Download Electricity in Home

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Electricity
in
Fuse or mcb L Live
N Neutral
E Earth
Home
Electricity in
The second circuit is used where there are two switches, for example at
each of two doors to a room. The type of switch used is called a two-way
switch and, if the light is off, as drawn, either switch will switch it on. If the
light is on, either switch can switch it off. Examine the circuit and see why
this is so.
the
N Neutral
How is electricity supply delivered to
a house?
L Live
N Neutral
the
Fuse or mcb
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The ESB maintains a national network of high tension power
Fuse or mcb L Live
lines. The voltages on these lines are as high as 400 kV. Such
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second
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switches,
for example at
voltages are not delivered to domestic premises. Instead the
Two-way switch
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each
of
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a
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type
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called
a two-way
voltage is stepped down at transformers to a more suitable
E Earth
switch and, if the light is off, as drawn, either switch will switch
it on.N Neutral
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lower value. A two-wire cable is used to bring electricity to
light
is
on,
either
switch
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switch
it
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circuit
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why
Fig.
the
home.
neutral is connected
a metal plate
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ESBThe
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this is so.
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Fig.3
Lighting circut, two two-way switches
lines. The voltages on these lines are as high as 400 kV.
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Other circuits
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voltages
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the
and
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Lighting circuits do not require large currents. Typically, a circuit breaker
independent radial circuits which are not
or fuse of 6 amps is used. The conductors in lighting cables therefore
Atvoltage
the house,
main fuse and
meter
installed.
transformers
to a more suitable
isastepped
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How is electricity supply delivered to
a house?
need not be very thick. One 100 Watt bulb uses less than half an amp as
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NNeutral
lower value. A two-wire cable is used to bring electricity
to
showers. Cookers and showers require
shown below.
How
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distributed
in thetohouse?
the home.
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is connected
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Fuse or mcb L Live
IV = Power
0.45 A x 220V = 100 W
The cable is then terminated on a consumer unit. From the consumer unit
Why use fuses and mcb
ground, and so is at 0V. Therefore, the neutral is said to be
Socket 1
Socket 2
different circuits are run to the various points where electricity is needed
Fig.3 Lighting circut, two two-way switches
A fuse is a wire that will get hot and mel
Neutralprotect a circuit feeding more than
Therefore,
- lights,
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fed with
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earthed.
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ten 100 W bulbs. In practice, the lighting circuits for a number of rooms are
the consumer unit, so all domestic circuits are in parallel.
Fuse or mcb
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reducing the
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and below this 50 times a second giving an effective
220V.
connected
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onenot
mcb.
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The live wire connection to every circuit is fed through a safety device
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At the
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the current
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lighting circuits in a house.
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Circuit breakers are faster and more pre
shown below.
reset. The circuit breakers on a distribu
can be a fuse or a miniature circuit breaker (mcb).
How is electricity distributed in the house?
Power circuits for appliances (sockets)
Fuse or mcb
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are called miniature circuit breakers.
A xa220V = 100 W
The term
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for =
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thing powered0.45
through
The cable is then terminated on a consumer unit. From the consumer
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plug and a flexible cable. The standard plug is designed to carry up to Socket
13
1
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different circuits are run to the various points where electricity isamps,
needed
What is a residual curre
though most appliances need considerably less. Inside the plug
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ten 100
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the consumer unit, so all domestic circuits are in parallel.
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Socket 2 Socket 3 Socket 4
electricity from a live wire going to earth
which cuts off the circuit if the current demanded becomes excessive.
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lighting circuits in a house.
is called a residual current or an earth-le
In general, almost all the power
consumed in a house is converted into
can be a fuse or a miniature circuit breaker (mcb).
NNeutral
Fig.1 Image of consumer unit and meter
The conductors in the circuit are copper and are insulated. The resistance
must be low enough that,
•
at the rated current, the drop in voltage between the consumer unit
and the load is low
•
the copper does not get too hot.
Cables with large diameters have less resistance than those with smaller
diameters. In general, domestic circuits are classified as lighting circuits
or power circuits.
Fuse or
mcb L Live
heat.
Appliances
that generate a lot of heat, like electric fires or kettles,
use large currents and consume a lot of power. At 220V, the current per
kilowatt is about 4.5 amps. Many other appliances such as radios or
mobile phone chargers need little power.
A fault current to earth has implications.
smaller current, 30 mA, can kill a p
Power circuits for applianceseven(sockets)
The RCD consists of a circuit breaker
The term appliance is a general term for any thing
powered through a
entering and leaving on the live and ne
N Neutral
E Earth
When sockets are fittedplug
as shown
the circuit
is called
radial circuit.
and below,
a flexible
cable.
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plug is designed
to carry
up usually
to 13 also tri
mA. Domestic
RCDs will
(It radiates out from theamps,
consumer
unit.) Because
each socket can
supply
63 A, is
exceeded.
though
most appliances
need
considerably
less.
