US2962573A - Electric circuit interrupter - Google Patents

Description

Nov. 29, 1960 T. J. SCULLY ELECTRIC CIRCUIT INTERRUPTER -Filed Oct. l, 1958 2 Sheets-Sheet 1 lli- H P z Inventor: T omas J. Scullg,

Nov. 29, 1950 T. J. scuLLY 2,952,573

ELECTRIC CRCUIT INTERRUPTER Filed oct. 1, 1958 2 sheets-sheet 2 Inventor:

Thomas J. Soul Ig,

bg is A tornei-J.

United States Paten f ELECTRIC CIRCUIT INTERRUPTER Thomas J. Scully, Bridgeport, Pa., assigner to General Electric Company, a corporation of New York Filed Oct. 1, 1958, Ser. No. 764,560

7 Claims. (Cl. 20G-166) This invention relates to electric circuit interrupters or breakers, and more particularly it relates to improvements in the contact structure of a low voltage air circuit breaker.

One object of the invention is the provision of a relatively simple and inexpensive circuit interrupter contact structure having a movable contact member pivotally connected to a stationary electroconductive support in a manner so that direct and positive electric contact is obtained between the movable member and its support without flexible braids or the like and without need for untoward precision in the manufacture and alignment of the various cooperating parts of the contact structure.

A general object of the invention is to provide an improved circuit breaker contact structure of the character described hereinafter.

In carrying out my invention in one form, an electroconductive bracket provided with at least one slide surface is mounted on the base of a circuit breaker in spaced relation to a relatively stationary contact member. A cooperating movable contact arm is pivotally supported by the bracket for rotation about an axis oriented approximately perpendicular to the slide surface. The movable contact arm is provided with a pertaining slide surface disposed in contiguous relationship with the slide surface of the bracket to form a current-conductng joint therebetween. One of the slide surfaces has a raised section relative to the other slide surface thereby to provide a straight-line contact which serves as a fulcrum for rocking movement by the movable contact arm with respect to the axis of rotation. Contact pressure between the contiguous slide surfaces of the current-conducting joint is maintained by resilient clamping means which, in one aspect of the invention, comprises an electroconductive spring member secured to the bracket and disposed in engagement with the movable contact arm to provide a second current-conducting joint therewith.

My invention will be better understood and its various objects and advantages will be more fully appreciated from the following description taken in conjunction with the accompanying drawings in which:

Fig. l is a side elevation of a circuit breaker contact structure embodying a preferred form of my invention, with the movable contact member of the contact structure shown in its closed circuit position;

Fig. 2 is a front elevation of the contact structure illustrated in Fig. 1, with the movable contact member to its open circuit position;

Fig. 3 is an enlarged partial section of the connection between the movable contact member and its supporting bracket in accordance with my invention; and

Fig. 4 is an exploded perspective View of the movable contact member and supporting bracket.

Referring now to Fig. l, l have shown an electric circuit breaker or interrupter comprising a base member 11, a relatively stationary Contact member 12 mounted on the base, an electroconductive bracket 13 mounted on the base in spaced relation to the stationary contact v 2,962,573 PatentedNov.v 29, 1960 member, a movable contact member 14 pivotally supported by bracket 13 and disposed in cooperative relationship with the stationary contact member 12, and actuating means such as a crossbar 15 coupled to the movable contact member 14 for moving this member into and out of circuit-making engagement with the stationary contact member 12. The components 12, 13 and 14 comprise the contact structure of one pole unit of an alternating or direct current circuit breaker or interrupter. It will be understood that other similar pole units (not shown) could be mounted for gang operation on the base member .11 adjacent to the unit that has been illustrated in Figs. l and 2.

The base member 11 supports the current-conducting studs of the breaker and other breaker parts connected directly to the studs. As illustrated in Fig. l, the oase member 11 comprises a sheet 16 of electric insulating material of substantially uniform thickness. The sheet 16 is shaped to form a channel-shaped section or depression at 17, and the bottom of this section is provided with an aperture for snugly admitting and partially supporting an upper breaker stud 18. For the purposes of the present description, the contact structure 12-14 will be considered mounted on the front of the base 11, and the breaker stud 18 is connected to a suitable electric power source or bus (not shown) located behind or to the rear of the base. The contact structure shown in the drawings and described herein to illustrate a preferred embodiment of my invention has been particularly designed for connection to an electric power bus rated 600 volts A.C. and capable of supplying as much as 25,000 amperes short-circuit current.

