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Circuit breaker 1
Circuit breaker
Part of a series on
Electrical wiringRegulation of Electrical Installations
BS 7671 IEC 60364 Canadian Electrical Code (CEC) National
Electrical Code (NEC)
Wiring Methods
Cable tray Electrical conduit Knob and tube wiring
Circuit Breakers and Devices
AFCI ELCB GFCI / RCD Receptacles / Sockets Sulfur
Hexafluoride
Electrical Distribution
Bus bar Distribution board Switchgear Switchboard
Transformer
Wiring by Region or Country
Hong Kong North America United Kingdom
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Circuit breaker 2
An air circuit breaker for low-voltage (less than1,000 volt)
power distribution switchgear
A two-pole miniature circuit breaker
Four one-pole miniature circuit breakers
A circuit breaker is an automatically operated electrical
switchdesigned to protect an electrical circuit from damage caused
byoverload or short circuit. Its basic function is to detect a
fault conditionand interrupt current flow. Unlike a fuse, which
operates once and thenmust be replaced, a circuit breaker can be
reset (either manually orautomatically) to resume normal operation.
Circuit breakers are madein varying sizes, from small devices that
protect an individualhousehold appliance up to large switchgear
designed to protect highvoltage circuits feeding an entire
city.
Origins
An early form of circuit breaker was described by Thomas Edison
inan 1879 patent application, although his commercial power
distributionsystem used fuses.[1] Its purpose was to protect
lighting circuit wiringfrom accidental short-circuits and
overloads. A modern miniaturecircuit breaker similar to the ones
now in use was patented by Brown,Boveri & Cie in 1924. Hugo
Stotz, an engineer who had sold hiscompany, to BBC, was credited as
the inventor on DRP (DeutschesReichspatent) 458329.[2] Stotz's
invention was the forerunner of themodern thermal-magnetic breaker
commonly used in household loadcenters to this day.
Interconnection of multiple generator sources into an electrical
gridrequired development of circuit breakers with increasing
voltageratings and increased ability to safely interrupt the
increasing shortcircuit currents produced by networks. Simple
air-break manualswitches produced hazardous arcs when interrupting
high currents;these gave way to oil-enclosed contacts, and various
forms usingdirected flow of pressurized air, or of pressurized oil,
to cool andinterrupt the arc. By 1935, the specially constructed
circuit breakersused at the Boulder Dam project use eight series
breaks andpressurized oil flow to interrupt faults of up to 2,500
MVA, in threecycles of the AC power frequency.[3]
Operation
All circuit breakers have common features in their operation,
althoughdetails vary substantially depending on the voltage class,
current ratingand type of the circuit breaker.The circuit breaker
must detect a fault condition; in low voltage circuitbreakers this
is usually done within the breaker enclosure. Circuitbreakers for
large currents or high voltages are usually arranged withpilot
devices to sense a fault current and to operate the trip
openingmechanism. The trip solenoid that releases the latch is
usually
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Circuit breaker 3
Molded-case circuit breaker
energized by a separate battery, although some high-voltage
circuitbreakers are self-contained with current transformers,
protective relaysand an internal control power source.
Once a fault is detected, contacts within the circuit breaker
must opento interrupt the circuit; some mechanically-stored energy
(usingsomething such as springs or compressed air) contained within
thebreaker is used to separate the contacts, although some of the
energyrequired may be obtained from the fault current itself. Small
circuitbreakers may be manually operated, larger units have
solenoids to tripthe mechanism, and electric motors to restore
energy to the springs.
The circuit breaker contacts must carry the load current
withoutexcessive heating, and must also withstand the heat of the
arc producedwhen interrupting (opening) the circuit. Contacts are
made of copper orcopper alloys, silver alloys and other highly
conductive materials.Service life of the contacts is limited by the
erosion of contact materialdue to arcing while interrupting the
current. Miniature circuit breaker(MCB) and molded-case circuit
breaker (MCCB) are usually discardedwhen the contacts have worn,
but power circuit breakers andhigh-voltage circuit breakers have
replaceable contacts.When a current is interrupted, an arc is
generated. This arc must be contained, cooled and extinguished in
acontrolled way, so that the gap between the contacts can again
withstand the voltage in the circuit. Different circuitbreakers use
vacuum, air, insulating gas or oil as the medium the arc forms in.
