US2943172A - Electric switch incorporating an automatic circuit breaker - Google Patents

Description

June 28, 1960 R, c, INGWERSEN 2,943,172

ELECTRIC SWITCH INGORPORATING AN AUTOMATIC CIRCUIT BREAKER Filed June 9, 1958 7 Sheets-Sheet 1 2 v E E INVENTOR. ic/zdr/Cjry we #5 e 71 June 28, 1960 R. c. INGWERSEN 2,943,172

ELECTRIC SWITCH INCORPORATING AN AUTOMATIC CIRCUIT BREAKER Filed June 9. 1958 '7 Sheets-Sheet 2 4 E BE; 5

INVENTOR. Eat/Z4716: JEywersen f g/aw June 28, 1960 R. c. INGWERSEN 2,943,172

ELECTRIC SWITCH INCORPORATING AN AUTOMATIC CIRCUIT BREAKER Filed June 9, 1958 7 Sheets-Sheet 3 W m ax/urns:

June 28, 1960 R. c. INGWERSEN 2,943,172

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. S INVENTOR.

June 28, 1960 Filed June 9, 1958 R. c. INGWERSEN 2,943,172

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, l 7 :1 I -2;; I l l I I I 257 l i 259 A I J g E 1 B K /J INVENTOR. X'ZCZdrZCT Jryweraew June 28, 1960 R. c. INGWERSEN ELECTRIC SWITCH INCORPORATING AN AUTOMATIC CIRCUIT BREAKER Filed June 9, 1958 7 Sheets-Sheet 6 June 28, 1960 R. c. INGWERSEN 2,943,172

ELECTRIC SWITCH INCORPORATING AN AUTOMATIC CIRCUIT BREAKER Filed June 9, 1958 v 7 Sheets-Sheet 7 INV EN TOR. fizv driCj/v zaers e)? I ray/K594 2,943,172 Patented June 28, 1960 ELECTRIC SWITCH INCORPORATING AN AUTOMATIC CIRCUIT BREAKER Richard C. Iugwersen, 'Jackson, Mich., assignor to lYlechanical Products, Inc., Jackson, Mich., a corporation of Michigan Filed June 9, 1958, Se'r. No. 741,207

17 Claims. (Cl. 200-116) This application is a continuation-in-part of my copending application, Serial No. 588,040, filed May 29, 1956, now abandoned.

This invention relates to improved electric circuit breakers and/or electric switches having automatic overload current protection.

The use of automatic circuit breakers in electrical circuits is, of course, old and well-known, and such devices are widely used to protect electrical circuits against overload current conditions. While various types of circuit breakers have heretofore been devised, many of them that have achieved commercial acceptance include bimetallic elements which expand, or deflect in response to heating so as to permit a movable contact of the circuit breaker to move out of engagement with a stationary contact and thus open the electric circuit. In such circuit breakers, the bimetal member usually acts as a latch and must be relatively strong mechanically in order to retain certain of the circuit breaker part-s in a desired relationship during normal circuit operation.

Such circuit breakers are generally not practicable for use in low current applications, or in applications where relatively rapid overload response is required. The need for mechanical strength requires that the bimetal member be of relatively large size, and, therefore, relatively insensitive, requiring relatively large currents to actuate it. Also, the thermal inertia of a relatively large member limits the response time of the device to a relatively long interval. In general, bimetal members of sufficiently high electrical resistance to be actuated by a current of five amperes or less do not have sufiicient mechanical strength to act as a latch or retaining element.

Many electrical circuits in use today require overload protection at current values of five amperes or less, and there is a present need for a circuit breaker that will act quickly and positively in low current circuits, and will protect electrical equipment, as well as the wiring in circuits designed to carry currents of as little as one quarter ampere or less.

In aircraft electrical systems in particular, the use of fuses is not satisfactory because of the necessity of carrying spare fuses to replace any fuse which might blow out. Circuit breakers, on the other hand, can be manually reset after a current overload condition, and replacement breakers need not be carried. This is, of course, important in that several hundred circuit breakers are used on most modern aircraft.

It is therefore one object of this invention to provide an improved circuit breaker having automatic overload current protection and which is adapted to be connected in a circuit designed to carry current of less than five amperes, so that the same will automatically operate to protect electrical equipment connected in the circuit, as well as the electrical wires of the circuit in the event of current overload exceeding a predetermined value.

Another object of this invention is to provide a circuit breaker of the aforementioned type which will operate almost instantaneously upon occurrence of current overload.

Another object of this invention is to provide a circuit breaker of the aforementioned type which is relatively unaffected by ambient temperature variations.

It is a further object ofthis invention to provide a circuit breaker of the aforementioned type including a current carrying wire which will almost instantaneously heat and expand upon the occurrence of current overload to permit a movable contact in the circuit breaker to 7 move out of engagement with a fixed contact thereof and thereby open a circuit.

It is a still further object of this invention to provide a circuit breaker of the aforementioned type which can be manually reset after current overload to again close an electric circuit.

It is a still further object of this invention to provide an improved circuit breaker of the trip free type and having substantially instantaneous reaction to current overload but adapted to carry currents in excess of five amperes.

It is a still further object of this invention to provide an electric switch having the aforementioned advantages, which may be manually moved between oii and on positions, and which incorporates automatic'current over-' load protection.

It is a still further object of this invention to providean electric switch and/or circuit breaker having the aforementioned advantages in which after the contacts have moved to open position and the current carrying wire has returned to its normal contracted position, elements of the circuit breaker will automatically move to a position to permit the circuit breaker to be latched in its on position upon subsequent manual actuation.

It is a still further object of this invention to provide an improved latch structure for normally retaining the movable contact in engagement with the fixed contact in a circuit breaker of the aforementioned type.

It is still further object of this invention to provide a circuit breaker of the aforementioned type which will complete a second circuit upon opening of the first circuit due to current overload.

It is a still further object of this invention to provide an electric switch and/or circuit breaker of the aforementioned type which is extremely efficient and durable in operation, but relatively inexpensive to manufacture.

These and other objects of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings in which:

Figure 1 is a longitudinal sectional view of an electric circuit breaker according to a first embodiment of the invention and illustrating the circuit breaker in its closed position;

Fig. 2 is a sectional view of the circuit breaker illustrated in Fig. 1 taken along the line 2-2 thereof;

Fig. 3 is a view similar to Fig. 1 illustrating the circuit breaker in its manually opened position;

Fig. 4 is asectional view of the circuit breaker illustrated in Fig. 3 taken along the line 4--4 thereof;

Fig. 5 is a longitudinal sectional view of a circuit breaker according to a'second embodiment of this invention;

Fig. 6 is a sectional view of the circuit breaker illustrated in Fig. 5 taken along the line 6--6 thereof;

Fig. 7 is a fragmentary longitudinal sectional view showing a modified form of the circuit breaker shown in Fig. 5;

Fig. 9 is a sectional view of the circuit breaker illustrated in Fig. 8 taken along. the line 9-9 thereof;

Fig. 10 is a fragmentary view similar to Fig. 8 illustratingthe circuit breaker in its; open, or tripped. positiom Fig. 11 is a longitudinal sectional view of a circuit breaker representing a fourth: embodiment of the in e tion, showing the circuit breaker inits; closed po it on;

Fig. 12 is a cross-sectional. view of. the circuit breaker shown in Fig. 11, taken generally along the. line. 12-42 thereof;-

Eig. 13 is. a longitudinal sectional view generally simi lartothe view of Eig; 11', but shOWingthe circuit-breaker in its open position; and

Fig. 1.4. is a fragmentary cross-sectional; view taken along the line l t-14 of Fig. 1.1...