The stationary contact member 12 is mounted on the upper breaker stud 18. As can be seen in Fig. l, the upper stud 18 is secured to the sheet 16 of base member 11 by suitable support means such as generally Lashaped angles 19 and 20. The angles 19 and 20 are respectively disposed above and below stud 18 and are fastened thereto by three copper rivets or the like. The lower angle 20 is provided with a pair of tapped holes, and a pair of appropriate bolts 21 is used to secure this angle to the base member 11. The supporting angle 19, which extends above the breaker stud 18 as is shown in Fig. 1, serves as an arc runner in cooperation with, the stationary contact member 12. This 'angle is provided with a stud 22 for securing it to the insulating sheet 16 of the base 11.

The end of breaker stud 18 extending forward from the base member is divided into two horizontally diverging branches, whereby this stud in plan view has a generally Y-shaped appearance. ln the preferred embodiment of my invention illustrated in Figs. 1 and 2, the stationary Contact member 12 comprises at least one pair of elongated contact elements or fingers 23, each iinger 23 being pivotally supported intermediate its ends on the outer end of a diderent diverging branch of the breaker stud 18. For this purpose, the outer ends of the diverging branches are respectively provided with generally cylindrical bearing surfaces having centerlines oriented in a vertical direction as viewed in Figs. l and 2. Each bearing surface is recessed so that shoulders are formed at its upper and lower ends to prevent vertical movement of the associated contact finger. lf desired, the length of the bearing surface can be made su'icient to accommodate more than one contact finger 23 in side-by-side relation.

Each of the two bearing surfaces at the outer ends of the diverging branches of the breaker stud 1S provides a fulcrum for at least one contact finger 23, and the pivotal connection between each contact finger and the breaker stud forms a current-conducting joint. As can be clearly seen in Fig. 2, the contact fingers 23 are re- Spectively supported on opposite bearing surfaces in opposing relationship With respect to each other. The opposing or inner ends of the contact lingers are movable in separate, relatively short arcuate paths disposed in a common horizontal plane, and the opposing ends are respectively provided with generally fiat, complementary contact surfaces 24 normally defining a common vertical plane as viewed in Figs. l and 2.

The inner end of each contact finger 23 is arranged to engage a common stop 25 for determining the limit of the arcuate movement of the contact surface 24 in one direction. The stop 25, as is indicated in Fig. 2, comprises a pin vertically disposed intermediate the divergent branches of the breaker stud 18 and fixedly connected to the upper and lower supporting angles 19 and 2li. Associated with the outer end 26 of each contact finger 23 is suitable spring means, for example, the illustrated tension spring 27 which may be anchored at one end to a xed member such as provided by a laterally extending lug 28 of the supporting angle 19. Thus, spring means 27 establishes a biasing torque in the contact finger 23 tending to move the contact surface 24 along its arcuate path in a forward direction away from the base member 11, and such movement by the finger is limited by stop pin 25. The above-described structure permits a relatively limited deflection of each contact finger in a rearward direction.

The biasing torque is opposed and overcome and each contact finger 23 of the relatively stationary contact member 12 is tilted slightly on its fulcrum by the action of the movable contact member 14. As will be more fully explained hereinafter, the movable contact member 14 in the illustrated embodiment of the invention includes a pair of arms respectively provided with contact surfaces 51 which move in parallel planes disposed approximately perpendicular to the plane defined by the arcuate paths of the contact surfaces 24 of the fingers 23. The actuating means 15 provides actuating force for moving each contact surface of member 14 into and out of circuit-making abutting engagement with the contact surface 24 of a different contact finger. During a circuit making operation, the contact surfaces 51 are jointly carried rearwardly from their open circuit position (Fig. 2) into substantial simultaneous engagement with both of the cooperating contact surfaces 24, and further rearward movement of the contact surfaces 51 to their f'ully closed positions (Fig. 1) forces the spring means 27 to yield as the relatively stationary contact fingers 23 tilt on their fulcrums. In this manner, conventional contact wiping action is obtained.

