US2666824A

US2666824A - Circuit breaker

Info

Publication number: US2666824A
Application number: US190825A
Authority: US
Inventors: Hiller D Dorfman
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1950-10-18
Filing date: 1950-10-18
Publication date: 1954-01-19
Anticipated expiration: 1971-01-19
Also published as: FR1048621A

Description

Jan. 19, 1954 H. D. DORFMAN 2,666,824

CIRCUIT BREAKER Filed Oct. 18, 1950 5 Sheets-Sheet l WITNESSES:

INVENTOR Hiller D.Dorfmon.

Jan. 19, 1954 Filed Oct. 18, 1950 H. D. DORFMAN CIRCUIT BREAKER 3 Sheets-Sheet 2 WITNESSES:

INVENTOR Hiller D.Dorfmon.

Patented Jan. 19, 1954 iiiumtiap PATENT fOFEI' CE om'curr BREAKER mmer-nanorrman'g neaver, -Pa.,assignor td'WeStnghouse Electric Corporation, East Pittsburgh,

iielasi a; corporation of Pennsylvania Afiiilicatiorioct'ober 18, 1950, Serial N0.L190,825

15Glaims.

This inventioniielatesto eircuit'dore'akers and more particularly to circuit-breakers of the type usedfor controlling lightingandmoderate-power distributioni'circuits.

"An" object *of? the'inventiomis-toi' provide a cir-- 'cuit'breaker 'with"means forefiecting openingof the breaker TIIIJOII aifa'rlurefofthe-insulation in electrical equipment.

- Another obiect *of theinvention is"to provide a circuitbreaker supplied Wifih,"i fort-supplying, electricah-current through-;'trailing cables-"with meanstfor-causingppening of the'breaker upon a breakdown "of. the cable.

: Another obj'ectbf theinvention ,isto "-provide a circuit";,breaker havingqg "ground-"current trip means for causingnpening'bfithe*breakerun response to. failure oi the insulationwitlrprotective means for*protectingthrtripmeans "upon repeated-attemptsto elos'eth'e breaker while apersistentground-faultexists.

'- Thenoverfeatures; that are-considered characteristic"ofitheinvention-aireset-forth"in particular "in the appendedt ciaims. "1 The invention itself,

however; bothas' to-structure andoperationytovgetherwithi additionaliiobj ectsaand advantages It thereofywili-be bestunderstood from-ithej-following detailed- -descriptionrf"thereof whemmead "in conjunction witlrj' 'the accompanyingdrawings.

" In said drawings Fig: l is a-vertica'l,:longitudinal section'al viewof a circuit breakercembodyingthetinventionirthe breaker-being shownjin the'closed'position;

Fig. 2- isa sectionalwiew onamenlarged scale of the overcurrent tripnievice;

i -Fig. 3"-isa sectional view Oman enlarged --scale= of the-ground-fault trip device;

1 Fig. 4 is a diagrammaticview or the circuit breaker-and the-connecting-cable7 and Fig. 5 is a" plan view 'of the *circuit breaker" with the cover removed.

- pole-brea=ken is mounted'-in an enclosingcasing for" a' three pole, breaker. The circuit-breaker comprises generally a-base=-Tand a--cover 9;-both of molded*insulatipge material, operating mechanismindicated generailyeat I l-7' an-over-current trip device indicated general1y-at1 (hand a ground fault-trip device indicated-generallyat l 5--(-Fig. 3) Thecasing' f'ermed *hyth base Fahd-rover 9 is 'divided' intothree longitudinal compartments by partition wallsi' 'l tonly one -being" shown) and matchingpartitiomwallsll 6. Stationarycontacts 25:18.,and cooperating movable contacts are disposed in atsleast :twoeiofakthe::compartments and, to-

a3ethenwitlrthercorrespandingsterminalsiana son--* necting-conductors; form the'two, poles "of'fthe breaker. Each pole "Ofthf breaker is provided with end terminals ll disposed; insuitableopenings in the base at'each 'end'thereof.

