US2864914A - Electric circuit breaker - Google Patents

Description

Dec. 16, 1958 w, COBURN 2,864,914

ELECTRIC CIRCUIT BREAKER Filed March 15, 1955 5 Sheefts-Sheet l hwuxtor ich A. LL/W .%M%M(M 12 Attorneys Dec. 16, 1958 w. A. COBURN 2,864,914

ELECTRIC CIRCUIT BREAKER Filed March 15, 1955 5 Sheets-Sheet 2 Attorneys Dec. 16, 1958 w. CQBURN 2,864,914

ELECTRIC CIRCUIT BREAKER Filed March 15, 1955 5 Sheets-Sheet 3 97 99 100 79 99 77 I0 57 M 92 76 w B9 as -5 M L @1175 I," a b2 59 O 7 63 m m u u v 4,9570 104- 1 8 I9 5 y 16 5 0555 17 k Z W l) 16 14 lhvuxtor ,d' Atter-mays Dec. 16, 1958 w, COBURN 2,864,914

- ELECTRIC CIRCUIT BREAKER Filed March 15, 1955 5 Sheets-Sheet 4 -10 1O '90 50 7o 90 Ambient Tampamburo Fabruxhut Dec. 16, 1958 w. A. COBURN 9.1

ELECTRIC CIRCUIT BREAKER Filed March 15, 1955 I 5 Sheets-Sheet 5 United States ELECTRIC CIRCUIT BREAKER Wallace A. Coburn, Brandon, Manitoba, Canada, assignor to C. T. Electrical Controls Limited, Brandon, Manitoba, Canada Application March 15, 1955, Serial No. 434,343 Claims priority, application Canada January 27, 1955 13 Claims. (Cl. 260-116) This invention relates to improvements in electric circuit breakers, and more particularly to current totalizing circuit breakers of the type described in United States Patent No. 2,600,734, issued to W. A. Coburn June 17, 1952.

One form of breaker constructed in accordance with Fig. 4 is a fragmentary view of the mechanism of the circuit breaker as viewed in Fig. 2, but in a different position;

Fig. 5 is a further fragmentary view of the mechanism seen in Fig. 2, many of the parts being shown in section along the line 55 of Fig. 1;

Fig. 6 is a sectional view along the line 6-6 of Fig. 1;

Fig. 7 is a view similar to Fig. 5, but showing the parts in a position intermediate that of Fig. 5 and Fig. 4; and

Fig. 8 is a diagram illustrating the operational advan tages of the circuit breaker seen in the other views.

Figures 9 to 11 are a series of diagrams demonstrating the mechanical operation of the circuit breaker seen in Figures 1 to 6, by showing a simplified version of certain parts of the same in three different positions.

This circuit breaker consists of a body shell 11 moulded from a suitable non-conducting synthetic resinous material, with a cover 12 moulded from a similar material. The underside of the shell 11 is formed with three paral lel longitudinally extending cavities 13, 14 and 15 (as best seen in Fig. 6), the central cavity 15 being substantially deeper than the outer cavities 13 and 14. On its upper side the shell 11 has two parallel longitudinally extending cavities 16 and 17, with a platform 18 extending therebetween.

The platform 18 has a transverse passage 19 (see Figs. 2, 3, 4, 5 and 7), this passage interconnecting the cavities 16 and 17 and accommodating a totalizing bar 2%) of insulating material extending transversely across the circuit breaker. This bar has bosses 21 (see Fig. 6) projecting downwardly into cavities 16 and 17. These bosses 21 are each formed with a rectangular hole 22, through each of which a bimetallic strip 23 extends, whereby upward movement of the metallic strips 23 may be transferred to the bar through adjusting screws 24.

One end of each of the bimetallic strips 23 is fastened to terminals 25 by rivets 26 (see Fig. 3). In use, wires (not shown) are connected to these terminals 25 by screws 27. The free end of each of the bimetallic strips 23 passes through one of the rectangular holes 22 in the bosses 21 of the bar 20, and carries a flexible connecting wire 29 whereby individual circuits are completed from 'ice the terminals 25 through the bimetallic strips 23 to a pair of movable contacts 28.

