US2214695A

US2214695A - Circuit breaker

Info

Publication number: US2214695A
Application number: US196929A
Authority: US
Inventors: Oliver S Jennings
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1938-03-19
Filing date: 1938-03-19
Publication date: 1940-09-10
Anticipated expiration: 1957-09-10
Also published as: DE759385C

Description

Patented Sept. 10, 1940 UNITED STATES PATENT OFFICE CIRCUIT BREAKER Pennsylvania Application March 19, 1938, Serial No: 196,929

20 Claims.

The invention relates to control devcies in general and more particularly to circuit breakers for controlling lighting and small motor circuits.

An object of the invention is the provision of circuit breaker having an improved operating mechanism that is manually operable to open and to close the breaker contacts and automati-= cally operable to efiect opening of the contacts in response to predetermined overload conditions.

Another object of the invention is the provision of a circuit breaker embodying an improved operating mechanism for eflecting quick make and break of the breaker contacts.

Another, object of the invention is the provision of a circuit breaker embodying an operating mechanism as previously described which when automatically operated eifects movement of the operating handle to an intermediate indicating position.

Another object of the invention is the provision of a circuit breaker embodying an improved operating mechanism of the snap action type which is releasable for opening the contacts on overload and trip free of the manual operating handle.

Another object of the invention is the provision of a circuit breaker of the above type which has a small number of parts arranged so that the breaker occupies a minimum amount of space, and which is inexpensive to manufacture.

80 Another object of the invention is the provision of a circuit breaker embodying an improved operating mechanism having a small number of parts which are readily assembled and disassembled.

85 Another object of the invention is the provision of a circuit breaker embodying an improved thermally responsive trip means for effecting automatic operation of the breaker.

Another object of the invention is the provision of a circuit breaker embodying an improved thermally responsive trip element which has a large controlling movement and yet which occupies a small amount of space.

Another object of the invention is the provision of a circuit breaker embodying an improved bimetallic control element which has a large controlling movement and yet which has a small height.

Another object of the invention is the provision of an improved thermally responsive control element which is pivotally mounted intermediate its ends to give a length of bimetal in two directions so that. the flexing movement of each leg produces a relatively large deflection of the free end of the element. I

The novel features that are considered characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to structure and operation together with additional objects and advantages 5 thereof will be best understood from the following detailed description of one embodiment thereof when read in connection with the accompanying drawings in which:

Figure 1 is a vertical sectional view of a cir- 1o cuit breaker constructed in accordance with the invention, the breaker being shown in closed circuit position,

Fig. 2 is a vertical sectional view similar to Fig.

1 showing the breaker in the manually opened 16 position,

- Fig. 3 is a sectional view similar to Fig. 1, showing the position-of the parts following a tripping operation, and

Fig. 4 is a horizontal sectional view of the cir- 20 cuit breaker taken substantially on the line IV-IV of Fig. 1.

Referring to the drawings, the reference numeral 1 designates an open sided casing of molded insulating material in which the breaker 25 contacts and operating mechanism are. mounted. A cover 9 (Fig. 4) also of molded insulating material closes the open side of the casing 1 and is removably mounted thereon by means of a plurality of bolts II.

A pair of end terminal strips l3 and ii of conducting material extend from within the casing I exteriorly thereof at each end. The strips l3'and' l5 are removably mounted on the casing by being slid edgewise into suitable mounting 35 recesses I! provided therefor adjacent each end of the casing. The outer end of the strips l3 and I5 are perforated for receiving terminal screws I!) which engage threaded inserts 2| embedded in the ends of the casing 1. The ter- 40 minal screws l9 serveto retain the strips l3 and IS in mounted position after they have been slid into place in the casing 1', and also serve to electrically connect the breaker in an external'circuit.

A stationary contact 23 is secured to the terminal strip 15 adjacent. its inner end in a position to be engaged by a movable contact 25 which is actuated to open and to closed circuit position by the actuating mechanism of the ac breaker.

The operating mechanism of the circuit breaker comprises in general a pivotally mounted support or carrier 21, a contact arm 29 pivotally mounted on the support 21, an overcenter toggle mechanism indicated generally at 3| for moving the contact arm to open and to closed circuit position and for biasing the pivoted support 21 to a tripped position, and a thermally responsive trip element indicated generally at 33 for releasably retaining the pivoted support 21 in an operative position.

