4.2.3 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 is 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

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

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 (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