US3535669A - Electrical circuit overload protector of the thermally responsive bimetal element type - Google Patents

Description

Oct. 20, 1970 u, CARTER ETAL j ELECTRICAL CIRCUIT OVERLOAD PROTECTOR OF THE THERMALLY RESPONSIVE BIMETAL ELEMENT TYPE 4 sheets-shut 1 Filed llay 13, 1968 Til I II... .|'.'.'1'|' II I Oct. 20, 1970 u, CARTER ETAL 3,535,669

, ELECTRICAL CIRCUIT OVERLOAD PROTECTOR OF HE THERMALLY RESPONSIVE BIMETAL ELEMENT TYPE Filed May 13, 1968 7 4 Sheets-Sheet 2 i l! I I l I l l L J W04 I l I w I I Lim Oct. 20, 1970 u. F. CARTER ETAL ELECTRICAL CIRCUIT OVERLOAD PROTECTOR OF THE THERMALLY RESPONSIVE BIMETAL ELEMENT TYPE 4 Sheets-Shet 3 Filed May 13, 1968 I I 19.8 Law an METAL (mm) I 5 Ina/I zxn METAL (Buss) OCII. 20, 1970 T u E ETAL 3,535,669

ELECTRICAL CIRCUIT OVERLOAD PROTECTOR OF THE THERMALLY RESPONSIVE 'BIMETAL ELEMENT TYPE Filed May 13, 1968 4 Sheets-Sheet 4 US. Cl. 337-347 7 Claims ABSTRACT OF THE DISCLOSURE An electrical circuit overload protective device of the thermally responsive bimetal type which can be selectively set for either automatic or manual reset modes of operation. Overload responsive units, for one or more circuit branches employing stacks of bimetal discs as thermally responsive elements, and are mounted within a housing on a common base. Each overload unit has an individual snap acting switch which opens in response to an overload condition as detected by the heat developed in a heater coil connected in the branch circuit which surrounds its thermally responsive element. The switches of the overload units are all connected in a single series circuit between terminals provided for connection to a circuit to be controlled. In a manual trip-free mode of operation a pushbutton lever upon subsidence of all overload conditions is depressed inwardly of the housing to aiford manual reset of the movable contact members of any switch tripped open by overload response. Alternately the reset lever may be latched in such depressed position wherein the contact opening movement of the movable switch contact members is so limited that they will individually automatically reset upon subsidence of the overload condition in their respective branch circuits. A modified form of ambient temperature compensated bimetallic disc type of overload responsive unit is pro- 'vided for use wherein the device will be subjected to high or widely varying ambient temperature conditions.

Features of the invention described in this application are disclosed and claimed in the copending Uriel F. Carter and Edward A. Mallonen application Ser. No. 729,496, filed May 13, 1968 and assigned to the assignee of this application.

This invention relates to an improved overload protective device of the thermally responsive, bimetal element type.

A primary object of the invention is to provide a protective device of the aforementioned type employing bimetal discs in a special stacked relation as the thermally responsive element in each of one or more overload units.

Another object is to provide in each overload unit a separate snap-action electric switch for individualized control by its associated thermally responsive element of the aforementioned type.

A further object is to provide a protective device of the foregoing type where the aforementioned switches of the individual overload units are electrically connected in a single series circuit so that the latter will be interrupted upon opening of any switch unit in response to an overload condition to which its associated thermally responsive element may be subjected.

Still another object is to provide an overload protective device of the aforementioned type which can be selectively set so that reset or tripped switches of the United States Patent 3,535,669 Patented Oct. 20, 1970 overload unit will automatically reset, or alternatively require manual operation of a reset lever to effect reset of the switches upon subsidence of the overload conditions in protected circuit branches.

An additional object afforded by the overload device is trip-free action of the switches of the respective overload elements in the event the overload condition has not subsided when the reset lever is manually operated.

A still further object is to provide a modified form of ambient temperature compensated overload responsive element of the aforementioned bimetal disc type which can be used interchangeably for the overload device for those aforementioned.

Other objects and advantages of the invention will hereinafter appear.

