US2127813A - Circuit interrupter - Google Patents

Description

All@ 23, 1938- H. c. GRAVES, JR 2,127,813

I CIRCUIT INTERUPTER K Filed June 6, 1936 2 Sheets-Sheet l @l BY f M an en@ ATTORNEY.

Aug- 23 1,938- kH. c. GRAVES, JR 2,127,813

CIRCUIT INTERRUPTER Filed June 6, 1956 2 ShevtS-Sheetl 2 xllllllll" M `70d' l@ E /f INVENTOR.

/AM' @j BY w1. am

ATTORNEY.

Patented Aug. 23, 1938 UNITED STATES 2,121,813 cracm'r INTERRUPTER.

^ Herbert C. Graves, Jr., East Bradford Township, Chester County, Pa., assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of New Jersey Application-June 6, 1936, Serial No, 83,857

2,2 Claims.

My invention relates to electric circuit interrupters or automatic circuit breakers, more particularly to new and improved separable contacts therefor, and has for an object the provision -of simple, rugged, and inexpensive contact structures of high'current-carrying capacity.

In carrying out my invention, in one form thereof, I provide a rigid self-aligning bridging member having one portion continuously biased into abutting engagement with a stationary contact structure and another portion movable into and out of engagement with another contact structure. The bridging member` is provided with a limited freedom of motion about two axes to insure line contact between it and said structures. Intermediate the contact structures, pressure is applied, through a fulcrum and at a single point, to the bridging element to equalize the current flowing to and from opposite ends thereof, and to provide the desired circuit-closing pressures without interfering with the freedom of motion of the bridging member.

Further in accordance with my invention, thel bridging member is particularly useful where the stationary contact structures have contact surfaces of considerable length disposed in a plane, or otherwise, as contrasted with relatively narrow or spherical contact surfaces, since the bridging member is readily'movable to a position to insure line contact between .its plane contact surface and the'surfaces of the respective contact structures, to insure maximum current carrying capacity for the circuit interrupter. In the closed circuit position the bridging member is rigidly locked in a'xed position.

` Preferably one contact structure includes aV plurality of resiliently'mounted contact elements whose contact pressures, upon displacement thereof, are substantial. Contact structures of this type are shown and described in my copending application Serial No. 60,017, filed January 2l,

1936, for Electric circuit interrupter, now Letters Patent No. 2,090,754, dated August 24, 193'1.

Further in accordance with my invention the bridging member is provided with a rounded end biased at all times into abutting contact engagement with one of the contact structures. Preferably the bias is increased as the bridging member is moved into abutting contact engagement with another of the stationary contact structures. A flexible conductor, connected in parallel with the continuously engaged surfaces, is connected to the bridging member above the fulcruin so that upon f low of large currents, a'substantial force is applied to increase the circuit closing pressure upon the aforesaid contact surface. The flexible conductor is relatively light, as .it is not called upon to carry or withstand the entire current carried by the bridging member.

For a more complete Aunderstanding of my in- (ol. 20o-a7) vention, reference may be had to the accompanying drawings in which:

Figure l is a vertical side elevation, partly in section, of a circuit breaker embodying my invention; v

Fig'. 21s a front elevation of the bridging meniberiof Fig. 1;

Fig. 3 is a cross-sectional view of the bridging member and bracket taken along .the line 3-3 of Fig.' 1; l

Fig. 4 diagrammatically illustrates, on a reduced scale, a toggle mechanism of a type suitable to operate and lock the bridging member in a closed circuit position.

Referring to the drawings, I have shown my invention in one form as applied toa circuit interrupter comprising a base or panel member I from which is supported a terminal stud or connector II connected to a stationary contact assembly or structure I2. `A second terminal stud or connector I3, also supported from the panel I0, is connected to a rigid stationary contact structure I4 having a roundedl contact surface I5 preferably curved like the surface of a cylinder.

Cooperating with the stationary contact structures. I2 and I4 to complete a circuit between or bracket 20. 'I'he outer ends of the pin I'I pass f through elongated openings or slots 2l and 22 in the flanges I8 and I9 of the bridging` member. These openings permit relative horizontal movement between the bridging member I6 and the ends of the pin I1 but substantially prevent vertical movement. By reason of the slots 2I and 22, and the pin I1, the bridging member I6 has a limited freedom of motion about two axes and 'readily aligns its contact face with the cooperating face I5'of structure Il.

