is alternating and hence induces an eddy current

Iep in the disc.

The load current passes through the current coil induces the flux Φs. This

flux causes the eddy current Ies on the disc. The eddy current Ies interacts

with the flux Φp, and the eddy current Iep interacts with Φs to produce

90
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

another torque. These torques are opposite in direction, and the net torque

is the difference between these two.

Basic switch board

A switchboard can consist of a single vertical structure or multiple

structures depending on the number and sizes of the loads being

powered.

An electric switchboard is a device that directs electricity from one or more

sources of power supply. In Switch Board, there are switch available to

operate electrical appliances individually.

A main structure will contain the main disconnects or main lugs and will

often contain utility and/or customer metering equipment and surge

protection.

Cabling

can enter

directly

into the

main

structure

or through a dedicated pull structure. Pull structures are commonly used in

service entrance switchboards. Cables can enter the structure from the

floor (bottom entry) or from above (top entry.)

Distribution structures divide and send power to branch circuit protection

devices and then to branch circuits to power downstream loads. Power

flows from the main structure to the distribution structure via cross bus.

91
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

In most installations, switchboards are mounted close to a wall and are

front accessible only. If required, the switchboard can be constructed to

allow both front and rear access. Rear access switchboards provide easier

access for installation and maintenance, but they are typically deeper

than front access only switchboards.

The primary components of a switchboard structure are the frame, bus,

overcurrent protective devices, instrumentation, enclosures and exterior

covers. The switchboard frame is the metal skeleton that houses all the

other components. The bus, which is either copper or aluminum, is

mounted within this frame. The bus distributes power from the incoming

cable conductors to the branch circuit devices. A horizontal bus distributes

power to each switchboard section. In contrast, a vertical bus distributes

power to the circuit protection devices within an individual section.

Switchboards are used to safely distribute electricity throughout

commercial and industrial facilities. A switchboard is a component of an

electrical distribution system which divides an electrical power feed into

branch circuits while providing a protective circuit breaker or fuse for each

circuit in a common enclosure.

Switchboards typically have a maximum voltage rating of 600 Vac/Vdc

and a maximum bus rating of 6000 A.

Electrical bell

An electric doorbell is a simple circuit that triggers a tone by pressing a

button when the circuit is complete. It is this simplicity that makes the

doorbell such a wonder. Doorbell's simple device implements the scientific

92
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

principles of electromagnetism in a meaningful way. To understand how

an electric bell works, we first need to know about electromagnet.

Electromagnet is a type of magnet where magnetic field is produced using

an electric current. When electric current flows through a wire tied around

an iron rod the iron rod behave like a magnet. the magnetic effect of

electric current has been used in making powerful electromagnet. the iron

rod around which the wire is wound is called a solenoid. The wire is

wrapped around the iron rod many times electric current is supplied to the

wire, the iron Rod behaves like a magnet as long as current is supplied. the

more the number of turns in the wire the stronger a magnetic effect.

Electromagnet is used in electric bulbs and also in powerful cranes.

Uses of an Electromagnet: Electromagnets are commonly used everyday

appliances today. They are used in doorbells, hard drives, speakers and

much more. Eye specialists use it for taking out foreign particles from the

eyes. They are also being used for industrial applications.

Working of an Electric Bell

The important things required for

construction of an electric bell are

a gong , hammer, electrometer

switch and soft iron armature or

hand.Now that you understand the

important things for an electric

bell, let's put up with a step-by-step explanation of how the electric bell

works. An electric bell has Electromagnet in it. It is made up of two rods of

cast iron. The iron rods have a coil wrapped around them. A metallic strip is

93
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

used and is kept parallel to the coils. This trip has a Hammer connected to

it at one end. The other part of the strip is connected with the circuit. A

gong is placed in such a position that it can be hit by a hammer. When

electric current is passed through the circuit the cast iron rod becomes

charged with electromagnetic energy and attracts the metallic strip. as a

result, the metallic hammer hits the ground the circuit breaks when the

metallic through peaceful towards Electromagnet and gets disconnected

from the point .since there is no magnetism left an Electromagnet the

spring pulls back the metallic stripped this cycle is repeated again and

again in the electric bell which produces a ringing sound .that is why it is

called as making brake circuit.

Indicator

Bell indicator circuit is used where a bell and buzzers are needed to control

from different locations. Bell Indicator circuit is also known as hotelling

circuit where an electric bell is controlled from more than one location. In

hotel wiring circuit, the bell can be operated from different locations such

as rooms by guests. It can be used to find the exact location and room

where the guest needs attendant help. When a guest presses the push

button, the specified indicator with room number starts to glow with ringing

bell at the hotel management and attendant panel. The room attended

then attend the exact room specified by indicator lamp where they seek

help.

There is one flaw in this circuit as if there in no one in the pantry, They won’t

be able to know who need assistance from which room. For this reason, an

advanced hotel wiring circuit can be made with the help of 2 nos of NO

94
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

(normally open) 230 or 120V contact blocks for one push button, 2 nos of

NC (normally closed) push / release buttons for 1 room, 230V or 120V relay

coil (NO) and 1.5mm 2 wires for phase and neutral.

This way, when a guest press the push button, the indicator bulb and bell

will ring until

someone in the

reception switch

off the bell and

indicator lamp by

pressing the push

button installed on

the panel board.

This way, it makes sure some one in the pantry is aware and going to

attend the guest in the specified room.

The bell indicator circuit used in hotels and restaurants where the bell and

different colors bulbs or assigned number to the lamps are configured in a

panel installed in reservation and reception. The indicator lamps and bell

are controlled from different location by push buttons switches.

For example, when a guest presses the push button in room 1, the circuit

completes which leads to glow the indicator bulb and bell rings. This way,

the attendant knows the exact room (specified by assigned number or

color to the lamps) and manage him accordingly.

The circuit follow the above sequence for other rooms i.e. pressing any

push button will complete the circuit, bell rings and bulbs start to glow.

95
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Fixing of tube lights and fans

Knowing how to wire a ceiling fan means taking some precautionary

steps:

• Make sure all circuit breakers related to the wiring are shut off.

• Make sure to strip the coating on the ends of the wires to expose the

copper end.

• Make sure the unused wires have caps or wire connectors at the

ends.

• Make sure your fan comes with wire nuts and push connectors. Both

of these will be needed when wiring your ceiling fan.

• Some manufacturers may use different color coding, so be sure that

you follow the instructions included with your fan.

Separate switches allow the fan and light to operate separately. It also

affords the option to install a dimmer for the light. (Don’t attach a dimmer

to the fan’s power. Its speed should only vary by use of its built-in controls.)

96
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

The power supply line (the black wire) should feed both switches and those

switches power the fan (black) or the light (blue).

To do this, the wire from the wall circuit to your light has to have three

wires. If you are replacing an existing fan on a two-switch setup, there may

be an existing three-conductor wire, which means a red wire will be in the

box. This will supply power for the light kit.

If you are installing a fan for the first time or adding a separate switch for a

light kit for the first time, you will need to run a new wire from the switch box

to the junction box in the ceiling, where the fan will be. You need to use a

new run of three-conductor wire.

• Connect black fan wire to the black ceiling wire.

• Connect the blue wire to the red wire.

• Connect white wires together.

• Connect green/bare copper wires.

In the switch box:

• Split the incoming hot wire into a "Y" and connect it to a terminal on

each switch.

• Connect the black wire to the screw located in switch No. 1.

• Connect the red wire to the screw in switch No. 2.

• Connect the white wires together.

• Connect green/bare copper wires together.

• Tuck all wires back in their boxes.

• Turn power on and test.

97
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Heavy equipment like AC, fridge, washing machine, oven, geyser, jet
pumps

3-phase power systems provide three separate currents, each separated

by one-third of the time it takes to complete a full cycle. But, as opposed to

single-phase, where the two hot legs are always 180 degrees apart, with 3-

phase, the currents are separated by 120 degrees.

When any one line is at its peak current, the other two are not. For example,

when phase 1 is at its positive peak, phases 2 and 3 are both at -0.5. This

means, unlike single-phase current, there’s no point at which no power is

being delivered to the load. In fact, at six different positions in each phase,

one of the lines is at peak positive or negative position.

For practical purposes, this means the collective amount of power supplied

by all three currents remains constant; you don’t have cyclical peaks and

valleys as with single-phase.

Computers and many motors used in heavy machinery are designed with

this in mind. They can draw a steady stream of constant power, rather than

98
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

having to account for the variation inherent in single-phase AC power. As a

result, they use less energy.

Among the benefits that 3-phase power brings is the ability to deliver

nearly twice the power of single-phase systems without requiring twice the

number of wires. It’s not three times as much power, as one might expect,

because in practice, you typically take one hot line and connect it to

another hot line.

To understand how 3-phase delivers more power, one must do the math.

The formula for single-phase power is Power = Voltage (V) x Current (I) x

Power Factor (PF). If we assume the load on the circuit is resistive only,

power factor is unity (or one) which reduces the formula to P = V x I. If we

consider a 120-volt circuit supporting 20 amps, the power is equal to 2,400

watts.

The formula for power of a 3-phase circuit is Power = Voltage (V) x Current

(I) x Power Factor (PF) x square root of three. If we assume the load on the

circuit is resistive only, power factor is unity (or one) which reduces the

formula to P = V x I x square root of three. If we consider a 120-volt, 3-phase

circuit and each phase supports 20 amps, the formula works out to 120

Volts x 20 Amps x 1.732 = 4,157 watts. This is how 3-phase can deliver nearly

twice the power of single-phase systems. This is a simplified example, but

it can be used to investigate the additional power available from circuits

supporting higher voltages (e.g. 208 or 480 volts) or currents (e.g. 30 amps

or greater).

99
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

3 phase power is a common

form of electrical power

supply for larger installations.

To give an example, it is a

popular method of electric

power transmission

throughout the national grid

system.

