4.2.3 - Domestic Uses and Safety

Electricity

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

Mains electricity is an a.c supply

a.c: Alternating current

d.c: Direct current

Define alternating current and direct current.

Alternating current: current that continuously changes direction at a specific frequency

Direct current: one directional current flow

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

Frequency: 50 Hz

Voltage: 230V

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

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

State the insulation colour used on the Earth wire.

Green and yellow stripes

State the insulation colour used on the live wire.

Brown

State the insulation colour used on the neutral wire.

Blue

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

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

What potential is the neutral wire at?

0 volts

State the potential difference between the live and earth wires.

230 volts

What is the purpose of the neutral wire?

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

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

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