The support 21 comprises two generally U- shaped plates 35 of sheet metal which are rigidly secured together in slightly'spaced parallel relation by means of a plurality of rivets 31, the plates being spaced by suitable spacers (not shown), The support 21 is pivotally and removably mounted in the casing l by means of a fixed p'ivot stud 39 which is molded in and projects from the side wall 4| of the casing and which extends through an opening provided therefor in one of the legs 43 of the support 21. The support 2'! is spaced from the side wall 4| by means of a spacer sleeve 45 (Fig. 4) which surrounds the pivot stud 39. The opposite leg 41 of the U-shaped support 2'! has a latch element 49 rigidly secured to the end thereof between the plates 35 by means of the rivets 31. The latch element 49 projects from the leg 41 of the support 21 and is adapted to be normally engaged by the free upper end of the thermally responsive trip element 33 to retain the support in operative position as shown in Fig. 1. The upper edges of the horizontal portions of the plates 35 of the support 21 form a limiting guide surface or track 5| for a roller of the overcenter toggle mechanism 3| as will hereinafter be described.

The contact arm 29 is pivotally mounted adjacent one end between the plates 35 of the support 21 by means of a pivot pin 53 which extends transversely between the horizontal portions of the plates 35 at a point substantially midway between the

legs

43 and 41 of the support 21. The movable contact 25 is rigidly secured to the forward end of the arm 29 for movement into and out of engagement with the stationary contact 23. The upper edge of the contact arm 29 has a curved recess 55 formed therein above the pivot pin 53 to provide oppositely inclined curved surfaces 51 and 59 on opposite sides of the pivot axis 53 which are adapted to project above the limiting guide surface 5| of the support 21 for engagement by the roller of the overcenter toggle mechanism as it is moved back and forth along the guide surface 5|.

The overcenter toggle mechanism for moving the contact arm 29 to open and to closed circuit position and for biasing the pivoted support 21 to a trip position comprises, in general, an operating handle 6|, a link 63, a roller 65 and an overcenter spring 61. The operating handle 6| is of molded insulating material and is pivotally mounted intermediate its ends on a pivot stud 69 which is molded in the material of the casing and projects into a recess '|I provided in the top wall of the casing for accommodating the hub portion of the handle. The end edges of the recess II are beveled to provide stops for limiting rotation of the handle 6|. The handle 6| has a knob portion I3 which projects outwardly of the casing and 8. depending forked portion I5 which carries a transverse pivot pin 11. The pivot pin extends transversely across the longitudinal slot formed by the two legs of the portion 15 and is frictionally held in openings provided therefor in the legs of the forked portion I5 of the handle 6|. The link 63 has its upper end slotted at 19 for slidably engaging the transverse pin 11 of the forked portion I5 of the handle 6|. The lower end of the link 63 has a forked projection 8| which carries a transverse pivot pin 83 on which is journaled the roller 65. The overcenter spring 61, which is of the coiled compression type, encircles the link 63 and is constrained between the forked projection 8| carried at the lower end of the link and a washer 85 slidably mounted on the link 63 which is in turn engaged by the rounded lower end of the handle 6|. The spring 61 thus serves to bias the roller 65 against the guide surface 5| of the pivoted carrier 21 so that the carrier 21 is always biased in a counterclockwise direction about its pivot axis 39. The width of the forked projection 8| is only slightly less than the inner width of the casing so that the roller cannot be laterally displaced off of the guide track 5|.

The thermally responsive trip element 33 comprises a strip 86 of bimetallic material having a high expansion-side 81 and a low expansion side 89. The strip 86 is bent sharply intermediate its ends as indicated at 9| to provide a vertical leg 93 and a horizontal leg which are substantially at right angles to each other. The strip 86 has a sleeve 91 rigidly secured thereto at the bend 9| to provide a pivotal mounting means for the strip. The strip has its sleeve pivotally mounted on a pivot stud 99 which is molded in and projects from the side wall 4| of the casing 'I. An adjusting screw IOI engages the low expansion side 89 of the strip 86 adjacent the end of the horizontal leg 95 thereof, the screw I0| being mounted in a threaded insert I03 embedded in the base of the casing 1. The horizontal leg 95 of the strip 86 is biased in engagement with the adjusting screw IN by means of a spring I05 carried by a stud I07 supported by the casing. The upper free end I09 of the vertical leg 93 of the strip normally engages the latch element 49 of the pivoted support 21 to restrain the support in operative position. One end of the bimetallic strip 86 is electrically connected to the movable contact 25 by means of a conductor I I, and the other end of the strip is electrically connected to the opposite end terminal I3 by means of a flexible conductor H3. The strip is thus electrically connected in series circuit with the

