US2545341A

US2545341A - Blow on arc tip

Info

Publication number: US2545341A
Application number: US532269A
Authority: US
Inventors: Arthur S Caswell
Original assignee: ITE Circuit Breaker Co
Current assignee: ITE Circuit Breaker Co
Priority date: 1944-04-22
Filing date: 1944-04-22
Publication date: 1951-03-13
Anticipated expiration: 1968-03-13

Description

March 13, 1951 A, s, CASWELL 2,545,341

BLOW oNv ARC TIP Filed April 22, 1944 6 Sheets-Sheet 1 1N VEN TOR.

/IJ CJWELL March 13, 1951 A S, CASWELL 2,545,341

BLOW ON ARC TIP Filed April 22, 1944 6 SheeoS-Sheei'l 2 March 13, 195l A. s. cAswELl. I 2,545,341

BLQW oN ARC TIP Filed Apr-i1 22, 1944 6 Sheets-Sheet 3 ELM@ IN VEN TOR.

J. (HJP/.ELL

Hg; 3 y -BY March 13, 1951 A. s. cAswELL. 2,545,341

BLOW ON ARC TIP Filed April 22, 1944 e sheets-sheet 4 IN VEN TOR.

March 13, 1951 A. s. cAswELL 2,545,341

BLOW 0N ARC TIP Filed April 22, 1944 e sheets-Sheet 5' INI/EN TOR.

` /ZJ (45h/ELL March 13', 1951 A, s, CASWELL 2,545,341

BLOW ON ARC TIP Filed April 2 2, 1944 6 Sheets-Shea?l 6 INVENTOR.

AS C/IJWELL Patented Mar. 13, 1951 BLOW oN Ano TIP Arthur S. Caswell, Philadelphia, Pa., assignor to I. T. E. Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Application April 22, 1944, Serial No. 532,269

(Cl. ZOU- 87) 3 Claims.

My present invention relates to circuit breaker contact lstructures and more particularly to a main stationary contact structure for circuit breakers which are constructed to provide a blow-on effect particularly of the arcing contacts; to magnetically blow the arc into the arc chute; and to substantially eliminate pigtails in conducting currents into moving members.

After the main contacts separate in response to a short circuit, it is desirable that the arcing contacts which carry the short circuit currents shall maintain good Contact until the instant of separation.

In accordance with my invention, I have so arranged the contact arm that the normal blow off effect of the short circuit current becomes a blow on action on the arcing contacts to ensure good contact pressure until the arcing contacts separate.

Accordingly, an object of my invention is to provide a novel blow on effect on the arcing contacts.

In the operation of circuit breakers, it is of course necessary to obtain proper contact pressure between the stationary and the movable contacts. Since the movable contact carrying arm has a positive mechanical movement toward the stationary contact, an unpredetermined variation of even minute extent in the length of the stroke of the moving contact arm due to even slight wear will of course interfere with contact pressure.

Accordingly, it has become common to mount the movable contact on the contact carrying arm so that it may pivot or have some other movement with respect thereto and to spring bias the movable Contact outwardly away from the contact carrying arm and toward the stationary contact. This spring bias ensures adequate contact pressure even though they length of the stroke of the movable contact carrying arm may vary slightly.

The pivotal mounting of the contact provides an inadequate current conductor from the contact to the contact carrying arm. Accordingly in the past, to ensure good current conduction, a pigtail connection from the contact to the contact carrying arm or from the contact directly to one of the terminals has been necessary.

Where the movable contact was made a rigid part of the contact carrying arm, it was necessary to make the stationary contact member pivotal or otherwise movable with respect to the stationary conductor and to spring bias the same outwardly from the end of the stationary conductor in order to obtain contact pressure. In this case the pigtail connection was required between the stationary contact member and the stationary conductor.

My invention contemplates the construction of a stationary contact member for. a circuit breaker which has a pivotal movement with respect to the stationary conductor and is spring biased outwardly away from the end of the stationary conductor but wherein no pigtail or other shunt connection is necessary in order to provide a current carrying path between the stationary contact and the stationary conductor.

Further, my invention contemplates as an object the provision of means in the mounting of the stationary contact on the stationary conductor for providing a current carrying path directly between the stationary contact and the stationary conductor.

