US3345591A

US3345591A - Electric circuit breaker with improved tripping means including a heater strip in the thermal tripping means and adjustable air gaps in the magnetic tripping means

Info

Publication number: US3345591A
Application number: US561456A
Authority: US
Inventors: James H Leonard; William H Woods
Original assignee: Square D Co
Current assignee: Schneider Electric USA Inc
Priority date: 1966-06-29
Filing date: 1966-06-29
Publication date: 1967-10-03
Anticipated expiration: 1984-10-03
Also published as: GB1148957A; DE1588732B1

Description

3,345,591 NG L LEONARD ET A Oct. 3, 1967 1. L

ELECTRIC CIRCUIT BREAKER WITH IMPROVED TRIPPI MEANS INCLUDING A HEATER STRIP IN THE THERMA TRIPPING MEANS AND ADJUSTABLE AIR GAPS IN THE MAGNETIC TRIPPING MEANS Filed J ne 29, 1966 3 Sheets-Sheet l fwerzn Jamal/Lawn@ Zdw 9:

Oct. 3, 1967 J. H. LEONARD ET AL 3,345,591

ELECTRIC CIRCUIT BREAKEH WITH IMPROVED TRIPPING MEANS INCLUDING A HEATER STRIP IN THE THERMAL TRIPPING MEANS AND ADJUSTABLE AIR GAPS IN THE MAGNETIC TRIPPING MEANS Filed June 29, 1966 3 Sheets-Sheet 2 @'4' ZE -f @Si 2f Jy @Jvw wf Oct. 3, 1967 1 H LEQNARD ET AL 3,345,591 D TRIPPING RIP IN THE THERMAL ABLE AIR GARS 1N ELECTRIC CIRCUIT BREAKER WITH IMPROVE MEANS INCLUDING A HEATER ST TRIPPING MEANS AND ADJUST THE MAGNETIC TRIPPING MEANS 3 Sheets-Sheet 3 4 Filed June 29, 19 zg/91,

United States Patent ELECTRIC CIRCUIT BREAKER WITH IMPRVED TRIPPING MEANS INCLUDING A HEATER STRIP IN THE THE TRIPPING MEANS AND ADJUSTABLE AIR GAPS IN THE MAG- NETIC TRIPPING MEANS `lames H. Leonard and William H. Woods, Cedar Rapids, Iowa, assignors to Square D Company, Park Ridge, Ill., a corporation of Michigan Filed .lune 29, 1966, Ser. No. 561,456 6 Claims. (Cl. 335-23) This invention relates generally to electric circuit breakers, and more particularly to a circuit breaker having improved tripping means.

An object of the invention is to provide an electric circuit breaker having improved thermal and magnetic tripping means.

Another object is to provide a multipole circuit breaker having a single adjusting means by which the air gaps in the magnetic circuits of the magnetic tripping means of all the poles may be adjusted.

A further object is to provide an improved arrangement of parts with respect to the thermal tripping means of a circuit breaker.

In the drawings, FIG. 1 is a reduced front view of a circuit breaker constructed in accordance with the invention, certain portions thereof being indicated by broken lines;

FIG. 2 is a fragmentary front view of the circuit breaker of FIG. l with the cover and handle removed;

FIG. 3 is a fragmentary front view of a terminal strap, bimetallic strip, heater, and contact arm sub-assembly of one of the poles of the circuit breaker of FIG. l;

FIG. 4 is a fragmentary sectional view taken generally along the line 4-4 of FIG. l;

FIG. 5 is a fragmentary sectional view taken generally along the line 5-5 of FIG. 1;

FIG. 6 is a sectional view taken generally along the line 6-6 of FIG. 4;

FIG. 7 is an enlarged fragmentary sectional view taken generally along the line 7 7 of FIG. 6;

FIG. 8 is an exploded perspective view of the air gap control member, cam, and air gap adjusting crossbar of the circuit breaker of FIG. l, the crossbar being fragmentarily shown;

FIG. 9 is an enlarged fragmentary sectional view taken generally along the line 9 9 of FIG. 6;

FIG. l() is a view similar to FIG. 9, but showing the partsrin different positions; and

FIG. 11 is a bottom view of the' air gap control member and cam.