Although for the sake of illustration I have shown and described cooperating Contact members constructed and arranged for abutting circuit-making engagement, I do not wish to be limited to such an abutting type contact structure. It will soon become apparent that the successful application of my invention does not depend in any respect on the particular nature of the cooperating relationship between the movable and stationary contact members. In lieu of the abutting arrangement illustrated the movable contact member could comprise, for example, a pair of generally parallel contact elements to slide over and be spread-apart by a cooperating bladelike member.

In Figs. 1 and 2 it can be seen that the electroconductive bracket 13 for supporting the movable contact member 14 is mounted on base member 11 by means of a pair of suitable bolts 30 or the like. The bracket 13 has a lower lip 31 provided with a hole for the purpose of connecting a suitable current-conducting member or another breaker stud (not shown) to the breaker. Part of the bracket is disposed adjacent the front surface of the insulating sheet 16 of base member 11, and a rigid reinforcing member 32 is disposed adjacent the rear surface of the sheet 16 in overlapping relationshfp with the bracket 13 and the lower supporting angle 20, re-

spectively. The reinforcing member 32 is provided so that the loading of the insulating sheet 16 in the area between bracket 13 and the relatively stationary contact member 12 will be in compression rather than in flexure. A channel 33 of insulating material is disposed intermediate the reinforcing member 32 and the rear of sheet 16 to provide additional electrical insulation between the sides of member 32 and the fastening bolts 21 and 30.

The bracket 13 includes a pair of distinct portions comprising spaced-apart upstanding lugs 34 and 35 projecting in front of base member 11. A removable pivot pin 36 is supported by the lugs 34 and 35, the axis of the pivot pin extendng in a horizontal direction generally parallel to the plane of the base member 11 as viewed in Figs. 1 and 2. The ends of the pivot pin 36 protrude on opposite sides of the lugs 34 and 35, respectively, and the pin is retained in place by a releasable clamp 37 disposed intermedate the lugs. As is most clearly seen in Fig. 4, the clamp 37 comprises a resilient helical coil loosely encircling pin 36, the length of the helix corresponding approximately to the span between the lugs 34 and 35. The opposite ends of the coil of clamp 37 extend tangentially therefrom and are arranged for movement between first and second cooperating positions. In Fig. 2 the ends are shown in a position wherein they releasably engage each other, and in this selflocked position the circumference of the coil is contracted for firmly grasping the encircled pin and preventing axial movement and removal thereof. By separating the ends and permitting them to assume their other position (shown in Fig. 4) in accordance with the resilience of the coil, the circumference of the coil can be expediently expanded for assembling or disassembling purposes.

The opposite sides of the upstanding lugs 34 and 35 are respectively provided with outwardly facing substantially flat, smooth slide surfaces 38 and 39, and the axis of pivot pin 36 is oriented approximately perpendicular to the slide surfaces 38 and 39. Disposed adjacent the slide surface 38 of lug 34 and rotatably mounted on a protruding portion of pivot pin 36 is one end 46 of an elongated contact arm 41; and disposed adjacent the slide surface 39 of lug 35 and rotatably mounted on the oppositely protruding portion of the pivot pin is one end 42 of an elongated contact arm 43. The contact arms 41 and 43 are arranged in generally parallel relation for joint operation and comprise the movable contact member 14.

The connection between each movable contact arm 41, 43 and the electroconductive bracket 13 is arranged to provide three separate current-conducting joints, The first such joint is provided by the bearing surfaces between the contact arm and the pivot pin 36 on which it rotates, that is, between pin 36 and the periphery of a hole 44 which has been located in the one end 4%, 42 to accommodate the pin 36. The surface of the pivot pin 36 and the periphery of hole 44 may be silver plated and burnished to ensure a wear-resistant, low electric resistance current-conducting path.

