US3517355A

US3517355A - Blow-open circuit breaker

Info

Publication number: US3517355A
Application number: US712041A
Authority: US
Inventors: Thomas M Cole
Original assignee: Federal Pacific Electric Co
Current assignee: CHALLENGER ACQUISITION Corp; CHALLENGER DPT Corp; CHALLENGER FUSE Corp; CHALLENGER LIC Corp; PROVIDENT INDUSTRIES Inc
Priority date: 1968-03-11
Filing date: 1968-03-11
Publication date: 1970-06-23
Anticipated expiration: 1987-06-23

Description

June 23, 1970 T. M. COLE 3,517,355

BLOW-OPEN CIRCUIT BREAKER Filed March 11, 1968 2 Sheets-Sheet 1 INVENTOR Thomas M. Cole ATTORNEY June 23, 1970 T, COL 3,517,355 7 I BLOW-OPEN CIRCUIT BREAKER Filed March 11, 1968 2 Sheets-Sheet 2 y 42d 42% Q i 1 1111/.- 62 I 1 J 1 52 4Zd a4 Fig-ill INVENTOR Thomas M. Cole BY f ATTORNEY 3,517,355 BLOW-OPEN CIRCUIT BREAKER Thomas M. Cole, Harrison, N.Y., assignor to Federal Pacific Electric Company, a corporation of Delaware Filed Mar. 11, 1968, Ser. No. 712,041 Int. Cl. H01h 77/10 U.S. Cl. 335--16 15 Claims ABSTRACT OF THE DISCLOSURE A circuit breaker is made electrodynamically responsive for high-speed opening to interrupt sudden high currents. The circuit breaker has a pivoted contact arm arranged as part of a blow-open current loop. The pivot of the contact arm has a stable normal position in which the contact arm is operable by a manual mechanism for opening and closing the circuit breaker. The pivot is shiftable to another position in which the contact arm is in its fully open current-interrupting position. The shift of the pivot is initiated electrodynamically, by the force in the blow-open current loop. Electrodynamic opening is independent of and unimpeded by the operating mechanism remaining in its closed configuration. The foregoing is part of a circuit breaker incorporating the usual trip-free operating mechanism including an overload release provision made for reset both in case of overload release and electrodynamic opening.

The present invention relates to circuit interrupters. The invention is described below in its application to molded-case circuit breakers, but in its broader aspects it applies to a variety of switching apparatus for clearing short-circuits in a bus having high available short-circuit capacity.

Circuit breakers commonly provide both overload protection and short-circuit protection. The usual overload release of a circuit breaker has a first nominal-rating level having an inverse time-current characteristic and an instantaneous release responsive to higher levels of overload. Usual circuit breakers inherently require some minimum time for responding to short circuits, first for the overcurrent release to function and then for the contactoperatiing mechanism to open the contacts. That type of action is too slow where the bus has a very high available short-circuit capacity. An object of the present invention resides in adapting circuit interrupters, especially circuit breakers, to nearly instantaneous response to shortcircuits, utilizing a novel electrodynamic arrangement of parts for driving the contacts open suddenly. A commercially important type of circuit breaker to which the present invention is especially applicable has a movable contact arm that carries a current-responsive latch. A manually operable toggle operates the contact arm about a pivot for closing and opening the breaker manually, and the latch releases the breaker automatically in response to an overcurrent. Circuit breakers of this type are shown for example in U.S. Pat. No. 2,681,396 issued June 15, 1954, to Cole et a1. Millions of circuit breakers are sold each year in the form shown in FIGS. 7 to 11 of that patent. Those circuit breakers are unusually rapid in their response to short circuits, being readily capable of releasing the overload responsive latch and opening the contacts in case of a short circuit of the 5000 A. level in only little more than one-quarter of a cycle in a 60 Hz. power circuit. However, this fast performance has been found inadequate where the short circuit level is much greater.

An object of the present invention resides in providing an improvement in circuit breakers of that type for opening the contacts electrodynamically and without depend- Unitcd States Patent "ice ing on release of the overcurrent latch and without allowing time for the overcurrent latch to be released.

A further object resides in modifying a circuit breaker of the type having a moving contact arm that carries an overcurrent latch and is operable about a pivot for opening the contacts, so that in the modified circuit breaker the contact arm is operable electrodynamically to an open position independent of the release of the overcurrent latch. A further object of the invention resides in modifying such a circuit breaker for enabling it to re spond electrodynamically to high level short circuits by providing a laterally shiftable pivot for the contact arm. More generally it is an object of the invention to provide a novel current interrupter operable electrodynamically in response to short circuits of high level with a pivot about which a contact arm normally operates for opening and closing the circuit where such pivot is shiftable for high speed electrodynamic opening operation of the contact arm.

