US2020332A

US2020332A - Automatic circuit breaker

Info

Publication number: US2020332A
Application number: US691139A
Authority: US
Inventors: Sachs Joseph
Original assignee: Individual
Current assignee: Individual
Priority date: 1933-09-27
Filing date: 1933-09-27
Publication date: 1935-11-12
Anticipated expiration: 1952-11-12

Description

Nov. 12, 1935. J. SACHS AUTOMATIC CIRCUIT BREAKER Filed Sept. 27, 1933 1 mm m b r .HE. D ,55. .C 2% 0. m

Patented Nov. 12, 1935 UNITED STATES PATENT OFFICE 2,020.33; I AUTOMATIC omourr BREAKER Joseph Sachs, West Conn.

Application September a1, 1933, serial No. 691,189

19 Claims. (01. zoo-11s) This invention relates particularly to an automatic circuit breaker of the type set forth in my Patents Nos. 1,811,970, 1,812,842, 1,812,843 and 1,812,848, all dated June 30, 1931, but as to some I of its features the invention is not so limited.

The general object of the invention is to provide a circuit breaker, particularly a circuit breaker of the type referred to, having the parts thereof so arranged as to reduce the width of the circuit breaker. This reduction in width is desirable for certain classes of service, particularly tor panel board use.

In accordance with the invention the movable contacts, instead of projecting outward from the 18 side elements of the contact member, as in the a patented constructions, are located between the side elements, or at least between the outer planes thereof, and the stationary contacts are similarly closely spaced, being also between the said outer planes.

In order to avoid any possibility of arcing, suitable barriers are preferably provided between the contacts and also adjacent the electro-responsive means carried by the contact member and prefk erably the paths of movement of the movable contacts are entirely surrounded by insulating walls.

In the accompanying drawing I have illustrated one suitable embodiment of the invention, but it will be understood that the drawing is intended for illustrative purposes only and is not to be construed as defining or limiting the scope of the invention, the claims forming a part of this specification being relied upon for that purpose.

Of the drawing:

' Fig-1 is a front view of. a circuit breaker embodying the invention.

Fig. 2 is a side View of the mechanism of the circuit breaker,'the insulating supporting and en closing members being in section along the line 2-2 ofFig.1.- f

Fig. 3 is a view similar to Fig. 2 but showing the mechanism in a'diflerent position with certain parts broken away, the insulating and supporting and enclosing members being in section along the line 3-3 of Fig. 1.

Fig. 4 is a transverse sectional view taken in the main along the line 4-4 of Fig. 2, the upper 'right hand portion, however, being taken along the line 4, l of Fig. 2;

Fig. 5 is a detail perspective view of parts of the movable contact member.

The mainsupport and enclosure for the circuit breaker consists of a front insulating member or support I and a rear insulating member or as will presently appear.

support 2. As shown all of the operating parts of the circuit breaker and also the main stationary contacts are carried by the front insulating support I. This feature of the construction is not herein claimed, as it is set forth and claimed 5 in my copending'application, Serial No. 690,585, filed September 22, 1933.

' The front insulating support I is oi. box-like iorm, being substantially closed at all iour sides and at the top. The rear insulating support 2 m is also of box-like form, being substantially closed at all four sides and at the bottom. when the two parts are assembled as shown there is provided an interior recess which contains all of the operative parts of the circuit breaker other is than the handle.

Carried by the support I at the rear of the front wall thereof are two rearward projecting parallel -metallic supporting

plates

3, 3 which are held in place by means of screws I, 8 extending through 20 the said front wall and engaging flanges on the said plates. Carried by the said

plates

3, 3 and extending transversely between them is a pivot pin 5. Pivotally mounted on the pin 5 is a contact carrying member which includes two paral- 25 lei insulating plates 6, 6 spaced apart transversely and suitably connected together to move as a unit. These plates have aligned bearing apertures through which the pivot pin 5 extends, shoulders on the pin serving to hold the plates in proper. spaced relationship. It will be observed that the plates are adjacent the inner walls of the main recess formed within the supports I and 2.