Inside the plug
13 amps there is a limit to the number of sockets that can be supplied by
there is a fuse. The fuse is usually either a 3-amp
(forforappliances
Thefuse
current
most or all ofup
the circuit
one cable.
which
is between
the main fuse and
to 660 Watts) or a 13-amp fuse (for appliances RCD
up to
almost
3 kilowatts).
Fig.4 A radial circut with
two sockets
Where
a 3-amp
fuse is sufficient it should be used. A fault then is more
Socket 1
likely to blow this fuse only, Socket
rather2 than both blow
it andis
also
tripearth
the mcb
What
the
rod?
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Fuse
orSocket
mcb L1Live
on the consumer
unit.
Socket 2 Socket 3 Socket 4
The earth wire in a domestic circuit is co
How lighting circuits are connected
Fuse or mcb
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ground which provides a low-resista
In general, almost all the power
consumed in athehouse
is converted into
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the transformer. At the transformer, the
Fuse
or
mcb
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heat. Appliances
that generate a lot of heat, like
firesis why
or kettles,
E Earth
theelectric
ground. This
electricity will flo
use large currents and consume a lot of power. At 220V, the current per
Fig.1 Image of consumer unit and meter
Fuse or mcb L Live
kilowatt is about 4.5 amps. Many other appliances such as radios or
An alternative approach is the ring circuit. Here the circuit takes the form
mobile phone chargers need little power.
The conductors in the circuit are copper and are insulated. The resistance
of a ring with both ends of the ring connected to the consumer unit. Both
N Neutral
N Neutral
Earth
must be low enough
that,
“live” wires are connected to one E
mcb,
both neutrals
to the neutral, both
When sockets are fitted as shown below, the circuit is called a radial circuit.
earths to earth. This has the advantage that the current demanded can
• at the rated current, the drop in voltage between the consumer
unit
(It
radiates
out
from
the
consumer
unit.)
flow two ways and is spread over two conductors. A ring circuit
canBecause each socket can supply
Fig.2 and
Lighting
switch
thecircut,
load one
is low
contain more sockets 13
thanamps
two radial
circuits.
there
is a limit to the number of sockets that can be supplied by
one cable.
• the copper does not get too hot.
Two simple lighting circuits are shown below. The first circuit is used where
there is a single switch, usually at the door of a room.
N Neutral
Cables with large diameters have less resistance than those with smaller
diameters. In general, domestic circuits are classified as lighting circuits
or power circuits.
Fuse or mcb
SocketA1radial
Socketcircut
2 Socket
3 Socket
4
Fig.4
with
two sockets
Socket 1
How lighting circuits are connected
Two simple lighting circuits are shown below. The first circuit is used where
there isFuse
a single
usually at the door
of a switch
room.
Two-way
L Live
or mcb switch,
FuseNNeutral
or mcb
L Live
Fuse or mcb
E Earth
L Live
N Neutral
N Neutral
E Earth
An alternative approach is the ring circuit. Here the circuit takes the form
of a ring with both ends of the ring connected to the consumer unit. Both
“live” wires are connected to one mcb, both neutrals to the neutral, both
earths to earth. This has the advantage that the current demanded can
flow two ways and is spread over two conductors. A ring circuit can
contain more sockets than two radial circuits.
N Neutral
Fig.2 Lighting circut, one switch
Socket 1
Socket 2
L Live
Socket 2
Socket 1 Socket 2 Socket 3 Socket 4
the
Socket 2
Fuse or mcb
Fuse or mcb
Fuse or mcb
L Live
L Live
N Neutral
N Neutral
L Live
N Neutral
Electricity in
the
Socket 1
E Earth
Home
E Earth
Home
How is electricity supply delivered to
a house?
The ESB maintains a national network of high tension power
lines. The voltages on these lines are as high as 400 kV. Such
voltages are not delivered to domestic premises. Instead the
more3suitable
voltage is stepped down Socket
at transformers
1 Socket to
2 aSocket
Socket 4
lower value. A two-wire cable is used to bring electricity to
the home. The neutral is connected to a metal plate in the
Fuse or mcb L Live
ground, and so is at 0V. Therefore, the neutral is said to be
earthed. The voltage on the live wire alternates to 311V above
and below this 50 times a second giving an effective 220V.
At the house, a main fuse and meter are installed.
N Neutral
E Earth
The second circuit is used where there are two switches, for example at
each of two doors to a room. The type of switch used is called a two-way
switch and, if the light is off, as drawn, either switch will switch it on. If the
light is on, either switch can switch it off. Examine the circuit and see why
this is so.
Socket 1 Socke
Fuse or mcb
L Live
Two-way switch
Fuse or mcb L Live
E Earth
NNeutral
N Neutral
Fig.
Fig.3 Lighting circut, two two-way switches
Other circuits
Lighting circuits do not require large currents. Typically, a circuit breaker
or fuse of 6 amps is used. The conductors in lighting cables therefore
need not be very thick. One 100 Watt bulb uses less than half an amp as
shown below.