The respective: stationary contacts 18'; one-"for each pole, are each'mount'ed'on-the lowerend of a conductor 2| secured to." the :base 1. i'Atits upper end the conductor 2| is" electrically ,connected to therespectiv'e, terminal 11.

The movable contact: structures 'for"the two polesrare the-same, forwhi'ch-reason ;o'nly-one will be described. 'jThe'movable' contactfiZD-for the pole disposed inithe'center compartment; is secured'to a'contact arm?! which is'loosely sup ported "on". a channelishapcd' switch arm"29 v (Fig. 1)

The two channelashaped switch arms are rigidly,fastened*for3unitary movementiby means'of a tie b31731 whichextends across both poles of the breaker. '2' The channel-shaped switch arm in the centerrcompartment 'isypivotally mountedby'means of" a.pivotcpin' .32 supported in aU-shap'ed frame" secured. to". the base 1.

The movable'contact structure,.'compriS I the switch arm 29;the tie bar 3| and the contact arm 21 for bothpoles of thebreakeryis adapted'topbe operated to open position: andito closed position by the'common operating mechanism II. This mechanism may. comprise .a, carrier'if33 pivotally arcuate protective po'rtion53 and side plates"*55 integral with'the; portions"53. jiThe..sidejplates of the 'handlefstrad'dleithe frame::25 andiare secured tothe two iegsbf' the operating lever 4|. The carrier 33 is normally heldcinnlatched .posi- 'tion', as; shown" in" Fig: 1: 7by a latch 58 (Fig: 2)

of 'the'trip *device' l 3which*-engages'-the free-end "of the center.

With the parts intheclosed positionras shown in Fig; lg the' contacts are -manuallyopened-by clock-wise movement of themperating handle fl -movement the overcentersprings 43 will snap overcenter below the center line of the toggle link 31 causing collapse of the toggle 31-33 and opening movement of the movable contact structure. The contacts are closed by movement of the handle 41 in the opposite direction to the position shown in Fig. 1. This movement causes the overeenter springs 43 to move over-center in the opposite direction and move the toggle 3'I-38 to the in-toggle position to simultaneously close all of the contact means.

The circuit breaker is trip ed open automatically in response to overload currents occurring in either pole of the breaker, by operation of the trip device I3 (Fig. 2). The trip device includes a bimetal elementfil and an electromagnetic trip means indicated generally at 33 for at least one of the two poles of the breaker. Each bimetal element 6| is rigidly secured to one turn of an energizing winding 65 for the electromagnet 83 of the corresponding pole. One

.end of the winding 85 is connected by means of a conductor S'I-to thelower terminal I1 and the otherend of the winding is secured to a conductor 69 which is connected by a. flexible conductor 'I'I to the movable contact arm for the corresponding pole. In addition to energizing the magnet 63, the winding 65 serves as a heater for the bimetal element 6|.

Each of the magnetic trip devices 63 comprises a U-shaped magnet yoke "I3 secured to an insulating support member I5 suitably mounted on the base I. A center core member TI is 'secured to the portion of the U-shaped yoke which lies adjacent the support I5 and extends downwardly therefrom through the energizing winding 65. An armature I9 is pivotally supported on one leg of the U-shaped magnet yoke '53 and is biased to unattracted position by means of a spring 8|. A common trip bar 83 of molded insulating material extends across the trip devices of the two poles and is operable by either of the bimetal elements 6| and also by the electromagnetic trip means 63 for either pole of the breaker. The trip bar 83 is pivotally mounted on a pair of brackets 85 (only one being shown) extending downwardly from the support member I5 and is biased in acounterelocklwise direction to latching position by means of a spring 81. The trip bar 83 is provided with a projection 83 for each pole suitably secured thereto and having one end disposed to be engaged by the armature I9 for its associated pole. Also secured to the trip bar 83 is an arm 9| for each pole having adjusting screws 93 mounted in'the free ends thereof to be engaged by the associated bimetal element 6|.