The nature of the invention and its further objects and advantages will become more fully apparent from the detailed description below of an illustrative embodiment which is shown in the accompanying drawings. Briefly, this illustrative embodiment of the invention includes a contact arm having a movable contact at one end that cooperates with a stationary contact, a pivot near the center of the contact arm and a pivoted actuator at the opposite end of the contact arm. A current responsive latch for the actuator is also carried by the contact arm. An operating toggle including a pivoted handle and a connecting toggle link is operable from a collapsed condition to an erect condition for driving the contacts from their open position to their closed position. The contact arm operates about the pivot when the circuit breaker is manually opened, as well as when the current responsive latch is released in case of an overcurrent. The current path through the circuit breaker includes a blow-off current loop in the region of the contacts. The pivot is laterally movable from a normal, stable operating location to another stable location when the contact arm is driven open electrodynamically. The electrodynamic opening operation occurs with high speed in response to high level short circuit without awaiting release of the overcurrent latch and without dependence on whether the overcurrent latch is or is not released. The shiftable pivot is biased so as to remain in what may be called its normal position, wherein it pivotally supports the contact arm for manual opening of the circuit breaker and for automatic opening in response to release of the overcurrent latch. After the pivot has been driven to its second stable position in case of electrodynamic opening of the contacts, the pivot can be reset to its normal position by manipulating the operating toggle. This illustrative embodiment of the invention is more fully described below and is shown in the accompanying drawings.

In the drawings:

FIG. 1 is a lateral elevation of a circuit breaker embodying features of the present invention, a side cover being removed to show the internal mechanism, and the contacts being closed;

FIG. 2 is another view of the circuit breaker in FIG. 1 in the condition assumed when the contacts are blown open electrodynamically and with the operating handle held in its on position;

FIG. 3 is another view of the circuit breaker of FIG. 1 with the parts in their normal position with the contacts open and in condition for a closing operation;

FIGS. 4, 5 and 6 are enlarged fragmentary cross sectional views at the section lines 44, 5-5 and 66 in FIGS. 1, 2 and 3, respectively;

FIGS. 7, 8 and 9 are force diagrams representing the action of spring 58 in FIGS. 5, 6 and 7, respectively;

FIG. is an enlarged fragmentary cross-sectional view of the circuit breaker shown in FIGS. 3 and 6 at the plane 1010 of FIG. 6, a portion thereof being broken away for clarity; and

FIG. 11 is the top plan view of one of component 42 of the circuit breaker of FIGS. 1 through 6'.

Referring now to the drawings and in particular to FIG. 1 there is shown one part of a molded case or enclosure 10 formed of molded insulation. A screw terminal 12 of the circuit breaker is fixed between the two halves of the circuit breaker case. Copper strip 14 extends integrally from terminal 12, and carries contact 16 at its end remote from terminal 12. Movable contact 18 is carried by copper strip 20 for cooperation with contact 16. A portion 20a of strip 20 extends along and close to strip 14, these conductors forming a reverse current loop through the contacts. A member 22 of sheet iron has an integral rivet 22c extending through copper strip 20, the fixed end of bimetal 24 and soft iron pole piece 26. Rivet 22c rigidly unites

parts

20, 22, 24 and 26 and provides a good electrical connection between bimetal 24 and copper strip 20, a connection that can be further improved by brazing. Strip 20 and member 22 as a unit are called the contact arm. Flexible conductive braid 28 as of copper is welded to the movable end of bimetal 24 remote from rivet 220. The opposite end of braid 28 is welded to plug-in terminal 30 of the circuit breaker. When the circuit breaker is closed (as shown in FIG. 1) a circuit may be traced from terminal 12, and along

parts

14, 16, 1-8, 20, 24 and 28 to plug-in terminal 30. Metal member 32, also called an actuator or bell crank, is mounted on an insulated pivot 34 at the end of member 22 remote from copper strip 20. An ambient temperature compensating bimetal 32a forms part of actuator 32. One end of bimetal 32a is secured about an upper pivot 36 of the actuator and at its lower end, bimetal 32a is latched by current-responsive bimetal 24. A U-shaped link 38, formed of stiff wire, has its respective legs extending into and forming pivots in member 32 and arm a of an operating handle 40. Arm 40a and link 38 constitute two links of an operating toggle. Handle 40 is of molded insulation and has integral pivots 4012 that operate in companion recesses (not shown) in the confronting parts of the molded case 10. When the circuit breaker is closed, as shown in FIG. 1, knee 41 of

toggle

38, 40a is slightly above an imaginary line between the centers of

pivots

36 and 40b. In this condition the toggle is said to be overset. The knee cannot rise beyond the slightly overset condition shown because handle 40 is arrested against further counterclockwise movement by engagement with casing 10.

