2.3

• Is mains electricity an a.c supply or a d.c supply?

  1. c supply
• What does a.c stand for?

  Alternating Current
• What does d.c stand for?

  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 of the UK mains electricity supply?

  50 Hz
• What is the voltage of the UK mains electricity supply?

  230V
• How many wires are usually in the cables connecting electrical appliances to the mains?

  Three wires
• Name the wires usually found in the cables connecting electrical appliances to the mains.

  1. Live wire
  2. Neutral wire
  3. Earth wire
• What is the insulation colour used on the Earth wire?

  Green and Yellow Stripes
• What is the insulation colour used on the live wire?

  Brown
• What is 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
• What is 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 and why?

  • 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