The two plates 8, 6 are additionally connected 36 and held in spaced relationship by means of an insulating member I which has several functions,

The member 1 is preferably structurally separate from the plates 8, 6, and as shown the plates are notched at 8, and the 40 member I has projections at 9 shaped to fit the notches in the plates. The two plates and the said insulating body I areheld in proper relationship by means-of tie rods or rivets III, III extending through suitable holes II, II and l2, I2. 45 Preferably the plates 6, 6 have arcuate outer edges concentric with the pivotal axis at 5 and the insulating body I is shaped to conform to these arcuate edges. 4

The two movable contacts [3 and I4, instead 50 bf projecting outward from the two side plates as illustrated in the patents referred to, are positioned entirely between the said side plates, or at least between the outer planes thereof. I have shown the two movable contacts as being in transverse u tact.

register with each other, but I do not so limit myself. when they are so placed each of them is held by its corresponding side plate and the two contacts are spaced apart transversely, the space between them, however, being relatively small. Figs. 4 and 5 clearly show the relationship between the two movable contacts and the two insulating side plates 6, 6. Preferably and as shown each of the side plates is provided with holes such as I5, adapted to receive corresponding lateral projections IS on the corresponding con- When the projections I6 are entered in the holes I5 the contact is firmly held in relationship to the corresponding side plate.

The two contacts l3 and 4, whether in transverse register or not, are electrically connected with each other, this electrical connection preferally being through a suitable electro-responsive means which is carried by and bodily movable with the contact member. Preferably and as shown this electro-responsive means is a bi-metallic thermostatic strip I1, and when the two contacts are in transverse register with each other the strip is U-shaped as clearly shown in Fig. 5. The two legs of the U-shaped strip are riveted to the respective contacts as shown, and the strip is provided with a projection or lug l3 which enables the strip to serve as a latch.

As already stated the spacing between the two contacts l3 and I4 is small, and in order to avoid any arcing between the said contacts it may be desirable to provide an insulating barrier such as l9. Preferably this barrier is formed as an integral part of the before-mentioned barrier member] and also by preference it is formed with opposite grooves, as shown, into which the inner edges of the two contacts project. Thus the barrier |9 serves not only to insulate the two contacts from each other, but also serves to assist in holding them in proper position. Preferably the barrier l 9 is extended as shown at 20 so as to occupy a position between the two legs .of the U- shaped strip |1, thus preventing any possibility of arcing between the two legs of the strip. It

- will be understood that during manufacture the contacts and thermal strip are first assembled with the barrier member, the side plates 6, 6 being put in place afterwards.

At the rear of the insulating support I are two similar substantially stationary main contacts 2| and 22 which are connected with the said support by means of more or less resilient bent conducting straps 23 and 24. These stationary contacts are arranged in accordance with the arrangement of the movable contacts I3 and I4, and when the movable contacts are in transverse register the stationary contacts 2| and 22 are also in transverse register. In any event the stationary contacts are positioned between the outer planes of the side plates of the contact member, so as to be adapted to be engaged by the respective movable contacts.

As shown the straps 23 and 24 are similar to each other and are U-form and project rearward from the support I into suitable recesses 25 and 26 formed in the rear support 2. The strap 23 is held in place by means of screws 21 which also hold a downward extending conductor 28. The conductor 28 is detachably connected by means of a screw 29 with another conductor 39 which extends along a recess in the bottom of the support 2 and is provided at its left hand end with a wire terminal at 3|. The conducting strap 24 is held in place by screws 32 similar to the. screws 21, these screws also holding a conducting strap 33 which projects at the right. This conducting strap may be provided with a wire terminal, or it may be connected directly with the bus bar of a panel board. At the bottom of the support 2 there is provided an insulating closure plate 34 which is held in place partly by a screw 35 and partly by a screw 36. It will be apparent that the before-mentioned

screws

29 and 36 cooperate with each other to hold the two main supports and 2- in proper relationship. When these supports are to be separated it is necessary to remove the plate 34 by loosening the two

screws

35 and 36 and then remove the screw 29 so as-to disconnect the two conductors 23 and 30.

From the foregoing description it will be apparent that the contact member may be moved to bring the movable contacts I3 and I4 into or out of engagement with the respective stationary contacts 2| and 22 to make or break the circuit. A suitable spring means is provided for biasing the contact member in the contact disengaging direction. As shown there are two

separate springs

31, 31 surrounding the pin 5 and positioned between the supporting

plates

3, 3 and the insulating plates 6, 6. I

There is provided a movable member 39 which I will term an actuator or actuating member, this member serving as the means for actuating the contact member for normal switching purposes or to effect closing of the circuit after automatic opening thereof. The actuator 38 is pivotally mounted on the pivot pin 5 between the supporting

plates

3, 3. As shown the actuator comprises two separate side plates which are connected at one end by a pin 39 and at the other end by a pin or roller 40. At normal temperatures the lug I3 on the thermal latch I1 engages the roller 40, and thus the said latch serves to mechanical connect the actuator with the contact member so that the two may move in unison.