A lever 42 of flexible leaf-spring stock has aligned hook portions 42a at opposite sides of a slot 42b. Member 22 is received in slot 42b, so that the two legs of lever 42 straddle member 22. Hook portions 42a lock with pin 44 that extends through member 22. A dimple 42c at the end of lever 42 remote from hooks 42a locates one end of a compression coil spring 46. The opposite end of the coil spring bears against a small projection 40c of the handle. In FIG. 1 compression spring 46 acts along a line slightly above the axis of pivot 40]), but in the condition of the parts shown,

toggle

38, 40a prevents clockwise movement of the handle.

Lever 42 has a curved mid-portion 42d that bears against

bosses

48 and 50 projecting inward from the inside surfaces of the case.

Bosses

48 and 50 act as a fulcrum for lever 42 which converts downward pressure of compression coil spring 46 to upward pressure against pin 44.

In the closed condition of the circuit breaker illustrated in FIG. 1,

members

22, 24 and 32 are locked together as a triangular unit. Upward spring force applied at pin 44 biases the contact arm 20, 22'clockwise about pivot 36 (FIG. 1) and thus provides resilient Contact pressure.

4 It is understood that

parts

22, 24 and 32, when latched as a triangular unit, are elfectively pivoted at 36.

As seen in FIG. 10 member 22 has a portion 22a that is off-set relative to the rest of member 22. Off-set portion 22a is laterally guided by the end face of boss 48, and the portions of member 22 adjoining offset 22a are guided by the end face of boss 50', there being a measure of looseness between member 22 and the guide surfaces of

bosses

48 and 50. As seen in FIGS. 4, 5, 6, and 10, a metal cup 52 is slidably received in a hole in portion 22a of member 22. In the condition of FIGS. 1 and 4, a flange 53 of the cup is spaced away from offset 22a, and the externally flat closed end of the cup presses against a bearing surface 54 in a recess 56 formed within boss 48. This recess or slot confines cup 52 to sliding parallel to the plane of the view in FIG. 4, slanting down and to the right, approximately perpendicular to a radius from pivot 36 when located as in FIG. 1. A cavity 57 is formed in the opposite boss 50 of the casing. A compression spring 58 acts against cup 52 to press the bearing end of the cup against the bottom of recess 56. Spring 58 advantageously has bearing

buttons

60 and 62 at its ends. Button 62 is notched so as to receive a rib or fulcrum 64 on the inside of the cup. In the closed condition of the circuit breaker in FIGS. 1 and 4, spring 58 acts along such a prominent slant angle that it applies a substantial component of upward force via cup 52 to the contact arm. This upward force is represented by vector A in FIG. 7. The total force of compression of the spring is represented by vector B. Vector C represents the pressure applied by cup 52 against bearing surface 54 of the molded case. Accordingly, spring 58 and cup 52 apply a substantial amount of bias to contact

arm

20, 22 in the contact-closing direction.

The bias of spring 46 applied to pin 44 by lever 42 biases the contact arm upward. This is opposite in one sense to the arrangement in the above-mentioned Pat. 2,681,396, wherein the reset compression spring applies downward bias to the contact arm. The particular mechanism involving spring 46 and lever 42 is shown and claimed in a companion patent application filed herewith, Mar. 11, 1968, Ser No.712,042, by J. I. Oravec, entitled Automatic Circuit Breakers. Other similar circuit breakers in which upward bias is provided on the contact arm are shown in Reissue Pat. 24,388 and Pat. 2,810,048, both issued to P. M. Christensen. The upward bias of spring 46 complements the upward bias of spring 58.