Within rectangular. openings in the lower ends ofthe flanges I8 and I9 is disposed a rectangular operating shaft 23, suitable insulation 24 being provided between the shaft 23 and the flanges I8 y and I9 of bracket 20. A U-shaped clamping memberA 25, encircling the insulated shaft 23, has

relatively -narrow extensions 26, which pass through the web 20a of bracket 20, riveted tightly against the web 20a to secure the bracket 20 I.

and shaft 23 together.

Any suitable'mechanism may be used to operate and lock the bridging member I6 in its closed circuit position, such for example as the mechanism disclosed in U. S. letters Patent Reissue No. 19,753, issued upon my application Serial No. 711,332. Briefly, such a mechanism, Fig. 4, may comprise a lever 21 rigidly secured to the shaft 2l. The lever21 is shown in the closed circuit position of the interrupter, a pair of toggle links 2l and 2l in conjunction with a crank arm 30 serving positively to lock the member 21 against movement under the influence of a powerful opening spring Il connected between pivot pins 82 and 88.

The lower end of the crank arm 30 is retained in position by a latch l5 releasable by any suitable electro-responsive device such as an overload magnet 3B. A spring 31 normally biases the latch to a position to engage the lower end of the arm I0. 'I'he respective toggle links 28 and 2l have stop portions 28a and 29a which engage with each other to prevent movement of the knee pivot 3l of the toggle beyond a slightly overset position. The spring 3l, however, having its line of action below pivot pin 39 connecting toggle link 29 to the arm 30, biases the crank arm lll for rotation in a clockwise direction. Upon occurrence of an overload, the armature of overload magnet 36 releases the latch 35 permitting the crank arm 30 to rotate in a clockwise direction to move the lever 21 and shaft 23 to the open circuit position. As this movement occurs, the knee pivot Il engages an inclined surface 41| and is thereby moved below its dead center position. The spring Il is then effective to collapse the toggle 2l, 2t downwardly, and at the same time the spring 31 returns the crank arm Il to a position to be engaged by the latch 35.

To reclose the circuit breaker an electromagnet 4I is energized to lift its plunger 42. The knee pivot pin 4l then being located at the lower end of an elongated slot 43 of plunger 42, is thereby lifted to straighten the tossle links 2l, 29 and finally to move them to the slightly overset position shown in Fig. 4.

Referring to Fig. 1, it will be observed that the stationary contact structure I4, shown as of solid copper, Is arranged so that its cin-ved contact surface Il is substantially in alignment with the shaft 23. 'Ihe cylindrical surface I5 is oi' relatively large radius, its axis and the axis`of the shaft 28, however. being disposed in a horizontal plane normal tothe panel III. 'Ihe lower end of the bridging member Il is providedwith a cylindrical. or curved, surface 44, the radius of which extends from the axis of the shaft 2l, though it Amay extend from an axis disposed slightly above that of shaft 24 and slightly nearer the bridging member I8. The plane contact surface of the bridging memberv Il is of course tangent to the curved surface 4l. Inany event the surface 4l iaformed so that it is not moved or forced, during the opening of the circuit interrupter, by the contact structure I4 toward the axis of the shaft 2l.

By means of `a spring 41 clamped by a steel plate 4l against the web of the bridging member It, the lower or curved end of the bridging member is at all times maintained in contact engagement with the structure I4. 'I'he spring 41 need not be heavy or particularly strong inasmuch as only a relatively light pressure is necessary to insure substantial conductance betweensurfaces Il and 4l.

In accordance with the present invention the continuous engagement of the surfaces Il and permits the use of a nexible conductor 4l of greatly reduced sise. Que end of the conductor 40' is securedto the contact struc'ure I4 by a cap screw 50, the conductor being looped around the shaft 23 and the bracket 20, with its opposite end secured by cap screw 5I to a lug or projection l2 integrally secured to the web of the bridging member I6 and extending outwardly between the flanges I8 and I9 of the bracket 2U.

