US3307124A - Pushbutton-controlled overload circuit breaker - Google Patents

Description

Feb. 28, 1967 J. ELLENBERGER 3,307,124

PUSHBUTTON-CONTROLLED OVERLOAD CIRCUIT BREAKER Filed June 24, 1965 4 Sheets-Sheet 1 WNTORHEIS Feb. 28, 1967 J. ELLENBERGER 3,307,124

PUSHBUTTON-CONTROLLED OVERLOAD CIRCUIT BREAKER Filed June 24, 1965 4 Sheets-Sheet 2 INVENTOR; M05 ELLENBERGE/g" Feb. 28, 1967 J. ELLENBERGER 3,307,124

PUSHBUTTON-CONTROLLED OVERLOAD CIRCUIT BREAKER Filed June 24, 1.965 4 SheetsSheet 3 BNVENTOR JHKOB ELLE/VBERGER MMW00W Feb. 28, 1%? J. ELLENBERGER 330579124 PUSHBUTTON-CONTROLLED OVERLOAD CIRCUIT BREAKER Fil ed June 24, 1965 4 Sheets-Sheet 4.

INVENTORJHKOB ELLENBERGER g7 a W United States Patent Office 3,307,124 PUSHBUTTON-CONTROLLED ()VERLOAD CIRCUKT BREAKER Jakob Ellenberger, Aitdorf, near Nurnberg, Germany, as-

signor to Ellenberger & Poensgen G.m.b.H., a German firm Filed June 24, 1965, Ser. No. 466,533 Claims priority, application Germany, June 30, 1964, E 27,312 7 Claims. (Cl. 33535) The present invention relates to a pushbutton-controlled overload circuit breaker for high rated currents which is provided with a thermal and electromagnetic release and with a trip-free release and, if desired, with a manual release.

The known overload circuit breakers of this type have the disadvantage of being of a relatively complicated design and large size and of lasting only for a short time since, even though they break the circuit instantaneously, they do not also close the circuit instantaneously and their contacts are therefore burned off very soon.

It is an object of the present invention to provide an overload circuit breaker of the above-mentioned type which overcomes these disadvantages of the known circuit breakers and is designed so as to be easily manufactured and installed, to occupy a very small space, to have a long service life, and to be insensitive to shocks, vibrations, and accelerations so as to render it suitable especially for use in a vehicle.

For attaining this object, the invention provides the circuit breaker with two current conductors which are located within the same plane and may be electrically connected with each other by a contact bridge which is movable vertically thereto and forms a substantially Q? shaped loop in which the core of the magnet for the electromagnetic release of the circuit breaker is provided and which is connected in parallel to the bimetal strip for the thermal release. The circuit breaker according to the invention is further provided between the loop and the contact bridge with a two-armed lever which is connected to the pushbutton when the latter is being depressed and the pivot pin of which is slidable within slots in the direction of movement of the pushbutton and is also pivotable within these slots. By an engagement of a pawl with this pivot pin, this lever may be arrested in a position in which its arm facing the contact bridge will press the contact bridge against the two current conductors by means of a spring which acts upon the other arm of the two-armed lever.

The substantially Q -shaped loop of the circuit breaker according to the invention forms the winding of the electromagnet, the magnet core of which is provided within the loop. This permits the circuit breaker to be made of a very small size. This small size is further due to the fact that the bimetal strip is connected in parallel to the loop, since within the area of the bimetal strip the loop is electrically designed so that, when heated and thereby bent, the bimetal strip will effect the desired thermal release. By the provision of a contact bridge, the make and break effects are distributed to and taken up by two connecting points. For attaining a trip-free release, the overload circuit breaker according to the invention is provided with a two-armed lever which for the purpose of saving in space is located between the loop and the contact bridge and is pivotable and slidable in the direction of movement of the pushbutton and .also adapted to be connected to the pushbutton when the latter is being depressed to the on position. This connection between the pushbutton and the two-armed lever is again severed 3,367,124 Patented Feb. 28, 1967 when the pushbutton is fully depressed. Therefore, when the pushbutton is in the on position, it is no longer connected to the two-armed lever and when the contact bridge is in the on position, this lever is then merely held by the pawl. Consequently, when the pawl is released by a thermal or electromagnetic action, the twoarmed lever and thus also the contact bridge may move independently of the pushbutton and thus permit a tripfree release of the circuit breaker.