It is typically installed in manufacturing and industrial environments

because the equipment being used consumes larger amounts of current.

The following electrical equipment usually requires three phase power:

• Air conditioning

• Plant and heavy machinery

• Heating systems

• Motors and pumps

• UPS systems

In domestic properties, electricity is supplied with one live (phase) wire,

which in the UK delivers power at 230 volts and requires a neutral

conductor (wire) to work.

However, a 3 phase supply uses three live wires. The voltage between these

live wires is 400 volts, as 3 phase consuming devices typically require more

power. Even so, most 3 phase systems still utilize a neutral wire, as some

electrical devices in industrial settings are still rated at 230 volts and

feature a 13 amp plug socket.

100
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Once a 3-phase system has been installed, the price per unit of electricity

is the same as single phase power. However, some 3-phase equipment

tends to be more efficient than single phase alternatives anyway.

When installing a 3-phase system, it is important that equal amounts of

current flow through each of the conductors. This is called phase

balancing.

Provisions for inverter

An inverter is a piece of standalone equipment that converts a DC voltage

to an AC voltage. The inverter performs conversion of direct current to an

alternating voltage by converting the energy stored in the dc sources like

battery and rectifiers. The batteries in the inverter store energy in the form

of direct current and the home appliances we use need alternating current

and this is how inverters work. In case of power cuts and such

emergencies, the inverter can be used to operate our appliances.

101
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Inverters play a crucial role in converting DC (Direct Current) from the

battery into AC (Alternating Current), which is used to power electrical

appliances. Ensuring the correct setup is crucial not only for the efficient

operation of your equipment but also for the safety and longevity of your

batteries and inverter.

Inverter batteries can be connected in series to double the

voltage or in parallel to double the capacity. Alternatively, they can be

connected in both series and parallel depending on the voltage and

capacity requirements of your inverter. Before proceeding with any

connections, you must confirm the voltage of your inverter.

For instance, if you have a 12-volt inverter, the battery bank must be wired

for 12 volts. You can connect more than one 12-volt battery, but the output

voltage must remain 12 volts. The reason for this is simple: over-voltage

can damage your inverter and appliances while under-voltage can cause

inefficient operation or even system failure.

Essential Steps to Connect an Inverter to a Battery

Step 1: Confirm Your Inverter's Voltage Requirement

The first step is to understand the voltage requirements of your inverter.

Check the manufacturer's specifications to ascertain this information. For

instance, a Mercury 2.4 kVA inverter requires a 24-volt connection.

Step 2: Choose the Correct Wiring Method

If you're using more than one battery, decide whether to connect your

batteries in series, in parallel, or a combination of both. Remember,

102
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

connecting in series increases voltage while retaining capacity, while

connecting in parallel increases capacity while retaining the same voltage.

24v & 48 V Battery Connection in Series

For a 24-volt inverter and four 12-volt batteries, you'll

need a series-parallel connection. This entails

connecting two sets of batteries in series (which

doubles the voltage) and then

connecting these sets in parallel

(which maintains the 24-volt level

but doubles the capacity).

24v-Battery-Connection-in-Series-and-Parallel

Step 3: Use the Correct Size Wires

Using the correct size wires is critical for the performance and safety of

your inverter connection. The wire size must be capable of carrying the

current without overheating. An undersized wire can lead to voltage drop,

inefficiency, and can even pose a fire risk

Inverter Size (kVA) Wire Size (AWG) Wire Size (mm2)

1-2 14 2.5

3-4 12 4

5-6 10 6

103
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Inverter Size (kVA) Wire Size (AWG) Wire Size (mm2)

7-8 8 10

9 - 10 6 16

Step 4: Connect Your Inverter to the Battery

Once your batteries are connected correctly, you can connect your inverter

to the battery bank. The inverter should be connected to the positive

terminal of the first battery and the negative terminal of the last battery in

your series-parallel setup.

Always ensure you connect the positive terminal first and the negative

terminal last when setting up your inverter connection. This method

reduces the risk of a short circuit.

Step 5: Test Your Connection

After connecting your inverter to the battery, it's vital to test the system to

ensure everything is working correctly. Check the voltage at the inverter

terminals using a multimeter. If it matches the manufacturer's

specifications, your connection is successful.

The power consumption is not the same as the inverter’s capacity,

although it does seem ideal for it to be that way. The incoming power to

the inverters is not as efficient, and hence the power factor measured for

residential use is 0.8.

Therefore, to calculate the required capacity of the inverter and know how

inverter works, you need to divide the total energy consumption (in Watts)

by 0.8 to derive an inverter’s capacity. This resultant capacity of the

104
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

inverter is measured in VA. This capacity denotes the maximum amount of

power load a respective inverter can handle when all the decided

appliances are used simultaneously.

The factors mentioned above will help you find the ideal inverter for your

needs, but it is also essential to select the correct battery size. The battery

size is measured in Ah.

For calculating the ideal battery size, you will need to know how inverters

work and decide on a particular time period for which you will need the

inverter to provide backup. You can calculate the battery size by

multiplying your inverter’s power by the number of hours you want to use

the inverter.

Once you are done multiplying, the resultant will be measured in VAh

(battery voltage x no. of batteries x capacity of batteries (AH)), but as the

vital inverter battery capacity is 12 V, you will have to divide the above-

calculated result by 12.

You will find the ideal inverter size based on your power needs and

preferences. If the exact battery capacity inverter is not available, you

should always opt for a higher capacity.

Some of the other factors you need to mind when opting for an inverter, the

battery types are an essential factor.

• Lead-acid: These are often used in batteries. The lead-acid batteries

are lightweight, easily rechargeable, and they do produce the

required amount of current. These batteries last for up to 3 – 4 years

with regular maintenance.

105
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• Tubular: Tubular battery type is the most popularly used inverter

battery. These are known for their high efficiency and long

operational life of up to 8 years. The various benefits and properties

of Tubular batteries make them expensive, but they are still a popular

choice.

• Maintenance-free: The maintenance-free batteries are sealed acid

batteries that can last up to 4-5 years and do not require frequent

check-ups or maintaining the electrolyte levels.

Inverters play a crucial role in converting DC (Direct Current) from the

battery into AC (Alternating Current), which is used to power electrical

appliances. Ensuring the correct setup is crucial not only for the efficient

operation of your equipment but also for the safety and longevity of your

batteries and inverter.

Gauge specifications of wires for various needs

Wire sizes come in their gauges and ampacity. Remember, the higher the

gauge, the lower the ampacity. It also means the conductor is thicker with

a higher gauge. Here are some gauges to help you familiarize yourself:

• 4-gauge – meant for electric furnaces and heaters at 60 amps

• 60-gauge – meant for cooktops at 40-50 amps

• 10-gauge – meant for dryers, 240-volt air conditioners, water heaters

at 30 amps

• 12-gauge – meant for kitchen, bathroom, and outdoor receptacles at

20 amps

• 14-gauge – meant for lighting fixtures, lamps, and circuits at 15 amps

106
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• 16-gauge – meant for extension cords at 13 amps

• 18-gauge – meant for low-voltage lighting and lamps at 10 amps

Electrical cable measurements

CROSS-SECTION in (AWG) CURRENT USED

mm2 CONSUMPTION

25 mm2 4 Very high Central air conditioning and

industrial equipment..

16 mm2 6 High air Conditioners, electric stoves and

electric power connections.

10 mm2 8 Medium high Refrigerators and dryers.

6 mm2 10 Medium Microwave and blenders

4 mm2 12 Medium Lighting

2.5 mm2 14 Under Lamps

1.5 mm2 16 Very low Thermostats, bells or security

systems.

Color Coding

Color coding is used on both the outer sheathing of cables and wires.

Knowing the coding can help you which wiring is used in a system. For

example, a white-sheathed cable is used for 15-amp circuits, while the

yellow cable is for 20-amp circuits. Some colors can include blue, gray, and

orange.

The coloring does not indicate the exact size and rating. But it does make it

a standardization for any circuit. For example, black and red wires are

typically used for carrying “hot” connections. White wires, in this case, are

for “neutral” conductors.

107
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Unit IV
POWER RATING AND POWER DELIVERED

conversion of electrical energy into different forms

Energy transformations are processes that convert energy from one type

(e.g., kinetic, gravitational potential, chemical energy) into another. Any

type of energy use must involve some sort of energy transformation.

Conversion of energy is the transformation from one form of energy to

another form. It is important to remember that energy can neither be

created nor destroyed and the total amount of energy present in the

system remains constant.

• There are various forms of energy such as thermal energy,

electromagnetic energy, mechanical energy, nuclear energy,

chemical energy, etc.

• These forms keep changing into one another depending upon the

tasks performed in everyday life.

The first law of thermodynamics states that:

“Energy can neither be created nor destroyed, it can only be transformed

from one form to another.”

Thus, it means the total energy is always constant in the universe.

Whenever energy is consumed in some work, it gets converted into another

form. For example, when water is boiled, the energy provided in the form of

heat gets converted into the kinetic energy of vapor molecules.

108
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Electrical energy is a versatile and easily convertible form of energy. Many

devices and appliances are designed to convert electrical energy into

other forms of energy to perform various tasks.

Electrical energy is often converted

into mechanical energy to generate

motion. This is achieved using devices

called electric motors. Electric motors

use the principle of electromagnetic

induction to create rotational or linear

motion. The interaction between the

magnetic field created by the electric

current and the external magnetic

field generates a force, which results in

motion. Some common applications of electric motors include:

• Fans

• Washing machines

• Electric vehicles

• Industrial machinery

Thermal Energy

Electrical energy can also be converted into thermal energy or heat. This

conversion occurs when electric current flows through a resistive material,

generating heat due to the internal resistance of the material. The heating

effect of electric current is called Joule heating. Devices that convert

electrical energy into thermal energy include:

109
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• Electric heaters

• Electric stoves

• Water heaters

• Hair dryers

Light Energy

Converting electrical energy into light energy is another common

application. Various types of light bulbs and lamps are designed to

achieve this conversion. The two main types of light bulbs are

incandescent and LED (light-emitting diode) bulbs.

