Talk:Circuit breaker

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"common trip" breakers[edit]

I modified the description of "common trip" breakers and took out the description of "low voltage". --Wtshymanski 19:21, 17 Dec 2004 (UTC)

I tweaked the description a little more with what I hope is better language explaining where two-pole, common trip breakers are used. By the way, does it conform to the code to tie two single-pole breaker handles together to try to form a common-trip breaker? Given "Free trip" mechanisms, I don't think you can assure that the handle tie will actually trip the "other" pole. I know I wouldn't want anything other than a true two-pole, common-trip breaker. Atlant 19:38, 17 Dec 2004 (UTC)
Yes, I like that much better. Of course you can have two-pole breakers on a 120/208V panelboard, or I suppose on a 240/415V board, or on a DC board. --Wtshymanski 19:40, 17 Dec 2004 (UTC)

Sorry don't have time to correct "(because RCDs need power to trip)", but the real reason is that they require a differential current to trip, which is higher than the typical lethal current flowing through a human (30ma vs 1ma potentially lethal current) — Preceding unsigned comment added by Fentlehan (talkcontribs) 22:32, 18 June 2012 (UTC)


Tiny circuit breakers, that you can put in a pocket, might be electronic components. Small breakers, that you can lift, maybe with the help of a friend, might be found in electrical distribution. Big breakers, that show up in SCADA screens at system control centers, are pretty plainly electric power transmission devices. And the 30,000 amp breakers attached to generators are power components. Am I the only one finding the categorization of the article to be unclear? That's why I like the category electrical engineering- it fits anything with wires on it. Do the extra categories actually help Wikipedia users? --Wtshymanski 22:44, 8 May 2005 (UTC)

I agree. But you also need to look at how the categories are arranged. It appears, for example, that Category:Electrical engineering includes as subcategories things like Category:Electric power and Category:Electrical components. So maybe it shouldn't be in the supercategory on electrical engineering, but rather in several different subcategories under that. I think that someone has been carried away with removing categories from several articles similar to this, but if there is problem itmay lie in a poorly thought out category structure. (Or the structure may be brilliantly arranged, I don't think I'm going to try to sort it all out, I'll let others put in their two cents' worth on that.) Gene Nygaard 23:16, 8 May 2005 (UTC)

High-voltage Circuit breakers[edit]

I have completed the text with a description of interrupting principles used for HV circuit breakers (SF6 breakers as it is the technology now used for breakers 72,5 kV and above) Dingy 23 July 2005

Thanks for this addition!
Atlant 11:35, 25 July 2005 (UTC)

The images that illustrate the interrupting principles have been published in many publications or conference papers in India, France, China, Algeria.... there is no copyright, I am in fact close to the source.

Concerning the title "Internal details of a European breaker" , now that the part on high-voltage circuit breakers is more developed I think that it is necessary to change the title to "Low voltage European Circuit breaker" or something like that..; dingy 26 July

Even if these images are not copyrighted, might it be a good idea to include a reference? I mention this especially because five of the six images used in the section "High-voltage circuit breakers" appear in one publication. The publication is: "Technical Trends in Circuit Breaker Switching Technologies", published in the CIGRE SC A3 Colloquium in Sarajevo, 2003. The authors are all listed as being from Alstom T&D (transmission and distribution). Although I have an electronic copy of the publication, online I have found referneces to it but no copy. Michapma, August 21
Good idea, you should do it Dingy 00:59, 22 August 2006 (UTC)

ELCBs and the USA[edit]

A comment in the article asked:

Were ELCBS that detect earth fault current directly ever used in the USA and if so what were they reffered to as?

If by ELCBs the questioner was referring to devices that measured, for example, the isolation between the power leads and ground/earth, then no, they have never been used in ordinary installations in the US. Because our power distribution systems almost always use a grounded neutral, there isn't any isolation to speak of.

Note that this is not true in specialized installations. For example, a large delta-connected motor, generator, or distribution circuit can certainly be isolated from ground and could be protected by an ELCB. Diesel-electric railroad locomotives frequently used just such an ELCB, energizing the traction motor circuits a small DC voltage away from ground and then measuring the current required to maintain that voltage (which ought to approach zero if the traction motor circuit was correctly isolated from the frame of the locomotive, but certainly became non-zero if, say, the traction motors became saturated with water).

But in ordinary practice, especially residential practice, it's all balance-fault interrupters.

Atlant 19:31, 17 July 2005 (UTC)

afaict what was reffered to as an ELCB in the uk had two seperate earth terminals and detected current flow between them. E.G. one terminal would be attached to the earthing system and one to the earth rod. I think they were only generally used on TT systems though.

