US2453546A - Circuit breaker - Google Patents

Description

E. 5. SMITH CIRCUIT BREAKER Nav. 9, 1948.

2 Sheets-Sheet l Filed Oct. 30, 1944 I SWlTCH OFF HEATER OFF SHUNT 7 MU M Q ma 5. fi m BF 9 H CIRCUIT OPEN Filed 001;. 30, 1944 Nov. 9, 1948; 5, 5mm, 2,453,546

CIRCUIT BREAKER 2 Sheets-Sheet 2 FIG.

FIG.6. 109

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Patented Nov. 9,

CIRCUIT BREAKER Ezra S. Smith, Attieboro, Mass, assignor to Metals & Controls Corporation, Attleboro, Mass., a corporation of Massachusetts Application ctober'30, 1944, Serial No. 560,929

This invention relates to electric circuit breakers, and more particularly to circuit breakers which automatically trip out on overload in the electrical circuit, and which are manuallyreset to close thecircuit again.

The invention is an improvement over that shown in the United States Patent 2,371,672, dated March 20, 1945, for Circuit breakers.

Among the several objects of the invention may be noted the provision of a thermostatic circuit breaker which has all of the advantages of the circuit breaker specified in said patent and which in addition is a two-rating breaker having a lower rating for the current under which thermostatic overload action occurs and a higher rating for functioning as a short-circuiting cutout; and the provision, of additional means whereby both the thermostatic and short-circuiting components may under emergency conditions be opened independently of the thermostatic and short-circuiting operations. Other objects will be in part obvious and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified 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 11- lustrated one of various possible embodiments of the invention.

Fig. l is a top plan view of the device;

Fig. 2 is a right end elevation of Fig. 1;

Fig. 3 is a bottom plan view of Fig. 1;

Fig. 4 is a section, on an enlarged scale, on the line 4-4 in Fig. l;

Fig. 5 is a section, on an enlarged scale, on the line 5-! in Fig. 1;

Fig. 6 is a section, on the line 6-6 in Fig. 2

with the thermal element dotted;

Fig. 7 is a section, on the line l| in Fig. 2; Fig. 8 is a section similar to Fig. 6 but with the 4 Claims. (Cl. 200-116) thermal element shown in full and the heater dotted;

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

Fig. 10 is a view similar to Figs. 4 and 9 but with the device in a diflerent position;

Fig. 11 is a view similar to Figs. 4, 9 and 10 but showing the device in stilianother position;

Fig. 12 is an isometric view of the operating handle mechanism; and

Fig. 13 is a perspective view ofa fusible shunt bar. much enlarged. 7

Similar numbers indicate correspondingparts 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. 7 i

If such a circuit breaker is operatlng under conditions near its tripping point, the contact pressure exerted by the thermal element, or its position in relation to the detent which it may be controlling, may be so critical that a slight jar will often prematurely trip it. Also, in some types of thermal circuit breakers the thermal element is so arranged that during its actuation it drags against other parts with considerable friction,

which results in non-uniformity of operation.

According to the present invention a circuit breaker is provided which is postive in its action, is not readily jarred into premature tripping, can be easily adjusted. opens the electrical contacts in a minimum of time and with ample opening to interrupt the arcs encountered in the circuit for which the circuit breaker is designed, and which is so arranged in relationship of its parts that the thermal element presents no hindering friction against any moving part. v I w The thermal element employed is an inherently snap-acting thermostatic member, plate or disc. Up to the point of tripping, this snap-acting element does not move, and hence maintains a positive latching action in conjunction with the detent which it releases, and hence is not readily Jarredfrom its detent position. In addition, when the snap-acting element does snap, it clears the moving parts completely and the device is therefore free of the disadvantage encountered where the friction above referred to is present. Also, the pressure exerted by other moving parts in the circuit breaker has but little efiect upon the calibration of the circuit'breaker of the present invention.

In some types of circuit breakers it is necessary to incorporate what is called a shorting 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 accomplished is to cause the thermal element itself to act as a shunt bar. This may give trouble since the overload conditions are then apt to overheat and change the calibration of the thermal element and hence of the circuit breaker. In this invention the shunt bar is used in such a way that it completely shunts out the thermal element and little, if any, current passes through the thermal element when the shorting bar is in use. In addition, this actuation of the shorting bar, whil being accomplished by the'same control handle which is used to reset the breaker,

' is so arranged as to haveno restraining effect on the thermal element, which isat all times free to Y move.