Incandescent bulbs work by passing an electric current through a thin

filament, which becomes hot and emits light as a result. On the other hand,

LED bulbs utilize semiconductor materials to emit light when an electric

current flows through them. LEDs are more energy-efficient and longer-

lasting than incandescent bulbs.

Work done by electrical energy

Consider a conductor with endpoints A and B, and assume that current I is

flowing through the conductor. Let us denote the potential at ends by

V(A) and V(B). Since the current is flowing from A to B, it means that the

potential is decreasing from point A to point B.

V = V(A) – V(B)

and

V>0

In time “t”, the charge Q travels from point A to point B.

110
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

The energy generated by the movement of the electrons from point A to B

is called Electrical Energy or Electrical Potential Energy. In general, the

energy derived from the kinetic and potential energy of the charged

particle is called the electrical potential energy.

the potential energy at point A is denoted by U(A) while the potential

energy at point B is denoted by U(B).

U(A) = Q×V(A) and U(B) = Q×V(B)

Let the change in potential energy be denoted by Unet

Unet = Final Potential Energy – Initial Potential Energy

Unet = U(B) – U(A)

Unet = {Q×V(B) – Q×V(A)}

Unet = – ∆Q.V (Now, I = ∆Q/∆t)

Unet = -I × ∆ t × V

If the charges inside the conductor moved freely, this potential energy

would have gotten converted into kinetic energy, so that the total energy

remains unchanged.

∆K = -∆U

Thus, in case the charges could move freely inside the conductor under the

action of the electric field, their velocity would have increased as they

move. However due to the collisions between electrons and different ions

inside the conductor. The charge carriers due to not move with

acceleration but with a steady velocity. During the collisions, energy is

111
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

transferred from these electrons to the ions which then vibrate more

vigorously, and that in turn increases the temperature. Thus the derivation

is given above indirectly calculates the energy dissipated in the conductor

in form of heat.

∆W=I×V×∆t

Electrical energy is generally measured in joules or watt-second. When one

ampere of current flows through the circuit for a second and the potential

difference applied to the conductor is one volt then we say one joule of

electrical energy is produced.

• SI unit for measurement of Electrical Energy is Joule. Its dimensional

formula is [ML2T-2]

• Another unit for the measurement of Electrical Energy is electron-volt

(eV).

It is known that power is the rate of work done. In this case, it can be

thought of as the amount of energy dissipated in form of heat when an

electric current is passing through the conductor. In all electrical

appliances, heat dissipation occurs. This heat dissipation is called power

loss or ohmic loss because these losses are due to resistances offered in

conductors.

Rewriting the previous equation,

P = ∆W / t

P=I×V

112
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Using ohm’s law relation V = IR for substituting the values inside the above

equation,

P = I × V = I × I × R = I2R

It can also be written as,

P = I × V = (V/R) × V = V2/R

Thus, the power dissipated in a conductor can be written as,

P = VI = V2/R = I2R

where,

P is the Power

V is the voltage applied

R is the resistance of the material

I is the current supplied

Power rating of electrical appliances

The energy consumed by an appliance is directly proportional to its power

rating, whose unit is expressed in watts (W). For example, an appliance

with a power rating of 2000 W will consume 2000 joules per second.

You can find the power rating of most devices and appliances in the

manual or on the appliance itself. Find its rated power to calculate its watt-

hour usage. However, keep in mind that not all appliances run 24/7. Some

operate for only a few minutes a day. For example, you use garage

openers for only a tiny fraction of an hour. The power consumed by a 500-

113
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

watt lawn mower may seem significant, but running it for only one hour a

week translates to 71 Watt-hours per day.

Moreover, some appliances, such as refrigerators, seem to run all day. In

reality, they operate for only 12 to 15 hours daily (they turn on and off as

needed). The same goes for air conditioning units. Thus, they don’t use the

maximum amount of energy all the time.

Some devices consume energy when remain plugged in. The current

drawn by these appliances or devices is typically small, often less than 1

watt. However, since they’re running 24 hours a day, that amount adds up,

sometimes by as much as 100 watt-hours in one day. Examples of

appliances that consume energy even when not in use include

microwaves, printers, and TVs.

The power rating for electrical equipment and devices specifies the

required supplied voltage for their smooth operation. It also defines the

maximum amount of current that can safely flow through the equipment

or appliance. If the current drawn by the equipment exceeds its power

rating, it could lead to a breakdown.

Appliance/Equipment Watts (Power rating)

Freezer (Upright – 15 cu. ft.) 1240 W (whole day)

Refrigerator (16 cu. ft.) 1200 W (whole day)

Air conditioner (room) 1000 W (continuous operation)

Air conditioner (central) 2000 to 5000 W (continuous operation)

Fan (ceiling) 120 W

114
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Fan (table) 10 to 25 W

Laptop computer 20 to 75 W

Desktop PC 80 to 200 W

Printer 100 W

LCD monitor 100 W

Heater 1000 W

Coffee machine 1000 W

Dishwasher 1200 to 1500 W

Electric kettle 1200 W

Microwave 600 to 1500 W

Electric oven 1200 W

Toaster 800 to 1500 W

Clothes washer 800 W

Iron 1000 W

TV (LCD) 150 W

TV (plasma) 200 W

Vacuum cleaner (upright) 200 to 700 W

CFL bulb (40 watt equivalent) 11 W

CFL bulb (100 watt equivalent) 30 W

LED bulb (40 watt equivalent) 10 W

115
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

LED bulb (100 watt equivalent) 23 W

Drill (½ inch) 750 W

Hedge trimmer 450 W

Energy consumption

Energy consumption is the use of power or energy of a system by making

use of supply. The consumption is done in Giga Joule per year, kilograms of

oil equivalent per year (kg/a), and in Watts.

Formula of Energy Consumption

The energy consumption formula is articulated as,

Where,

• E is energy in kilowatt-hours(kWh),

• P is power in Watts,

• t is hours

Calculating Annual Electricity Consumption and Costs

Follow these steps for finding the annual energy consumption of a product,

as well as the cost to operate it.

Estimate the number of hours per day an appliance runs. There are two

ways to do this:

- Rough estimate

- Keep a log

116
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Find the wattage of the product. There are three ways to find the wattage

an appliance uses:

- Specified on the appliance

- Multiply the appliance ampere usage by the appliance voltage usage

- Use online sources to find typical wattages or the wattage of specific

products you are considering purchasing.

Find the daily energy consumption using the following formula:

(Wattage × Hours Used Per Day) ÷ 1000 = Daily Kilowatt-hour (kWh)

consumption

Find the annual energy consumption using the following formula:

Daily kWh consumption × number of days used per year = annual energy

consumption

Energy Consumption Solved Problems

Problem 1: Compute the energy consumption in a system that consumes

190 Watts of power and works for 3 hrs a day.

Answer:

Given: Power P = 190 W, total number of hours = 3 hrs

E =(190*3*60*60)/1000

E =2052 kWh

Therefore, the energy consumption is 2052 kWh

Problem 2: A toy car consumes energy of 500 Watts of power if it works for

2 hrs a day using it. Calculate the energy consumption a day.

117
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Answer:

Given: Power P = 500 W, total number of hours= 2 hrs

E = (500*2*60*60)/1000

E =3600 kWh

There are various factors that directly influence energy consumption such

as:

The activity that takes place in the home or business.

The number of people in a household or workers.

The consumption habits of each person.

The energy performance of household appliances.

Electrical energy unit in kWh

A kilowatt-hour, otherwise known as a kWh, is a way to measure how much

energy you’re using. It’s not the number of kilowatts you’re using in an hour,

even though that seems to make sense.

A kWh equals the amount of energy you would use by keeping a 1,000 watt

appliance running for one hour.

For instance, if you turned on a 100 watt bulb, it would take 10 hours to use

one kilowatt-hour of energy. A 2,000 watt appliance, on the other hand,

would only take half an hour. It all comes down to dividing the number of

watts in an appliance into 1,000.

What is a Kilowatt-Hour?

A kilowatt-hour is a unit of measure for energy usage. It’s using one

kilowatt of power (1000 watts) used for one hour. It’s abbreviated as kWh.
118
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Kilowatt-Hour vs. Kilowatt

Difference between a kilowatt hour (kWh) and a kilowatt (KW)

A kilowatt (kW) is 1,000 watts and is a measure of how much power

something needs to run. In metric, 1,000 = kilo, so 1,000 watts equals a

kilowatt.

A kilowatt hour (kWh) is a measure of the amount of energy something

uses over time.

Think of it this way: a kilowatt (kW) is the amount of power something

needs just to turn it on. A kilowatt hour (kWh) is the amount of power that

device will use over the course of an hour.

How do I calculate what 1 kWh will power?

1. Locate the wattage for the device.

2. Convert the wattage from watts (W) to kilowatts (kW). To do that, just

divide the number of watts by 1000.

3. Divide the number of kilowatts into 1kWh to see how long it takes for

your device to use 1 kWh.

Calculation of EB bill

In India, electricity tariffs are regulated by the State Electricity Regulatory

Commissions.

1. Meter Reading:- The first step in calculating your electricity bill is

meter reading. A meter reader from your electricity distribution

company will come to your house and take a reading of your

electricity consumption. The meter measures the amount of

119
Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

electricity you have used since the last meter reading. The meter

reading is typically recorded in units of kilowatt-hour (kWh).

2. Tariff Rates:- The next step is to determine the tariff rates. Tariff rates

are set by the State Electricity Regulatory Commission and are based

on various factors such as the cost of generating and distributing

electricity, fuel prices, and other operational expenses. The tariff rates

may vary based on the category of consumers, such as residential,

commercial, or industrial. The tariff rates are published on the

DISCOM’s website and can also be obtained by contacting their

customer care.

