US2371672A

US2371672A - Circuit breaker

Info

Publication number: US2371672A
Application number: US450143A
Authority: US
Inventors: John D Bolesky
Original assignee: Metals and Controls Corp
Current assignee: Metals and Controls Corp
Priority date: 1942-07-08
Filing date: 1942-07-08
Publication date: 1945-03-20
Anticipated expiration: 1962-03-20

Description

March 20, 1945. J. D. BoLEsKY CIRCUIT BREAKER Filed July 8, 1942 2 Sheets-Sheet 1 FIG .4

swlTcH oFF HEATER oFF sHuNT CIRCUIT OPEN J. D. BOLESKY CIRCUIT BREAKER Filed .my e, .1942

E FICQ.

SWITCH ON HEATER SHUNTED SHUNT CIRCUIT CLOSED al a5 MANUAL oN 5 HEATER oN SHUNT CIRCUIT OPEN SWITCH F'IG. IO.

2 Sheets-Sheet 2 FIG .7.

MANUAL 45 SWITCH oN HEATER OFF SHUNT CIRCUI 4 CLOSED qg f/ 5 TE' 33 /3 Z5 4g. f -97 ai 7 23 Patented Mar. 20, 1945 UNITED STATES .PATENT orrlcr.

CIRCUIT BREAKEB John D. Boleky, Attleboro, Mass., assignor to Metals Controls Corporation, Attleboro, Mass., a corporation of Massachusetts Application my s, im, serien N. 45o,-143 1s clean. (ci. zoo-11s).

'rms invention relates to e1eetne dreun, breakere, and more particularly to circuit breakers which automatically trip out on overload in the electrical circuit. and which are manually reset to close the circuit again.

The invention is an improvement over tha shown in my United States patent application, Serial No. 408,917, iiled August 30, 1941, now

' Patent N0.,2,345,451, March 28, 1944, for Switch.

Among' the. various `objects 'of the invention may be noted theprovision of a'thrr'nostatic circuit breaherwhich ispoeitive in its action and not readily Jarrod into premature tripping; the

provision of'a devioeof the class described which has more positive 'and reliable switch-opening movement vgreatertheln that Provided for by thermostatic movement per se; the provision of an arrangement of the thermal element such that during its actuation frlctional drag is minimized and the uniformityoi `operation therefore improved; theprovision o'imeans for shunting out the thermal element if desired bythe same' control handle which, is used to reset the breaker and without interfering with free movement of the thermal element; vand, the provision of a cir- Fig. 12 is an isometric view oi the operating handle mechanism.`

Similar numbers indicate corresponding parts throughout the several views of the drawings.

Circuit breakers are of many different types.

. The present invention is concerned with thermaltype circuit breakers which utilize a thermal element .both to open 'the circuit and to release associated mechanism.` Circuit breakers, in general, utilize either creep-acting thermal elements alone, or such creep-acting elements in conjunction with other apparatus to render the device snap-acting. Such structures have disadvantages for many purposes.

If such a circuit breaker is operating under oggsitions near its tripping point, the contact p ure exerted by the thermal element, or its position in relation to the detent which it may be controlling, may be socritical that a slight .lar willoften prematurely trip it. Also. in some types of thermal circuit breakers the thermal element is so arranged that' during its actuation, it

cuit breaker of the class described which is compact, foolproof andslmple' in itsl operation and economical to manufacture. Other oblects will.

be in part obvious andinafter. 'I'he invention accordingly comprises the eleiypart DOinted out herements and combinations/oi elements, features of construction, and arrangements of parts which will be exempliiled in the structures hereinafter described, and the scope of the application of which will be" indicated in the following claims.

In the accompanying drawings, in which is illustrated one of various possible embodiments of the invention,

A with the tnenmu element dotted;`

Fig. 7 is a section, on the line 1-1 in Fig. 2; Fig. 8 is a section similar to Fig. 6"but with drags against other parts with considerable friction, which results in non-uniformity of operation. l

According to the present invention a circuit breaker is provided which is positive in its action, is not readily jarred into premature trip. pingcan be easily adjusted, opens the electrical contacts in a minimum of time, and with ample `opening to interrupt the arcs'encountered inthe circuit for which the circuit breaker is designed,`

' and which is so arranged in relationship oi its the thermal element shown in full and'the heater dotted:- y

Fig. 9 is a view similar to Fig. 4 but showing the device in another position;

Fig. l0 isa view similarto Figs. 4 and 9 but with the device in avdiiierent position;

Fig. 1l is a view similar to'Figs. 4, 9 and 10 but showing the devicein still another position;

parts that, the thermal element presents no hindering friction against any moving part.

