Domestic electricity

• unit power used

  kW killowatt
• equation used to calculate cost of electricity

  energy kWh = power kW × time h

  cost = units used × cost per kWh
• is mains electricity an a.c. supply or d.c supply

  a.c supply
• what is direct current

  one direction of current flow
• what is alternating current

  continuously changes direction at a specific frequency
• frequency and voltage of UK mains electricity supply

  . frequency 50Hz

  . voltage 230V
• wires in cables

  live wire

  earth wire

  neutral wire
• colour used for earth wire

  green and yellow stripes
• colour used for live wire

  brown
• colour used for neutral wire

  blue
• explain when the earth wire does and doesn't carry a current

  . no current flows through earth wire

  . if a fault occurs in appliances current will flow
• what potential is the neutral wire

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

  230 Volts
• purpose of neutral wire

  completes circuit by connecting the appliance back to mains supply
• what does MCB stand for

  miniature circuit breaker
• what does RCCB stand for

  residual current circuit breaker
• for metal appliances where is the earth wire connect to and why

  . connected to metal casing of appliance

  . if live wire becomes loose and touches the casing, the casing will become live

  . the current will flow through the earth wire, preventing electrocution
• purpose of live wire

  carries current to appliance at a high voltage
• purpose of earth wire

  safety wire carries current safely to ground if fault develops in metal framed appliance