Circuit breakers according to, the present invention include, overload. sensitive elements comprising one or more relatively fine; Wires. arranged. in, the electrical circuit within the circuit breaker and mechanically tensioned. The arrangement; is such that when the wires are heated by a predetermined overload current, theyexpand, causing the release of a. latch mechanism which normally retains the contacts in; a closed position. The circuit breakers of the present invention are lightweight and extremely compac They may e made responsive to; relatively small. currents. and. to. have extremely rapidreaction. to irc it; overloa s. The over oad. sensi ive wires. bein Of relatively; mall; gauge... have. a. relatively high. resistance and very small thermal inertia. They can, therefore, be heated. to the. tripping temperature. by relatively small currents, andboth the. reaction and the; recovery times are. rela ively hort.

Referring-now to. Figs. 1 to 4. of the drawings, it will beseen that the circuit. breaker: illustrated therein includes a hollow casing 11 which may be made of plastic or other suitable material and is preferably formed, in two halves secured togetherby suitable fastening devices 13. Supported in and projecting fromthe casing 11 are terminals 15; and 17 which are adaptedto be connected in an electric circuit so that current flows, from one terminal through the circuit breaker to, the. other; terminal, and so that if the circuit breaker moves to itstripped, or. open position due to current overload or manual. actuation, current: flow through the circuit. is. interrupted. A fixed contact 19 is disposed withintheeasingll and connected with the terminal 172 A, plunger; 21 is-slidably supported in the casing for-in? and out movement. A plunger extensipnmemberlIa isconnected to the lower, or outer end of? the plunger and projects beyond, the casing 11, through a recessed collar-like member; 25,. whichabuts the bottom of the; casing and. is. fixed. with respect thereto. A knob 27 is secured to the outer endof the plunger ex-- tension 23;. by means of;- a; screw 29.

A pair ofplastic spacers or ring-like members 311and. 32 ;are disposed between the plunger extension .23 and the. knob 27. The knob 27 and the spacers 31 and 32 are all differently colored. The ring-like member 31 is, normally confined within the collar 25,.and the member 32 and knob 27 are exposed when the plunger is in its normal contact closed position as illustrated in Fig. 1. When the plunger is manually. moved to its outermost contact open position, the knob and both members 31 and 32 are visible as illutrated'in, Fig. 3. When the circuit breaker is automatically tripped due to a current overload condition, the plungermoves inwardly, as will be hereinafter described, so that only the knob 27 is visible, with the members-31 and 32-being confined within the collar member 25. Thus the-userof the switch can determine at a glance whetherthe contacts are open or closed, and if open-whether manuallyor, automatically so positioned.

The plunger 21 is urged inwardly by a spring 33, the upper, endcffwhich abuts: the bottom of the plunger 21, and thedower end of which is supported. in a spring seat member 35-fixedtothe casing near the bottomthereof.v A generally U-shaped spring 39, supported in the casing 11, and opposed laterally projecting flanges. 37, adjacent to the lower end of the plunger 21, cooperates to releasably retain the plunger in its out position when it has been manually moved to such position. That is, when it is desired to manually open the switch, the user may grasp the plunger knob. 27 and pull it outwardly, thus moving the plunger 21 downwardly and compressing the coil spring 33'. When theiplnnger. flanges. 37- havemoved outwardly beyond the detents, or projections 41 on the opposed spring legs, the detents' will retain the plungerin its out position, against. the urging of. the spring 33 until the user manually pushes the knob 27 inwardlyto force the plunger flanges 3.7 inwardly past the spring detents 41.

An arm 43 is pivotally supported at4'5 on the plunger 21. A contact 47 is carried on one end of the arm in position to engage the fixed contact 19. A coil spring 49 is connected between the; arm 43 and the. plunger: 21, tending to pivot the contact carrying end of the armaway from the fixed contact 19 so as. todisengage the contacts. The contact 47 is, however, normally'retained in engagement with the fixed contact 19 by means of. a lever 51, having a latching shoulder 53 adjacent to its upper end, and pivotally supported in. the casing 11 by a pivot pin The; lever 51 is of a generally Lshapedconstruction, and the vertical leg thereof is considerably longer. thanthehorizontal. leg 57 so. that. a. limited, movement of the. horizontal leg 57- will-cause. substantialmoves ment of the. vertical. leg having the. latchingshonlder 53 which. engages a complementary shoulder 59 adjacent to the opposite end of. the contact caryingarms 43.from the contact 47. The lever 51 isnormally retained in engagement with the contact carrying, armby a coil spring 61,. which is seated between a fixed portion of the. casing 11 and the horizontal lever arm 57 so as to yieldably maintain the latching shoulder 53 at the upper end of the lever in engagement with the contact arm.

in. order for the lever 51 to moveout of. engagement with the contactcarrying arm shoulder 59, and thus to permit the contact 4-7 to move away. from the contact 19 in response to overload current. conditions, it is necessary for the vertical arm of thelever 51 to swing clock- 7 wise as viewed in Fig. 1 to thereby permit the. spring 49 to pull the contact. 47- ont of. engagement with the contact 19. In this connection, a currentcarrying wire 63. is provided, theupper end-of; which is: connected with the terminallS andthe lower endofwhich is connected with an abutmentiplate 65. The wire 63 extends.- through a hollow casing, or. cartridge 67 which is supported in the,- casing 11, and thelower end ofthe, casing- .6.7 is recessed at 69 to receive a coilspring 71. The lower end of. the-spring 71 abuts an abutment plate extension 73, which isslidably disposed in the recess 69. Current. can thus flow from the. terminal 15, through the-wire 63, the abutment 65, the lever 51, through apigtail 75- tothe contact carrying arm 43, to the contact 47', thence to the contact 19 and.to. the term-inallfl', thus. completing a circuit through. the circuit breaker. Upon the occurrence of. an overload current, thewirefifi will. heat up. and expand, and the spring 71; which is stronger than'thespring;

61, will move the. abutment plate 65 downwardly and.

cause the, horizontal leg of. the lever 51 to pivotin a clockwise direction around the pivot pin 55, thus moving the latching shoulder 553. on the upper endof the lever out of engagement with its engaging shoulder 59 on the contact carrying armed thereby freeing. the'contact can tying arm so that the spring/l9 pivots itcounterclockwise and. moves the contact 47 out. of engagement with the contact 19, thus interrupting the flow of current through the circuit. breaker and through the. circuit. in which the breaker. is connected. The Wire. 63 will, when. the current exceeds a predetermined value, heat almost instantaneously, in substantially the samemanner as the filament of a light bulb, so. that the. contacts will move to open position very rapidly. As the resistance in the wire 63 is relatively high, this circuit breaker can be used to control overload current conditions in circuits carrying less than five amperes and in circuits carrying one-half ampere or less. Thus, this circuit breaker can be used in low current carrying circuits and actuates rapidly upon the occurrence of an overload current condition.

When the contact carrying arm 47 is pivoted in a counterclockwise direction by the spring 49, the portion of the arm just below the contact 47 will engage an abutment 77 on the casing, while the shoulder 59 will move upwardly above the lever 51. At the same time, the spring 33 will push the plunger upwardly, or inwardly so that only the knob 27 will be visible with the ring members 31 and 32 being disposed within the recess in the collar 25. There is thus visual indication to the user that the circuit breaker is in its contact open position due to the occurrence of a current overload. In order to reset the switch to its contact closed position, and assuming that the wire 63 has returned to its normal unexpanded position, the knob 27 is manually pulled outwardly and the contact carrying arm 43 will slide along the angular face 81 adjacent to the upper end of the lever 51, and pivot the lever 51 in a clockwise direction until the arm shoulder 59 drops below the lever latching shoulder 53. The knob 27 is then released to allow the spring 33'to move the plunger 21 back inwardly and to pivot the arm 43 to bring the contact 47 into engagement with the contact 19. The engagement of the lever and the contact arm and the engagement of the contact will retain the spring 33 in a partially compressed position so that the elements of the switch will be held in the position shown in Fig. 1.