The thermal element employed is an inherently snap-acting thermostatic member, plate or disc.

Up to the point of tripping, this snap-acting ele-v ment does not move, and hence maintains a posi- -tive latching actionin conjunction with thel detent which it releases, and hence is not readily jarred from its detent position. In addition, when the snap-acting element does snap, it clears the moving partsA completely and the device is therefore free of the disadvantages encountered where the friction labove referred to is present.

Also, the pressure exerted by other moving parts lin the circuit breaker has but little effect upon the calibration of the ycircuit breaker of the 4 present invention.

In some types of circuit breakers itis necessary to incorporate' what is called a snorting or shunting bar so that in an emergency the circuit -may be closed to give a temporary control over the circuit in spite of the fact that the circuit is under overload conditions. In certain of these circuit breakers the manner in which this is accomplishedistocausethethermalelenientiinelftol actas a shunt bar. This may give trouble since'v the overload conditions are then apt to overheat and change the calibration of the thermal ele-- inent and hence of the circuit breaker. In this invention the shunt bar is used in suolil a way that it completely shunts out the thermal element and 1ittle,.ifl any, current passesv through the thermal element when the shorting bar is used. in addition, this actuation of the shorting bar,

.while being accomplished by the' same control handle which is used to reset the breaker, is so Varranged as to have no restraining eiect on the thermal element, which is at all times free' to Referring now to the drawings, numeral i indicates a frame or base made of an electrical inmating material such as a molded synthetic resin of the Bakelite type. The base l is constructed of two parts il and t. Moldedinto this base are grooved abutments, etc. illustrated generally at i (Fig. 6) tending to hold the various parts in alignment. Extending from the base are upright partitions s which form a channel itin which the boat or cani member ijl rides. Pegs iii are irlserted nrnily and immovably in the base and serve as anchors for ends of the springs il. The other ends of the springs il are respectively attached to the stirrup i9.

- is provided with the proper abutments and shouling contact material such as, for example, silver y or silver alloys or any other proper electrical conducting material. Bar l has two holes 53 therein, which holes receive the extensionsdi of the slide 2| to guide the shorting bar. The shunt bar 5i is shown mounted in position on the base with the extensions di passing through the holes 53 (see Figs. 6 and 9). A spring 55 rests 'in a properly provided groove 5l molded in the base i. -A metallic tube 5S serves to guide the spring and provide a mounting for it. Spring E35 is of such length as to keep the snorting-bar 5i pressed away from the end of the base and toward the center of the base in a non-contact-making position.

Referring again to Figs. i and bimetallic disc di is shown threadably mounted by means of hub 29 on the post 25. The hub 29 ders in the usual way so that disc @l is relatively free to rotate thereon. Thus by'turning the disc hub 29 on the threaded hub 2l, the position of disc ti is changed relative to the base S. By this rnc construction cr the aimable boat se is iilustrated particularly by Fig. i2. The boat is, as

indicated. of two main portions, the slide 2i and the frame 23. These are formed oi thin sheet metal with sumcient rigidity to keep their shape. n'addition'to these two main parts there is a third part, the disc post indicated generally at 2t. This post 25 is formed of steel or some other such metal. It hasV a threaded hub .2l which threads into the disc hub 29 (see Fig. e), and a circular base portion Si. Two pins 33. project from diametrically opposite points on the circular portion 3i and are slidably engaged in the cam slots of the frame 23. Bent-over ears 3l on the frame 2d serve to slidably hold-the slide t to the frame 23, thus providing for a relative sliding between the frame 23 and slide 2i.- Thls motion is in a lengthwise direction. The slide 2i is provided withl 'an elongated center opening 39,

`through which the threaded hub Eil ofthe disc post 25 is allowed to extend'i'reely when the boat f' is assembled.

lSlide 2i is also supplied with projecting ends fdi, the purpose of which will subsequently be described.v The other end of slide 2i is provided with a projection d3 to which the knob dit is attached. The knob may be held on by any. of the `customary means. The frame 23 has at one end 'notches il which serve to be engaged by the stirward, the springsl I1 provide a return bias.