Different techniques are used toextinguish the arc including:
Lengthening / deflection of the arc Intensive cooling (in jet
chambers) Division into partial arcs Zero point quenching (Contacts
open at the zero current time crossing of the AC waveform,
effectively breaking
no load current at the time of opening. The zero crossing occurs
at twice the line frequency, i.e. 100 times persecond for 50Hz and
120 times per second for 60Hz AC)
Connecting capacitors in parallel with contacts in DC
circuits.Finally, once the fault condition has been cleared, the
contacts must again be closed to restore power to theinterrupted
circuit.
Arc interruptionLow-voltage MCB uses air alone to extinguish the
arc. Larger ratings have metal plates or non-metallic arc chutes
todivide and cool the arc. Magnetic blowout coils or permanent
magnets deflect the arc into the arc chute.In larger ratings, oil
circuit breakers rely upon vaporization of some of the oil to blast
a jet of oil through the arc.[4]
Gas (usually sulfur hexafluoride) circuit breakers sometimes
stretch the arc using a magnetic field, and then relyupon the
dielectric strength of the sulfur hexafluoride (SF6) to quench the
stretched arc.Vacuum circuit breakers have minimal arcing (as there
is nothing to ionize other than the contact material), so thearc
quenches when it is stretched a very small amount (
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Circuit breaker 4
Circuit breakers are usually able to terminate all current very
quickly: typically the arc is extinguished between 30ms and 150 ms
after the mechanism has been tripped, depending upon age and
construction of the device.
Short-circuit currentCircuit breakers are rated both by the
normal current that they are expected to carry, and the maximum
short-circuitcurrent that they can safely interrupt.Under
short-circuit conditions, a current many times greater than normal
can exist (see maximum prospective shortcircuit current). When
electrical contacts open to interrupt a large current, there is a
tendency for an arc to formbetween the opened contacts, which would
allow the current to continue. This condition can create
conductiveionized gases and molten or vaporized metal, which can
cause further continuation of the arc, or creation ofadditional
short circuits, potentially resulting in the explosion of the
circuit breaker and the equipment that it isinstalled in.
Therefore, circuit breakers must incorporate various features to
divide and extinguish the arc.In air-insulated and miniature
breakers an arc chute structure consisting (often) of metal plates
or ceramic ridgescools the arc, and magnetic blowout coils deflect
the arc into the arc chute. Larger circuit breakers such as those
usedin electrical power distribution may use vacuum, an inert gas
such as sulfur hexafluoride or have contacts immersedin oil to
suppress the arc.The maximum short-circuit current that a breaker
can interrupt is determined by testing. Application of a breaker in
acircuit with a prospective short-circuit current higher than the
breaker's interrupting capacity rating may result infailure of the
breaker to safely interrupt a fault. In a worst-case scenario the
breaker may successfully interrupt thefault, only to explode when
reset.MCB used to protect control circuits or small appliances may
not have sufficient interrupting capacity to use at apanel board;
these circuit breakers are called "supplemental circuit protectors"
to distinguish them fromdistribution-type circuit breakers.
Standard current ratings for EuropeInternational Standard--- IEC
60898-1 and European Standard EN 60898-1 define the rated current
In of a circuitbreaker for low voltage distribution applications as
the maximum current that the breaker is designed to
carrycontinuously (at an ambient air temperature of 30 C). The
commonly-available preferred values for the rated currentare 6 A,
10 A, 13 A, 16 A, 20 A, 25 A, 32 A, 40 A, 50 A, 63 A, 80 A, 100
A,[5] and 125 A (Renard series, slightlymodified to include current
limit of British BS 1363 sockets). The circuit breaker is labeled
with the rated current inamperes, but without the unit symbol "A".
Instead, the ampere figure is preceded by a letter "B", "C" or "D",
whichindicates the instantaneous tripping current that is, the
minimum value of current that causes the circuit breakerto trip
without intentional time delay (i.e., in less than 100 ms),
expressed in terms of In:
Type Instantaneous tripping current
B above 3 In up to and including 5 InC above 5 In up to and
including 10 InD above 10 In up to and including 20 InK above 8 In
up to and including 12 In For the protection of loads that cause
frequent short duration (approximately 400 ms to 2 s) current
peaks in normal operation.