If it is desired to open the switch manually, the knob 27 is pulled outwardly until the flanges 37 engage the detents 41 on the spring 39, thus moving the contact carrying arm 43 outwardly to the position illustrated in Fig. 3, in which position both the ring members 31 and 32 are visible to the user, indicating that the switch has been opened by manual actuation.

It will thus be appreciated that a combination manually actuatable switch and automatic circuit breaker is provided which is actuatable by current overload as well as by manual manipulation, and it will be appreciated that the device may be easily reset to its contact closed position. It will, furthermore, be appreciated that the aforementioned advantages of substantially instantaneous action and ability to respond to extremely small overload currents provide an improved device of this character.

Another circuit breaker representing a second embodiment of the invention is illustrated in Figs. 5 and 6. This circuit breaker cannot be manually actuated from its closed to its open position and therefore is not a switch in the conventional sense. It is only a circuit breaker, subject to actuation due to overload current conditions and subject to being manually reset. In this circuit breaker, a casing 111 is provided which may be made of plastic and in two halves as previously described. A pair of terminals 113 and 115 are supported in the casing and are adapted to be connected in an electric circuit, so that when the circuit breaker contacts are closed, current can flow through the circuit breaker. A fixed contact 117 is connected with the terminal 113. A plunger 119 is supported in the casing for in and out movement relative thereto, and a coil spring 121 acts against the inner end of the plunger to normally retain the same in its outermost position. A contact carrying arm 123 is pivotally supported at 125 on the plunger 119 and carries adjacent to one end thereof a contact 127 which normally engages the fixed contact 117. A spring 129 extends between the arm 123 and the plunger 119, urging the arm 123 in a counterclockwise direction to move the contact 127 away from the contact 117.

i In order to normally retain the contact 127 in engagement with the contact 117, a lever 131 is provided which is pivotally supported near its lower end on a pin 133 supported in the casing 111. A pawl 135 is pivotally supported at 137 on the upper end of the lever 131 and is yieldingly held in engagement with a shoulder 139 on the arm 123 by means of a leaf spring 141. A coil spring 143, stretched between an anchor in the casing 111 and the lower end of the lever 1'31, urges the lever to swing in a clockwise direction to move the pawl 135 away from the contact carrying arm shoulder 139. Such movement is, however, normally prevented by means of a current carrying wire 147 which has one end thereof connected with the lever 131, and the opposite end connected with an angled-shaped plate 149 which rests upon a plate 151 which is in current carrying engagement with the terminal 115. One leg of the plate 149 has a slotted aperture 153 therein, while the opposite leg has a threaded aperture to receive a stud 155, the head of which is seated in the casing sothat rotation of the stud will cause movement of the plate 149 toward or away from the lever 131. A suitable pin or stud 157 extends through the slot 153 in the plate 149 and into the plate 151 so that by adjusting the stud the tension on the wire 147 and the calibration of the circuit breaker can be adjusted.

The terminal 115 is electrically connected with the terminal 113 through the plate 151, the plate 149, the wire 147, the lever 131, a pigtail 159, the current carrying arm 123, contact 127 and contact 117. When an overload current condition occurs, the wire 147 will heat and expand as previously described thus permitting the spring 143 to swing the lever 131 in a clockwise direction to move the pawl 135 out of engagement with the contact carrying arm shoulder 169, whereby the spring 129 will swing the arm 123 in a counterclockwise direction mov-.

ing the contact 127 out of engagement with the contact 117 and moving the contact carrying arm into engagement with an abutment 161 on the casing. The spring 121 will then push the plunger 119 outwardly so that the contact carrying arm 123 moves past the pawl 135.

In order .to reset the circuit breaker, and assuming that the wire 147 has recovered to its normal, unexpanded position, the outer end of the plunger 119 is pressed inwardly, thus moving the current carrying arm 123 inwardly past the pawl 135, which swings laterally against the action of the spring 141 to permit the arm to move therebelow. Thereafter, the spring 121 will attempt to move the plunger outwardly, but the engagement of the current carrying arm shoulder 139 with the pawl 135 and the engagement of the contact 127 with the contact 117 will vantages as the circuit breaker described in the preceding.

embodiment with the exception that the device of this embodiment is only a circuit breaker and not a circuit breaker and switch.

The circuit breaker illustrated in Fig. 7 of the drawings is substantially identical to that illustrated in Figs. 5 and 6 except that it is designed to carry a much higher current than the device shown in Figs. 5 and 6. This is accomplished by providing a shunt wire 171 between the plate 151 and the current carrying arm 123. Therefore, a considerable portion of the current will flow through the shunt 171 and a much smaller portion will flow through the wire 1 47. That is, depending upon the size of the shunt, a desired proportion of the electric current flowing through the circuit breaker can be carried through the shunt, and even though the current exceeds five amperes and is considerably in excess of the current which the wire 147 alone could carry, the wire 147 will still heat up and expand upon the occurrence of a current flow in excess of the flow that it is desired that the shunt 171 and the wire 147 together shall carry. The circuit breaker thus operates in substantially the same manner as previously described, except that this device will, as stated,

carry" a. larger currentand is designed for systems having higher current capacities than the circuit breakers previously described. Such a shunt wire arrangement could, of course, be used in any of the other embodiments of this invention without departing from the scope thereof.

In the embodiments illustrated in Figs; 8' through 10, still another circuit breaker according to the invention is illustrated which is adapted to be connected with two diiferent' electrical circuits. One of the circuits would be a primary electrical circuit to be protected, and when this primary circuit is interrupted by the circuit breaker a secondary circuit is closed to energize a bell, buzzer, light or the like, so that when the primary circuit is broken, the buzzer, bell, or light will be energized to indicate that current flow through the primary circuit has been interrupted. Such a circuit breaker is especially useful, for example, in telephone centralofliceequipment or the like.

The circuit breaker includes a casing 211 made of plastic or the like, preferably molded in two halves which are secured together by suitable fastening devices or the like 213. A terminal 215 is supported in the upper end of. the circuit breakercasing 211 and is normally enclosed by a snap-on cover 217, and the terminal 215 is adapted to be connected with a conductor in a primary circuit. A second terminal 219 is provided in the lower portion ofthe casing'211 and likewise is adapted to be" connected in the primary circuit. A fixed contact 211 is disposed in the casing 211 and connected with the terminal 219. A movable contact 223 is carried by an arm 225 which is pivotallysupported at 227 ona plunger 229 which is sup ported in the casing for in and out movement. The plunger 229 has a knob-like extension 231 connected therewith and projecting through the lower end of the casing, and a coil spring 23 3 is disposed between the knob and the bottom of the casing to normally retain the plunger in its out position. A coil spring 235' is connected between the contact carrying arm 225' and the plunger 229 tending to rotate the arm in a counterclockwise direction to move the contact 223 out of engagementwith the contact 221. The contact 223 is normally held in engagement with the contact 221 by a lever 237 which is of a generally inverted L shape and is' pivotally supported in the casing at 239. A pawl 241 is pivotally connected to the lower end of the lever 237 and has a latching shoulder 242 which normally engages the under side of a shoulder 243 on the contact carrying arm 225 to retain the same in its generally horizontal position with the contact 223 in engagement with the contact 221. A

leaf-type spring 245 normally retains the upper portion of the pawl in engagement with lever 237, but the pawl can pivot in a counterclockwise direction on the lever to permit resettingof the circuit breaker, as will hereinafter appear.