The projecting pins 33 of the disc post 25 ex- 'tend beyond the sides of the framel 23, and t slidably into vertical notches 49 which are molded into the upright partitions 9. Thusfwhen the post 25 cannot move along with'it, but must move up' and down in a direction perpendicular to the base, as viewed in Fig. 1. This up-and-down movement is caused by engagement of the pins 33 in the cam slots 35 in the sides of the frame 23.

Referring now to Fig. 8, there is shown a shunting or snorting bar 5I, which is made of conductmeans temperature adjustment of the disc is made. Contacts t3. are electrically welded on 'disc 5l, or otherwise mounted and electrically connected to thedisc di. l

- Referring now to Fig. '1, the terminal and stationary contact assembly is shown withthein= ternal heater. These are as follows: One terminal jcomprising a strip of conducting metal of the proper thickness and sizev to nt in the grooves 'i molded in thebase, is shown pressed into position. This terminal has a contact di on its side facing the central portion oi the circuit breaker positioned to engage one of the disc contacts et. The other terminal Sd is likewise mounted on the base, and to it is-attached at one -end a heater ii. The other end of heater li is attached toa third metal support i3 which likewise engages the molded grooves in the base i. Support it is not in electrical contact with terminal to; except through the heater li. Support it carries on its inner surface a contact. i5 which is adapted to engage the other contact 68 on the bimetallic disc Si. In addition to these contacts,

terminal to carries on it an additional stationary -v general, the switches with lower current ratings boatv I3 is pushed along the base, the disc carrier Y require the heater because a point is reached where mechanical operation of a cross section of the disc cannot be reduced t0 a small-enough section to bring about the heating required in view of the current available. It is in such cases that the. auxiliary heater is used because its cross section is independent of any mechanicalstrength requirements. `Its cross section may bel 8| having a threaded portion 83 and a projecting stem 85. This post button screws into the b ase portion 5 (see also Fig. 3), which has a hole 81 i threaded for that purpose. Projecting stem 85 .slidably nts into `the/hole 89 which is provided centrally in the disc post 25. This stem portion` and the notches serve as the bearings on- 3, a snap-acting l which the post rides up and down when the boat '.13 moves back and forth in the base. It

will be observed that a molded portion (see Fig. "6) serves to engage the extending ears 93 of the disc 6,! and thus maintain the respective contacts in alignment.

It will be observed that as the boat I3 moves along the base in its channel Ii, the disc post 2e rides up and down in a direction perpendicular to the plane of motion of the boat I3. As the disc post 25 does this, it carries up and down with it the snap-acting bimetallic disc 6l. Thus the contacts 93 are brought into engagement with the stationary terminal contacts as the boat i3 slides along ,the base against the tension of the springs i1, and vice versa. The operation of these rnctions is such that when the boat is moved by means of the knob 45 along the base, the pins 33 are forced by the cam slots 35 inan upward direction (as Figs. 6 and 8 are drawn) r se as to bring the disc and its mating circuit-closing contacts into engagement with the stationary contacts B1 and 15. `When the disc contacts 53 reach the

stationary contacts

61 and 15 the motion of the perimeter of the disc is stopped, but

further motion of the slide forces the center oi spring characteristic of the disc itself. When the boat is pushed further along, the pins 33 ride up over the curved detent parts 95 of the cam slots 35. To make the pins ride up over the detent parts $5 against the pressure of cold disc 6l, an additional force is required. Consequently when thkpins drop down behind the detent parts 95, the spring pressure of disc 6| serves to hold the "boa in position against the tension of springs l1, as 1 ng as the pressure is maintained against the pins by the cold disc 6l. The ends 91 of the slots .35 back of each detent part 95 are preferably thus a little longer than actually required, to make sure that the pins 33 will drop down.

Assuming that the parts are in this position, we will see that there is an electrical circuit through the terminal G5, contact 61, the correspending contact 6 3 of the disc, disc Bl, the other 1| and terminal 99.` I

Theoverload tripping operation of the device on overload conditions is as follows:

When the device is subjected to the overload current which itis designed to interrupt, the heater 1I heats up as does the disc Gt (since it is subjected to the current also). After a pre determined given interval of time, the heat generatedi is sufficient to cause the disc to snap to its other (hotypositicn of concavity. This motion ofthe disc in its snap opens the contacts and also serves to release thepressure; of the pins 33 against the detent 95, and the biasing springs l1 are now free to pull lthe boat i3 back into its original position. This motion of the boat` I3 'causes the cam slots 35 todrawrthe hot disc 6! away. froml the

stationary contacts

61 and 15. It will fbe observed that if the knob and boat are held in the circuit-closing position, themotlon of the disc snaps the contacts 63 away from contacts 9'1 and 15, thus opening the circuit. -The automatic movement of the disc caused by the boat Il and its cam action is large compared `to the vmotion obtained from the thermal movement of the disc alone and gives the breaker additional circuit-interrupting capacity. In addition, this movement caused by the cam action is suiilciently large so that when the disc cools and snaps back aa'rnovn to its original cold position, the contacts G3 do not make contact with

thestationary contacts

81 and 15 mounted on

terminals

65 and 89. Thus, with the disc in its cold position, and until reset, the circuit is maintained in an open position.

It will accordingly be observed that the opening of the circuit is caused by a combination of the motion of the disc andthe motion of the boat. Also, that the motion of the disc alone is sumcient to open the circuit, and the device is thus trip-free of the handle when the latter is in its normal circuit-closed position. That is,

.pushing in the handle While the disc is to hot position will not :re-close the circuit through the disc.

The purpose and. operation ci the snorting par is as'iollotvs: y

lt sometimes happens that in an emergency it necessary to prevent the circuit "ci-eener crc interrupting the circuit, or else to quickiy .reclose the circuit if the circuit breaker has opened it. To this end the shunting bar is provided. By referring to Fig. l2, it will be seen that the slide 2i can move relative tothe frame 23. Conm sequently inward pressure on the knob t5 will cause the slide 2i to slide in a little further. This further sliding action results in the end of the slide 2l striking the shunt bar 5I as shown in Figs. 9 and 1i, and forcing the bar 5I into engagement with the

stationary contact

11 and 19. Consequently this further forward motion of the slide 2| will enable the circuit to be closed, regardless of the position of the disc (see Figs. 9 and 11; Fig, 9 illustrates the condition where the disc is in its cold position and Fig. l1 where the disc is in its hot position).

From'the above it will be understood that this further forward motion of the slide 2i will enable the circuit to be closed, regardless of the position of the disc, and likewise that this in no way interferes with the operation of the disc. It will be observed that the shunting bar 5i effectively shunts out the heater 1l and the disc 6I,

' so that neither is injured by the overload cui'- fait rent. When the pressure on knob. is relieved, the spring 55 forces the snorting bar away from the

contacts

11 and 19, thus opening the shunting circuit.

An important factor of this construction is that by allowing relative movement between the slide 2l and the trarne 3, the spring 55 can be made fairly light and stili be strong enough to force the slide 2i back, and hence open the shunt bar circuit. it has been round that ii the disc ti is in its cold circuit-closed position there is considerable pressure exerted against the frame 23. It frame 23 and slide 2i were all of one piece, the whole of said piece would have to be moved inward to close the snorting bar. The friction caused by the disc pressure against the frame 23 and the frame against the base would be suilicient to hold the shorting bar closed, even if the knob were released, unless a very strong spring were used. As a practical matter, it isv found that the spring 55 would have to be so strong as tokmake it qiflicult, if not impossible, to fit it into" the small space required by efficient design of a circuit breaker of this type. Also, the use of such a strong spring would'make it very diilicultto close the shorting bar. Bythe present construction a light spring is allowed to work against the freely-moving slide 2| to open the snorting bar. Also, the lost-motion between prongs 4I and bar 5i avoids a largeinitial delectionin the spring 55 such as would be necessary if the bar 5i partook of the full stroke of 2i. This is further conducive to a short spring.

From the above it is clear that the vpresent circuit breaker is the type which utilizes a thermal means to initiate the mechanical motion,

lsaid mechanical motion further moving the thermal element. The motion of the thermal element per se will serve to open the circuit with a snap action. This quick opening tends to minimize burning of the contacts by arcing. Also, the disc when in its hot position exerts-no pressure against the boat, and hence the boat is free to be moved back by springs., il. The

` use of a snap-acting thermal element'thus miniare held so that they cannot turn. Then the frame 01 which serves to mount the breaker by means of screws |09 which engage the nuts N3.