These movable contacts 28 (as best seen in Fig. 2) each consist of a bent strip of conducting metal, such as copper, the lower end 30 of each of these contacts 28 being permanently secured to an insulating carrier bar 33 extending transversely across the circuit breaker. The upper end of each of the contacts 28 carries a raised contact-making surface 34 of suitable material such as silver.

The carrier bar 33 which carries the contacts 28 has a centrally positioned aperture through which a brass guide rod 35 extends. This rod serves to mount the carrier bar 33 in the circuit breaker and a helical spring 36 is mounted on the rod 35 between a'fixed projection 38 extending upwardly from the platform 18, and a surface on the carrier bar 33. The aperture in this carrier bar is elliptical in cross-section so that the spring 36 will at all times bear against the edges of such aperture to urge the lower part of the carrier bar 33 to the right while permitting such bar a degree of freedom of tilting motion as later more fully explained. When the spring 36 takes charge urging the carrier bar 33 to the right as seen in Figs. 1, 2 and 5 the circuit breaker is in the open position. The rod 35 is firmly secured to the projection 33 by means of a pin 37. The other end of the rod 35 is vertically forked to provide a vertical recess into which a portion of the mechanism later to be described may travel, this forking not being visible in the drawings.

The movable contacts 28 cooperate with fixed contacts 39 each formed of a strip of suitable conducting material, such as copper, and each secured to a terminal 41 and to the shell 11 of the circuit breaker by means of a rivet 40. These fixed contacts 39 have mounted on their free ends contact-making surfaces 43 inclined to the plane of the platform 18.

Fastened directly to the undersurface of the platform 18 by means of a screw 45 is an ambient temperature compensating device, incorporating means for correcting the operation of the breaker depending upon the ambient temperature. This device includes a channelled bracket 46, the flat bottom surface 47 ofwhich is provided with a pair of slots 48 and 49 (see Figs. 5 and 7). The two side walls 50 of the bracket 46 have a maximum height at the end nearer the carrier bar 33 and taper to a minimum height at the other end. At the former end a pair of holes are drilled in the side walls 50 to act as bearings for a shaft 51 which acts as a pivot for a generally U- shaped bimetallic 'strip 52. One end of the bimetallic strip 52 has an upwardly bent leg 53 projecting into the transverse passage 19 extending across the platform 18, while the other end thereof is provided with a hole for cooperation with a screw 55 which is threaded into the centre of the bar 20 and acts to transmit the vertical movement of such bar to the bimetallic strip 52.

The manually operated mechanism of the circuit breaker consists of an operating handle 10 moulded from a suitable non-conducting material in the shape of a fiat segment of a circle. This operating handle 10 is pivotally mounted on a pin 56 extending between the main side walls 58 of a frame member 57 (see especially Figs. 1, 2 and 4), these side walls 58 being extended into a pair of wings 59 spaced more widely apart from each other than the side walls 58 (Fig. l). The frame member 57 also includes a bottom surface 60 (Figs. 5 and 7) interconnecting the side walls 58, and an end surface 61 bent up from such bottom surface 60. The bottom surface 60 includes a tapped hole into which the fixing screw 45 extends, such screw acting to fasten both the bracket 46 and the frame member 57 to the platform 18 of the shell 11. The end surface 61 of the frame member 57 also includes a tapped hole into which an adjusting screw 62 engages. This screw 62 acts to hold the operating mechanism in the shell 11, and to position the same relatively to the fixed parts by virtue of abutment of its head against a moulded projection 63 of the platform 18. The wings 59 of the frame member 57 are interconnected by a pin 64.

The operating mechanism also includes a second frame member 67, slidably mounted in relation to the first frame member 57. This second frame member 67 comprises a pair of side walls 73 joined by an end wall 92 at the end of the frame member 67 remote from the operating handle 10, and a ledge 68 situated at the end near the operating handle 10. The end wall 92 is perforated to permit passage of the rod therethrough. The side walls 73 of the second frame member 67 are provided with a pair of slots which cooperate with the pin 64 extending between the wings 59 of the first frame member 57. The spacing apart of the side walls 73 of the second frame member 67 is less than the spacing of the wings 59 of the first frame member 57, and the sec ond frame member slides between such wings 59.