It has been found that satisfactory performance of the contact structure will not be realized if the only current-conducting path between a movable contact arm and its supporti-ng bracket is that provided by the pivot pin. This is because pivotal movement of the arm during a circuit breaking operating causes the bearing surfaces and consequently the point of contact between the pivot pin and the cooperating arm to shift from one side of the pin to the other. Such shifting of the Contact point during circuit .interruption will rapidly lead to an undesirable pitted or eroded condition at this rst currentconducting joint unless means is provided for shunting current from the joint while such shifting is taking place. Accordingly, it has been customary to provide a flexible braid or conductor connected in shunt with the pivot pin aseasvs.

between the movable arm and its stationary support.

However, this solution to the problem is not entirely satisfactory. Strong magnetic forces present during the interruption of high short-circuit currents tend to deform the flexible braid and cause it to loose the necessary degree of freedom and flexibility. The brad is subject to fatigue and becomes brittle after a time. I prefer not to use a flexible braid.

In accordance with my invention, the first joint provided by the pivot pin 36 is shunted by a second currentconducting joint electrically interconnecting each movable contact arm 41, 43 and bracket 13. This second joint is a relatively simple and compact one obtainedY by providing the pivoted end 40, 4Z of each movable contact arm with a smooth, pertain-ing slide surface 46 on its relatively broad inner side, i.e., on the side of the contact arm facing the supporting bracket 13. Each slide surface 46 is disposed generally parallel to the respective adjoining slide surface 3S or 39 of the bracket 13, and therefore all of the slide surfaces 38, 39 and 46 are substantially perpendicular to the axis of pivot pin 36 which corresponds to the axis of rotation of the movable contact arms 41 and 43. The slide surface 46 of each movable contact arm includes at least one raised section 47 which, as can best be seen in Figs. 3 and 4, preferably comprises a convex portion of a cylinder whose axis is disposed perpendicular to the axis of pivot pin 36. The crest of the raised section 47 is intersected by the hole 44 provided for pivot pin 36, and it is oriented at approximately a right angle with respect to the longitudinal centerline of the associated Contact arm.

The crests `of the raised sections 47 of the two slide surfaces 46 respectively cooperate with and are contiguous to the slide surfaces 38 and 39 of bracket 13, and pivotal movement of the contact arms 41 and 43 on pin 36 causes each crest to slide over the associated surface of the relatively stationary bracket 13. The contiguous portions of each pair of cooperating slide surfaces define a straight-line contact which provides the second currentconducting joint between each movable contact arm and the supporting bracket. This straight-line contact is intersected by the axis of pivot pin 36; therefore the second joint actually comprises two short, collinear lines of contact on opposite sides of hole 44, and parallel paths are provided for current flow between the bracket 13 and each contact arm 41, 43. Of course, as an obvious alternative to the specific arrangement illustrated and described above, the raised sections could be located on slide surfaces 33 and 39 and the slide surfaces 46 could -be made substantially iat. Furthermore, similar results could be effected by substituting, for example, a spherical portion on slide surface 46 for each half of the cylindrical raised section 47, whereby the second current conducting joint would comprise two parallel points of contact.

Contact pressure at the joints formed by the respective contiguous slide surfaces is maintained by means of an electroconductive spring member 43 which comprisesy in one embodiment of my invention, for example, a U- shaped spring clip. As is seen inPigs. 1 and 4, the resilient upstanding elements 49 and 50 ofthe clip 48 are each split into two fingers and are disposed slidably to bear against the relatively broad outer sides of the contact arms 41 and 43, respectively, at rst and second respective points on each side of bracket 13 disposed on opposite sides of the pivot pin 36. The electroconductive spring member 48 is securely anchored to the bracket 13, and since it also slidably engages each movable contact arm it provides the third current-conducting joint. In addition spring member 4S applies a sidewise force which maintains contact pressure at the contiguous surfaces of both pairs of cooperating slide surfaces 38, 46 and 39, 46. The spring member is arranged so that this sidewise force is relatively weak whereby the movable 6. contact member 14 can be freely pivoted on its supporting bracket 13. This is possible because the sidewise force is supplemented by a strong electromagnetic force whenever the movable contact memberis conducting current.

