US2052564A - Circuit breaker - Google Patents

Description

Sept. 1, 1936. s. s. GRADY 2,052,564

CIRCUIT BREAKER Original Filed April 30, 1931 4 Sheets-Sheet 1 Jay! INVENTOR ATTORN EY Sept. 1, 1936. s, s. GRADY CIRCUI T BREAKER 4 Sheets-Sheet 2 Original Filed April 30, 1951 INVENTOR AMI/J61- ATTORN EY Sept. 1, 1936. s s GRADY 2,052,564

CIRCUIT BREAKER Original Filed April 30, 1931 4 Sheets-Sheet 3 INVENTOR ATTORNEY Sept. 1, 1936.

s. s. GRADY 2,052,564

CIVRCUIT BREAKER Original Filed April 30, 1951 4 Sheets-Sheet 4 INVENTOR ATTORNEY Patented Sept. 1, 1936 CIRCUIT BREAKER Stephen S. Grady. Magnolia, N. 0., assignor to Fusoid Electric 00., Inc

York

., a corporation of New Application April 30, 1931, Serial No. 533,948

' Renewed November 22, 1935 19 Claims. (Cl. 200-48) My present invention relates generally to circuit breakers, and has particular reference to circuit breakers of the type wherein an insulating member, hereinafter referred to as an interposer, is adapted to be interposed between a pair of complementary contacts when the circuit is to be broken.

A circuit breaker of the type to which my invention relates is usually composed of a suitable housing within which a pair of contact members are mounted, the contacts being spring-pressed toward each other so as to be normally together. The interposer is usually mounted for slidable movement, a spring urging it into an operative position between the contacts and a releasable latch serving to hold it in a normally retracted and poised position. A control handle may be manipulated to set the interposer into its latched position, and a trip mechanism is provided for releasing the latch whenever the circuit is to be broken.

A general object of my present invention is to provide an improved circuit breaker of this general character, and, more particularly, one which is more compact and reliable, less expensive to manufacture, less complicated in structure and operation, and of improved efliciency.

A particular object of my invention is to provide a circuit breaker which may be employed in any position, thereby permitting it to be used under a wide variety of conditions which different requirements may present.

In all circuit breakers of this general type, the objective sought to be accomplished is tobreak an electric circuit whenever the load in the circuit exceeds a certain predetermined maximum. Provision must be made, however, for transient or momentary overloads due, for example, to opening and closing the circuit. In accordance with my present invention, I provide not only a mechanism, responsive to load variations, which serves to operate the trip mechanism directly under predetermined overloads, but also a normally inoperative auxiliary device for taking care of lesser overloads of a sustained character. The auxiliary device is relatively sluggish in operation and is preferably in the form of a thermostat. Under certain predetermined overloads, less than are necessary to operate the trip mechanism directly, this thermostatic deiice will operate the-trip mechanism if such overloads are sustained; but

due to its sluggish character, the thermostat will not operate the trip mechanism under momentary or transient overloads. 7

It is a particular feature ofmy present inveneration of any undesired heat.

tion to provide an arrangement whereby the thermostat is normally short-circuited and therefore totally inoperative. Although thermostats have been employed in circuit breakers in the past, I am not aware of any prior arrangement which does not require current to be constantly flowing through the thermostat. By avoiding this, I am enabled to provide a device which is more easily set or adjusted to predetermined loads, and which operates for long periods of time without gen- Furthermore, the operation of my device involves no losses due to voltage drop across the thermostat, or deterioration of the thermostat due to overheating; and my present circuit breaker operates efliciently and in a predetermined manner regardless of external temperature conditions,

A further feature of my invention lies in providing an improved mechanism for setting the interposer. In accordance with my present invention, an extremely simple and compact mechanical arrangement prevents the interposer from being controllably moved or adjusted except when the contacts are separated. Any unwarranted or deliberate attempt, therefore, to hold the interposer out of operative position is wholly unsuccessful, and my present device is therefore entirely foolproof, resisting and preventing any purposeful attempts to render the circuit breake inoperative and thereby permitting passage of t e.

very.overloads which the circuit breaker is designed to prevent.