A more speciiic object of my invention is the provision of means for creating a tight frictional current carrying engagement between the stationary contact and the stationary conductor of a circuit breaker so that a proper current carrying path is provided between them.

While my invention is directed more specically to the construction and arrangement of a stationary contact member which may be pivotal with respect to the stationary conductor and in which the necessity for pigtail or other shunt connections between the stationary contact and the stationary conductor is eliminated, it will be clear that the structure of the stationary contact may, in appropriate cases, be incorporated in the movable contact structure to perform the same function and to obtain the same results.

My invention also contemplates the arrangement of the arcing contact arm and the mounting thereof in such a manner outside the main contact arm so that the skin effect of the assembly would help the arcing contacts take more current, and, therefore, increase the main contact protection.

A further object of my invention is the arrangement of the arcing contact in such a manner that the inertia thereof will assist in maintaining contact between the arcing contacts during contact opening.

A further object of my invention is the arrangement of the spring and pigtail connections for the arcing contact arm so that they are very near the pivot point of the entire assembly, and so that they will thus have less effect in slowing down the opening speed of the circuit breaker.

The foregoing and many other objects of my invention will become apparent in the fol-lowing description and drawings, in which v Figure 1 is a side view of a circuit breaker contact structure embodying the principles of my invention. Y

Figure 1A is a side view of the stationary contact elements embodying the principles of my invention. Y

Figure 2 is a front View of Figure 1A.

Figure 3 is a iront view partly broken away of the movable contact arm of Figure 1.

Figure 4 is a side View of a modified form of a stationary.contactmember.

Figurezisaf-iront lView partly broken awaylof the stationary contact member of Figure 4.

Figure 6 is a side View or" a modied form of circuit breaker contact structure embodying substantially the structure of Figure l but showing a pigtail-less connection foi-.the arcing contact;V

Figure 7 is a front View partially broken-.away

Referring,j now. to. Figure .1, ,the circuit .breaker contact structure l comprises anupper station:

ary-terminald l, tol-.which are secured, by means;` OIapprOpr-iate .bolts ...I 2,. the oppositespaced ,plate extensions |3,;.I3 ,(see.alsoFigureZ). Thesta.- tionarycontact blockl 5, hereinafter morespeci-l cally described, .ispivotally mounted .on a. pin. |6.-.supported..between the. opposite plates l 3,'. .i

The; contact block: .i is providedzwith :arbore 2li-.in whichrthe compression spring 2i 'is posi-- tioned..'. One end..of..the .compressionspringr 2E` bearsagainst the. basent. :the :bore ,.and., the op.-y

posite endof the spring 2l bearsagainst the-leg.

22.01 lthepositioning.bracket 23.'

The positioningr .bracket 23 is secured. .to` the front end of..'the.stationaryconductor. il in any suitablevmanner, asfor instance by the .screwsf Bracket, 23.-,also has af refentrant extf-:nsionY 2l' which enters intoa .slot 23 in the lowerendbf .the contact block: l5to. limit boththe.zoutwardland inward- 1movenfient ofthe Contact. block la. as vrit.

rotates aboutthef pin.. lli..v That'is, when the.

movable-.contactais...moved :away from. the sta,-

tionarywontact, the. spring 2l drives the lower,Y endY of.l the. stationary: contact.. block.. l 5I to the.

right -.until athe left yhand- `wallof ,slot .bears against the refentrant flange 2l.

The -ri-ght -hand wall. of ,slot Edensures .that .the

movable icontact...blocl ..l5 `.will ,not be rotatedfto. the yleft for.. sogreatav distance as. to result inY injuryfto the springllor damageto .the sta tionary =contact .structure...

The .Contact :block l 5 .isf provided.with va .main

Contact surfacefSll .and an.- arcing contact surface 31.., The-.main contact surface. 3E .-is, engaged by the-V movable ,main. ,contact .32 lwhich is. positioned 'i on the movable contact arm 38.