The operating mechanism also includes a latch mechanism mounted within the frame member 67. The primary element of this latch mechanism is a latch member "/tl pivotally mounted between the side walls 73 of the frame member 67 by means of a pin 71, and having a free end 69 extending downwardly and towards the operating handle 10 so as, in the closed position of the circuit breaker (as seen in Fig. 4) to be in register with the upwardly extending bent leg 53 of the bimetallic strip 52. Mounted on a further pin 75 extending between the side walls 73 of the frame member 67, is a cam 77 having a step 76 normally in register with the end of the latch member remote from the end 69 thereof already referred to. The cam 77 also has a step 86 arranged to cooperate with a further pin 79 extending between the side walls 73 of the frame member 67. The cam 77 is connected to the operating handle 10 by means of a pair of links 89 pivotally mounted both to the cam 77 and to the operating handle 10 by pins 91 and 90 respectively. The cam 77 is urged in a clockwise direction, as seen in the side views, by a spring 78 mounted on the pin 75. The latch member 70 is urged in a clockwise direction as seen in the side views, by means of a tongue shaped wire spring 72. A bushing 83 is positioned on the pin between the cam 77 and one of the side walls 73 of the frame member 67, to retain such cam centrally of such frame member, the spring 78 serving a similar purpose on the other side of the cam.

The operating handle 10 isbiased to the open position of the switch, i. e. the position shown in Figs. 2 and 5, by means of a coiled spring 84 extending between a projection 85 on the undersurface of the operating handle til and a recess 86 formed aroundv a central column 87 projecting from the platform 18, an adjusting screw 83 extending through the platform 18- and along the column 87. The position of this screw determines/the limit of anti-clockwise movement of the operating handle 10.

The operating mechanism is restrained from lateral displacement by means of a pair of parallel projections 93 extending upwardly from the platform 18, and engaging the outer edges of the wings 59 of. the frame member 57.

The carrier bar 33 is formed with a pair of hoods 97 arranged over the contacts 28, and with a vertically extending central recess in its rear surface. The face of this recess, which is pressed by the spring 36 against the end wall 92 of the second frame member 67, consists of two inclined portions. The upper portion 99 of this face extends downwardly and slightly to the rightas seen in Figs. 5 and 6, and the lower portion 96 is inclined downwardly and inwardly of the carrier bar 33, these two portions 99 and 96 forming at their line of junction a ridge 100 which is the part against which the wall 92 normally bears in the open position of the switch (see Fig- 5).

The shell 11 of the circuit breaker is moulded to provide two pairs of arc chutes 101 (Fig. 3) interconnecting cavities 1S and 16 and cavities 14- and 17. In longitudinal alignment with these are chutes 101, there is a further pair of arc chutes 102 (see Fig. 1) formed in the side walls of the circuit breaker. A tapped hole 95 is provided in the platform 18 to receive a screw (not shown) employed for holding the cover 12 in position over the mechanism of the circuit breaker. This cover 12 has a slot 103 of conventional design, through which the finger grip portion of the operating handle 10 extends and along which such finger grip portion may travel. A slot 104 is formed in the platform 18 to allow movement of the screw 45 on adjustment of the first frame number 57.

The operation of the circuit breaker is as follows:

in the off position of the circuit breaker, shown in Figs. 2, 5 and 9 the carrier bar 33 carrying the moving contacts 28 is in its extreme right hand position and is pressed lightly by the spring 36 against the end wall 92 of the second frame member 67. In this position the bar 33 is tilted somewhat anti-clockwise, as seen in Figs. 2, 5 and 9. When the circuit breaker is to be placed in the on position, the operating handle it) is moved manually in an anti-clockwise direction to exert a closing force, as demonstrated by the arrow C in Figs. 9 to 11, acting through the wall 92. The carrier bar may be considered as having two motions:

(a) Translatory motion between a contacts-disengaged position and a contacts-engaged position (this takes place along the line X which defines the axis of the rod 35); and

(b) Limited tilting motion, about ridge 100, between two orientations.

The first orientation is such that the plane P2 defined by the fiat contact-making surfaces of the bar-mounted contacts 34 is parallel to the plane P1 defined by the contact-making surfaces of the fixed contacts 43. This orientation is illustrated in Figure 11, where the planes P1 and P2 are in fact coincident, the contacts 34 and 43 being fully engaged face to face. This view corresponds to Figure 4 of the structural drawings and the on position of the circuit breaker.