I achieve the foregoing objects and advantages, and such other objects and advantages as may hereinafter appear or be pointed out, in the manner illustratively exemplified in the accompanying drawings, wherein- Figure 1 isa cross-sectional elevation through a circuit breaker of the present character, this view being taken substantially along the line li of Figure 2;

Figure 2 is a plan view of Figure 1 with the cover removed and with certain parts omitted or sectioned for the sake of clearness;

Figure 3 is a cross-sectional view taken substantially along the line 3-3 of Figure 1;

Figure 4 is a. view similar to Figure 1. showing the circuit breaker in its normal inoperative position, 1

Figure 5 is a cross-sectional view taken substantially along the line 5--5 of Figure 4;

Figure 6 is a cross-sectional view taken substantially along the line 6--6 of Figure 4;

Figure 6A is a; perspective view of one of the structural elements:

Figure 6B is a perspective view of the interposer;

Figure 7 is a perspective view of certain portions of the trip mechanism;

Figure 8 is an enlarged fragmentary view taken in the direction of Figure 4;

Figure 9 is a plan view of Figure 8;

Figure 10 is a view similar to Figure 8 showing the parts in the relationship they assume after the interposer is set into poised position;

Figure 11 is a plan view of Figure 10 with the parts in the full-line positions of Figure 10;

Figure 12 is a plan view of Figure 10 with the parts in the dot-and-dash positions of Figure 10;

Figure 13 is a fragmentary cross-section along the line I3l3 of Figure 11;

Figure 14 is a similar view taken substantially along the line |4--l4 of Figure 12; and

Figure 15 is a diagrammatic view showing the electrical connections.

The housing of my present circuit breaker consists, in general, of two parts, a bottom part or container 20 and a top part or cover 2i. These two elements are provided-with recesses, openings, depressions, shoulders, and the like to accommodate the several parts which will be hereinafter described in greater detail. The cover is held in position by means of the studs 22 and 23, and the entire circuit breaker is adapted to be mounted upon a panel board or the like by studs or the like which are adapted to pass through the bores 24 and 25 provided for this purpose.

The contact member 26 is secured as at 21 to the housing and is adapted to cooperate with the complementary contact member 28 mounted within the housing. The member 28 is carried upon a stem 29 of copper or the like, and is constantly engaged by a leaf spring 30 which tends to hold the contacts 26 and 28 together, as shown in Figure 1. It is these contacts which are to be separated by my present device under certain overload conditions.

The separation of the contacts is accomplished by means of the interposer 3| which is shown in retracted poised position in Figure 1, and in forwardly projected operative position in Figure 4. A pair of coiled compression springs 32 constantly urge the interposer forwardly into the position of Figure 4, wherein it will be noted that the contacts 26 and 28 are held in separated position.

A latch arrangement, presently to be described,

serves to hold the interposed in its retracted position, against the action of the springs 32, whenever the circuit breaker is in use; and the trip mechanism and manner of operation thereof for releasing the latch and permitting the springs 32 to function will be hereinafter described in greater detail.

The interposer by itself is shown most clearly in Figure 63. It is substantially flat, having a wedge-shaped forward edge 33 and two rearwardly disposed ears 34 adapted to engage with the forward ends of the springs 32 respectively. A longitudinal slot 35 has a forward transversely enlarged portion 33 which defines the shoulder 37. By means of a separate metallic member 38 riveted in position as at 39, a downwardly projecting shoulder 48 is provided behind the shoulder 31.

Before describing the other mechanism, I will point out that. in setting the interposer into its retracted position, a tongue engages the shoulder 37 to force the interposer rearwardly. After a predetermined rearward movement, the shoulder 40 engages a complementary relatively fixed shoulder and thereby latches the interposer in rearward position. When the latch is released, the interposer must be free to advance forwardly under the action of the springs 32, and, in accordance with my present invention, it is impossible to prevent these springs from operating once the interposer has been set. This is accomplished by an arrangement whereby the tongue for engaging the shoulder 31 is excluded-from the enlarged space in front of the shoulder 37 at all times except when the contacts 26 and 28 are separated. As soon as the contacts 26 and 28 are closed, the interposer is rendered trip free, which means that the control tongue is forced laterally away from in front of the shoulder 31, and, more particularly, into the longitudinal slot 35.

The'interposer 3| rests slidably upon the base 4| of the housing 28, and this baseis provided with the two longitudinal channels 42 which are adapted to accommodate the springs 32 when the parts are assembled. Within a depression 43', the latching and trip mechanism are arranged, this portion of my device being most clearly illustrated in Figure 7 and in the succeeding figures.