The flexible conductor or shunt 49, connected in parallel with the contact surfaces I5 and 4l, is not called upon to carry currents of large magnitude during normal operation of the circuit interrupter. It is preferably included, however, in order substantially entirely to eliminate arcing between the surfaces I5 and 48. Since it is of light weight, as contrasted with the heavy ilexible conductors heretofore used, it is not subject to failure due to repeated operations, as it is highly flexible; moreover, it does not interfere in any way with the opening and closing operations of the circuit breaker.

.Application of circuit closing pressure to the bridging member I6 is provided by means of a pressure applying member or button 54, disposed below the projection 52 and carried by the web 20a of the arm or bracket 20. As best shown in Fig. 3, the member 54 comprises an enlarged head having a hardened steel surface 54a which is aY part of the surfaceof Ya sphere. An integral threaded extension 54h extends through an opening in the web 20a and is clamped into position by means of a. nut 55. A plurality of relatively thin washers 56 are placed between the head of the member 54 and the outer face of the web to provide' for adjustment of the member with respect to the web 20a. Cooperating with the hardened steel surface 54a is the steel plate 48 which, by rivets 58, is secured to the web of the bridging member I6, and, as mentioned above, is clamped against the spring 41.

The upper contact structure I2 is preferably of a type similar to that shown in my aforesaid Patent No. 2,090,754. More particularly, a piurality of relatively narrow rigid bridging elements 5I, each of which has a rounded end pivoted in a recess 62, are respectively supported by means of spring supports 8l and associated springs 44. The spring supports 63 at their uppe'r ends rest upon re-entrant portions of a contact block il forming a part of the structure I2. Their opposite and lower ends rest in recesses formed in side plates of the contact structure I2, only one of which, the side plate 66, is shown. In the closed circuit position, shown in Fig. 1, it will be observed that each of the bridging'elements 6I has been rotated in a clockwise direction against the bias of its associated spring B4. If desired, a plurality of rigid bridging elements Il may be assembled in groups within the same recess, each element of each group being supported by its own spring. For greater current carrying capacity a plurality of Ielements and a plurality of recesses may be provided in a single contact structure, or,` two or more structures may be electrically connected in parallel to form one current path of a circuit, the remaining current carried by an arm`12. itself iournaled on a lpivot pin 13 supported between the aforesaid side plates of the'structure I2. A biasing spring 14 2,127,813 4stationary pin 15 is eective to maintain the conductor 16, is connected to the contact block 65 of structure I2. In this instance a heavy conductor may be safely used without danger of failure due to fatigue, or repeated operations, since the pivotal movement of the arcing contact 1I is relatively small. In consequence, the conductor 16 is not placed under excessive stress; it neither impedes nor interferes withmovement of the arcing contact` 1I. Outward movement of the arcing contact may be limited by engagement of the lower end 11 of the arm 12 with the pin 15. The lower part of the arcing contact 1I and a cooperating part of the bridging member 'I6 are respectively provided with inserts 18 and 19 formed of arc-resistant conductive material, such as, for example, a material containing tungsten.

It will now be assumed that the .bridging memy ber I6 is in its open circuit position and that the electromagnet 4I has been energized to close the circuit interrupter. As its associated core 42 straightens the toggle 28, 29, the arm 21 ro.- tates the shaft 23 in a counterclockwlse direction, as viewed in Figs. 1 and 4, to move the arm or bracket 26 and the bridging m'ember l I6 toward the closed circuit position.

At all times, and during the aforesaid movement, the surfaces I5 and 46 are maintained in contact engagement. During the closing movement the relative radii of surfaces I5 and 46 are creases, or, the lower'end 46 of the bridging -member I6 is moved, against the bias of spring 41, toward shaft 23. Since both surfaces I5 and 46 are cylindrical, or are generated respectively by parallel lines moving in predetermined curved paths, they at all times engage one another along a line as contrasted with a point. Line `contact is assured since the bridging element I6 is free 'to move, because of the openings 2| and 22, an

amount sumcient to take care of any inherent inaccuracies incident to manufacture or assembly Y of the parts. Moreover, closing movement of the bridging member I6 by the arm or bracket 20 -is relatively independent-of the pin 'I1 since the pressure applying member or button 54 is utilized to apply the circuit closing pressure to the bridging member It. During closure of the interrupter the pin I1 serves merely as a sup-- port for the bridging member and prevents vertical movement thereof.