For reducing the size of the circuit breaker to a further extent, the pawl may in its locking position engage directly upon the armature of the electromagnetic release which is acted upon by the bimetal strip. A relatively small force will then suflice in order to pivot the armature to its inactive position. This permits an extremely rapid release of the circuit breaker by means of such small forces that the magnetic system of the electromagnetic release may be made of a relatively small size.

Another feature of the invention consists in providing the arm of the two-armed lever which faces the loop with at least one projection which extends in the direction toward the current conductors and is provided with a recess which, when the contact bridge is in the on position, is located outside of the path of movement of a catch on a control rod which is rigidly secured to the pushbutton and preferably provided with a longitudinal slot along which it is guided on the pivot pin of the pawl. When the contact bridge is in its off position in which the mentioned arm of the two-armed lever engages upon a stop, the recess in the projection on this .arm is located within the path of movement of this catch. In the off position, this arm of the two-armed lever which faces the loop therefore engages upon a stop, and the pivot pin of the two-armed lever engages upon the upper end of the guide slots so that the two-armed lever will then be in an inclined position, while when the lever is in the on position, it will be in a horizontal position in which it cannot be acted upon by the catch on the control rod so that the trip-free release will then be possible. If the pushbutton is depressed when the contact bridge is in its off position, the two armed lever will be taken along by the catch on the control rod and the pivot pin of this lever pivots the pawl to its locking position. When the finger is then taken off the pushbutton, the pivot pin of the two-armed lever engages against the pawl. As soon as the catch on the control rod disengagcs from the recess in the projection on the two-armed lever, the latter is suddenly pivoted by spring action which, in turn, causes the contact bridge to be suddenly moved to its on position. Due to this rapid connecting movement, the switch contacts of the circuit breaker according to the invention will be protected and the circuit breaker will remain properly operative for a very long time. The manner of guiding the control rod by means of a slot on the pivot pin of the pawl has the advantage that the pushbutton and the control rod will be very simply prevented from turning.

The contact bridge may be secured to a slide member which is acted upon by a disconnecting or release spring and is provided with an aperture or recess into which the other arm of the two armed lever engages. When the circuit breaker is in its on position, this arm engages upon the lower end of the aperture or recess against the action of the release spring, and when the circuit breaker moves to its off position, this arm engages under the action of the spring against the upper end of the aperture or recess. When the circuit breaker is released, the pawl disengages from the pivot pin of the two-armed lever so that the spring which acts upon the arm of the lever which faces the loop presses this arm against its associated stop and the entire two-armed lever is thereafter pivoted about this stop. During this pivoting movement, the

other arm of the two-armed lever which faces the contact bridge hits against the upper end of the aperture or recess in the slide member carrying the contact bridge and thereby supports and increases the action of the release spring and accelerates the disconnecting movement of the contact bridge.

For simplifying the manufacture, assembly, and installation of the switch mechanism of the circuit breaker, this mechanism is preferably mounted within a metal frame which is provided on the upper side from which the pushbutton projects with an insulating plate which is secured to the base of the circuit breaker by means of bolts which also secure the current conductors to the base.