Referring to Figure '7, and also to Figures 8 and 10, I will point out that the member with which the projection 40 engages, in order to latch the interposer, is in the form of a strip of metal 43 whose rear edge is centrally cut out to provide a shoulder 44 which positions itself directly in front of the projection 40 when the interposer is latched.

At its forward end, the strip 43 curves downwardly as at 45, and immediately behind this portion a downward tab 46 is struck out of the material, leaving an opening 41.

At its rear edge, the strip 43 is bent downwardly and then rearwardly to provide the tab 48. Pressure downwardly upon the tab 48 withdraws the shoulder 44 from in front of the projection 40 and thereby releases the latch. I

Riveted to the under-surface of the strip 43 is the forward end of a U-shaped bimetallic thermostat, the two arms 49 and 50 of which are provided at their rear ends with the openings 5| and 52 respectively. Insulating strips 53 are arranged on opposite sides of the forward end of the thermostat as'shown most clearly in Figure 8, since the strip 43 forms no part of the operative electric circuit. I

Underneath the arms 49 and 50 are the conductive strips 54 and 55, respectively, attached at their rear ends to the rear ends of the arms 49 and 50. The thermostat is normally shortcircuited by a copper bridge 56 which engages the under-surfaces of the strips 54 and 55 under normal conditions.

The bridge 56 is carried upon the arm 51 of a bell crank whose other arm 58 extends vertically and is provided with the pivot pins 59. The forward end of the arm 51 is arranged over the tab 48, so that when the arm 51 moves downwardly this forward end encounters the tab 48.

Under normal conditions, the bell crank is in the position of Figure 1, a spring 60 hearing upwardly against the arm 57. It will be noted that electric circuit hereinafter to be described. It the arm 58 is moved forward no further than this, any sustained minor overload will cause the thermostat to flex downwardly, carrying the strip 43 with it and releasing the latch. Momentary or transient minor overloads will not trip the latch. On the other hand, if the arm 58 is moved forwardly by a greater amount than illustrated in Figure 7, the latch will be tripped immediately and directly by virtue of the downward pressure of the arm 51 upon the tab 48.

Regardless of the manner in which the latch is tripped, it will be understood that as soon as the interposer has broken the circuit which controls the movements of the arm 58, the spring 60 will immediately restore the thermostat and its associated parts to the relationship of Figure 1. l

The pivots 59 are journaled in the U-shaped bearing 6| which is mounted in the housing 20 by means of the stud 62.

The upper end of the arm 58 is engaged by one of the laminations of the core 93 of the solenoid 64, as shown most clearly in Figures 1 and 4. It is the energizati'on of this solenoid to lesser or greater degrees which controls the corresponding movements, hereinbefore described of the arm 58.

A spring 65 normally urges the core 63 outwardly, i. e., toward the right as shown in the figures; and in its normal position, this core is engaged by a detent 66 as shown in Figure 1. This detent consists of a cantilever strip mounted, as at 61, to the housing and adjustable to an accurate degree by the adjustment screw 68. If the screw 68 is adjusted, the detent 66 engages the core with greater or less force,

- thereby requiring a correspondingly greater or less current to draw the core 63 into the solenoid.

It is the adjustment of the screw 68 which predetermines the loads under which the circuit breaker will operate. For example, the screw 58 may be accurately adjusted so that a load of, say, 18 amperes is necessary to move the core 63. .If this adjustment is made, then any currents less than this amount will leave the device in the normal condition of Figure 1, the thermostat being short-circuited and the interposer being latched. The solenoid may be so designed that currents between, say, 18 amperes and about 135 amperes will be suflicient only to move the arm 58 into the position-of Figure 7; whereas currents greater than 135 amperes will move the arm 58 by a greater degree. With a structural design of this illustrative character, currents between 18 and 135 amperes will not trip the latch if momentary, but will trip the latch if sustained beyond a transient degree. And, in any event, currents greater than 135 amperes will cause an immediate release of the latch by the direct operation of. the arm 51 upon the tab 48.

Arranged over the interposer 3! is the cover plate 69 which is illustrated most clearly in Figure 6A. It is substantially H-shaped, the cross portion 10 being slightly depressed and provided with the two apertures 1|. Upon the depressed portion 10, the rear ends of the contact strip 29 and the leaf spring 30 rest, being secured in position by means of the screws 12. The springs 32 are accommodated beneath the-parallel side arms One of the arms of the plate 69 is bent downwardly, as at 16, and is connected to the rear of the thermostat arm 49 by means of the stud 11 which engages through the opening 5|. This stud also holds the arm 49 securely to the housing 20 as shown in Figure 5; and a similar stud 18 passes through the opening 52 in the thermostat arm 50 and secures this arm to the housing 20.