The accompanying drawings illustrate preferred embodiments of the invention which will now be described in detail it being understood that the embodiments disclosed are susceptible of modification in respect of details without departing from the scope of the appended claims.

BRIEF DESCRIPTION OF'DHE DRAWINGS FIG. 1 is a top plan view of an overload circuit protector switch incorporating the invention;

FIG. 2 is a front elevational view of the switch;

FIG. 3 is a left end elevational view of the switch with portions of the housing broken away;

FIG. 4 is a view similar to FIG. 3 but showing the switch in another operating mode;

FIG. 5 is a top plan view of the inside of the housing base showing the overload responsive switch mechamsm;

FIG. 6 is a fragmentary cross sectional view taken generally along the line 66 of FIG. 1 showing an overload responsive element;

FIG. 7 is a view similar to FIG. 6 but showing a modified form of overload responsive element;

FIG. 8 is a view in.cross section to greatly enlarged scale of a portion of a stack of bimetal disc elements shown in FIGS. 6 and 7;

FIG. 9 is a more or less schematic representation of the overload element depicted in FIG. 6;

FIG. 10 is a view like FIG. 9, but showing the overload device in another operating condition;

FIG. 11 is a view like FIG. 5 but 'with the overload responsive and switch elements removed; and

FIG. 12 is an isometric view of a switch drive lever and movable member shown in FIGS. 5, 6 and 7.

DETAILED DESCRIPTION Referring to FIGS. 1 to 3, they show a circuit protector switch having a metal mounting plate 10, a unitary insulating housing 12 to which plate 10 is attached, and an insulating bottom cover and base member 14. The switch has a reset button 16 mounted on the end portion of a metal lever 18 which is reciprocably movable in a guide passage 12a formed in housing 12.

The top opening recesses 20' are provided on housing 12. Intermediate partition portions 22, 24, 26 and right-hand end wall 28 of housing 12 provide electrical barriers between the recesses. Spaced apart pairs of combination wire terminal and overload heater mounting plates 30 are secured in place in each of the recesses by screws 32 which take into threaded recesses. One of each pair of plates 30 located at the rear is mounted at a higher level than the plate at the front. The center recess between partitions 24 and 26 is at a higher elevation to provide increased electrical and heat clearance between each adjacent sets of recesses and to provide for clearance for the interfit of a terminal mounting member 98.

As thus far described, the housing 12 and elements mounted thereon are exactly the same as a counterpart housing shown and described in the Carter et al. application, Ser. No. 699,270, filed Jan. 19, 1968 and now Pat. No. 3,478,292, and assigned to the assignee of the present application. Housing 12 was designed to be interchangeably used in both tyes of overload protector switches.

Each of the aforementioned top opening recesses in housing 12 has mounted therein between the spaced plates 30, a plate 34 to which is fastened a metal cylindrical tube 36 which has an anodized insulating exterior surface. The plates 34 are secured in place by screws 38. As will hereinafter be more fully explained, bimetal disc overload elements are centered without appreciable peripheral clearance in each of the tubes 36, and as shown in the left-hand recess between partitions 22 and 24, a helical heater coil 40 is positioned around and in contact with each of the tubes 36 and secured to the upper and lower terminal plates by screws 42.

The terminal plates 30 have outward and slightly downwardly projecting tabs 30a to which are secured wire retaining members 44 by screws 46. In actual service, the other two recesses would also be fitted with heater coils 40, the same having been omitted in FIGS. 1 and 2 to clarify construction details of the plates 34 and tubes 36.

With each pair of terminals 30 wired in series in branches of a three-phase A.C. circuit it will be apparent that the heater coils 40 will be subjected to the load current in their respective branches. Heat generated by such current flow will transfer by conduction to the tubes 36, and as will hereinafter be explained, causes movement of the bimetal discs of the overload elements.

As shown in FIGS. 5, 6 and 11, the overload responsive elements and switches controlled thereby for each of the three branches are mounted on the inside of base 14. As best seen in FIGS. and 6, each overload responsive element comprises a support bracket 48, a rectilinear movable rod 50, a stack of bimetal discs or washers 52, a loading spring 54, a spring gland 56, an adjusting pin 58 and adjusting screw 60. A flanged cylindrical insulating member 62 seats against the flanged end portion 50a of rod 50 and provides a spindle on which the stack of discs 52 are mounted. A cylindrical insulating spacer 64 abuts at its upper end against the lowermost bimetallic washer and has the lower end portion of spindle 62 projecting into its bore.