3. Energy Consumption Calculation:- The energy consumption is

calculated by subtracting the previous meter reading from the

current meter reading. The difference is then multiplied by the tariff

rate per unit of electricity consumption. For example, if your previous

meter reading was 1000 kWh, and the current reading is 1200 kWh,

then your energy consumption would be 200 kWh (1200 – 1000). If the

tariff rate is Rs. 5 per kWh, then your energy consumption cost would

be Rs. 1000 (200 x 5).

4. Fixed Charges:- Apart from the energy consumption charges, the

DISCOMs also charge a fixed fee, also known as a service connection

charge, which is charged every month regardless of the amount of

electricity consumed. The fixed charges may vary based on the type

of connection, such as single-phase or three-phase, and the

category of consumers.

120
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

5. Taxes and Other Charges:- Finally, taxes and other charges such as

meter rent, electricity duty, and others are added to the bill. In India,

the GST (Goods and Services Tax) on electricity is levied at a rate of

5%.

Calculating electricity bills involves meter reading, determining tariff

rates, calculating energy consumption, adding fixed charges, taxes, and

other charges. It is important to note that energy consumption is the

primary factor in determining the electricity bill, and reducing energy

consumption through energy-efficient practices can significantly reduce

the bill amount. Understanding the billing process and taking steps to

conserve energy can help consumers save money and contribute to a

sustainable future.

To calculate your electricity bill, follow these steps:

Watts = (amps) x (volts)

Kilowatt-hours = (watts) x (usage) / 1000.

Cost = (kilowatt-hours) x (electricity rate)

• Subtract the current meter reading from the previous month’s

reading to find the energy consumption.

• Multiply the units consumed by the per-unit charges based on the

applicable slabs (e.g., Rs. 4.22 for 1-100 units, Rs. 5.02 for 101-200

units).

• Add the fixed charge and energy duty (e.g., Rs. 40 fixed charge and

Rs. 0.15 per unit) to the energy charges.

121
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• The sum of the energy charges, fixed charge, and energy duty gives

you the total bill amount.

• Example: If you consumed 250 units with the applicable slabs

mentioned above, the energy charges would be Rs. 1218. Adding the

fixed charge and energy duty, the total bill amount would be Rs. 1296.

Some energy-saving tips to reduce the EB bill in India:

• Use energy-efficient appliances and LED lighting.

• Turn off lights, fans, and electronics when not in use.

• Opt for natural lighting during the day.

• Set air conditioners to moderate temperatures.

• Insulate doors and windows to prevent heat loss.

• Unplug chargers and unused electronics.

• Use power-saving modes on devices.

• Regularly maintain and clean appliances for optimal efficiency.

• Use sunlight for drying clothes instead of using a dryer.

• Educate and encourage family members to practice energy-saving

habits.

Problem:

We want to heat up 0.5 liter of water with a resistive heater that carries 5 A

at 120 V. How long will it take to bring the water from 27 oC to the boiling

point? How much does this cost at Rs. 7/kWh? The specific heat of water is

4.19 kJ/(kgC).

Solution:

122
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

The energy required to raise the temperature of the water by ΔT is ΔU =

mcΔT, where m is the mass and c is the specific heat of the water.

The power dissipated by the heater is P = IV = energy/time. The time t

required to convert an amount of electrical energy ΔU into thermal energy

is t = ΔU/P.

Details of the calculation:

ΔU = (10-3 kg/cm3)(500 cm3)(4.19 kJ/(kgoC))(73oC) = 153 kJ.

P = IV = (5 A)(120 V) = 600 W.

The time t required to convert 153 kJ into thermal energy therefore is

t = ΔU/P = (153000/600) s = 255 s = 4.3 minutes.

The electrical energy converted into heat in units of kWh is

U = (0.6 kW)(255 s)(1 hour/3600 s) = 0.043 kWh.

At Rs. 7/kWh, we spend Rs. 0.30 to heat the water.

2. Calculate the electricity bill amount for a month of 31 days, if the

following devices are used as specified:

a) 3 bulbs of 30 watts for 5 hours

b) 4 tube lights of 50 watts for 8 hours

c) 1 fridge of 300 watts for 24 hours

Given the rate of electricity is Rs. 7 per unit.

Solution

The energy consumed by the bulbs,

123
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

As we know enegry=power×time

3 bulbs × 30 watts × 5 hours × 31 days = 13950 Wh

The energy consumed by the tubes,

4 tubes × 50 watts × 8 hours × 31 days = 49600 Wh

The energy consumed by the fridge,

1 fridge × 300 watts × 12 hours × 31 days = 111600 Wh

Therefore, the total energy consumption is given by,

13950+49600+111600 = 175,150 Wh = 175.15 KWh

We need to convert it into units, where 1 unit = 1 kWh

So, electricity bill = 175.15 units × Rs. 7 = Rs. 1226.05

Joule’s heating

The amount of heat that is produced within an electric wire due to the flow

of current is expressed in the unit of Joules. When the current flows through

the wire there is a collision between electrons and atoms of the wire which

leads to the generation of heat. Joule’s Law states that when a current

flows in a conductor the amount of heat generated is proportional to

current, resistance, and time in the current flowing.

Mathematical Representation of Joule’s Law

When in a current conducting wire the time of the flowing of current and

the resistance of the wire is constant, the amount of heat produced and

the square of the amount of current flowing the wire are proportional to

each other.

124
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Equation 1 : Hαi2 (Where R and T are Constant) When in a current

conducting wire the time of the flowing of current and the current of the

wire are constant, the amount of heat produced and the amount of

electrical resistance of the wire are proportional to each other.

Equation 2: HαR (Where R and T are Constant) When in a current

conducting wire the amount of the electrical resistance and the amount of

current are constant, the heat produced and the time of current flowing

are proportional to each other.

Equation 3: Hαt (Where R and i are Constant)

When equations 1, 2, and 3 are merged, the resulting formula is

Hαi2.Rt (i, R, and t are variables)

H=(1/J).i2RT (where J is a Joule’s Constant)

The joule’s constant J is defined as the number of work units that furnishes

one unit of heat when converted completely into heat.

Electrical Power: The rate at which the work is done in an electric circuit in

order to maintain the steady current is known as the electrical power of

that circuit. It can also be stated as the rate at which the electrical energy

is converted into other forms of energy. The SI unit of electrical power in

watts W.

P=w/t=I2Rt/t=I2R=IV=V2/R

Solved Example

Calculate the heat energy produced in resistance of 5 Ω when 3 A current

flows through it for 2 minutes.

125
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

The amount of heat produced by the conductor is given by the formula:

Q = I2 R T

Substituting the values in the above equation we get

Q = 32× 5 × 2 × 60 = 5400 J

Useful energy and energy loss

When energy is transformed from one form to another, or moved from one

place to another, or from one system to another there is energy loss. This

means that when energy is converted to a different form, some of the input

energy is turned into a highly disordered form of energy, like heat.

Functionally, turning all of the input energy into the output energy is nigh

impossible, unless one is deliberately turning energy into heat (like in a

heater). As well, whenever electrical energy is transported through power

lines, the energy into the power lines is always more than the energy that

comes out at the other end. Energy losses are what prevent processes

from ever being 100% efficient.

Types of Energy Losses

Energy undergoes many conversions and takes on many different forms as

it moves. Every conversion that it undergoes has some associated "loss" of

energy. Although this energy doesn't actually disappear, some amount of

the initial energy turns into forms that are not usable or we do not want to

use. Some examples of these losses include:

• Heat energy, potentially as a result of air drag or friction. Heat energy

is the most easily dissipated form of energy.

126
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• Light energy is frequently energy seen in combustion, and is a type of

wave motion.

• Sound energy is another type of wave motion caused by the

vibration of molecules in the air. Like heat energy, sound is a type of

energy that is generally lost.

Overall, the goal is to reduce the amount of energy lost to increase

efficiency. As well, collisions that are inelastic refer to collisions where there

is some "loss" of energy during the collision.

Electricity use is a good example that illustrates energy loss in a system. By

the time the energy associated with electric power reaches the user, it has

taken many forms. Initially, the process begins with the creation of the

electricity through some method. For example, the burning of coal in a

power plant takes the chemical energy stored in the coal and releases it

through combustion, creating heat that produces steam. From here the

steam moves turbines and the mechanical energy here turns a generator

to produce electricity. A typical coal fired electrical plant is around 38%

efficient, so ~1/3 of the initial energy content of the fuel is transformed into

a usable form of energy while the rest is lost. Further losses occur during

the transport of this electricity. In the transmission and distribution of

electricity, about 6% of the electricity is lost in these processes. Finally, the

electricity reaches its destination. This electricity could reach an

incandescent light bulb wherein a thin wire is heated until it glows, with a

significant amount of energy being lost as heat. The resulting light contains

only about 2% of the energy content of the coal used to produce it.

127
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Changing to CFL light bulbs can improve this by about 4x, but that only

takes it up to 8% of the initial chemical energy in the coal.

There are also significant energy losses within a car's internal combustion

engine. The chemical energy from the gasoline (or diesel) - which

originates from the Sun as it is a fossil fuel - is then converted into heat

energy, which presses on pistons in the engine. The mechanical energy is

then transported to the wheels which increases the kinetic energy of the

car. Some of this kinetic energy is lost to the sound of the engine, light from

combustion, and to heat energy from the friction between the road and the

tires. Current vehicles are only able to use around 20% of the energy

content of the fuel as power, the rest is lost.

Single and three phase connections

Single phase power circuits have a single power wire, which is known as

the phase wire, and a neutral wire.

In a two-wire alternating power circuit, the current flows between the

power wire and neutral wire. The power current or voltage reverses

periodically, flowing one way on the hot wire to deliver power to a load, and

the other way on the neutral wire.

The voltage reverses 50 to 60 times every second, with a full power cycle

taking place with every 360-degree phase change.