In order to prevent the circuit breaker from being accidentally released due to impacts, strong vibrations, shocks or accelerations which may occur, for example, if the circuit breaker is installed in a vehicle, it is provided with a pair of manual release knobs which are mounted on the insulating plate at the opposite sides of the pushbutton so as to be slidable toward each other in a direction vertical to the axis of the pushbutton, and with a two-armed safety lever which is mounted on the insulating plate so as to be pivotable against the action of a return spring about the axis of the pushbutton. One arm of this safety lever is provided with an end surface which in the neutral position of this lever is located Within the path of movement of a pin on one of the manual release knobs and thus prevents this knob from being moved and the pin thereon from acting upon the armature, while the other arm of this lever is provided with an inclined slot into which the pin engages which is secured to the other manual release knob. This construction has the advantage that it permits the circuit breaker to be released only if both manual release knobs are actuated simultaneously. If only one of these release knobs is actuated, for example, the knob which acts upon the armature, its release pin will hit against the end surface of the first arm of the safety lever and thus prevent this knob from moving. If only the other manual release knob is actuated, the safety lever will merely be pivoted without affecting the first knob. If, however, both knobs are moved simultaneously toward each other, the two-armed safety lever will first be pivoted about the axis of the pushbutton by the knob, the pin of which slides along the slot in the one arm of the lever so that the end surface of the other arm of the lever will move laterally away from the pin on the other knob which acts upon the armature so that this knob will then be free to be moved so as to effect the manual release of the circuit breaker.

In order to prevent the armature of the electromagnetic release also from being affected by strong vibrations, impacts, shocks, or accelerations, this armature is provided in the form of a two-armed lever, one arm of which when in the attracted position nearly closes the magnetic circuit between the magnet core and a magnet yoke which is pivotable with considerable friction on the magnet core, While the other arm of this lever is substantially U-shaped and one side wall of the U is adapted to hold the pawl in its locking position, while the other side wall of the U may be acted upon by. the pin on the manual release knob which is associated with the mentioned end surface of the safety lever.

Since the armature forms a two-armed lever, it may be designed so that its center of gravity is located at or near its pivot point. This construction prevents the armature from being pivoted as the result of impacts, strong vibrations, accelerations or the like, and it insures that the armature will only be pivoted at the occurrence of excess currents or short circuits.

The features and advantages of the present invention will become more clearly apparent from the following detailed description thereof which is to be read with reference to the accompanying drawings, in which- FIGURE 1 shows a side view of a fully enclosed overload circuit breaker according to the invention;

FIGURE 2 shows a view of the circuit breaker, as seen from the left of FIGURE 1;

FIGURE 3 shows a vertical longitudinal section of the circuit breaker according to FIGURE 1 in the on position;

FIGURE 4 shows a view of the circuit breaker, as seen from the left of FIGURE 3, and partly in a vertical section which is taken within a plane passing through the loop of one of the current conductors;

FIGURE 5 shows a vertical section similar to FIGURE 3, but in which the circuit breaker is shown in the off position;

FIGURE 6 shows a view similar to FIGURE 4, but in which the circuit breaker is shown in its off position according to FIGURE 5;

FIGURE 7 shows a top View of the circuit breaker according to FIGURES 4 and 6, and partly in a section which is taken within a plane passing through the two manual release knobs; while FIGURE 8 shows the same top view as in FIGURE 7, but with the two manual release knobs being shifted to the position toward the pushbutton.

As illustrated in the drawings, the overload circuit breaker according to the invention comprises a housing of insulating material which consists of a base 1 and a cap 2, and two terminal strips 3 and 4 projecting in opposite direction from and between the base 1 and cap 2, and carrying connecting screws 5 with nuts 6 thereon. A pushbutton 7 and two manual release knobs 8 and 9 project through the upper side of the housing 2. At the inside of the housing, the terminal strip 3 continues as a current conductor 3' which forms a loop 10 in which the core 12 of an electromagnet is secured by means of a screw 11. This core carries a yoke 14 which is connected to the core 12 by means of a rivet 13 in a manner so as to be pivo ta'ble with such a considerable friction that its position relative to the core 12 can be changed only by means of a suitable tool. Yoke 14 has an arm 15 which is bent so as to extend in the direction toward an arm 16 of the armature 17 of the magnet. Yoke 14 is pivotable as described for the purpose of adjusting the size of the air gap between the yoke and the arm 16 of the armature 17 and for thus adjusting the electromagnetic release of the circuit breaker. The arm 16 of armature 17 has a pair of tabs 18 thereon which are adapted to be directly acted upon by a 'bimetal strip 19 which may be U-shaped and the two arms of which are secured to the current conductor 3, for example, by being screwed, soldered or welded thereto. The gap 20 in the contact bar 3 underneath the loop 10 is bridged by the bimetal strip 19. The bimetal strip carries an angular part 21 which engages upon a conical tip 22 of a setscrew 23. By turning this setscrew 23 it is possible to move the bimetal strip 19 more closely toward or farther away from the tabs 18 on the arm 16.

