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A circuit breaker is a piece of equipment which is designed to protect an electrical apparatus from damage caused by overload or short circuit. Unlike a fuse which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.Circuit breakers are often implemented with a solenoid ( electromagnet) whose strength increases as the current increases and eventually trips the circuit breaker. Alternatively a bimetallic strip may be used which heats and bends with increased current. Some circuit breakers incorporate both techniques. This allows the properties of the circuit breaker to be tailored to suit the application, with the electromagnet generally responding to short, large surges in current (short circuit) and the bimetallic strip responding to smaller but longer-term (overload) overcurrent conditions.
Under short-circuit conditions a current of several thousand amps can flow (see maximum prospective short circuit current) and when a circuit breaker tries to interrupt this current an arc may form allowing the flow of current to continue even though the contacts of the circuit breaker are open. Some smaller circuit breakers incorporate a device which divides and extinguishes this arc. Larger circuit breakers such as those used in electrical power distribution may use an inert gas such as sulfur hexafluorideSulfur hexafluoride (SF) is a gas that consists of one part sulfur and six parts fluorine. It is colorless, odorless, non- toxic, and non- flammable. It is soluble in water and some other liquids. It is generally transported as a liquified compressed gas. or be immersed in oilOil is a generic term for fluids that are not miscible with water. The name comes from Latin oleum for olive oil. Oil is frequently used to refer to petroleum an "oil shortage" generally means an inadequate supply of petroleum rather than cooking oil. to suppress the arc.
Circuit breakers are either installed directly in equipment, or are arranged in a breaker panel.
1 Internal details of a European breaker
Photograph of the inside of a 10 amp European DIN-rail mounted thermal-magnetic miniature circuit breaker. Circuit breakers such as this are the most common style in modern domestic consumer unitA consumer unit is a box of fuses or breakers usually arranged in a single row. This can be contrasted with a distribution board which has multiple rows of fuses or breakers and usually serves two (which may be split phase, two phase or two phases taken fs and commercial electrical distribution boardA distribution board (known in the United States as a circuit breaker panel or just breaker panel is a mounting enclosure for multiple electrical circuit breakers. Single-phase boxes, with the breakers in just one row, are known as consumer units. They ars throughout Europe. Unfortunately while the size and shape of the opening in the front and its elevation from the rail are standardised the arrangements for busbarA busbar (often pronounced "buzz bar") refers in electrical power distribution to thick strips of Copper or other material that conduct electricity around a switchboard or distribution board. The size of the busbar is determined by the maximum amount of c connections are NOT so you should take care that the breaker you select fits the busbar in your board and preferably is the same make and range.
- Actuator leverIn physics, a lever is a rigid object that is used with an appropriate fulcrum or pivot point to multiply the mechanical force that can be applied to another object. This is also termed mechanical advantage, and is one example of the principle of moments. - used to manually trip and reset the circuit breaker. Also indicates the status of the circuit breaker (On or Off/tripped). Most breakers are designed so they can still trip even if the lever is held or locked in the on position.
- Actuator mechanism - forces the contacts together or apart.
- Contacts - Allow current to flow when touching and break the flow of current when moved apart.
- Terminals
- Bimetallic strip
- Calibration screwThis article refers to the threaded fastener. For other meanings, see Screw (disambiguation A screw is a shaft with a helical groove formed on its surface. Its main uses are as a threaded fastener used to hold objects together, and as a simple machine use - allows the manufacturer to precisely adjust the trip current of the device after assembly.
- Solenoid
- Arc divider / extinguisher