When the parallel contact arms 41 and 43 conduct alternating current, a magnetic force is established tend- 4ing to reduce thespacing between these two arms. Since the supporting bracket 13 is disposed intermediate the contact arms, this sidewise magnetic force effectively establishes additional contact pressure atkthe contiguous slide surfaces 38, 39 and 46. In order to obtain optimum performance of the contact structure, it is particularly important that high contact pressure be maintained at the contiguous slide surfaces while these surfaces are moving relative to each other during circuit interruption. The desired strength of contact pressure, which is suflicient to ensure good electrical contact and prevent pitting of the cooperating slide surfaces during a circuit interrupting operation, is provided by the laterally-exerted magnetic force Whose magnitude is proportional to the square of the current magnitude. Thus, the greater the current being interrupted the greater will be the contact pressure at the contiguous slide surfaces.

The diameter of hole 44 in the movable contact arms is made slightly greater than the diameter of pivot pin 36. This loose mounting arrangement permits the contact arms 41 and 43 to rock on pivot pin 36. The crests of the raised sections 47 of the slide surfaces 46 provide fulcrums for the rocking movement of the arms, and the plane of the rocking movement includes the axis of the pivot pin 36. This arrangement allows for a certain degree of misalignment of the various parts and a liberal manufacturing tolerance without adversely affecting the positiveness of the electric contact between the movable elements and the supporting bracket 13.

Since the contiguous portions of the cooperating slide surfaces of each movable contact arm and the supporting bracket dene a single straight line corresponding to the crest of the respective raised section 47, and since this straight lineis oriented at approximately a right angle with respect to the longitudinal centerline of the associated contact arm, a positive electric contact at the joint formed by the slide surfaces is ensured throughout a circuit breaking operation of the contact structure. It has been noted above that strong magnetic forces are exerted on the parallel contact arms when they conduct shortcircuit current during circuit interruption. These lateral forces tend to deflect each arm, but in spite of such deflectionthe effectiveness of the current-conducting joint is not impaired and positive electric contact remains made at the fulcrum provided by the crest of raised section 47.

By utilizing three parallel current-conducting joints for each of the two parallel arms of the movable contact member 14, the overall electric resistance of the direct connectionk between each arm yand the bracket 13 is efiiciently reduced, and in the illustrated embodiment of my invention this resistance is sufficiently low to enable the contact structure to carry 60Gk amperes continuously at 600 volts A.-C. without exceeding permissible limits of` temperature rise. The above-described arrangement permits significant economies to be realized in the required minimum sizes of the various current-carrying parts, and a successful contact structure is obtained without the conventional flexible braids or conductors. 1t will be noted tha'tl there are actually ten parallel paths for current to flow between the movable contact member 14- and the supporting bracket 13. There are tive parallel paths for each arm; namely, one path through pivot pin 36, two pathsV through the straight-line contact comprising the respective portions of raised section 47 that are separated by the pin 36, and two paths through the fingers of resilient element 49 that engage bracket 13 at respectively spaced points. Adequate contact pressure atY thev current-conducting joints formed by the contiguous slide surfaces 38, 46 and 39, 46 is maintained independently of the force being supplied to the movable contact member 14 by the actuating means 15 and without the necessity of untoward precision in the manufacture and alignment of the parts.

In the illustrated embodiment of my invention, the corresponding free ends of the contact arms 41 and 43 are provided respectively with transverse contact surfaces 51 disposed for abutting engagement with the contact surfaces 24 of the relatively stationary contact fingers 23. Rotary movement of the contact arms on pivot pin 36 carires the contact surfaces 51 through arcuate paths which define vertical planes intersecting at approximately right angles the horizontal plane of movement of the relatively stationary contact surfaces 24, as viewed in Figs. l and 2. This arrangement permits the convenient utilization of more than one stationary contact finger for each movable contact arm, whereby more than two separate points of circuit-closing engagement can be provided between the movable contact member 14 and the relatively stationary contact member 12.

The cooperating contact surfaces 24 and 51 preferably are made of silver tungsten carbide material which will successfully perform the continuous current-carrying funtcion of the contacts and also the required circuit making and breaking duty without appreciable contact erosion or pitting or contact welding as a result of electric arcing. Therefore it is not necessary to provide separate arcing and main contacts. With the various parts shown in Figs. 1 and 2 appropriately dimensioned, the contact structure will safely carry at least 225 amperes continuously at 600 volts A-C, and the same contact structure can be modified to carry at least 600 amperes continuously merely by changing the relatively stationary contact member 12 so that two additional contact fingers (23) are respectively disposed adjacent those shown and by appropriately extending the contact surfaces 51 of the movable Contact arms.