The armature 17 is pivotably mounted on a pin 24 which is secured within a frame 25, and its upper part is U-shaped. One side wall 26 of this U-shaped part is acted upon in a radial direction of pin 24 by a pawl 27, while the other side wall 28 which has an inclined surface 30 may be acted upon by a pin 29 on a manual release knob 8 when the latter is shifted in the direction toward the axis of the push-button 7 so that the armature 17 will then be pivoted in a counterclockwise direction, as seen in FIGURE 4, and against the action of a torsion spring 31 which is mounted on pin 24, so that the side wall 26 will then disengage from the pawl 27. One arm of the torsion spring 31 acts upon the side wall 28 of the U- shaped part of the armature 17, while the other arm of this spring acts upon a part 32 of the frame 35.

Pawl 27 is made of sheet metal and bent so as to be substantially U-shaped, and it is pivotably mounted on a pin 33 which is secured to the frame 25. Each of the two parallel arms or walls of pawl 27 is provided with a detent 34 and a projection 35. By means of the detents 34, pawl 27 is adapted to hold a two-armed lever 36 in the horizontal position as shown in FIGURE 3. The left arm 37 of lever 36 is acted upon 'by the upper end of a compression spring 38 which is loosely wound around a rod on pin 39 which is rigidly secured to a part 40 of frame 25 which supports the lower end of spring 38. The arm 37 of lever 36 is provided on both sides thereof with downwardly projection lugs 41 between which the pin 39 with the spring 38 thereon is located. Near its lower end, each of these lugs 41 has a recess 42.

The two current conductors 3' and 4 are provided with fixed contacts 43 and 44 which are operatively associated with corresponding contacts on a contact bridge 45 which, when the circuit breaker is in the on position as shown in FIGURE 3, are in firm engagement with the contacts 43 and 44. The contact bridge 45 is secured to a slide member 46 which is movable in the vertical direction by being guided in apertures in the horizontal parts 47 and 48 of the frame 25. Slide member 46 is provided with a recess 49 into which the arm 50 of the two-armed lever 36 engages. In the on position of the circuit breaker as illustrated in FIGURE 3, this arm 50 engages upon the lower end 51 of the recess 49. Arm 50 may also cooperate with the upper end 52 of recess 49 in a manner as will be later described.

The two-armed lever 36 is provided with a pair of bent-over tabs 53 in which a pivot pin 54 is secured which in the on position of the circuit breaker as shown in FIGURE 3 engages with the detents 34 on lever 36. This pivot pin 54 is slidable in the vertical direction and also pivotable in slots 55 in the two side walls 25 and 25" of frame 25.

When the circuit breaker is in the oil? position as shown in FIGURE 5, the arm 37 of the two-armed lever 36 engages upon a stop member 56, while the pivot pin 54 is then in engagement with the upper end of the slots 55.

The pushbutton 7 is provided and preferably integral with a control rod 57 of insulating material which has a projection 58 thereon which is adapted to engage into the recesses 42 in the lugs 41 of lever 36. The pushbutton 7 is acted upon in the usual manner by the upper end of a compression spring 59, the lower end of which is supported on an insulating plate 60. This insulating plate 60 forms the support on which the frame 25 is rigldly secured. The insulating plate 60 as well as the current conductors 3 and 4 are secured by four bolts 61 and nuts 62 to the base 1 which consists of insulating material. The cap 2 is removably connected to the insulating plate 60 by means of a pair of screws 63.

