Electrical safety and the mains supply

Question 1

What does the phrase ‘alternating current’ (A.C.) describe?

Answer 1

A current that frequently reverses direction, usually many times a second.

Question 2

What does the phrase ‘direct current’ (D.C.) describe?

Answer 2

A current that does not reverse direction, but flows in the same direction at all times.

Question 3

The electrical supply to your home is called the ‘mains.’ What is the frequency of the mains supply?

Answer 3

50Hz

Question 4

The electrical supply to your home is called the ‘mains.’ What is the voltage of the mains supply?

Answer 4

240V

Question 5

The electrical supply to your home is called the ‘mains.’ Is it an A.C. or a D.C. supply?

Answer 5

It is an A.C. supply (alternating current)

Question 6

A battery is a store of chemical energy. It can be used to supply electrical current. Is it an A.C. or a D.C. supply?

Answer 6

It is a D.C. supply (direct current)

Question 7

Once ‘cycle’ is when a current reverses direction and then returns to its original direction. An A.C. supply completes 20 cycles per second. What is the frequency of the supply?

Answer 7

20Hz (which means ‘20 cycles per second’)

Question 8

Once ‘cycle’ is when a current reverses direction and then returns to its original direction. An A.C. supply completes 10 cycles per second. What is the frequency of the supply?

Answer 8

10Hz (which means ‘10 cycles per second’)

Question 9

A kettle draws a current of 5A during normal use. Which of the following fuses should be used with the kettle? A 3A fuse, a 5A fuse or a 13A fuse?

Answer 9

The 13A fuse.

Question 10

A television draws a current of 4A during normal use. Which of the following fuses should be used with the kettle? A 3A fuse, a 5A fuse or a 13A fuse?

Answer 10

The 5A fuse.

Question 11

A radio draws a current of 1A during normal use. Which of the following fuses should be used with the kettle? A 3A fuse, a 5A fuse or a 13A fuse?

Answer 11

The 3A fuse.

Question 12

A kettle draws a current of 5A during normal use. What will happen if it is fitted with a 5A fuse?

Answer 12

The fuse will melt when the kettle is used normally, breaking the circuit. So the kettle will not work.

Question 13

A radio draws a current of 1A during normal use. What is the danger if it is fitted with a 13A fuse?

Answer 13

The radio could malfunction and draw a much larger current than it is supposed to, (e.g. 10A) but the 13A fuse would still not melt.

Question 14

A radio draws a current of 1A during normal use. A 1A fuse is the best choice for this appliance. True or false?

Answer 14

False. The correct fuse to use is one with:

1) a higher current rating than the appliance
2) a current rating as close as possible to the device rating

Question 15

A radio draws a current of 12A during normal use. A 13A fuse is a good choice for this appliance. True or false?

Answer 15

True. The correct fuse to use is one with:

1) a higher current rating than the appliance
2) a current rating as close as possible to the device rating

Question 20

An appliance malfunctions and draws a much larger current than it should do. What is the name for this fault?

Answer 20

A short circuit.

Question 21

A fuse can protect against electrical fires due to short circuits. If an appliance malfunctions and draws a large current, what happens to the fuse?

Answer 21

The fuse will heat up and melt, breaking the circuit and making it safe.

Question 22

What colour is the earth wire?

Answer 22

Green, or green and yellow.

Question 23

To which part of an appliance must the earth wire be connected?

Answer 23

To the metal casing.

Question 24

Electrical wires are insulated with plastic. Some appliances also have a plastic casing. What is the name for this?

Answer 24

Double insulation.

Question 25

Which wire is not needed for double insulated appliances, the live, the neutral or the earth wire?

Answer 25

The earth wire.

Question 26

When wiring a plug, what colour is the live wire?

Answer 26

Brown.

Question 27

When wiring a plug, what colour is the neutral wire?

Answer 27

Blue.

Question 28

When wiring a plug, to which wire should the fuse should be connected?

Answer 28

The live wire.

Question 29

In a plug, which is the low voltage wire responsible for completing the circuit?

Answer 29

The neutral wire.

Question 30

You use a 3kW microwave oven for half an hour. (0.5 hours) How many ‘units’ or kilowatt hours (kWh) of electrical energy have you used?

Answer 30

1.5kWh, or 1.5 ‘units’

Question 31

Fill in the blank: “A fault may mean that …. . If so, the earth wire provides an easy route for the current. A large current will flow and the fuse will melt, breaking the circuit.”

Answer 31

the live wire touces the metal casing of an appliance

Question 32

Fill in the blank: “A fault may mean that the live wire touches the metal casing of an appliance. If so, the earth wire provides …. A large current will flow and the fuse will melt, breaking the circuit.”

Answer 32

an easy route for the current

Question 33

Fill in the blank: “A fault may mean that the live wire touches the metal casing of an appliance. If so, the earth wire provides an easy route for the current. A large current will flow and … .”

Answer 33

the fuse will melt, breaking the circuit

Question 34

You use a 5kW heater for 3 hours. How many ‘units’ or kilowatt hours (kWh) of electrical energy have you used?

Answer 34

15kWh, or 15 ‘units’

Question 35

You use 3 ‘units’ or 3 kilowatt hours (kWh) of electrical energy. The electricity company charges 15p per unit. How much will they charge you?

Answer 35

45p

Question 36

You use 10 ‘units’ or 10 kilowatt hours (kWh) of electrical energy. The electricity company charges 16p per unit. How much will they charge you?

Answer 36

160p

Question 37

Electricity companies measure how much electrical energy you have used in ‘units.’ What is another name for one of these ‘units’?

Answer 37

A kilowatt hour (kWh)