contacts

23 and 25 of the breaker so as to be traversed by the current flowing through the circuit controlled by the breaker. The bimetallic element 86 being pivotally mounted intermediate its ends provides a length of bimetallic material in two directions from the pivot axis, so that the deflection of the free end I09 thereof is produced by the combined flexing action of the two

legs

93 and 95. When the bimetallic element 86 is heated a predetermined amount by the passage of an overload current therethrough, the end of the horizontal leg 95 tends to deflect downwardly against the adjusting screw IOI. This causes the bimetallic element to be partially rotated in a counter-clockwise direction to produce a deflection or movement of the free upper end I09 in a direction away from the operating mechanism of the breaker. Since the upper leg 93 is also heated by the current, the deflection of the upper free end I09 is increased by the flexing of the upper leg 93. It will thus be seen that the total deflecting movement is provided by the flexing of each of the two

legs

93 and 95. The bimetallic element 86 being bent substantially in the shape of a right angle and pivoted intermediate its ends at the bend, in addition to giving a large deflecting movement, also allows the element to be advantageously mounted between a corner of the casing 1 and a comer of the operating mechanism to provide a very compact structure and to reduce the total space occupied by the breaker.

The trip characteristic or tripping point of the bimetallic trip element 86 is adjustable by means of the adjusting screw llll. Turning the adjusting screw in or out serves to change the amount of overlap between the upper free end I99 of the trip element 86 and the latch element 69 carried by the pivoted support 21. Since the bimetallic trip element 86 has a relatively large deflecting movement, its trip characteristic'may be adjusted over a considerable range by means of the screw ml.

The pivotally mounted bimetallic trip element 86 is spaced from the side wall M of the casing 1 by means of a spacer sleeve 6 mounted on the pivot stud 99 between the sleeve 91 and the side wall 4|. A pair of spacer sleeves I I9 mounted on the ends of the

studs

39 and 99 serve to space the pivot supportv 21 and the bimetallic trip element 86 from the inner surface of the cover 9 and these sleeves cooperate with the sleeves 45 and 5 to prevent lateral displacement of the support 21 and the trip element 86.

When two or more circuit breaker units as described above are required, the units may be assembled together side by side, and in this case the side wall 4| of one unit serves to close the open side of the next adjacent unit and to retain the parts thereof in mounted position.. Where several units are assembled together side by side, a single cover 9 is used to close the open side of the end casing 1.

The assembly and disassembly of the circuit breaker unit is facilitated by reason of the fact that all of the main parts of the breaker are removably mounted through the open side of the casing, the operating handle 6|, the movable support 21 and the bimetallic trip element 86 being mounted by being slid onto their corresponding pivot studs which project from the side wall of the casing 4|, and the end terminals l3 and I5 being slid into the recesses provided therefor as previously described. The cover 9 serves to retain the assembled parts in mounted position.

Further features of the operating mechanism will be more fully understood in connection with the following description of the operation thereof. With the breaker in the closed circuit position as shown in Fig. 1, it will be noted that the actuating roller 65 engagesthe inclined surface 51 of the contact arm 29 which is disposed above the guide surface 5| of the pivoted support 21, and the line of action of the overcenter spring 61 and the roller 65 biased thereby is to the right of the pivot pin 53 which pivotally supports the contact arm 29. The contact arm is thus biased by the spring 61 and roller 64 to closed circuit position with a predetermined force to maintain the