FIG. 3 shows the parts of the circuit breaker in their open condition, in readiness for the circuit breaker to be closed. As seen there, lever 42 transmits the force of compression spring 46 to pin 44, the lever operating about the fulcrum represented by bosses 4 8, 50. Handle 40 is in its off position, remote from the on position in FIG. 1. There is a slight clearance between the end of bimetal 24 and the latch end of actuator 32. The

toggle comprising ling

38 and 40a of the handle is buckled, the knee being well below an imaginary line between the axes of pivot 40b and pivot 36. A portion 20b of conductive strip 20 bears against a fixed stop 66 integral with the molded case.

When handle 40 is initially moved away from the closed extreme position in FIG. 1 toward the position in FIG. 3, the toggle starts to collapse. Spring 58 has an initial upward component of force A (FIG. 7) that acts to displace cup 52 and member 22 upward, until the cup reaches the upward limit of cavity 56. Thereafter portion 20b of the contact arm is biased by compression spring 46 to move toward the open condition in FIG. 3. Spring 46 thus acts as a push-off spring to open the contacts, driving member 22 counterclockwise about cup 52 as a pivot. At the same time, the line of action of spring 46 is shifted further away from the axis of pivot 40b, so that spring 46 strongly biases the handle in the off direction.

For closing the circuit breaker, handle 40 is moved away from the position in FIG. 3 toward that in FIG. 1

and

erectstoggle

38, 40a, driving the latched

triangular unit

22, 24,.32 clockwise about cup 52 as a pivot until the contacts engage. The tOggle is not fully erect at the time of contact engagement and therefore, during the further erecting travel of the toggle links, pivot 36 is driven downward while contact 18 acts as a fulcrum of the contact arm. This motion drives cup 52 downward so as once again to assume the position of FIG. 4. I

The circuit breaker shown actually does not close gradually but closes with an abrupt snapping motion due to the cooperation of a hooked portion 42e of lever 42 with a shoulder portion 70in the molded case. Closing motion of the contact arm pushes a portion 22b of member 22 against lever 42 which then pushes hook portion 42e against shoulder 70. This occurs before the toggle links are erect, and before the contacts touch. Further erecting motion of the toggle shifts cup 52 downward, thereby applying bias of spring 58 to arm 22. This further erecting motion of the toggle also draws pin 44 downward and to the right, pulling hook portion 42e to the right and, ultimately, free of shoulder 70'. Thereafter the contact-biasing effects of

springs

46 and 58 close the contacts with a snap. This snap-closing mechanism involving shoulder 70, lever 42 and spring 46 is claimed in the above-mentioned patent application filed concurrently herewith by J. .T. Oravec.

The breaker operates automatically from the closed condition of FIG. 1 to that of FIG. 3 in a manner similar to the manual opening operation described above. The automatic opening is initiated by downward deflection of bimetal 24, to release actuator 32. The bimetal deflects downward in response to the current flowing through it. A moderate persistent overload will cause enough thermal deflection to release actuator 32. A sudden severe overload will produce in core 26 a suflieient flux to attract bimetal 24 and deflect the bimetal magnetically. Such deflection occurs in response to currents of at least times the thermal tripping rating.

Magnetic tripping can result in full contact opening in about A cycle in small commercial circuit breakers of the type in patent 2,681,396, but this is too slow to clear extremely high levels of short-circuit current. If such a circuit breaker were operated to close against a short circuit in a circuit having an available current capacity of the order of 5000 amperes, it is readily capable of opening and interrupting the current. Through refinements, higher interrupting ratings can be realized. By modifying circuit breaker to effect electrodynamic opening of the contacts,

a considerable increase in short-circuit interruption capacity can be achieved.

The reverse current loop in conductors 14 and a of the present circuit breaker produces an instantaneous electrodynamic force that drives

contact arm

20, 22 apart at enormous speed, to the position represented in FIG. 2. The handle may be free when the short-circuit occurs or the short-circuit may exist while the breaker is being operated to close the contacts. Here the handle is assumed to be hand-held in the on position at the time of the short-circuit. FIG. 2 represents the condition of the parts after occurrence of a short-circuit but before the bimetal 24 has time to deflect downward, and for that reason actuator 32 is shown as being latched. These conditions, of the handle being held on and the operating linkage being still latched at the time of the electrodynamic impulse are the most severe set of conditions for the circuit breaker. Handle 40, link 38, and the triangular unit con sisting of member 22 and actuator 32 latched by bimetal 24 are all virtually rigid parts and yet they do not interfere with the electrodynamic opening operation of the contact arm. Opening of the circuit breaker electrodynamically does not depend on release of the overcurrent release means. This is because the pivot about which the contact arm swings in a normal contact-opening operation, namely cup 52, is capable of being driven downward against the bias of spring 58. This pivot when shifted, as-