The second tilted orientation is defined as being such that the bar-mounted contacts 34 are displaced towards the fixed contacts 43 with the planes P1 and P2 inclined to each other. This second orientation of the bar is illustrated in Figure 10, while as already indicated Figure 9 shows the relaxed condition when the switch is fully open and before the closing force C or opening force 0 have any significant tilting effect.

The spring means (force 0) urge the bar 33 both into contacts-disengaged position, i. e. to the right in respect of translatory motion, and into the second tilted orientation, i. e. anti-clockwise" about the point of contact of the ridge and the plate 92. The closing means (force C) act on the bar 33 for moving such bar against the force 0 from the contacts-disengaged position towards the contacts-engaged position. The initial effect of the operation of such closing force is demonstrated in Figure 10 in which the main part of the translatory motion of the bar towards the engaged position has taken place, and in which the spring means, which began effectively to tilt the bar to its second orientation as soon as the closing translatory movement began, still prevail to hold the bar in such second tilted orientation. It will thus be apparent that the closing means are such as to move the bar towards contacts-engaged position to effect tilting of said bar from said second orientation to said first orientation on engagement of the contacts,.the manner of this operation appearing from a comparison of Figures 10 and 11. Once the contacts touch there will be a reaction force exerted by the fixed contacts 43 on the bar-mounted contacts 34. This force is indicated by the arrow R in Figure 10 and it will be seen that it acts substantially along the surface S (which is the imaginary surface traced out by the centre points of the bar-mounted contacts in moving in contacts-engaged position) and thus exerts a clockwise turning moment on the bar about its point of pivot which is the ridge 16f}. This clockwise turning moment will overcome the anti-clockwise turning moment of the combined forces 0 and C so that the bar will be turned from the second to the first tilted orientation with the contact surfaces engaging firmly with their faces in the same coincident plane, i. e. the Figure 11 condition. If the circuit breaker were of the single pole type which is within the contemplation of the invention, then the surface S traced out by the line joining the centre points of the bar mounted contacts is effectively replaced by a line traced out by movement of the single bar-mounted contact.

In the closed position of the circuit breaker the pin 90 is below the line joining the pin 91 to the pivot pin 56 of the operating handle 10, so that the compression force in the links 89 acts to hold the operating handle in the newly acquired position against the force of the spring 84.

The operation just described whereby the contact surfaces 34 and 43 act to rotate the carrier bar 33 causes them to slide along one another to produce a wiping and rolling action between the individual contacts of each pair which is highly advantageous for cleaning the surfaces. This action takes place both in closing and opening of the circuit breaker. The reverse action on opening of the circuit breaker facilitates separation of the surfaces 34 and 43 in the event that there may have been some welding action between such surfaces due to over-heating.

It is a further valuable feature of the invention that one single main spring 36 is used both to open the circuit breaker on tripping and also to provide pressure between the contacts when the circuit breaker is held in the closed position by the toggle-like mechanism of links 89 and operating handle 10. This main spring provides the contact pressure by virtue of the low position at which it bears against the carrier bar 33. The force 0 of the spring when it is compressed in the closed position of the circuit breaker (Figure 11) tends to rotate the carrier bar 33 anticlockwise about the ridge 109. This anticlockwise turning moment forces the contact surfaces 34 and 43 firmly together.

During the movement of the circuit breaker from the off to the on position the cam 77 has acted merely to transmit the force applied to the operating handle 10, and has remained in its extreme clockwise position, being held in this position by the latch member 70. The cam 77 then lies between the forked ends of the rod 35.

If the circuit breaker is to be moved manually from the on position to the off position, this is accomplished by movement of the operating handle 10 in the clockwise direction with simple reversal of the movements already described.

On' i h e occurrence of an overload on either of the two circuits controlled by this circuit breaker, one or other or both of the bimetallic strips 23 will be caused to flex and press upwardly on the screws 24 of the bosses 21 of the totalizing bar 20. This has the effect of elevating the centre of such bar to an extent dependent upon the main elevation of the two ends of the bar 20. The movement of the center of the bar 20 is thus a function of the total overload in the two circuits flowing through the circuit breaker.

