1.4 - Domestic Electricity

• The electrical circuits in your home are connected using a ring main circuit.
• Live wire carries a current into the house at a high voltage
• There are 3 wires in the ring main circuit
• Earth wire whilst operating normally carries no current.
• Neutral wire completes the circuit and has the same current as the live wire but a lower voltage.
• MCB

  • Stops the current if it becomes too large.
  • Reacts more quickly and can be reset.
  • This prevents the device overheating.
• live wire is red
• earth wire is green
• neutral wire is blue
• fuse

  • Stops the current if it becomes too large, by melting the wire in the fuse
  • prevents the device overheating.
• the unit of power normally used for domestic electricity is kW (kilowatt)
• mains electricity is an a.c. supply which stands for alternating current
• Direct Current - one directional current flow
• Alternating current - current that continuously changes direction at a specific frequency
• The frequency for the UK mains electricity supply is 50 Hz and the voltage is 230V
• Which wires are usually in the cables connecting electrical appliances to the mains?

  live wire, neutral wire, earth wire
• Insulation colour used on the earth wire is green and yellow stripes
• insulation colour used on the live wire is brown
• insulation colour used on earth wire is blue
• the earth wire usually doesn't carry a current however if a fault occurs in the appliance the current will flow
• neutral wire is at 0 Volts
• potential difference between live and earth wires is 230 volts
• purpose of the neutral wire is to complete the circuit by connecting the appliance back to the mains supply
• MCB stand for Miniature Circuit Breaker
• RCCB stand for Residual Current Circuit Breaker
• For metal appliances the earth wire is connected to the metal casing of the appliance so if the live wire touches the casing and becomes live, the current will flow through the earth wire preventing electrocution