20 pius augustine household electricity

1
Household electricty and wiring

Electric Power
&
Household Electricity
Dr. Pius Augustine, SH College, Kochi
This PPT is part- Physics for all (free material)
Target: IIT JEE, AIEEE, JAM, CSIR-UGC, GATE, JEST, interviews, competitive exams
Grades 9 and above
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ng
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Love of Science and Humanity

Electricity is the most useful energy form
But Handle With Care
Warning!!
This PPT is prepared only to get a basic
understanding on household electrical wiring. Not
for experimenting.

The rate of work or, the rate
of dissipation of electrical
energy, is called elelctric
power
Measured in watt. (W)

It is the product of voltage
and current which can
flow through an electrical
device.

kilowatt hour (kWh)
kWh is the electrical energy
consumed when electrical
appliance of power 1kW working
for 1hour
1kWh = 1kW *1h = 1000W * 3600 s
= 3.6 * 106 J

1 kWh – 1 unit electricty

A house is having following instruments. Number of
hr/day in use is given. Calculate monthly bill
assuming the rate is Rs. 6/unit.
Bulb (60W) – 3 hrs
2 CFL lamp (20 W each) – 5 hrs
Electric iron (600 W) – 15 min
Fridge (250 W) - 24 hrs
3 Fan (100 W each) – 8 hrs

Daily use
Bulb (60W) – 3 hrs = 0.06 kW x 3hrs = 0.18
2 CFL lamp (20 W each) – 5 hrs = 2 x 0.02 kW x 5 =0.2
Electric iron (600 W) – 15 min =0.6 kW x 0.25 h =0.15
Fridge (250 W) - 24 hrs = 0.25 kW x 24 = 6
3 Fan (100 W each) – 8 hrs = 3 x 0.1 x 8 = 2.4
Total consumption/day = 8.93 kWh = 8.93 unit
Total consumption/month = 8.93 x 30 = 267.9 unit
Monthly bill = 267.9 x Rs.6 = Rs. 1607.4

How can I bring down
my electricity bill?
Do an electricity audit and work out the way to
reduce the consumption, not only to reduce the
electricity bill but for a greater reason……

60 W bulb has greater resistance
Hint : P = V2/R
V constant for both

i. Square of current I2
ii. Resistance of the conductor R
iii. Time for which current is passed. t
H = I2Rt

During their motion the electrons
collide with one another and hence
lose some kinetic energy.
Loss in kinetic energy is dissipated
as heat across the conductor

 Electric heater
 Electric iron
 Electric geyser
 Soldering iron
 Electric kettle

The power expended by a
source is said to be 1watt, if
one ampere of current flows
through it under a potential
difference of 1volt
1 watt = 1 J/s

Because it has high melting
point and high resistivity
and does not easily react
with air.

Porcelain fuse

Cartidge fuse

 Safety device in an electric circuit.
 Weakest point – melts and
breaks circuit when large
current flows due to
i. Short circuiting
ii. Overloading
iii. fluctuation
Fuse ?

 The fuse is a short piece of wire made of an
alloy of lead and tin having a low melting
point.
 When electric current is passed through it the
fuse gets heated.
 If the current passing through the fuse
exceeds the safe guard limit the heat
produced melts the fuse and this breaks the
circuit.

i. Tin (63%) + lead (37%) alloy
ii. Low melting point 200oC
iii. Having high resistivity compared to
copper
(temperature of fuse wire rises rapidly
compared to copper connecting wire
when current in circuit increases)

Every instrument has a safe limit of
current and a maximum permitted
current (without heating the
appliance)
Fuse should be of lower value of
current (safe current) rather than the
maximum current which circuit can
tolerate.

So that it melts and breaks the
circuit as soon as the safe
limit of current is exceeded.

If connected in neutral wire – still it
will melt and break circuit.
But, appliance will continue in
contact with the live wire.
A person touching the appliance
will get shock.

1. Proper wiring.
Away from wood work,
curtains or other inflammable
materials.
Minimum no. of joints,
covered with insulating tapes.

wires

2. Proper rating of wire.
Depend on the current it can
tolerate.
Different types of wires for
different appliance.

Improperly Grounded Appliance with Short

Grounded Appliance

3. Proper earthing
Electric appliance such as oven, heaters, table fans
etc are frequently touched by us with bare hands.
Sometimes live wire of the circuit may touch the
casing making it live.
If body of the device is earthed, high current flows
to earth and melts fuse and protect the person
who touches the appliance from electric shock.

Switches - always in live wire ?
In the ‘off mode’ no current will flow through a
person who happens to touch the appliance.
If switch is in neutral, (serve the purpose of switch
– on and off) person touching the appliance may
get shock even in off mode, due to completion
of circuit to ground through the person.

Socket: serves the purpose of source
3 hollow brass cylinders embedded in
insulating material
Earth connection should be of larger
diameter
Live – right, neutral - left
Earth – big upper cylinder

Avoid using adaptors:
More instruments are connected from
the same socket using adaptors, total
current in the socket may cross the
upper limit for the socket, which is
dangerous.

Plugs: to connect portable appliances to
mains.
3 cylindrical brass pins.
Capable of being fit in the cylinders of
socket
Upper thick and long – earth
Lower right – live
Lower left - neutral

Have fun ….but careful

Long: Earth pin will be the first one to
make connection
Thick: offers less resistance to the flow
of current to earth, in case live wire
comes in contact with body of the
appliance

Process in which metal body of appliance is
connected to a thick copper plate buried
into the earth surrounded by a mixture of
charcoal and common salt by means of a
copper wire.
Earth – An electric sink which can receive or
release any amount of electrons keeping
its potential zero.

Electric disaster

The resistance of the immersed portion
decreases and so the current through the
entire wire increases. This is why the
portion outside the water becomes
brighter.