Continuing with the circuit-closing operation, as the upper end of the bridging member I6 approaches its closed circuit position, its arc-resistant insert 19 is moved into engagement with the insert 16 of the arcing contact 1I to form a current path through the interrupter. Substantially all of the current flows from one of terminals Il and I3 to` the other terminal, by way of the bridging member I6.; only a small fraction of the current flows by way of the ilexible conductor 49.

As the closing movement continues, the arcing contact 1I is rotated about its pivot 13 and against the bias oi' the spring 14. The opposition oifered by the spring 14 not only increases the contact pressure between inserts 16 andv 19 but also effects a further increase in the contact pressure between surfaces I5 and 46. 'I'his is desirable since contact conductivity increases the bridging member I6 as a lever pivoted for movement over. the fulcrum or pressure applying member 54. The force acting outwardly on the'upper end of the bridging member I6 produces an opposite force on the lower end of the l .with increased pressure. The reason for the' .increased pressure will be clear by considering bridging member I6 effective to press surface 4,6

against surface I5.

Upon further movement of the bridging member I6 the lowermost one of bridging elements 6I is first engaged by the bridging member I6.

.Additional movement of the bridging member I6 forces that bridging element downwardly against'.

the bias of its associated spring. In the same manner the remaining bridging elements 6I are successively engaged by the bridging member I6 and each of them is forced downwardly against the bias of its associated spring, the associated contact surfaces engaging and wiping each other clean to insure minimum resistivity.

By deflection of the elements 6I against the bias of their springs, the contact pressure-between contact surfacesv I5 and 46 is further increased. As before, the pressureapplying member .'54 located intermediate the contact structures I2 and I4, serves substantially to produce equal conductivities at the engaging contact surfaces.A

In the fully closed position, Figs. 1 and 4, the toggle 28, 29, has been moved slightly beyond its -dead center position and the pressures upon the contact surfaces are suflilcient to. insure a maximum current carrying capacity.

In case additional contact pressures are desired, or in the event of wear of the engaging surfaces, additional laminations or washers may be interposed between the enlarged end or head of the pressure applying member 54 andthe web 26a. The additional laminations, by varying the position of member 54, adjust the position of the bridging member I6 with respect to the arm or bracket 20 and cause a greater movement of the arcing contact 1I and of the respective bridging elements 6I against the bias of their associated springs. On the contrary, if the number of laminations are decreased, the contact pressures, or the extent of vmovement of the bridging member I6 to its fully closed position are decreased.

l,Upon the occurrence of an overload, particularly overloads of short-circuit magnitude, a substantial amount of current momentarily flows through the flexible conductor 49. At the same time, the increased lcurrent flowing from contact structure I4 .through the bridging element I6 may produce magnetic forces of a magnitude'tending greatly to decrease the contact pressures between surfaces I5 and 46. However, the increased current flowing. through the looped conductor 49 likewise produces magnetic forces producing tension in the conductor 49. 'I'hese forces are applied to the projection or post 52 in a direction to produce a torque on the bridging member I6 which acts in a clockwise direction about the fulcrum or member 54. Therefore the forces produced by current flowing inv the conductor 49 Aact in direct opposition to the forces produced pressure at both terminals during now of overload current.

Heretolore, -under short-circuit conditions, bridging members, themselves being resilient, or resiliently mounted as by springs interposed between the operating arms and the bridging member, have been subject to the forces tending to move the bridging member out and away from contact-engagement with associated contact structure. The result was a decrease in the current carrying capacity of the interrupter at the very time a maximum current carrying capacity was desired.

As shown above, however, in accordance with my invention, tendency of the bridging member IB to move away from the associated contact structure M is effectively prevented by the rigid fulcrum or pressure applying member 54, and by the arrangement of the circuit connections so that the magnetic forces produced are ineil'ective. As more fully explained in my aforesaid co-pending application, the assembly of elements 6| is such that the magnetic forces tend to increase the pressures upon oppomte ends thereof. Similarly, any current ilowing through flexible conductor 'Il produces magnetic forces tending to increase the contact pressure upon the inserts 'Il and 19.

