Overview
This lecture explains the different wires found in UK plugs and cables, their functions, and why touching certain wires can cause electric shock.
Mains Electricity Supply
- The UK National Grid supplies mains electricity as alternating current (AC) at 230 volts and 50 hertz.
- Plugging an appliance into a socket connects it to the mains supply.
Three-Core Cables and Wires
- Most appliances use a three-core cable containing the live wire, neutral wire, and earth wire.
- Each wire is made of copper for conductivity and covered in colored insulating plastic for safety.
- The color of each wire is specific and must be memorized for exams.
Wire Functions and Colors
- The live wire is brown and delivers the 230V alternating potential difference from the mains.
- The neutral wire is blue and completes the circuit by carrying current away, with 0V potential difference.
- The earth wire is striped green and yellow, does not usually carry current, and also has 0V potential difference.
Earth Wire and Safety
- The earth wire prevents the appliance casing from becoming live if the live wire touches it.
- It provides a path for dangerous current to flow safely away, reducing the risk of electric shock.
Electric Shock Risk
- The large voltage difference between the live wire (230V) and neutral/earth wires (0V) drives current flow.
- Humans also have 0V potential, so touching the live wire allows current to flow through the body, causing shock.
- Plug sockets should never be touched, even when switched off, as the live wire still carries voltage.
Key Terms & Definitions
- Mains Supply — The national distribution of electricity to homes, usually AC at 230V and 50Hz in the UK.
- Live Wire — Brown wire supplying 230V from the mains.
- Neutral Wire — Blue wire completing the circuit and carrying current away at 0V.
- Earth Wire — Green/yellow striped wire for safety, providing a path to earth at 0V.
- Alternating Current (AC) — Electric current that reverses direction, typical in mains supply.
Action Items / Next Steps
- Memorize wire colors and their functions for the exam.
- Review mains supply properties: voltage, frequency, and wire purposes.