Three phase power is vital because it is capable of delivering much more

power, in a more efficient way, than single phase power ever could. And

while single phase power is perfectly suitable for a huge range of different

128
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

uses, when it comes to powering vast data centers and other businesses

that require vast amounts of electricity, three phase power is essential.

Three phase power works using three separate currents, which are

separated by one-third of the time it takes to complete a full cycle.

In single phase power, the two hot legs remain 180 degrees apart at all

times. By contrast, in three phase power, currents are separated by a

smaller 120 degrees.

Three phase power is a three-wire circuit. It’s a widely used method of

alternating current power generation, transmission and distribution.

• In a single-phase connection, the flow of electricity is through a

single conductor. A three-phase connection, on the other hand,

consists of three separate conductors that are needed for

transmitting electricity.

• In a single-phase power supply system, the voltage may reach up to

230 Volts. But on a three-phase connection, it can carry a voltage of

up to 415 Volts.

• For smooth flow of electricity on a single-phase connection, it

requires two separate wires. One represents the neutral wire and

another one represents a single phase. These are required to

complete the circuit. In a three-phase connection, the system

requires one neutral wire and three-phase wires to complete the

circuit.

• Maximum power gets transmitted on a three-phase connection

compared to a single phase power supply.

129
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• A single-phase connection consists of two wires that make a simple

network. But the network is complicated on a three-phase

connection because there are four different wires.

• Because a single-phase connection has one phase wire, if anything

happens to the network, the complete power supply gets interrupted.

However, in a three-phase power supply, if anything happens to a

single phase the other phases still work. As such, there is no power

interruption.

• Regarding efficiency, a single-phase connection is less compared to

a three-phase connection. This is because a three-phase supply

needs less conductor compared to a single-phase power supply for

the same circuit.

Measures to save electrical energy – energy audit

As per the Energy Conservation Act, 2001, Energy Audit is defined as "the

verification, monitoring and analysis of use of energy including submission

of technical report containing recommendations for improving energy

efficiency with cost benefit analysis and an action plan to reduce energy

consumption".

The type of Energy Audit to be performed depends on: - Function and type

of industry - Depth to which final audit is needed, and - Potential and

magnitude of cost reduction desired Thus Energy Audit can be classified

into the following two types. i) Preliminary Audit ii) Detailed Audit

The information to be collected during the detailed audit includes: - 1.

Energy consumption by type of energy, by department, by major items of

130
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

process equipment, by end-use 2. Material balance data (raw materials,

intermediate and final products, recycled materials, use of scrap or waste

products, production of by-products for re-use in other industries, etc.) 3.

Energy cost and tariff data 4. Process and material flow diagrams 5.

Generation and distribution of site services (e.g. compressed air, steam). 6.

Sources of energy supply (e.g. electricity from the grid or self-generation)

7. Potential for fuel substitution, process modifications, and the use of co-

generation systems (combined heat and power generation). 8. Energy

Management procedures and energy awareness training programs within

the establishment.

Energy conservation is the act of reducing the usage and wastage of

energy. Switching off the AC, light, etc., when nobody is in the room are a

few practices that help in energy conservation.

An energy audit is a tool, which is the start of every activity to improve

energy efficiency. Under the concept of an energy audit, many activities

actually take place – from simple analyses of energy consumption, which

are implemented within expert groups in organizations, to comprehensive

energy audits, which enable the creation of a quality mid-term energy

strategy. If a comprehensive review of possibilities for energy consumption

optimization isn't implemented, some opportunities are lost, which is

evident in higher energy costs. When conducting an energy audit, it is

important to ensure suitable expertise and independence of the

contractor. Based on good cooperation with expert groups within

organizations, we can identify and also implement simpler measures that

don't require higher investments. Within the energy audit, we create a plan,

131
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

which proposes possible organizational and investment measures and

also enables systematic achievement of savings. With every measure, the

level and return of investment and a sensible priority of measure

implementation are determined alongside energy and cost savings.

Recorded energy cost savings, which fluctuate between 5 and 15 percent

of total energy cost in organizations, depend on multiple factors. These

factors are mostly energy complexity of organizations, existing energy use

control and organizational and expert qualifications of responsible

persons. A well implemented energy audit is a foundation for an efficient

upgrade of an energy management system, which is a tool for continued

increase of energy efficiency and cost reduction.

According to the energy auditors we can easily save between 5 and 10% of

their energy consumption (and costs) by changing our behaviour such as

switching electrical equipment off at the mains rather than leaving it on

standby, turning off lights when they’re not being used. Saving Electrical

Energy will directly save money so it is very necessary to understand

bigger unit or amount which we are paying without using the appliances to

that level.

The major appliances in our college are air conditioners, choke bulbs, fans,

computers and they account for a big chunk of the college monthly utility

bill. And if the air conditioner or computer is more than a decade old, a lot

more is spend on energy than you need to. Today’s major appliances don’t

hog energy the way older models do because they must meet minimum

federal energy efficiency standards. These standards have been tightened

over the years, so any new appliance you buy today has to use less energy

132
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

than the model you’re replacing. For instance, if you buy one of today’s

most energy-efficient air conditioner, it will use less than half the energy of

a model that is 12 years older.

Lighting

• Get into the habit of turning lights off when you leave a room. —-Saving

Energy 0.5 %

• Use task lighting (table and desktop lamps) instead of room lighting. •

Take advantage of daylight

• De-dust lighting fixtures to maintain illumination—–Saving Energy 1 %

• Compact fluorescent bulbs (CFL): 1. CFL use 75% less energy than Normal

bulbs. 2. CFL are four times more energy efficient than Normal bulbs. 3. CFL

can last up to ten times longer than a normal bulb.

• Use electronic chokes, in place of conventional copper chokes.—-Saving

Energy 2 %

• Get into the habit of turning lights off when you leave a room. • Use only

one bulb for light fittings with more than one light bulb, or replace

additional bulbs with a lower wattage version.

• Use energy-saving light bulbs that can last up to ten times longer than a

normal bulb and use significantly less energy. A single 20 to 25 watt

energy-saving bulb provides as much light as a 100-watt ordinary bulb.

• Use tungsten halogen bulbs for spotlights—they last longer and are up to

100% more efficient.

• Fit external lights with a motion sensor.

133
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Air Condition Unit

• Replace air conditioner filters every month.

• Turn off central air conditioning 30 minutes before leaving your home.

• Consider using ceiling or portable fans to circulate and cool the air.

• Try increasing your air conditioner temperature. Even 1 degree higher

could mean significant savings, and you will probably not notice the

difference.

• Keep central air conditioner usage to a minimum—or even turn the unit

off – if you plan to go away.

• Consider installing a programmable thermostat. Just set the times and

temperatures to match your schedule and you will save money and be

comfortably cool when you return back.

• Replace air conditioner filters every month.

• Buy the proper size equipment to meet your family’s needs – an oversized

air conditioner unit will waste energy.

Computer / Laptop

• Buy a laptop instead of a desktop, if practical. —-Saving Energy 5 %.

• If you buy a desktop, get an LCD screen instead of an outdated CRT.

• Use sleep-mode when not in use helps cut energy costs by approx 40%.

Turn off the monitor; this device alone uses more than half the system’s

energy.

• Screen savers save computer screens, not energy.

• Laser printers use more electricity than inkjet printers.

134
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Fan

• A ceiling fan in operation throughout night will gobble up 22 units in a

month.

• There is a wrong notion that fan at more speed would consume more

current.

• Fan running at slow speed would waste energy as heat in the regulator.

• The ordinary regulator would take 20 watts extra at low speed.

• The energy loss can be compensated by using electronic regulator.

Insulate the ceiling/roof: Buy efficient electric appliances:

• They use two to 10 times less electricity for the same functionality, and are

mostly higher quality products that last longer than the less efficient ones.

In short, efficient appliances save you lots of energy and money.

• In many countries, efficiency rating labels are mandatory on most

appliances. Look Energy Star label is used.

• The label gives you information on the annual electricity consumption. In

the paragraphs below, we provide some indication of the consumption of

the most efficient appliances to use as a rough guide when shopping. Lists

of brands and models and where to find them are country-specific and so

cannot be listed here.

• Average consumption of electric appliances in different regions in the

world, compared with the high efficient models on the market.

• Educate everyone in the home, including children and domestic helpers.

135
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

UNIT V

SAFETY MEASURES

Insulation for wires

Electrical insulators are materials with a high resistivity (resistivity is a

property of the material) so they can make objects with a high resistance.

This allows insulators to prevent electric current from flowing where it's not

wanted.

Insulators are useful for coating wires, or acting as dielectrics in capacitors.

An insulator (such as plastic, rubber, or glass) can have 1020x the resistivity

of a metal like copper. Often times these insulators are colour-coded to

make it easy to tell what function the wire inside is serving, see figure 1 for

an example.

Air (like in the atmosphere) is actually an excellent electrical insulator. This

means that electricity can be sent through a conductor and it won't jump

through the air. Air does have an upper limit to the voltage it can handle,

which is called the average breakdown voltage (to learn more about

average breakdown voltage, please see all about circuits. This breakdown

voltage is related to lightning.

A copper wire allows the flow of electricity through them easily and to

protect this copper wire from surrounding environment, generally copper

wires are coated with insulator materials such as plastic or enamel which

prevents the charging of wire and it helps in managing any other

environmental effects such as moisture, humidity and temperature and

136
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

protects the safe flow of electricity through copper wires.

These insulated wires are widely used in inductors, transformers, motors,

speakers, electromagnets and many other electrical devices wherever

necessary. If we don’t insulate our copper wires from insulating materials

there is a possibility of wires getting damaged easily due to its surrounding

humidity, moisture and other environmental factors which can affect

copper wires easily.

Colour specification for mains, return and earth

Types of Wiring Color Codes in India

• Single-phase wiring

• Three-Phase Wiring

• Control Wiring System

Single-Phase Wiring

Single-phase wiring is mainly used for residential or domestic purposes.

• Red: Red wires are used as phase wires and they carry electrical

current.

