The miniature circuit breaker (MCB) is the core protection device among current protection devices in low-voltage power distribution systems.
When a short circuit or overload occurs in the circuit, it will automatically cut off the power supply to ensure the safety of electrical equipment and prevent property losses and personal injuries caused by electrical fires.
Next, a detailed overview of the working principle of the miniature circuit breaker (MCB) will be provided.
Core Components and Functions of Miniature Circuit Breakers (MCBs)
- The function of a trip unit is to identify faults and trigger disconnection: When the circuit is operating normally, the trip unit is in a dormant state and does not interfere with the circuit’s on-off status.
Once it detects abnormal current/voltage in the circuit (such as excessive current during overload, a sudden surge in current during short circuit, or unbalanced current between the live wire and neutral wire during leakage), it will push the latching mechanism of the miniature circuit breaker (MCB) to release, causing the moving and static contacts of the circuit breaker to separate and ultimately cutting off the power supply.
- Operating Mechanism (hub of action execution): It consists of key components such as connecting rods and springs that form a linkage system. It serves to connect the “tripper trigger signal” and the “contact on-off action”, enabling bidirectional operations including “manual closing/opening” and “automatic tripping in case of faults”.
- The contact system is the conductive and on-off executive component of a miniature circuit breaker (MCB). During normal circuit operation, the contact system serves as the main channel for current. When an overload or short circuit occurs in the circuit, after the tripping mechanism is triggered, the contact system will immediately perform a “disconnection action”: it quickly separates the contacts to cut off the current, and at the same time can extinguish the arc generated when the cut-off current is large, thus preventing arc damage.
- Arc-Extinguishing Chamber (guarantee for safe interruption): It is made entirely of flame-retardant materials. It can quickly extinguish the electric arc generated when contacts separate, preventing arc breakdown and component burnout, and ensuring the safe interruption of the circuit.
- Enclosure (Basic Protective Structure): It physically isolates internal components from the external environment, preventing electric shock, dust, and moisture, so as to ensure the stable operation of the device itself.
Next, a detailed overview of the working principle of the miniature circuit breaker (MCB) will be provided.
Working Process of Miniature Circuit Breakers (MCBs)
1. Normal Operation State
When the circuit breaker is in normal operation, current flows through the regular conduction path: incoming terminal → fixed contact → moving contact → outgoing terminal.
During this period, the tripper remains inactive, the operating mechanism stays in the closed position, and the contacts maintain a stable state of tight contact.
2. Overload Protection Principle
When the thermal tripper generates excessive heat due to “overload current”, the bimetallic strip bends under heat. The bent bimetallic strip pushes the connecting rod of the operating mechanism, breaking the mechanism’s balance.
The operating mechanism then drives the moving contact and fixed contact to separate quickly, thereby cutting off the overloaded circuit.
After the bimetallic strip cools down and resets, the circuit can be restored to conduction by manually operating the handle to close the breaker.
3. Short-Circuit Protection Principle
When a short circuit occurs in the circuit, the suddenly increased current causes the coil of the electromagnetic tripper to generate a strong magnetic field, which attracts the armature to act rapidly.
The armature strikes the operating mechanism, instantly breaking the closed balance.
The contacts separate quickly, and the arc-extinguishing chamber extinguishes the electric arc simultaneously, preventing the short-circuit current from continuously damaging equipment.
After the short-circuit fault is eliminated, the operating mechanism must be manually reset to ensure the fault is completely resolved before power supply is restored.
4. Reset Process After Fault Elimination
- It enhances the safety of household electricity use, preventing fires caused by line short circuits due to household appliance overload and protecting the safety of people and property.
- It stabilizes industrial power distribution, ensuring production equipment is not affected by abnormal current and reducing losses from work stoppages and production halts.
- It provides more comprehensive protection for low-voltage power grids, implementing hierarchical protection for the grid terminal and preventing the expansion of faults.
- Its precise protection function and low-power design enable your electricity needs to operate in a more green and efficient manner.
Conclusion
In summary, the working principle of a miniature circuit breaker (MCB) revolves around three core links: “real-time monitoring of circuit current, precise response to fault signals, and safe interruption of faulty circuits”.
Through the coordinated cooperation of core components such as thermal trippers, electromagnetic trippers, and operating mechanisms, it achieves precise protection against two common circuit faults—overload and short circuit.
Ultimately, this ensures the safe operation of electrical equipment and prevents electrical fires at the source.
CNTN® is committed to manufacturing miniature circuit breakers.
All miniature circuit breakers manufactured by CNTN are only allowed to leave the factory after passing strict tests.Please feel free to contact us if you have any requirements.