The latch member '58 which engages and normally restrains the carrier in operative position is pivotally and slidably mounted on a pin 95 supported in the legs of ayoke-shaped bracket 91 mounted on the support member I5. A spring 99 biases the latch 58 in a counterclockwise direction. The latch member 58 is normally prevented from moving in a clockwise or unlatehing direction by engagement of the portion IOI thereof with a latching projection I03 on the trip bar.

85 on which it is mounted, and when heated a predetermined amount in response to persistent low overload currents, deflects downwardly engaging and actuating the trip bar in unlatehing direction to release the latch member 58. Release of the latch member 58 effects release of the carrier 33 which is then rotated counterclockwise carrying the ,centerline of the toggle link 31 overceriter above the line' of action of the overcenter spring 43 whereupon the springs 43 cause collapse of the toggle 3l39 and opening movement of the switch member 29.

Release of the carrier 33 is also effected by operation of. the electromagnetic means 63 in response to overload currents above 1000% of normal, or a short circuit. Upon the occurrence .of a heavy overload or a short circuit current, the electromagnet of the affected pole is energized an amount sufficient to attract the armature 19 causing the armature to engage the projection 89 and instantaneously actuate the trip bar 83 to effect release of the carrier 33 and opening of the contacts.

Before the contacts can be closed following an automatic tripping operation, it is necessary to reset and relatch the carrier 33. This is accomplished by moving the handle 41 clockwise as far as it will go. During this movement of the handle a'projeetion I85 on the operating lever 4| engages the carrier and moves it therewith until the end of the carrier wipes by the latch 58. This action also effects relatching of the latch members 58 with the projection I83 on the trip bar 83. The contacts can now be closed in the previously described manner by upward movement of the handle to the position shown in Fig. 1.

The circuit breakermay betripped open response to a loss of voltage by means of an undervoltage trip device which is shown schematically at I01 in Figs. 4 and 5. Theundervoltage trip device is located in the right hand compartment of the three compartment housing (Fig. 5) and may be of any suitable well known type, preferably of the type disclosed in copending application Serial No. 187,555, filed. September 29, 1950, by T. W. Slebodnik and assigned to the assignee of the instantapplication. Such undervoltage trip devices usually comprise a voltage coil and an armature that is held in attracted position so long as the coil is energized by normal voltage but which is released and caused to engage and actuate the trip'means upon a predetermined loss of voltage.

- The undervoltage trip device IIJ'I (Fig. 5) co prises a voltage coil I08, a U-shaped magnet yoke IIII mounted by means of a bracket H2 and a block II4 on the insulating support member I 5, an armature H6 and aatrip rod II8 secured to the armature H6. The armature H6 is biased by means of a spring (not shown) in a direction to cause the rod II8 to engage and actuate the trip bar 83 but is normally held in attracted position by energization of the coil I08 in response to normal voltage. Upon a predetermined loss of voltage, the armature I I6 is released and the spring (not shown) functionsto actuate the trip rod H8 and eiTect tripping-of the breaker.

The armature H6 is reset by movement of the operating handle '41 to the reset position to reset the breaker mechanism. When the handle 41 is moved to the reset position the side plate 53 thereof engages an arm I20 seeured'to a shaft I22 rotatably mounted in the block H4 and rotates the shaft in a direction to cause an arm I24 secured. to theotherendof the shaft-tozengageand move the: armature: I 16. to its..-'attractedposi-.- tion. If normal voltage: has been restoredto the coil IllB the magnet will be energized and hold the armaturein its attracted position and the breaker may be closed. If, however,. the normal voltage has not been restored then upon movement of the handle 41 away from. the reset position, the spring. (not shown) will again actuate the trip rod- I I8 to trip the breaker;

For certain applications. it is. desirable that the circuit breaker shall open: the circuit immediately upon the: occurrence. of a. breakdown of the insulation of. the equipment. or in the: event: that the insulation deteriorates to such a point that leakage currents to the frame reach a predetermined value; This: protection is. provided by means of a. ground fault trip device;- indicated generally at; I5 (Figs. 3 and 4-), connected in a circuit. connecting the frame: of the protected equipment, toground.