There is one more use in the US. Installations over 250V to ground and 1200A require a variant of the ELCB. Normally, these use electronics and CT's to measure the current and react accordingly. — Preceding unsigned comment added by LightRobb (talkcontribs) 02:12, 21 January 2015 (UTC)


I do not agree with this analysis. Circuit breakers in combination are called switchgears, which should be stated.

Well, this is Wikipedia so you know what to do: be bold!
Atlant 21:07, 14 August 2005 (UTC)

A circuit breaker is a type of Switchgear that is designed to break load current and extinguish an arc. Generally switchgear is the description given to any high voltage electrical switching equipment and covers a variety of equipment such as circuit breaker, air break switch disconnectors (ABSD's), earthing switches etc..

  • Switchgear is a general term covering switching devices and their combination. A circuit breaker is a switching device. You can conclude. Dingy (talk) 06:24, 4 August 2012 (UTC)

Close. Switchgear and switchboards are a type of CB installation. The CB's, and aux. equipment, are mounted in the gear or boards (I won't go into the differences here), and provide the required protection. You can also find fused switchboards, though they are a bit specialized. Note also that gear comes in both low (208V, 480V) voltage and high voltage flavors, boards are mostly low voltage. — Preceding unsigned comment added by LightRobb (talkcontribs) 02:15, 21 January 2015 (UTC)

high voltage[edit]

This page gives the impression that in high voltage engnineering cuircuit breaker means something somewhat different from what it means in low voltage wiring. in low voltage wiring a cuircuit breaker is something that detects a fault and automatically disconnects the supply. it seems in high voltage it means a device that breaks the cuircuit (which may be triggered by hardware sensing overcurrent that doesn't seem to be part of the breaker). Is this impression correct and if so should it be worked into the article somehow.

also the high voltage cuircuit breakers section is getting HUGE we should probablly break it out into a seperate article. Plugwash 16:43, 22 January 2006 (UTC)

That is correct. Any breaker rated in multiple KV will generally have a trip coil operated by external protective relays, which might be anything from electromechanical plunger-type relays up to digital (numeric) multi-function systems capable of significant programmability and complexity. The "detection" and "interruption" are done in separate places, and if this is new to some then it's good that Wikipedia includes this data. Unluckily we've got a lot of electrical articles written at the home handyman level and as important as that level is in its own sphere, encyclopedia articles need to be more inclusive.
There's quit a lot on arc interruption but it is important and presents the fundamental issue in circuit breaker design. It's important to show the contrast between small breakers and large breakers...the illustration of the small Euro breaker is great. Bitty breakers are kind of dull..HV is cool. --Wtshymanski 23:32, 22 January 2006 (UTC)
Hehe... well, it's electrical safety equipment. I don't think "being cool" is on the list of desired characteristics, unless you mean temperature-wise. Reliable to the point of boredom, now that's on there... (talk) 11:26, 30 September 2010 (UTC)

I'm not saying we shouldn't keep some information on high voltage breakers here and it *IS* interesting but right now that section is bigger (in terms of rendered screenfulls) than the rest of the article combined. definately a case for sumarising and moving to a more specialist article. Plugwash 01:09, 23 January 2006 (UTC)

Hi, in the French version done later ("Disjoncteur à haute tension"), I made a separate article, a little more complete. The same could be done here, while keeping some text in this one. Dingy 04:02, 23 January 2006 (UTC)

Switching speed[edit]

"The double motion technique halves the tripping speed of the moving part" - I take this to mean that the total execution time has doubled? Perhaps the author meant tripping time instead?--Hooperbloob 08:05, 27 November 2006 (UTC)

sorry for my bad english, the meaning is as flows : if one contact (of a 245 kV breaker) moves you ned a speed of 8 m/s, if both contacts move in opposite direction, each needs a speed of 4 m/s (halved) in order to have the same relative speed of 8 m/s. Is it clear now ? Dingy 13:42, 27 November 2006 (UTC)

Type Of MCBs[edit]

Could anyone tell me where are we suppose to use Type B MCB, Type C MCB and so on...?