The two slide knobs 8 and 9 for the manual release of the circuit breaker are slidably mounted in the insulating plate 60. On its lower side, knob 9 is likewise provided with a pin 29. Each knob 8 and 9 is acted upon by a compression spring 64. A flat plate-shaped lever 65 is mounted on the insulating plate 60 so as to be pivotable about the axis of the control rod 57. One arm of this lever 65 has an end surface 66, while the other arm is provided with an inclined slot 67 into which the pin 29 of the manual release knob 9 engages. When the circuit breaker is in the position as shown in FIGURE 7, the end surface 66 of lever 65 is located directly in front of the pin 29 of the other manual release knob 8 and thus prevents this knob 8 from moving.

The manner of operation of the overload circuit breaker according to the invention is as follows:

In the event that, when the pushbutton 7 is depressed and the circuit breaker is in its on position as shown in FIGURES 3 and 4, an excess current occurs, the bimetal strip 19 will be heated and thereby bent and pivoted in the clockwise direction, as seen in FIGURE 4, until it presses against the tabs 18 on the arm 16 of the armature 17 and pivots the latter in the counterclockwise direction. The side wall 26 of the armature 17 thereby disengages from the pawl 27 so that under the action of the compression spring 38 on pin 39 and the release spring 46' on the slide member 46, pawl 27 will then be pivoted counterclockwise to its'inactive position as shown in FIG- URE 5. During the upward movement of lever 36, the arm 37 thereof engages upon the stop member 56, as shown in FIGURE 5, so that under the action of the compression spring 38 and the release spring 46 the lever 36 will then be pivoted in the counterclockwise direction about the stop member 56, and the right arm 50 of lever 36 will hit against the upper end of the recess 49 in the slide member 46 so that the opening or circuit-breaking movement of the contact bridge 45 which has already been started by the release spring 46' will be accelerated. In this off position of the circuit breaker which is shown in FIGURES 5 and 6, the pivot pin 54 engages upon the upper end of the slots 55 in the frame 25, and the pushbutton 7 together with the control rod 57 are likewise moved to their 0E position in which a lateral projection on the control rod 57 engages upon the pivot pin 54 of lever 36. When the circuit breaker as shown in FIGURES 3 and 4, this lateral projection of the control rod 57 is likewise in engagement with the pivot pin 54.

In the event that a short circuit occurs, the electromagnet 10 to 15 will be energized so that the arm 16 of armature 17 will be attracted and effect the release of the circuit breaker in the same manner as above described.

If the circuit breaker is to be switched off by hand, both manual release knobs 8 and 9 must be shifted simultaneously toward the pushbutton 7. By the movement of the knob 9, its pin 29 slides along the inclined slot 67 in one arm of the two-armed lever 65 and thereby pivot-s the latter in the clockwise direction, as seen in FIGURE 7, to the position as shown in FIGURE 8, in which the end surface 66 of the other arm of lever 65 is located outside of the path of movement of pin 29 of the release knob 8 so that this knob may then be moved in the direction toward the other knob 9, whereby the pin 29 on knob 8 will pivot the side wall 28 of armature 17 so that its other side wall 26 will be disengaged from the pawl 27 and the circuit breaker will be released to its off position.

When the circuit breaker is in its off position as shown in FIGURES 5 and 6, the projection 58 on the control rod 57 is located within the path of movement of the recesses 42 in the lugs 41 of lever 36. Therefore, when the pushbutton 7 is depressed and moved from the fulllme position according to FIGURE 5 to the position as shown in dot-and-dash lines, the projection 58 on the control rod 57 will engage into the recesses 42 and take along the two-armed lever 36 to the position as shown in dotand-dash lines in FIGURE 5. The pivot pin 54 of lever 36 then acts upon the projections 35 on pawl 27 and thereby pivots the latter in the clockwise direction to the positronas indicated in dot-and-dash lines in FIGURE 5, in which under the action of the torsion spring 31 the side wall 26 passes underneath and holds thepawl 27. If the finger is then taken off the pushbutton 7, pivot pin 54 of lever 36 will be applied against the detents 34 of pawl 27. As soon as the projection 58 on the control rod 57 disengages from the recesses 42 in the lugs 41 of lever 36, the action of the compression spring 38 causes a rapid pivoting movement of lever 36 in the clockwise directron, whereby the slide member 46 together with the contact bridge are pivoted against the action of the release spring 46' to the on position as illustrated in FIGURE 3. The overload circuit breaker according to the invention is :herefore movable instantaneously to the on and off posiions.

