1.4 Domestic Electricity

State the equations used to calculate the cost of electricity.

Energy (Kwh)= power (kW) x time (h)

Cost= units used x cost per unit energy (kWh)

Define direct current.

A current which flows in one direction only.

Define alternating current.

A current that continuously changes direction at a specific frequency.

What supply is mains electricity?

A.C supply (alternating current)

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

Frequency- 50Hz

Voltage- 230V

Name the 3 wires that are usually in cables connecting electrical appliances to mains?

1. Live wire

2. Neutral wire

3. Earth wire

State the insulation colour used on the live wire.

Brown

State the insulation colour used on the neutral wire.

Blue

State the insulation colour used on the earth wire.

Green and yellow stripes

Explain why 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 metal casing becoming live), current will flow through the earth wire.

What voltage is the neutral wire at?

0V

State the voltage between the earth and live wires.

230V

What is the purpose of the neutral wire?

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

What does MCB stand for?

Miniature Circuit Breaker

What does RCCB stand for?

Residual Current Circuit Breaker

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

1. Earth wire is connected to the metal casing of the appliance

2. If live wire became loose and touches the casing, the casing becomes live

3. The current will flow through the earth wire, preventing electrocution.

Describe how a fuse work.

The fuse contains a piece of thin metal wire.

If the current in the wire becomes too large:

- The wire heats up and melts

- This causes the wire to break, breaking the circuit and stopping the current from flowing.