Electrical safety

1. Electric shock: Damaged insulation exposes live wires, creating a path for current to flow through a person if they touch the appliance.
2. Fire: Exposed wires can cause a short circuit, generating heat that can ignite flammable materials nearby.

Overloading an extension lead (rated for 5A) with a total current draw of 10A causes excess current. This leads to overheating of the cables within the extension lead. The heat can melt the insulation, creating a fire hazard and potentially causing an electric shock if the live wires are exposed.

If the switch is on the live wire, when the switch is open (off), the live wire is disconnected from the appliance. This ensures that the appliance is no longer at a dangerous high potential relative to earth, even if the neutral wire is still connected. If the switch were on the neutral wire, the appliance would still be connected to the live wire when the switch is off, posing a shock hazard.

1. Live wire: Carries the alternating potential difference from the power supply.
2. Neutral wire: Completes the circuit and is at or near earth potential.
3. Earth wire: Provides a low-resistance path to earth for fault current, preventing electric shock if a live wire touches the metal casing of an appliance.

A fuse contains a thin wire that melts and breaks the circuit if the current exceeds the fuse's rating.

The most appropriate fuse rating is 5A.

1. Calculate the current drawn by the appliance: I = P/V = 800W / 240V = 3.33A
2. Choose the next highest standard fuse rating above the calculated current. 3A would blow during normal operation, so 5A is the smallest suitable value, providing protection without nuisance tripping. 13A fuse would be too high and not protect effectively.

If a fault occurs and the live wire touches the metal casing, the casing becomes live.
The earth wire provides a low resistance path to ground.
A large current flows through the earth wire, tripping the circuit breaker or blowing the fuse.
This cuts off the electricity supply, preventing electric shock if someone touches the casing.

Plastic is a non-conductor (insulator) of electricity.
Therefore, even if a live wire comes into contact with the plastic casing, the casing will not become live.
There is no risk of electric shock if a person touches the hairdryer, as no current will flow through them to earth.

A fuse protects the circuit by melting and breaking the circuit if the current exceeds the fuse's rated value. This prevents damage to the cabling and appliance, protecting against fire or further damage. The double insulation ensures that even if a fault occurs, the user cannot touch a live part.

When a fault causes a large current (exceeding 3.0 A) to flow in the hairdryer, the fuse wire heats up rapidly. The heat causes the fuse to melt, breaking the circuit. This immediately cuts off the current to the hairdryer, preventing overheating and potential fire hazards. Since the appliance is double-insulated and has no earth wire, the fuse provides the primary protection by interrupting excessive current flow.