US2633515A - Thermally actuated automatic overload circuit breaker - Google Patents

Description

' cuits.

Patented Mar. 31, 1953 UNITED STATES ATENT OFFICE THERMALLY ACTUATED AUTOMATIC OVERLOAD CIRCUIT BREAKER Application October 29, 1951,y Serial No. 253,655

3 Claims.

My invention relates to automatic circuit breakers which are hereby dened as devices through which an electric current is passed and which open the circuit and automatically interrupt said current whenever certain undesired conditions occur in the circuit.

My invention relates to a device by which the circuit is interrupted whenever the current in the circuit so increases that it is desirable to open the circuit.

My invention further relates to such an overload cir-cuit breaker which opens whenever a thermostatic member forming a part of the breaker is heated above a predetermined temperature.

During the last twenty years there has been a strong tendency to replace fuses by thermally operated, automatic, overload circuit breakers, especially for use on circuits supplying current for domestic use, a field at one time wholly occupied by fuses. In spite of strong eiorts to make the replacement of fuses easy and safe, these eorts were not entirely successful and there has been an increasing demand for cir-cuit Abreakers for use in domestic service. Such breakers are used only on 110 or 220 volt service and have a rated full load capacity of 50 amp. or below. They are used on both A. C. and D. C. cir- It is an object of my invention to provide a novel and useful circuit breaker adapted to meet the demand for such domestic breakers.

For some time there have been many circuit breakers available for use in such service but such breakers have cost the consumer several dollars, whereas the fuses and fuse blocks usually supplied for this service cost only a small fraction of a dollar. It is a. further object of my invention to provide a circuit breaker which will adequately perform the functions needed in domestic service and which, when made under good manufacturing, costs little more than the fuse block and fuse.

These breakers are usually installed in metal.

boxes with a hinged cover and such boxes often also carry the watt-hour meter. An ordinary house will have several circuits each protected by a circuit breaker, all of these breakers being Yamp., that is to. say, to supply circuit breakers which can be set to open on an overload of 15, 25, 3G, 4G or 50 amp. At the present time the breakers are built and adjusted at the fa-ctory to open at a single denite amperage so that a supply house has to carry at least ve sizes of such breakers. It is a further object of my invention to provide a breaker which can be adjustedto open at any one of several over-load values.

Further objects and advantages of my invention will be made evident hereinafter.

The invention resides in new combinations of elements by which the above recited objects are attained. The particular embodiment of the invention illustrated in the drawing, and hereinafter described, consists of a box and a movable assembly mounted in the box, this assembly consis-ting of a sleeve movable axially in, and projecting outside of, one wall of the box, and a stern moving axially in, and having an outer end that, in certain positions of the parts, projects outside of, the outer end of the sleeve. To close the breaker, the sleeve and stem are pushed inwardly and to open the breaker the sleeve and stem are pulled outwardly. When the breaker opens on overload, the stem moves outwardly without moving the sleeve. The mechanism inside the box is very simple, the levers, toggles, and latches usually found in conventional circuit breakers being absent.

In the drawings which illustrate preferred embodiments of my invention:

Fig. 1 is a section on a plane indicated by the line l-I in Fig. 3 of the breaker in its closed position, the position of its stem and connected parts in the half-open position of the breaker being shown in dotted lines;

Fig. 2 is a section on the same plane as Fig. 1 of the breaker in its full open position;

Fig. 3 is a section on a plane indicated by the line 3--3 of Fig. 1;

Fig. 4 is a top view of the circuit breaker shown in Figs. l, 2, and 3;

Fig. 5 is a view similar to Fig. 1 of a modified form of circuit breaker;

Fig. 6 is a section on an enlarged scale on a plane indicated by the line 6-6 of Fig. 2 of the detent used to prevent rotation of the sleeve; and

Fig. 7 is a diagram showing hcw the current trip value of the breaker may be changed.

In the embodiment of the invention shown in the drawings the box or casing il is formed or" molded material having good dielectric characteristics. A cover l2 secured by screws en closes a central chamber i4 in the box il. A rst terminal member I5 and a second terminal I6 are embedded in and project from the bottom Il of the box, as seen in Figs. l, 2, and 5. Screws i3 are provided on the outer ends of each of the terminals l and I6. Wires from an eX- ternal circuit may be connected to the terminals I5 and i6 by use oi thev screws i5 and the 'function of the circuitbreaker is to'maintain the continuity of said circuit as long as the circuit breaker is closed, and to open the circuit whenever the circuit breaker is manually or automatically opened because of an overload in the zcircuit.

