2.2.5 Mains Electricity

Mains:

• Mains electricity is an AC supply. In the United Kingdom, the domestic electricity supply has a frequency of 50 Hz and is about 230 V.
• AC is alternating current, which comes from the mains o Current continuously varies, from positive to negative (charge changes direction)
• DC, direct current, is the movement of charge in one direction only o Cells and batteries supply direct current

Direct and Alternating Currents recap

Electrical Plugs

Most electrical appliances are supplied electricity by three core cables. Each cable is made from a copper wire and a coloured plastic coating. The colours are always the same for each type of wire so that they can be easily identified:

Cabling:

• In a plug, there are 3 wires:

  
  • Live Wire
  • Brown, at 230 V
  • Carries the alternating potential difference from the supply.
  • This wire can be dangerous even if the mains circuit is off, as current may still be flowing through it.
  • Neutral Wire
  • Blue, at 0 V
  • Completes the circuit.
  • Earth Wire
  • Green and yellow stripes, at 0 V
  • It only carries a current if there is a fault.
  • Acts as a safety wire to prevent the appliance from becoming live.
  • It is connected to the earth and the casing.
  • If the live wire touches the metal casing of the appliance, the casing will become live. Touching it could result in a serious electric shock, as the current would flow through you to the ground.

Mains Electricity

Wiring and Components

Wire Composition

• Materials:
  • Copper: Good conductor of electricity.
  • Plastic Coating: Does not conduct electricity.

Types of Wires

• Live Wire:
  • Function: Carries the alternating P.D. from the supply (230V).
  • Safety: Connected to a fuse in the plug.
• Neutral Wire:
  • Function: Completes the circuit.
  • P.D.: 0V
• Earth Wire:
  • Function: Safety wire to stop the appliance from becoming live.
  • P.D.: 0V

Safety Mechanism

• Metal Case:
  • Attached to the Earth wire.
• Earth Wire Connection:
  • Connected to the ground with a metal rod.
• If Case Becomes Live:
  • A huge current flows to Earth.
  • The fuse melts and shuts off the current.
  • Prevents electric shock from touching the case.