Circuit Breaker Types

Circuit breakers have an in-built fixed electric current load capacity which when breached causes automatic circuit shutdown. It basically detects the fault condition like a short circuit or overload in the circuit, interrupts the continuity, and immediately stops the current flow. This safety feature makes installation of a circuit breaker an essential part in an electrical circuit. Overloading in an electrical circuit occurs when the wires are forced to carry and conduct an electric charge more than their capacity. This causes the wires to heat up and results in insulation breakdown and an electrical fire. Short circuit occurs when two points in the circuit having different potential difference accidentally come in contact. This causes unwanted current flow from one node to another which may result in excessive heating, circuit damage, explosion or even fire. Therefore, circuit breakers are used to protect the circuit from unwanted consequences of wire overloading and accidental short circuiting.

Circuit Breaking Mechanism
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 an '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 on the '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. Though most circuit breakers have common features in their operation, the mechanism may vary substantially as per the voltage class, current rating, and type. In low voltage circuit breakers, when a fault condition is detected, it is rectified within the breaker enclosure, whereas in those meant for large currents or high voltages, special pilot devices like relays are arranged to sense the fault current and rectify it by employing a trip opening mechanism.

Types of Circuit Breakers
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. They can be installed in multi-tiers in LV switchboards or switchgear cabinets. 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. Medium voltage circuit breakers use discrete current sensors and protection relays, and can be attached into the circuit by bolted connections to bus bars or wires. 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 breakers use a three dimensional electromagnetic coil whose pulling force increases with the current. The contacts are held closed by a latch so that when the current in the coil goes beyond the rating of the circuit breaker, the coil's 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. At high heat levels, this strip bends at an angle that pulls the lever down and breaks the connection between the circuit breaker's contact plate and the stationary contact plate.

Rated circuit breakers, common trip breakers, Earth leakage circuit breakers are another type. One of the most important difference 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. Circuit breakers come in different sizes, varying from a small device that protects a single household appliance to a large switchgear manufactured to defend high voltage circuits feeding an entire city.