• Be able to describe and explain how the fuse and
earth wire work together to protect the user.
•
Know that some appliances are double insulated and
that these appliances do not need an earth wire.
• Be able to calculate the correct fuse for an
appliance, given information about its power.
Task 1 - Recap
Remind the person next to
you:
• The difference between AC
and DC current.
• The colours and purpose of
the three wires in a UK mains plug.
• The name of each of the
parts of the plug in the diagram below.
Task 2
Watch and listen as your teacher demonstrates
'Dangerous Kettle Man'. He is not a superhero but he does sound
like one! Unfortunately he cannot fly and is made of coat hanger
wire.
• Watch the ammeter carefully.
• Think about the ideas of current and resistance.
Can you see how the fuse and
earth wire work together to protect the user if there is a fault?
Task 3
Your teacher will give you a
copy of the skeleton
below. Use the skeleton to come up with a series of
paragraphs that tell the story of what is happening.
Try to use the following keywords in your explanation.
You can redraft your work several times if
you find that helpful.
appliance
live
wire
earth
wire
metal casing
path
conducting
ground
resistance
current
increase
flow
heating effect
heat energy
generated
temperature
melt
circuit
breaks
broken
prevent
Extension /
MAT work:
1. Explain what
happens if an appliance that has not been fitted with an
earth wire develops a fault, and what would happen if a user
touched the appliance.
2. Explain what
is meant by a “double insulated” appliance, and why double
insulated appliances do not need an earth wire.
Task 4
Your teacher will give you a
copy of
this sheet. Try to match up the images to each of the
descriptions, and put them in the correct order to give a pictorial
explanation of how the fuse and earth wire work together.
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