2.3 Domestic uses and safety

Question 1

Is mains electricity an AC supply or a DC supply? What do each of these stand for?

Answer 1

Mains electricity is an AC supply. AC stands for alternating current and DC stands for direct current.

Question 2

Define alternating current and direct current

Answer 2

Alternating current is a current that is continuously changing direction at a specific frequency.

Direct current is a current with one directional flow.

Question 3

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

Answer 3

Frequency: 50 Hz
Voltage: 230 V

Question 4

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

Answer 4

● Live wire
● Neutral wire
● Earth wire

Question 5

State the insulation colour used on the earth wire

Answer 5

Green and yellow stripes

Question 6

State the insulation color used on the live wire

Answer 6

Brown

Question 7

State the insulation color 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 to 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 difference does the neutral wire have?

Answer 9

0 V

Question 10

State the potential difference of the earth and live wires

Answer 10

230 V

Question 11

What is the purpose of the neutral wire?

Answer 11

To complete the circuit by connecting the appliance back to the main supply

Question 12

For metal appliances, where is the earth wire connected to? Why?

Answer 12

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