I3he-ground fault trip device; I5 is: located in the left hand compartment: in. the three compartment housing (Fig. 5.)- and. may comprise an electromagnet indicated. generally at I09 (Fig. 3) having an energizing, coil III: connectediniseries. relation. in the ground circuit- One. end of the coil III is supported on. a. rigid conductor 3 which is connected by means of! a. flexible con..-

ductor to: the contact arm 21 the left hand of a bimetal element [191 having; its other end.

rigidly supported on a. conductor I2I which, in:

turn, is connected to a terminal. I'2.3.. shown schematically in Fig. 4. A; U=-shaped magnet" yoke I25, similarto' the magnet yoke 1.3 of the overcurrent trip device, is mounted. on. the support member 15. and-has; anarmature I21 pivot ally mounted on one; of. the legs thereof. magnet yoke I25 (Figs. 3 and 5;).- has :-a' center core member I29 similar tothe; center core member I29 similar to the; center member I! for theother. polesextendingthrough: the center of. thecoil III. and; a. spring; Iil compressed between the armature I21. and the; center core member I29 biaseszther armature to unattracted. position. member I32 rigidly-s secured to the trip: bar 83;. is: disposed. to; be engaged by the armature I21 upomoperation thereof to actuate the;trip bar.

The circuitbreaker is preferablyprovided with: a. switch arm and; contact. means to open: the: ground circuit. upon; opening of the; breaker. in. order to. protect two pieces. of: ungrounded; electrical equipment; the framesof which may come into contact with each. other, However,- the. switch arm may be omitted f-romsthe; ground circult and. the ground currenttrip device; may be. connected directly to the-upper. terminal H5 by a solid conductor. q

The electromagnet. I09. is? designed to'trip the. breaker in response to. a groundzfaultt current. of predeterminedmagnitude of,. for instance, 10. amperes. Upon the occurrence oiaground fault, the electromagnet I09. (-Fig. 3). is energizedthere! by. and attracts the-armature I21 to.-actuatethetrip bar 83 and efiect instantaneous tripping of; the breaker.

While, the circuit. breaken'inay beusedto. pro,- tect" any ungrounded electrical equipment, "has The;

6'? been shown schematicallyiii FigiA as: applied to an ungrounded mobile piece'of equipment which utilizes. a trailing. cable tosupply power thereto: from a supply line; Referring: to Fig. 4, a dis tribution breaker A is: connected to' a supply line I33. The distribution breaker is connected by means of a cable indicated schematically at I35 to load breaker B'which in turn, is connected to the electrical equipment indicated atM; The main power supply line-eXtends-through the mainc'ont'acts I8'-2fl and theovrciir rentti-ip device I 3 or each of. the: two 'polesaof the: distribution break-- er A, wires I31 in the cable i351 andthrough the" main contacts 18-20 and overcurrent trip de' vices I3of each. ofthetwo poles of theloadbreak ertothe equipment The: undervol'tage trip device-lei for the; distribution breaker- A is cons nected across the main power lines and through the cable I35 by wires I39; the circuit being: com;- pleted by a conductor MI across the connecting.- terminals on the load breaker B. The ground'i circuit is connected from the frame of the equip ment- II serially through the ground fault trip device I 5 of load breaker B; wi-re- I43 in cable: I35,

' the ground fault trip device I5 oi distribution scribed. The ground fault'current will, however,

be interrupted by openingiol the main contacts I32li. Should the breaker be closed before the cause of the ground fault current has been eliminated, current will again flow through the ground circuit. This can result in a. dangerous condi tion since the frame of the equipment becomes charged to a dangerous potential above ground potential. It has been found that when a piece of portable equipment becomes disabled due: to a ground fault, workmen. attempt to inch the disabled equipment to an ou't-of-the-wa-yposition by repeatedly closing the circuit breaker while the ground fault condition exists; Such repeated. closing of the breaker under this condition. may. cause the ground fault trip coil III- to become excessively heated and burn. out.

