2.3 Domestic Uses and Safety

Question 1

is mains electricity an a.c. supply or a d.c. supply? what do each of these stand for?

Answer 1

mains electricity in an a.c supply
a.c: alternating current
d.c: direct current

Question 2

define alternating current and direct current.

Answer 2

• alternating current: current that continuously changes direction at a specific frequency
• direct current: one directional current flow

Question 3

how many wires are usually in the cables connecting electrical appliances to the mains? name these wires.

Answer 3

1. live wire
2. neutral wire
3. earth wire

Question 3

what is the frequency and voltage of the UK main electricity supply?

Answer 3

• frequency: 50 Hz
• voltage: 230V

Question 4

state the insulation colour used on the earth wire.

Answer 4

green and yellow stripes

Question 4

state the insulation colour used on the earth wire.

Answer 4

blue

Question 5

state the insulation colour used on the live wire.

Answer 5

brown`

Question 5

explain when the earth wire does and doesn’t carry a current.

Answer 5

• under normal circumstances, no current flows through the earth wire
• if a fault occurs in the appliance (such as a surge or the casing becoming live), current will flow to the ground

Question 6

what potential is the neutral wire at?

Answer 6

0 volts

Question 7

state the potential difference between the live and earth wires.

Answer 7

230 volts

Question 8

what is the purpose of the neutral wire?

Answer 8

to complete the circuit by connecting the appliance back to the mains supply.

Question 9

for metal appliances, where is the earth wire connected to? why?

Answer 9

• earth wire is connected to the metal casing of the appliance
• if live wire becomes loose and touches the casing, the current will flow through the earth wire, preventing electrocution