The hotplate shown in the diagram below is earthed. Suppose a fault causes the metal casing of the hot plate to become “live” and a very large current flows through the live and earth wires.  What prevents the user from getting electrocuted when he touches the "live" casing of the hot plate?

1. Understanding the Scenario: The hotplate has a metal casing that is earthed. A fault causes the metal casing to become "live," meaning it is now at a high voltage.

2. Role of Earthing: The earthing of the metal casing is a safety feature. It provides a low-resistance path for the electrical current to flow directly to the ground in case of a fault.

3. Current Flow During Fault: When the casing becomes "live," a very large current flows through the live wire and the earth wire due to the low resistance path provided by the earthing.

4. Activation of Safety Mechanism: The large current flowing through the earth wire will cause the circuit breaker or fuse in the electrical system to activate. Circuit breakers and fuses are designed to detect unusually high currents and disconnect the electrical supply to prevent damage and hazards.

5. Disconnection of Power: Once the circuit breaker trips or the fuse blows, the electrical supply to the hotplate is cut off. This stops the flow of electricity to the hotplate, making it safe.

6. Prevention of Electrocution: With the power supply disconnected, the metal casing of the hotplate is no longer "live." Therefore, if the user touches the casing, there is no risk of electrocution because there is no electrical current flowing through the casing.

In summary, the earthing of the hotplate and the activation of the circuit breaker or fuse prevent the user from getting electrocuted by disconnecting the electrical supply when a fault occurs.