• Black or Yellow: These wires are used for neutral wires. These wires

complete the circuit and provide a return path.

• Green or Green with yellow stripes: These wires are used as

grounding conductors. They also reduce the risk of electric shock.

Three-Phase Wiring

Three-phase wiring is used for industrial purposes.

137
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• Red, Yellow, Blue: These wires carry alternating currents with a 120-

degree phase difference between them.

• Black: It is used for neutral connection and it also provides a return

path for unbalanced currents.

• Green: It is used for grounding conductors.

Control Wiring System

It is used for low-voltage signals to control various electrical devices.

• Red: It is used for power supply lines for control circuits.

• Yellow: It is used for interlock and safety circuits.

• Blue: It is used for control signal lines.

• Black: It is used for grounding.

Wiring Color Codes for AC Power System

Wiring color codes are used to identify and distinguish between the

conductors having different functions.

Phase conductor (Line or Live)

• Single phase: A single-phase system is common in residential wiring

in which Red or Brown color is used. This shows that the wire is

connected to the single-phase supply.

• Three-phase: Three-phase systems are commonly used for

industrial and commercial purposes in which Red, Yellow, or Blue are

used for the three-phase system.

138
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Neutral Conductors

• Light Blue or Black color is used for neutral conductors. It shows a

return path of the current to the source.

Earth Conductor

• Green or Green with a Yellow strip is used for earth conductors. It

ensures safety by providing an earth connection.

Wiring Color Codes for DC Power System

The wiring color codes for the DC power systems are not as standardized

as AC power systems. Different appliances and different industries have

their different wring color for DC power systems.

However a common wiring color code for DC power systems:-

• Positive voltage : Red or orange is used for positive voltage or to

indicate the positive terminal of the battery or conductor.

• Negative voltage : Black or Blue to indicate the negative terminal of

the battery or conductor.

• Earth conductor : Green color is used to indicate the earth conductor

or safety terminal.

Properties of Wiring Color Codes

• The major property of wiring color codes is to identify and distinguish

between different wires or conductors. The different colors used for

color codes specify a unique function which makes the identification

very easy.

139
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• Another major property of wiring color codes is that They ensure the

safety of the appliances and the person working on them.

• Wiring color code is that it makes requirements and maintenance

very easy.

• Standardized color codes make it very easy for a person from one

country to work or repair some appliances in another country.

Standards of Wiring Color Codes

Some of the common color codes accepted in every country are called

Standard wiring color codes.

Some standard Wiring Color Codes for AC Power System are as follows:

Phase Conductors (Line wire)

• Black color is used in single-phase systems.

• The red color is used in 3-phase systems.

• The brown color is used in 230V single-phase systems.

Neutral Conductor

• White or Gray color is used for the neutral conductor, which carries

the return current.

Earth Conductor

• The green color is used for the grounding conductor for safety.

Standard Wiring Color Codes for DC Power System

• Positive Voltage – Red or Orange is used to indicate the positive

terminal of the battery or conductor.

140
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• Negative Voltage – Black or Blue is used to indicate the negative

terminal of the battery or conductor.

• Earth Conductor – Green or Green with a Yellow strip is used to

indicate ground.

Benefits of Standard Wiring Color Codes

The benefits of standard wiring color codes are the same as the wiring

color codes. But this has one major advantage as having the standard

wiring color code is that it helps everyone from any country working with

the appliances safely.

Advantages of Wiring Color Codes

• It helps us to identify specific wires.

• It ensures safety as it provides a visual of the wire’s purpose and also

provides protection to those working on it.

• It ensures safe and effective electrical installations and

maintenance.

• Color codes are the reason for the production of machinery in one

country and shipped worldwide.

Disadvantages of Wiring Color Codes

Though wiring color seems very important for industry and domestic

purposes it still has a few major disadvantages.

• Color codes are very difficult for color-blind people to work on.

• Overheating or dirt accumulation sometimes makes it difficult to

distinguish between similar colors like brown and red.

• The use of many colors may sometimes lead to confusion.

141
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Understanding of fuse and circuit breakers

While selecting the proper fuse and its rated size for electrical appliances is

based on different factors and environments.

Fuse Rating = ( Power / Voltage ) x 1.25

For example, you have to find the right size of fuse for 10A two pin socket.

(1000W / 230V ) x 1.25 = 5.4A

In the above example, 1kW is the power rating which can be controlled

through the 2 pin socket and the main supply voltage is single phase 230V

AC (120V AC in US).

But you should go for the max i.e. 6A fuse rating instead of 5.4A for safe and

reliable operation of the circuit.

142
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

The electrical circuit or the electric circuit is an interconnection of electrical

components to perform a specific function. These circuits use two types of

power, one is alternating current and the other is direct current. The AC

current is generated by power stations and is used for large devices

whereas the DC current is used for batteries, machines, and electrical

appliances. When this current is flowing through the devices, the power

may increase or decrease suddenly. To protect that circuit breakers or

fuses are arranged in series with the components to prevent damage to

the whole circuit.

In relation to the electronics, the fuse is an electrical device that provides

protection to the electrical circuit from the over current. It is called a

sacrificial device because the fuse is a metal strip or a metal wire so

whenever there is an overflow of current in the circuit, this strip melts and

interrupts the current flow. When the fuse is damaged depending on the

type used it must be replaced or rewired. Some of the reasons for fuse

operation are short circuits, device failure, mismatched load, or overload. It

is used to remove the power automatically from a faulty device. In recent

times, the fuses are sometimes replaced by a special device called circuit

breakers. But significantly both share different characteristics.

Fuse - Construction: A fuse consists of a wire or metal strip that has a small

construction compared to all the electrical conductors. These are

arranged in series in order to carry the current flowing through the circuit.

Due to the current flow the resistance of the element liberates heat. When

there is too much flow of current in the circuit then either the fuse will melt

directly or the soldered part in the fuse will melt which makes the circuit

143
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

open. The fuse elements are made up of desired elements in order to

provide stable and predictable characteristics, these elements are copper,

zinc, aluminum, silver, or alloys. To increase the heating effect the fuse

elements are shaped. The current is divided in between the multiple strips

in case of large fuses. To avoid the strain on the fuse these are supported

by steel or nichrome wires.

Fuses are used as safety for the electrical circuits. They are less costly. The

reliability of the fuses is very good. As the age of the fuse increases, its

speed remains the same. There is no necessary to maintain the fuse often.

To have a high interrupting capacity it is not necessary to pay for the high

premiums.

Circuit breakers are automatically operated switches that are specially

designed to protect the circuits from damage. As its basic function is the

same as that of the fuse it is not necessary to replace the circuit breaker

with a new one, instead, they can reset by themselves or manually to

continue performing its operation. The size may vary as they are made to

protect the small household appliances from the large switch gears that

pass high voltage. The circuit breaker that removes the power from the

faulty device is also abbreviated as OPCD - Over Current Protective Device.

The circuit breaker first detects the fault. The detection in the low voltage

circuit is done by itself. In the case of high voltage devices, a separate

protective relay is been arranged, and hence for the operation of these

relays, an extra power supply is required. Once the fault is detected, the

circuit must open by removing the connection in between the contacts

and this is done by the energy stored in the circuit breaker. The stored

144
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

energy is such as the battery, or compressed air or the thermal expansion,

or magnetic field. Once the contacts are removed, the small or miniature

devices are discarded and in the case of high voltage circuit breakers or

power circuit breakers, the contacts can be replaceable.

In the case of the power connection, the flow of electricity takes place

through the circuit box. The fuse or the circuit breaker performs the same

operation, they help the devices to protect the circuit from damage and

they act as a switch. These can be operated manually or automatically.

Once these are operated on the faulty devices, they can either be replaced

or sometimes they can reset themselves to continue the operation.

145
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Types of fuse: kit-kat, HRC, cartridge, MCB, ELCB

Fuses can be classified as “One Time Only Fuse”, “Resettable Fuse”, “Current

limiting and non – current limiting fuses” based on the usage for different

applications.

One time use fuses contain a metallic wire, which burns out, when an over

current, over load or mismatched load connect event occurs, the user has

to manually replace these fuses, switch fuses are cheap and widely used in

almost all the electronics and electrical systems.

There are different types of fuses available in the market and they can be

categories on the basis of Different aspects.

Fuses are used in AC as well as DC circuits.

Cartridge Fuses

Cartridge fuses are used to protect electrical appliances such as motors,

air-conditions, refrigerator, pumps etc, where high voltage rating and

146
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

currents are required. They are available up to 600A and 600V AC and

widely used in industries, commercial as well as home distribution panels.

There are two types of Cartridge fuses. 1. General purpose fuse with no time

delay and 2. Heavy-duty cartridge fuses with time delay. Both are available

in 250V AC to 600V AC and its rating can be found on the end cap or knife

blade.

HRC fuse

A high rupturing capacity fuse contains a fuse wire that safely carries the

short-circuit current for a given time period. During this period, if the fault is

removed, the fuse does not blow off; otherwise, it will melt and disconnect

the circuit from the electrical supply, ensuring the circuit remains safe.

The common material used to make an HRC fuse is glass, but this is not

always the case. Other chemical compounds are also employed in the

147
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

manufacturing and construction of HRC fuses based on different factors.

The external enclosure is made fully airtight to prevent the atmosphere’s

effect on the fuse materials. A major concern with HRC fuses is the low and

uncertain breaking capacity of semi-enclosed fuses.

An HRC Fuse consists of a highly heat-resistant material (such as ceramic)

body with metal end caps, which are welded to a silver current-carrying

element. The internal space of the fuse body is completely filled with a

powder. The material used to fill the inner space may include plaster of

Paris, quartz, chalk, marble, dust, and cooling mediums, among others. This

filling prevents overheating, allowing the fuse to carry normal current.

The heat produced vaporizes the silver element. A chemical reaction

occurs between the silver vapor and the filling powder, resulting in a high-

resistance substance. This substance helps quench the arc in the fuse.