How is electricity distributed
inAthe
Fig.5
ring house?
circut with four sockets
What
L Live is ESB Customer Supply?
0.45 A x 220V = 100 W
Fuse or mcb
IV = Power
The cable is then terminated on a consumer unit. From the consumer unit
different circuits are run to the various points where electricity is needed
- lights, sockets, cookers etc. These circuits are all fed with the 220V from
the consumer unit, so all domestic circuits are in parallel.
Other types of domestic load use larg
independent radial circuits which are not
The most common are immersion (wat
showers. Cookers and showers require
Socket 1
Socket 2
Why use fuses and mcb
ESB Customer
Supply supplies electricity
toa wire
1.8 that
million
A fuse is
will get hot and mel
Neutralprotect a circuit feeding more than
Other circuits
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rated current.
By
melting, the fuse disco
customers
(on
the
basis
published
tariffs).
It
provides
ten 100 W bulbs. In practice,
the lighting circuits
for a number
ofof
rooms
are
or mcb
L Live
reducing the risk of overheating and fire
Other types of domestic load use large currents and are supplied
byFuse
connected
in parallel and
supplied through one mcb. It is not convenient
customers
with services which meet their needs (for
The live wire connection to every circuit is fed through a safety device
Neutral
toNhave
all lights fail at the same time so it is common to have two or more
independent
radial circuits which are not connected to any other appliance.
Like a fuse, a miniature circuit breaker
which cuts off the circuit if the current demanded becomes excessive. This
Earth
E
circuits in a house.
example,
budget accounts, direct debit and
other
current
is too payment
large. It is a switch with
The
most
arecircuit
immersion
(water) heaters, cookers and lighting
electric
can be
a fusecommon
or a miniature
breaker (mcb).
breakers
are faster
showers. Cookers and showers require very thick conductors.
options) and with appropriate advice Circuit
to help
them
use and more pre
reset. The circuit breakers on a distribu
Power circuitselectricity
for appliances
(sockets)
more efficiently while saving
money
at circuit
the breakers.
are called
miniature
The term appliance is a general term for any thing powered through a
Why use fuses and mcbs?
same
time.
plug and a flexible cable. The standard plug is designed to carry up to 13
What is a residual curre
amps, its
though most appliances need considerably less. Inside the plug
A fuse is a wire that will get hot and melt (“blow”) if the circuit is above
Customer
Supply
approximately
650 people
there is a fuse. The fuseESB
is usually
either a 3-amp
fuse (foremploys
appliances up
One device that reduces the likelihood of h
rated current. By melting, the fuse disconnects the live wire from the
load,
to 660 Watts) or a 13-amp
fusein(for
appliances
up toissues
almost 3 11
kilowatts).
Electricity
enters andover
leaves a house th
and
any
one
year
million
bills
and
handles
reducing the risk of overheating and fire.
Where a 3-amp fuse is sufficient it should be used. A fault then is more
Normally, the amount of electricity ent
3 million
telephone
from
customers.
likely to blow this fuse only,
rather than
both blow it calls
and also
trip the
mcb
same amount leaving. If there is a fault
Two-way switch
Fuse
orSocket
mcb L1Live
Like a fuse, a miniature circuit breaker disconnects the live wire
on if
thethe
consumer
unit.
Socket 2 Socket 3 Socket 4
electricity from a live wire going to earth
current is too large. It is a switch with contacts that open very quickly.
As
a
business
unit
within
ESB, into
Customer
Supply
hascurrent
over or an earth-le
is called
a residual
In general, almost all the power
consumed in a house is converted
NNeutral
Circuit breakers are faster and more precise than fuses and theyheat.
can or
be
Fuse
mcb L Live
Appliances
that generate
a
lot
of
heat,
like
electric
fires
or
kettles,
75 years experience in providing electricity
services
to implications.
A fault current
to earth has
reset. The circuit breakers
onImage
a distribution
very compact
and currents and consume a lot of power. At 220V, the current per
use large
Fig.1
of consumerboard
unit andare
meter
even smaller current, 30 mA, can kill a p
customers
throughout
Ireland.
kilowatt
is
about
4.5
amps.
Many
other
appliances
such
as
radios
or
are called miniature circuit breakers.
The RCD consists of a circuit breaker
entering andmarkets
leaving on in
the live and ne
Ireland has one of the fastest-growing electricity
N Neutral
E Earth
When sockets are fitted as shown below, the circuit is called a radial circuit.
mA. Domestic RCDs will usually also tri
• at the rated current, the drop in voltage between the consumer unit
(It radiates out from the consumer
unit.) Because
each socket
can over
supply 40 per
the developed
world.