The electrical circuit may now be traced with the aid of Figure 15, from the contact 26 through the contact 28 and the conductive strip 29 to the cover plate 69, thence through the portion 16 to the thermostat arm 49. When the thermostat is short-circuited, the circuit continues through the strip 54 across the bridge 56 to the strip 55 and thence directly to the stud 18. When the thermostat is operative, the circuit must be traced through the thermostat itself to the stud 18. From the latter stud, an electrical connection (not shown, except in Figure 15) extends, as at 19, to one end of the coil of the solenoid 64, and the other end of the solenoid is connected by a lead to the binding post 8 I, and thence through the strip 82 to the terminal 83. The main outer circuit connects with the contact 26 and also with the terminal 83.

The strip 82 is attached to the housing by means of the stud 84, as shown most clearly in Figure 1.

The manner in which the interposer 3| is set is most clearly illustrated in Figures 8-14. A control handle projects through the top wall. 2| and is pivoted, as at 9!, in the opposite side walls of the housing to permit the handle to be swung between the positions of Figures 1 and 4. Pivoted to the"handle 90 within the housing, as at the pivot 92, is a tongue 93 which is adapted to pivot in a transverse direction, i. e., from the position shown in Figures 6 and 13 to the position shown in Figure 14. A small, relatively weak spring 94 is associated with the pivot 92 and engages the tongue 93 to urge the latter normally into the position of Figures 6 and 13.

The leaf spring 39 and also the contact strip 29 are provided with the openings 95 and 96, respectively, through which the tongue 93 projects, and the extreme lower end of the tongue extends through the slot in the interposer, either through the slot portion 35 or the enlarged portion 36, depending upon the lateral position of the tongue. I

The tongue 93 is provided with the projection or abutment 91 which is shown most clearly in Figures 13 and 14. I Assuming that the parts of the device are in the normally inoperative relationship of Figures 4, 8, and 9, it will be observed that the spring 94 is holding the tongue 93 in front of the interposer shoulder 31, this disposition of the tongue 93 being permitted by virtue of the fact that the contacts 26 and 28 are separated, whereby the abutment 91 may position itself beneath the leaf spring 30, as shown in Figure 13. When the handle 99 is'pushed into the position of. Figure 1, the tongue 93 engages the interposer shoulder 31 and forces the interposer rearwardly, but; at the same time, the abutment 91 bears against the under-surface of the leaf spring 39 and tends to hold the latter in a raised condition. The

withdrawal of the interposer from the position b of Figure 8 into that of Figure 10 leaves the leaf spring 30 free to push the contact 28 downwardly from the full-line position of Figure 10 to the dot-and-dash position. It is impeded, however, by the abutment 91,and as long as there is frictional engagement between the tongue 93 and the shoulder 31, the tendency of the spring 30 to cam the abutment 91 laterally out of its way is insuificient to accomplish this deflection. As a result, merely swinging the handle 90 into the position of Figure 1 does not close the contacts 26 and 28, and as long as pressure is exerted upon the handle 90 the parts remain in the intermediate relationship illustrated in full-lines in Figure l0 and also illustrated in Figures 11 and 13. The moment pressure upon the handle 90 is released, however, the frictional engagement between the tongue 93 and the shoulder 31 becomes insufiicient to Withstand the tendency of the spring 30, whereupon the latter snaps down wardly into the dot-and-dash position of Figure 10 (illustrated also in Figures 12 and 14), and in doing so deflects the tongue 93 into the position of Figures 12 and 14. In this position, it is observed that the tongue is no longer in front of the interposer shoulder 31 but is disposed within the slot portion 35. The interposer is thus rendered trip free the instant that contact is established between the contacts 26 and 28.