FIG. l shows a three-pole circuit breaker 20 constructed in accordance with the invention and having a casing ncluding a cover 21. An operating handle 22 protrudes through an aperture 23 in the cover 21, the cover being provided with suitable ON and OFF indicia.

The cover 21 is secured to a base 24 (FIG. 2) by a plurality of screws 25 received in suitable apertures in the cover. Further, the cover 21 is provided with a plurality of apertures 26 affording access respectively to a plurality of socket-head clamping screws 27 which respectively form parts of a plurality of electrical connectors by which a plurality of electrical power conductors (not shown) may be connected to the circuit breaker 20.

The cover 21 is also provided with an aperture affording access, by means of a t-ool such as a screwdriver (not shown) or the like, to an air-gap control member 2S provided in accordance with the invention and hereinafter described. The control member 28 controls the position of an air-gap adjusting crossbar 29 hereinafter described.

:3,345,591 Patented Oct. 3, 1967 ICC Adjacent the control member 23, the with suitable LO and HI indicia.

A center pole space of the circuit breaker 20 is provided with operating mechanism substantially identical to that disclosed in copending application, Ser. No. 375,571, tiled on J une 16, 1964, to which reference may be had for a fuller disclosure. As shown in FIG. 5, the cover 21 holds the handle 22 on a generally U-shaped handle eX- tension member '30 opposed leg portions of which straddle and are pivotally mounted respectively on a pair of frame members 31 and 32 (FIG. 2) secured to the base 24. The handle extension member 30 pivots on a pair of rivets 33 disposed respectively in the frame members 31 and 32, only one of the rivets 33 being shown in FIG. 5.

Opposed leg portions of a generally U-shaped releascover 21 is provided ably latchable cradle mem-ber or trip lever 34 are pivotally mounted between and respectively on the frame members 31 and 32 by means of a pair of rivets 35 disposed respectively therein, only one of the rivets 35 being shown in FIG. 5. The frame members 31 and 32 are joined -by a tubular stop pin 36 secured in place by a pair of screws (not shown) extending respectively through the frame members 31 and 32 and threaded respectively into opposite ends of the stop pin 36.

A pair of upper links 38 are pivotally mounted between `and respectively on opposed leg portions of the trip lever 34 respectively by a pair of rivets 39, only one link 38 and one rivet 39 being shown in FIG. 5. The edge of each upper link 38 is recessed at the end thereof opposite its associated rivet 39 to receive a toggle pin 40 held in the upper links '38 by a tension spring 41 hooked at one end to the toggle pin 40 and at the other end to the handle extension member 30.

Pivotally mounted adjacent one end on the toggle pin 46 is a lower link member 42 having a drive pin 44 pivotally mounted therein adjacent its other end. The lower link member 42 includes two parallel Hat elongated link portions connected together generally centrally of a longer edge of each of the link portions. Thus, the lower link member 42 is generally U-shaped in cross section in a portion thereof between the toggle pin 40 and drive pin 44.

As previously pointed out, the leg portions of the handle extension member 36 are respectively mounted on the rivets 33 on the outer sides of the frame members 31 and 32. On the inner sides of the frame member 31 and 32, a drive arm 45 is pivotally mounted adjacent one end on the inner end portions of the rivets 33. A Contact arm mounting pin 46 is mounted in the drive arm 45 adjacent the other end thereof. The drive arm 45 is shaped similarly to the lower link member 42 in that a central portion thereof is generally U-shaped in cross section and the leg portions thereof are elongated in a direction parallel to the bight portion thereof, each of the leg portions being pivotally mounted on one of the rivets 33 and opposite end portions of the drive pin 44 and the contact arm mounting pin 46 being mounted respectively in the leg portions of the drive arm 45. As disclosed in thev aforesaid copending application, one end portion of the drive pin 44 may be adjustably keyed to the drive arm 45 and the portions of the pin 44 received respectively in the opposed link portions of the lower link member 42 may be provided respectively with eccentric cams, whereby the eective length of the connection between the toggle pin 40 and the drive arm 45 may be adjusted.