sumes a stable lower position with contact 18 in its extreme open position. Cup 52 shifts downward from bearing surface 54 to a more recessed bearing surface 72, as shown in FIG. 5. At this point there is only a limited upward component of force A" acting on member 22 (FIG. 8) and this force is prevented from shifting cup 52 upward because of a slant step 73 between the lower bearing surface 72 and the other bearing surface 54 in recess 56. Consequently, where the circuit breaker opens in response to conditions producing the requisite electrodynamic force, the contact arm remains in its open condition without any tendency to reclose after the current has been interrupted.

The present circuit breaker has prominent currentlimiting characteristics. This may be attributed in large measure to the high-speed response of the contact arm in opening during the rise of current to levels suflicient to cause electrodynamic separation of the contacts. The achievement of current limitation is important in that the arcing energy that develops during fault-clearing is limited far below the arcing energy that would develop otherwise. By this means, a relatively small circuit breaker is given the capacity of safely interrupting potentially severe short-circuit current surges.

Any suitable configuration of the arc-extinguishing chamber may be used to interrupt the are between

contacts

16 and 18. Two are vents 74 are illustrated in this embodiment for venting the arcing space or arc chute 76. For minimizing the strain on the case, it is desirable to line the arc chute with a non-gas-evolving material, mica for example.

Following a blow-open operation of contact arm 22, pivot cup 52 is in the position of FIG. 5, and the operat ing handle 40 has shifted only a little way from the on position of FIGS. 1 and 2. The handle does not move appreciably during the sudden opening motion of the contact arm, and once the contact arm has reached the position of FIGS. 2 and 5 and pivot cup 52 has been shifted, the linkage between the contact arm and the handle prevents spring 46 from resetting the handle.

Before the circuit breaker is to be closed once again, pivot 52 has to be reset. This is done by moving handle 40 forcibly to the off position of FIG. 3. During this motion, the handle and the connecting linkage act to swing contact arm 22 counterclockwise about portion 20b bearing on abutment 66, acting as a pivot in this operation. At one point in the clockwise movement of handle 40 from FIG. 2 to FIG. 3, the force applied to the handle pulls on bell crank 32 via link 38. Counterclockwise rotation of member 32 about its pivot 34 is limited by a guide surface 68 in the two-part casing. As a result. clockwise operation of handle 40 pulls upward on pivot 34 so as to swing member 22 upward. This action results: in forcible lifting of cup 52 from the position in FIG. 5 to that in FIG. 6. The shift from the configuration of FIG. 5 to that of FIG. 6 may be accompanied by an elongation of spring 58. The relative compressive forces of that spring in its two conditions of FIG. 5 and FIG. 6 are represented by vector B in FIG. 8 and vector B in FIG. 9. Incidentally, the shift from the configuration of FIG. 5 to FIG. 6 involves a lifting of off-set portion 22a of the contact arm toward the spring lever 42. During this motion, cup 52 is guided laterally by the guide surfaces at the sides of recess 56, FIG. 10, and cup 52 is forced to climb up and across the slant step 73.

The circuit breaker shown in the drawings and described in detail above involves a number of novel features that have both broad and specific advantages. In a broad

sense contact arm

20, 22 is operated by a more or less positive acting linkage to drive the contacts closed, the contact arm moving about a pivot in that operation; and because the pivot is shiftable the contact arm can respond to electrodynamic contact opening forces irrespective of the condition of the contact-closing mechanism. Reverse operation of the linkage from the blownopen condition to the normal open circuit condition is effective to reset the pivot to its normal condition. In this aspect of the invention, no mention has been made of the overload release portion of the circuit breaker. However, the laterally shiftable pivot represents a unique arrangement for adapting circuit breakers to electrodynamic operation in response to high-level faults. In particular the laterally shiftable pivot makes possible the electrodyna-mic opening operation of circuit breakers of the type having a pivoted contact arm that carries an actuator latched by a 'bimetal or the like, where the actuator is operated by a toggle for closing the contacts. This particular type of circuit breaker has achieved very wide commercial acceptance, so that in adding the electrodynamic contact opening feature to such circuit breakers represents a specific distinctive advance in the art.