The lower end of spacer 64 seats against the upper end of adjusting screw 60 which is centrally bored to accommodate rod 50, and exteriorly threaded to be adjustable in the complementally threaded insert 66 molded in place in the upper arm 48a of bracket 48. Adjusting screw 60 has a laterally and upwardly extending arm 60a which extends through an arcuate slot 34a formed in cover plate 34. As will hereinafter be explained, lever 60a within the limits of slot 34a affords a certain range of adjustment for controlling the compression loading of the stack of discs 52.

Adjusting pin 58 has a cylindrical flanged end portion 580:, an intermediate portion 58b which is rectangular in transverse cross section and an upper cylindrical end portion 580 of reduced diameter. The upper end portion 580 is internally threaded and the lower end portion of rod 50 is threadedly engaged therein. Also the upper end portion 580 projects into an opening 56a which extends from the lower end of gland 56 to the bottom of the spring receiving recess 56b that opens to the upper end of the gland. Loading spring 54 is of the coiled compression type and seats at its upper end in a shallow recess 48b formed in the lower surface of arm 48a of bracket 48 and at its lower end against the bottom of recess 56b in gland 56.

As shown in greatly enlarged cross section in FIG. 8, the bimetal discs 52 comprise two metal layers; layer 52a having a relatively high coeflicient of thermal expansion and the other 52b having a relatively low coeflicient of thermal expansion. In plan view the discs 52 are annular, and as shown in FIG. 8, they are convexly warped in transverse cross sectional form similar to that found in Belleville washers. They are stacked on the spindle portion of the guide 62 in the arrangement shown in FIG. 8 with one pair abutting along respective concaved edges, and an adjacent pair abutting on respective opposed convexed surfaces, etc., in a repeating alternate series. At ambient or room temperature the distance between hottoms of concaved surfaces on alternate pairs will be some distance X.

As the temperature of the discs 52 increase they will individually flatten and each of the distances X will decrease with increasing temperature. Consequently, the total height of the stack of discs 52 will decrease as a function of the sum of the individual decrease in X, between alternate pairs of discs in the stack. If the temperature of the discs 52 thereafter decreases the individual distance X increases as the individual discs in the stack return to their ambient temperature warped or dished shape in cross section depicted in FIG. 8.

The foregoing arrangement of the discs 52, in affording decrease in individual warpage with increase in temperatiire is an advantage. As the stresses between the discs decrease with rise in temperature, subjection to thermal shock temperature rises which can occur during high electrical overload conditions will prevent the elastic limit of the discs from being exceeded. Accordingly, repeatability of change in total stack height and hence the force developed by the discs 52 for a given temperature change is considerably enhanced.

The lower end of glaid 56 bears against arcuate protrusions 68a formed on each of the arms 68b of a switch drive lever 68. Drive lever 68 is provided with a central rectangular opening 680 which accommodates the rectangular portion 58a of adjusting pin 58. The arms 68b which are disposed on opposite sides of opening 68c also have arcuate protrusions 68d which bear against the upper surface of the end portions 58a of pin 58. Drive lever 68 has upstanding end portions 68a and 68 which are provided with V-shaped notches 68g and 6811, respectively. Portion 68a engages within its notch 68g the inner edge of an opening of a movable, flat leaf switch member 70 which carries a contact 72 (see FIGS. 6 and 12). A C- shaped snap spring 74 seats along one edge in the notch 68h of lever 68 and has attached within, a slot 7411 with outer arms 70a and 70b and intermediate contact carrymg portion 700 of member 70.

The opposite end portion 70d of member 70 is sandwiched together with portion 76a of current conductor 76 between an upstanding boss 14b formed on the inside surface of boss 14 and the lower surface of the mounting pad 480 of bracket 48. As best shown in FIG. 5, screws 78 which penetrate alined openings in pad 480, portion 70d of member 70 and portion 76a of conductor 76 secure the member 70 and conductor 76 in electrical contact in place on base 14.