Theiarcingcontact surface 3l is engagedby the movable arcing; contact 33. 36,:is, pivotally mountedon .the pin'l Vcarried .by the-movablecontact arm 38 .and is providedwith an arcing horn 35 along whichLthe.arcismagr netically driven.. The lower end..of.the arcing contact l.arm S l is. provided .with spring4 bias (hereinafter, described whichtends.. to rotate thearcing .contact `arzrnSG inA a ,counterclockwise di'lcctipnso. that "the, arcing` contact 331s biased Arcing' contact arm.A

3) which are connected together at their upper ende vby lthe contact blockfr .sothat they operate together.

A bolt 55 is secured in any suitable manner to .u the center of the bridging plate f5!) which interconnects the arcing contact arms 36a and 35D, and thisbolt passes between the movable contact carryingplates 38aand 33D and projects beyond the-front `ofvthe movable contact arno. An additional pin interconnects the two movable contact .arms 38a and 381) and pivotally receives the link-2li'which-"operates the contact bridge 38 betweenetheiopen and closed position by means of an appropriate operatingmechanism.

A .compression springl surrounds .the .bolt 55 and.'is .compressed between thebridginglplate d.

andthe head.,3 ofthe threaded bolty55.' The opposite l,endlof the bolt 55.is.provided..with.,a plate 12..whic`h` bears against theirontsurface of the. main. contact v.bridgearms. 33a and. 3819. andv issecuredin .placewitl't respect tothe plate ,2 by. meansofthenutllS..v Alocknut 59 maintains.

the predetermined.. adjustment. The.l compression .spring Vthereio`r-e;biases the: arcing contact arm 3b `toward Vcounterclockwse rotation so that the movablearcing contact. 33-is biased. outwardly toward the left of the movable contact arm 38.

A .pigtail Sli vis. connectedbetween the. arcing contact arm..36J-and .the pigtail boss'i. It will, of course, bek clear tbata separate pigtail'll is providedon each side. The plates 38a'and 3819 of.. the movable contact arm are mounted on either side of the lower stationary conductorw.. Arrbolt 63 Ypasses through appropriateregistering openingsf-invv the contact arm platesla and 138m and in the stationary conductor 62.

Aspringwasher 64 of highly conductive materialis. placed4 between the, heady of the. boltlS and .the contactarmplatezlla on one-sideof .the structure andan additional v.washerlv5 ofsimilar materialisplaced between the nut $6 of the contact larmplatebon the other sideof the structure; The nut 66. isr tightened andfsecuredin tightened. position.

Contact arm 38 comprising` plates. 38a andy 33h now has rotative movement around the shaft ofthebolt t3.` riheinner. surfaces of the platesy 38a andb are in tightfrictional engagement with theouter surface offtheflower conductor'iZ, thus creatingy an; appropriate current carryingI path betweenithe movable. contact-arm 38. andA thelower .conductor S2.-

In. order `further Ato ensure an appropriate cur-- rent carrying relationshipt between therA lower conductor 52 'and-.the lower endsof-'the plates 38a, and 3531 additional washers 6l and 68 maybe placed .between 'ther-lower conductor G52 and fthe plates 35a and'SSb.

The. currrent carrying path betweenfthey contact-armand the'lower conductor 62 is essentially-a clivided'patli.v Aportion'of the current passes fromathe outerr surface of each-of the plates SM1-and V33h to the springwashersewand 55, thento-the head ofthe bolt land the nut lythenztothe shaft-.0f the bolt and through the shaft :Ot they-bolt to-thelower conductor 52. The remainder of the-current passes s." directly from the inner 'surfaces of plates 33t/:and 33h through the washers-57 and @S tothe surfacefc-f the lower conductor i162.' By this: means pigtail -connection'v between the movable contact arm Salon-the movable contact 32; to. the: lower: conductor 52? is obviated.

The .pigtail te betweenzithe larcingfcontact arm 36s' and thermovable; contactparmfSilcmayfbecobe viated in a similar manner by providing for a similar mounting at 31 of the contact arm 36 on the movable contact arm 318, although in order to provide a freely rotatable bearing surface at 31, the actual current path inFigure 1 is provided by the pigtail 60 in Figure l.