Kit-kat fuse

Kit Kat Fuse is a rewireable, semi-

enclosed fuse developed primarily for

residential wiring and small-scale

applications. The supplied fuse is

manufactured at our in-house facility,

where we use the proper method and

high-grade raw materials in accordance with IS standards. Sentinel

Engineers, one of India's leading Kit Kat Fuse Manufacturers, offers a wide

range of alternatives. Before it reaches the clients, we make sure it meets

all of the quality standards.

148
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Kit Kat Fuse has the following advantages:

1. It is simple and quick to install, and it takes very little time to replace.

2. It is incredibly cost-effective and is the most cost-effective type of fuse.

3. Throughout its service life, the offered Electrical Kit Kat Fuse requires little

to no maintenance.

4. With typical handle and lugs options, the range is available from

16A to 500A.

MCBs are time-delay tripping circuit breakers. The operating time of these

devices is controlled by the magnitude of the overcurrent passing through

them, which means that the device operates whenever an overload exists

for long enough to endanger the circuit being protected.

Transients such as motor starting currents or switch surges do not affect

MCBs. These devices are typically designed to operate in less than 2.5

milliseconds when there is a short circuit fault and between 2 seconds and

2 minutes when there is an overload.Under normal operating conditions,

the MCB acts as a switch (a manual switch) to turn the circuit on or off.

The device automatically trips in the event of a short circuit or overload.

This will cause a

current interruption

in the load circuit,

resolving the issue.

The trip is visually indicated as the operating knob automatically moves to

the OFF position. The automatic operation/ tripping MCB can be obtained

in two ways; magnetic tripping and thermal tripping.

149
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

When there is an excessive flow of electric current in a circuit, the M.C.B.

automatically falls and switches off the circuit in a very short time. It is

raised after the fault has been corrected. M.C.B.s do not need to be

replaced every time a high current pass through them, but fuses must be

replaced because they melt and break. Thus, in this way M.C.B is superior

to the fuse wire.

ELCB fuse

An Earth-leakage circuit breaker (ELCB) is a safety device used in electrical

installations with high earth impedance to prevent shock. It detects small

stray voltages on the metal enclosures of electrical equipment and

interrupts the circuit if the voltage level exceeds danger threshold.

The working principle of voltage ELCB

is quite simple. One terminal of the

relay coil is connected to the metal

body of the equipment to be

protected against earth leakage and

other terminal is connected to the

earth directly.

If any insulation failure occurs or live phase wire touches the metal body, of

the equipment, there must be a voltage difference appears across the

terminal of the coil connected to the equipment body and earth. This

voltage difference produces a current to flow the relay coil.

If the voltage difference crosses, a predetermined limit, the current through

the relay becomes sufficient to actuate the relay for tripping the

150
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

associated circuit breaker to disconnect the power supply to the

equipment.

The typicality of this device is, it can detect and protect only that

equipment or installation with which it is attached. It cannot detect any

leakage of insulation in other parts of the system.

Purpose of earth line

In every circuit, one wire is connected to the earth, the main function of the

earth wire is to protect the sudden damage of the electrical appliances or

the electrical instruments due to the sudden voltage increase or the

leakage of the current. Earth wire is also used for the safety measures.

Accidently if any current is leaked, earth wire helps to ground the leakage

of current.

Necessity of the earth wire in metallic electric appliances:

The metallic body of the electrical instruments will be connected to the

earth or ground by means of the earth wire or ground wire, if there will be

the leakage of the current the current is sent to the ground by means of

earth wire. When the earth wire is connected to the metallic body, it gives

the low conducting path to the current. Thus, the earth wire keeps the

potential of the leaked current to the earth. So, that the user of the metallic

electric component may not get the shock.

The main reason for doing this in electrical network is for the safety. When

all metallic parts in electrical equipment are grounded then if the

equipment fails there are no dangerous voltages present in the

equipment’s outer case.

151
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Purpose of Earthing

1. Safety for Human life/Building/Equipment

To save human life from danger of electrical shock i.e. to provide an

alternative path for the fault current to flow so that it will not endanger the

user

To protect buildings, machinery & appliances under fault conditions

To ensure that all the exposed conductive parts do not reach a dangerous

potential

To provide safe path to dissipate lightning and short circuit currents

To provide stable platform for operation of sensitive electronic equipment

2. Over voltage protection

Lightning, line surges or unintentional contact with higher voltage lines can

cause dangerously high voltages to the electrical distribution system.

Earthing provides an alternative path around the electrical system to

minimize damages in the system.

3. voltage stabilization

There are many sources of electricity. Every transformer can be considered

a separate source. If there were not a common reference point for all these

voltage sources, it would be difficult to calculate their relationships to each

other.

Methods of earthing

1. plate type earthing

152
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Cast iron/ galvanized iron (GI)/copper plate is buried deep into the earth in

the vertical position and GI strip is bolted with the plate which is brought up

to the ground level. These types of earth pit are generally filled with

alternate layer of charcoal & salt.

2. pipe type earthing

GI pipe with holes for connecting the earth wires are buried into the earth.

pit are also filled with alternate layer of charcoal & salt.

Factors affecting the earth’s resistivity

1. Soil condition – different soil conditions give different soil resistivity

2. Moisture – dry soils are poor conductors of electricity, because they

have high resistivity

3. Dissolved salts – salt content can improve the conductivity of the

soil; but it corrodes metal

4. Physical composition – rocky or gravel soils generally have high

resistivity

Lighting arrestors

Lightning arresters can be made from a variety of components and

function similar to a switch, either preventing or allowing electrical flow

through them. To do this, a lightning arrester uses semi-conductor

materials that act like conductors under some conditions

and insulators under other conditions. At normal line voltage the device

acts like a high resistance open switch so that electricity cannot flow

through it and must stay in the distribution conductors where it normally

belongs.

153
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

A lightning arrester on a distribution line

Once a lightning strike hits the distribution system, however, the higher-

than-normal voltage causes the lightning arrestor material to become a

conductor and provides an easy, purpose-designed path for the lightning

to flow from the distribution system conductors into the earth. Once the

energy from the lightning strike leaves the system and the voltage returns

to normal levels, the components inside the arrester again act like an open

switch thus removing the temporary path to the earth.

Lightning arresters

are devices

installed to shield

power lines, homes,

and structures

from dangerous

power surges. As

the name suggests, they’re primarily designed to safeguard against

damage caused by lightning strikes. However, they can also protect the

structure from various other sources.

154
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Lightning arresters are cylindrical objects, one- to two feet long, consisting

of a series inductor and a spark gap.

Lightning arresters are typically installed near a critical entry point or

appliance, including generators and electrical panels. When a bolt of

lightning strikes, the arrester activates and deflects the lightning to the

ground, where it disperses harmlessly.

These components don’t actually stop lightning strikes, as that would be

too dangerous. Instead, they limit the electrical charge and divert it, giving

it a safe route to pass through the ground instead of essential electrical

devices.

Main features of a fully functional lightning arrester:

The spark-over voltage must exceed the abnormal or normal power

frequency occurring in the system. Additionally, it shouldn’t draw any

electricity in regular operating conditions.

It must break down rapidly due to any abnormal voltage above its

breakdown value, providing a safe path to the ground.

When breakdowns take place, the arrester should carry the discharged

electricity without sustaining damage. Also, the voltage across the element

shouldn’t surpass the breakdown threshold.

It must interrupt the current after the breakdown the moment the transient

voltage falls below the breakdown threshold.

The lightning arrester should be placed near the equipment it protects. It’s

generally linked between ground and phase in an AC arrangement and

155
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

ground and pole in a DC system. Furthermore, AC systems contain a

separate arrester in each phase.

Surge diverters are installed in extra-voltage AC arrangements to shield

the generator, bus bars, circuit breakers, lines, transformers, and other

components. Likewise, HVDC structures include an arrestor to safeguard

against filters, reactors, valve converter units, and similar elements.

Moreover, there are various types of lightning arresters that protect

different power systems. The choice largely depends on several common

factors. The list includes the line frequency, voltage, weather conditions,

reliability, and cost.

To determine the perfect arrester for your household, reach out to a

seasoned electrician. They can also install the component efficiently

without any safety risks.

Short circuiting and over loading

Overload refers to the situation where the current of the electric load

exceeds its rated value for a long time. A short circuit refers to an

accidental or intentional conductive path between two or more conductive

components, forcing the potential difference between these conductive

components to be equal to or close to zero.

Other definitions of short circuit:

• An unwanted low-resistance connection between two points in the

circuit.

• The circuit is abnormal.

156
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• This happens when a circuit path is created between the positive

and negative poles of a battery, power supply, or circuit.

• What happens when the hot wire and the neutral wire touch each

other.

• An accidental connection between two points in a circuit, such as a

tree branch or an animal connecting the gap between two

conductors.

Other definitions of overloading:

Electrical overload is a kind of overcurrent, the current through the wire or

circuit exceeds its capacity, which leads to overheating, and there is a risk

of fire or damage to the equipment.

Voltage level

For any finite current flowing through a short circuit, the voltage across the

short circuit is zero. On the circuit diagram, a short circuit is represented by

157
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

an ideal wire with zero resistance. In the case of overload, the voltage can

be very low, but not zero.

Current level

The maximum value of the short-circuit current is directly related to the

size and capacity of the power supply, and has nothing to do with the

circuit load current protected by the protection device. The greater the

capacity of the power supply, the greater the short-circuit current. The

overload current is directly related to the capacity of the load. This is why

the short-circuit current level is much higher than the overload current. The

short circuit is a multiple of the rated current. The overload is close to the

rated current.

Danger

Short circuit is more dangerous than overload. Because the current level is

higher. In high voltage applications, short circuits are extremely dangerous.

The energy transfer is fast in a short circuit, and energy transfer is slow in

an overload.