The particular new features in connection with the present improvement are as follows:

I First, the shunt or shorting bar is arranged as a new and improved fuse element which has a higher current rating for blowing than the current rating at which thermostatic operation occurs.

Second, manual means is provided for reopening the switch at will.

Referring now to the drawings, numeral I indicates a frame or base made of an electrical insulating material such as a molded synthetic resin of the "Bakelite" type. The base i is constructed. of two parts 3 and I. Molded into 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 9 which form a channel il in which the boat or cam member l3 rides. Pegs II are inserted firmly and immovably in the base and serve as anchors for ends of the springs IT. The other ends of the springs II are respectively attached to the stirrup l9.

4 The projecting pins 33 of the disc post 28 ex .tend beyond the sides of the frame 23, and lit slidably into vertical notches 39 which are molded into the upright partitions I. Thus,-when the boat i3 is pushed along the base, the disc carrier 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 The construction of the slidable boat i3 is 11- lustrated particularly by Fig. 12. The boat is,

as indicated, of two main portions, the slide 2i and the frame 28. These are formed of thin sheet metal. with sufllcient rigidity to keep their shape.

addition to these 'two main parts there is a third part, the disc post indicated generally at 25, This post 2!!- is formed of steel or some other I such metal. It has, a threaded hub 21 which threads into the disc hub 29 (see Fig. 4), and a circular base portion 3|. Two pins 33 project from diametrically opposite points on the circular portion 3| and are slidably engaged in the cani slots 35 of the frame 23. Bent-over ears 3'! on the frame 23 serve to slidably hold the slide 2| to the frame 23, thus providing for a relative sliding between the frame 23 and slide 2|. This motion is in a lengthwise direction. The slide 2L is provided with an elongated center opening 38, through which the threaded hub 21 of the disc post 25 is allowed to extend freely when the boat is assembled.

Slide 2i is also supplied with projecting ends I, the purpose of which will subsequently be described. The other end of slide 2i is provided with a projection 43 to which the knob 45 is attached. The knob may be held on by any of the customary means.

One point in regard to the structure of the breaker of the former patent was that it was not intended manually to be reopened because the knob 35 was of plain cyllndric form. Not enough friction would be obtained between such a form and the fingers, even with knurling of the knob to accomplish opening. As will appear from the following, opening action requires a substantial force. Therefore, herein the knob 45 is provided with a head 48. Thus the presentconstruction provides an additional function.

The frame 23 has at one end notches H which serve to be engaged by the stirrup i8, and thus guide the stirrup in position on the frame 28, the stirrup being kept in position against the frame 23 by the springs l1.

Fig. 6 shows the boat mounted in'the base I. It will be observed that the stirrup i9 is engaging the end of the frame 23 in notches M so that when the knob 45 is pressed to slide the boat inward, the springs l'l provide a return bias.

in the cam slots 35 in the sides of the frame 23.

Referring now to Fig. 13, there is shown a shunting or shorting bar 5!.

in said patent. In the present case it is composed of an insulating strip 2, composed, for example, of compressed Bakclite" impregnated cloth. Any insulating fibre is satisfactory if not frangible. On one side of the strip 2 is a facing 4 which is composed of a thin sheet of fusible copper, the ends of which are made up as two silver contacts 9. The latter are formed over the ends of the strip 2. Through this assembly are formed two holes 53, which holes receive the extensions ll of the slide 2| to guide the shorting bar. The shunt bar ii is shown mounted in position on the base with the extensions 3i passing through the holes 59 (see Figs. 6 and 9). A spring 55 rests in a properly provided groove 61 molded in the base I. A metallic tube 59 serves to guide the spring and provide a mounting for it. Spring 55 is of such length as to keep the shorting bar -Il pressed away from the end of the base and toward the center of the base in a non-contactmaking position. 1

The fusible facing 3 is intended to fuse at a current rating which is higher than that causing operation of a bimetallic disc 6| hereafter to be described in detail, but below the point at which other parts in the circuit would be damaged under shunt or short-circuiting conditions. A typical example will be specified later.

Referring again to Figs. 4 and 8, a thermostatic snap-acting bimetallic disc 6| is shown thread ably mounted by means of hub 29 on the post 25. The hub 29 is provided with the proper abutments and shoulders in the usual way so that disc 6| is relatively free to rotate thereon. Thus by turning the disc hub 29 on the threaded hub 21, the position of disc BI is changed relative to the base 5. By this means temperature adjustment of the disc is made. Contacts 63 are electrically welded on disc ill, or otherwise mounted and electrically connected to the disc 6|.