Z above 2 In up to and including 3 In for periods in the order
of tens of seconds. For the protection of loads such as
semiconductor devices ormeasuring circuits using current
transformers.
In the United States, Underwriters Laboratories (UL) certifies
equipment ratings, called Series Ratings (or integrated equipment
ratings), using a two-tier rating. For example, a 22/10 rating.
This rating means that the meter
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Circuit breaker 5
pack has a 22 kAIC tenant breaker, feeding a 10 kAIC loadcenter
with 10 kAIC branches, where kAIC stands forThousand Ampere
Interrupting Capacity. Common meter pack ratings are 22/10, 42/10
and 100/10.[6]
Types of circuit breakers
Front panel of a 1250 A air circuit breakermanufactured by ABB.
This low voltage power circuit
breaker can be withdrawn from its housing forservicing. Trip
characteristics are configurable via DIP
switches on the front panel.
Many different classifications of circuit breakers can be
made,based on their features such as voltage class, construction
type,interrupting type, and structural features.
Low-voltage circuit breakers
Low-voltage (less than 1,000 VAC) types are common in
domestic,commercial and industrial application, and include:
MCB (Miniature Circuit Breaker)rated current not more than100 A.
Trip characteristics normally not adjustable. Thermal
orthermal-magnetic operation. Breakers illustrated above are inthis
category.
There are three main types of MCBs: 1. Type B - trips between
3and 5 times full load current; 2. Type C - trips between 5 and
10times full load current; 3. Type D - trips between 10 and 20
timesfull load current. In the UK all MCBs must be selected
inaccordance with BS 7671.
MCCB (Molded Case Circuit Breaker)rated current up to2,500 A.
Thermal or thermal-magnetic operation. Trip currentmay be
adjustable in larger ratings.
Low-voltage power circuit breakers can be mounted in multi-tiers
in low-voltage switchboards or switchgearcabinets.
The characteristics of low-voltage circuit breakers are given by
international standards such as IEC 947. Thesecircuit breakers are
often installed in draw-out enclosures that allow removal and
interchange without dismantlingthe switchgear.Large low-voltage
molded case and power circuit breakers may have electric motor
operators so they can trip (open)and close under remote control.
These may form part of an automatic transfer switch system for
standby power.Low-voltage circuit breakers are also made for
direct-current (DC) applications, such as DC for subway lines.
Directcurrent requires special breakers because the arc is
continuousunlike an AC arc, which tends to go out on each
halfcycle. A direct current circuit breaker has blow-out coils that
generate a magnetic field that rapidly stretches the arc.Small
circuit breakers are either installed directly in equipment, or are
arranged in a breaker panel.
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Circuit breaker 6
Inside of a circuit breaker
The 10 ampere DIN rail-mountedthermal-magnetic miniature circuit
breaker is themost common style in modern domestic consumerunits
and commercial electrical distribution boardsthroughout Europe. The
design includes thefollowing components:
1. Actuator lever - used to manually trip and resetthe circuit
breaker. Also indicates the status ofthe circuit breaker (On or
Off/tripped). Mostbreakers are designed so they can still trip
evenif the lever is held or locked in the "on" position.This is
sometimes referred to as "free trip" or"positive trip"
operation.
2.2. Actuator mechanism - forces the contactstogether or
apart.
3.3. Contacts - Allow current when touching andbreak the current
when moved apart.
4.4. Terminals5.5. Bimetallic strip.6. Calibration screw -
allows the manufacturer to
precisely adjust the trip current of the device after
assembly.7.7. Solenoid8.8. Arc divider/extinguisher
Magnetic circuit breakersMagnetic circuit breakers use a
solenoid (electromagnet) whose pulling force increases with the
current. Certaindesigns utilize electromagnetic forces in addition
to those of the solenoid. The circuit breaker contacts are
heldclosed by a latch. As the current in the solenoid increases
beyond the rating of the circuit breaker, the solenoid's
pullreleases the latch, which lets the contacts open by spring
action. Some magnetic breakers incorporate a hydraulictime delay
feature using a viscous fluid. A spring restrains the core until
the current exceeds the breaker rating.During an overload, the
speed of the solenoid motion is restricted by the fluid. The delay
permits brief current surgesbeyond normal running current for motor
starting, energizing equipment, etc. Short circuit currents provide
sufficientsolenoid force to release the latch regardless of core
position thus bypassing the delay feature. Ambient
temperatureaffects the time delay but does not affect the current
rating of a magnetic breaker
Thermal magnetic circuit breakersThermal magnetic circuit
breakers, which are the type found in most distribution boards,
incorporate both techniqueswith the electromagnet responding
instantaneously to large surges in current (short circuits) and the
bimetallic stripresponding to less extreme but longer-term
over-current conditions. The thermal portion of the circuit
breakerprovides an "inverse time" response feature, which provides
faster or slower response for larger or smaller overcurrents
respectively.