As seen more particularly in Figure 2, the stationary contact block I5 is made up of tWo contact iingers I5ar and I5b. Contact lingers I5a and I5b are rotatably mounted onV the pin I3 between the plates I3, I3 as above pointed out. Each of the contact fingers I5a and I5b is provided with a lateral opening through which the pin I6 passes.

The inner surface of each of. the contact blocks I5a and I5b is counterbored at 1I to produce two co-axial and adjacent openings which register with each other to form a single continuous housing for the compression spring 13. Compression spring 13 bears against the opposite bases of the counterbore 1I to drive the contact iingers |501n and I5b apart. A spacer washer 15 of highly conductive material is provided around the pin I6 between the outer surface of each of the contact fingers I5a and I5b to provide an efcient current carrying path between the respective contact fingers to the plates I3, I3. The compression spring 1I thus ensures that the contact block I5 comprising the contact fingers I5a, and I5b will be in appropriate current carrying relationship with the plates I3, I3 and hence with the upper stationary conductor II.

By this means therefore, although the main stationary contact 36 is pivotal around the pin I6 and is provided with a spring bias urging it away from the upper stationary conductor II, nevertheless a pigtail connection from the main stationary contact to the upper stationary conductor II is made unnecessary. The spring 1I and the spacer washers 15 provide for such a current carrying path. Since the main stationary contact 30 is thus provided with the necessary spring bias to ensure appropriate contact pressure, the main movable contact 32 may be rigidly secured to the movable contact arm 38.

Since, however the stationary arcing contact tip 3| is mounted on that portion of the contact block I5 which has relatively the smallest amount of rotation and has substantially no inward or outward movement with respect to the upper stationary conductor I I, the movable arcing contact 33 is mounted on the pivotal arm 36 and is provided with the necessary spring 51 to ensure proper arcing contact pressure.

As will now be obvious, when the circuit breaker is open, the arcing contact 33 is rotated to a substantial extent counter-clockwise with respect to the movable contact arm 38 by means of the spring 51 so that the arcing contact tip 33 projects substantially beyond the movable main contact 32.

Accordingly on a closing operation of the circuit breaker the arcing contacts 3l and 33 will meet first. On completion of the closing movement however the main movable contact 32 moves into engagement with the main stationary contact 33, the contact block I5 is rocked about its pivot I5 compressing spring 2| until the right hand side of slot 28 engages re-entrant flange 21. At the same time the spring 51 on the movable contact arm which applies the necessary bias to the arcing contact tip 33 is progressively compressed.

On the initiation of the opening movement of the movable arm 38, movable contact 32 Will move to the right followed by contact 30 under the action of spring 2`I until the left wall of the slot engages projection 21. Thereafter contact 32 will separate from the stationary main contact 36 while the spring 51 maintains the movable arcing contact tip 33 in engagement with the stationary arcing contact tip 3|. When the base of the U-shaped bracket 4I] moves into engagement with the back surface of the movable contact arm 38, then the movable arcing contact will be withdrawn from engagement with contact 3l. It will thus be seen that the arcing contacts open last in order to protect the main contact surfaces. This is obtained of course by the spring bias of compression spring 51, as above pointed out.

This result is also obtained, however, by reason of the mechanical arrangement of the arcing contact arm 36. As is well known, current in the loop formed by the conductor 62, the contact arm 38 and conductor II provides a magnetic force tending to rotate the movable arm 38` clockwise about its pivot. On short circuit this blow off action assists in the disengagement of

contacts

32 and 30.

This same magnetic action acting on arm 36 will provide a rotative force on the arcing contact arm 36 driving the part of the arm belovvV pivot 31 in a counterclockwise direction, and the part of the arm above pivot 31 in a clockwise direction. However, since leverage for the portion below the pivot 31 includes not only the arm 36 but also the pigtail 6l) extending down to the conductor 62, the total force providing the counterclockwise rotation about pivot 31 is greater than the force tending t0 produce a clockwise rotation.

Accordingly, the net magnetic force of the short circuit current is to drive the arcing contacts 3I and 33 into engagement while the main contacts separate. This force added to that produced by the compression spring 51 already described insures a firm arcing contact engagement during the initiation of Contact separation.

Thus the Varc will be drawn at the arcing contacts only and the main contacts will be protected.