As fully explained in United States Patent No. 2,600,734, issued to W. A. Coburn, June 17, 1952, the arrangement of a totalizing bar with a pair of bimetallic strips engaging each end of the bar provides a movement of the centre of the bar which is particularly suitable for operation of the tripping mechanism of a circuit breaker employed in a three-wire single phase type of supply circuit. It is common, for example, to rate such a totalizing circuit breaker as, say, 25-41 amps. This means that with a perfectly balanced load the circuit breaker will trip at a given overload, usually approximately 125 percent, of a rated load of 25 amps. in each strip, i. e. in each half of the three-wire circuit. When the load is totally unbalanced, that is to say if all the load is on one half of the three-wire circuit, all the current will pass through one of the bimetallic strips and no current will pass through the other. Under these conditions the breaker will trip at the same overload (125 percent) on the rated current of 41 amps. in the loaded strip. It will be noted that this current of 41 amps. in one half of the circuit represents 82 percent of the load that would be imposed upon the secondary of the transformer from which the circuit is supplied with balanced currents of 25 amps. in each half of the circuit. Approximately percent of the transformer rated load is normally about the maximum load that can be safely imposed upon one half of the secondary of a normal supply transformer when the other half of the transformer is unloaded.

The fact that it does not require 50 amps. in one of the strips, when the other strip carries no current, to move the centre point of the totalizing bar the same distance as it would be moved by a current of 25 amps. in each of the strips, follows from the fact that the heat generated in each strip is a function of the square of the current passing through such strip. This tends to reduce the unbalanced current at which the circuit breaker will trip, but acting to increase thi current is the further fact that the rate of loss of heat from the bimetallic strip carrying the high load is disproportionately great by reason of its higher temperature. The former factor prevails however and in most cases reduces the unbaianced tripping current to about 80 percent of the sum of the two balanced currents. Special provision can be made for varying this percentage by control of the heat dissipation from the bimetallic strips or by variation of the manner in which the strips are connected to the totalizing bar. The strips may be connected other than through the adjusting screws 24, and, in particular, they may bear directly against flat surfaces on the ends of the totalizing bar so that, as such bar is tilted, edges of the strips rather than flat surfaces thereof engage the bar, these edges then being at different distances from the central point of the bar. In this Way the lever arms between the strips and the centre of the bar can be varied, leading to variation in the percentage of the full load at which the circuit breaker can be tripped by a fully unbalanced load.

It will be appreciated that, in practice, a completely balanced or a completely unbalanced load is seldom obtained. With semi-unbalanced loads conditions intermediate between the two extremes already discussed, will pertain.

In the circuit breaker under consideration as an embodiment of the present invention, the upward movement of the centre of the totalizing bar 20 is transmitted through the screw 55 to the bent bimetallic strip 52 and thus to the upwardly bent leg 53 thereof by rotation of the strip 52 as a whole about the pin 51. When an overload for which the circuit breaker has been set, is reached, the leg 53 will have been moved upwardly sufficiently to come into contact with the end 69 of the latch member 70, to force such end 69 upwardly and rotate the latch member 70 about its pivot pin 71 until the other end of such latch member 70 is moved away from the step 76 on the cam 77. This movement frees the cam 77 for anti-clockwise rotation. Only a slight anti-clockwise rotation of this cam is necessary to reduce the com pression in the links 89 sufficiently to allow the spring 84 acting on the undersurface of the operting handle 10 to take charge of such operating handle 10 and rotate it clockwise. Fig. 7 has been provided to illustrate the positions that the parts will assume instantaneously very shortly after this tripping action. As soon as the toggle type of mechanism formed by the links 89 has thus been broken, the spring 36 takes charge of the carrier bar 33 to return it to the off position. Moreover, as the parts begin to move backwardly to the off position, the spring 78 returns the cam 77 to its original position with the step 89 abutting against the pin '79 and preventing further clockwise rotation. This return movement of the cam 77 moves the step '76 to the left again so that the end of the latch member '70 may move up into re-engagement therewith as soon as the leg 53 of the bimetallic strip 52 has moved downwardly after sufficient cooling of the bimetallic strips 23.