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Circuit breaker 7
Common trip breakers
Three-pole common trip breaker for supplying athree-phase
device. This breaker has a 2 A rating
When supplying a branch circuit with more than one live
conductor,each live conductor must be protected by a breaker pole.
To ensure thatall live conductors are interrupted when any pole
trips, a "commontrip" breaker must be used. These may either
contain two or threetripping mechanisms within one case, or for
small breakers, mayexternally tie the poles together via their
operating handles. Two-polecommon trip breakers are common on
120/240-volt systems where 240volt loads (including major
appliances or further distribution boards)span the two live wires.
Three-pole common trip breakers are typicallyused to supply
three-phase electric power to large motors or furtherdistribution
boards.
Two- and four-pole breakers are used when there is a need
todisconnect multiple phase ACor to disconnect the neutral wire
toensure that no current flows through the neutral wire from other
loadsconnected to the same network when workers may touch the
wiresduring maintenance. Separate circuit breakers must never be
used for live and neutral, because if the neutral isdisconnected
while the live conductor stays connected, a dangerous condition
arises: the circuit appears de-energized(appliances don't work),
but wires remain live and RCDs don't trip if someone touches the
live wire (because RCDsneed power to trip). This is why only common
trip breakers must be used when neutral wire switching is
needed.
Medium-voltage circuit breakersMedium-voltage circuit breakers
rated between 1 and 72 kV may be assembled into metal-enclosed
switchgear lineups for indoor use, or may be individual components
installed outdoors in a substation. Air-break circuit
breakersreplaced oil-filled units for indoor applications, but are
now themselves being replaced by vacuum circuit breakers(up to
about 40.5 kV). Like the high voltage circuit breakers described
below, these are also operated by currentsensing protective relays
operated through current transformers. The characteristics of MV
breakers are given byinternational standards such as IEC 62271.
Medium-voltage circuit breakers nearly always use separate
currentsensors and protective relays, instead of relying on
built-in thermal or magnetic overcurrent sensors.Medium-voltage
circuit breakers can be classified by the medium used to extinguish
the arc: Vacuum circuit breakersWith rated current up to 6,300 A,
and higher for generator circuit breakers. These
breakers interrupt the current by creating and extinguishing the
arc in a vacuum container - aka "bottle". Long lifebellows are
designed to travel the 6 to 10 mm the contacts must part. These are
generally applied for voltages upto about 40,500 V,[7] which
corresponds roughly to the medium-voltage range of power systems.
Vacuum circuitbreakers tend to have longer life expectancies
between overhaul than do air circuit breakers.
Air circuit breakersRated current up to 6,300 A and higher for
generator circuit breakers. Trip characteristicsare often fully
adjustable including configurable trip thresholds and delays.
Usually electronically controlled,though some models are
microprocessor controlled via an integral electronic trip unit.
Often used for main powerdistribution in large industrial plant,
where the breakers are arranged in draw-out enclosures for ease
ofmaintenance.
SF6 circuit breakers extinguish the arc in a chamber filled with
sulfur hexafluoride gas.Medium-voltage circuit breakers may be
connected into the circuit by bolted connections to bus bars or
wires, especially in outdoor switchyards. Medium-voltage circuit
breakers in switchgear line-ups are often built with draw-out
construction, allowing breaker removal without disturbing power
circuit connections, using a motor-operated or hand-cranked
mechanism to separate the breaker from its enclosure. Some
important manufacturer
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Circuit breaker 8
of VCB from 3.3 kV to 38 kV are Eaton, ABB, Siemens, C&S
Electric Ltd., Jyoti and BHEL.