Referring now to Fig. '7, the terminal and stationary contact assembly is shown with the internal heater. These are as follows: Oneterminal 65, comprising a. strip of conducting metal of the proper thickness and size to fit in the grooves l molded in the base, is shown pressed into position. This terminal has a contact 61 on its side facing the central portion of the circuit breaker positioned to engage one of the disc contacts 83. The other terminal 69 is likewise mounted on the base, and to it is attached at one end a heater 7|. The other end of heater 1| is attached to a thirdmetal support 13 which likewise engages the molded grooves in the base I. Support 13 is not in electrical contact with terminal 89, except through the heater ll. 13 carries on its inner surface a contact '15 which is adapted to engage the other contact 63 on the bimetallic disc 6|. In addition to these contacts, terminal 65 carries on it an additional stationary contact Tl adapted to be engaged by one end of the shunt bar 5!, and terminal 69 carries a sta- This bar in the present structure is improved over the bar shown Support tionary contact II which adapted be Qlga edby the other end of the shunt bar II.

It is to be understood that the heater element ll may be omitted in this case where the rated current is great enough that the heating caused by its passage through the disc Ii alone is great enough to cause the thermostatic action of the disc. In general, the switches with lower cur-' current available. In other words, the disc has a limiting thinness for proper mechanical operation. It is in such cases that the auxiliary heater is used because its cross section is independent of any mechanical strength requirements. Its cross section may be made whatever is necessary to bring about the heating desired.

Referring to Fig. 5, there is shown a post button 8i having a threaded portion I! and a projecting stem 85. This post button screws into the base portion (see also Fig. 3), which has a hole s1 threaded for that purpose. Projecting stem '5 slidably fits into the hole a which is provided centrally in the disc'post ll. This stem portion 8| and the notches ll serve as the bearings on which the post I! rides up and down when the boat It moves back and forth in the base. It will be observed that a molded portion (see Fig. 6) serves to engage the extending ears SI of the disc 6i, and thus maintain the respective contacts in alignment.

It will be observed that as the boat It moves along the base in its channel II, the disc post 25 rides up and down in a direction perpendicular to the plane of motion of the boat It; As the disc post 25 does this, it carriesup and down with it the snap-acting bimetallic disc ll. Thus the contacts 63 are brought into engagement with the stationary terminal contacts as the boat l3 slides along the base against the tension of the springs I1, and vice versa. The operation of these motions 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 in an upward direction (as Figs. 6 and 8 are drawn) so as to bring the disc and its mating circuitclosing contacts into engagement with the stationary contacts 61 and 15. when the disc contacts 83 reach the stationary contacts 61 and IS, the mot-ion of the perimeter of the disc is stopped, but further motion of the slide forces the center of the disc still farther upward, thus putting pressure-on the cold disc which is resisted by the 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 95 against the pressure of cold disc ll an additional force is required. Consequently when the pins drop down behind the detent parts 95, the spring pressure of disc 8| serves to hold the boat in position against the tension of springs 11, as long as the pressure is maintained against the pins by the cold disc 6|. The ends 91 of the slots as 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 65. contact 61, the corresponding contact as of the disc, disc II, the other 6 disc contact ll, the stationary contact ll, heater H and terminal ll. I The overload tripping operation of the device on overload conditions is as follows:

When the device is subjected to the overload current which it is designed to interrupt, the heater 1| heats up as does the disc ii (since it is subjected to the current also). After a predetermined given interval of time, the heat generated is sumcient to cause the disc to snap to its other (hot) position of concavity. This motion of the disc in its snap opens the contacts and also serves to release the ressure of the pins II against the detent N, and the biasing springs. I! are now free to pull the boat I! back into its original position. This motion of the boat I! causes the cam slots to draw the hot disc 6i away from the stationary contacts 61 and II. It will be observed that if the knob and boat are held in the circuit-closing position, the motion of the disc snaps the contacts 83 away from contacts I! and I8 thus opening the circuit. The automatic movement of the disc caused by the boat I! and its cam action is large compared to the motion obtained from the thermal movement of the disc alone and gives the breaker additional circuitin'terrupting capacity. In addition. this movenient caused by the cam action is sufliciently large so that when the disc cools and snaps back to its original cold position, the contacts is do not make contact with the stationary contacts 81 and II mounted on terminals 85 and 89. Thus, with the disc in its cold position, and until reset, the circult is maintained in an open position.