The design of the stationary contacts as has above been pointed out obviates the necessity for any pigtail or shunt connections of any kind whatever. These contact structures have been found under test to operate eiiiciently with only normal temperature rise. lThe only possible disadvantage which at least for the present is theoretical rather than actual, is that the two parallel iingers carrying the parallel currents may be magnetically attracted under conditions of very high short circuit te such an extent that they may be pulled out of contact. The construction shown in Figures e and 5 obviates even this possibility. In Figures i and 5 l have shown a modied form of stationary contact structure within the spirit of my invention. It is suiiicient to point out, however, that the movable contact members which cooperate with the stationary contact members shown in Figures 4 and 5 are fully rigid-that is, both the movable arcing and movable main contact are rigidly secured to the movable contact arm.

In Figure 4, the upper stationary conductor or main connection stud is a simple rectangular bar III. A pair of contact arms H551, and I|5b are mounted on either side of the upper connected stud HI and are rotatably secured thereto by means of the bolt II6 which passes through the in slowing the opening speed of the circuit breaker as a whole.

In addition, this structure has the advantage that the direction of the current in the moving arcing tip is in the direction to drive the current to the upper end of the tip, by its own magnetic field, thus hastening the movement of the arc into the arc chute (not shown) and its rupture there.

Usually in an air circuit breaker or contactor, the arcing tips are provided with magnetic blow out coils to quickly drive the arc to the top of the arcing tip and into the arc chute. This action is aided by the shape of the arc tip, shown in Figure 1, and is a decided improvement over the usual inverted arc tip.

It should, of course, be recognized that this type of contact arrangement may be as important for an ordinary contactor as it is in a circuit breaker.

In the usual power system, a feeder breaker is used to distribute power to a load consisting of one or more motors. The circuit breaker is primarily for the purpose of providing fault protection and is designed to interrupt any short circuit that may develop. At each motor, there is installed a contactor which is provided with an overload device, usually in the form of a thermal overload relay, having a long time delay corresponding to the heating curve of the motor. The contactor is designed to open overloads a large number of times but is not designed to open short circuits.

Should a short circuit occur on the load side of the contactor, the operation requires that theA contactor remain closed and that it should not attempt to open the circuit. The contactor is thus required to carry the short circuit current without opening, It is, therefore, important that the contacts of the contactor do not blow open due tothis high current.

Accordingly, a contactor may be constructed, substantially in the form shown in Figure'l, to have the blow on effect herein described.

In Figure 6 I have shown a modiiied form of the moving contact structure of the circuit breaker of Figure 1. The essential distinction between the structures of Figures 1 and 6 is that the movable member is pigtail-less.

The contact structure 5||l comprises a main stationary contact 2|2 and a stationary arcing contact 2|3 mounted on a stationary contact block 2| 4, which, in turn, is pivotally mounted at 2|5 on the upper stationary conductor 2|6. The stationary contact structure of Figure 6 is identical with the stationary contact structure of Figure 1.

The movable contact bridge 526 is pivotally mounted at 52| on the lower conductor 522. Movable contact bridge 52S is operated between open and closed position by means of an appropriate operating mechanism connected thereto by the link 525 which is controlled by any wellknown tripping mechanism of a circuit breaker.

Link 525, as shown in Figures 6 and '7, is connected between the plates 5250i and 5201) of the movable contact bridge 520 by a pin 525a passing through suitable matching openings in the plates 52M and 52013; and the link 525 is secured in position by cotter pins 52 5b.

Movable contact bridge 520 carries the main movable contacts 526 which engage the main stationary contacts 2|2.

The arcing contact arm 535 is pivotally mounted on the movable contact bridge or arm 520 by means of the pin 532.

As may more readily be seen in Figure 7, the arcing contact lever 536 comprises a pair of arms 530a and 5301) mounted on the outside of the movable contact bridge 520 and pivotal with respect thereto.

The arms 535:1 and 5301) are interconnected at their upper ends by the arcing contact member 535 which carries the movable contact tip 536 and the arcing horn 531 along which the arc is magnetically driven.

The lower ends of the arms 530:1 and 5301i are interconnected by the plate 538 which is provided with an appropriate opening through which the bolt 539 passes.