It is the function of the: bimetal' element H9 (Figs. 3 and 4) to prevent repeated. reclosures of: the circuit breaker against a persistent ground fault current. The bimetal element I I9 does not: operate in response to ordinary ground fault currents. since the coil Ill effectstripping of the breaker before the bimetal element. 15 heated suificiently to trip the breaker. However, alter the breaker is closed afew times against: a ground fault current, the bimetal. element H9 becomes heatedby the excessive current flowing. there.- through and by the heatfrom the; coil. When. heated, a predetermined. amount, the bimetal element IE9 deiiectsdownwardly (Fig. 3). and

engages an adiusting screw. Mri carried: by a pro.- jecting member lei; secured to the. trip bar 83 and aotuates the tripbar totheunlatcnmgposition. The bimetal' element H9 willhold the trip bar inunlatching position untilxthebimetal cools Having described the invention in accordance with the patent statutes, it is to be understood that various changes and modifications may be made in the structural details without departing from some of the essential features of the invention.

I claim as my invention:

1. A ground current limiting circuit breaker for controlling an electrically operated device having an ungrounded frame comprising a plurality of sets of relatively movable main contacts, operating means therefor including means for manually opening and closing said sets of main contacts, overcurrent trip means responsive to overload currents traversing said sets of main contacts to effect automatic opening of said sets of main contacts, terminals on said breaker for connecting said breaker in a circuit connecting the frame of said electrically operated device to ground, one of said sets of said main contacts being connected in a circuit between said terminals, an electromagnetic trip device responsive to abnormal current flowing through said one set of contacts to effect opening of said sets of main contacts and opening of said circuit between said terminals, and thermally responsive means heated in response to said abnormal current flowing through said one set of contacts upon repeated closing of said sets of main contacts and operable when heated a predetermined amount to prevent further closing of said sets of main contacts and said circuit through said one set of contacts until said thermally responsive means has cooled.

2. A circuit breaker for controlling an electrically operated device having an ungrounded frame comprising a plurality of sets of relatively movable contacts, operating means for said sets of contacts including an operating handle for manually opening and closing said sets of contacts, a trip member operable to cause an auto matic opening operation of said operating means, trip means operable in response to predetermined abnormal current conditions in the circuit controlled by said breaker to actuate said trip member, terminals on said breaker for connecting said brakear in a circuit connecting the frame of said electrically operated device to ground, one of said sets of contacts being connected in a circuit between said terminals, electromagnetic trip means comprising an energizing winding energized in response to excessive current flowing through said one set of contacts and an armature operable upon energization of said winding in response to excessive current of predetermined magnitude to instantaneously actuate said trip member, and a thermally responsive element connected to be heated in response to excessive current flowing through said one set of contacts upon repeated closing of said sets of contacts with excessive current in said circuit and. operable when heated a predetermined amount to engage and actuate said trip member to thereby limit the number of closing operations.

3. A circuit breaker for controlling an electrical translating device having an ungrounded frame comprising a plurality of sets of relatively movable contacts, operating means releasable to effect automatic opening of said sets of contacts, said operating means including an operating handlemovable to an on position and to an oif position for manually opening and closing said sets of contacts, a trip bar operable to release said operating means, a trip device responsive to abnormal conditions in the circuit controlled by the breaker to actuate said trip bar. terminals on said contacts being connected in a circuit in said breaker between said terminals, electromagnetic trip means comprising an energizing coil energized in response to predetermined currents occurring in said circuit between said terminals, an armature operable upon energization of said coil to actuate said trip bar, and a bimetal element disposed to be heated in response to said currents in the circuit between said terminals upon repeated closure of said contacts and operable when heated a predetermined amount to engage and actuate said trip bar and hold said trip bar in actuated position for a predetermined time.