It is to be understood the duration o! a current of short-circuit magnitude is very short. In fact. as soon as a predetermined current iiows, the overload magnet Il is eiiective to release the latch ll. Thereupon, and as described above, the crank arm Il is released and the powerful spring ll quickly moves the arm 2l and the bridging member Il to the open circuit position. In this instance the pin VII is moved into engagement with the right hand walls, or sides,v

, 'Ihe circuit is opened as soon as the inserts 'Il and Il are separated. I! an arc forms between the inserts Il and ,current continues to iicw. Since the contact pressure between surfaces Il and l0 has been decreased by the movement of bridging member It to its open-circuit position, it is highly desirable'to prevent arcing between surfaces I'l and 4I, to provide the shunt or flexible conductor Il in all cases where the circuit interrunter is called upon to open circuits `carrying current oi' short-circuit magnitude.

Circuit interrupters of the type shown are usually provided with arc extinguishing means eirective to extinguish quickly the Consequently even though a substantial amount of current may iiow through the conductor Il.' the duration of its flow is so short that the conductor 4l is in no way damaged.

While I have shown a'particular embodiment of my invention it will be understood that I do not limit myself thereto, since many modifications may be made, and I, therefore, contemplate by the appended claims to cover any such modiiications as fall within the spirit and scope oi' my invention.

1.In a circuit breaker having spaced contact structures one oi which is'resilient. a bracket rotatable about a nxed axis' 'located adjacent one oi said structures, a rig'idbridging member sup- :Jamais ported by said bracket with one end portion thereof adjacent both said axis and said one oi' said contact structures, operating means rigidly connected to said bracket for rotating said bracket and said bridging member from an open circuit position to a closed circuit position, and means operable during all circuit-opening and circuit-closing movement of said bridging member for biasing said end portion of said bridging member into abutting engagement with said one of said contact structures, said operating means including a rigid pressure-applying member disposed in abutting engagement with an intermediate portion of said bridging member for displacing said bridging member and said resilient contact structure to produce between both of said contact structures and said bridging member circuit-closing contact pressures.

2. A circuit lnterrupter having spaced contact structures, an actuating member, a rigid bridging member loosely connected to said actuating member for limited freedom of motion about two axes, a rigid pressure transmitting member supported by one of said members and engaging the other of said members at a single point lying between said contact structures, and means for applying a circuit-closing pressure to said actuating member, said bridging member pivoting about said pressure-applying member to insure line contacts between one face thereof and said contact structures. 1

3. In a circuit interrupter, spaced contact structures, a self-aligning bridging member for completing a circuit between said contact structures, operating means therefor including a connection providing limited freedom of motion of said member relative to said operating means, means biasing one end of said bridging member into abutting engagement with one of said structures during all opening and closing movement of said member, and means for applying circuitclosing pressure to said bridging member without interfering with its freedom of motion to insu're minimum contact resistance between said bridging member and said contact structures.

4. In a circuit interrupter, a rigid bridging member, associated spaced contact structures, means, including a bracket pivotally supporting said bridging member, for applying pressure to said member intermediate its opposite ends, resilient means, without the path of current through said member and said structures, operable by saidl pressure for development of circuitclosing contact pressures between said member and both of said structures, means for operating operating means to control the magnitude oi said circuit-closing pressures.

5. In a circuit interrupter.- spaced contact structures, a solid bridging member formed of high conductivity material provided with a plane contact surface for engaging said structures and with integral flanges extending away i'rom said i surface, a steel plate carried by said member intermediate said flanges, "a supporting bracket loosely pivoted'to said flanges adjacent one end of said bridging member, a pressure-applying member carried by said bracket for abutting engagement with said plate at a region intermediate said spaced contact structures. u

means connected to said brackets for applying, through said pressure-applying member and said plate, circuit-closing pressure to said bridging member.