Passing through, but rigidly secured in, the top 2l oi the box il is a dielectrictube 22 which has a cylindrical bore in which a sleeve-23, prei"- erably formed of material having good dielectric characteristics, can slide axially. Carried on and rigidly secured to the sleeve 23'is a brass shell 2d having two shallow grooves 25 and 255 formed therein, the outer surface of said shell 2d between and adjacent to the grooves-.25 and 2e being-toothed orindented as shown at Y26 in Fig. 6. The yupper end of the sleeve 23 is grooved as shown at '27 to form a knob 28. An important feature of the sleeve assembly is a calibration plate 2Q, preferably formed on the bottom of the brass shellfZli, the periphery of lthe plate being eccentric to the axis of the sleeve 25.

Mounted in a cavity 3i in the top 2i is a ball-i2 which is forced toward the axis of the sleeve 23 by a spring 33 held in place vby a screw 3d. The ball projects through the dielectric tube 22 and engages the upper `groove 25 whenever the breaker isv closed, engaging the lower groove 26 whenever the circuit vbreaker is opened manually. The ball 32 and grooves Eandit form a cor.- venient friction producing device adapted to- .tend to hold the sleeve 2t in either extreme position, and toallow the operator to move the sleeve 23 from-'either'extreme position to the other position'by pulling or pushing on the knob 28.

Sliding freely in a hole extending through the sleeve'23is a stern 'di which has a knob l2 at its upper end, the knob e2 being entirely inside ya cavityformed in the top of the sleeve 23 when the stem d! is in its lowestposition with relation to the sleeve 23. The lowerv end of the stem vii ypasses through a lug d3 projecting from, and preferably formed as a unitary part of, the-box H. The'stern di is acted Aupon bya'spring which tends to force the stem all upwardly in the sleeve Two methodsof so'mounting the spring are shown in Figs'l and 5 and other methods might, of course, be used. Fig. 5 shows a'compression spring 44 in the cavity which contains the knob 42, and Fig. 1 shows a ycompression spring t5 pressing against the lug #it and against a `pin d5 carried by the stern lll.

Rigidly secured to the stem lll near the lower portion thereof is a bimetallic, thermally responl`sive strip 5l which is bent out to missthe lug 43 and up so that its upper end may engagethe calibration plate 29. The upper end'of the strip 5i is connected to the terminal it througha flexible lead 52, current passing through said lead 52, the strip 5i, and the stem di to a stationary contact 53 formed on the lterminal l5 whenever the circuit breaker is closed. l)The bend in the strip 5l is engaged in a slot 5d formed in a projection 55 from the box ii so that the strip 5l and the stem 4l to which it is rigidly attached cannot turn with relation to the box H. The sleeve 23 can, however, turn in the box Il but is irctionally restrained from turning by a spring detent 56 (Fig. 6) placed in a cavity 51 in the top 2| of the box ll. The free end'of .4 the detent 56 engages the knurling 26' on the shell 24 but may be readily released if the sleeve 23 is turned by turning the knob 28.

The strip 5I is formed of two metals having radically diierent rates of heat expansion, such thermally Aresponsive bimetallic members being commonly used for many purposes. 'When heated, a flat portion of such a strip tends to assume 'an arcuate shape and if one end of such a strip is held rigid, the other end of the strip tends to -move in a direction perpendicular to the plane of the strip. When the member 5i is heated by `thefpassage of electric current therethrough, the

ofsaid stripare functions of the C2R loss in the strip.

The strip 5l performs a double function as it is not only a heat responsive `member but .it.also acts as alatch. VWhen the strip "5l 'isfc'old "its upper end engages the calibrationjplate29,.beinghel'd in contact 'withth'at plateby either the springiM orthe spring Al'sothat the st'emwvith its knob 'd2 inside the cavity of the sleeve 23 moves in and out with the sleeve '23.V "Wheni'the sleeve is `pushed toward the box l' i,"thei"stern"4l moves vdownfand engages the jstationarycontact 53 and the "circuit is "closed, DIi"thelnobZB"is pulled away fromthe box ll,.the stein"4l moves with the sleeve'ZS and the'circuit' is'ope'ned.

if, however, the calibration.'plate29 is'engaged by theV upper end of the stri'pi in [the position shown in Figs. land 5, .andlthes'triplis so` heated that the upper VVend'of thestrip movestotheright and disengages from the.'calibrationlplate1`2`9,lthe spring wordt will jerk thestem'lH `upiari'd thus open the circuit. .nother words,.theicircuit'ivlll be opened Whenever the 'current'inthe circuit exceeds a pre-established or calibrated value.