The opposite end of the bolt 539 is provided with a plate 542 which bears against the front surface of the main contact bridge arms 520m and 5201).

A compression spring 546 is mounted between a head 54| of the bolt 539 and the front plate 542.

The end of the bolt 539 opposite the head 54| and outside the plate 538 is provided with a nut 543 and a lock nut 5430i which maintains compression of the spring 54E.

It will thus be seen that the compression spring 54|), acting between the head 54| of the bolt 539 and the plate 542, biases the arcing contact arm 530 toward counterclockwise rotation, so that when the contactor or circuit breaker is in open circuit position, the arcing contact 536 projects substantially beyond the lower main movable contact 526.

'The arcing contact arm plates 23M and 23612 are each provided with a frontwardly projecting lug 555 through which the mounting pin 532 passes which secures them to the main movable contact bridge 520. The pin 532 is held in position by the cotter pins 532a.

The pivot or mounting of the main contact arm 520 at 52| on the lower conductor 522 is eX- actly the same as that described for the similar mounting of the lower end oi the contact arm of Figure 1 on the lower conductor-that is, a tight pigtail-less connection is provided.

However, instead of the pigtail connection between the arcing contact arm and the lower conductor which is shown in Figure l, a similar pigtail-less connection is provided between the arcing contact arm 535 of Figure 6 and the main contact arm 520.

A bolt 555 passes through matching slots 55| in the plates 52a and 526D of the contact arm 520 and through appropriate openings in the plates 53H01, and 535D of the arcing contact arm.

The slots 55| in the plates of the main contact arm 52B are suilicientlylong as to permit the desired maximum rotation of the arcing contact arm 530 with respect to the main contact arm Spring washers 555 are provided between the head 556 of the bolt 55!) and the securing nut 551 of the bolt and are tightened against the outside surfaces of the plates 533m and 530D of the arcing Contact arm 536 by the nut 551 which is then secured in position by the lock nut 558.

The lower ends of the plates 53a and 53th of the arcing contact arm 535 are inwardly curved at 566 and 55| to provide a pressure contactingsurface for these plates to make contact with the surfaces of plates 520a and 5202) of the main contact arm 52B. Tightening of the nut 557 and the lock nut 558 of the bolt 555 will draw these curved extensions of the arcing contact arm plates inwardly toward each other into tight contacting current carrying engagement with the plates 0i l the main .contact arm. Byk this means, therefore. a pigtail connection between the arcing-contact arm and the lower conductor is obviated.

` The principles, however,..vvhich. govern the operation of the contact structure of'FiguresJGand f: 7 .are the samefas .thosewhich govern' theoperation of the contactistructurezof Figure' 1,1 and. all

of the previous discussion I.withy respect .toFigure 'f lapplies to the construction of Figuresandffl.

In Figure 8 I have shown. a moving. Contact structure. adapted-to cooperate Awit'nthe stationary Contact structure. of. Figures' 4 and. 5.

' i The stationary contact `structure"-.Elillis-kexactly the same in every respect asthat shovvniin vFigures 4v and 5. Sincey the stationary contact -structure hasan arcing contact whichlmaypivot with respect thereto,l the moving contact structure may be an arcing contact whichis rigidly axed to. said moving contact structure.

Y The moving Contact structure comprisesfa' contact arm S25 which may preferably be composed of a pair oi plateswhich are bridged'ftogether by the cross-pieceEila on Which thevmain moving contact 52@ is mounted. The' lower Aends'of the plates which form thermoving-fcontact-arm @2Q are secured at @2l to' thelovver conductorLSZZ in the manner described in connection-With. Figures 1 anolv.

An' operating .link 625 is connected to the: -pin 625:1 securedbetween the plates ofthe movable contact arm Gfandheldin position by the cotter pins i'a. The.operatinglinkl 525may be connected to any suitable operating mechanismf as Vpreviously described.

The movable arcingf -oontactlG35-isfV secured' to the bridging plate 52M of the armlt' by-means of bolts'i passing throughl thev clamping-*plate 66E. and the flange-562 of thearc'ingcontacte into the bridging platel 62B.