Let's say a 20A Type-B MCB is connected to a current carrying conductor. At what current will the MCB trip? Is it slightly above 20A or 3-5 times the rated current as stated in the article? —The preceding unsigned comment was added by LHW (talkcontribs) 10:30, 15 December 2006 (UTC).ll;'mkomikkpkoi hiu njhukj njmo

MCBs are thermal magnetic hybrids, the thermal part follows a smooth curve of faster tripping as current increases and deals with overloading but even in the best cases its pretty slow to trip. The magnetic part trips at the points given in the article and when it trips it trips as fast as the mechanism can physically move (iirc the standard says less than 100ms). Plugwash 01:11, 16 December 2006 (UTC)
Not all MCBs are thermal/magnetic. Last time I took apart a Square D "Q0" breaker, it was thermal-only.
Atlant 17:44, 16 December 2006 (UTC)

type B MCB can be used for domestic lighting purposes while type C MCB can be used for the motoring circuits. B type MCB's are recommended for lamps, fans, ovens, washing machines, house wiring etc C type MCB's are recommended for Air conditioners, transformers and industrial loads. —Preceding unsigned comment added by (talk) 06:46, 8 June 2008 (UTC)

further to do i know which MCB to be used...6A or 10A or 16A or 20A....for domestic lighting purposes. —Preceding unsigned comment added by (talk) 06:47, 4 July 2009 (UTC)

Standars Values[edit]

It should be noted that the listed standard low voltage molded case braker values are British or European sizes based on European standards and 240v system. The US sstandard values are different. —Preceding unsigned comment added by Mattmia2 (talkcontribs) 13:12, 20 September 2007 (UTC)

Speed up Arc Extinction[edit]

There are various types of high current, high voltage circuit breakers used by Power Industries, such as Air Blast, Minimum Oil, Vacuum, SF6 gas filled, Magnetic arc-quenched varieties etc. Apart from making or breaking the current flows in Power Lines, their main functions are to extinguish electric arcs that follow a circuit-current break. In an arc channel between two parting contacts one may delineate three distinct regions, viz, two thin regions attached to the parting electrodes and a central column. The thin regions act as interfaces conjoining the high density and low velocity e-flow within the electrodes and the low density and high velocity e-flow in the usually long central column. Such interfaces at anode are rather diffused and current densities are relatively low whereas at cathode end they are focused and current densities are high. The Electrical parameters on either side of this interface are widely separated and the mechanisms operative here are very complex. Only at low pressures, the interfaces at cathode end are spread out and some theoretical analyses as well as diagnostics of the arc parameters have been attempted.

All circuit breakers in general, are designed to extinguish the arcs by drawing out their central columns using an air blast, a gushing oil stream or a pinching magnetic field etc guided more by mechanical constructional conveniences. But, in general, an arc is relatively ‘strong’ and ‘stable’ at the mid-column regions and rather weak at the electrode interfaces, particularly at Cathode surface. Attempts to extinguish arcs at such weakest points should be beneficial as regards total energy dissipation and delay to extinction and hardly any report on such efforts is available. Initial experiments to verify the concepts may be pursued with only simple, plane parallel, stationary electrodes. Would any users be interested to participate in developing the theories / devising the experiments in this direction? We shall develop a model of the processes active in the cathode interface of the arcs shortly. —Preceding unsigned comment added by (talk) 08:23, 25 October 2007 (UTC)

duplication of text[edit]

In the headlines "Rated current" and "Short circuit current". —Preceding unsigned comment added by Yossso (talkcontribs) 23:10, 20 August 2008 (UTC)

reasons for complexity of high voltage circuit breakers[edit]

The amount of content in the high voltage section suggests that stopping the current from flowing is not trivial. Perhaps this should be stated explicitly. Reading the article I infer that arcing is a normal occurence when trying to stop the current flow, and requires special measures to stop it (stop it safely?). I am no expert on the subject so I'm hesitant to edit. Walworth (talk) 11:40, 21 January 2009 (UTC)

More basic information needed by prospective users.[edit]

The reason most prospective users are interested in looking up circuit breakers, is for help in choosing an appropriate type. Of paramount importance is how the breaker attaches to the buss bar. The amount of space allotted to extraneous technical details crowds pertinent information off the page. As a user who has experienced breaker failure due to poor engineering I am in interested in basic construction. How about someone who has the needed information creating a simple page which contains information that is needed by the prospective customer. Pictures of the lever arrangement for opening and closing the circuit are fine, but one is enough since "if you've seen one you've seen 'em all" but the attachment arrangements of hooks and catches, of which there is great diversity, are considered unimportant by the average technical writer. On Wikipedia the more things change the more they stay the same. How about some basic circuit breaker information and limit the technical verbosity on at least one page. Please. (talk) 23:30, 28 October 2009 (UTC)