To adjust the circuit breaker tothe proper rating, the button 8l is unscrewed, thus giving access to the disc hub. 2l. This is turned (thus changing the temperature adjustment of the disc) untilvthe disc snaps at the correct interval of time, with the calibrating current flowing through it. A drop of solder is then placed on the hub to solder it i!! post-.25, and thus to prevent it from further turning and getting outof adjustment. y

While the thermostatic member 6i is, according to the present example, inherently stressed to be concave toward the rst contacts and 1i when cold, and vice versa, it is clear that this" relationship of conditions could be reversed without changing the inventive principles. In other words the second contacts 63 could be carried from the iirst contacts upon cooling, the two conditions of stability of the thermostatic member being reversed as regards temperature.

overload contact, a carrier for said disc and movable for actuation toward and away from said overload contact, the disc having a cold position concave toward the contact and a hot position concave away fromthe contact, a follower on the carrier, a cam movable with respect to the frame and cooperating with the follower and shaped so that upon onel movement it drives the disc toward the overload contact a distance to bring together the disc contact and the overload contact and to tension said disc, the cam and the tensioned disc cooperating to hold the tensioned disc in position, means biasing the cam in the reverse direction tending to 'release the follower and draw it in a, direction to `move the disc away from the overload contact, biasing action automatically occurring when the tension is removed from the disc by snapping of the disc to its hot position.

2. A circuit-breaker comprising a frame part carrying an overload contact and a shunting contact, a snap-acting thermostatic disc carrying a mating contact for the overload contact, a carrier for said disc and movable for actuation toward and away from said overload contact, the Y disc having a cold position concave toward the contact and a hot position concave away from the contact, a follower on the'carrier, a cam cooperating with the follower and shaped so that upon one movement it drives the disc toward the overload contact a distance to bring together the disc contact and the overload contact and to tension said disc and locking the disc in tensioned position, means biasing the cam in the reverse direction tending to unlock the follower and draw it in a direction to move the disc away from the overload contact, biasing action occurring when the tension is removed from the disc by snapping on the proper panel is held firmly to the base of the disc to its hot position, and manually operable means having a lost-motion connection with said cam to drive it against its bias, a shunting bar associated with said shunting contact, a lost-motion between the manual'means and the cam allowing the manual means to drive the shunting bar into shunting position against the shunting contact.

3. A circuit breaker comprising a. frame part carrying an overload contact and a shunting con- 'tact, a snap-acting thermostatic disc carrying a mating contact for the overload contact, a carrier for said disc and movable for actuation toward and away from said overload contact, the

. disc having a cold position concave toward the contact and a hot position concave away from the contact, a follower on the carrier, a cam cooperating With the follower and shaped so that upon one movement it drives the disc toward the overload contact a, distance to bring together the disc contact and the overload contact-and to tension said disc and locking the disc in tensioned position, means biasing the cam in the reverse direction tending to unlock the follower and draw it in a direction to move the disc away from the overload contact, biasing action occurring when the tension is removed from the disc' by snapping of the disc to its hot position, andv ,manually operable means having a lost-motion connection with said cam to drive it against its bias, a shunting bar associated with said shunting contactfand also having a lost-motion connection with said manually Voperable means, the lostmotion between the bar and the manual means being taken up during actuation of the follower by the cam, thereafter lost-motion between the manual means and the cam allowing the manual means to drive the shunting bar into shunt circuit against the shunting contact. v

4. A circuit breaker comprising a frame carrying a circuit contact, a snap-acting thermostatic member operating a mating circuit-closing contact for said circuit contact, a carrier for said thermostatic member movable for actuationtoward and away from said circuit contact, the thermostatic member having a cold position concave toward the circuit contact and a hot position concave, away from it, a follower on `the carrier,

closing cooperating with the follower and shaped so that upon one movement it drives the thermostatic member toward the circuit contact a distance to-bring together both of said contacts and to tension said thermostatic member, the cam and the tensioned thermostatic member cooperating to hold the tensioned thermostatic member in position, means biasing the cam in the reverse direction tending to release the follower and permit its movement in a direction to withdraw the thermostaticmember from the circuit contact, biasing action automatically occurring when the tension is removed from the thermostatic met' ber by snapping ci the thermostatic member to its hot position.