The upper horizontal leg portion 247 of the lever 237 carries a stud or fastener device 249 to which the lower end of a current carrying wire 251 is connected. The upper end of the wire 251 extends through the casing 211 and isconnected with the terminal 215' so that normally current in the primary circuit can flow from the terminal 215, through the wire 251, the lever 237, the pawl 241, the arm 225, the'contact 223 and the contact 221, to the ter minal 219. A coil spring 253 has its upper end engaging the wall of a recess in casing 211 and its lower end engaging the top of the lever horizontal arm 247, and tends to rotate the lever 237 in a clockwise direction so as to move the pawl latching shoulder 242 out of engagement with the. contact carryingarm shoulder 243, whereby the spring 235 can pivot the arm to. move the contact 223 out of engagement'with the contact 221. The spring 253 is held inoperative by the current carrying wire 251 until the wireheats and. expands due to a current overload condition, at which time the spring 253- can cause thepivotal movemcntiof the lever.v tov unlatchthet contact carrying arm,

8. whereby current flow through the primary circuit is interrupted.

Immediately upon release ofthe contact carrying 225 the plunger 2 29 moves downwardly to-clo'se the secondary circuit which is connected between the terminal" 219 and an auxiliary terminal 255. A conductive contactwasher 257 is mounted on the inner end of the knob 231 and is insulated from the plunger 229. The inner end ofthe terminal 255 lies along the wall ofthe casing 211 adjacent tothe knob 231, and a contact member'259 secured to the terminal 219' also extends close to the knob 231, being spaced from the terminal 255 and normally electrically separated therefrom. The conductivewaslrer 257 bridges across the inner end of the terminal 255 and the contact member 259 when the plunger is in its extended position, completing the secondary circuit between the terminal 219 and the terminal 255.

When it is desired to reset the circuit breaker to again complete current flow through the primary circuit, and assuming that the wire 251 has returned to its normal unexpanded position so that the lever 237 and pawl 241 have returned to their normal position shown in Fig. 8, the knob 231 is pressed inwardly against the action of the spring 233. The contact carrying arm will then engage the pawl below the latching shoulder 242 and the pawl: will swing in a counterclockwise direction about itsipivotal' connection to the lever and against the action of the.

spring 245' to permit'the contact arm to move above the shoulder 242. Thereupon, when the knob 231 is released, the spring 233 will move the plunger downwardly to again bring the contact carrying arm shoulder 243 into engagement with the pawl shoulder 242 and the contact carrying arm will be swung in a clockwise direction. to bringthe contact 223 back into engagement with the contact 221, whereupon current flow through the primary circuit will again be completed.

A. circuit breaker representing a fourth embodiment of theinvention is illustrated inFigs'. 11-14 and includes two hot wires 390 and 302 connected tin series to provide. a circuit breaker of extremely compact construction and great sensitivity. This circuit breaker includes a somewhat different mechanical latchingarrangement from the circuit breakers shown in the preceding figures.

The. circuit breaker shown in Figs; 11-14 is mounted within a housing 334, which may be made of any desired material having sufiicient strength and rigidity such as,

for example, a plastic, and which may be made, as shown, in two pieces secured together by any desired fastening means such as the screws 336 illustrated. A pair of terminals 308 and 310 are fixed in the housing 304 and extend therefrom for connecting the circuit breaker in an external circuit. A fixed contact 312 is secured to the inner end of the first terminal 308. The second terminal 310 is connected by means of a pigtail 314' to one end of the first hot wire 300. The two hot wires 300 and 302 are electrically and mechanically connected together at their upper ends, as viewed in the drawings, by a pivoted lever 3'16, and the lower end of the. second hot wire 302 is" is mounted for limited in and out. sliding movementwithin. thev housing 304 and extends into a guideway 328 atthe upper end of the housing 304. A pin 333wfixed1 to the housing304 extends through a slot 330 near. the upper end of the inner plunger forlimiting the travel: thereof. At its lower end, the innerplunger 326 carries a pin 334- which extends through a slot 336 in the outer plunger 338. The outer plunger 338 extends throughtheforward 79' wall of the housing 304, and a knob 340, preferably of an insulating material such as plastic, is secured to its outer end exteriorly of the housing 304 for manual actuation of the device.

The outer plunger 328 is urged outwardly by a compression coil spring 342 seated within the knob 340 and hearing at its inner end against a fixed abutment plate 344 within the housing.

The inner plunger 326 is urged outwardly by a tension coil spring 346, one end of which is connected to the contact carrying arm 324, near the left-hand end thereof as viewed in Figs. 11 and 13. The other end of the spring 346 is connected by means of an insulating link 347 to a lever 348, which is pivoted ona fixed pivot 350 adjacent to the plungers 326 and 338. The lever 348 carries a roller 352, which is urged into notches 354 and 356 in the inner plunger 326 and the outer plunger 338, respectively, by the tensioned spring 346. The spring 346 is sufiiciently strong so that when it is tensioned to the position shown in Fig. 11, it holds the roller 352 in the notches 354 and 356 and thereby holds the outer plunger 338 in its advanced position against the urging of the biasing spring 342, and also holds the inner plunger 326 in its advanced position against the outward urging of the spring 346 acting through the leverage of the contact carrying arm 324.

The notch 356 of the outer plunger 338 is relatively gently sloped so that when the tension of the spring 346 is relieved, the sloping side of the outer plunger notch 356 earns the roller 352 laterally out of both of the notches 354and 356, thus releasing both of the plungers 326 and 338 for outward movement responsively to the urging of the biasing spring 342. The outward force of the biasing spring 342 is then transmitted to the inner plunger 326 through the pin-in-slot connection 334, 336', between the two plungers. During the initial movement of the roller 352 out of the notches, the inner plunger 326 is moved slightly inwardly, and the slot 330 at the innermost end of the inner plunger and the connecting slot 336 are shaped accordingly to permit such inward travel of the inner plunger beyond its normal position without obstruction by the respective pins 333 and 334.

The contact carrying arm 324 is normally held against rotating responsively to the urging of the spring 346 by a latch 360 formed at one end of a lever 362 pivoted within the housing 304. The latch 360 engages the end of the contact carrying arm 324 opposite from the movable contact 322, and normally holds the contact carrying arm against the urging of the spring 346, thus keeping the movable contact 322 in full pressure engagement with the fixed contact 312." The lever 362, as perhaps best shown in Fig. 14, fits loosely within a notch 364 defined by a guide member 366, which also encloses a spring 368 arranged to urge the lever 362 laterally toward the contact carrying arm 324.

The lever 362 is in the form of a bellcrank and has a relatively short arm 370 positioned adjacent to one end of the second hot wire 302, The arrangement is such that when the hot wires 300 and 302 expand responsively to a current overload, the bellcrank arm 370 is moved downwardly, as viewed in the drawing, by the hereinafter described action of the spring 384, thus tripping the circuit breaker. The sequence of action is as follows:

. downward movement of the arm 370 pivots the lever 362 in a clockwise direction, moving the latch 360 to the right out of engagement with the contact carrying arm 324, and allowing the contact carrying arm to pivot in a counterclockwise direction responsively to the urging of the spring 346. This relieves the tension on the spring 346 and permits the roller 352 to be cammed out of the notches 354 and 356 by the plungers 326 and 338 responsively to the urging of the biasing spring 342, thus releasing the plungers, which then move outwardly to open the switch contacts 322 and 312.

The circuit breaker illustrated in Figs. 11-14 is also manually actuatable, and may be opened manually by pulling outwardly upon the knob 340 with sufilcient force to overcome the force on the spring 346 and to cam the roller 352 out of the plunger notches, thereby opening the contacts even though the lever 362 is in its normal, non-overload position.