It grew
cent
over
the
last
63 A, is exceeded.
and the load is low
13 amps there is a limit to the number of sockets that can be supplied by
10 years, far ahead of average growth in The
thecurrent
rest of
for Europe.
most or all of the circuit
One
device
reduces
thehot.
likelihood of harm from electric shock is the
oneRCD.
cable.
• the
copperthat
does
not get too
RCD
which
is
between
the main fuse and
The
market
has
been
fully
opened
to
competition
since
Electricity
enters
and leaves
a house
through
thewith
live
and neutral wires.
Cables with large
diameters
have less
resistance
than those
smaller
Fig.4 A radial circut with two sockets
diameters. Inthe
general,
domestic
circuits are classified
circuitsby exactly the
Normally,
amount
of electricity
enteringasislighting
matched
February 2005.Socket 1
Socket 2
or power
circuits. leaving. If there is a fault however, it often involves some
What is the earth rod?
same
amount
The conductors in the circuit are copper and are insulated. The resistance
must be low enough that,
mobile phone chargers need little power.
What is a residual current device (RCD)?
electricity from a live wire going to earth, possibly through a person. This
How
connected
is
calledlighting
a residualcircuits
current or are
an earth-leakage
current.
Two simple lighting circuits are shown below. The first circuit is used where
Fuse or mcb
You can
L Livefind
N Neutral
Athere
fault
to earth
hasatimplications.
Even 100 mA can cause a fire. An
is acurrent
single switch,
usually
the door of a room.
even smaller current, 30 mA, can kill a person.
Fuse or mcb
The earth wire in a domestic circuit is co
out more about ESB Customer Supply
bywhich
logging
the ground
provides a low-resista
onto www.esb.ie and www.sciencetechnologyaction.com
the transformer. At the transformer, the
E Earth
the ground. This is why electricity will flo
L Live
An alternative approach is the ring circuit. Here the circuit takes the form
The RCD consists of a circuit breaker which is tripped if the currents
of a ring with both ends of the ring connected to the consumer unit. Both
entering and leavingNon
the live and neutral wires differ by more “live”
than wires
30 are connected
Be
careful
withto electricity
Neutral
to one
mcb, both neutrals
the neutral, both
mA. Domestic RCDs will usually also trip if a certain current, for example
earths to earth. This has the advantage that the current demanded can
flow two ways and is spread
over two
conductors.
ring circuit
can
63 A, is exceeded.
‘Electricity
is so
much aA part
of modern
living that we can often
Fig.2 Lighting circut, one switch
contain more sockets than two radial circuits.
take it for granted. It is a powerful and versatile energy but can be
The current for most or all of the circuits in modern houses is fed via an
dangerous if not used properly.’
RCD which is between the main fuse and their mcbs or fuses.
Socket 1 Socket 2 Socket 3 Socket 4
What is the earth rod?
Fuse or mcb
The earth wire in a domestic circuit is connected to an earth electrode in
the ground which provides a low-resistance path via the ground itself to
the transformer. At the transformer, the neutral is connected to a plate in
the ground. This is why electricity will flow from
live to earth.
Two-way switch
Fuse or mcb L Live
NNeutral
Serious accidents with electricity in the home are rare but each year
L Livethere is a small number of fatalities and serious injuries. Most of
the accidents that occur are due either to carelessness or to a lack
of awareness of some basic rules that should always be observed
when using electricity.’
E Earth
N Neutral
The above is an extract from the booklet The Safe Use of Electricity
in the Home which is produced by the ESB in cooperation with the
Electro Technical Council of Ireland. The booklet contains essential
information on electrical safety in general and also hints and rules
which you should always follow.
The booklet is available on www.esb.ie.
Socket 1
Socket 2
Fuse or mcb
L Live
L Live
N Neutral
Electricity in
E Earth
Home
Electricity in
How is electricity supply delivered to
a house?
The ESB maintains a national network of high tension power
lines. The voltages on these lines are as high as 400 kV. Such
voltages are not delivered to domestic premises. Instead the
voltage
is stepped
down at transformers to a more suitable
Syllabus
Reference
lower value. A two-wire cable is used to bring electricity to
the
home. The
neutral is Physics:
connected to a metal plate in the
Leaving
Certificate
ground,
and7,
soDomestic
is at 0V. Therefore,
Electricity
circuits the neutral is said to be
earthed. The voltage on the live wire alternates to 311V above
and
below
this 50 timesScience:
a second giving an effective 220V.
Junior
Certificate
At
the
house,
a
main
fuse
and
are installed.
Section 3C5, Electricity
in meter
the home
How is electricity distributed in the house?
The cable is then terminated on a consumer unit. From the consumer unit
different circuits are run to the various points where electricity is needed
- lights, sockets, cookers etc. These circuits are all fed with the 220V from
the consumer unit, so all domestic circuits are in parallel.
The live wire connection to every circuit is fed through a safety device
which cuts off the circuit if the current demanded becomes excessive. This
can be a fuse or a miniature circuit breaker (mcb).