contacts

25 and 23 in pressure engagement. Since the line of action of the overcenter spring 61 passes to the left of the pivot stud 39, the movable support 21 is biased by the spring 61 in a counter-clockwise direction but is retained in the operative position shown by means of the bimetallic trip element 86. In this position of the parts, the line of action of the overcenter spring 61 and the roller 65 is substantially perpendicular to the tangent of the inclined curved surface 51 at the point of engagement of the roller 65 therewith. To manually open the circult breaker, the operating handle 6| is moved in a counter-clockwise direction from the position shown in Fig. 1 to the position shown in Fig. 2. This movement of the operating handle moves the pivot pin 11 carried by the lower end of the handle to the right causing the roller 65 to roll down the inclined surface 51. As soon as the axis of the pivot pin 11 crosses the imaginary line joining the axis of the pivot stud 69 and the pivot pin 83, the roller 65 will be moved to the left along the guide surface 6| with progressively increasing acceleration due to the expansion of the overcenter spring 61. During this movement of the actuating roller 65 to the left along the guide surface 5|, it engages the opposite inclined surface 59 of the contact arm 29 and ef-- fects counter-clockwise rotation of the contact arm from the closed circuit position to the open circuit position as shown in Fig. 2. I

In closing the circuit breaker substantially the reverse action takes place. The operating ham-1 dle 6| is moved in a clockwise direction from the position shown in Fig. 2 to the position shown in Fig. 1. This clockwise movement of the operating handle 6| moves the pivot pin 11 to the left compressing the spring 61. As soon as the pivot pin 11 crosses the imaginary line, joining the pivot stud 69 and the pivot pin 83, the roller is moved to the right along the guide surface 5| with progressively increasing acceleration due to v the expansion of the spring 61. During this movement of the roller to the right along the guide surface, it engages and rides up upon the guide surface 51 of the contact arm 29 to effect clockwise rotation of the contact arm 29 to the closed circuit position shown in Fig. 1. The fact that the roller 65 engages the inclined surface 51 at a point above the guide surface 5| of the movable support 21 provides a definite pressure engagement between the movable contact 25 and the stationary contact 23 and also provides a certain amount of follow-up to compensate for burning or wearing away of the contacts. From the above description it will be seen that the contact arm 29 is moved by the overcenter toggle mechanism 3| to open and to closed circuit position with a snap action to secure quick make and break of the contacts irrespective of how slowly the operating handle 6| is moved by the operator.'

In the event that an overload or short circuit condition occurs in the circuit in which the breaker is connected, the abnormal current flowing through the bimetallic trip element 86 heats the same causing the upper free end I09 thereof to be deflected to the left away from the support 21 to effect release of the pivoted support 21. When thus released, the support 21 is rotated in a counter-clockwise direction about its pivot axis 39 as a result of the biasing action of the overcenter spring 61. This movement of the support 21 causes the arm 29 to rock counterclockwise on the contact 23 as a fulcrum to change the inclination of the surface 51. This causes the roller 65 to be moved to the left down the inclined surface 51 of the contact arm and also down the now tilted guide surface 5|, by the expansion of the overcenter spring 61. The movement of the roller 65 down the inclined surface 51 and also down the now tilted guide surface 5| is assisted and accelerated due to the fact that the line of action of the spring 61 changes as the roller moves down the inclined surface to aid movement of the roller. During this rolling movement, the roller engages the opposite inclined surface 59 of the contact arm 29 to effect rotation of the contact arm to open circuit position as shown in Fig. 3. The counterclockwise movement of the pivoted support 21 is limited by a pivot stud I23 which is molded in .and projects from the side wall 4| of the casing l. The movement of the actuating roller 85 from the position shown in Fig. 1 to the tripped position shown in Fig. 3 also causes movement of the operating handle Bl in a counter-clockwise direction. This counter-clockwise movement of the operating handle is stopped by an inwardly projecting portion N of the leg 43 of the pivoted support 27, so that the operating handle assumes an intermediate indicating position as shown in Fig. 3 to indicate the fact that the breaker has been tripped in response to an overload.