High-voltage circuit breakers
Russian 110 kV oil circuit breaker
400kV SF6 live tank circuit breakers
Electrical power transmission networks are protected and
controlled byhigh-voltage breakers. The definition of high voltage
varies but inpower transmission work is usually thought to be
72.5kV or higher,according to a recent definition by the
International ElectrotechnicalCommission (IEC). High-voltage
breakers are nearly alwayssolenoid-operated, with current sensing
protective relays operatedthrough current transformers. In
substations the protective relayscheme can be complex, protecting
equipment and buses from varioustypes of overload or ground/earth
fault.
High-voltage breakers are broadly classified by the medium used
toextinguish the arc. Bulk oil Minimum oil Air blast Vacuum SF6
CO2Some of the manufacturers are ABB, General Electric, Eaton,
TavridaElectric, Alstom, Mitsubishi Electric, Pennsylvania Breaker,
Siemens,Toshiba, Konar HVS, BHEL, CGL, Square D (Schneider
Electric)and Becker/SMC (SMC Electrical Products).
Due to environmental and cost concerns over insulating oil
spills, mostnew breakers use SF6 gas to quench the arc.
Circuit breakers can be classified as live tank, where the
enclosure thatcontains the breaking mechanism is at line potential,
or dead tank withthe enclosure at earth potential. High-voltage AC
circuit breakers areroutinely available with ratings up to 765kV.
1,200 kV breakers werelaunched by Siemens in November 2011,
followed by ABB in Aprilthe following year.
High-voltage circuit breakers used on transmission systems may
bearranged to allow a single pole of a three-phase line to trip,
instead oftripping all three poles; for some classes of faults this
improves thesystem stability and availability.
A high-voltage direct current circuit breaker uses DC
transmission lines rather than the AC transmission lines
thatdominate as of 2013. An HVDC circuit breaker can be used to
connect DC transmission lines into a DC transmissiongrid (which is
more efficient than an AC transmission grid), thereby making it
possible to link renewable energysources and even out local
variations in wind and solar power.
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Circuit breaker 9
72.5 kV Hybrid Switchgear Module
Sulfur hexafluoride (SF6) high-voltage circuit breakers
A sulfur hexafluoride circuit breaker uses contacts surrounded
bysulfur hexafluoride gas to quench the arc. They are most often
used fortransmission-level voltages and may be incorporated into
compactgas-insulated switchgear. In cold climates, supplemental
heating orde-rating of the circuit breakers may be required due to
liquefaction ofthe SF6 gas.
Hybrid Switchgear Modules
A hybrid switchgear is one that combines the components of
traditionalair-insulated switchgear (AIS) and SF6 gas-insulated
switchgear (GIS)technologies. It is characterized by a compact and
modular design,which encompasses several different functions in one
module.
Disconnecting circuit breaker (DCB)
72.5 kV carbon dioxide high-voltagecircuit breaker
The disconnecting circuit breaker (DCB) was introduced in 2000
and is ahigh-voltage circuit breaker modeled after the SF6-breaker.
It presents atechnical solution where the disconnecting function is
integrated in thebreaking chamber, eliminating the need for
separate disconnectors. Thisincreases the availability, since
open-air disconnecting switch main contactsneed maintenance every
26 years, while modern circuit breakers havemaintenance intervals
of 15 years. Implementing a DCB solution also reducesthe space
requirements within the substation, and increases the reliability,
dueto the lack of separate disconnectors.
In order to further reduce the required space of substation, as
well assimplifying the design and engineering of the substation, a
fiber optic currentsensor (FOCS) can be integrated with the DCB. A
420 kV DCB withintegrated FOCS can reduce a substations footprint
with over 50 % comparedto a conventional solution of live tank
breakers with disconnectors andcurrent transformers, due to reduced
material and no additional insulationmedium.
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Circuit breaker 10
Carbon dioxide (CO2) high-voltage circuit breakersIn 2012 ABB
presented a 75 kV high-voltage breaker that uses carbon dioxide as
the medium to extinguish the arc.The carbon dioxide breaker works
on the same principles as an SF6 breaker and can also be produced
as adisconnecting circuit breaker. By switching from SF6 to CO2 it
is possible to reduce the CO2 emissions by 10 tonsduring the
products life cycle.
Other breakers
Residual current circuit breaker with overloadprotection
The following types are described in separate articles. Breakers
for protections against earth faults too small to trip an
over-current device: Residual-current device (RCD, formerly
known as a residual
current circuit breaker) detects current imbalance, but doesnot
provide over-current protection.