But an encyclopedia is not a catalog. Choosing the appropriate type of circuit breaker for a given application requires more expertise than can be reasonably put into an encyclopedia article. It is appropriate to talk about basic common principles here, not exhaustively list (as one of thousands of possible examples) which brands and models of miniature molded-case circuit breakers fit which brands and models of panel boards without violating UL approval. Which circuit breakers would you have us describe here - the 3 Amp one that protects a TV set, or the one that failed and blacked out an entire 230,000 kV service for a large city? You could easily fill a Wikipedia with circuit breaker descriptions, application guides, and outline drawings - but this is the job of the manufacturers, not of an encyclopedia. --Wtshymanski (talk) 20:05, 13 November 2009 (UTC)

The 400 KV image does not show any breaker or switchgeer. It shows a small part of the 'visual indidicator of an open circut' which sits on both sides of a breaker. When a breaker opens then on both sides rods open to provide a visual indication that the circuit is not currently engaged. The Circut breaker for a 400KV line is much larger. —Preceding unsigned comment added by (talk) 11:09, 7 March 2010 (UTC)

I came to article looking for information about response time of household AC panel circuit breakers -- the 15A - 100A types one would find in entrance panel. Found nothing. Also interested in response time of small resettable breakers attached to power strips, UPS's, various appliances (these range from 3-15A generally). None of article's external links gave any of this info either. Some mention would be useful, as well as one sentence indicating that because of this delay (xx-xxx millisec.?) that GFCI protection devices would be needed to protect users of equipment. I don't recall if article presently states that circuit breaker's main role is to protect circuitry and equipment, NOT users! But it should. —Preceding unsigned comment added by PapaJupe (talkcontribs) 16:10, 2 April 2010 (UTC)

I am new to wiki so if I violate any guidelines, please delete There are so many manufactures styles and vintages that images and specs would take thousands of pages If specs, size AIC ratings or pictures of cicuit breakers are needed, I will be happy to furnish them. — Preceding unsigned comment added by Circuit breakers (talkcontribs) 19:22, 6 December 2016 (UTC)

Medium-voltage circuit breakers ... are often built with draw-out construction[edit]

When they can be fixed needs clarification. This seems to indicate drawout construction is really optional. —Preceding unsigned comment added by (talk) 18:02, 29 May 2010 (UTC)

Instantaneous tripping current terminology / formula[edit]

OK, am I just not getting something fundamental here, is it an esoteric sort of equation which needs further inline (or linked) explanation for a layman (i.e. the everyday wiki searcher) to understand, or it it an outright mistake?

The rating is described as being of the form "x/n", where x is determined by the rating (e.g. 2~3 for "B"), and, I can only assume, n is the breaker's normal rated current (ie long term sustained current).

Now what this means is, if I understand how this is written, for and within each of the classes - B, C, D, etc - the higher the sustained current rating, the lower the instantaneous tripping current, in a classical inverse relationship. E.G. for a B-class breaker, rated at 6A continuous, the ITC is between 0.333 and 0.5A (2-3/6, or 1/3-1/2). But one rated at 20A continuous has an ITC of only 0.1 to 0.15A (2/20-3/20...)

This surely can't be correct. So where's the misunderstanding/mistake? (talk) 11:44, 30 September 2010 (UTC)

Hydraulic-magnetic circuit breaker[edit]

I think the following topic is missing in the article:

Hydraulic magnetic circuit breakers incorporate an hydraulic machanism for overload protection. This usually substitutes the thermal part of magneto-thermic breakers. Basically, the magnetic coil tries to pull a ferromagnetic rod which is confined in a liquid medium. A spring tries to keep the rod at the rest position. Depending on the overload, this rod moves faster or slower towards the tripping end. At the time it reaches the tripping end, the breaker opens the circuit. Different curves are possible by adjusting the liquid flow by means of a small hole of calibrated diameter. Therefore, the pair coil-spring (force and counter-force) adjusts the steady current capacity, and the pair liquid-hole (drag force) adjust the tripping curve. Hydraulic magnetic switches are preferred to magneto-thermic ones in that the operation does not depend on the temperature, and therefore these dispositives are able to be rearmed immediately after a trip and function as the first time. In other words, they have no memory effect.