Before the breaker can be reclosed it is necessary to reset the support 2?? to its operative latched position shown in Fig. 1. To reset the breaker following a tripping operation, the operating handle Si is moved in a counter-clockwise direction from the position shown in Fig. 3 to the open circuit position shown in Fig. 2. During this resetting movement of the operating handle, the legs of the lower forked end of the handle ill engage and move the inwardly projecting upper end I of the support 2'i effecting clockwise rotation of the support about its pivot axis 39 to return the latch element i9 carried by the support into latching engagement with the upper free end MB of the bimetal trip element 86 which has been returned to its original position after being cooled. The breaker cannot be closed until after the mechanism is reset as described above. Thus if the operating handle is moved directly from the tripped position to the closed position without first resetting the mechanism, the line of action of the spring 6'! will not be changed a sufflcient amount to cause movement of the roller to the right up the tilted surface 5!. After the breaker has been reset as previously described, the contacts may be reclosed by moving the operating handle 6| in a clockwise direction as previously described. It will be noted that the point of engagement of the latch element 49 with the upper free end 509 of the bimetallic trip element 86 is disposed in a vertical line substantially directly above the pivot stud Q9 of the bimetallic trip element, so that the line of action of the force exerted by the support 2? on the bimetallic trip element 86 passes substantially through the pivot axis 99 of the bimetallic trip element. Thus the only force which must be overcome by the bimetallic trip element 36 as it deflects is that of the friction between the upper free end Hi9 thereof and the latch element 39.

The operating mechanism of the breaker is such that the movable contact 25 is entirely tripfree of the operating handle 6!. That is to say. the tripping of the breaker in response to an overload will effect opening of the contacts even though the operating handle Si is held in closed circuit position. I

While the invention has been disclosed in accordance with the provisions of the patent statutes, it is to be understood that various changes in the structural details thereof may be made withoutdeparting from the spirit of the invention. It is desired, therefore, that the appended claims be given the broadest reasonable construction permissible in the light of the prior art.

I claim as my invention! 1. In a circuit breaker, a movable support member, means releasably retaining said support menrber in an operative position, a contact mem ber pivotally mounted on said support member, one of said members having a guide surface, actuating mechanism including a means movable back and forth along said guide surface for moving said contact member to open and to closed circuit position.

2. In a circuit breaker, a movable support having a guide surface, means releasably retaining said support in an operative position, a contact arm pivoted on said support, means including a member movable back and forth along said guide surface for moving said contact arm to open and to closed circuit position, an overcenter spring for actuating said member and for biasing said support to a tripped position, said support when released causing movement of said contact arm to open circuit position.

3. In a circuit breaker, a movable support having a guide surface, a bimetallic trip element normallyreleasably retaining said support in an operative position, a contact arm pivotally mounted on said support, means including an actuating member movable back and forth along said guide surface for moving said contact arm to open and to closed circuit position, said trip element being operable in response to predetermined conditions to release said support.

4. In a circuit breaker, a movable support having a guide surface, means releasably retaining said support in an operative position, a contact arm pivotally mounted on said support, means including an over-center toggle and a roller mov-- able thereby back and forth along said guide surface for moving said contact arm to open and to closed circuit position.

5. In a circuit breaker, a movable support having a guide surface, means releasably retaining said support in an operative position, a contact arm pivotally mounted on said support, a toggle mechanism comprising a roller movable back and forth along said guide surface for moving said contact arm to open and to closed circuit position, an operating handle movable to open and to closed position and an over-center spring movable by said handle for actuating said roller, said support when released being moved by said spring to a tripped position to cause movement of said contact arm to open circuit position.

6. In a circuit breaker, a movable support having a guide surface, means releasably retaining said support in an operative position, a contact arm pivotally mounted on said support, a toggle mechanism comprising a roller movable back and forthv along said guide surface for moving said contact arm to open and to closed circuit position,

an operating handle movable to open and to closed position and an over-center spring movable by said handle for actuating said roller, said support when released being moved by said spring to a tripped position to cause movement of said contact arm to open circuit position, and said handle to an intermediate indicating position.

7. In a circuit breaker, a movable support,

means releasably retaining said support in an ing movement of said contact arm to an open circuit position, and current responsive means operable to eflect release of said support.

8. In a circuit breaker, a movable support, means releasably retaining said support in an operative position, a contact arm pivotally mounted on. said support, actuating means including anactuating member movable in one di' rection for engaging a portion of said arm on one side of its pivot axis to rotate said arm to closed circuit position, and movable in an opposite direction for engaging another portion of said arm on the oppositeside of its pivot axis to rotate said arm to open circuit position, said support being movable when released to cause said contact arm to move to open circuit position.

9. In a circuit breaker, a movable support, means releasably retaining said support in an operative position, a contact arm pivoted on said support, actuating means for moving said arm to open and to closed circuit position and for moving said support when released, said means comprising an actuating roller having rolling engagement with a portion of said arm, a movable operating handle and an over-center spring for actuating said roller to move said arm to open and to closed circuit position, said support when released causing said spring and roller to move said contact arm to open circuit position.

