Question

What is the main working principle of MCB?

Answer 1

The main working principle of a **Miniature Circuit Breaker (MCB)** is to automatically disconnect the electrical circuit in case of an overload or short circuit. It does this using two mechanisms:

1. **Thermal Mechanism (for overload protection):**  
   - This works through a bimetallic strip. When the current flowing through the MCB exceeds the rated current for a certain period, the bimetallic strip heats up and bends due to the difference in the expansion rates of the two metals.
   - When the strip bends enough, it triggers a mechanism that opens the circuit, cutting off the current and protecting the wiring from overheating or damage.

2. **Magnetic Mechanism (for short-circuit protection):**  
   - This operates through an electromagnet. In case of a short circuit (a very large current that develops suddenly), the current flowing through the MCB creates a magnetic field.
   - If this magnetic field becomes too strong (indicating a short circuit), it pulls a trip mechanism that quickly disconnects the circuit, preventing damage or fire.

### In summary:
- The **thermal** part protects against sustained overloads.
- The **magnetic** part provides fast action for short circuits.

This combination ensures that your electrical system is protected from both prolonged overcurrent and sudden, dangerous surges.