`It `is for the purpose of'making itpossibleto set the circuit breaker Yto open .at any :one of several .current values vthat .the calibratinplate is made eccentric to theffixed axis ofthesleeve 2.3, which is also .theffixedaxisof -thelstem l4l. As the :sleeve 23 is rotated':aboutthisv axis A,and

lthe eccentric *calibration .platef29 is tur-ned,..the

distance through Whichthe send of .the .istrip 5i mustmovemay be varied. Referringtoliig.

y7, the sleeve vr23 maybe turnedthrough. 180" so that 'the calibration `plate assumes ,either the position YA or-the positionB. rIn-positi'on.2A`,the

VVend of the stripl needs to moveonly thedistance fa to release, While-inposition B the-,end-,ofthe .strip 5- .mustmove thefdistanceb. Obviously only a higher-.current value will move it this longer distance.

Themethod of operation Aoi vtheYinVentIionis as followszlf the circuitbreaker has beenopened manually, the parts will be in they position shown in.l Fig. 2 in which .the sleeve. 23, .has beenpulled toits open or-outer position, r, the `baur-32resting inthe lower groove-Zd-andthefupper `ericloff-the vstrip l5i being lbelow. and V latched against .fthe

calibration plate 29. The breaker-can. be. closed byl pushing in :on'the end of the-.sleeve 23, .the ball- 32 then engagingtheupper groove v'MS-@artid holding the sleeve 23 in its lower .position ,.(Figs.

`i Iand 5). "The stem-ll moveswith .thesleeveZ'B during said'manual closing, .being heldingiixed relationship with the sleeve .by.thelstriplfacting. as a latch, `and the spring-'M or'lll.

If, while the parts are inthe closed rposition as in .Fig..l5 or as shown infull lines .in/.'Fig.' 1,'an overload occurs, vthat is, current in excess'ofa predetermined amperage flows in the circuit protected by the breaker, this current must ypass from the terminal l5 to the terminal I6 or vice versa. In this passage, the current must pass through the bimetallic strip 5|. It is a characteristic virtue of this strip that it responds only very slightly to momentary overloads which do not heatv the strip to such a degree that itunlatches from the calibration plate 29. The apparatus protected by the circuit breaker is not vulnerable to such momentary overloads. If, however, the overload persists for a sufficient time, the upper end of the strip 5I moves to the right as shown in the drawing and the spring 44 or 45 snaps the stem up into half open position as shown in dotted lines in Fig. 1. In this position the sleeve'23 'remains in its lower position as shown in Figs. 1 and 5 but the stem is in its upper position, the knob 42 projecting from the upper end of the sleeve 23. The length of the sleeve is such that when it is pushed down it will reset the strip 5l as a latch, the upper end of which catches the calibration plate 29.

To reset the breaker, it is necessary to pull the sleeve 23 into its upper position, as shown in Fig. 2. As it is pulled up, the strip 5l strikes against the lug 43 and is held so that the upper end of the strip 5l can latch under the calibration plate 29. The breaker is then in the open position shown in Fig. 2 and it can be closed by pushing the sleeve 23 from its upper position to its lower or closed position as shown in Fig. 5 and in full lines in Fig. 1. It is an advantage of this breaker that if the sleeve 23 is pushed into its closed position, as shown in Fig. 5, before the conditions producing the overload are remedied, the breaker will open even if the sleeve 23 is held in its closed position.

The calibration of the circuit breaker is adjusted at the factory to open on any overload within a certain range; for example, between l and 50 amperes. Referring to Fig. '7 in which the calibration plate 29 is shown in full lines A with the breaker set to trip at a sustained overload of 10 amperes, as shown by the arrow 6l, on the top of the sleeve 23, which points to a calibration mark 10 on the outside of the top of the box Il. The end of the strip I is shown in full lines in its cold position and it will be evident that when it is heated enough to move through the distance a to the position 62, it moves away from the plate 29 and the circuit breaker will open. However, if the sleeve 23 is turned through an angle of 180 so that the arrow 6l points to the calibration mark 50, the calibration plate 29 is turned into the dotted line position B and the end of the strip 5i must move to a position 63 through a distance b to allow the breaker to open. This will only occur when the strip has had a sustained overload of 50 amperes. Obviously, the plate 29 need not be of circular contour but may have a cam-shaped conguration between the calibration marks and 50.