10. In a circuit breaker, a movable support, means releasably retaining said support in an operative position, a contact arm pivoted on said support, an over-center toggle mechanism including a spring biased roller movable back and forth along a portion of said arm for moving said arm to open and to closed circuit position, said support when released causing said mechanism to move said contact arm to open circuit position.

11. In a circuit breaker, a movable support, means releasably retaining said support in an operative position, a contact arm pivoted on said support and having a curved surface on one side of its pivot axis, actuating means for moving said contact arm to open and to closed circuit position and for moving said support when it is released to a tripped position to cause movement of said contact arm to open circuit position, said actuating means comprising an actuating roller movable back and forth along said curved surface to actuate said arm, a movable operating member and an over-center spring for actuating said roller.

12. In a circuit breaker, a pivoted support having a guide surface on one side or its pivot axis, means releasably retaining said support in operative position, a contact arm pivoted on said support and having portions on opposite sides of its pivot axis adapted to extend above said guide surface, an over-center toggle mechanism including a roller movable thereby back' and forth along said guide surface for engaging said portions to rotate said am to open and to closed circuit position, said support when released causing said mechanism to rotate said contact arm to open circuit position.

18. In a circuit breaker, a casing, relatively movable contacts in said casing, actuating means in said casing operable to open and to close said contacts, a thermally responsive trip element operable to cause opening of said contacts in response to predetermined conditions comprising a strip of bimetallic material having a high and a low expansion side and bent intermediate its ends to provide two legs at an angle to each other, means pivotally mounting said strip at its bend on a ilxed support in said casing adjacent one corner oi! said casing so that its legs are substantially parallel to the walls terminating in said comer, a stop engaging the low expansion side of said strip adjacent the end of one leg and means holding the end of said leg against said stop.

14. In a circuit breaker, a casing, relatively movable contacts in said casing, actuating mechanism in said casing operable to open and to close said contacts, trip means in;said casing operable to cause said mechanism to open said contacts in response to predetermined conditions, said trip means comprising a strip of bimetallic material having a high and a low expansion side heated in response to the current flowing in the circuit, said strip being pivotally mounted intermediate its ends on a fixed support and disposed substantially parallel to and adjacent the inner surface of said casing, a stop engaging thelow expansion side of said strip adjacent one end and means holding said end in engagement with said stop.

15. In a circuit breaker having relatively movable contacts and a spring biased member releasable to efiect opening of said contacts, a. thermally responsive trip means normally restraining said. element and operable in response to predetermined conditions to release said member, said means comprising a. strip of bimetallic material having a high and a low expansion side pivotally mounted intermediate its ends on a fixed support, one end of said strip normally engaging and restraining said member, a stop engaging the low expansion side of the strip adjacent its other end, the line of action of the force applied to said strip by said member passing substantially through the pivot axis of said strip. 16. In a circuit controlling device, relatively movable contacts, a thermally responsive control element operable in response to predetermined conditions to control said contacts, said element comprising a strip of bimetallic material having a high and a low expansion side, means pivotally-mounting said strip intermediate its ends on a fixed support, a stop engaging the low expansion side of said strip adjacent one end and means holding said end in engagement with said stop.

17. In a circuit controlling device, relatively movable contacts, a thermally responsive control element operable in response to predetermined conditions to control said contacts, said element comprising a strip of bimetallic material having a high and a low expansion side, means pivotally mounting said strip intermediate its ends on a fixed support, an adjustable stop engaging the low expansion side of said strip adjacent one end for adjusting the control characteristic of said strip, and means biasing said end in engagement with said stop. I

18. In a control device, a thermally responsive control element comprising a strip of bimetallic material having a high and a low expansion side, said strip being'pivotally mounted intermediate its ends on a fixed support, and a stop engaging the low expansion side of said strip adjacent one end.

19. In a control device, a thermally responsive control element comprising a strip of bimetallic material having a high and a low expansion side, said strip being pivotally mounted intermediate its ends on a fixed support, and an adjustable means holding said strip adjacent one end.

thermal means comprising a. strip of bimetallic material pivoted intermediate its ends on a fixed support, and means holding said strip adjacent one end.

OLIVER 3. JENNINGS.