I ,It will accordingly be observed that the opening of the circuit is caused by a combinationoi the motion of the disc and the 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 whenthe latter is in its 1 It sometimes happens that in an emergency it is necessary to prevent the circuit breaker from interrupting the circuit, or else to quickly re-close the circuit if the circuit breaker has opened it.-

To this end the shunting bar BI is provided. By relierring to Fig. 12, it will be seen that the slide H can move relative to the frame 23. Consequently a further inward pressure on the knob will cause the slide 2| to slide in a little further. This further sliding actionresults in the end of the slide II at the ends of its extensions 4| striking the shunt bar II as shown in Figs. 9 and 11, and forcing the bar 5| into engagement with the stationary contacts I1 and 18. Consequently this further forward motion of the slide II 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. 11 where the disc is in its hot position).

From the above it will be understood that this further forward motion of the slide 2! 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 5| efl'ectively shunts out the heater II and the disc 6|, so that neither is injured by the overload current. When the pressure on knob 45 is relieved, the spring it forces the shorting bar away from the contacts 11 The substantial force is due to the fact that this requires some forceful flattening of the disc in its thermostatic operation occurs and a higher rating at which the fusible element 4 burns out. For example, a typical rating for action of thermostatic disc 6l might be 5m 50 amperes and 600 amperes for the fusible link 4. lit is to be understood that these ratings are only exemplary and that others might be used. The insulating stiffening bar 2 allows the fusible short-circuiting bar' to be designed thin enough for any desired capacity without rendering the bar as a whole too flexible for proper mechanical operation,

An important factor of this construction is that by allowing relative movement between the slide 2i and the frame 23, the spring 55 can be made fairly light and still be strong enough to force the slide 2'! back, and hence open the shunt bar circuit. It has been found that if the disc 6| is in its cold circuit-closed position there is considerable pressure exerted against the frame 23. If frame 23 and slide 2| were all of one piece, the whole of said piece would have to be moved inward to close the shorting bar. The friction caused by the disc pressure against the frame 23 and the frame against the base would be sufficient to hold the shorting bar closed, even if the knob 45 were released, unless a very strong sprin 55 were used. As a practical matter, it is found that the spring 55 would have to be so strong as to make it difficult, if not impossible, to fit it into the small space required by eficient design of a circuit breaker of this type. Also, the use of such a strong spring would make it very difficult to close the shorting bar. By the present construction a light spring is allowed to work against the freely-moving slide M to open the shorting bar. Also, the lost motion between prongs 4i and bar 5! avoids a large initial deflection in the spring 55 such as would be necessary if the bar 5! partook of the full stroke of 2!. This is further conducive to a short spring.

From the above it is clear that the present circuit breaker is the type which utilizes a thermal means to initiate the mechanical motion, said mechanical motion further moving the thermal element. The motion of the thermal element per so 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 IT. The use of a snap-acting thermal element thus minimizes friction, since such an element occupies either its hot or cold position, any intervening position being of extremely short duration.

The spring 55 automatically re-opens the fusible circuit through the short-circuitirig bar when the button 45 is released. Pull on the button is not needed for this purpose. Pull on the button afforded by the enlargement 46 allows the boat or cam member I3 to be pulled back so as to draw open the thermostatic switch member at when the latter is in a thermal condition otherwise to close the circuit. The reason for providing the enlargement .46 in order to obtain a positive manual grip is that a fairly substantial force is required to pull the detent 95 under the pins 55.

cold position against the contact II. It will be noted on the other hand that a feature of the detent 95 is that it, in view of the tension from the disc 5|, prevents the opening action of the switch from being too critical, that is, from opening accidentally under vibrating conditions due to action of the springs l1. Thus means is provided on the one hand for preventing accidental vibratory opening and on the other hand positively operable manual means providing for manual opening.

A portion of the knob 45 below the head 46, indicated at 48', may be colored differently than the remainder, such as, for example, red. Hence when the knob is pushed in, this part will be hidden by an encircling flange 50 of the plate or panel I017. When the knob 45 is pulled out, this differently colored portion will be exposed to indicate that the thermostatic disc BI is in open position.

An advantage of the particular form of :bar 5| is that if a manufacturer desires to make some part of his production of switches without the short-circuiting feature, it is only necessary to eliminate the fusible link 4 along with its contact 6 simply by not assembling them on the insulating bar 2. Then the holes in the bar 2 will still function to receive the fingers 4|, but the short-circuiting operation wil1.be dead. This is to be distinguished from leaving out also the spring 55 and the bar 2 for the elimination of short-circuiting, in that the holes 53 in the insulating bar 2 still act as guides for the fingers fl.