5. A circuit breaker comprising a ironic carrying a circuit contact, a tbermostatic member carrying a mating circuit-closing contact. for said circuit contact, a carrier for said thermostatic member movable for actuation ci the thermostatie member toward and from said circuit contact, the theirnostatic member having a cold position concave toward the circuit contact and a not position concave away from it, a iollower on the carrier, a cam movable with respect to the frame and having a driving portion terminated by a locking portion, said cam cooper'- ating with the follower so that upon cam movement by means of said driving portion it first drives the thermostatic member towards the circuit contact ,a distance to bring together both rler for said thermostatic member movable for actuation of the thermostatic member toward and away from said circuit contact and simultaneously tensioning the thermostatic member, the thermostatic member having a cold position concave toward the circuit contact and a hot position concave away from it, a follower on the carrier, said slot cooperating with the iollower so that upon initial movement the sloping part of the slot drives the follower and tensions the thermostatic member to bring together both oi said contacts and upon iinal movement the locking notch.- locks the follower in view of said tension, means biasing the cam in reverse direction tending to unlock the follower to withdraw thermostatlc member to contact opening position, biasing action automatically @warring when the tension is removed from the tliermostatic member by snapping of the to its "not position.

d. A circuit breaker comprising a frame forming a straight-line guide, 9, cam member sliding in the guide, said cam member having a sloping slot therein terminated by a locking notch, means biasing the cam member toward a startingposition, a circuit contact on the frame. a snapactlng thermostatic member operating e circuitclosing contact ior said circuit contact, a carof said contacts and tension the thermostatic member and then by said locking portion locks the thermostatic member in a tensioned contactclosing position, means biasing the cam away from its locking position but not strong enough to unlock except upon movement ofthe thermostatic member toward its hot position.

6. A circuit breaker comprising a frame carrying a circuit contact, a, snap-acting thermostatic member carrying a mating circuit-closing contact for said circuit contact, a carrier for said thermostatic member movable for actuation of the thermostatie member toward and away from said circuit contact, the thermostatlc member having a'cold position concave toward the circuit contact and a hot yposition concave away,

from it, a follower on the carrier, a cam movable with respect to the frame and having a sloping portion terminated by e. positively-holding notched portion, said cam cooperating witi'i the follower so that upon cam movement by means of said sloping portion it first drives the thermostatic member towards the circuit contact a, distance to bring together both of said contacts and'tension the tncrmostatic member and then by means of said notched portion to lock the tbermostatlc member in a tensicned contactclosing position, means biasing the cam away from its locking position but not strong enough to unlock except upon movement of the thermostatic member toward its hot position, said sloping and notched portions of the cam coml prising a slot cooperating with the follower in a manner positively to draw the follower and the supported thermostatic member in a contactopening direction.

contact for said circuit contact, a car-x rier for said thermostatic member movable for actuation of the thermostatic member toward 'and away from said circuity contact and simultaneously tensioning the thermostatic member, the thermostatic member having a cold position concave toward the circuit contact and a hot position concave away from it, a follower on the carrier, said slot cooperating with the Iollower so that upon initial movement it drives the follower and tensions the thermostatic member to bring together both of said contacts and upon final movement to lock, means biasing the cam in reverse direction tending to unlock the follower and to withdraw the thermostatic member to contact opening position, biasing action automatically occurring when the tension is removed from the thermostatic member by snapping of the samev to its not position, manual operating means for the cammember comprising a slide having a lost motion with respect thereto, a. shunt contact, a movable shunt bar cocperable with the shunt contact, lost ci the slide with respect to com member upon manual operation extending the slide 'mth respect to the cam member 'to move the citant bar to engage the shunt contact regardless of the loot or cold condition oi the therrncstatic member and means biasing the shunt bar away from the shunt contact and to taire up said lost motion whenever the cam member is allowed to move to its starting position.

9. A' circuit breaker comprising a frame carrying a circuit contact, a snap-acting thermostatic member operating a mating circuit-closing contact for said circuit contact, a carrier for said thermostatic member, a guide for the carrier, said thermostatic member being movable for actuation toward and away from said circuit contact, the iihermostatic member having a cold position concave toward the circuit contact and a hot position concave away from it, a follower on the carrier, a cam movable in respect tothe frame crosswise to said guide and having a driving portion terminated by a positively-holding portion, said Acam cooperating with the follower so that upon movement it first drives the thermostatic member towards the circuit contact a distance to bring together both of said contacts and then to lock the thermostatic member in a tensioned contact closing position, the movement of the cam during actuation being greater than that of the carrier, and cneans biasing the cam away from its locking position but not strong enough to unlock except upon movement of tfhe thermostatic member toward its hot position.

