Electrical Safety

Electrical Safety

by Azizah Mutiarani

​Learning Goals!

• ​State the hazards of: damaged insulation, overheating of cablesdamp conditions

• State that a fuse protects a circuit

• Explain the use of fuses and circuit breakers and choose appropriate fuse ratings and circuit-breaker settings

• Explain the benefits of earthing metal cases

​Common hazards include:

• Damaged Insulation – if someone touches an exposed piece of wire, they could be subjected to a lethal shock

• Overheating of cables – Passing too much current through too small a wire (or leaving a long length of wire tightly coiled) can lead to the wire overheating. This could cause a fire or melt the insulations, exposing live wires

• Damp conditions – If moisture comes into contact with live wires, the moisture could conduct electricity either causing a short circuit within a device (which could cause a fire) or posing an electrocution risk

​A fuse is a safety device designed to cut off the flow of electricity to an appliance if the current becomes too large (due to a fault or a surge)

​The circuit symbol for a fuse – take care not to confuse this with a resistor

• Fuses usually consist of a glass cylinder which contains a thin metal wire.

• If the current in the wire becomes too large:

  • The wire heats up and melts

  • This causes the wire to break, breaking the circuit and stopping the current

​Fuses come in a variety of sizes (typically 3A, 5A and 13A) – in order to select the right fuse for the job, you need to know how much current an appliance needs

• If you know the power of the appliance (along with mains voltage), the current can be calculated using the equation:

​The fuse should always have a current rating that is higher than the current needed by the appliance, without being too high –

​Earthing

• Many electrical appliances have metal cases

• This poses a potential safety hazard:

  • If a live wire (inside the appliance) came into contact with the case, the case would become electrified and anyone who touched in would risk electrocution

• The earth wire is an additional safety wire that can reduce this risk​

The earth wire provides a low resistance path to the earth

It causes a surge of current in the earth wire and hence also in the live wire

The high current through the fuse causes it to melt and break

This cuts off the supply of electricity to the appliance, making it safe

​Summary!

​​Common hazards include:

Damaged Insulation

​Overheating of cables

​Damp conditions

​​A fuse is a safety device designed to cut off the flow of electricity to an appliance if the current becomes too large (due to a fault or a surge)

​Fuses come in a variety of sizes (typically 3A, 5A and 13A) – in order to select the right fuse for the job, you need to know how much current an appliance needs

If a live wire (inside the appliance) came into contact with the case, the case would become electrified and anyone who touched in would risk electrocution. The earth wire is an additional safety wire that can reduce this risk​