In order to obtain a compact arrangemnet at the cooperating contact surfaces 24 and 51, the contact arms 41 and 43 are spaced closer together at their corresponding free ends than at the pivot pin 36. As is shown in Figs. 2 and 4, this has been accomplished by axially offsetting the free ends of the contact arms with respect to their pivotally connected ends 40 and 42, respectively. in addition, the contact arms are oppositely offset at intermediate portions 52. As is indicated in Figs. 3 and 4, the offset portion 52 of each arm is provided with a transverse hole 53 the centerline of which is oriented parallel to the pivot pin 36.

An actuating member such as a cylindrical irnpelling shaft 54 is rotatably disposed in the holes 53 of both contact arms 41 and 43, and by this means actuating force is applied to the movable contact member 14 for jointly moving the contact arms 41 and 43 between open and closed circuit positions. In the vicinity of the offset portions 52 of the contact arms, protrusions 55 are formed. These protrusions, which preferably are in the form of curved embossments on the inner sides of the contact arms, are respectively disposed to extend in overhanging relationship with the lugs 34 and 35 of bracket 13. See Fig. 3. In this manner, the current-conducting joints formed by the two pairs of contiguous slide surfaces 38, 46 and 39, 46 are shielded from the electric arc and arc products which may be produced during circuit breaking action of the contact structure. The protrusions 55 will prevent particles of foreign matter generated during circuit breaking action from entering these joints by straightline paths from the area of arc interruption. Such foreign matter, if permitted to enter the joint, could cause excessive wear and increased contact resistance.

The irnpelling shaft 54 ts relatively loosely in the holes 53 in the offset portions 52 of the movable contact arms 41 and 43, whereby each arm can slide ou shaft 54 8, while rocking on pivot pin 36. Thus the contact surface 51 of each arm is free to move in a lateral or transverse direction, and such lateral movement is controlled by resilient means associated with the contact arm. As is shown in Figs. 2-4, the resilient means preferably comprises a helical spring 56 disposed on irnpelling shaft 54 intermediate the contact arms 41 and 43. The spring 56 applies a transverse force to each contact arm and establishes in the arm a relatively weak biasing torque with respect to the pivot provided by the line contact at the joint formed by the associated pair of contiguous slide surfaces. This biasing torque is in a direction tending to spread apart the contact arms. Such movement of each contact arm is stopped and its normal position is determined by a bushing 57 disposed on shaft 54 between a retaining ring 58 and the circular outer side of the olset portion 52 of the arm.

During circuit making action of the contact structure, each contact surface 51 comes into abutting engagement with a contact surface 24 of a relatively stationary contact finger 23, and as the cooperating contact surfaces wipe the contact finger 23 is tilted in opposition to its biasing torque. The arrangement is such that transverse force is supplied to contact surface 51 by contact surface 24 as the contact finger 23 is tilted. Due to the resilient means 56 and the fulcrum provided by the crest of the raised section 47 of the contiguous slide surfaces, the movable contact arm is able to yield to this transverse force and contact surface 51 moves laterally while following the arcuate path of contact surface 24. As a result, the relative movement between the cooperating contact surfaces 24 and 51 is reduced thereby reducing the amount of fric-, tion between these cooperating surfaces and improving the performance of the contact structure.

The movable contact member 14 is coupled to the actuating means or crossbar 15 by means of the impelling shaft 54 and a generally U-shaped connecting link 59 securely fastened to the crossbar. Each leg of the connecting link 59 is provided with an extension 60, which as is clearly seen in Fig. l, is connected to the pivot pin 36. In this manner the crossbar 15 is supported for pivotal movement on the same pin 36 that provides pivotal support for the movable contact member 14.

