A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload, short circuit and ground fault. Unlike fuses that must be replaced after operation, a circuit breaker can be reset manually or automatically to resume normal operation, making it the most widely used protection device in low-voltage distribution and high-voltage power transmission systems.

The basic working principle of a circuit breaker relies on two protection mechanisms. The thermal protection element responds to sustained overload current: a bimetallic strip heats up and bends, triggering the tripping mechanism after a certain delay to protect cables and equipment from overheating damage. The magnetic protection element responds to instantaneous short-circuit current: a high current generates a strong magnetic field that instantly attracts the armature and triggers tripping, cutting off the fault current within milliseconds to prevent arc damage and fire risks. High-voltage circuit breakers add a dedicated arc-quenching medium to safely extinguish the high-energy arc generated during interruption.

Circuit breakers are classified into multiple categories by voltage level and structure. Low-voltage circuit breakers include miniature circuit breakers (MCB) for terminal distribution, molded case circuit breakers (MCCB) for secondary distribution and motor protection, and air circuit breakers (ACB) for main incoming circuits with high current ratings. High-voltage circuit breakers mainly include vacuum circuit breakers for medium-voltage distribution and SF6 gas circuit breakers for high-voltage transmission systems, selected based on voltage level, breaking capacity and installation environment.

Key parameters for circuit breaker selection include rated voltage, rated current, ultimate breaking capacity and tripping characteristics. Rated voltage must match the system voltage, and rated current must be higher than the maximum normal operating current of the circuit. Breaking capacity must be greater than the maximum prospective short-circuit current at the installation point to ensure safe fault interruption. Tripping curves are selected according to load type — B curve for lighting and resistive loads, C curve for general motor and mixed loads, D curve for high-inrush loads such as heavy motors and transformers.

Circuit breakers are installed in every link of power systems, from residential distribution boards and commercial building switchrooms to industrial motor control centers and high-voltage substations. Correct selection and configuration directly affect the safety and reliability of the entire power distribution network. For complex systems, it is recommended to carry out selective protection coordination to ensure that only the fault nearest circuit breaker trips, minimizing power outage scope.

We supply a complete range of low-voltage and high-voltage circuit breakers with standard certifications, covering residential, commercial and industrial application scenarios. Contact our technical team for model selection, parameter matching and bulk pricing.