A circuit breaker has an in-built fixed electric current load capacity, which when breached, causes an automatic shutdown of the circuit. It basically detects a faulty condition like a short circuit or an 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 a 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 an insulation breakdown and maybe even a fire.
Here, we will have a look at the different types of circuit breakers that are used for different purposes.
Low-voltage Circuit Breaker
Such a circuit is used for electrical circuits that are rated at less than an energy supply of 1,000 VAC (Voltage in Alternating Current). They are made for direct current (DC) applications, and are commonly used in domestic, commercial, and industrial fields. These 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. The types of low-voltage circuit breakers are:
- Miniature Circuit Breaker (MCB): These devices carry less than 100 ampere of current.
- Molded Case Circuit Breaker (MCCB): These devices carry less than 1,000 ampere of current.
Medium-voltage Circuit Breaker
These can be used for indoor as well 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. The types of medium-voltage circuit breakers are:
- Vacuum Circuit Breaker: These devices interrupt the electrical flow by suppressing the electric arc in the vacuum.
- Air Circuit Breaker: These devices use compressed air to suppress the electric arc, but they are not as durable as vacuum circuit breakers.
- SF6 Circuit Breaker: These devices use sulfur hexafluoride in a gaseous state to put out the circuit.
High-voltage Circuit Breaker
These are mainly used in electric power transmission devices and networks. There is no specific lower limit for high voltage, but usually, a voltage of 72.5 KV or higher is considered as high voltage. They can use different mediums to suppress the elastic arc. Following are some commonly-used mediums:
- SF6 ( Sulfur Hexafluoride)
- Bulk Oil
- Compressed Air
Magnetic Circuit Breaker
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 coils pull releases the latch, which allows the contacts to open with a spring action.
Thermal Circuit Breaker
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.
Ground Fault Current Interrupter (GFCI)
These devices can detect the imbalance in electric current when it is leaked through a person's body who is accidentally touching the energized part of a circuit. They are used in wet areas like bathrooms, swimming pools, kitchens, etc.
Arc Fault Circuit Interrupter (AFCI)
These devices work by disconnecting an electric arc that is undesirable in the circuit. They are mainly used to avoid fires.