P2 Electricity 3

Question 1

Is UK 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

What is the frequency and voltage of the UK mains electricity supply ?

Answer 3

• Frequency: 50 Hz
• Voltage: 230V

Question 4

How many wires are usually in the cables connecting electrical appliances to the mains ? Name these wires

Answer 4

3
1. Live fire wire
2. Neutral wire
3. Earth wire

Question 5

State the insulation 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 used on the neutral wire

Answer 7

Blue

Question 8

Explain when the Earth wire does and doesnt carry a current

Answer 8

• 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 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

What is the 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

• 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