Domestic uses and safety

• What does a.c stand for

  Alternating current
• What does d.c stand for

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

  Mains electricity is an a.c supply
• Define alternating current

  Current that continuously changes direction at a specific frequency
• Define direct current

  One directional current flow
• What is the frequency and voltage of the UK mains electricity supply?

  Frequency: 50 Hz Voltage: 230 V
• How many wires are usually in the cable connecting electrical appliances to the mains? Name these wires

  1. Live wire
  2. neutral wire
  3. earth wire
• State the insulation colour used on the earth wire

  Green and yellow stripes
• State the insulation colour used on the live wire

  Brown
• State the insulation colour used on the earth 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 current will flow to the ground
• What potential is the neutral wire at

  0 volts
• State the potential difference between the live and earth wires

  230v
• What’s 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?

  • earth wire is connected to the metal casing of the appliance
  • if live wire becomes loose and touches the casing, the current will flow through the earth wire , preventing electrocution