Low voltage circuit breakersare the type that most homeowners and private citizens are familiar with. They are small, easily replaceable, and are installed in breaker panels for easy access. The smallest of the low voltage circuit breakers are called MCBs, or miniature circuit breakers. They are rated to carry a current of no more than 100 amps and can withstand a charge of no more than 1,000 amps. Any charge higher will cause the breaker to burnout. The next largest low voltage circuit breaker is the one we see most commonly. MCCB's or molded case circuit breakers are good for 1,000 amps and will safely disconnect a current that exceeds 10 times this number. They are all considered magnetic circuit breakers as they use an electromagnetically powered solenoid to break the circuit when too much power runs through it.
Medium Voltage Circuit Breakers
Medium voltage circuit breakers are capable of withstanding between 1,000 and 72,000 volts before they break, depending on the model. These are found in large buildings and businesses, either on the roof in enclosed switchboxes or indoors in cabinets. Of the medium voltage circuit breakers there are: vacuum, air and SF6 circuit breakers. Vacuum circuit breakers maintain a power arc in a vacuum, meaning that air is let back into the breaker when the breaker is tripped, stopping the arc. Air circuit breakers have two spring loaded contacts close together in an air filled environment. When the breaker is tripped, the spring loaded contacts snap open, pushing the contacts away from one another. SF6 circuit breakers have an arc generated in a chamber of sulfur hexafluoride gas. The gas itself reacts to the presence of higher-than-average voltage by increasing in density, stopping the arc.
High Voltage Circuit Breakers
Any kind of circuit breaker which deals with more than 72,500 volts of electricity is considered a high voltage breaker. These are found outdoors in chain-link enclosures along high-voltage power lines. All high voltage circuit breakers are operated by means of a solenoid which, when too much power runs through it, engages to fill the arc-chamber where the power is flowing with an inert material. The material varies. Be it gas, oil or something else, the point is that it stops the electricity from arcing from one contact to the next until the breaker can be reset.
Operating Mechanism
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