1. The Problem

• The metal casing can become live if a fault occurs (if the live wire touches it).

• Without protection, a person touching the kettle could get an electric shock.

2. The Protection System

• The kettle uses a three-core cable:

  • Live (brown)

  • Neutral (blue)

  • Earth (green/yellow)

3. How the Protection Works
The Earth wire is connected to the metal casing.
If the Live wire touches the metal casing:

• A large current flows from Live → Earth → ground.

• This current also passes through the fuse in the Live wire.
  The large current causes the fuse to blow (melt).
  This disconnects the kettle from the Live supply.
  The metal casing becomes safe again.

4. Key Points

• The Earth wire does not go through the fuse.

• The fuse blows because a large current still flows through it during the fault.

• The Earth wire gives the fault current a safe path to ground.

• This protection prevents electric shock.

1. The Problem

• If an appliance has no metal casing, the user could still get a shock if internal wires touch accessible parts.

2. The Solution: Double Insulation
The appliance is designed so that no part the user can touch can ever become live.
It uses two layers of insulation:

• First layer → around the wires themselves (normal wire insulation).

• Second layer → around the entire internal components (plastic casing or extra insulation inside).

Because of this design:

• There is no need for an Earth wire — the user is protected even if a fault occurs.

3. Examples of Double Insulated Appliances

• Hairdryer with a plastic body

• Electric drill with a plastic case

• Mobile phone charger

• Desk lamp with a plastic body

4. Symbol

• These appliances are marked with this symbol:
  ➜ A square inside another square 

5. Key Points

• Double insulation means no exposed metal parts can become live.

• No Earth wire is required.

• The fuse still protects against large fault currents.

1. Fallen Power Lines

• Heavy rain is often accompanied by strong winds or lightning, which can knock down trees or branches onto power lines.

• When power lines fall, they can cause widespread outages until they’re repaired.

2. Short Circuits and Electrical Faults

• Rainwater can seep into transformers, junction boxes, or cables if they’re not properly sealed.

• Water conducts electricity, so it can cause short circuits or tripping of protective systems, shutting down power as a safety measure.

3. Lightning Strikes

• Lightning can strike power lines directly or indirectly, damaging electrical equipment like transformers or causing circuit breakers to trip.

• Utilities often shut parts of the grid down briefly to prevent damage or fire hazards.

4. Poor Infrastructure or Maintenance

• In some areas, aging power infrastructure (like rusted transformers or exposed wires) is more vulnerable to weather.

• Lack of maintenance makes it easier for rain to trigger faults or weaken equipment.

5. Flooding

• Floods can damage underground power lines, substations, and switchgear, leading to prolonged outages.

• Electrical utilities often cut power proactively in flood zones to prevent electrocution.

Summary:

Rain causes blackouts mainly due to equipment failure, falling trees, short circuits, or preventive shutdowns. The more vulnerable the infrastructure, the more likely a blackout becomes during storms.