Residual current breaker with over-current protection (RCBO)
combines the functions of an RCD and an MCB in onepackage. In the
United States and Canada, panel-mounteddevices that combine ground
(earth) fault detection andover-current protection are called
Ground Fault Interrupter (GFI)breakers; a wall mounted outlet
device or separately enclosedplug-in device providing ground fault
detection and interruptiononly (no overload protection) is called a
Ground Fault CircuitInterrupter (GFCI).
Earth leakage circuit breaker (ELCB)This detects earth
currentdirectly rather than detecting imbalance. They are no longer
seenin new installations for various reasons.
AutorecloserA type of circuit breaker that closes automatically
after a delay. These are used on overhead powerdistribution
systems, to prevent short duration faults from causing sustained
outages.
Polyswitch (polyfuse)A small device commonly described as an
automatically resetting fuse rather than acircuit breaker.
References[1] Robert Friedel and Paul Israel, Edison's Electric
Light: Biography of an Invention, Rutgers University Press, New
Brunswick New Jersey
USA,1986 ISBN 0-8135-1118-6 pp.65-66[2][2] "1920-1929 Stotz
miniature circuit breaker and domestic appliances", ABB,
2006-01-09, accessed 4 July 2011[3] Charles H. Flurscheim (ed),
Power Circuit Breaker Theory and Design, Second Edition IET, 1982
ISBN 0906048702 Chapter 1[4] B. M. Weedy, Electric Power Systems
Second Edition, John Wiley and Sons, London, 1972, ISBN
0-471-92445-8 pp. 428-430[5] http:/ / bonle. en. alibaba. com/
product/ 50348671/ 51680889/ Switch/ MCB___MCCB. html[6] http:/ /
www. claytonengineering. com/ training/ myweb6/ Module11/ Output/
ImportantConcepts. html[7] A few manufacturers now offer a
single-bottle vacuum breaker rated up to 72.5 kV and even 145 kV.
See http:/ / www3. interscience. wiley.
com/ journal/ 113307491/ abstract?CRETRY=1& SRETRY=0
Electrical Engineering in Japan, vol 157 issue 4 pages 13-23
BS EN 60898-1. Electrical accessories Circuit breakers for
over-current protection for household and similarinstallations.
British Standards Institution, 2003.
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Circuit breaker 11
External links How Circuit Breakers Work (http:/ / electronics.
howstuffworks. com/ circuit-breaker. htm). L. W. Brittian:
Electrical Circuit Breakers (http:/ / www. mikeholt. com/
mojonewsarchive/ EES-HTML/ HTML/
ElectricalCircuitBreakers~20030621. htm) http:/ / hyperphysics.
phy-astr. gsu. edu/ hbase/ electric/ bregnd. html The Reality of
Counterfeit Circuit Breakers (http:/ / www. dealersourceinc. com/
get-real/ combating-counterfeit/
).
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Article Sources and Contributors 12
Article Sources and ContributorsCircuit breaker Source:
http://en.wikipedia.org/w/index.php?oldid=573273796 Contributors: A
man without a country, A. Carty, A876, Adelpine, Akendall, Akilaa,
Alerante, Alistair1978,Alvin-cs, Andrewpmk, Archenzo,
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Babushona, Baffclan, Behtis, [email protected], Bidgee, Bige1977,
BillC, Biscuittin,Bradandvanessa, Bubba hotep, Bushytails, Buster7,
CAJ, CWenger, Camw, Canley, Carmichael, Cdmarcus, Chirag.goel25,
Chongkian, ChrisGualtieri, Circuitbreakerguy, Closedmouth,
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Image Sources, Licenses and ContributorsFile:AEG Circuit breaker
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ownFile:Four 1 pole circuit breakers fitted in a meter box.jpg
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Circuit breakerOriginsOperationArc interruptionShort-circuit
currentStandard current ratings for EuropeTypes of circuit
breakersLow-voltage circuit breakersMagnetic circuit
breakersThermal magnetic circuit breakersCommon trip
breakersMedium-voltage circuit breakersHigh-voltage circuit
breakersSulfur hexafluoride (SF6) high-voltage circuit
breakersHybrid Switchgear ModulesDisconnecting circuit breaker
(DCB)Carbon dioxide (CO2) high-voltage circuit breakers
Other breakersReferencesExternal links
License