The circuit breaker as illustrated may be employed for heavy-duty operation for rated currents of to 400 amperes and short-circuit currents up to 10,000 amperes at a direct-current voltage of about 30 volts.

Although my invention has been illustrated and described with reference to the preferred embodiments thereof, I wish to have it understood that it is in no way limited to the details of such embodiments but is capable is in its on position,

one of said conductors being bent at a point spaced from its contact so as to form a substantially Q? -shaped loop, said magnet core being mounted within said loop and being connected in parallel to said bimetal strip, a cOntact bridge, means :for moving said contact bridge within said housing in a direction vertical to said plane for connecting said contact bridge simultaneously with said contacts and for disconnecting the same simultaneously therefrom, and a two-armed lever located between said loop and said contact bridge, means for connecting said pushbutton to said lever when said pushbutton is being depressed, stationary supporting means within said housing having guide slots therein extending in the direction of movement of said pushbutton, said lever having a pivot pin pivotable within said slot-s and slidable therein in said direction of movement of said pushbutton, a spring acting upon the first arm of said lever at the side thereof facing said loop, and a pawl pivotably mounted in said housing and adapted to engage upon said pivot pin to arrest said lever in a position in which the second arm of said lever at the side thereof facing said contact bridge presses said contact bridge under the action of said spring against said two contacts.

2. An overload circuit breaker as defined in claim 1, in which, when said pawl is in its arresting position, it engages directly upon said armature which is acted upon by said bimetal strip.

3. An overload circuit breaker as defined in claim 1, further comprising a control rod secured to said push button and movable therewith and having a catch thereon, said first arm of said lever having at least one projection thereon extending toward said conductors and having a recess which, when said contact bridge is in its on position in connection with said contacts, is located outside of the path of movement of said catch, said control rod having a longitudinal slot, said pawl having a pivot pin mounted in a fixed position in said housing and engaging into said slot so as to guide said control rod, a stationary stop member in said housing, said first arm engaging upon said stop member when said contact bridge is in its off position, said recess in the projection of said first arm then being located within the path of movement of said catch.

4. An overload circuit breaker as defined in claim 1, in which said means for moving said contact bridge comprise a slide member secured to said contact bridge and adapted to guide the same in said vertical direction, a second spring acting upon said slide member and tending to move said contact bridge to its off position and said slide member having an aperture, said second arm of said lever engaging upon the lower end of said aperture against the action of said second spring when said contact bridge is in its on position, said second arm engaging upon the upper end of said aperture under the action of said first spring when said lever is moved to its ofi" position.

5. An overload circuit breaker as defined in claim 1, in which said housing consists of insulating material and comprises a base and a cap, said stationary supporting means comprising a metal frame within said housing, an insulating plate secured to the upper side of said frame from which said pushbutton projects through said cap toward the outside, and bolts securing said insulating plate and also said conductors to said base.

6. An overload circuit breaker as defined in claim 5, further comprising a pair of knobs slidably mounted on said insulating plate at the opposite sides of said pushbutton and adapted to be moved substantially simultaneously in opposite directions to each other vertically to the axis of said pushbutton for manually releasing said circuit breaker to its off position, each of said knobs having a pin thereon projecting toward the inside of said housing, the pin on the first of said kno'bs adapted to act upon said armature when said first knob is moved in the direction toward the second knob, a second two-armed lever on said insulating plate pivotable about the axis of said pushbutton, a spring acting upon said second lever and tending to maintain the same in a position in which an end surface of the first arm of said lever is located within the path of movement of the pin on said first knob so as to prevent said first knob from being moved toward the second knob, the second arm of said second lever having an inclined slot into which the pin on said second knob engages so that when said second knob is moved toward said first knob, said pin thereon slides along said inclined slot and thereby pivots said second lever to a position in which said first arm of said second lever is located outside of the path of movement of said pin on said first knob so that said first knob may then be moved so as to act upon said armature.