The hot wires 300 and 302 in the present embodiment of the invention are arranged in series, both electrically and mechanically, thus providing an increased sensitivity for actuating the circuit breaker responsively to relatively small overload currents. Also, the increased sensitivity provided by the use of two hot wires permits the use of a greater latching arrangement between the latch 360 and the contact carrying arm 324 than is possible with a single short length hot wire. overload, the two hot wires 300 and 302 provide twice the elongation of a single hot wire, and thereby provide twice as much movement of the latching lever 362. This consideration is of special importance where the circuit breaker is to be subjected to vibration or physical shock during use, since if the latching engagement is relatively small the latch 360 may be disengaged merely by such vibration, or shock, particularly when the circuit breaker is conducting currents relatively close to its rated capacity. The arrangement is also extremely compact, and is of particular advantage for use in applications where weightand space requirements are severe.

The location of the lever biasing spring 368 as shown in Figs. 11 and 13 to work against the long arm of the lever 362 is of importance and of advantage in connection with the resistance of the circuit breaker to vibration and physical shock. By placing the spring 368 as closely as practicable to the latch end of the lever 362, instead of against the short arm 370, the mechanical advantage of the spring 368 relative to the inertia of the system is maximized, thus minimizing the possibility of the latch 360 being released by vibration or physical shock.

The hot wires 300 and 302 are enclosed within separate glass tubes 372 and 374 mounted adjacent to each other in a unitary assembly 380 within the housing 304. The first hot wire 300 is fixed at one end to a conductive plug-like member 376, which is fitted within and rests upon the forward end of the first tube 372, and to which the pigtail 314 is attached to'connect the hot wire assembly to the second terminal 310. At the rear of the housing 304, both of the hot wires 300 and 302 are fixed to the lever 316, which is pivoted on a fixed pivot 378.

The forward end. of the second hot wire 302 is fixed within a plug-like member 382 which is slidably fitted within the forward end of the second glass tube 374, and is urged forwardly by a spring 384 fitted around the tube 374 and seated between 'a rearwardly facing shoulder on the plug 382 and the forward end of a mounting block 386, through which the tubes 372 and 374 extend. The spring 384 is fitted around the outside of the tube 374 and is thereby protected to a large extent against the heat dissipated by the hot wire 302 within the tube, thus avoiding excessive heating of the spring, which might otherwise alfect the temper of the spring and weaken it. The reliable service life of the circuit breaker is thus improved since the spring 384 retains its initial resilience and operating force indefinitely. It should be noted that the hot wires 300 and 302 are normally heated to relatively high temperatures when they are subjected to;

circuit overloads, and in the absence of heat insulating means such as the glass tubes 372 and 374, the heat emitted by the wires may have a pronounced effect on" the spring 384 after only a relatively few overload occurrences.

The hot wire assembly 380 constitutes a separate rially reducing manufacturing costs, and also permitting For a given current ready and simple replacement in the event it is desired to change the current carrying capacity of the circuit breaker. As perhaps best shown in Fig. 12, the subassembly 380 is firmly fixed within the housing 304 by means of appropriately positioned ledges and notches (not separately designated) molded into the housing. For added rigidity, and to facilitate assembly, a screw 331 may be used to secure the mounting block 386 to one portion of the housing 304.

The bellcrank arm 370 of the lever carries an adjustable abutment member 388, which may be threaded as illustrated for ready adjustment, and which is positioned adjacent to the plug member 382. An aperture 39b is provided in the forward wall of the casing to permit manual adjustment of the abutment member Elfib for adjusting the response of the circuit breaker to a preselected current overload value.

The spring 384 is restrained under compression by the hot wires 300 and 302, which are thereby tensioned, and when the hot wires 300 and 302 expand responsively to current overload heating, the spring 384 drives the plug member 382 forwardly, that is, downwardly as viewed in the drawings, pushing upon the abutment memher 388 and pivoting the lever 362 in a clockwise direction to release the contact carrying arm 324, and thus to open the circuit breaker as hereinabcve described.

The spring 384 is substantially stronger than the biasing spring 368 and is sufiiciently strong to drive the lever 362 clockwise against the urging of the biasing spring 368 and to compress the biasing spring 368, as

shown in Fig. 13, when the hot wires expand under.

heating.

When the circuit breaker is tripped responsively to a current overload, it initially arrives atthe position shown in Fig. 13, wherein the extension arm 32% rests upon an abutment shoulder 392 formed in the housing 304, and both the inner and outer plungers 326 and 338, respectively, are moved to their out or retracted positions. Immediately thereafter, the hot wires 300 and 302 start to cool, withdrawing the plug member 332 to its initial, or normal position, compressing the spring 384 and permitting the latch biasing spring 353 to advance the lever 362 back to its normal position where it can be engaged by the contact carrying arm 324. After this is accomplished, through the cooling and contraction of the hot wires 300 and 302, the circuit breaker may again be closed merely by pushing inwardly upon the knob 340 to drive the plungersinwardly until the roller 352 falls within the notches 354 and 356 to retain the plungers in their advanced position.

It should be noted that the contacts 312 and 322 cannot be held closed under continuing current overload conditions merely by holding the knob 340 in its advanced position. The circuit breaker will not automatically recycle under such circumstances, because after it is once tripped responsively to current overload, its contacts 312 and 322 cannot again be closed until after the inner plunger 326 has travelled outwardly to bring the contact carrying'arm 324 past the latch 36h.

If, for example, it is attempted to close the circuit breaker and hold it closed despite a continuing current overload condition, the contacts will closemomentarily for the extremely short time required for the hot wires 300 and 302 to heat up and for the contact carrying arm 3241c be unlatched. The contact. carrying arm then pivots in a counterclockwise direction, responsively to the spring 346, movingthe movable contact 322' out of engagement with the fixed contact 312. It", now, the knob 340'is-hcld in-its fully advanced-position, to prevent the plungers 326' and 338 from being retracted by the biasing spring 342, the contact carrying arm 324 is held above the latch 360' and the lever 362 is blocked by the contactv carrying arm and cannot re-engage it. The contacts cannot again be closed until after the plunger 326 is permitted to move forwardly.

All of the circuit breakers according to the present invention are of the trip free type, being arranged so that they cannot be manually held closed by means of the reset buttons if a current overload condition persists in the circuit, and so that they will not automatically recycle it the reset buttons are manually held in the on" position. The arrangement is such that after the circuit breaker opens in response to a current overload it can be reset only after the overload responsive element has recovered from the overload shock, and recovery of the overload responsive element cannot by itself cause the contacts to close even if the reset button is retained in its closed position during the recovery period. The reset button must be actuated subsequently to the recovery of the overload sensitive element in order to reclose the contacts. This feature prevents automatic recycling of the circuit breakers, which may cause damage to the protected circuit and also to the circuit breaker itself.

In the illustrated embodiments, the hot wires are shown as round in cross section, but the invention is not so limited. It is only necessary to provide an elongated, electrically conductive member having a positive temperature co-efiicient of expansion, and the member may be of any desired cross-sectional shape. In fact, for circuit breakers intended for conducting relatively high currents it is prefered to use a hot wire of relatively flat, ribbon-like shape, particularly in the embodiment shown in Figs. 11 to 14-. In this embodiment, a certain degree of flexibility is needed in the wires in order to accommodate pivoting of the cross-bar lever 316. Such flexibility is more readily achieved in a flat, ribbon-like wire than in a round wire of comparable cross-sectional area and current carrying capacity. With a ribbon-like wire, itis also possible to use a pulley, or an arcuate slideway in place ot the cross-bar lever 316, since the added flexibility of the wire would permit use of a single wire trained around such pulley or slideway. Such variations, however, will be within the skill of those familiar with the art and need not be discussed in detail herein.