Learning Objectives
The second circuit is used where there are two switches, for example at
each of two doors to a room. The type of switch used is called a two-way
switch and, if the light is off, as drawn, either switch will switch it on. If the
light is on, either switch can switch it off. Examine the circuit and see why
this is so.
Socket 1 Socke
Fuse or mcb
L Live
Two-way switch
Fuse or mcb L Live
Activities
E Earth
NNeutral
•
the
N Neutral
the
Fuse or mcb
N Neutral
Energy saving devices make sense, look at the difference in running
costs for a CF and incandescent bulb.
Fig.
Fig.3 Lighting circut, two two-way switches
Other
circuits
If you are watching the light from a lamp when
a kettle,
or something
types ofmay
domestic
load use larg
Lighting circuits do not require
currents.
Typically,
else, large
is also
switched
on, aacircuit
smallbreaker
reduction in Other
brightness
be seen.
circuits which
or fuse of 6 amps is used.
The conductors
lighting
cables
therefore
Ohm’s
law saysinthat
if the
current
through a independent
resistanceradial
increases
the are not
The most common are immersion (wat
need not be very thick. One 100 Watt bulb uses less than half an amp as
voltage
across
it
increases.
It
seems
strange
to
think
of
the
conductors
showers.
Cookers
and
showers
require
shown below.
as a resistance but they are and the 220V supply in the house is
Fuse or mcb L Live
IV = Power reduced
0.45 by
A x the
220Vvoltage
= 100 Wdrop caused by the extra
Whycurrent.
use fuses and mcb
•
Socket 1
Socket 2
A electricity
fuse is a wire
willelectric
get hot and mel
Neutral
N safely
• could
In the
1950s,
it was
common
for a
ruralthan
house with
tothat
have
Therefore, a 6 amp mcb
protect
a circuit
feeding
more
ratedHow
current.
Bylife
melting,
the fuse disco
ten 100 W bulbs. In practice,
the lighting
circuits and,
for a number
of rooms
are
lights,
one
socket
possibly
an
electric
cooker.
has
changed
Fuse or mcb
L Live
reducing the risk of overheating and fire
connected in parallel and
supplied
through
one
mcb.
It
is
not
convenient
in the last 50 years? How many sockets are there in your home?
Neutral
toNhave
all lights fail at the same time so it is common to have two or more
Like a fuse, a miniature circuit breaker
E Earth
lighting circuits in a house.
current
too large.switches.
It is a switch with
• Consider the second lighting circuit which has
two is
two-way
Circuit breakers
faster and more pre
If a third (or even a fourth or fifth) switch is required,
this are
is possible
On completing this section, the student should be able to:
reset. The circuit breakers on a distribu
Power circuits for
appliances
(sockets)
by inserting
a different
type of switch in the are
circuit
between the twocalled miniature circuit breakers.
•
Describe the ideas behind electricity distribution and use in The term appliance is a general
way switches.
This
switch
is called
term for any
thing
powered
throughan
a intermediate switch. It has four
the home
plug and a flexible cable. The
standardYou
plugcan
is designed
to carry
up as
to 13
terminals.
insert as
many
you wish. Can you guess what an
What is a residual curre
amps, though most appliances
need considerably
less. Inside the plug
intermediate
switch does?
• Outline some safety aspects of using electricity
there is a fuse. The fuse is usually either a 3-amp fuse (for appliances up
One device that reduces the likelihood of h
to 660 Watts) or a 13-amp
fuse (forthe
appliances
up to almost
kilowatts).
• Check
cable attached
to3an
appliance. ItElectricity
usually enters
has three
wires.
and leaves
a house th
• Identify different types of circuits and protective devices
Where a 3-amp fuse is sufficient it should be used. A fault then is more
Normally, Looking
the amountinto
of electricity
ent
These are coloured brown, blue and green/yellow.
the
likely to blow this fuse only, rather than both blow it and also trip the mcb
amount leaving. If there is a fault
Two-wayoff,
switchthere aresame
L1Live
Fuse
orSocket
mcb plug
when
the back
is4 taken
three
pins and a cord
• State the formula relating power, voltage and current
on the consumer
unit.
Socket
2 Socket
3 Socket
electricity from a live wire going to earth
grip visible. The green yellow earth wire is isconnected
to the
pinorin
called a residual
current
an earth-le
In general, almost all the power
consumed in a house is converted into
NNeutral
the top
neutral
wire
is blue and connected to the pin on
Fuse or
mcb L Live
heat.
Appliances
that generate
a lotcentre.
of heat, The
like electric
fires
or kettles,
A fault current to earth has implications.
the lefta lot
(normally
“N”).
The
the smaller
right is
the 30
livemA,
pin
use large currents and consume
of power. marked
At 220V, the
current
perpin on even
Fig.1 Image of consumer unit and meter
current,
can kill a p
kilowatt is about 4.5 amps.
appliances
as radios
andMany
it isother
connected
tosuch
a fuse.