10. A circuit breaker comprising a frame` part carrying a iirst contact, an inherently snap-acting thermostatic member carrying a second and mating contact for the first contact, a carrier for said thermostatic member movable for actuation 'toward and away from said rst contact, the

thermostatic member having at one temperature inherent stresses therein which tend to move I parts of it carrying the second contact toward the iirst contact and at another temperature having inherent stresses which tend to move said parts carrying the second contact away from the iirst contact, a follower on the carrier, a cam movable with respect to the frame and cooperating with the follower and shaped so that upon one movement it bodily drives the thermostatic member towardthe iirst contact a distance to bring together the second contact and the rst contact and to apply stress to said thermostatic member, the cam and the stressed thermostatic member .cooperating to hold the stressed disc in position, means biasing the cam in the reverse direction tending to release the follower and draw it in a direction to move the thermostatic asraerc l2. A circuit breaker comprising a frame carrying a first contact and a shunting contact, an

inherently snap-acting thermostatic member carrying' a second contact for cooperation with the rst contact, a carrier for said thermostatic membermovable for actuation toward and away from said irst contact, the thermostatic member having at one temperature a position in which inherent stresses therein tend to' move parts of it carrying the second contact toward the first contact and at another temperature another position in which inherent stresses therein tend to move said parts carrying the second contact away from the first contact, a follower on the carrier, a cam cooperating with the follower and shaped so that upon one movement it .bodily drives the thermostatic member toward the rst contact a distance to bring together the second contact and the first contact .and to apply stress to the thermostatic member while locking it in stressed position, means biasing the cam in the reverse direction tending to unlock the follower and draw it in a direction to move the thermostatic member bodily away from the first contact, biasing action occurring when the stress is re- .moved from the thermostatic .niember by the member bodily away from the first contact, bias- Y ing Aaction automatically occurring when the stresses are removed from the thermostatic member bysnapping of the thermostatic member to its position away from the first contact.

11. A circuit-,breaker comprising a frame part carrying a first contact and a shunting contact, an inherently snap-acting thermostatic member carrying a second contact mating with the first contact, a carrier ior said thermostatic member movable for actuation toward and away from said iirst contact, the thermostatic member having a position'V at one'temperature in which inherent stresses therein tend to move parts of it carrying the second contact toward the first contact and another at another temperature in which inherent stresses therein tend to move said parts rcarrying the second contact away from said rst contact, a follower on the carrier, a cam cooperating with the follower and shaped so that upon one movement it bodily drives the thermostatic member toward the first contact a distance to bring together the second contact and the rst contact and to apply stress to the thermostatic member and locking the thermostatic member in stressed position," 'means biasing 'the cam in the reverse direction tending to unlock the follower and draw it in a direction to move the thermostatic member bodily away from the rst'contact, biasing action automatically occurring-when the stress is removed from the thermostatic member by its snapping to itsposition away from the first contact, and manually operable means having a lost-motion connection with said cam to drive it against its bias, a shunting bar associated with tween the manual means and the cam allowing the manual means to drive the Jshunting bar into shunting position against the shunting contact.

I snapping of it to its position away from the first contact, and manually operable means having a lost-motion connection with said cam to drive it against its bias, a shunting bar associated with said shunting contact, and also having a lostmotion connection with said manually operable means, the lost-motion between the bar and the manual means being taken up during actuation of the follower bythe cam, thereafter lost-motion between the manual means and the cam allowingthe manual means to drive the shunting bar into shunt circuit against the shunting contact.

13. A circuit breaker comprising a frame carrying a circuit contact, a snap-acting thermostatic member operating a mating circuit-closing contact for said circuit contact, a carrier for said thermostatic member movable for actuation toward and away from said circuit contact, the thermostatic member having two positions of stability due to its own inherent stresses, in one of which positions said contacts may be closed and in the other opened, said positions of stability being determined by temperature, said thermoy static member being movable from one position y erating with the follower and shaped so that upon one movement it drives the thermostatic member toward the circuit contact to bring together both of said contacts and to apply stress to said thermostatic member, the cam and the stressed thermostatic member cooperating to hold the thermostatic member in contact-closed position.

l means biasing the cam in the'reverse direction .said shunting contacts, and a lost-motion betending to release the follower and permit. its movement ina direction to withdraw the thermostatic member from contact closing position, biasing action automatically voccurringwhen the stress is removed from the thermostatic member by snapping of it to its position of stability