The purpose of the bimetallic strip 52 is to compensate for variations of ambient temperature. The effect of this compensation is illustrated by the diagram of Figure 8 which shows approximately the balanced load performance of a totalizing circuit breaker rated at 254l amps, firstly without ambient temperature compensation (line A) and secondly with ambient temperature compensation (line B). The diagram of Figure 8 has been prepared on the basis of a completely balanced lead but corresponding effects would be obtained with partly and wholly unbalanced loads. It will be seen from the temperature scale forming the abscissa of this diagram that the uncompensated circuit breaker has been adjusted to provide correct operation at a temperature of 72 F., i. e. the temperature at which line A crosses the scale marking of 3t amps, i. e. approximately 125 percent of the rated 25 amps. To the right of this point on the diagram, that is to say under the conditions likely to occur in summer, especially if the circuit breaker is exposed to the direct rays of the sun, it will be seen that line A drops well below line B and that at the extreme edge of the diagram, i. e. 140 F., the circuit breaker will trip at a balanced load of approximately 22 amps, which is even below the rated tripping current and allows no provision for overload. The reason for this drop of the curve, is, of course, that the main operating bimetallic strips 23 are already considerably heated by the atmosphere before the effects of the current are felt. Since it is common to settle the terms of supply of electric power to the consumer on a basis of the maximum demand that the consumer may draw from the mains, as determined by the setting of the circuit breaker, the consumer will clearly be penalized under these conditions.

On the other hand, in winter, when the heat supplied by the current to the bimetallic strips will be required to compensate for the effects of the low ambient temperature, the consumer will be able to draw from the mains a current in excess of that agreed upon with the utility as being his maximum. Under these conditions it is the supplying utility that suffers, as is illustrated by the left-hand end of line A.

It will be seen from line B that when an auxiliary bimetallic strip is employed substantially a uniform tripping of the circuit breaker at 125 percent overload of the rated current will be achieved at all normal operating temperatures. To achieve this effect, it is theoretically desirable to make the bimetallic strip 52 equal in effective length to each of the bimetallic strips 24. As a practical matter, the length of the bimetallic strip 52 will normally be made slightly greater than the length of each of the strips 24 in order to off-set a slight loss of lever arm incurred in transmitting the movement of the tripping force through the strip 52 to the latch mechanism.

An important feature of the present invention is the arrangement of the ambient temperature compensating strip 52 in a cavity of the shell of the circuit breaker well insulated from the cavities in which the main bimetallic strips 24 are housed. If this were not so, the strip 52 would tend to have its temperature raised above the ambient temperature by transfer of heat from the main strips 24. The particular arrangement of the embodiment of the invention illustrated in the accompanying drawings in which a centrally raised platform 18 forms at each side the cavities l6 and 317 for the strips 24, while underneath providing the cavity 15 for the compensating strip 52, is a particularly satisfactory and compact arrangement which admirably accomplishes this end.

Other important features of the invention are the wiping and rolling action which takes place when the contact surfaces 34 and 43 are brought together (by virtue of the ridge on the carrier bar 33) and the reverse wiping and rolling action which takes place when the circuit breaker is opened. This reverse action, i. e. a sliding one upon the other of the contact surfaces 34 and 43 greatly facilitates separation of these surfaces in the event that there may have been some welding action between such surfaces due to over-heating.

It is also a valuable feature of the invention that one single main spring 36 is used both to open the circuit breaker on trippingand also to provide pressure between the contacts when the circuit breaker is held in the closed position shown in Figure 4 by the toggle-like mechanism of links 89 and operating handle 10. This main spring provides the contact pressure by virtue of the low position at which it bears against the carrier bar 33. The force of the spring when it is compressed in the closed position of the circuit breaker tends to rotate the carrier bar 33 anti-clockwise about the ridge lltiti which is situated above the point of bearing of the spring 36 against such bar, as seen from Figures 2, 4, 5 and 7. This anti-clockwise turning moment forces the contact surfaces 34 and 43, which in turn are above the level of the ridge 100, firmly together.

Under certain circumstances, such as when the manufacturing costs are of paramount importance, the ambient temperature compensating device and its supporting parts may be omitted from the circuit breaker, the totalizing bar then bearing directly on the latch member 78 or through some suitable direct connection.