The orother end of the fuse (normally
The RCD consists of a circuit breaker
mobile phone chargers need
little
power.
The conductors in the circuit are copper and are insulated. The resistance
marked “L”) is connected to the brown live wire.
When wiring a plug
entering and leaving on the live and ne
N Neutral
E Earth
must be low enough that,
When sockets are fitted asitshown
below, the circuit
is called
a radial
is important
that the
cord
gripcircuit.
grips the outer
sheath RCDs
and not
just also tri
mA. Domestic
will usually
• at the rated current, the drop in voltage between the consumer unit
(It radiates out from the consumer
unit.)Some
Becauseappliances
each socket can
supply
A, is exceeded.
the wires.
only
have two 63
wires,
brown and blue.
and the load isLearning
low
13 amps there is a limit to the number of sockets that can be supplied by
General
Points
Connect them as above.
The current for most or all of the circuit
one cable.
•
the copper does not get too hot.
• Small
electric
currents
kill.
Cables
with large
diameters
have can
less resistance
than those with smaller
diameters. In general, domestic circuits are classified as lighting circuits
or
circuits.
• power
People
conduct electricity. A typical person has a
RCD which is between the main fuse and
Fig.4 A radial circut with two sockets
resistance of
between 1.5 kΩ and 5 kΩ. It varies with the individual and whether
How
thelighting
skin is wetcircuits
or not. are connected
Two simple lighting circuits are shown below. The first circuit is used where
there
is a single
switch, usually
the7mA
door of
a room.
• Even
a current
as lowatas
can
prevent the victim from
•
True or False
Fuse or mcb
N Neutral
letting go.
L Live
Indicate whether the following are
E Earth
by drawing
a circle around T or F.
What is the earth rod?
The earth wire in a domestic circuit is co
the ground which provides a low-resista
truethe(T)
or false
(F)transformer, the
transformer.
At the
the ground. This is why electricity will flo
T
F
T
F
Fuses do not protect people
than
T
F
T
F
(e) A 6A fuse can cater for 10 100W bulbs
T
F
(f) People
good
insulators
Socket 1 are
Socket
2 Socket
3 Socket 4
T
F
(g) When switched on, a kettle uses less electricity than a 100W
bulb (the bulb is obviously much hotter).
T
F
(h) All domestic circuits are in series
T
F
T
F
(j) The fuse in a plug is in series with the live wire
T
F
(k) A 6A fuse can cater for a 2.5 kW kettle
T
F
(l) Big fuses are best because they blow less often
T
F
personcircut,
is much
lower
Fig.2a Lighting
one switch
•
Socket 2
(a) Fuses protect people from shocks
Fuse or mcb L Live
and
For a resistance of 1.5 kΩ the current would be about 150 mA
An alternative
approach is the ring circuit. Here the circuit takes the form
the ring
connected
the consumer
unit.
Both
(b)ofYour
electricity
billtocharges
for the
total
voltage you have used
from arm to arm through the heart. This is likely to be fatal. of a ring with both ends
N Neutral
•
Socket 1
“live” wires are connected to one mcb, both neutrals to the neutral, both
green/yellow
wire
in a plug
goes can
to the earth pin at the top
earths
to earth. This (c)
has The
the advantage
that the
current
demanded
from shocks, the current required
to kill
flow two ways and is spread over two conductors. A ring circuit can
the rating of any household fuse.contain more sockets(d)
A
two-way
switch
is
needed
to
light
two
bulbs at the same time
than two radial circuits.
For simplicity, no earth wire was shown in the lighting circuits but
metal light fittings must be earthed.
•
Most electricity is converted into heat. Where a lot of heat is generated,
Fuse or mcb
a lot of electricity (energy) is consumed.
•
220 V is an effective mean, the peak voltage is 311 V (220 x √2)
because the neutral is earthed it is at 0V.
Two-way switch
Fuse or mcb L Live
NNeutral
L Live
(i) NModern
Neutral
E Earth
supplies will cut off if an earth-leakage of 50 mA is
detected
Check your answers to these questions on
www.sciencetechnologyaction.com
Socket 1
Socket 2
the
Fuse or mcb
L Live
L Live
N Neutral
N Neutral
Electricity in
the
Fuse or mcb
E Earth
Home
Home
How is electricity supply delivered to
a house?
The second circuit is used where there are two switches, for example at
each of two doors to a room. The type of switch used is called a two-way
switch and, if the light is off, as drawn, either switch will switch it on. If the
light is on, either switch can switch it off. Examine the circuit and see why
this is so.
Socket 1 Socke
The ESB maintains a national network of high tension power
Fuse or mcb L Live
lines. The voltages on these lines are as high as 400 kV. Such
voltages are not delivered to domestic premises. Instead the
Two-way switch
Fuse or mcb L Live
voltage is stepped down
at transformers to a more suitable
Biographical Notes
Examination
Questions
N Neutral
E Earth
NNeutral
lower value. A two-wire cable is used to bring electricity to
Fig.