A movable contact arm 47 carrying a movable contact 4S adjacent one end is pivotally mounted on the pin 46. The bight portion of the drive arm 45 is riveted or otherwise secured to a contact arm crossbar 56 formed of insulating material and preferably reinforced with a metallic strip 51. A contact pressure spring 52 biases the contact arm 47 counterclockwise as viewed in FIG. 5.

The trip lever 34 is normally held in a latched position by engagement of a tongue 34a provided on the bight portion thereof with the bight portion of a generally U-shaped intermediate latch member 54 the leg portions of which are pivotally mounted on a pin 55 mounted adjacent opposite ends respectively in the frame members 31 and 32. The intermediate latch member 54 is normally held in a latched position by engagement of one of the leg portions thereof with a latch plate 56 secured, as by a rivet 56a (FIG. 6), to a trip bar 57 pivotally mounted in a pair of spaced intermediate wall portions 24a (FIG. 2) of the base 24. The wall portions 24u and a corresponding pair of wall portions 21a of the cover 21 divide the casing of the circuit breaker 20 into three side-by-,side pole spaces or compartments.

The contact arm crossbar 50 extends into the two outer pole spaces of the circuit breaker 20. Each of the opposite end portions of the crossbar Si) has a generally U-shaped mounting bracket 58 (FIGS. 2 and 4) secured thereto, the bight portion of each bracket 58 preferably being riveted to the crossbar 50 and an extension 58a of the bight portion being wrapped partially around the crossbar, as shown in FIG. 4. Opposed leg portions of each bracket 58 carry a mounting pin or rivet 59. Each of the outer poles includes a movable contact arm 47, a movable contact 48, and a biasing spring 52 identical with those of the center pole, the contact arms 47 of the two outer poles being pivotally mounted respectively on the pins 59.

Each of the three poles includes a line terminal strap 60 secured to the base 24 and accessible from one end of the casing of the circuit breaker and having a stationary contact 61 secured to an inner end portion thereof and engageable by a respective one of the movable contacts 48. Further, each of the poles includes a load terminal strap 62 secured to the base 24 and accessible from the other end of the casing and having a bimetallic strip member 64 and a heating strip member 65 secured to an inner end portion thereof.

In accordance with the invention, each bimetallic strip member 64 lies between its associated terminal strap 62 and heating strip member 65, and each bimetallic strip member 64 and its associated heating strip member 65 extend from their fixed end portions at the inner end portion of their associated terminal strap 62 generally in the same direction their associated terminal strap 62 extends from its inner end portion. Each bimetallic strip member 64 thereby has its associated terminal strap 62 and heating strip member 65 disposed relatively closely thereto on opposite sides thereof so as to respond rapidly to radiant heat generated by tlow of electrical current through the terminal strap 62 and heating strip member 65. Each bimetallic strip member 64 is also heated by conduction due to the flow of electrical current through its fixed end portion. The particular arrangement is especially useful in circuit breakers with current ratings high enough to make it impractical to pass the current through the entire length of the bimetallic strip members.

Each heating strip member 65 is electrically connected to a respective contact arm 47 by a pair of exible cables 66. The free end portion of each bimetallic strip member 64 is adapted to engage the strip bar 57 and pivot it clockwise as viewed in FIGS. 4 and 5 upon sustained flow of moderate overload current through its respective pole of the circuit breaker 20, thereby releasing the intermediate latch member 54 from the latch plate 56 and the trip lever 34 from the intermediate latch member 54 to effect movement of the contacts 48 in all three poles to open position.