I claim as my invention:

l. A circuit breaker comprising: a hollow casing of insulation material having an axial bore in one wall thereof; a cylindrical sleeve of insulation material having a calibration plate secured to the lower end thereof, said sleeve being mounted to move axially in said hollow casing with its outer end at all times in a position to be available to an operator; friction means for restraining the movement of said sleeve in its open or extreme outer axial position and in its closed or extreme inner position; a stem having its inner portion of conductive material and extending throughvsaid sleeve and adapted to move axially with relation thereto from an open or extreme outer axial position to a closed or extreme inner position; a stationary contact fixed with relation to said hollow casing in such position as to be in electrical contact with the inner end of said stem when both the stem and sleeve are in their inner or closed positions, said stationary contact being provided with means for connecting it in the circuit to be interrupted by said circuit breaker; a thermostatic element rigidlysecured to said inner conductive portion of said stem near the lower end of said stem, the upper end of said element being in such a position that, when cold, it engages said calibration plate on the lower end of said sleeve and thus holds said stem in its closed or lower positionv with relation to said sleeve; and a flexible conductive member connected at one end in the circuit to be interrupted by the circuit breaker and at the other end to said thermostatic element in such a position as to cause current to flow through said thermostatic element whenever the circuit breaker is closed and current flows in said circuit.

2. A circuit breaker comprising: a hollow casing of insulation material having an axial bore in one wall thereof; a cylindrical sleeve of insulation material having a calibration plate secured to the lower end thereof, said sleeve being mounted to move axially in said hollow casing with its outer end at all times in a position to be available to an operator; friction means for restraining the movement of said sleeve in its open or extreme outer axial position and in its closed or extreme inner position; a stem having its inner portion of conductive material and extending through said sleeve and adapted to move axially with relation thereto from an open or extreme outer axial position to a closed or extreme inner position; a stationary contact fixed with relation to said hollow casing in such position as to be in electrical contact with the inner end of said stem when both the stem and sleeve are in their inner or closed positions, said stationary contact being provided with means for connecting it in the circuit to be interrupted by said circuit breaker; a lug projecting from said hollow casing, the lower portion of said stem passing through an opening through said lug; a compression spring surrounding said stem above the lug, one end of said spring pressing on said lug and the other end of said spring pressing on a projection on said stem, said spring being of such length that it is under compression whenever said stem is in its inner or closed position, said spring being too weak to force said sleeve out of its inner or closed position; a thermostatic element rigidly secured to said stem near the lower end of said stem, the upper end of said element being in such a position that, when cold, it engages said calibration plate on the lower end cf said sleeve and thus holds said stem in its closed or lower position with relation to said sleeve; and a flexible conductive member connected at one end in the circuit to be interrupted by the circuit breaker and at the other end to said thermostatic element in such a position as to cause current to now through said thermostatic element whenever the circuit breaker is closed and current ilows in said circuit.

3. A circuit breaker comprising: a hollow casing of insulation material having an axial bore in one wall thereof; a cylindrical sleeve of insulation material having a calibration plate secured to the lower end thereof, said sleeve being operi orextreme outer ,axial'fposilzionendih its y their vinner `.or closel positions, `^`salici .stationery Contact ,being provided witlimeansfforiconneeting it vin :the circuit ,to be Yinternipiled 'by .Saidfircut breaker.; rai1c.QIn1.111,2SSQn:Spr-illeolocedfine geriet? in .the outer gend., off said Sleeve vemol surrounding sadeleeve endithe outer endof V'isoidvsprillg'louf me .on e :projection from said etero, said spring being of ysuch ,length ,ee `Ato lbe `under substantial compression .when :said `stem ,sn.1ts`10wlr .0T

closed position; e jhermostati Aelement,rlgifcllll v2 5 ioe'ci of lower' position' `JWN;

o. eeve, :and o rexible ionductvefmemher con- A ted :et @no Lend in themiiitV stgo vbeinterrupted b y loereircuit breaker @iid et" theeoigherzendzgo-aid l0 xlierniostatiefelemerit lign f-Suo'h a A:position :als ,t0

REFERENCES yihe :following :references vare Yf of record in :delle *UNITED STATS

Images