During the movement of the tongue 93 from the position of. Figure 8 to that of Figure 10, the lower end thereof will have wedged its way over the forward end of the strip 43, so that when the interposer is set in poised latched position, the lower end of the tongue 93 is disposed within the opening 41. The purpose of this will now be clear, because if it is desired to operate the circuit breaker by hand, it is merely necessary to press the handle 90 from the position of Figure 1 toward the position of Figure 4; and as the tongue rides over the tab 46, it will deflect the strip 43 downwardly and thereby release the latch and permit the interposer to snap into its forward operative position. Under these conditions, the tongue 93 is again free to position itself in front of. the shoulder 31, the abutment 97 again engaging bencath the leaf spring 39. If desired, a

tongue 93 to be deflected out of the path of the interposer, so that under overload conditions a release of the latch will permit the interposer to advance rapidly forwardly and separate the contacts 26 and 28. Any attempt to hold the interposer in retracted position, other than by means of the latch arrangement, will be. unsuccessful, because although the interposer may be held rearwardly as shown in full-lines in Figure 10, the contacts will not close until pressure upon the handle 99 is released; and when such pressure 'is released the closing of the contacts automatically thrusts the tongue 93 out of the path of the interposer and leaves the latter free to function in its contemplated manner under predetermined overloads.

It will be obvious that changes in the details herein described and illustrated for the purpose of explaining the nature of my invention may be made by those skilled in the art without departing from the spirit and scope of the invention as. expressed in the appended claims. It is therefore intended that these details be interpreted as illustrative, and not in a limiting sense.

Having thus described my invention and illustrated its use, what I claim as new and desire to secure by Letters Patent is- 1. In a circuit breaker, a pair of contacts, an interposer for separating the contacts, an electric circuit, a trip for normally anchoring said interposer in circuit making position, a normally inoperative and relatively sluggish device adapted to operate said trip, and means responsive to load variations in said circuit for rendering said device operative under certain loads and for operating the trip directly under certain greater loads.

2. In a circuit breaker, an electric circuit including a pair of contacts normally in engagement with one another, an interposer for separating the contacts, and a trip for normally anchoring said interposer in circuit making position, said circuit also including a normally inoperative thermostat adapted to operate said trip, said thermostat being responsive to load variations in said circuit and operative under certain loads.

3. In a circuit breaker, a pair of contacts, a device for separating the contacts, an electric circuit, a trip for normally anchoring said device in circuit making position, a normally inoperative thermostat adapted to operate said trip, and

means responsive to load variations in said circuit for rendering said thermostat operative under certain loads and for operating the trip directly under certain greater loads.

4. In a circuit breaker, a pair of contacts, an interposer for separating the contacts, an electric circuit, a trip for normally anchoring said interposer in circuit making position, a normally short-circuited device in said circuit adapted to operate said trip, and means responsive to load variations in said circuit for destroying said short-circuit and thereby rendering said device operative under certain loads.

5. In a circuit breaker, a pair of contacts, an interposer for separating the contacts, an electric circuit, a trip for'normally anchoring said interposer in circuit making position, a device in said circuit adapted to operate said trip, a movable member normally short-circuiting said device to render it inoperative, and an electromag netic mechanism responsive to load variations in said circuit for moving said short-circuiting member and thereby rendering said device operative under certain loads.

6. In a circuit breaker, a pair of contacts, an interposer for separating'the contacts, an electric circuit, a trip for normally anchoring said interposer in circuit making position, a normally short-circuited thermostat in said circuit adapted to operate said trip, and means responsive to load variations in said circuit for destroying said short-circuit and thereby rendering said thermostat operative under certain loads.

7. In a circuit breakena pair of contacts, an interposer for separatingv the contacts, an electric circuit, a trip for normally anchoring said interposer in circuit making position, a thermostat in said circuit adapted to operate said trip,

a movable member normally short-circuiting said thermostat to render it inoperative, and an electromagnetic mechanism responsive to load thermostat operative under certain loads.

8. In a circuit breaker, a pair of contacts, a

a device for separating the contacts, an electric circuit, a trip for normally anchoring said device in circuit making position, a normally shortcircuited thermostat in said circuit adapted to operate said trip,- and means responsive to load variations in said circuit for destroying said short-circuit and thereby rendering said thermostat operative under certain loads and for operating the trip directly under certain greater loads.

9. In a circuit breaker, a pair of contacts, a device for separating the contacts, an electric circuit, a trip for normally anchoring said device in circuit making position, a thermostat in said circuit adapted to operate said trip, a movable member normally short-circuiting said thermostat to render it inoperative, and an electromagnetic mechanism responsive to load variations in said circuit for moving said short-circuiting member and thereby rendering said thermostat operative under certain loads, said electromagnetic mechanism being adapted to operate said trip directly under certain greater loads.