Alessandro
Volta
2004
Higher
Level
the home. The neutral is connected to a metal plate in the
ground,
and
so
is
at
0V.
Therefore,
the
neutral
is
said
to
be
antwo
Italian
physist
famous as a pioneer in electricity. He was professor of
Read the following passage and answer the following questions.
Fig.3 Lighting circut,
two-way
switches
Other circuits
earthed. The voltage on the live wire alternates to 311V above
physics at the Royal School in Como and then at the University of Pavia. He
Your
home is
supplied
with
at 230
50 Hertz.
and below
this
50 times
a electricity
second giving
anvolts,
effective
220V.At the electrical
of domestic
load use larg
Lighting circuits do invented
not require the
largeelectrophorus
currents. Typically,
circuitan
breaker
in a1775,
instrumentOther
that types
produced
charges
supply
intake aposition
is and
yourmeter
mainare
consumer
theof 6 amps is used. The conductors in lighting cables therefore
independent radial circuits which are not
fuse
At the house,
main fuse
installed.unit or fuse board.orAt
of static electricity. He also developed the voltaic pile, a type of battery. In
The most common are immersion (wat
needand
not be very thick. One 100 Watt bulb uses less than half an amp as
position you will find your main switch. Your sockets, immersion group
honour of his work, Napoleon made him a Count in
1810.Cookers and showers require
showers.
shown below.
bathroom
heater (or shower)
are protected
by Residual
How is electricity
distributed
in the
house?Current Devices
Live
L
Fuse
or
mcb
(RCD) installed in your fuse board. These provide a high degree of safety
IV = Power
0.45 A x 220V = 100 W
The cable is then terminated on a consumer unit. From the consumer unit
Why use fuses and mcb
Georg Simon
OhmSocket 2
Socket 1
on
these circuits and it is important that they are tested at least every 3
different circuits are run to the various points where electricity is needed
A fuse is a wire that will get hot and mel
Neutralprotect a circuit feeding more than
N safely
months.
The final
circuits
are protected
byfedMiniature
Circuit
Therefore, a 6 amp was
mcb could
- lights, sockets,
cookers
etc. These
circuits are all
with the 220V
from Breakers.
a German
physicist, whilst working as a high school teacher, started
rated current. By melting, the fuse disco
ten 100 W bulbs. In practice, the lighting circuits for a number of rooms are
the consumer unit, so all domestic circuits are in parallel.
or mcbhis Lresearch
with the recently invented electrochemical
invented
by and fire
Live
reducing cell,
the risk
of overheating
It is advisable to contact your local ESB about cheaper night tariffs,
these Fuse
connected
in parallel and
supplied through one mcb. It is not convenient
The live wire connection to every circuit is fed through a safety device
Count
Volta.
Using
of his own creation, Ohm
Neutral
toNhave
all lights fail Italian
at the same
timeAlessandro
so it is common
to have
two orequipment
more
could
make significant savings to your electricity bill. Storage heaters
may
Like a fuse, a miniature circuit breaker
which cuts off the circuit if the current demanded becomes excessive. This
E Earth
that the current that flows through a wire
is proportional
toaits
lighting circuits in a determined
house.
current
is too large. It is
switch with
be
to avail
of these
cheaper
canused
be a fuse
or a miniature
circuit
breakerrates.
(mcb).
cross sectional area and inversely proportional to Circuit
its length.
Thisareisfaster
Ohm’s
breakers
and more pre
reset.I The
circuit breakers
Each plug top contains a small cartridge fuse. Cartridge fuses are supplied
law and
be written as
V = IR where V is voltage,
is current
and R on
is a distribu
Power circuits
for can
appliances
(sockets)
are called miniature circuit breakers.
with a rating of 1A, 2A, 3A, 5A and 13A. A fuse should never be replaced
resistance.
The term appliance is a general term for any thing powered through a
by anything other than a suitable fuse.
plug and a flexible cable. The standard plug is designed to carry up to 13
amps, though most appliances need considerably less. Inside the plug
(Adapted form ‘Home Safety’, Register of Electrical Contractors of Ireland.
RECI)
Marie
there is a fuse. The Andre
fuse is usually
either aAmpere
3-amp fuse (for appliances up
to 660 Watts) or a 13-amp fuse (for appliances up to almost 3 kilowatts).
