The correct answer is option 4: It compares the incoming and outgoing currents to detect imbalance, indicating leakage to earth.

An Earth Leakage Circuit Breaker (ELCB), also known as a Ground Fault Circuit Interrupter (GFCI), operates on the principle of current balance. Unlike a standard circuit breaker that responds to overcurrent, an ELCB is designed to protect against earth leakage currents – dangerous situations where current flows unintentionally to the ground, often due to faulty insulation or accidental contact.

Here's how it works:

• Current Measurement: The ELCB continuously monitors both the incoming and outgoing currents in the circuit. Ideally, these currents should be equal.
• Imbalance Detection: If there's a leakage to earth, a portion of the current will not return through the normal circuit path. The ELCB detects this imbalance between the incoming and outgoing currents. Even a small difference, typically a few milliamps, triggers the device.
• Trip Mechanism: When an imbalance is detected beyond a preset threshold, the ELCB immediately trips, cutting off the power supply to the circuit. This prevents electric shock and potential fires caused by the leakage current.

Options 1, 2, and 3 describe the functions of other safety devices. Option 1 describes a voltage monitoring system. Option 2 describes a device regulating earthing, and Option 3 describes a standard circuit breaker.