As best shown in FIGS. 6 and '11, contact 72 through movement of member 70 is adapted to engage with a stationary contact 80 secured to the portion 82a of a current conductor '82 which is in turn secured to a boss 14c on base 14 by a screw 84.

Switch member 70 together with snap spring 74 and drive lever provide a snap action type of electrical switch such as that disclosed and claimed in Pat. No. 3,207,868. Reference should be made to that patent for detailed information on the formation and arrangement by switch member 70 and snap spring 74.

Reference will now be made to FIGS. 9 and 10, to provide an understanding how each of the overload responsive devices and snap switches function under normal and overload electrical conditions. The representations in FIGS. 9 and 10 are simplified showings with certain parts of the overload devices hereinbefore described deleted. Numerals of like parts have been designated with additional prime postscripts. The overload device and switch as shown in FIG. 9 are in positions assumed under non-overload conditions. The bimetal discs 52' are enlarged and shown with exaggerated curvature for purposes of illustration.

It will be seen that spring 54' urges gland 56 downwardly against switch drive lever 68' and tends to cause the left end of snap spring 74' to move downward, and hence tends to toggle member 70' upwardly to disengage contact 72 from contact 80'. However, a balancing upward force exerted on drive lever 68' by adjusting pin 58' due to the counter force action of the bimetal discs 52' acting through rod 50' holds the snap switch in the contact engaged position depicted in FIG. 9.

Now assume that a current overload condition occurs and persists. Thus the heat transferred by conduction from the current carrying coil 40 to the discs 52' will cause them to flatten in a direction decreasing the degree of their individual convexed curvature. Thus the distance Y in FIG. 9 between the upper flanged end of rod 50 and spacer 64' will decrease to the distance depicted in FIG. 10 and rod 50 consequently moves downwardly. The force exerted by spring 54 then causes gland 56 to move downwardly and hence move drive lever 68' downwardly. When the left end of snap spring 74 is moved across the plane of leaf member 7 0', snap action toggling of the latter member in the upward direction occurs to disengage contact 72' from stationary contact 80' as depicted in FIG. 10. Drive lever 68' during such snap movement pivotally moves by virtue of its protrusions 68a and 68d rocking on the upper surface of portion 58a and the lower end of the spring gland 56. In the first position member 70' bears against a stop-reset bar 86'.

It may be assumed that when the overload condition has subsided, discs 52 will cool and hence assume their normal or ambient temperature curvature condition. Thus the distance Z depicted in FIG. 10 will increase and rod 50 will be moved upwardly to correspondingly move drive lever 68 upward. With stop-reset bar 86' set in the rotaryposition depicted in FIGS. 9 and 10, the apex of notch 68h will not move upwardly beyond the plane of member 70' by the time rod 50 and drive lever 68' reach their respective normal, or non-overload position depicted in FIG. 9. In other words, the overload responsive switch will not automatically reset upon subsidence of the overload condition, and member 70' must then be manually reset (moved downwardly across the apex of notch 68h) to return it to the circuit closed position of FIG. 9. This will hereinafter be more fully explained in conjunction with FIGS. 4 and 5.

If stop-reset bar 86 is instead set at the rotary pos tion depicted for bar 86 in FIG. '6 when the aforedescnbed overload condition occurs, member 70' upon snap upward movement will assume a switch-open position intermediate those depicted in FIGS. 9 and 10. Hence, upon subsequent subsidence of the overload condition the apex of notch 68h will move across the plane of member 70' to cause snap toggling of the latter to the circuit closed position shown in FIG. 9. In other words, the switch will automatically reset upon return of the overload responsive device to normal or non-overload conditions. This action will also be more fully described in conjunction with FIGS. 4 and 5.

Now referring to FIG. 11, it will be seen that con ductor 82 has an integral portion 82b like portion 76a of conductor 76. A second conductor 82 is also secured on boss 14c on base 14 to the right of the first mentioned conductor 82. A third conductor 88 is secured to boss 140 by a screw 90 and has a stationary contact 92 secured thereto. Conductor 76 has an integral L-shaped portion 76b which seats within a complementally formed recess 14d in member 14 and a portion 76c which extends upwardly at a right angle to aflford electrical connection between portion 76b and a terminal end portion 76d. Conductor 88 has a portion 88a lying in a shallow recess in base member 14 that connects with a portion 88b which is bent upward at right angles and then laterally toward the left as viewed in FIG. 11. Portion 88b connects with a terminal end portion 88c like portion 760 of conductor 76.