4. A circuit breaker for controlling an electrical translating device having an ungrounded frame comprising a plurality of sets of separable contacts, operating means releasable to effect automatic opening of said sets of separable contacts, said operating means including an operating handle movable to an on position and to an ofi position for manually opening and closing said sets of separable contacts, a trip bar normally restraining said operating means and operable to release said operating means, a trip device responsive to abnormal conditions in the circuit controlled by said breaker to actuate said trip bar, terminals on the breaker for connecting said breaker in a circuit connecting the frame of said electrical translating device to ground, one set of said separable contacts being connected in a circuit in said breaker between said terminals, electromagnetic trip means comprising a coil energized in response to currents of predetermined value flowing through said one set of contacts, an armature operable upon energization of said coil to actuate said trip bar and cause automatic opening of said sets of separable contacts, and a current traversed bimetal element heated in response to excessive currents flowing through said one set of separable contacts and disposed adjacent to said coil to be heated in part thereby, and said bimetal element when heated a prede termined amount upon repeated closing of said contacts bending in a direction to engage and actuate said trip bar and hold said trip bar in actuated position until said bimetal element cools.

5. A circuit breaker for controling an electrically operated device having an ungrounded frame comprising separable contact means, operating means including an operating handle for manually opening and closing said separable contact means, said operating means being releasable to effect automatic opening of said separable contact means, a trip member normally restraining said operating means in operative position and movable to a position to release said operating means, trip means responsive to overload currents in the circuit controlled by said breaker for moving said trip member to releasing position, terminals on said breaker for a circuit connecting the frame of said electrically operated device to ground, a circuit in said breaker between said terminals controlled by said separable contact means, a trip device responsive to excessive currents in said circuit between said terminals to move said trip member to releasing position, and a current traversed bimetal element heated by excessive currents in said circuit between said terminals only upon repeated closure of said contacts following operation of said trip device in response to excessive currents flowing in said circuit between said terminals,

saidbiifietal trespassin Nheated aipreaeteir;

minedlamcunfi bending inifa direction tol'engage I,

and {movesa'idltripi inembergto releasing? position and holding said trip lrnenilclixin, re1easingllposia tion for e; predetermined tiuie;

6.1111124 circuit br'eakelrl having a plurality .of

current paths therethrou'gh, a trip "unit compris ing. ,a singlertriu. barsoperable to. eitect automatic opening -of said br'eaker -la first trip-device 1 calie brated t'obe responsiveto overloadcurrentsrabove normal ratedcurrent :of thevunit in one of said currentpaths for actuating said trip bar, a second: trip .idevice comprisingsand electromagnet calibrated to actuate said triplbar in resronse-to excessive currents =of ;predetermined-value in an otherof said current paths" and a therma device i heated by eXcessive-currents-insaidother current pathmpon closely successive repeated. o erations of said second trip/ device and operable when heated --a predetermined amount tmengaqe' and actuatesaid trip bar to trirped position and hold said trip bar intripped positionunril said thermal device has cooled. r

7, In a circuit breaker having =a" plurality of current paths therethrough; a trip: unit coinoris-i:

inst-a single trip. bar operable-to efiect automatic-- opening of i said" breaker -a first trip device ca1i.--

currents above normal. i in-one :of' said; current pathsforactuatingr-saidgwtrip bar-,- :a second trip brated to: be responsive -to. rated [current bi the u device comprising an. e ectromagnetv calibrated to .actuatesaid trio bariniresnonseto' currents of 1 predetermined value in another of said currents trip bar" in tripping positionuntil said bimetalif element has cooled;-