The foregoing represents a presently preferred embodiment of the invention in its various aspects, and illustrates both broad and detailed features of novelty. However, it will be appreciated that those skilled in the art will readily adapt the novel features to other applications, and will readily introduce modifications in matters of detail. Consequently, the invention should be construed broadly in accordance with its full spirit and scope.

What is claimed is:

1. A circuit interrupter operable mechanically to make and break a circuit and operable automatically to break the circuit under severe short circuit conditions, said circuit interrupter including a first contact, a contact arm carrying a movable contact and having a pivot, means connected to said contact arm for operating said contact arm about said pivot when the pivot is in a first location for opening and closing the contacts, said pivot being movable between said first location and a second location wherein said contact arm is in its open position in which the contacts are parted amply for interrupting short-circuit currents, means forming a current path through the circuit breaker when closed, including said contacts and at least part of said contact arm and further including a circuit part acting with said part of said contact arm to form an electrodynamic blow-open current loop, and means normally supporting said pivot in said first location, said supporting means being yieldable in response to short circuit electrodynamic forces developed in said blowopen loop by current above predetermined level to allow said pivot to shift to said second location and thereby to allow said contact arm to be moved to said open position without dependence on the configuration of said contactarm operating means.

2. A circuit interrupter in accordance with claim 1, wherein said pivot supporting means provides stable support for said pivot in each of said locations.

3. A circuit interrupter in accordance with claim 1, wherein said pivot supporting means includes a spring disposed to bias said contact arm in the contact-closing direction when the pivot is in said first location.

4. A circuit interrupter in accordance with claim '1, wherein said pivot supporting means includes a spring disposed to bias said contact arm in the contact-closing direction when the pivot is in said first location, and wherein shifting of said pivot to said second location shifts the line along which the spring acts for at least reducing the contact-closing bias thereof.

5. A circuit interrupter in accordance with claim 1, wherein said pivot supporting means includes a spring disposed to bias said contact arm in the contact-closing direction when the pivot is in said first location, further including a detent for disabling said biasing means from providing contact closing bias when said pivot has been shifted by electrodynamic force to said second location.

'6. A circuit interrupter in accordance with claim 1, wherein said pivot includes a cup slidable along a bearing surface opposite to said contact arm, and wherein said supporting means includes a compression coil spring having one end disposed in said cup and acting along a slant line for providing a component of resilient force to said contact arm in the contact closing direction.

7. A circuit interrupter in accordance with claim 6, wherein said operating means includes resilient contactopening means and wherein said contact arm carries current-responsive latching means releasable to allow opening of the contacts by said contact-opening means.

8. A circuit interrupter in accordance with claim 6, wherein said cup, when moving from said first location to said second location, traverses a surface having an abutment that obstructs return of the cup from said second location to said first location.

9. A circuit interrupter in accordance with claim 8, wherein said means for operating said contact arm has a driving connection to said contact arm and operable in a resetting motion for driving said cup across said abutment from said second location to said first location.

10. A circuit interrupter in accordance with claim 1, wherein said operating means includes overload-responsive contact opening means for driving said contact arm open about said pivot when in said first location.

11. A circuit interrupter in accordance with claim 1, wherein said operating means includes a toggle that is erect when said contacts are closed.

12. A circuit interrupter in accordance with claim 1, wherein said operating means includes resilient contactopening means and wherein said contact arm carries current-responsive latching means releasable to allow opening of the contacts by said contact-opening means.

13. A circuit interrupter in accordance with claim 12 wherein said operation means includes a toggle operable via said latching means to drive said contacts closed.

14. A circuit interrupter in accordance with claim 1, wherein said means for operating said contact arm about said pivot includes an operating linkage articulated to said contact arm at a point spaced from said pivot by a distance that causes the portion of the contact arm between the pivot and the articulated connection to act as a lever arm.

15. A circuit interrupter in accordance with claim 1, wherein said means for operating said contact arm includes current-responsive latching means carried by said contact arm, an actuator pivoted to said contact arm at a point spaced from said pivot and normally latched by said latching means when the circuit interrupter is closed, and a manually operable toggle connected to said actuator and arranged to become erect when the circuit interrupter is closed, shifting of said pivot to the second location occurring as aforesaid despite the manually operable toggle remaining erect.

References Cited UNITED STATES PATENTS 2,681,396 6/1954 Cole 337-67 3,317,866 5/1967 Hanafusa 33523 OTHER REFERENCES 1,238,994 4/1967 Germany.

BERNARD A. GILHEANY, Primary Exaimner HAROLD BROOME, Assistant Examiner