An automated circuit breaking device for stopping the flow of current in an electric circuit as a safety measure. There are intended to protect an electrical circuit from damage caused by overload or short circuit.

Circuit breakers detect faults in a circuit and interrupting continuity. They are designed to immediately halt electrical flow. Unlike a fuse, which can only be used once, a circuit breaker can be reset to restart operation. Circuit breakers come in different sizes. The smaller are used to protect household appliances. The larger switchgear type is designed to protect high voltage circuits. All circuit breakers, especially GFI type are designed for safety; to protect individuals from potentially lethal shock.

History

The first circuit breakers were produced by Thomas Alva Edison in 1879, but were only used in homes. Back then fuses were being used in commercial electrical systems. They were reliable to handle faulty conditions and current disruptions. Today, circuit breakers are used by both small and large scale to accommodate the growing demand for electricity.

The three common types of Circuit Breakers:

Magnetic Type Circuit Breakers:
The magnetic circuit breaker uses a type of electromagnetism to interrupt a circuit. Some designs incorporate the use of a solenoid. As current increases, so does the pulling strength. When excessive current passes through magnetic breakers, the electromagnetic energy increases as well. As the load reaches a tipping point, the magnetic force becomes strong enough to flip a switch, moving a contact plate.

Thermal Type Circuit Breakers:
This type of circuit breaker uses heat to interrupt a circuit. Many electrical distribution boards use thermal circuit breakers. Thermal breakers use a bimetallic strip in series with a circuit. The heat produced by the current at the time of an overload deforms the bimetallic strip and flips the breaker.

Hybrid Type Circuit Breakers:
Hybrid breakers use both electromagnetism as well as heat for protection. These types of breakers have an electromagnet that guards against abrupt surges in the electrical circuit and a bimetallic strip that shields against extended electrical load and overheating. Other types of circuit breakers include: Medium voltage circuit breakers, High voltage circuit breakers and Sulfur hexafluoride high-voltage circuit-breakers.

Ground Fault Interrupter Circuit Breakers

These breakers are sometimes called GFCI,(Ground fault Circuit Interrupters), or GFI’s (Ground Fault Interrupters). In Australia they are commonly identified as safety switches, and in the UK, like with common breakers, they’re known as trips.

For residential, GFI’s are code required for receptacles in bathrooms, certain kitchen receptacles, various outside receptacles, and outlets near swimming pools. Code requires GFI’s for circumstances such as dropping a hair dryer or radio into a bathtub, potentially causing electrocution. A more common circuit breaker interrupts a circuit at 20 amps, but can take only 100 milliamperes to electrocute a person. The GFI is designed to detect currents of a few milliamperes and trip a breaker at the receptacle or breaker panel thus eliminating shock danger.

GFI’s safeguard from electrocution by interrupting an electrical circuit when a variance is detected between the hot and neutral wires. Detection such as this indicates atypical current from the hot wire is occurring. Or maybe electricity is flowing in the ground wire, like a leaky capacitor or faulty printed circuit. Or more vitally, a person has come into contact with the circuit. When a circuit is working properly, all current flowing to and from an appliance is the same, so the occurrence of a variance between hot and neutral indicates a failure which can be dangerous.

Arc-fault circuit interrupter

Similar to GFI an Arc Fault Circuit Interrupter (AFCI) is a circuit breaker intended to prevent fires. A substantial portion of electrical fires can be credited to arc faults. An arc fault is the flow of electricity over an inadvertent route. These arcs can surpass temperatures of 9,000º F and easily ignite combustible materials in the home. AFCIs are devices that protect your home by detecting dangerous arcs and interrupting the circuit.

Common circuit breakers only respond to overloads and short circuits; they don’t protect against arcing. An AFCI is selective and does not allow normal arcs to break current. The AFCI is intelligent in that it continuously screens the current and differentiates between normal and excessive arcing conditions. Once an unwanted arc is sensed, the AFCI opens its contacts, breaking the circuit and reducing the possibility for fire. An AFCI should not trip during usual arcing conditions, which can happen when flipping a switch or a plug is pulled from a outlet.

High Voltage Circuit Breakers

High voltage breakers are used to protect transmission networks. High voltage applications differ but general use is understood to be 72.2 kV or higher, conferring to the IEC. High voltage breakers are usually solenoid type, with sensitive relays going through transformers protecting from current overload or fault. They are categorized by the medium used to extinguish the arc. Bulk oil, Minimum oil, Air blast, Vacuum or SF6. Because of environmental concerns and oil spills, most new High voltage breakers use SF6 gas to extinguish the arc.

High Voltage Breakers can be categorized as live tank, where the enclosure that contains the breaking mechanism is at line potential, or dead tank with the enclosure at earth potential.

These circuit breakers may be organized to permit a single pole of a three phase system to trip, instead of tripping three poles which can improve permanence and accessibility.

Sulfur hexafluoride (SF6) high-voltage circuit-breakers
In this breaker type, contacts are surrounded by sulfur hexafluoride gas to extinguish the arc. They may be used with compact gas insulated switchgear. Liquefaction of the SF6 gas may occur in cold climates. Warming of the circuit breakers may be essential.

Disconnecting circuit breaker (DCB)
The disconnecting circuit breaker (DCB) appeared in the year 2000 and is fashioned after the SF6 breaker. The breaking function happens in the breaking chamber, removing the need for separate disconnects. This reduces maintenance from every 6 years to every 15 years. Using a DCB also reduces the space requirements.