Reason

Through careful system and equipment design, as well as proper

installation and maintenance, the power system should avoid short circuits

and overloads as much as possible. However, even if these precautions are

taken, short circuits and overloads still occur.

The reasons for the short circuit are:

• There are pests and rodents in the equipment.

158
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• Loose connection.

• Voltage surge.

• Deterioration of insulation.

• Accumulation of moisture, dust, concrete sap and contaminants.

• Intrusion of metal or conductive objects, such as fish belts, tools,

jackhammers or loaders.

Some reasons for overloading are:

1) Excessive consumer load.

2)Malfunctioning electrical appliances.

3)Poor wiring and grounding.

4)Misuse.

Protective device

Short circuits and overloads must be quickly eliminated from the power

system. This is the job of the circuit protection device. In order to do this, the

protection device must have the ability to interrupt the maximum current

that can flow at the equipment location.

Fuses and circuit breakers can protect the system from overload and short

circuit. Thermal overload relays can only prevent overload. Magnetic circuit

breakers can only protect short circuits.

When a short circuit occurs in the power system, several things happen-

they are all bad:

• In the short-circuit position, arcing and burning may occur.

159
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• The short-circuit current flows from different power sources to the

short-circuit location.

• All components that carry short-circuit current are affected by

thermal and mechanical stress.

• The system voltage drop is proportional to the magnitude of the

short-circuit current.

The consequences of overloading are:

• Residual current caused by line isolation problems increases power

consumption.

• Direct contact with damaged wires may cause personal accidents.

• Continuous overload may cause a short circuit.

In industrial and commercial power systems, the calculation of short-

circuit current is essential for selecting appropriate rated protection

devices and equipment. Nowadays, the power system carries a larger

power block and has higher requirements for safety and reliability. There

are many parameters to consider when calculating short circuits.

Therefore, the short-circuit calculation is not easy and must be performed

carefully.

The protection device reacts very quickly to a short circuit. However, the

opening time of the overload protection device will be delayed. Fast

tripping is essential in short-circuit protection.

An overload will cause a thermal trip, and a short circuit will cause an

electromagnetic trip of the protection device.

160
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

It should be turned off only when the heat generated by the overload

exceeds a predetermined limit. Therefore, the trip time of a smaller

overload is correspondingly longer than that of a larger overload. The

short-circuit current should be disconnected immediately.

Electrical safety

We rely on electricity, but sometimes underestimate its capability of

causing injury. Even household current (120 volts) can stop your heart. UW

personnel need to be aware of the hazards electricity poses, such as shock,

fire and explosion, and either eliminate or control those hazards.

Shock

Electrical shock happens when current passes through the body. Electricity

travels through closed circuits, and people, sometimes tragically, can

become part of the circuit. When a person receives a shock, electricity

flows between parts of the body or through the body to a ground.

This can happen if someone touches both wires of an energized circuit,

touches one wire of the circuit while standing unprotected or touches a

metal part that has become energized.

Electrocution refers to the injury or lethal dose of electrical energy.

Electricity can also cause forceful muscle contraction or falls. The severity

of injury depends on the amount of current flowing through the body, the

current's path through the body, the length of time the body remains in the

circuit and the current's frequency.

161
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Fire/Explosion

Electrical fires may be caused by excessive resistance that generates heat

from any of the following:

• Too much current running through wiring where overcurrent

protection fails or does not exist

• Faulty electrical outlets resulting in poor contact or arcing

• Poor wiring connections and old wiring that is damaged and cannot

support the load

An explosion can occur when electricity ignites a flammable gas or

combustible dust mixture in the air. Ignition from a short circuit or static

charge is possible.

Tips to avoid electrical shock

• Don't work with exposed conductors carrying 50 volts or more.

• Make sure electrical equipment is properly connected, grounded and

in good working order.

• Extension cords may not be used as permanent wiring and should be

removed after temporary use for an activity or event.

• Surge suppressors with built-in circuit breakers may be used long-

term and are available with three, six and 15 foot-long cords.

• High amperage equipment such as space heaters, portable air

conditioners and other equipment must be plugged directly into

permanent wall receptacles.

162
Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

• Do not access, use or alter any building’s electrical service, including

circuit breaker panels, unless you are specifically qualified and

authorized to do so.

• Wet environments can increase the risk of an electrical shock.

• Inspect portable cord-and-plug connected equipment, extension

cords, power bars, and electrical fittings for damage or wear before

each use. Repair or replace damaged equipment immediately.

• Always tape extension cords to walls or floors when necessary. Do

not use nails and staples because they can damage extension cords

and cause fire and shocks.

• Use extension cords or equipment that is rated for the level of

amperage or wattage that you are using.

• Always use the correct size fuse. Replacing a fuse with one of a larger

size can cause excessive currents in the wiring and possibly start a

fire.

• Be aware that unusually warm or hot outlets or cords may be a sign

that unsafe wiring conditions exists. Unplug any cords or extension

cords from these outlets and do not use until a qualified electrician

has checked the wiring.

• Always use ladders made with non-conductive side rails (e.g.,

fibreglass) when working with or near electricity or power lines.

• Place halogen lights away from combustible materials such as

cloths or curtains. Halogen lamps can become very hot and may be

a fire hazard.

• Risk of electric shock is greater in areas that are wet or damp. Install

Ground Fault Circuit Interrupters (GFCIs) as they will interrupt the

163
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

electrical circuit before a current sufficient to cause death or serious

injury occurs.

• Use a portable in-line Ground Fault Circuit Interrupter (GFCI) if you

are not certain that the receptacle you are plugging your extension

cord into is GFCI protected.

• Make sure that exposed receptacle boxes are made of non-

conductive materials.

• Know where the panel and circuit breakers are located in case of an

emergency.

• Label all circuit breakers and fuse boxes clearly. Each switch should

be positively identified as to which outlet or appliance it is for.

• Do not use outlets or cords that have exposed wiring.

• Do not use portable cord-and-plug connected power tools if the

guards are removed.

• Do not block access to panels and circuit breakers or fuse boxes.

• Do not touch a person or electrical apparatus in the event of an

electrical incident. Always disconnect the power source first.

First aid for electrical shock

If you think someone is suffering from electric shock, approach with

extreme caution.

The first step is to separate the person from the source of electricity as

quickly as possible. The best way of doing this is to turn off the supply, for

example, by unplugging the appliance or by turning the mains off at the

fuse box (consumer unit).

164
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

If this isn’t possible, then try to remove the source of electricity from the

person using a piece of insulating material, such as a length of wood.

Assess the Situation: The first and most critical step is to ensure your

safety and the safety of others. If the area is still hazardous, such as in the

case of exposed live wires, refrain from approaching the victim until you

have shut off the power source or have received professional assistance.

Call for Help: Dial emergency services immediately to request professional

medical assistance.

Do Not Touch the Victim: Avoid direct contact with the victim until you are

sure the power is off or the electrical source has been isolated. Touching

an electrified person without proper precautions could lead to a second

victim.

Cut the Power: If possible, disconnect the power source or turn off the

electricity supply at the main circuit breaker or fuse box. Use a non-

conductive material, such as a wooden stick or a dry cloth, to turn off the

power if you can't reach the breaker without getting too close to the victim.

Check for Breathing and Pulse: Once the power is off and it is safe to

approach, check the victim for signs of breathing and a pulse. If the person

is unresponsive and not breathing, begin cardiopulmonary resuscitation

(CPR) immediately.

Move with Caution: If the victim is in immediate danger, such as near a fire

or immersed in water, use a non-conductive object to gently move them

away from the hazardous area before starting CPR.

165
 Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

Cover Burns: If the victim has suffered burns due to the electrical contact,

cover the affected areas with a sterile, non-adhesive dressing. Avoid using

creams, ointments, or ice, as they can worsen the injury.

Keep the Victim Warm: Electric shock victims can experience hypothermia

even in warm weather. Cover them with a blanket or clothing to help

maintain body temperature while waiting for medical help.

Support Emotional Well-Being: Electric accidents can be traumatic for

both the victim and witnesses. Offer reassurance and emotional support to

those involved.

Fire safety for electric current

About 60% fires are of electric origin on account of electric short circuit,

overheating, overloading, use or non-standard appliances, illegal tapping

of electrical wires, improper electrical wiring, carelessness and ignorance

etc. It can lead to serious fire and fatal accidents, if proper instructions are

not followed. Such incidents can be minimized to a great extent if

adequate fire precautions are observed. Electrical fires spread rapidly

especially in buildings and cause loss of lives and property. It is, therefore,

necessary to act fast. Raise an alarm for help. Switch off power supply to

de-energise the equipment. Use dry sand, CO2, dry powder or Halon

extinguishers.

1. Use I.S.I. certified appliances.

2. Use good quality fuses of correct rating, miniature circuit breakers

and earth leakage circuit breakers.

3. Use one socket for one appliance.

166
Manonmaniam Sundaranar University, Directorate of Distance & Continuing Education, Tirunelveli

4. Switch off the electric supply of the fire affected areas.

5. Fuses and switches should be mounted on metallic cubicles for

greater safety against fire.

6. Replace broken plugs and switches.

7. Keep the electrical wires away from hot and wet surface.

8. Switch off appliance after use and remove the plug from the socket.

9. Switch off he ‘Main’ switch when leaving home for a long duration.

10. Do not overload outlets.

11. Plug heat generating appliances directly into an outlet, not into a

power strip or extension cord.

12. Don't put electrical cords underneath rugs or pinched behind

furniture

13. Charge laptops and phones only on hard surfaces, not on beds or

sofas.

14. Have a licensed electrician review your home’s electrical system

every ten years. Small upgrades and safety checks can prevent

larger problems.

15. Consider installing tamper resistant (TR) outlets in homes with small

children.

16. When charging devices that use lithium-ion batteries, always use the

manufacturer’s battery, cord, and power adapter made specifically

for the device. Disconnect charging equipment when the device is

charged. Overcharging and aftermarket/generic accessories have

been linked to serious Li-ion battery fires.

167