Transcript 9. Electrical Safety

Electrical Safety
21 July 2015
Objectives
To understand the dangers of electricity and how
to wire a plug safely.
HSW: AF2 – Understanding the applications and implications of
science
Used before in: lesson 1 –
household electricity
Will use again in: lesson 3 –
fuses and circuit breakers
PLTS: Team workers – Work collaboratively with others.
Used before in: lesson 1 –
household electricity
Will use again in: lesson 3 –
fuses and circuit breakers
Keywords:
Neutral, live, earth, current, voltage, double-insulation, cable, cable-grip
Dangers of Electricity (Literacy exercise)
Read through the sheet and jot down the 3 most important
things you have learnt from the leaflet
1 of 34
© Boardworks Ltd 2007
Learning outcomes:
• All students must know when electricity is
being used dangerously and that the 3
pins of a plug are connected to Earth, Live
and Neutral.
• Most students should be able to describe
if a plug has been wired properly or not
from a diagram.
• Some students could be able to explain
what a fuse and the Earth wire do.
2 of 34
© Boardworks Ltd 2007
Starter
• Literacy Exercise
• What have you learnt?
• Why did you think that these were the
most important things from the leaflet?
3 of 34
© Boardworks Ltd 2007
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.
4 of 34
© Boardworks Ltd 2007
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.
5 of 34
© Boardworks Ltd 2007
How does earthing work?
6 of 34
© Boardworks Ltd 2007
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.
7 of 34
symbol on double
insulated appliance
© Boardworks Ltd 2007
What are the parts of a plug?
earth
terminal
live
terminal
fuse
neutral
terminal
cable
grip
cable
8 of 34
© Boardworks Ltd 2007
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.
9 of 34
insulating plastic
© Boardworks Ltd 2007
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.
10 of 34
© Boardworks Ltd 2007
Materials and properties of plug parts
11 of 34
© Boardworks Ltd 2007
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.
http://www.youtube.com/watch?v=1NlUb5FRnx4
12 of 34
© Boardworks Ltd 2007
Plugs, Fuses and Eathing
• Task
• You must use the keywords to describe
how electricity is dangerous and then label
the diagram of the plug correctly.
• You should describe and colour in the
wires correctly and be able to describe
what a plug is made from and why.
• You could be able to explain what a fuse
and the Earth wire do using the keywords.
Peer marking – swap over and mark somebody else’s as the mark scheme
says – if time revise your work because of comments from marker
13 of 34
© Boardworks Ltd 2007
Fuse
Yellow
Bottom Left
Blue
Earth
Double
Insulation
Neutral
Middle
Live
14 of 34
© Boardworks Ltd 2007