BC In a circuit breaker-having a'" pluralityi of '3 current paths therethroughza tripunit comprrs-"i ing' two trip 'devices foractu'ating a single? trip bar-to effect automatic op'ening'of "said breaker;

one of said trip devices being' calibrated to be responsive to" currents above the normal rated cur-- rent for saidunit in at leastl'onerofi-said current paths, the other of'saiu trip devices comprising an electromagnet calibrated to be responsive to pre. determined currents below the normal rated current for said unit in another of said current paths, and a thermal device heated by excessive currents in said other current path in response to closely successive repeated operations of said other trip device to engage and actuate said trip bar and hold said trip bar in actuated position until said thermal device has cooled.

9. In a circuit breaker having a p urality of current paths therethrough, a trip unit comprising two trip devices for actuating a single trip bar to effect automatic opening or said breaker, one of said trip devices being calibrated to be responsive to currents above the normal rated current for said unit in one of said current paths the other of said trip devices comprising an electromagnet calibrated to be responsive to predetermined currents below the normal rated current for said unit in another of said current paths, and a bimetal element connected to be traversed by currents in said other current path, said bimetal element being heated by excessive currents in said other current path in response to closely successive repeated operations of said other trio device and operable when heated a predetermined amount to engage and move said trip bar to tripped posi- 1o nos-anorenemesis-nip bar in tripii' idi'pqsititih I". untilts'aidbimetal'ieleinenthastcooled l g 10i A multi-pol'et circuit breaker havln'gyja movable switch" arm in one 'orfim'oreof each of'f'f two DQI'BS' and operating means therefor, a trip 11;

barf-movable toxa trippingpositionto effect openi-- mg; 01""said': "brealre'rf'an:overload'" trip (device in one or more? of the circuits throughsaid vone'or 11 moreiswitch arm's calibrated to be resp'on'sivato overload; currentsoi'" relativelyx'high" value for? movingsaid )trip bar"to"tripping' po'sition, an "adf. dit'i'onal circuit in" 'saidcircuit" breaker f having a magnetic. overcurrentitrip device .connected in; said'i'additio'nai "circuit iand traversed b1" the'en "'tire"'currcntl flow inf sai'di additional circuit at all? times and calibrated to be responsive"toicurrents .t of'irelatii' ely"lo'\v value in'saidadditional circuit;

form'ovingsaid trip bar totrip'pin'gpositibngand"'i a thermal device'heated in response to currents" 'in 'said additional'circuit and operative onlyifol-ef lowing an operation of'the magnetic overcur-i" rent'trip device in said additional circuit to? em gageand move said trip bar to tripping position.

11. A multi -pole" circuit breaker-having a movable switch armj inlione or} more 'of' ea'ch' of 1' ticintojeffect opening of said breaker; an over? less current'fresp'onsivel trip fdevice." in one or. morefof reach of s'aidt'w'o' poles operative tomo've "saidtripibar to tripping position, anadditi'onal circuit in said breake'r'fha'vingIan mammal- 1 movablesw'itch arm therein, a common operate?- ing mechanism -forfisaid"switch""arms, a current responsivejtrip; device in said I add tional icircu'iti comprising an "electromagnet 5 connected in said' additional, circuitand' traversed bygthe entire current" how: inv said. ,"addit'ional Icircuit at fall times, said electromagnetbeing' cperative intre -"f spouse to currents'oiipred'etermined value insai'd 1 additional circuit .tdmovesaidtriri ibar' to 'tr'ip-r 7 pinigliposi'tion, 'andia 'bir'n'etal' element connected to be'ftraversedibyicurrent in said'fadditional c'ir' cuitf'said bimetal'ibe ingdis'posed" toibe heated-p9 thcu'rrent in said:additionalcircuit and op'era erations"-'ofsaid *eIettrbmag'net "to engage an'd movesaid jtrip barrows spins positions p 122 A "tw'o pole circuit breaker ccrmpri'si'rig"air enclosing casing having therein three compartments positioned side by side, a trip bar mova-t ble to a tripping position to cause automatic opening of said breaker, a movable switch arm in one or more of each of two of said compartments, operating means for said switch arms, an overload trip device in one or more or said two of said compartments calibrated to be responsive to currents of predetermined value and operative to move said trip bar to tripping position, an additional circuit in the third of said compartments, a trip device in said additional circuit comprising an electromagnet connected in said additional circuit and traversed at all times by the entire current flowing in said addi-- tional circuit, said electromagnet being calibraterl to be res onsive to currents below said predetermined value and operative to mo e said trip bar to tripping position and a bimetal element heated by current in said addit onal circuit upon closely successive repeated operations of said clectromagnet and operative when heated a predetermined amount to engage and move said trip bar to tripping position and to hold said trip bar in tripping position until said bimetal has cooled.