10. In a circuit breaker, a pair of contacts, an interposer for separating the contacts, an electric circuit, a trip for normally anchoring said interposer in circuit making position, a thermostat in said circuit adapted to operate said trip, a movable member normally short-circuiting said thermostat to render it inoperative, and an electromagnetic mechanism responsive to load variations in said circuit for moving said short-circuiting member and thereby rendering said thermostat operative under certain loads, said mechanism comprising a magnet coil, an armature under the influence of said coil, and a lever ations' in said circuit for moving said short-circuiting member and thereby rendering said thermostat operative under certain loads, said electromagnetic mechanism being adapted to operate said trip directly under certain greater loads;

said mechanism comprising a magnet coil, an

armature under the influence of said coil, and a lever operatively interposed between said armature and said short-circuiting member, said lever being adapted to engage said trip directly after predetermined movement of said lever.

12. In a circuit breaker for an electric circuit,

the combination with a pair of contacts in the circuit, of a device for separating said contacts into circuit breaking position, a trip for,normally anchoring said device in circuit making position where said contacts engage one another, 8. normally inoperative and relatively sluggish device operatively associated to operate said trip, and a mechanism responsive to load variations in said circuit for rendering said sluggish device operative upon partial actuation under light overloads and for operating said trip directly upon more pronounced actuation under heavy overloads.

13. In a circuit breaker for 'an electric circuit, the combination with a pair of contacts in the circuit, of a movable interposer, means for urging said interposer to separate said contacts into circuit breaking position, a trip for normally anchoring said interposer in circuit making position where said contacts engage one another, a normally inoperative and relatively sluggish device operatively associated to operate said trip, and a mechanism responsive to light overloads in the circuit for partial actuation to render said device operative in turn to actuate said trip and also responsive to heavy overloads for more pronounced actuation to actuate said trip directly.

14; In a circuit breaker for an electric circuit, a pair of contacts in the circuit, a movable interposer, springs for urging said interposer to separate said contacts into circuit breaking position, a trip for normally anchoring said interposer in circuit making position where said contacts engage one another, a normally inoperative and relatively sluggish device operatively associated to operate said trip, and a mechanism including a short circuiting member and a lever and being responsive to load variationsin said circuit for partially actuating said lever in turn to actuate said short circuiting member to render said sluggish device operative upon light overthe combination with a pair of contacts in the circuit, of a device for separating said contacts into circuit breaking position, a trip for normally anchoring said device in circuit making position where said contacts engage one another, a normally inoperative thermostat operatively associated to operate said trip, and an electromagnetic mechanism responsive to load variations in said circuit for rendering said thermostat operative upon partial actuation under light overloads and for operating said trip directly upon more pronounced actuation under heavy overloads.

16. In a circuit breaker for an electric circuit, the combination with' a pair of contacts in the circuit. of a movable interposer, means for urging said interposer to separate said contacts into circuit breaking position, a .trip for normally anchoring said interposer in circuit making position where said contacts engage one another, a normally inoperative thermostat operatively associated to operate said trip, and an electromagnetic mechanism responsive to light overloads in the circuit for partial actuation to render said thermostat operative in turn to actuate said trip and also responsive to heavy overloads for more pronounced actuation to actuate saidtrip directly.

17. In a circuit breaker for an electric circuit, a pair of contacts in the circuit, a movable interposer, springs for urging said interposer to separate said contacts into circuit breaking position, a trip for normally anchoring said interposer in circuit'making position where said contacts engage one another, a normally inoperative thermostat operatively associated to operate said trip, and a mechanism including a short circuiting member and a lever and being responsive to load variations in said circuit for partially erative upon light overloads and for actuating said lever more pronouncedly under heavy overloads to operate said trip directly.

18. In a circuit breaker, an electric circuit including a pair of contacts normally in engagement with one another in circuit making position, an interposer for separating the contacts into circuit breaking position, and a trip, said circuit also including a normally inoperative thermostat fixed to said trip, said trip normally anchoring said interposer in circuit making position, said thermostat being responsive to load variations in said circuit and being operative under certain loads to retract said trip out of interposer anchoring position.

19. In a circuit breaker, an electric circuit including a pair of contacts normally in engagement with one another in circuit making posi- 10 tion, an interposer, yieldable means for normally to anchor said interposer in circuit making 5 position, said thermostat being responsive to load variations in said circuit to be thereby deflected and therewith to deflect said trip to release said interposer.

STEPHEN S. GRADY. 10

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