Electrical safety and the mains supply Flashcards
What does the phrase ‘alternating current’ (A.C.) describe?
A current that frequently reverses direction, usually many times a second.
What does the phrase ‘direct current’ (D.C.) describe?
A current that does not reverse direction, but flows in the same direction at all times.
The electrical supply to your home is called the ‘mains.’ What is the frequency of the mains supply?
50Hz
The electrical supply to your home is called the ‘mains.’ What is the voltage of the mains supply?
240V
The electrical supply to your home is called the ‘mains.’ Is it an A.C. or a D.C. supply?
It is an A.C. supply (alternating current)
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?
It is a D.C. supply (direct current)
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?
20Hz (which means ‘20 cycles per second’)
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?
10Hz (which means ‘10 cycles per second’)
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?
The 13A fuse.
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?
The 5A fuse.
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?
The 3A fuse.
A kettle draws a current of 5A during normal use. What will happen if it is fitted with a 5A fuse?
The fuse will melt when the kettle is used normally, breaking the circuit. So the kettle will not work.
A radio draws a current of 1A during normal use. What is the danger if it is fitted with a 13A fuse?
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.
A radio draws a current of 1A during normal use. A 1A fuse is the best choice for this appliance. True or false?
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
A radio draws a current of 12A during normal use. A 13A fuse is a good choice for this appliance. True or false?
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
An appliance malfunctions and draws a much larger current than it should do. What is the name for this fault?
A short circuit.
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?
The fuse will heat up and melt, breaking the circuit and making it safe.
What colour is the earth wire?
Green, or green and yellow.
To which part of an appliance must the earth wire be connected?
To the metal casing.
Electrical wires are insulated with plastic. Some appliances also have a plastic casing. What is the name for this?
Double insulation.
Which wire is not needed for double insulated appliances, the live, the neutral or the earth wire?
The earth wire.
When wiring a plug, what colour is the live wire?
Brown.
When wiring a plug, what colour is the neutral wire?
Blue.
When wiring a plug, to which wire should the fuse should be connected?
The live wire.