As best shown in FIGS. 2, 5 and 11, terminal members 94 and 96 are secured together with terminal portions 76d and 880, respectively, to a lower surface of side boss portions 98a and 98b of an insulating terminal mounting member 98 which has an intermediate barrier portion 98c. As best seen in FIGS. 2 and 5, terminals 94 and 96 have outwardly and slightly downwardly depending tabs 94a and 96a to which are secured by screws 100, wire retaining members 102 of a form similar to the aforementioned members 44.

Now referring to FIGS. 5 and 11, it will be seen that the overload switch device comprises three overload switch devices. With their respective switches closed, it will be apparent that current Will be completed from terminal member 94 to 96. Thus with terminals 94 and 96 appropriately connected in the energizing circuit of an electromagnetic contactor or relay (not shown) such circuit will be maintained when no overload condition exists in any of the branches of the polyphase circuit in which the heater coils 40 associated with the respective overload devices are connected.

In the event an overload occurs in any such branch circuit sufficient to cause opening of its associated overload responsive switch the circuit will, of course, be opened between terminals 94 and 96, thereby opening the circuit to any electromagnet or other circuit that may be connected thereto.

Referring to FIGS. 3, 4 and 5, it will be seen that stop-reset bar 86 is journaled for rotation on cylindrical end portions 86a in the bearing brackets 14 and 14g formed integrally with member 14. Immediately adjacent bearing 14 in FIG. 5, rod 86 is provided with an arm 86b, and between the latter and its opposite end portion 8611 it has a portion 86c with the cross sectional form best shown in FIGS. 6, 9 and 10.

The arm 86b of rod 86 is disposed within the opening 104a of an insulating member 104 which is molded about and is an extension of reset lever 18. A coiled compression spring 106 seats at one end within a recess 14h formed in base 14 and at its other end fits about a short cylindrical boss 104b formed on member 104. Spring 106 biases member 104 and lever 18 upwardly to normally assume the position depicted in FIG. 4. In moving to that position the lower lip portion 104c at the entrance of opening 104a in member 104 engages arm 86b and rotates it clockwise to the position depicted in FIG. 4. In this latter position the portion 86c will be rotated to assume the position depicted for rod 86 in FIGS. 9 and 10.

If reset lever 18 is moved inwardly of housing 12 to the position depicted in FIG. 3, the upper lip portion 104d of member 104 engages arm 86b of rod 86 and rotates the latter to the position depicted in FIG. 3 wherein the portion 86c then assumes the rotary position depicted in FIG. 6. It will be seen that in this last mentioned rotary position for the portion 86c the clearance distance between the free ends of the movable switch member 70 is considerably less than in positions depicted for rod 86' in FIGS. 9 and 10.

If with the rod 86 in the rotary position depicted in FIG. 6, an overload occurs, the free end of any switch member 70 which moves to contact disengaging position will engage the rod 86 and thereby limit its movement. With the contact opening movement of any member 70 so limited, any tripped switch will automatically reset upon subsidence of the overload condition as aforedescribed. It will also be understood that after responding to an overload condition, a switch member 70 is moved to an open position depicted for member 70' in FIG. 10 that 7 subsequent rotation of rod 86 to the position shown in FIG. 6 following subsidence of the overload condition will cause it to engage the end of. the member 70' and move it downwardly sufficiently so that snap spring 74 will then toggle the same to the contact engaged position shown in FIGS. 6 and 9.

When lever 18 is moved to its inward extreme position shown in FIG. 3, it can be retained latched in that position by moving a lever 108 into engagement in a notch 18a formed in lever 18. Thus rod 86 will be retained in the rotary position wherein its portion 86c assumes the position depicted in FIG. 6. Accordingly, the overload device will be set in its automatic reset mode, and upon subsidence of overload in all branches circuit completion between terminals 94 and 96 will be automatically restored.