What is a residual curre
One device that reduces the likelihood of h
Electricity enters and leaves a house th
(a) Name and give the colour of the wire that should be connected
to the
a isFrench
physicist,
is best
for defining
to measure the flow of
Where a 3-amp fuse
sufficient
it should be
used. known
A fault then
is more a way
Normally, the amount of electricity ent
fuse in a standard three-pin plug. (7)
likely to blow this fuse
only, rather
than
both
blow it and
tripthe
the ampere.
mcb
current,
which
was
named
afteralso
him,
He also laid the foundation
(b) Explain why replacing a fuse with a piece of aluminium
foil is dangerous. (7)
(c) A table lamp has a power
ratingofof
100W. unit
What
the
Fig.1 Image
consumer
andismeter
most suitable fuse for the lamp? (7)
The conductors in the circuit are copper and are insulated. The resistance
(d)
mustSome
be low electrical
enough that,appliances are supplied with two-pin plugs.
is thecurrent,
earth the
wire
notinrequired
in these
(7)
• atWhy
the rated
drop
voltage between
the devices?
consumer unit
and the load is low
(e) Sketch a voltage-time graph of the 230V supply. (7)
•
the copper does not get too hot.
(f)
Explain
how
a Residual
Current
Device
operates.
Cables
with large
diameters
have less
resistance
than(RCD)
those with
smaller (7)
diameters. In general, domestic circuits are classified as lighting circuits
Two-way switch
Fuse
orSocket
mcb L Live
on the consumer
unit.
Socket 2 Socket
3 Socket 4
for the1 science
of electrodynamics.
The RCD consists of a circuit breaker
entering and leaving on the live and ne
N Neutral
E Earth
When sockets are fitted as shown below, the circuit is called a radial circuit.
mA. Domestic
will usually also tri
You can find out more about these and
other RCDs
great
(It radiates out from the consumer unit.) Because each socket can supply
63 A, is exceeded.
scientists
at www.sciencetechnologyaction.com
13 amps there is a limit to the
number of sockets
that can be supplied by
The current for most or all of the circuit
one cable.
RCD which is between the main fuse and
mobile phone chargers need little power.
Fig.4 A radial circut with two sockets
(g)
Givecircuits.
one advantage of a Residual Current Device (RCD)
or power
over a Miniature Circuit Breaker. (MCB) (7)
Socket 1
How
lighting
circuits
are heat
connected
(h)
Storage
heaters
have a large
capacity. Why? (7)
Two simple lighting circuits are shown below. The first circuit is used where
Fuse or mcb
L Live
Socket 2
L Live
N Neutral
For
further
examples
there is
a single switch,
usually at of
the past
door of paper
a room. exam questions check
out www.sciencetechnologyaction.com
Fuse or mcb
same amount leaving. If there is a fault
from a live wirewas
going to earth
Among hiselectricity
accomplishments
is called a residual
or an earth-le
In general, almost all
the power
a house is the
converted
into of a magnetic
figuring
outconsumed
a way toin measure
strength
field incurrent
relation
NNeutral
Fuse or
mcb L Live
heat.
Appliances
that
a lotcurrent,
of heat, like
electric
or kettles,theorem.
to generate
an electric
known
asfires
Ampere’s
Ampere’s
law
is has
a rule
A fault
current to
earth
implications.
use large currents and consume a lot of power. At 220V, the current per
even smaller
current, 30 mA, can kill a p
that deals with the mutual interaction of current-carrying
wires.
kilowatt is about 4.5 amps. Many other appliances such as radios or
E Earth
What is the earth rod?
The earth wire in a domestic circuit is co
the ground which provides a low-resista
the transformer. At the transformer, the
the ground. This is why electricity will flo
An alternative approach is the ring circuit. Here the circuit takes the form
of a ring with both ends of the ring connected to the consumer unit. Both
“live” wires are connected to one mcb, both neutrals to the neutral, both
earths to earth. This has the advantage that the current demanded can
flow two ways and is spread over two conductors. A ring circuit can
contain more sockets
than you
two radial
circuits.
Can
recall
the meaning of these
Revise the Terms
N Neutral
Did You Know?
Fig.2 Lighting circut, one switch
terms? Revising the
terminology is a powerful aid for recall and retention.
• When the State was founded in 1922, hundreds of small electricity
schemes existed. These provided limited electricity supply in cities
and towns.
Socket 1 Socket 2 Socket 3 Socket 4
Fuse or mcb
• There was also a proposal to dam the river Shannon near Limerick and
build a hydro-electric electricity station. The government appointed
Siemens, a German engineering firm, to provide a detailed scheme for
this. The work was started in 1925.
Two-way switch
Fuse or mcb L Live
• This was a giant project and associated with it was a vision of a properly
planned and organised
electricity supply needed for the development
NNeutral
of the new State.
• Legislation was passed to create the organisation to do this and the
ESB was formed in 1927. It gradually took over the major existing
suppliers and created an essential national electricity supply body.
Socket 1
Socket 2
Transformers; neutral; earthed; live; consumer unit; parallel; fuse;
miniature
circuit breaker (mcb); insulated; resistance; load; lighting circuits;
L Live
power circuits; two-way switch; appliance; radial; ring; residual current;
earth-leakage current; electrode
E Earth
N Neutral
Check the Glossary of Terms for this lesson at
www.sciencetechnologyaction.com