I claim:

1. An electric circuit breaker having a pair of fixed contacts, a pair of ganged contacts movable into and out of contact each with one of said fixed contacts whereby to make and break a pair of independent electric circuits, a totalizing bar, a pair of main bimetallic elements each arranged to be heated by the current in one of said circuits and each acting on one end of said totalizing bar, a latch mechanism for tripping the movable contacts, arranged for actuation by movement of a part of said bar intermediate its ends, and auxiliary bimetallic means arranged in the path of transmission of movement from said main bimetallic elements to said latch mechanism, said auxiliary bimetallic means being arranged so as to compensate for deflection of the main bimetallic elements due to ambient temperature fluctuations.

2. An electric circuit breaker having a pair of fixed contacts, a pair of ganged contacts movableinto and out of contact, each with one of said fixed contacts whereby to make and break a pair of independent electric circuits, a totalizing bar, a pair of main bimetallic elements each arranged to be heated by the current in one of said circuits and each acting on one end of said totalizing bar, a latch mechanism for tripping the movable contacts, and an auxiliary bimetallic element co-acting with a part of said bar intermediate its ends to transmit movement thereof to said latch mechanism, said auxiliary bimetallic element being arranged so as to compensate for deflection of the main bimetallic elements due to ambient temperature fluctuations.

3. A circuit breaker as claimed in claim 2, wherein said auxiliary bimetallic element is separated from said main bimetallic elements by partition walls.

4. A circuit breaker as claimed in claim 2, including a rectangular supporting shell of insulating material having a central longitudinally extending platform with partition walls depending from the lateral edges thereof to define a pair of longitudinally extending lateral cavities on one face of the shell and a longitudinally extending central cavity on the other face of the shell, the latter cavity being separated from the former cavities by said partition walls, wherein said main bimetallic elements are in the form of elongated strips each extending along one of said lateral cavities, and the auxiliary bimetallic element is in the form of an elongated strip disposed in the central cavity. a

5. A circuit breaker as claimed in claim 4, wherein the auxiliary bimetallic strip is bent upon itself, one end of said strip being coupled with the intermediate point of the totalizing bar while the other end is positioned for cooperation with said latch mechanism, which latter is mounted on said platform.

6. An electric circuit breaker having a pair of fixed contacts mounted in side-by-side relationship, a rod, an elongated bar extending transversely to said rod and loosely slidably mounted at its centre thereon, said bar carrying a contact at each end positioned for cooperation with one of said fixed contacts, closing means for moving said bar to contacts-engaged position, a coil spring extending along said rod between a fixed abutment and a surface of said bar and urging said bar to contacts-disengaged position, a surface on the centre of said bar presenting to said closing means a longitudinally extending ridge parallel to the line joining the contacts mounted on said bar, said ridge lying in a plane intermediate between and parallel to a pair of mutually parallel planes in one of which lies said line and in the other of which lies the longitudinal axis of the rod.

7. An electric circuit breaker having a pair of fixed contacts counted in side-by-side relationship, a loosely slidably mounted bar carrying a pair of contacts positioned each for engagement with a respective one of said fixed contacts, spring means urging said bar to contacts-disengaged position, said spring means acting on said bar at a point displaced from a surface generated by the line joining the center points of the bar-mounted contacts in moving into contacts-engaged position, and closing means for moving said bar to contacts-engaged position, said closing means acting on said bar between said surface and the plane parallel thereto which passes through the point of said bar acted upon by the spring means.

8. An electric circuit breaker having a pair of fixed contacts mounted in side-by-side relationship, a loosely slidably mounted elongated bar carrying a contact on each end positioned for engagement with a respective one of said fixed contacts, spring means urging said bar to contacts-disengaged position, said spring means acting on a central point of said bar intermediate between said bar-mounted contacts and displaced from a surface generated by the line joining the center points of the barmounted contacts in moving into contacts-engaged position, and closing means for moving said bar to contacts-engaged position, said closing means acting centrally on said bar between said surface and the part of said bar acted upon by said spring means.

9. An electric circuit breaker having a pair of fixed contacts mounted in side-by-side relationship, a loosely horizontally slidably mounted, elongated, horizontally extending bar carrying a contact at each end positioned for engagement with a respective one of said fixed contacts, spring means urging said bar to contacts-disengaged position, said spring means acting on a central part of said bar intermediate between said bar-mounted contacts and at a level different from that of a surface generated by the line joining the center points of the bar-mounted contacts in moving into contacts-engaged position, and closing means for moving said bar into contacts-engaged position, said closing means acting centrally on said bar at a level between said surface and the level at which said spring means act on said bar.