7. An overload circuit breaker as defined in claim 6, in which said electromagnetic means further comprise a magnet yoke mounted on said magnet core so as to be pivotable only with considerable friction, said armature forming a third two-armed lever having one arm which, when said armature is in its attracted position, nearly closes the magnetic circuit between said magnet core and said magnet yoke, the other arm of said third lever being substantially U-shaped so as to have two opposite side Walls, one of said side walls being adapted to hold said pawl in its arresting position, and the other side wall adapted to be acted upon by the pin on said first knob when being moved toward said second knob.

References Cited by the Examiner UNITED STATES PATENTS 1,912,109 5/1933 Van Valkenburg et al 200l16 2,895,023 7/1959 Ellenberger 200 88 2,952,757 9/1960 Ellenberger 200-116 BERNARD A. GILHEANY, Primary Examiner,

E, SPRINGBORN, Assistant Examiner,

Claims (1)

1. A PUSHBUTTON-CONTROLLED OVERLOAD CIRCUIT BREAKER FOR HIGH RATED CURRENTS HAVING A HOUSING, A PUSHBUTTON SLIDABLY MOUNTED IN SAID HOUSING AND PROJECTING TO THE OUTSIDE THEREOF, THERMAL RELEASING MEANS IN SAID HOUSING COMPRISING A BIMETAL STRIP, ELECTROMAGNETIC RELEASING MEANS IN SAID HOUSING COMPRISING A MAGNET CORE AND AN ARMATURE, TWO CURRENT CONDUCTORS ADAPTED TO BE CONNECTED TO AN ELECTRIC CIRCUIT AND HAVING CONTACTS THEREON WITHIN SAID HOUSING AND DISPOSED WITHIN A COMMON PLANE, ONE OF SAID CONDUCTORS BEING BENT AT A POINT SPACED FROM ITS CONTACT SO AS TO FORM A SUBSTANTIALLY $ -SHAPED LOOP, SAID MAGNET CORE BEING MOUNTED WITHIN SAID LOOP AND BEING CONNECTED IN PARALLEL TO SAID BIMETAL STRIP, A CONTACT BRIDGE, MEANS FOR MOVING SAID CONTACT BRIDGE WITHIN SAID HOUSING IN A DIRECTION VERTICAL TO SAID PLANE FOR CONNECTING SAID CONTACT BRIDGE SIMULTANEOUSLY WITH SAID CONTACTS AND FOR DISCONNECTING THE SAME SIMULTANEOUSLY THEREFROM, AND A TWO-ARMED LEVER LOCATED BETWEEN SAID LOOP AND SAID CONTACT BRIDGE, MEANS FOR CONNECTING SAID PUSHBUTTON TO SAID LEVER WHEN SAID PUSHBUTTON IS BEING DEPRESSED, STATIONARY SUPPORTING MEANS WITHIN SAID HOUSING HAVING GUIDE SLOTS THEREIN EXTENDING IN THE DIRECTION OF MOVEMENT OF SAID PUSHBUTTON, SAID LEVER HAVING A PIVOT PIN PIVOTABLE WITHIN SAID SLOTS AND SLIDABLE THEREIN IN SAID DIRECTION OF MOVEMENT OF SAID PUSHBUTTON, A SPRING ACTING UPON THE FIRST ARM OF SAID LEVER AT THE SIDE THEREOF FACING SAID LOOP, AND A PAWL PIVOTABLY MOUNTED IN SAID HOUSING AND ADAPTED TO ENGAGE UPON SAID PIVOT PIN TO ARREST SAID LEVER IN A POSITION IN WHICH THE SECOND ARM OF SAID LEVER AT THE SIDE THEREOF FACING SAID CONTACT BRIDGE PRESSES SAID CONTACT BRIDGE UNDER THE ACTION OF SAID SPRING AGAINST SAID TWO CONTACTS.

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