T2 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

a.c supply

ac = alternating current
dc = direct current

Question 2

define alternating current and direct current

Answer 2

ac: current that continuously changes direction at a specific frequency
dc: one directional current flow

Question 3

frequency and voltage of the UK mains electricity supply

Answer 3

frequency: 50Hz
voltage: 230V

Question 4

how many wires are usually in the cables connecting electrical appliances to the mains

name these wires

Answer 4

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

Question 5

state the insulation colour used on the Earth wire

Answer 5

green and yellow stripes

Question 6

state the insulation colour used on the live wire

Answer 6

brown

Question 7

state the insulation colour used on the neutral wire

Answer 7

blue

Question 8

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

Answer 8

• under normal circumstances, no current flows through the Earth wire
• if a fault occurs in the appliance, current will flow to the ground

Question 9

what potential is the neutral wire at

Answer 9

0 volts

Question 10

state the potential difference between the live and earth wires

Answer 10

230 volts

Question 11

purpose of the neutral wire

Answer 11

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

Question 12

for metal appliances, where is the Earth wire connected to

why

Answer 12

• 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