Circuit Breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow.
Generally, a circuit breaker panel consists of a switch and a moving, conductive contact plate, which moves with the switch. When the switch is 'on' position, the contact plate touches a stationary plate, which is connected to the circuit so that the electric current can flow. But when the switch is 'off' position, due to overloading or short circuit, the contact plate moves away from the stationary plate and the circuit gets opened and the electric current ceases to flow.
Circuit breaker types can be classified according to their characteristics like voltage class, construction type, interrupting type, and structural features.
Low Voltage Circuit Breakers: These breakers are made for direct current (DC) applications and are commonly used in domestic, commercial, and industrial fields. Low voltage circuit breakers are usually placed in draw-out enclosures that permit removal and interchange without dismantling the switchgear. Miniature circuit breakers (MCB) and molded case circuit breakers (MCCB) are some common types of low voltage circuit breakers.
Medium Voltage Circuit Breakers: These breakers can be assembled into metal enclosed switchgear line ups for indoor applications, or as individual components for outdoor applications like substations. Vacuum circuit breakers, air circuit breakers and SF6 circuit breakers are some examples of medium voltage circuit breakers.
High Voltage Circuit Breakers: These breakers help in protecting and controlling electrical power transmission networks. They are solenoid operated and are employed with current sensing protective relays that function through current transformers.
Magnetic Circuit Breakers: These circuit breaker contacts are held closed by a latch so that when the current in the coil goes beyond the rating of the circuit breaker, the coils pull releases the latch which allows the contacts to open with a spring action.
Thermal Circuit Breakers: These breakers employ heat to break the circuit current flow and consist of a bimetallic strip, made of two types of materials welded together.
One of the most important differences between circuit breakers and fuses is that circuit breakers can be reset either manually or automatically to resume normal operation, whereas fuses once used, have to be replaced.