For manually operating the actuator 33 I provide a handle member 4| which is mounted on a pin 42 extending between upward extensions on the two supporting

plates

3, 3. The handle projects through an opening in the front wall of the support I. A spring 43 serves to bias the handle toward its open-circuit position. The handle member 4| is connected with the actuator 38 by means of two similar links 44, 44, the links being pivoted to the handle member at 45 and to the actuator at 39.

When the parts are in the relative positions shown in Fig. 3 the links 44 cooperate with the handle member itself to form a toggle action which lock the parts in position with the movable contacts l3 and I4 pressed into firm engagement with the stationary contacts 2| and 22. Continued movement of the handlein the clockwise direction is prevented by the engagement of an extension 46 thereon with the pivot pin 5. The pivotal axis at 45 is above a straight line connectingthe pivotal axes at 39 and 42, and thus the handle member and the links 44 serve to resist the tendency of the contact member to move in the clockwise direction under the influence of the

springs

31, 31 and of the resilient strips 23 and 24 supporting the contacts 2| and 22. At the same time the toggle action holds the handle member 4| in its right hand or closed-circuit 'position, resisting the tendency of the spring 43 to move it in the counter-clockwise direction.

The above described toggle action can be released by pressing the handle toward the left, the parts then moving under the action of the springs 31 and 43 to the relative position shown in Fig. 2.

The movable contacts I: and M are thus disengaged from the stationary contacts 2| and 22 and the circuit is broken at two separation places. By moving the handle toward the right the several parts can be restored to their relative posi-v tions as shown in Fig. 3'and the circuit can be reestablished.

As already explained, the bi-metallic strip I! is electrically connected between the movable contacts I3 and l4. It is adapted to be deflected outward upon the passage of excess current therethrough with the result that the lug i8 is disen gaged from the roller 40. when this occurs the contact member moves automatically to the position shown in Fig. 2, this movement not being in any way dependent upon the handle and the actuator. In fact the handle may be held in the closed-circuit position without in any way interfering with the automatic releasing action. It will be understood however that,as already ex-- plained, the handle is ordinarily held in its closedcircuit position only by reason of pressure transmitted through the links 44. As soon as the ther-,

mal strip is released from its engagement with the actuator, this pressure through the links 44 is instantly released,and the handle member and the actuator immediately move to their open-circuit positions whereupon the lug i8 is again engaged with the roller .40 as shown in Fig. 2. Movement of the handle member and actuator to their open-circuit positions occurs substantially simultaneously with the movement of the contact member. The parts can. be restored to their closed-circuit positions as shown in Fig. 3 by nearly moving the handle toward the right.

In view of the close spacing of the stationary contacts 2| and 22 it is preferable to provide a suitable insulating barrier between them, and in order that this barrier may not interfere with the movement of the movable contact member and of the contacts thereon, I prefer to provide a barrier 41 which is carried by the contact member and is movable therewith. As'shown this barrier 41 is formed as an integral part of the beforementioned barrier member 1. It projects radially outward and extends between the two stationary contacts, as clearly shown in Figs. 3 and i.

In my copending application for Automatic circuit breakers, Serial No. 690,584 filed September 22, 1933, I have shown a construction wherein the path of movement of each movable contact is substantially enclosed at all four sides thereof so as to confine and control any arc-formed gases. As disclosed in the said application there are two movable walls and two stationary walls associated with each movable contact. This same arrangement of walls is incorporated in the present circuit breaker. From an inspection of the drawing it will be apparent that each movable contact has associated with it the adjacent fiat wall or surface of the barrier 41 and the adjacent convex wall or surface 48 of the main body of the member 1. The two stationary walls associated with each movable contact are formed on the rear insulating support 2, thesaid body having adjacent each movable contact a flat wall 49 and a concave arcuate wall 50. Between the two

concave surfaces

50, 50 there is provideda groove 55 into which the barrier 41 extends. An inspection of Figs. 2 and 4 will show that the path of opening movement of each movable contact is enclosed by the four walls at 41, 48, 49 and 50.