10. An electric circuit breaker having a fixed contact, a loosely slidably mounted member carrying a contact positioned for co-operation with said fixed contact, opening means acting continuously on said member to urge it to contacts-disengaged position, said opening means acting on a part of said member displaced from a line generated by the center point of the member-mounted contact in moving into contacts-engaged position, and closing means having flat contact-making surfaces lying in a first common plane; a bar carrying a pair of contacts for cooperation each With a respective one of said fixed contacts, such bar-mounted contacts having flat contactmaking surfaces lying in a second common plane; means mounting said bar for translatory motion between a contacts-disengaged position and a contacts-engaged position and for limited tilting motion between two orientations, said tilting motion being about an axis parallel to the line joining the bar-mounted contacts, the first of said orientations being such that said planes are parallel to each other and the second of said orientations being such that the bar-mounted contacts are displaced towards the fixed contacts with said planes inclined to each other; spring means urging said bar to contacts-disengaged position and into said second tilted orientation; and closing means for effecting translatory movement of said bar against the force of said spring means from contactsdisengaged into contacts-engaged position whereby to eifect tilting of said bar from said second orientation to said first orientation on engagement of said contacts.

12. An electric circuit breaker comprising: a pair of fixed contacts mounted in side-by-side relationship and having flat contact-making surfaces lying in a first common plane; a bar carrying a pair of contacts for cooperation each with a respective one of said fixed contacts, such bar-mounted contacts having fiat contact-making surfaces lying in a second common plane; means mounting said bar for translatory motion between a contacts-disengaged position and a contacts-engaged position and for limited tilting motion between two orientations, said tilting motion being about an axis parallel to the line joining the bar-mounted contacts, the first of said orientations being such that said planes are parallel to each other and the second of said orientations being such that the bar-mounted contacts are displaced towards the fixed contacts with said planes inclined to each other; spring means urging said bar to contacts-disengaged position and into said second tilted orientation; and closing means for effecting translatory movement of said bar against the force of said spring means from contactsdisengaged into contacts-engaged position whereby to etfect tilting of said bar from said second orientation to said first orientation on engagement of said contacts, said spring means acting on a part of said bar displaced from a surface generated by the line joining the center points of the bar-mounted contacts in moving into contacts engaged position, and said closing means acting on said bar between said surface and the plane parallel thereto which passes through the point of said bar acted upon by said spring means.

13. An electric circuit breaker comprising a fixed contact having a flat contact-making surface defining a first plane, a loosely slidably mounted member carrying a contact positioned for co-operation with said fixed contact, such member-mounted contact having a flat contactmaking surface defining a second plane, means mounting said member for translatory motion between contactsdisengaged position and contacts-engaged position and for limited tilting motion between two orientations, such tilting motion being about an axis generally transverse to a line generated by the center point of the membermounted contact in moving into contacts-engaged position, the first of said orientations being such that said planes are parallel to each other and the second of said orientations being such that the member-mounted contact is displaced towards the fixed contact with said planes inclined to each other, spring means acting on said member to urge it to contacts-disengaged position and into said second tilted orientation, and closing means for etfecting translatory movement of said member against the force of said spring means from contacts-disengaged into contacts-engaged position whereby to effect tilting of said member from said second orientation to said first orientation on engagement of said contacts, the manner of mounting of said member being such that in moving into contacts-engaged position, said membermounted contact wipes across the face of said fixed contact.

References Cited in the file of this patent UNITED STATES PATENTS 1,886,477 Getchell Nov. 8, 1932 12 OKeeffe May 23, 1933 Jackson Oct. 11, 1938 Von Hoorn Dec. 26, 1939 Van Valkenburg et al. Aug..19, 1947 Overturf Feb. 8, 1949 Randell Ian. 8, 1952 Coburn June 17, 1952 Ingwersen Jan. 13, 1953 Allen Oct. 20, 1953 Dyer et a1. Jan. 19, 1954 Cole et a1 June 15, 1954 Cellerini et a1 Nov. 2, 1954 Hulbert Mar. 1, 1955 Walton et a1. June 5, 1956 FOREIGN PATENTS France Nov. 3, 1938

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