Each pole space includes a generally U-shaped magnetizable core member 67 the bight portion of which is disposed beneath the respective terminal strap 62 and held in spaced relationship thereto by a leaf spring member 68. Each pole space also includes a multipurpose bracket 70, an armature rod 71, an armature 72, an actuating member 73, and an armature return spring 74. Each armature 72 is secured in place on its respective armature rod 71, and each actuating member 73 is threadedly mounted on an end of its respective armature rod 71. Each armature rod 71 and its associated armature 72 and actuating member 73 thereby reciprocate as unit, the actuating member 73 being guided in its associated bracket 70 and the armature rod 71 being guided at the end portion thereof opposite its associated actuating member 73 in its associated terminal strap 62. Each spring '74 is hooked at one end to its associated armature 72 and at the other end to its associated bracket 70. Upon flow of severe overload current through any one of the terminal straps 62, magnetic flux established in its associated core member 67 attracts the associated armature '72 and the associated actuating member 73 pivots the trip bar 57 clockwise as viewed in FIGS. 4 and 5, thereby releasing the intermediate latch member 54 and the trip lever 34 to effect movement of the contacts 48 in all three poles to open position.

In accordance with the invention, and as best shown in FIGS. 6 to l1, the air-gap adjusting crossbar 29 controls the position of each of the armatures 72 with respect to its associated core member 67, and thus controls the air gap therebetween. The crossbar 29 is pivotally mounted in two of the three brackets 70, in flange portions 7051 thereof, as best shown in FIGS. 6 and 7, and is provided with three round-headed screw members 76, one in each pole space. Each screw member 76 is engageable with the actuating member 73 in its pole space. As previously mentioned, the control member 28 is accessible from the outside of the cover 21. An arrowshaped slot 28a (FIG. 8) is provided in an outer end portion of the control member 28 for reception of a screwdriver (not shown), the arrowhead cooperating with the HI and LO indicia (FIG. 1) on the cover 21. The outer end portion of the control member 28 is pivotally mounted in the cover 21, and an intermediate portion and an inner end portion of the control member 28 are respectively pivotally mounted in liange portions 70h vand 70e, of one of the brackets 70, as best shown in FIG. 7. A compression spring 77 surrounding the control member 28 and disposed between the cover 21 and an enlarged portion 28b of the control member 28 establishes friction between the control member 28 and the bracket 70 so that the control member 28 is maintained in an adjusted setting thereof. Pivotal movement of the control member 28 is limited by a stop portion 28e which cooperates with a tongue portion '70d of the associated bracket 70. A cam member 78 is keyed to the control member 28 by a at portion 28d (FIG. 8) provided on the control member 28. The cam member 78 cooperates with and pivotally adjusts the air-gap adjusting crossbar 29, as best shown in FIGS. 9 and l0. The screw members 76 on the crossbar 29 thereby respectively adjust the positions of the actuating members 73 and the spacing of the armatures 72 from their respective core members 67. l

1. A multipole electric circuit breaker comprising a molded casing having a plurality of elongated longitudinally side-by-side compartments therein, a plurality of stationary contacts disposed respectively in said compartments, a plurality of elongated contact arms pivotally mounted respectively in said compartments, a plurality of movable contacts disposed respectively in said compartments, each of said movable contacts being secured to a respective one of said contact arms and being engageable with a respective one of said stationary contacts, an