End portions 61 of irnpelling shaft 54 extend laterally from the contact arms 41 and 43 and are made eccentric with respect to the cylindrical body of the shaft, as is shown in Figs. 3 and 4. The end portions 61 are coupled to the connecting link 59 in a manner permitting controlled rotation of the shaft 54. This has been done by providing each end portion 61 with flat sides forming a hexagon, parallel sides of the hexagon being positively but resiliently locked between a shoulder 62 of the connecting link 59 and a cooperating cantilever flat spring 63 carried by link 59. See Fig. 1.

By means of a conventional open-end wrench applied to the hexagonal end portion 61, the shaft 54 may be rotated to any one of six angular positions. In each of these six positions, the movable contact member 14 is located in a different relative angular position with respect to the crossbar 15 and with respect to the relatively stationary contact member 12. The purpose of this adjustment is to accurately establish the fully closed position of the movable contact member regardless of liberal manufacturing tolerances, whereby the desired amount of contact wipe can be precisely obtained.

The crossbar 15 is connected to a circuit breaker operating mechanism by means of another link 64 and a connecting member 65. The operating mechanism, which has not been shown, may be of any suitable type for moving the connecting member 65 in a generally horizontal direction (as viewed in Figs. 1 and 2) and thereby reciprocally carrying the crossbar 15 about its pivot between rst and second relatively fixed positions.

The crossbar 15 may be extended across the width of the circuit breaker for connection in a similar manner to other pole units of a multipole circuit breaker. An isolatmg barrier 66 of insulating material is shownmounted on the crossbar in Fig. 2. Other barriers 67 are provided `for the purpose of isolating the various current-conducting parts of the illustrated pole unit from the corresponding parts of adjacent pole units and from ground. A suitable arc chute, not shown in the drawings, may be mounted on the base member 11 to enclose the cooperating contact surfaces 24 and 51 for the conventional purpose of arc extinction.

While I have shown and described a preferred form of my invention by way of illustration, many modifications will occur to those skilled in the art. Therefore, I contemplate by the concluding claims to cover all such moditications as fall within the true spirit and scope of my invention What I claim as new and desire to secure by Letters Patent of the United States:

1. In the contact structure of an electric circuit interrupter: a base member; an electroconductive bracket mounted on the base member and provided with at least one slide surface; a relatively stationary contact member mounted on the base member in spaced relation to the bracket; a cooperating movable contact arm pivotally supported by the bracket for rotation about an axis oriented approximately perpendicular to the slide surface of said bracket, the movable contact arm having a pertaining surface disposed in contiguous relationship with said slide surface to form a current-conducting joint, one of the surfaces being substantially at and the other surface having a single raised section defining with the iiat surface a straight-line contact, whereby the joint provides for rocking movement by the movable contact arm with respect to the axis of rotation; resilient clamping means for maintaining contact pressure between the contiguous surfaces forming the joint as the movable contact arm rotates; and actuating means coupled to the movable contact arm for moving said arm into and out of circuit making engagement with the stationary contact member.

2. In the contact structure of an electr'c circuit interrupter: a base member; an electrocondctive bracket mounted on the base member and including at least one distinct portion having a relatively smooth surface; a relatively stationary contact member mounted on the base member in spaced relation to the bracket; a co operating movable contact arm pivotally supported by the bracket for rotation about an axis oriented approximately perpendicular to the surface of the dist'nct portion of said bracket, the movable contact arm having a pertaining surface disposed in contiguous relationship with the surface of said distinct portion to form a current-conducting joint, one of the surfaces being substantially flat and the other surface having a raised section defining with the fiat surface a straight-line contact intersected by the axis of rotation, whereby the joint provides a pivot for rocking movement by the movable contact arm in a plane including the axis of rotation; means for maintaining contact pressure between the contiguous surfaces forming the joint; and actuating means coupled to the movable contact arm for rotating said arm into and out of circuit making engagement with the stationary contact member.

3. In the contact structure of an electric circuit breaker: a base member; a relatively stationary contact member mounted on the base; an electroconductive supporting bracket mounted on the base in spaced relation to the stationary contact member; an elongated movable contact member pivotally connected to the bracket for rotat'on about an axis, the connection between supporting bracket and movable contact member including contiguous slide surfaces disposed generally perpendicular to the axis of rotation to form a current-conducting joint, one of said surfaces being substantially flat and the other surface being raised so that the contiguous portons of the surfaces define a single straight line oriented at approximately a right angle with respect to the longitudinal centerline of the movable contact member; means for maintaining contact pressure between the contiguous surfaces forming the joint; and actuating means coupled to the movable contact member to move said member into and out of circuit making engagement with the stationary contact member.