For optimum tripping characteristics and maximum service life without loss of calibration accuracy, it is preferred to use as large a wire size as is practicable, that is, as large a wire as will be heated to' a temperae ture significantly higher than the highest expected ambient temperature by minimum overload current. This is desirable in order to avoid stretching of the wire, which tends to take place whenever the wire is heated, and which ecome's increasingly troublesome as the temperature increases. The twowirecircuit breaker shown in Figs. 11 to 14 permits the achievement of sufficient Wire el0ngation for reliable operation with only a minimum heating of the wire. In practical, commercialdevices' according to this embodiment, the circuit breakers are tripped by current overload heating of the hot wires 300 and 3612 to only about 500* F.,. which temperature the wires can readily withstand without any significant stretch-- it has been found unexpectedly that the circuit breaker according to this last described embodiment of the in vention' is substantially unaffected by ambient temperature variations, and will retain its initial calibration throughout a wide temperature range without additional adjustment.- This is an important advantage for many applications, particularly in aircraft wherein the circuit breakers are almost constantly subjected to relatively wide ambienttemperature changes.

Moreover, the sensitivity of circuit breakers according to this embodiment may be made surprisingly high, so

.- that, for example, they will trip quickly and reliably upon r the circuit designer toinakeuseof conductors and other circuit components having much lower safety factors than usual, thus elfecting substantial savings in weight and cost of materials and permitting the use of relatively sensitive electrical devices in the protected circuits.

It will thus be appreciated that in all of the embodiments of this invention, a hot wire, which will expand upon the occurrence of a current overload condition in the circuit in which the circuit breaker is connected, is provided so as to substantially instantaneously break or interrupt the current fiow upon the occurrence of an overload current condition, and it will likewise be appreciated that the circuit breakers and/or switches of this invention can be readily adapted for carrying either extremely low currents, or relatively high currents. The invention provides an improved circuit breaker, which is extremely efficient and durable in construction and relatively inexpensive to manufacture.

What is claimed is: H

1. An electric circuit breaker having automatic overload current protection, including a casing, terminals carried by said casing and adapted to be connected in an electric circuit, fixed contact means electrical-1y connected with one of said terminals, plunger means supported in said casing and movable between a first position and a second position, an pivotally supported on said plunger within said casing, contact means supported on; said arm and movable therewith between a positionin engagement with said fixed contact means and a position out of engagement with said fixed contact means, spring means connected with said arm and attempting to urge said arm and its contact means out of engagement with said fixed contact means, levermeans pivotally supported in said casingand .engageable with said contact arm to'notrrnallyretain said contact inengagement with said fixed contact :means when said plunger, is in its, first position; spring means attempting to urge said plunger means to its second position butnormally re-' strained by the engagement of said lever means with said arm and the engagementof said arm contact means with said fixed contact means, spring means attempting to urge said lever out of engagement'with said arm, and means normally retaining said lever means in engagement with said arm and including a current carrying wi-re electrically connected with-the other of said terminals and with said movable arm contact means, said current carrying wire being operative in conjunction with said lever means toretain the same in engag'ementwith said arm means but effective upon the occurrence of an overload current to substantially instantaneously expand and permit said lever means to be moved by its spring means out of engagement with said arm, whereby said arm'spring means will move said arm contact means out of engagement with said fixed contact means and whereby said plunger spring means will move said plunger to its second position.

2. .The structure as claimed in claim 1 wherein said arm and said lever means have complementary cam surfaces permitting said arm to move into engagement with said lever when said plunger is manually pushed to its first position and when said current carrying wire is in its normally unexpanded condition so that said circuit breaker can be reset with the contact means in engagement by pushing the plunger inwardly.

3.An electric switch including automatic over-load current protection, including a casing, terminals carried by said casing and connectable in an electric circuit, fixed contact means in said casing electrically connected with one of said terminals, plunger means supported in said casing for movement between a first position and a second position, arm means pivotally supported on said plunger in said casing, contact means carried by said arm means and engageable with said fixed contact means, resilient means connected with said arm means and attempting to urge said arm contact means to a position out of engage ment with said fixed contact means, lever means pivotal- 14 1y supported in said casing and engageable with said arm means to retain said arm contact means in engagement with said fixed contact means, spring means attempting to urge said lever means out of engagement with said arm means, a current carrying wire electrically connected with the other of said terminals and with said arm contact means, said wire having one end thereof anchored in said casing and the opposite end thereof operatively arranged with said lever means so that upon predetermined heating and expansion of said wire said lever means may be actuated by its spring means and moved out of engagement with said arm means to thereby permit the spring means connected between said arm means and said plunger to move said arm contact means out of engagement with said fixed contact means, spring means urging said plunger to said second position upon movement of said lever means out of engagement with said arm means, said plunger being manually movable to its first position to bringsaid arm means into engagement with said lever means and the arm contact means into engagement with said fixed contact means upon the return of said wire toits unexpanded position, said plunger means being movable toa third position beyond its reset position to move said arm contact means out of engagementwith saidfixedcontact means, and means engageablewith said plunger when in its third position to retain the same in such position in opposition to the force exerted by said plunger spring means, thereby permitting the movable contact means to be manually moved out of engagement with said fixed contact means, said last plunger retaining'means releasing said plunger for movement to said first position upon exertion of a predetermined manual force to said plunger means to again permit the contact means to be moved into engagement with each other,

4. A trip free electrical circuit breaker of compact construction comprising a casing, a first terminal fixed in said casing and extending exteriorly thereof for connection to an external circuit, a contact fixed within said casing and electrically connected to said first terminal, a movable contact positioned within said casing for travel into and out of pressure engagement with said fixed contact, a second terminal electrically connected to said movable contact, resilient means for urging said movable contact away from said fixed contact, a releasable latch for holding said movable contact in pressure engagement with said fixed contact against the urging of said resilient means and movable between a holding position and a release position, actuating means for moving said movable contact into engagement with said fixed contact when said latch'is in itsholding position, means disabling said actuating means from so moving said movable contact when said latch is in its release position, a. wire electrically connected in the circuit between said first and second terminals for conducting thermal current, and resilient means for tensioning said wire, said resilient tensioning means being arranged to move said latch to ward said release position responsively to thermal elongation of said wire whereby thermal expansion of said wire caused by an overload current of a predetermined value is efiective to release said latch and thereby to trip said circuit breaker.

5. A trip free electrical circuit breaker of compact construction comprising a casing, a first terminal fixed in said casing and extending exteriorly thereof for connection to an external circuit, a contact fixed Within said casing and electrically connected to said first terminal, a movable contact positioned within said casing for travel into and out of pressure engagement with said fixed contact, a second terminal electrically connected to said movable contact, resilient means for urging said movable contact away from said fixed contact, a releasable latch for holding said movable contact in pressure engagement with said fixed contactfagainst the urging of said resilient 'means andmovable between a holding position, anda estates release position, manually opcr'a'table actuating means for moving said movable contact into engagement with said fixed contact when said latch is in its holding position, said actuating means being disabled when said latch is in its release position, a wire having a plurality of juxtaposed portions connected electrically and mechanically in series and electrically connected in the circuit between said first and second terminals for conducting thermal current, and resilient means for tensioning said wire portions, said resilient tension'ing means being arranged to move said latch toward said release position responsively to thermal elongation of said wire, whereby thermal expansion of said wire caused by an overload current of a predetermined value is e'fiectiv'e to release said latch and thereby to trip said circuit breaker.

