Transcript Electric Safety PPT

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How safe is this office?
Can you spot the electrical hazards in this busy office?
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Why is electricity dangerous?
Warning signs are used to alert
people to the presence of high
voltage electricity.
When a current passes through
living material, it causes an
electric shock.
This interferes with nerve signals
from the brain to the body, and
can cause a heart attack, muscle
spasms and breathing difficulties.
Other dangers are overheated
and faulty appliances, which may
lead to electrical fires.
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How can electricity be used safely?
Although electricity can be very dangerous, it is also
incredibly useful and is essential for modern life.
What precautions can be taken to make electricity safer?
 Do not overload sockets.
 Wire plugs correctly.
 Never mix water and electricity.
 Regularly check cables for
breaks and lose wires.
 Do not stick anything other than a plug in a socket.
 Use earth wires, fuses and circuit breakers to prevent
accidents, in case faults develop.
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Electrical safety – true or false?
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What is inside an electrical cable?
An electrical cable contains
three wires.
copper
These wires are made of copper
because it is a good conductor of
electricity. Each wire is made of
thin strands of copper to keep the
cable flexible.
Each wire is encased in plastic
to stop the wires touching and
causing a short circuit. Plastic is
used as it is a good insulator, as
well as being tough and flexible.
The whole cable is encased in
another layer of plastic.
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insulating plastic
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Why do plugs have three pins?
The three pins in an electrical
plugs are connected to the
three wires inside a cable.
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Two of the wires form the
electrical circuit. The third
is a safety feature.
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How are wires identified?
A standard colour scheme is used for the plastic casing
to show the function of each type of wire.
How does this colour scheme help avoid confusion?
live
earth
neutral
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What does each wire do?
The live wire carries a current
that alternates between a
negative and positive voltage.
The earth wire is a
safety wire that is needed
to earth appliances with
a metal case.
This makes it safer to
touch the appliance if it
develops a fault.
The neutral wire completes the
circuit. It is kept at a zero voltage
by the electricity company.
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What does each wire do?
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What is an electrical socket?
Electrical sockets make
mains electricity available
for use.
They connect the plugs on
appliances to the mains
electricity system, through
the three different types of
wire (live, neutral and earth).
Remember, the electricity in a plug socket is at 230 V, which
could kill you, if you get a shock.
NEVER PUT ANYTHING OTHER THAN A PLUG
IN AN ELECTRICAL SOCKET!
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How do plugs and sockets carry current?
Plugs and sockets are a safe and
convenient way of using electricity.
An electrical plug is inserted
into a socket and the cable that
is attached to the plug carries
electricity to the appliance.
A plug has three pins which fit the three
holes on a socket in one way only, so
the plug cannot be wrongly connected.
The pins are made of brass, which is
a good conductor. It is also hard and
so will not bend.
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Materials and properties of plug parts
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What are the parts of a plug?
earth
terminal
live
terminal
fuse
neutral
terminal
cable
grip
cable
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How do you wire a plug?
When wiring a plug, always check the following:
 Make sure that the
wires are connected to
the correct terminals:
blue to neutral
/green to earth
brown to live
 There are no loose or
bare wires.
 The grip should firmly
hold the cable in place.
 A fuse of the correct
value is fitted.
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Can you wire a plug?
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Identifying wrongly-wired plugs
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Electrical plugs – true or false?
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What is a fuse?
A fuse is a safety device,
which breaks the circuit,
if the current is too high.
fuse
This protects the cable from
overheating and catching fire.
Sockets and extensions that
are overloaded with
appliances are especially at
risk of catching fire.
All UK plugs are fitted with
fuses. Fuses are available
in a range of amperes to
suit different current values.
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How do fuses work?
A fuse contains a thin wire, which
melts if the current is too high.
This breaks the circuit and so
electricity is unable to flow
through the appliance.
The appliance stops working
and any danger has been
averted.
thin
wire
Fuses act as an early warning
system, preventing appliances
from being damaged by surges
in electricity and warning
owners of faults.
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What is earthing?
Earthing is a process used to increase the safety of
electrical appliances.
Cables contains an earth wire to provide an alternative path
for current if appliances develop faults.
An earth wire is essential for an
appliance with a metal case.
If the live wire becomes loose
and touches the metal case, a
very large current flows to earth
and blows the fuse, breaking
the circuit.
When an appliance is working correctly, no electricity
flows through the earth wire.
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How does earthing work?
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Why do some plugs only have two pins?
Some sockets in Europe have two round slots for the pins.
Does this mean that the appliances are not earthed?
Instead of having a pin for
the earth connection, the
plug has a clip on the side.
This clip corresponds to a
contact point in the socket
and connects the
appliance to earth.
This plug and socket
system is sometimes
referred to as “Continental
European”.
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What does ‘double insulated’ mean?
Another way of improving the safety of electrical appliances
is to make them double insulated.
Double insulated appliances
have plastic cases, without
any wires connected to the
case.
This means that the case
cannot become live,
because plastic does not
conduct electricity.
So, if one layer of insulation
is damaged the appliance is
still safe for the user.
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symbol on double
insulated appliance
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Earthing and fuses – true or false?
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Glossary (1/2)
 double insulated – An appliance that contains internal
insulation and a non-conducting case.
 earthing – A method to improve the safety of appliances
by providing a low resistance path for current to flow to earth.
 earth wire – A safety wire that connects the metal case of
an appliance to earth. It is covered with a yellow and green
insulator.
 electric shock – A danger associated with electricity.
When current runs through living matter it can cause heart
attacks, breathing difficulties and muscle spasms.
 fuse – A safety component containing a length of wire,
which heats up and melts (‘blows’) if the current is too high.
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Glossary (2/2)
 live wire – A wire that carries mains electricity to an
appliance. It is covered with a brown insulator.
 neutral wire – A wire that carries current away from an
appliance to complete the circuit. It is covered in a blue
insulator.
 plug – A device that fits into a socket to connect an
appliance to the mains electricity.
 socket – A connection point for a plug, which makes
mains electricity available for use.
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Anagrams
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Multiple-choice quiz
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