I proper control, I provide a vent or a series of vents adjacent the path of movement of each contact. The details of construction are the same for the two movable contacts, the vents and duct for the contact l4 being clearly shown in Fig. 2. The concave wall 50 is provided with one 5 or more rearward extending vents 52, 52 which communicate with a duct 53 extending toward the left and then in a forward direction to an outlet at 54. Any gases that may be formed when the contacts separate pass rearward through the 10 vents 52, 52 and are then discharged through the duct 53 and the outlet 54, being thus sufllciently cooled to eliminate all possible danger.

If it be assumed that the circuit breaker is to be used in a panel box, it may be held in place 16 partly by the connection between the bus bar and the conducting strap 33, and partly by a screw extending through the hole 55.

What Iclaim is:

1. An automatic circuit breaker comprising in 20 combination, two stationary electric contacts, a

movable contact member comprising two transversely spaced insulating side elements and two contacts electrically connected with each other and positioned between the outer planes of the 25 said side elements, the said contact member being movable to bring the movable contacts into or out of engagement with the respective stationary contacts and the said member being biased for movement in the contact disengaging direc- 30 tion, and electro-responsive means normally holding the contact member in the contact engaging position and arranged to be energized upon the attainment of an abnormal current condition in the circuit so as to release the said contact member and permit it to automatically move in the contact disengaging direction.

2. An automatic circuit breaker comprising in combination, two stationary electric contacts, a movable contact member comprising two transversely spaced insulating side elements and two contacts positioned between the outer planes of the said side elements, the said contact member being movable to bring the movable contacts into or out of engagement with the respective stationary contacts and the said member being biased for movement in the contact disengaging direction, and a iii-metallic thermostatic strip bodily movable with the contact member and electrically connected between the two movable contacts I with the result that upon the attainment of an abnormal current condition in the said strip it is deflected so as to mechanically release the contact member and permit it to automatically move to open-circuit position.

3. An automatic circuit breaker comprising in combination, two stationary electric contacts, a pivotally movable actuating member, a pivotally movable contact member comprising two transversely spaced insulating side elements and two contacts electrically connected with each other and positioned between the outer planes of the said side elements, the said contact member being movable to bring the movable contacts into or out of engagement with the respective stationary contacts and the said member being biased for movement in the contact disengaging direction, and a bi-metalic current carrying strip on the contact member between the side elements thereof and serving as an electro-thermally releasable mechanical latch normally connecting the contact member with the actuating member.

4. The combination in an automatic circuit breaker, of two stationary electric contacts, a movable contact member comprising two transversely spaced insulating side elements and two movable contacts electrically connected with each other and positioned in transverse register with each other between the outer planes oi! the said side elements, thesaid contact member being movable to bring the movable contacts into or out of engagement with the respective stationary contacts and the said member being biased for movement in the contact disengaging direction, and electro-responsive means normally holding the contact member in the contact engaging position and arranged to be energized upon the attainment of an abnormal current condition in the circuit so as to release the said contact "member and permit it to automatically move in the contact disengaging direction.

5. The combination in an automatic circuit breaker, of two stationary electric contacts, a pivotally movable contact member comprising two transversely spaced insulating side elements and two movable contacts electrically connected with each other and positioned in transverse register with each other between the outer planes of the said side elements, the said contact member being movable to bring the movable contacts into or out of engagement with the respective stationary contacts and the said member being biased for movement in the contact disengaging, direction, an insulating barrier between the two movable contacts, and electro-responsive means normally holding the contact member in the contact engaging position and arranged to be energized upon the attainment of an abnormal current condition in the circuit so as to release the said contact member and permit it to automatically move in the contact disengaging direction.

6. The combination in an automatic circuit breaker, of two stationary electric contacts, a movable contact member comprising two transversely spaced insulating side elements and two movable contacts electrically connected with each other and positioned in transverse register with each other between the outer planes of the said side, elements, the said contact member being movable to bring the movable contacts into or out of engagement with the respective stationary contacts and the said member being biased for movement in the contact disengaging direction, an insulating barrier carried by and movable with the contact member and positioned between the two movable contacts, and electro-responsive means normally holding the contact member in the contact engaging position and arranged to be energized upon the attainment of, an abnormal current condition in the circuit so as to release the said contact member and permit it to automatically move in the contact disengaging direction.

