Electrical Hazards (CIE IGCSE Physics: Co-ordinated Sciences (Double Award))

Heating effect of current

• When a current passes through a resistor (or wire), energy is transferred to heat
• The temperature of the resistor (or wire) increases due to the collisions of the free electrons within the wire
• Some of the energy is dissipated into the surroundings by heating

The heating effect of current is used in many applications, such as electric hobs

Hazards of electrical systems

• Mains electricity can be dangerous if safety procedures are not followed
  • Voltages as low as 50 V can pose a serious risk of electrocution

• Common electrical hazards include:
  • damaged insulation
  • overheating cables
  • damp conditions
  • excess current from overloading of plugs, extension leads, single and multiple sockets when using a mains supply

Electrical danger sign

The risk of electrocution is indicated by hazard signs but other risks which would not be signposted are listed below

Damaged insulation

• If the insulation around an electrical cable is damaged, the metal part of the wire may become exposed
• If a person touches the exposed wire, they could be subjected to a lethal electric shock
• There is also a chance that current will flow between the exposed wire and any piece of metal it comes into contact with

Overheating of cables

• If an excess of current flows in a wire, this can lead to overheating
• This could cause the insulation to melt, or even cause a fire

Damp conditions

• Damp conditions can be dangerous in the presence of electricity since water is an electrical conductor
• If moisture comes into contact with a live wire, this could set up
  • a short circuit within the device, which could cause a fire
  • a conductive path for current to flow through a person to the earth, which could cause electrocution

Excess current from overloading

• An excessive current may flow if too many plugs, extension leads or sockets are connected to the mains supply
• The heat created could cause the insulation to melt, or even cause a fire

Electrical fire due to excessive current

Too many appliances plugged into an extension lead can cause overheating and fire