6. In a circuit interrupter, a rigid bridging member, associated contact structures, a bracket pivotally supporting said bridging member at one end thereof, a rotatable operating member connected to the opposite end of said bracket for rotating said bracket to move said bridging member into and out of abutting engagement with said associated contact structures, and a member carried by said bracket and adjustable to change the angular position of said bridging member with respect to said bracket.

7. In a circuit interrupter, spaced contact structures, at least one of which is resilient, a bridging member movable into and out of abutting engagement with at least one of said structures, a bracket pivotally connected to said bridging member, an adjustable member for changing the angular position of said bridging member with respect to said bracket, means for rotating said bracket to, move said member into and out of contact-engagement with one of said contact structures, and a spring effective at all times-'to bias said member into engagement with another of said structures.

8. In a circuit interrupter having spaced contact structures at least one of which is resilient, an operating member extending in front of said structures, a bridging member loosely connected to said operating member for movement into abutting engagement with said structures, cooperating members supported respectively by said bridging member and said operating member for `applyinga. circuit closing pressure to said bridging member intermediate said contact structures, and a spring interposed between said members for biasing them away from each other, and a iiexible conductor `connected tov said bridging member and to one of said structures.

9. In an electrical circuit interrupter, cooperating spaced contact structures, one of which includes a plurality of diagonally disposed rigid bridging elements, and associated leaf springs for opposing movement of said bridging elements, and the other of which includes a rigid contact face; a bridging member having a limited freedom of motion about two axes, an actuating member for moving said bridging member into and outof abutting contact engagement with at least one of said structures, a fulcrum disposed intermediate theends of said bridging member and between said structures, a shaft supporting said actuating member and said bridging member for rotation about an laxis adjacent one of said structures, and biasing means at all -times maintaining contact engagement between said bridging member and said last-named contact structure.

10. In a circuit interrupter, a rigid channelshaped bridging member formed of copper and having flanges to impart rigidity thereto, a channel-shaped' bracket disposed between said anges and pivotally connected at one end'thereof to said member, and an operating member secured to the opposite end of said bracket.

11. In a circuit interrupter, a bridging member formed of copper and provided with flanges to impart rigidity thereto, a channel-shaped bracket disposed between said flanges and pivotally connected to said member, an operating member secured to said bracket for rotating said bracket to move saidbridging member between predetermined positions,` stationary contact structure engaged by said bridging member during its said movement, a spring supported between said bracket and said bridging member for biasing at al1 times one portion of said bridging member into engagement with said contact structure, and another stationary contact structure engageable and disengageable by said bridging member.

12. In a circuit interrupter, a bridging member formed of copper and provided with flanges to impart rigidity thereto, a bracket disposed .between said flanges and pivotally connected at one end thereof to a corresponding end of said member and means for rotating said bracket to move bracket to said operating member, a terminalA member secured to said bridging member and extending between said flanges and outwardly to one side of said bracket, resilient means interposed between said bracket and said bridging member for producing a bias tending to separate said bracket and said bridging member, stationary contact structure associated with said bridging member, and a exible conductor connected to said structure and to said terminal member.

14. In a circuit interrupter, a movable contact structure comprising a rigid bridging member having opposite ends rounded away from a connecting plane contact surface, flanges integral with said member, an operating member, a bracket having flange portions -disposed between the flanges of said bridging member, pivot means interconnecting corresponding upper portions of said bracket and said bridging member, means securing the lower portion of said bracket to said operating member, and resilient means supported by, and interposed between, said bracket and said bridging member for exerting a bias tending to separate the lower portions of said bracket and of said bridging member, and stationary contact structures one of which is disposed adjacent the lower portionl of said bridging member, and another of which is disposed adjacent the upper portion thereof, each of said stationary contact structures presenting contact surfaces for abutting engagement by said bridging member.

15. In a circuit interrupter having spaced contact structures one of which is displaceable against an associated biasing means, a rigid bridging member one portion of vwhich is continuously in abutting contact-engagement with one of said structures, an operating member for moving another portion of said bridging member into and Aout .of abutting contact-engagement with the other of said structures, and means for producing predetermined contact-pressures lupon -pf which is displaceable against an opposing biasing means, a rigid bridging element, one surface of which is continuously in abutting engagement with a surface of one oi.' said structures, an operating member movable from one position to another position, means loosely connecting said bridging member to said operating member to insure line contact between said abutting surfaces, said operating member being effective to move another contact i'ace of said bridging member into and out of abutting engagement with a vcontact face of another of said structures, and

means for controlling the displacement of the resiliently biased structure comprising a member intermediate said contact structures, and between said operating member and said bridging member, and engaging one of them at a single point about which said bridging member has a limited freedom of motion.