6. A trip free electrical circuit breaker comprising a compact casing, 21 first terminal axes in said casing and extending exteriorly thereof for connection to an external circuit, a contact fixed within said casing and electrically connected to said first terminal, a movable contact positioned Within said casing for travel into and out of pressure engagement with said fixed contact, a second terminal electrically connected to said movable contact, resilient means for urging said i'nova-ble contact away from said fixed contact, a releasable latch for holding said movable contact in pressure engagement with said fixed con tact against the urging of said resilient means and mov able between a holding position and a release position, manually operatable actuating means for moving said movable contact into engagement with said fixed contact when said latch is in its holding position, means disabling said actuating means from so moving said movable con tact when said latch is in its release position, and overload responsive tripping means for moving said latch to its re lease position responsively to a current overload of pre* determined value including a wire electrically connected for conducting the thermal current in said circuit breaker, and resilient means for tensioning said wire, said resilient tensioning means being arranged to move said latch to its release position responsively to elongation of said wire such as may be occasioned by overload current heating.

7. A trip free electrical circuit breaker comprising a compact casing, a first terminal fixed in said casing and extending exteriorly thereof for connection to an external.- circuit, a contact fixed within said casing and electrically connected to said first terminal, a movable contact positioned within said casing for travel into and out of pressure engagement with said fixed contact, a second termis nal electrically connected to said movable contact, re silient means for urging said movable contact away from said fixed contact, a releasable latch for holdingsaid movable contact in pressure engagement with said fixed contact against the urging of said resilient means and movable between a holding position and a release position, manually operatable actuating means for moving said movable contact into engagement with said fixed contact when said latch is in its holding position, said actuating means being disabled from so moving said movable contact when said latch is in its release position, and overload responsive tripping means for moving said latch to its re,- lease position responsively to a current overload of predetermined value including a wire having a plurality of juxtaposed portions connected electrically and mechanically in series and electrically connected in the circuit between said first and second terminals for conducting thermal current, and resilient means for tensioning said wire portions, said resilient tensioning means being arranged to move said latch toward said release position responsively to thermal elongation of said wire, whereby thermal expansion of said wire caused by an overload current of a predetermined value is effective to release said latch and thereby to trip said circuit breaker.

8. A trip free electrical circuit breaker comprising a compact casing, a first terminal hired in said casing and extending exteriorly thereof for connection to' an external circuit, a contact fixed within said casing and electrically connected to said first terminal, a movable contact positioned within said casing for travel into and out of pressure engagement with said fixed contact, a second terminal electrically connected to said movable contact, resilient means for urging said movable contact away from said fixed contact, a releasable latch for holding said movable contact in pressure engagement with said fixed contact against the urging'of said resilient means and movable between a holding position and a release position, manually operatabl'e actuating means for moving said movable contact into engagement with said fixed contact when 'said latch is in its holding position, said actuating means being disabled from so moving said movable contact when said latch is in its release position, and overload responsive tripping means for moving said latch to its release position responsively to a current overload of ma determined value including a wire electrically connected for conducting the thermal current in said circuit breaker, resilient means for tensioning said Wire, said resilient tensioning means being arranged to move said latch to its release position responsively to elongation of said wire such as may be occasioned by overload current heating, and a conductor connected in shunt with said wire whereby in operation, said wire carries only a predetermined proportion of the total electrical current passing through said circuit breaker.

9. A trip free electrical circuit breaker of compact construction comprising a casing, a first terminal fixed on said casing and extending exteriorly thereof for connection to an external circuit, a contact fixed within said casing and electrically connected to said first terminal, a movable contact positioned withinsaid casingfor travel into and out of pressure engagement with said fixed contact, a second terminal electrically connected to said movable contact, resilient means for urging said movable contact away from said fixed contact, a'releasable latch for holding said' movable contact in pressure engagement with said fixed contact against the urging of said resilient means and movable between a holding position and a release position, manually operatable actuating means for moving said movable contact into engagement with said fixed contact when said latch is in its holding position, said actuating means being disabled from so moving said movable contact when said latch is in its release position, a wire having two juxtaposed portions, an electrically conductive lever centrally pivoted within said casing, adjacent ends of said wire portions being fixed to the opposite ends of said lever, the end of one of said portions opposite from said lever being fixed with respect tosaid casing, the end of the other one of said portions opposite from said lever being fixed to a movable member, said movable member being positioned adjacent to said latch and being operative when it is moved in the wire tensioning direction to re lease said latch, and means for resiliently urging said movable member in the wire tensioning direction thereby to release said latch responsively to thermal expansionof said Wire portions as caused by an overload current.

10. A trip free electrical circuit breaker of compact construction comprising a casing, a first terminal fixed in said casing and extending exteriorly thereof for consection to an external circuit, a contact fixed within said casing and electrically connected to said first terminal, a movable contact positioned within said casing for travel into and out of pressure engagement with said fixed con tact, a second terminal electrically connected to said movable contact, resilient means for urging said movable contact. away from said fixed contact, a releasable latch for holding said movable contact in pressure engagement with said fixed Contact against the urging of said resilient means and movable between a holding position and a release positiomm'anually operatable actuating means for moving said movable contact into engagement with said fixed contact when said latch is in its holding position, said actuating means being disabled from so moving said movable contact when said latch is in its release position, a tensioned wire electrically series connected in the circuit between said first and second terminals, and means responsive to elongation of said wire for moving said latch toward its release position, a third terminal fixed in said casing and extending exteriorly thereof for connection to an external circuit, an auxiliary contact fixed within said casing and electrically connected to said third terminal, and contact means including a movable conductive member associated with said actuating means for electrically connecting said auxiliary contact to said first-named fixed contact during times when said movable contact is out of engagement therewith.

11. A trip free, multi-pole electrical circuit breaker of compact construction comprising a casing, a first terminal fixed in said casing and extending exteriorly thereof for connection to an external circuit, a first fixed contact mounted within said casing and electrically connected to said first terminal, a movable contact positioned within said casing for travel into and out of pressure engagement with said first contact, a second terminal electrically connected to said movable'contact, resilient means for urging said movable contact away from said fixed cont-act, a releasable latch for holding said movable contact in pressure engagement with said fixed contact against the urging of said resilient means and movable between a holding position and a release position, actuating means for moving said movable-contact into engagement with said fixed contact when said latch is in its holding position, said actuating meansincluding a manually operatable plunger slidably mounted in said casing and movable therein between an actuated position and a fnon-actuatedposition, said actuating means further being disabled from so moving said movable contact when said latch is in its release position, a wire electrically connected in the circuit between said first and second terminals for conducting thermal current, resilient means for tensioning said wire, said resilient tensioning means being arranged to move, said latch toward said releaseposition responsively to thermal elongation of said wire such as may be causedby overload current heating, a thirdterminal fixed in said casing and extending exteriorly thereof for connection to an external circuit, a second fixed contact mounted within said casing and electrically connected to said third terminal, and switch means including a-conductive member carried by said plunger for connecting said second fixed contact electrically to said first fixed contactwhen said plunger is in its non-actuated position, the arrangement being such that said plunger is moved automatically from its actuated to its non-actuated position when said circuit breaker is tripped by reason of a current overload, whereby an auxiliary circuit connected between said first terminal and said third terminal is normally closed immediately upon disengagement of said movable contact from said first fixed contact.