'7. The combination in an automatic circuit breaker, of two stationary electric contacts, a pivotally movable actuating member, a pivotally movable contact member comprising two transversely spaced insulating side elements and two contacts electrically connected with each other and positioned in transverse register with each other between the outer planes of the said side elements, the said contact member being movable to bring the movable contacts into or out of engagement with the respective stationary contacts and the said member being biased for movement in the contact disengaging direction,a bimetallic U-shaped strip carried by the contact member between the side elements thereof and serving as an electrothermally releasable mechanical latch normally connecting the contact member with the actuating member, and a barrier carried by and movable with the contact member and positioned in part between the two movable contacts and in part between the two legs 0! the U-shaped strip.

8. In an automatic circuit breaker, the combination 01 a movable contact member comprising two transversely spaced insulating side elements and two contacts electrically connected with each other and positioned in transverse register with each other between the outer planes of the said side elements, two stationary electric contacts closely spaced in transverse register with each other and adapted to be engaged by the movable contacts, an insulating barrier extending between the two stationary contacts, means for biasing the said contact member for movement in the contact disengaging direction, and electro-responsive means normally holding the contact member in the contact engaging position and arranged to be energized upon the attainment of an abnormal current condition in the circuit so as to release the said contact member and permit it to automatically move in the contact disengaging direction. v

9. In an automatic circuit breaker, the combination of a movable contact member comprising two transversely spaced insulating side elements and two contactselectrically connected with each other and positioned in transverse register with each other between the outer planes of the said side elements, two stationary electric contacts closely spaced in transverse register with each other and adapted to be engaged by the movable contacts, a movable insulating barrier on the movable contact member extending between the two stationary contacts, means for biasing the said contact member for movement in the contact disengaging direction, and electro-responsive means normally holding the contact member in the contact engaging position and arranged to be energized upon the attainment of an abnormal current condition in the circuit so as to release the said contact member and permit it to automatically movein the contact disengaging direction.

10. In an automatic circuit breaker, the combination of a pivotally movable contact member comprising two transversely spaced insulating side elements and two contacts electrically connected with each other and positioned in transverse register with each other between the outer planes of the said side elements, two stationary electric contacts closely spaced in transverse register with each other and adapted to be engaged by the movable contacts, an arcuate movable insulating barrier on the movable contact member extending radially outward between the two stationary contacts, means for biasing the said contact member for movement in the contact disengaging direction, and electro-responsive means normally holding the contact member in the contact engaging position and arranged to be energized upon the attainment of an abnormal current condition in the circuit so as to release the said contact member and permit it to automatically move in the contact disengaging direction. 7

11. In an automatic circuit breaker, the combination of a pivotally movable contact member comprising two transversely spaced insulating side elements and two contacts electrically connected with each other and positioned in transverse register with each other between the outer planes of the said side elements, two stationary electric contacts positioned in transverse register with each other between the said outer planes of the side elements of the contact member and adapted to be engaged by the movable contacts,

means for biasing the said contact member for movement in the contact disengaging direction, electro-responsive means normally holding the contact member in the contact engagin position and arranged to be energized upon the attainment of an abnormal current condition in the circuit so as to release the said contact member of movement of the respective movable contacts and having a groove for receiving the said movable barrier betweenthe stationary contacts.

12. An automatic circuitbreaker comprising in combination, two stationary electric contacts, a manually operable handle, a movable contact a member comprising two transversely spaced insulating side plates and two movable electric contacts adapted to engage and disengage the respective stationary contacts, the said contact member being biased in the contact 1 t 1 t: i direction, an electro-responsive means on the contact member positioned between the side plates and electrically connected between the movable contacts, the said means normally serv= ing to mechanically connect the said contact member with the handle and being automatically releasable upon the passage of excess current to permit independent circuit-opening movement of? the contact member, and a movable barrier member structurally separate from the said side plates and positioned between them at the cut= side of the electro-responsive means.