17. In a circuit interrupter having spaced contact structures one of which is rigid and another of which is displaceable against an opposing biasing means, a rigid bridging element, one surface of which is continuously in abutting engagement with a surface of one of said structures, an operating member movable from one position to another position, means loosely connecting said bridging member to said operating member to insure line contact between said abutting surfaces, said operating member being effective to move another contact face of said bridging member into and out of abutting engagement with a contact face of another of said structures, means for controlling the displacement of said biased structure comprising a member intermediate said contact structures and between said operating member and said bridging member and engaging one of them at a single point about which said bridging member has a limited freedom of motion, and a spring for maintaining contact pressure between said continuously engaged surfaces.

i8. In a circuit interrupter having spaced contact structures one of which is rigid and another of which is dlsplaceable against an opposing biasing means, a rigid bridging element, one surface of which is continuously in abutting engagement with a surface of one oi' said structures, an operating member movable from one position to another position, means loosely connecting said bridging member to said operatingmember to insure line contact between said abutting surfaces, said operating member being effective to move another contact face of said bridging member into and out of abutting engagement with' a contact face of mother oi' said structures, means for controlling the displacement of said biased structure comprising a pressure-applying member intermediate saidv contact structures and between said operating member and said bridging member and engaging one of them at a single point about which said bridging member has a limited freedom of motion, a iiexible conductor connected in parallel with said continuously'en- 'gaged surfaces, and la spring for maintaining contact pressure between said continuously engaged surfaces.

19. In a circuit interrupter having spaced con- `tact structures, a bridging member disposed for abutting contact engagement with-V said structures to complete a circuit therebetween, a ilexibie conductor one end of which is connected to` onev oi said stnictures, means connecting' the opposite end of said conductor to said bridging member, said conductor forming a loop around one end of said bridging member, an operating I of said loop.

20. In a circuit interrupter having spaced contact structures one of which is displaceable against an opposing biasing means, a bridging member disposed for abutting contact engagement with said structures to complete a circuit therebetween; the path of current between one of said contact structures and said bridging member producing a magnetic force tending to separate them, a fulcrum locked in a fixed position against said bridging member, and a flexible conductor secured to said bridging member and forming a current path to produce aA magnetic force on the side of said fulcrum remote from said one contact structure and in a direction to oppose said first-mentioned magnetic force.

21. A circuit interrupter comprising spaced contact structures formed of rigid members, a rigid bridging member in circuit-closing'v position disposed in abutting contact engagement with said members, the path of current between each structure and said bridging member producing a force tending to separate them, resilient means spaced from the regions of said abutting contact engagement for producing circuit-closing contact pressures between said bridging member and said structures, releasable operating means for rigidly locking said bridging member in circuit-closing position, and rigid means actuated directly by said operating means and engaging said bridging member intermediate its ends to form a fulcrum about which said magnetic forces oppose each other, and for equaiizing said contact` pressures.

22. A circuit interrupter comprising spaced contact structures, a rigid bridging member,

biased to a circuit-opening position, having spaced non-resilient contact surfaces for abutting contact engagement with non-resilient contact surfaces of said structures to complete a circuit for current now between them, the-paths of the current entering and leaving said member respectively producing magnetic forces tending to separate said abutting surfaces, resilient means adjacent one end of said bridging member, without said paths of current, for developing circuit-closing contact pressures between all of said abutting surfaces, means for operating said bridging member to open close said circuit and including'releasable mea'ns locked in circuitclosing-position and engaging said bridging member intermediat'e'its ends rigidly' to restrain it in circuit-closingl position and to maintain said resilient means under stress for said development of said contact pressures. said engaging means while locked in said circuit-closing position forming a iuicum about which said magnetic ioroes xopposeeach other, and means for releasing said :uw 1H' C. GRAVES, t7l.

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