13. A two-pole circuit breaker comprising an enclosing housing having therein three compart--- trip device in one or more of the circuits through said switch arms for moving said trip bar to tripping position, an additional switch arm in the third of said compartments, operating means for said switch arms, an electromagnetic trip device connected in the circuit through the additional switch arm and traversed at all times by the entire current flowing in the circuit through said additional switch arm in said third compartment, said electromagnetic trip device being responsive to current in the circuit through said additional switch arm for moving said trip bar to tripping position, and a bimetal element in said third compartment connected to be traversed by the current in the circuit through said additional switch arm, said bimetal element being heated only upon closely successive repeated operations of said electromagnetic trip device to an amount suificient to engage and move said trip bar to tripping position, and said bimetal element then holding said trip bar in tripping position until said bimetal element has cooled.

14. A two-pole circuit breaker comprising an enclosing casing having therein three compartments, a single trip bar movable to a tripping position to effect automatic opening of said breaker, a movable switch arm in each of said three compartments, operating means for said switch arms, two overload trip devices in the circuits through two of said switch arms calibrated to move said trip bar to tripping position in response to overload currents above a predetermined value in the circuits through said two movable switch arms, an electromagnetic trip device connected in series in the circuit through the switch arm in the third of said compartments and traversed at all times by the entire current flow in the circuit through the switch arm in said third compartment, said electromagnetic trip device being calibrated to move said trip bar to tripping position in response to currents below said predetermined value, and a bimetal element heated in part by excessive our- 12 rents flowing in the circuit through the switch arm in said third compartment and disposed to be heated in part by the heat of said electromagnet, said eleotromagnet being operative only when heated during a plurality of closely successive repeated operations of said electromagnet to engage and move said trip bar to tripping position.

15. A two-pole circuit breaker comprising an enclosing casing having therein three compartments, a single trip bar movable to a tripping position to effect automatic opening of said breaker, a movable switch arm in each of said three compartments, operating means for said switch arms, two overload trip devices in the circuits through two of said switch arms calibrated to move said trip bar to tripping position in response to overload currents above a predetermined value in thecircuits through said two movable switch arms, an electromagnetic trip device connected in series in the circuit through the switch arm in the third 01' said compartments and traversed at all times by the entire current flow in'the circuit through the switch arm in said third compartment, said electromagnetic trip device being calibrated to move said trip bar to tripping position in response to currents below said predetermined value, and a thermal device in the circuit through the said switch arm in the third compartment calibrated to cause movement of said trip bar to tripping position in response to two or more closely successive operations of saidelectromagnetic trip device.

HILIER D. DORFMAN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,652,999 Benson Dec. 20, 1927 2,154,703 Sandin Apr. 18, 1939 2,349,632 May May 23, 1944 2,435,305 Grissinger et al.' Feb. 3, 1948 2,561,985 Jones et al. July24, 1951 FOREIGN PATENTS Number Country Date 110,707 Australia May 27, 1940