Cut the heater coil in to two equal halves (R/2)
Join the ends of the coil and apply 110V across it.
Parallel combination of two R/2.
Power consumed in each half will be P/2.
In parallel, Peff = P1 + P2 = (P/2 + P/2)
So total power is P.
2202/R1 = 1102/R2= (110 x 2)2/R1. R2 = R1/4

Yes,
If a battery of large emf is connected
in opposition to the emf of the cell.
Eg. During charging of a battery.

Heating wire must have high reisistivity
and high melting point.
Fuse wire must have high resistance
and low melting point.

The resistance of the wires connected to
the bulb is very low (copper), therefore,
less heat is produced.
Heat produced is H = I2Rt
Since I and t are same for both heating and
connecting wires, R matters.

Resistance of the circuit is halved
and current will increase.
Amount of heat produced in the
same time will be twice the
previous amount H =(2I)2 (R/2) t.

Higher power instrument will have less
resistance.(designed for same p.d.)
Current is same in series connection
Eergy conversion is better in instrument
having high R.
40W bulb glow better in series connection

 Opens the circuit when current in a house
wire exceeds the allowed current for that
circuit
 Protects people from being electrocuted to
death
 Protects from burning down the house.
 When circuit overloads cause the generation
of heat

Usually 15 amp
breaker
30 amps or greater

Ordinary breakers are rated as 15 amps
Bigger breakers provided for such circuits
that require 240 volts e.g. Dryers and
water heaters.
Instead of circuit breakers some electrical
devices have fuses. Often electric stoves
have fuses.

1. Frayed electrical wires
2. Octopus outlets
3. Water and electrical wires
4. Plug receptacles to protect
small children
5. Over loading electrical circuits

Double pole iron clad switch
Cut off live and neutral wires by
operating single lever
Iron body is earthed

Even if one device gets fused, others
continue working.
All the devices work on same voltage.
Parallel connection overall resistance of
circuit decreases, so that each
appliance receives optimum amount
of current.

Generally water contains minerals make
it conducting.
If moisture on hands, comes in contact
with terminal of switch, receives
electric shock.

If fuse is in neutral, high
current due to short
circuiting of live and earth
will not melt fuse.

For tight fitting in to the socket.
No spark and over heating.

For high voltage and large current
special wires are prepared by
twisting together number of thin
copper wires and providing them
with heavy insulation.

i. Longer wires are required for wiring
various rooms.
ii. One fuse melts, disconnects all appliances
in that circuit.
iii. Requires plugs and sockets of different
current vale for different appliances.
iv. Installation – expensive

i. Separate fuse for each appliance. If one
stops due to melting of fuse, others
unaffected.
ii. Length of wire needed is small
iii. Increase or decrease thickness of wire
according to requirement of appliance-
save a lot on installation charges.
iv. Easier to install.

i. Good resistivity (high resistance in
minimum length) for better electric to
heat conversion
ii. Should not get oxidised (upto 1000 oC)
iii. High melting point
iv. Thermal expansion should not be very
large (control loosening)

Nichrome : Ni – 60%
iron – 25%
chromium – 15%
Manganin : Mn – 83%
Cu – 13%
Ni – 4%

i. High melting point
ii. High resistivity
iii. Should not be brittle at high
temperature
iv. Should be ductile
Eg. Tungsten (W) M.P 3300oC

Double pole type.
When electric appliance is connected
properly using a pair of dual switch,
it can be switched on or off from
any of the dual switches.
Eg. Maindoor light - two switches

Explain the transmission of
electric power from the
generating station to your
house.

Why is the electric power
from the generating
station transmitted at a
high voltage ?

What is the voltage and
frequency of the a.c.
supplied for domestic use in
India ?

Name the three connecting wires used
in a house hold circuit. Which two
wires are at the same potential ?
In which of the wire the switch is
connected ?

What is the pole fuse ?
Write down its current
rating

Name the two systems of
house wiring. Which of the
two systems is economical ?

Draw a labeled diagram with necessary
switch, regulator etc, to connect a
bulb, a plug socket and a fan with the
mains. In what arrangement are these
connected to the mains . Series or
parallel ?

Connected after kWh meter
Higher current rating, it will not
melt even if all the instruments
are working normally together.
Protect in case of high current

Watt-hour meter

Types of Plugs
Used in the
Home
Drier Plug or
Stove Plug
(Ground)
Lamp Plug or
Hair Dryer
(Polarized)

Power transmission

Entire India is divided into 5 regions of
transmission
N, E, S, W and NE regions
Power grid corporation of India is the
agency responsible for inter state
transmission of electricity
NTPC - 75%, NHPC- 21% and NPCL – 4%

Generating station (11kV)
Grid sub station (132kV)
Main substation (33kV)
Heavy industries
Intermediate substation (11kV)
light industry
City substation (220V)
consumers

11 kV

Draw circuit diagram for tube
light ?

Q. Do the following wiring with the power board (motor plug is
attached to the socket) given.
i) Motor is on when switch is turned on, indicator lamp also turns
on?
ii) Indicator is always on irrespective of the switch is on or off?
iii)Indicator is off always. But when the motor is turned on, motor
doesnot work but indicator is on.

Red – Live
Black – Neutral
Green - Earth
Tester lamp is in series with a very high resistance.
When a person touches the rear end of the tester- the lamp,
resistance and human body form the series circuit!
(current is too low- sufficient for lamp to glow)

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Dr. Pius Augustine, SH College, KochiDr. Pius Augustine, SH College, Kochi

95
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Dr. Pius Augustine, Dept of Physics, Sacred Heart College, Thevara
we will
overcome
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Dr. Pius Augustine, Asst. Professor, Sacred Heart College, Thevara, Kochi.

20 pius augustine household electricity

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