Electrical Supply and Wiring

Electrical Supply at Home

• There are two types of electric:
• direct current
• alternating current
• The electric current that is supplied to consumers at home through the mains is an alternating current.
• The voltage of the supply is 240V.
• The electrical energy used is calculated in kilowatt-hours (kWh) or joules (J).

Electrical Wiring System

• The electricity supply in homes are distributed through electric cables.
• Electric cables are  divided into two types:
• the live wire
• the neutral wire
• The live wire carries current at a voltage of 240 V from the local substation to homes.
• The neutral wire returns the current to the substation from the homes to be earthed.
• The voltage of the neutral wire is close to zero.
• The neutral wire completes the circuit.
• The electrical wiring system consists of the main fuse, the electric meter, the main switch, circuit breakers, live wire, neutral wire and earth wire.
• The main fuse acts as a safety device. If there is a large current flowing through it, this fuse will melt and the circuit will break.
• The electric meter will record the amount of electrical energy that has been used up.
• The consumer unit controls the current that flows through the different parts of the house. It consists of the main switch and circuit breakers.
• The main switch, when turned off, will cut off the current that flows through the circuit in the house.
• The circuit breakers will cut off the electric current flowing through the circuit under abnormal conditions.
• There are two types of wiring circuits at home
• lighting circuit
• power circuit.
• In the lighting circuit, all the lights are connected in parallel to prevent the circuit from breaking when there is one light that is faulty.
• The power circuit is the circuit connected to electrical appliances such as irons and cookers.
• There are two types of wiring systems:
• single-phase wiring system usually used in homes
• three-phase wiring system usually used in commercial and industrial areas

Single-phase and Three-phase Distribution Lines

• Electrical power is usually distributed from substations on three-phase distribution lines.
• Single-phase distribution line
• Sufficient for consumers in residential areas who need a low voltage such as 240V.
• It is common to tap single-phase lines off a three-phase line.
• Three-phase distribution line
• Runs along major streets, and commercial and industrial areas.
• Used in places in need of high voltage such as 415V.

Three-pin Plug

• Electrical appliances are connected to wall sockets through three-pin plugs.
• Figure X shows the wiring inside a three-pin plug.
• The international colour code is used to identify the different wires in the three-pin plug.
• Table X shows the colours of insulation and the functions of the wires in the three-pin plug.
  Live wire:
  Covered with brown insulation
  Carries current from the mains to the electrical appliance
  Neutral wire:
  Covered with blue insulation
  Carries current from the electrical appliance to the mains
  Earth wire:
  Covered with green and yellow insulation
  Carries any leaking current to the earth
  Fuse:
  Wire with high resistance and low melting point
  Connected to the live wire
  Melts and breaks the circuit if there is large current flow or a short circuit