13. An automatic circuit breaker comprising in combination, two stationary electric contacts, a pivota'lly movable actuating member, a pivotally movable contact member com two trans= versely spaced insulating side platm and two movable electric contacts adapted to engage and disengage the respective stationary contacts, the said contact member being biased in the contact disengaging direction, an eiectro-responsive means on the contact member positioned betwem the side plates and electrically connected between I the movable contacts, the said means m, a,

It serving to mechanically connect the said con= tact member with the actuating member and being automatically releasable upon the passage or excess current to permit independent circuit opening movement of the contact member, and a movable barrier member separate from the said side plates and itioned between them at the outside oi the clectro=responsive means on the contact member positioned between the side plates and electrically connected between the movable contacts, the said means normally serving to mechanically connect the said contact member with the handle and being automatically releasable upon the passage of excess current to permit independent circuit-opening movement oi the contact member, and a movable barrier positioned between the side elements in part. at the outside of the electro-responsive- 5 means and in part between the two movable con- 15. An-automatic circuit breaker comprising in combination, two stationary electric contacts, a pivotally movable actuating member, a pivotally 10 movable contact member comprising two transversely spaced insulating side elements and two movable contacts positioned in transverse register with each other between the outer planes of the said side elements and adapted to engage and 15 disengage the respective stationary contacts, the

said contact member being biased in the contact disengaging direction, an electro-responsive means on the contact member positioned between the side plates and electrically connected between 2 the movable contacts, the said means normally serving to mechanically connect the said contact member with the actuating member and being automatically releasable upon the passage of excess current to permit independent circuit-openg5 ing movement of the contact member, and a movable barrier positioned between the side elements in. part at the outside of the electro-responsive means and in part between the two movable contacts.

16. An automatic circuit breaker comprising in combination, two stationary electric contacts, a ually operable dle, a movable contact member comprising two transversely spaced in.-

sulating side elements and two movable contacts .5

positioned in transverse register with each other between the outer planes of the said side elements and adapted to engage and disengage the respective stationary contacts, the said contact member being biased in the "contact disengaging w direction, on electro-responsive means on the contact member positioned between the side plates and electrically connected between the movable contacts, the said means normally serving to mechanically connect the said contact 5 member with the handle and being automatically releasable upon the passage of excess current to permit independent circuit-opening movement of the contact member, and a movable barrier positioned between the side elements in part at w the outside oi the electro-responsive means and in part between the two'movable contacts, the said barrier being formed to directly engage the contacts to assist in holding them in position.

17. An automatic circuit breaker comprising in 55,

' combination, a movable contact member comprising two transversely spaced insulating side elements and two contacts electrically connected with each. other and positioned in transverse register with each other between the outer planes w of the said side elements, two stationary electric contacts positioned in transverse register with to be engaged by the movable contacts, means for .5

b the said contact member for movement in the contact disenga direction, an electroresponsive means on the contact member positioned between the side plates and electrically connected between the movable contacts, the 70 said means normally serving to mechanically connect the said contact member with the actuating member and being automatically releasable upon the passage oi excess current to permit independent circuit-ope movement oi the contact 15 member, and a movable barrier positioned between the side elements in part at the outside,

01 the electro-responsive means and in part between the two stationary contacts.

18. An automatic circuit breaker comprising in combination, two stationary electric contacts, a pivotally movable actuating member, a pivotally movable contact member comprising two transversely spaced insulating side plates and two electric contacts adapted to engage and disengage the respective stationary contacts, the said contact member being biased in the contact disengaging direction, a bi-metallic thermal strip on the contact member positioned between the side plates and electrically connected between the movable contacts, the said strip normally serving as an electro-thermally releasable mechanical latch normally connecting the said contact member with the actuating member, and a movable barrier member positioned between the side plates of the contact member and structurally separate therefrom, the said member being at the outside of the thermal strip and extending circumferentially substantially from one end of the strip to the other.

19. An automatic circuit breaker comprising in combination, two stationary electric contacts, a pivotally movable actuating member, a pivotally movable contact member comprising two transversely spaced insulating side plates and two electric contacts positioned in transverse register with each other between the said side elements and adapted to engage and disengage the respective stationary contacts, the said contact member being biased in the contact disengaging direction, a bi-metallic U-shaped strip carried by the contact member between the side elements, thereof and serving as an electro-thermally releasable mechanical latch normally connecting the contact member with the actuating member, and a movable barrier member positioned between the side plates of the contact member at the outside of the thermal strip and extending circumferentially substantially from one end of the strip to the other, the said barrier having an extension thereon positioned between the two movable contacts and between the two legs of the U- shaped strip.

JOSEPH SACHS.