Understanding Mains Electricity and Three Core Cable Connections

Objectives

• Describe how appliances are connected to mains electricity using a three-core cable.
• Identify and explain the functions of the live wire, neutral wire, and earth wire.

Mains Electricity in the UK

• Type: Alternating Current (AC)
  • Electrons flow in both forward and reverse directions.
• Frequency: 50 Hertz (Hz)
• Potential Difference: Approximately 230 Volts (V)

Three Core Cable

• Used to connect electrical appliances to the mains supply.
• Construction:
  • Copper Wires: Good conductors of electricity.
  • Plastic Coating: Insulates and prevents electric conduction.

The Wires in a Three-Core Cable

1. Live Wire (Brown)

• Carries a potential difference from the supply (~230 V).
• Connected to a fuse in the plug.
• Danger: Can be fatal if touched due to high voltage.

2. Neutral Wire (Blue)

• Completes the circuit with the live wire.
• Potential Difference: Around 0 Volts compared to the live wire.

3. Earth Wire (Green and Yellow Stripes)

• Acts as a safety wire.
• Function: Prevents electric shocks by directing the current to the ground if the case becomes live.

Safety Mechanisms

• Fuses: Connected to the live wire; melts and shuts off the current if too much current flows.
• Earth Connection: Appliances like washing machines with metal cases are connected to the earth wire.
  • If the live wire touches the metal case, the earth wire directs the current to ground.
  • This prevents electric shock by causing the fuse to melt.

Important Notes

• Live wires are hazardous even when switches are open because the wire leading to the switch is still live.
• The earth itself has a potential difference of 0 volts, providing a path for current to flow if a fault occurs.
• Knowledge of these concepts is crucial for understanding the safety and function of household electrical systems.

Additional Resources

• For more practice and questions, refer to the revision workbook available through the provided link.