1. 8.9 Household Electricity
A. Check your concepts
Study each of the following statements. Put a ‘T’ in the box against a correct statement and a ‘F’ against an incorrect statement.
1. The mains voltage in Hong Kong is 220 V. T
2. The ring circuit is a series circuit. F

2. 3. The fuse in a three-pin plug is connected to the live wire.
4. The earth wire is a safety device and normally does not carry electricity. T

3. B. Label the diagram (a) (b) (c) (d) wire fuse earth neutral live
cable grip
fuse
earth
neutral
live

4. Complete the table on the colour of wires.
Colour code
Live
Neutral
Earth
brown
blue
yellow and green

5. C. Questions
mains supply
Fig. 1
Fig. 2
1.Two appliances are connected to a ring mains circuit (Fig. 1) and to a parallel (Fig. 2) respectively.
In which case (Fig.1 or Fig. 2) will the two appliances still work if the wire is broken at point X? ___________________ (1 mark)
Fig. 1

6. 2. The operating currents of several appliances are shown below.
Electric kettle
Refrigerator
TV set
Air conditioner
Operating current
10 A 1A
7 A
They are all connected to the same socket with a 15 A fuse.
15 A fuse
mains supply socket

7. It will melt and break the circuit.
(a) If all these appliances were switched on together, what would be the main current? (1 mark) _____________________________________
28 A
(b) What will happen to the 15 A fuse? (1 mark) _____________________________________
It will melt and break the circuit.
(c) How could you avoid this? (1 mark) _____________________________________ _____________________________________
Do not connect too many appliances to the same socket.

8. -The fuse should be connected to the live wire.
The above electric iron was returned to the electrical appliances company by a careful customer. Give TWO reasons to explain why the customer did so. (2 marks) _______________________________________ _______________________________________ 3.
The electric iron does not have an earth wire.
-The fuse should be connected to the live wire.

9. 4. 1 4 3 5 2 Live wire touches the metal casing.
Fuse
Cable grip
Earth wire
Neutral wire
Outer insulation
Electric cooker
Live
Neutral
Earth
Connecting to casing
Three-pin plug
An electric cooker is connected to a three-pin plug as shown in the diagram above. Arrange the order of what will happen when he live wire accidentally touches the metal casing of the electric cooker.
Live wire touches the metal casing.
Electric current stops flowing.
The fuse in the plug will blow.
The man is safe.
The current will become excessively large and flows through the earth wire. 4. 1 4 3 5 2