4. In the contact structure of an electric circuit interrupter: a base member; an electroconducitve bracket mounted on the base member; a relatively stationary contact member mounted on the base in spaced relation to the bracket; a cooperating movable contact comprising an elongated member pivotally connected near one end to the bracket for rotation about an axis, the connection between bracket and movable contact member including contiguous slide surfaces disposed generally perpendicular to the axis of rotation to form a current-conducting joint, one of said surfaces being substantially tiat and the other surface having a raised section defining with the tiat surface a straght-line contact intersected by the axis of rotation and oriented at approximately a right angle with respect to the longitudinal centerline of the movable contact member, whereby the straight-line contact provides a fulcrum for rocking movement by the movable contact member with respect to the axis of rotation; means for maintaining contact pressure between the contiguous surfaces forming the joint; and actuating means coupled to the movable contact member for rotating said member into and out of circuit making engagement with the stationary contact member.

5. An electric circuit breaker contact structure comprising: a base member; an electroconductive bracket including a pivot pin mounted on the base, the pivot pln being disposed to protrude on opposite sides of the bracket and said opposite sides respectively having outwardly facing slide surfaces disposed generally perpendicular to the axis o-f the pivot p'n; a relatively stationary contact member mounted on the base in spaced relation to the bracket; a cooperating movable contact member including a pair of generally parallel arms loosely mounted for pivotal movement on the protruding portions of the pivot pin, respectively, said arms being provided with pertaining surfaces respectively disposed in contiguous relationship with the slide surfaces of said bracket to form a pair of parallel current-conducting joints, one of the contiguous surfaces of each joint being substantially tiat and the other being raised to define with the flat surface a line contact; resilient clampng means for maintaining contact pressure between the respective contiguous surfaces of each joint; and actuating means coupled to the movable contact member for pivotally moving said member into and out of circuit making engagement with the stationary contact member.

6. In the contact structure of an electric circuit interrupter: a base member; an electroconductive bracket including a pivot pin mounted on the base, the pivot pin being disposed to protrude on opposite sides of the bracket and said opposite sides respectively having outwardly facing slide surfaces disposed generally perpendicular to the axis of the pivot pin; a relatively stationary contact member mounted on the base in spaced relation to the bracket; a cooperating movable contact member including a pair of generally parallel arms connected for pivotal movement to the protruding portions of the pivot pin, respectively, said arms being provided with pertaining surfaces respectively disposed in contiguous relationship with the slide surfaces of said bracket to form a pair of parallel current-conducting joints, one of the surfaces of each joint being raised relative to the other so that the contiguous portions of the surfaces forming each joint define a single straight line; means for maintaining contact pressure between the respective contiguous surfaces of each joint; and an actuating member pivotally supported by said pivot pin and coupled to the movable contact member for moving said latter member into and out 114 of circuit making engagement with the stationary contact member.

7. In the contact structure of an electric circuit interrupter: a base member; an electroconductive bracket mounted on the base member and having a substantially at surface; a relatively stationary contact member mounted on the base member in spaced relation to the bracket; a cooperating movable contact arm pivotally supported by the bracket for rotation about an axis oriented approximately perpendicular to the flat surface of said bracket, the movable contact arm having a pertaining surface disposed in contiguous relationship with said at surface to form a rst current-conducting joint, the pertaining surface having a relatively curved section defining with the fiat surface a line contact intersected by the axis of rotation, whereby the rst joint provides for rocking movement by the movable contact arm with respect to the axis of rotation; an electroconductive spring member anchored to the bracket and bearing against the movable contact arm to maintain contact pressure at the first joint and to provide a second current-conducting joint with the movable contact arm; and actuating means coupled to the movable contact arm for moving said arm into and out of circuit making engagement with the stationary contact member.

References Cited in the le of this patent

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