12. A trip free electrical circuit-breaker comprising a compact casing, a first terminal fixed in said casing and extending exteriorly thereof for connection to an external circuit, a contact fixed within said casing-and electrically connected 'to said first terminal, 'a movablecontact positioned within said casing for travel into and out of pressure engagement with said fixed contact, a second terminal electrically connected to said movable contact, resilient means for urging said movable contact away from said fixed contact, a releasable latch for holding said movable contact in pressure engagement with said fixed contact against the urging of said resilient means and movable between a holding position and a release position, manually operatable actuating means for moving said movable contact into engagement with said fixed contact when said latch is in its holding position, said actuating means being disabled from so 'moving said movable contact when said latch is in its release position, overload responsive tripping means for moving the latch to its release position responsively to a current overload of predetermined value including a wire electrically connected in the circuit breaker for conducting thermal current, a heat insulating tube enclosing said wire, a coil spring fitted externally around said tube and being thereby insulated from heat emitted by said wire, and means for connecting said spring to said wire so that said spring tensions said wire, said connecting means including a member positioned adjacent to the latch and arranged to be moved by said spring responsively to elongation of said wire such as may be occasioned by overload current heating for moving the latch to its release position to trip the circuit breaker.

13. A trip free electrical circuit breaker of compact construction comprising a casing, a first terminal fixed, in said casing and extending exteriorly thereof for connection to an external circuit, a contact fixed within said casing and electrically connected to said first terminal, a movable contact positioned within said casing for travel into and out of pressure engagement with said fixed contact, a second terminal electrically connected to said movable contact, resilient means for urging said movable contact away from said fixed contact, a releasable latch for holding said movable contact in pressure engagement with said fixed contact against the urging of said resilient, means and movable between a holding position and'a release position, said latch including a bellcrank having arms of unequal length, a resilient biasing member disposed near the outer end of the longer one of said arms for urging said bellcrank toward the'holding position, actuating means for moving said movablecontact into engagement with said fixed contact when said latch is in its holding position, said actuating means being disabled when said latch is in its release position, a wire electrically connected in the circuit between said first and second terminals for conducting thermal current, and resilient means for tensioning said wire, said resilient tensioning means being arranged to move said latch toward said release position responsively to thermal elongation of said wire whereby thermal expansion of said wire caused by an overload current of a predetermined value is effective to release said latch and thereby to trip said circuit breaker.

14. A trip free electrical circuit breaker comprising acompact casing, a first terminal fixed in said casing and extending exteriorly thereof for connection to an external circuit, a contact fixed within said casing and electrically connected to said first terminal, a movable contact positioned within said casing for travel into and out of pressure engagement with said fixed contact, a second terminal electrically connected to said movable contact, resilient means for urging said movable contact away from said fixed contact, a releasable latch for holding said movable contact in pressure engagement with said fixed contact against the urging of said resilient means and movable between a holding position and a release position, manually operatable actuating means for moving said movable contact into engagement with said fixed contaot when said latch is in its holding position, and an overload responsive tripping mechanism for mov-; ing the latch to its release position responsively to-a cur-' rent overload of predetermined value, said mechanism being contained within a compact subassembly which is separately removable from said casing and which includes a mounting block, a heat insulating tube secured to and extending through said block, an'electr-ically conductive wire mounted within said tube and extending generally axially therealong, a coil spring surrounding said tube and being thereby insulated from heat emitted by said wire, means for connecting said spring to said wire so that said spring tensions said wire, said connecting means including a member positioned adjacent to the latch and arranged to be moved by said spring responsively to elongation of said wire such as may be occasioned by overload current heating for moving the latch to its release position to trip the circuit breaker, means for fixedly positioning said mechanism in said casing, and means for electrically connecting said Wire in the circuit between said first and second terminals whereby said wire will be heated by and will elongate responsively to an increase in current carried by said circuit breaker.

15. A trip free electrical circuit breaker comprising a compactcasing, a first terminal fixed in said casing and extending exteriorly thereof for connection to an external circuit, a contact fixed within said casing and electrically connected to said first terminal, a movable contact positioned within said casing for travel into and out of pressure engagement with said fixed contact, a second terminal electrically connected to said movable contact, resilient means for urging said movable contact away from said fixed contact, a releasable latch for holding said movable contact in pressure engagement with said fixed contact against the urging of said resilient means and movable between a holding position and a release position, manually operatable actuating means for moving said movable contact into engagement with said fixed contact when said latch is in its holding position, and an overload responsive tripping mechanism for moving the latch to itsrelease position responsively to a current overload of predetermined value, said mechanism being contained within a compact subassembly which is separately removable from said casing and which includes a mounting block, a pair of heat insulating tubes secured to and extending in juxtaposed position through said block, a first electrically conductive wire portion mounted within a first one of said tubes and extending generally axially therealong, a second electrically conductive wire portion mounted within the second tube and extending generally axially therealong, a centrally pivoted electrically conductive lever mounted adjacent to one end of said tubes and having its opposite ends connected to said first and second wire portions, respectively, a securing member fixed to the end of said first wire portion opposite from said lever and arranged to engage said first tube and thereby to hold said first wire portion against axial tension, a movable securing member fixed to the end of said second wire portion opposite from said lever and guidingly received in said second tube, a coil spring surrounding said second tube and being thereby insulated from heat emitted by said second wire portion, said coil spring being held in compression between said block and said movable securing member and being thereby effective to tension both of said wire portions, said movable securing member being positioned adjacent to the latch and arranged to be moved by said spring responsively toelongation of said wire portions such as may be occasioned by overload current heating for moving the latch to its release position to trip the circuit breaker, means for fixedly positioning said mechanism in said casing, and means including said securing members for electrically connecting said wire portions in series in the circuit between said first and second terminals whereby said wire portions will be heated by current carried by said circuit breaker.

16,. Electrical current overloadresponsive mechanism for use in an electrical circuit breaker of the type having a movable trip lever, said mechanism comprising a mounting block, first and second heat insulating tubes fixed to. and extending side by side through said block, a first electrically conductive wire portion disposed within and extending generally axially along said first tube, a second electrically conductive wire portion disposed within and extending generally axially along said sec ond tube, a centrally pivoted electrically conductive lever mounted adjacent to one end of said tubes and having its opposite ends connected to said first and second wire portions, respectively, a securing member fixed to the end of said first wire portion opposite from said lever and arranged to engage said first tube for holding said first wire portion against axial tension, a movable securing member fixed to the end of said second wire portion opposite from said lever and guidingly received in said second tube, a coil spring fitted externally around said second tube and being thereby insulated from heat emitted by said second wire portion, said spring being held in compression between said block and said movable securing member and being effective to tension both of said wire portions and to cause said movable securing member to move axially responsively to expansion of said wire portions, and electrical contact means for connecting said wire portions in series will each other in an electrical circuit in a circuit breaker for conducting thermal current therein,

-17. Electrical current overload responsive mechanism for use in an electrical circuit breaker of the type having a movable trip lever, said mechanism comprising a mounting block, first and second tubes fixed to and extending side by side through said'block, an electrical conductive wire having adjacent juxtaposed portions extending axially in said tubes and connected electrically and mechanically in series, a member fixed to one end of said wire and retaining said wire end against movement relative. to one of said tubes, an electrical conductor member secured to the other end of said wire and movable relative to said other tube, spring means resiliently tensioning said wire and resiliently urging said movement of said conductor member so as to cause said conductor member to move axially of said other tube in response to expansion of said wire portions.

References Cited in the file of this patent UNITED STATES PATENTS 554,557- Whitehead Feb. 11, 1896 1,046,499 Schneider Dec. 10, 1912 1,627,029 Greenway et al May 3, 1927 1,990,122 Hauser' Feb. 5, 1935 FOREIGN PATENTS 147,220 Austria Oct. 10, 1936 91,711 Switzerland Apr. 1, 1922 383,105 Germany Oct. 10, 1923 394,057 Germany Apr. 12, 1924 443,870 Germany May 12, 1927

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