Lever 108 is provided with an elongated opening and a screw 110 penetrates such opening and takes into a threaded recess a housing 12. When lever 108 is engaged within the notch 18a of lever 18 tightening of screw 110 insures retention of reset lever in the automatic reset mode. Of course, when lever 108 is out of engagement with lever 18 it can also be held in that position by tightening of screw 110.

The temperature trip point of any of the aforedescribed overload responsive switches is determined by the adjustment of adjusting pin 58 on the threaded end of rod 50. Turning pin 58 further on to rod 50 will, through its bearing on drive lever 68, move the latter upwardly a corresponding amount. Drive lever 68 because it bears against the lower end of gland 56 will move the latter upwardly and spring 54 will be correspondingly compressed. Spring 54 then exerts increased force downwardly on gland 56, drives lever 68, pin 58 and rod 50. Thus discs 52 will be caused to be compressed, and their stack height reduced. Accordingly, the upward force exerted on rod 50 by the stack of discs will then counterbalance the inward force of spring 59 acting downwardly on drive lever 68 at its new upper position.

It will be apparent that with drive lever 68 moved upwardly that the apex of its notch 68h will be moved upwardly a corresponding amount above the plane of movable contact member 70. Hence lever 68 will have to be moved downwardly a greater distance before the apex of notch 68h passes the plane of member 70 at which point snap-action toggling of the latter to contact opening position occurs. Accordingly, the aforedescribed change in adjustment of pin 58 results in an increase of the trip point temperature. It will be apparent from the foregoing that if adjusting pin 58 is backed farther down from an initial position on rod 50, that the trip point temperature will be decreased.

Screw 60 affords another more limited adjustment of the trip point temperature of each overload device. If lever 60a is turned counterclockwise in slot 34a in plate 34, as viewed in FIG. 1, screw 60 will advance upwardly in insert 66 thereby moving spacers 62 and 64 upwardly which results in increased compression and hence decrease in the height of the stack of discs 52. As a consequence of this drive lever 68 is moved upwardly to a new ambient temperature position. Conversely, if lever 60a is rotated clockwise in slot 34a the height of the stack of discs 52 will decrease resulting in a corresponding lowering of the ambient temperature position of drive lever 68. The arcuate length of the slot 34a determines the range of change in trip point temperature that can be effected by adjustment of the screw 60.

Normally the basic trip point temperature is determined after assembly of the overload device by adjustments of pin 58- to afford a trip" point temperature which is some specified value above normal ambient temperature. Then with selection of a heater coil most appropriate for the particular load conditions, screw 60 permits a limited range change to partially compensate for the fixed increments existing between a heater coil of a given rating and those available which are immediately above or below it in rating tables.

FIG. 7 shows a modified form of ambient temperature compensated overload responsive switch unit which can be used in place of those aforedescribed. In this modified form the loading spring 54 is deleted and a stack of bimetal discs 112 together with a spacer 114 inserted in its place. The discs 112 are the same in form as the discs 52, but somewhat greater in outer diameters, and warped depth at the same ambient temperatures. They are also stacked in the same arrangement as shown for discs 52 in FIG. 8.

It will be apparent that if the modified overload re sponsive switch units are subjected to ambient temperature conditions which vary relatively widely, that change in forces developed by the discs 52 with temperature will be oifset by a corresponding change in forces developed by the discs 112. Consequently, the distance of the notch 68h of drive lever 68 above the plane member 70 (in contact closed position) will not change appreciably as the ambient temperature varies. Thus the trip point temperature of the compensated overload devices will not be appreciably affected by ambient temperature changes that may be encountered in certain conditions of mounting and housing of the overload devices.

The use of the ambient temperatures compensated overload responsive units is desirable when the overload protection switches are inside of enclosures which are subject to internal generation of heat by other equipment mounted therein, or to external heat such as by the sun or other heat radiating sources.