The arcing conta'otmember-S carries amovable arcing contact andan arcing hornl-'GSI for vpurposes previously described.

In the embodiment V.herelshovvn'--in 'Figuref8,

the arcing contactstructurelI 535-. is thusvvv rigidly connected and has no motion-with respect tolthe 'movable contact arm-62ljsinceithefstationary arcing Contact itl is'movably Amounted,"-asfipreyviously described .in connection l.with Figures '+4 and 5. Thus, the arrangement-offthelstationary contact of Figure 1 4 permits the .use ofc a simplied movable contact structure as-abovedescfribed;

Inlthe foregoing,v I have described Imylinven tion onlyin connection withpreferrediembodiland. arms, 'said studs, contacts :and first movable .arm forming a U-fshaped'loop,v saidsecondsmovable 'arm' having. an. elongated por-tionextending VAwithin said U-shapedloopgenerally parallel .with v.said rst movable armandiormingf.a'parallel,

electrical path therewith whereby amutualmag- -netic. attraction urges `said rstlandifseconclfarrns to'wardfeach. other and ini-the same '.directioniz-as said -rst movablearm, anI ar'cng contacten said --second movablearm, cooperating contact means for said-main andf'movable contacts, studs connected to said cooperating contact mea-nsf'and `arms, saidstlds; contacts andrst movablearm forming a U-sha-p d*loop,:said` second-movable f arm having -f an elongated portion extending @within said U"shaped loop generally parallelwith sad'frst movable arm and'u forming a'- parallel electric'al'path therewith whereby a 'mutual mag netic attraction urgesl 'saidrst andI secondl arms "toward each` other'and inthe samedirection as thermagnetic yforces 'tending' Ato `extend the-loop,

thev distance from 'the' pivot-of' said second arm to said arcing contact being smallerthanA `from saidpivot totheend'of said second vmovable arm opposite the'. end `on which4 said arcing r`Contact is *mounted `3. 'In` a circuit'. breaker" having ai'irst movable arm, a main. contact" mounted on said movable .arnna second movable arm pivotallyimounted on ,.saidr'stmovable arm, anr arcing. contact onsaid secondmovable arm, cooperating contact'means `for said main and'movable contacts, 'studsconm nected..to-said cooperating contactmeansand ..a1ms,.v said. studs, contacts .andi-lrst movablev arm forming aV U-shaped' loop, said second movable arm having :an elongated Yportion .extending within said .Ushaped-loop. generally parallel with said rst. movableY arm and forming .a parallel electricalpath therewith whereby. a mutualmagnetic .attraction urgessaidliirstand secondarms toward each other...and .ine-the .same direction .as the -magnetic-forces Atending to .extend the loop, the distance from the,.pivot.ofsaid second .arm to said.. arcing contact. being smaller. than .from saidfpivotto the end. of-.saidsecond .movable arm opposite-the. endon-which -saidarcing conatact is fmounted, and V a .movable .memberzfor -said-pivotalusupport for moving saidmovable .contact out..of engagement with said. cooperat- -fing contact.v

REFERENCESvl GITED The? follovvingi'vreferences: are L ofv record'- ini the UMTED b,S'IATICEIS PATENTS .-.Number Name .Date

1,395,327 Aalborg Nov. 1,? 1921 11,395,348 MacNeill Nov. 1,'11921 1;560,308 .Perry 1 Nov.. 3, :1925 v1,762,604 .--Ainsworth '.uner 30,- `1930 1,763,027 "Wilnis June '10, 1930 "1,804,628 .'MacNeill May 1931 11g-935,428 @Atwood Nov..14, '1933 2,955,114 vWoernley 1 Sept.: 22,.' 1936 :2,214,471 Ludwig et 1al. '.LSept.'v 10,1940 I2',227,=160 f.. Seaman f;l3ec.` 31,. 1940 '2,285,890 fBlosser. June"9, 1942 12,328,313 tfWood Aug.'21, 1943 FOREIGN' PATENT S -Number Country r`:Date

.182,315 -Great Britain July/.6,1922 541,281 Great Britain. zNov. 20,: `1941 546,435 '.GreatBritain July1l14, :1942 834,834 f France ':1Sept.25,'.1988