Google returns several links under "hydraulic magnetic". Here is one: [1]

Thanks. —Preceding unsigned comment added by Jsola (talkcontribs) 07:56, 6 May 2011 (UTC)

Hydraulic-magnetic breakers do indeed exist. The were and still are still manufactured in the UK by a company called Crabtree. Their most popular model being the C50, available in both single and three phase versions, though they are quite large compared to modern designs.
Your description of operation is not quite correct (but close). The mechanism consists of an oil filled dashpot with a ferrous core spring loaded to one end. On moderate overload, the current draws the core along the dashpot against the spring. As the core moves, the magnetic field concentrated at the other end increases until it is strong enough to trip the breaker. As the overload increases, the speed of movement through the dashpot increases, but the core does not need to move as far. Near instantaneous operation occurs if the overload is large enough that the magnetic field is able to trip the breaker before the core starts to move. The exact design of the dashpot and core determines the breaker's characteristics (the assembly being common among like type breakers), with the energising coil determining the current rating. Unlike thermal breakers, hydraulic-magnetic breakers have to be designed for AC circuits or for DC because their characteristics are markedly different on such circuits. Contrast a thermal breaker which van be used on either circuit provided its contacts are DC rated.
You are incorrect to assert that the operation is independent of temperature. The viscosity of the oil in the dashpot is very temperature dependent and the time -v- current characteristic shortens as temperature rises more rapidly than the equivalent characteristic of a thermal breaker.
You are correct (if I read your English correctly) that a Hydraulic magnetic breaker fully resets very quickly once it has tripped as the spring restores the ferrous core to the end of the dashpot almost immediately. Contrast a thermal breaker where the heated parts takes a significant time to cool down. Unfortunately, I cannot locate any material on the operation so cannot cite an addition to the article. HasAnyoneSeenMyMarbles (talk) 14:57, 8 February 2017 (UTC)
At least the type is mentioned now. The lack of discussion of this type in my local standard electrical references comforts me that this was not a major oversight in the article as it stood, though. --Wtshymanski (talk) 20:36, 9 February 2017 (UTC)

US 15A/20A most common breakers[edit]

Please add a sample picture of the most common 15A/20A US circuit breakers. Please add the fact that 15A and 20A are the most common sizes of residential circuit breakers in the US. - (talk) 14:50, 11 July 2014 (UTC)

trip speed[edit]

The "Instantaneous tripping current" section is too theoretical.

We need a graph illustration like this one:

Speed Delay
Opening speed, or delay, defines the relationship between the percentage by which the fuse or circuit breaker is operating over its Amperage Rating and the length of time that will be required for it to open. The opening of a fuse or circuit breaker is determined not just by the amperage rating, but by the amount of time and the percentage over its amperage rating at which it is being operated. The higher the % of current flow to amperage rating, the faster the circuit protector will open.
A chart such as the one shown here commonly represents this relationship.

and text that both explains the general concept and gives a maximally relevant ordinary-case example. So if this graph did apply to a common US 20A circuit breaker, we would say that the breaker would be expected to pass up to at least 22A on a continuous basis, and would pass a surge of at least 60A for a tenth of a second without tripping, but could be expected to trip within 1-sec max at 40A. At 25A it might trip as quickly as half a sec, but might take up to about a half min.

And we should specifically mention "nuisance tripping", and explain that motors have short-term peak surge currents when they start, so circuit breakers are designed to not trip too quickly. - (talk) 16:39, 11 July 2014 (UTC)

Lever positions - Article states "Also indicates the status of the circuit breaker (On or Off/tripped)." We should edit the parenthetical remarks to say (On, tripped, Off, Reset). If no one objects here, I shall return and make the correction. Sponsion (talk) 20:14, 20 January 2017 (UTC)

UL standards (USA) are confusing and lacking (with broken refs)[edit]

I wish the USA's standards were described as well as internation ones. From the article: "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 pack has a 22 kAIC tenant breaker, feeding a 10 kAIC loadcenter with 10 kAIC branches, where kAIC stands for “Thousand Ampere Interrupting Capacity.” Common meter pack ratings are 22/10, 42/10 and 100/10."

As a engineer with a masters (not to boast, just for context), I can't understand this jargon at all. The reference [1], is broken with no Google cache. What's a tenant breaker? What's a loadcenter? — Preceding unsigned comment added by (talk) 22:15, 18 February 2013 (UTC)

UL listing means the original equipment manufacturer (OEM) prepares a white paper about their product and states emphatically the stringent safety test(s) the OEM will perform during manufacture of their product. UL regularly visits the OEM and certifies the OEM is testing their product based upon the OEMs stated safety test(s). Sponsion (talk) 19:52, 20 January 2017 (UTC)


how often do circuit breakers go bad themselves? Jeff Kizziar 01/03/15-- (talk) 21:30, 3 January 2015 (UTC)

miniature history[edit]

why we cal circut breaker miniature?????Mohammadsdtmnd (talk) 12:58, 26 October 2015 (UTC)

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