What is claimed is:

1. A thermally responsive overload switch comprising, in combination:

an electric switch having an operating lever movable in opposite directions to eifect opening and reclosing of switch contacts, and

a thermally responsive switch operating mechanism comprising:

a stationary abutment,

a guide member in engagement with said operating lever,

a coil compression spring disposed between said guide member and said abutment,

a reciprocally movable member,

an adjusting member threaded on said reciprocally movable member and engaging said operating lever in opposed relation to said guide member, a plurality of stacked dished annular bimetal discs disposed about said reciprocally movable member(s), and bearing against the latter and said abutment,

said discs under ambient temperature conditions biasing said reciprocally movable member in a direction opposing movement of said operating lever in said contact opening direction.

2. The combination according to claim 1, wherein said switch operating mechanism further includes a second adjusting member threaded into said abutment and bearing against stacked washers, said second adjustable member being adjustable over a limited range to increase or decrease the static compression between said bimetal discs.

3. A thermally responsive overload switch comprising in combination:

an electric switch having an operating lever movable in opposite directions to eifect opening and reclosing of switch contacts, and a thermally responsive switch operating mechanism comprising:

a reciprocally movable member, an adjusting member threaded on one end of said reciprocally movable member and engaging said operating lever, a stationary abutment, a guide member in engagement with said switch or operating lever,

a plurality of dished, annular bimetal discs disposed about said reciprocally movable member and bearing against the other end of the latter and one side of said abutment,

a second stack of dished annular bimetal discs disposed about said reciprocally movable member and bearing against the other side of said abutment and said guide member,

said two stacks of bimetal discs under ambient temperature conditions oppositely biasing said reciprocally movable member and said guide member so that said switch operating lever is maintained in said contact closed position, and

said first mentioned stack of bimetal discs under overload temperature conditions transversely flattening to a degree such that the bias exerted by said reciprocally movable member on said switch operating lever is so reduecd that the latter can move to its contact opening position.

4. In an electric overload circuit protector, in combination:

a housing having a plurality of recesses in the upper side thereof with insulating barriers therebetween for electrically isolating said recesses from each other,

at least one thermally responsive switch unit each having an electric switch with a movable contact element mounted interiorly of said housing, a constricted stack of dished, annular bimetal discs disposed within one of said recesses, and having means within said housing responsive to flattening of said discs under high temperatures to operate the movable contact element of said switch to open circuit condition,

means including a pair of terminals mounted exteriorly of said housing and conductors within said housing interconnecting the switches of all the aforementioned switches in series between said terminals, electric heater coils mounted concentrically about each stack of bimetal discs and when connected in series in different branches of an electric circuit subjecting their respective associated stacks of bimetal discs to temperatures which are a function of the currents in such branches.

5. The combination according to claim 4, together with means including a reciprocally lever extending exteriorly of said housing which is depressible to eifect reset of any tripped overload responsive switch upon subsidence of overload conditions, said lever being alternatively latchable in depressed position to limit the degree of switch opening movement of the movable contact element any overload tripped switch so that they will individually automatically reset upon return of their stacks of bimetal discs to ambient temperature states.

6. The combination according to claim 5, wherein said means including said reciproca ly lever further includes a member mounted for rotation within said housing and having a portion overlying the paths of movement of the movable contact elements of all the aforementioned switches, said reciprocally lever engaging said rotatable member and when moved to its depressed position rotating said rotatable member to a given position wherein the contact carrying members of any tripped switches are moved an amount insuring their reset when the bimetal discs return to ambient temperature states.

7. The combination according to claim 5, wherein said overload circuit protector includes at least two thermally responsive switch units, wherein said bimetal discs in each stack are mounted so that alternate pairs of discs have their concaved surfaces opposing each other and the layer of metal on such concaved surfaces has the higher coeffi: cient of thermal expansion, and wherein said housing is in two parts with a first hollow part having the aforementioned recesses formed therein and a second bottom cover part having the thermally responsive switch units mounted thereon.

References Cited UNITED STATES PATENTS 3,315,054 4/1967 Langley 337-72 XR 3,172,971 3/1965 Roeser. 3,140,370 7/1964 Harper 337-112 XR 3,044,295 7/ 1962 Shivers 73-3635 XR GEORGE HARRIS, Primary Examiner D. M. MORGAN, Assistant Examiner U.S. Cl. X.R. 337348, 354

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