Referring to Figs. 1 and 3, through the holes 99 are passed rivets which serve to hold the two halves of the base together. Referring again to Figs. 6 and '7, just before the'two halves of the base are put together, nuts E03 are inserted in properly shaped hexagonal recesses I05 in each half of the base, so that'when the two halves are put together nuts I03 are held so that they cannot turn. Then the frame l0! which serves to mount the breaker on the proper panel is held firmly to the base .by means of screws I09 which engage the nuts I05.

To adjust the circuit breaker to the proper rating, the button 8! is unscrewed, thus giving access to the disc hub 21. This is turned (thus changing the temperature adjustment of the disc) until the disc snaps at the correct interval of time, with thecalibrating current flowing through it and its heater. A drop of solder is then placed on the hub to solder it to post 25, and

thus to prevent it from further turning and getting out of adjustment. In order to prevent tampering and resetting in the field, a. cover disc 85 is cemented in place over the button 8|.

While the thermostatic member 6| is, according to the present example, inherently stressed to be concave toward the first contacts 15 and TI out changin the inventive principles.

when cold, and vice versa, it is clear that this relationship of conditions could be reversed with- In other words, the second contacts 63 could be carried from the first contacts upon cooling, the two conditions of stability of the thermostatic member being reversed as regards temperature. I

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

l. A circuit breaker compr sing separable contacts, a tripping mechanism for said contacts including a thermostatic element, manually operable means having a lost-motion connection with said tripping mechanism for reclosing said contacts after separation thereof and cooling of said thermostatic element, and a shunt switch adapted to be closed by said manually operable means upon taking up said lost motion for shunting said separable contacts and closing the circuit, the movable contact element of said switch comprising a fuse, thereby providing for insertion of a fuse into the circuit only upon shunting operation, control of said circuit being restorable to said separable contacts and tripping mechanism upon opening cf'said switch whether or not the i use has blown during the shunting operation.

2. A circuit breaker comprising separable contacts, a tripping mechanism for said contacts including a thermostatic element, manually operable means having a lost-motion connection with said tripping mechanism for reclosing said contacts after separation thereof and cooling of said thermostatic element, and a shunt switch adapted to be closed by said manually operable means upon taking up said lost motion for shunting said separable contacts and closing the circuit, the movable contact element of said switch comprising a fuse, thereby providing for insertion of a fuse into the circuit only upon shunting operation, control of said circuit being restorable to said separable contacts and tripping mechanism upon opening of said switch whether or not the fuse has blown during the shunting operation, said fuse having a higher rating than the rating of the tripping mechanism for the separable contacts.

3. A circuit breaker comprising separable contacts, a tripping mechanism for said contacts including a thermostatic element, manually operable means having a lost-motion connection with said tripping mechanism for reclosing said contacts after separation thereof and cooling of said thermostatic element, and a shunt switch adapted to be closed by said manually operable means upon taking up said lost motion for shunting said separable contacts and closing the circult, said switch comprising a pair of fixed spaced contacts and a movable contact element comprising a strip of insulating material having a facing of fusible conducting material and adapted to bridge said fixed spaced contacts and to fuse upon passage of an overcurrent therethrough, thereby providing for insertion of a fuse into the circuit only upon shunting operation. control of said circuit being restorable to said separable contacts and tripping mechanism upon opening of said switch whether or not the fuse has blown during shunting operation.

4. A circuit breaker comprising separable contacts, a tripping mechanism for said contacts ineluding a thermostatic element, manually operable means having a lost-motion connection with said tripping mechanism for reclosing said contacts after separation thereof and cooling of said thermostatic element, said manually operable means being provided with means thereon where- I by substantial force may be manually applied directly thereto to open said contacts when said thermostatic element is heated and said contacts I are closed, and a shunt switch adapted to be "closed by said manually operable means upon taking up said lost motion for shunting said separable contacts and closing the circuit in an emergency, said switch comprising a pair of fixed spaced contacts and a movable contact element comprising a strip of insulating material having a facing of fusible conducting material and adapted to bridge said fixed spaced contacts and to fuse upon passage of an overcurrent therethrough, thereby providing for insertion of a fuse into the circuit only upon emergency operation, control of said circuit being restorable to said separable contacts and tripping mechanism upon opening of said switch whether. or not the fuse has blown during shunting operation, said fuse having a higher protective rating than the ratin of the tripping mechanism for the separable contacts.

EZRA 8. SMITH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS

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