elongated contact larm crossbar disposed in said casingV and extending transversely of said compartments, means operatively connecting said contact arm crossbar to each of said contact arms, a releasably latchable trip lever pivotably mounted in one of said compartments and releasable fro a latcii position of effect separation of said movable contacts respectively from said stationary contacts, means in said one compartment operatively connecting said tr-ip lever and said contact arm crossbar, an elongated trip bar mounted in said casing and extendin'g transversely of saidcompartments, said trip bar normally being eilective to maintain said trip lever in a latched position and being pivotable to effect release of said trip lever, a plurality of elongated terminal straps each having an inner endl portion disposed in a respective one Vof said compartments and an outer end portion extending out of its respective compartment adjacent an end of said casing, a plurality of ma-gnetizable core members disposed respectively in said compartments in electromagnetic relationship respectively with said terminal straps whereby ow ofcurrent through each of said terminal straps establishes magnetic flux in its associated core member, a plurality of armature members disposed respectively in said compartments in spaced relationship respectively to said core members, each of said armature members being biased away `from its associated core member and being attractable thereto upon ow of severe overload current through its associated terminal strap, a plurality of actuating members disposed respectively in said compartments, means operatively connecting said actuating members respectively to said armature members, each of said actuating members being engage/able with said trip bar upon being attracted toward its asSociated core member tol pivot said trip bar Iand eiect release of said trip lever, a movable elongated air-gap adjusting crossbar disposed in said casing and extending transversely of said compartments, means operatively connecting said air-gap adjusting crossbar to each of said armature members, an adjustable air-gap control member disposed in said c-asing, said casing having an aperture therein providing access to said control member from said outside said casing, means operatively connecting said control member to said air-gap adjusting crossbar whereby adjustment of said control member simultaneously adjusts the spacing between each of said armature members and its associated core member, a plurality of bimetallic strip members disposed respectively in said compartments, each of said bimetallic strip members having a xed end portion secured to the inner end portion of a respective one of said terminal straps and an opposite free end portion engageable with said trip bar upon sustained flow of moderate overload current through its associated terminal strap to pivot said trip bar and effect release of said trip lever, a plurality of heating strip members dis posed respectively in said compartments, each of said heating strip members having a fixed end portion secured to the xed end portion of a respective one of said bimetallic strip members and an opposite free end portion, and a plurality of flexible conductors disposed respectively in said compartments, each of said flexible conductors electrically connecting the free end portion of a respective one of said heating strip members to a respective one of said contact arms, and each of said bimetallic strip members and its associated heating strip member extending from their xed end portions generally in the same direction their associated terminal strap extends from its inner end portion, whereby each of said Ibimetallic strip members has its associated terminal strap disposed relatively closely thereto on one side thereof and has its associated heating strip member disposed relatively closely thereto on the other side thereof so as to be heated along it-s length relatively rapidly by radiant heat from its lassociated terminal strap and heating strip member upon sustained flow of moderate overload current therethrough as well as by heat of conduction at its xed end portion.

2. A multipole `electric circuit breaker comprising a molded casing having a plurality of elongated longitudinally` side-by-side compartments therein, a plurality of stationary contacts disposed respectively in said compart- Cil ments, a plurality of elongated contact arms pivotally mounted respectively in said compartments, a plurality of movable contacts disposed respectively in said compartments, each of said movable contacts being secured to a respective one of said contact arms and being engageable with a respective one of said stationary contacts, an elongated contact arm crossbar disposed in said casing and extending transversely of said compartments, means operatively connecting said contact arm crossbar to each of said contact arms, a releasably latchable trip lever pivotally mounted in one of said compartments and releasable from a latched position to ettect separation of said. movable contacts respectively from said stationary contacts, means in said one compartment operatively connecting said trip lever and said contact arrn crossbar, an elongated trip bar mounted in said casing and extending transversely of said compartments, said trip bar normally being eiective to maintain said `trip lever in a latched position and being pivotable to effect release of said trip lever, a plurality of elongated terminal straps each having an inner end portion disposed in a respective one of said compartments and an outer end portion extending out of its respective compartment adjacent an end of said casing, a plurality of magnetizable core members disposed respectively in said compartments in electromagnetic relationship respectively with said terminal straps whereby llow of current through each of said terminal straps establishes magnetic ux in its associated core member, a plurality of armature members disposed respectively in said compartments in spaced relationship respectively to said core members, each of said armature members being biased away from its 'associated core member and being attractable thereto upon flow of severe overload current through its associated terminal strap, a plurality of actuating members disposed respectively in said compartments, means operatively connecting said actuating members respectively to said armature members, each of said actuating members being engageable with said trip bar upon being attracted toward its associated core member to pivot said trip bar and effect release of said trip lever, a movable elongated air-gap adjusting crossbar disposed in said casing and extending transversely of said compartments, means operatively connecting said air-gap adjusting crossbar to each of said armature members, an adjustable air-gap control member disposed in said casing, said casing having an aperture therein providing access to said control member from outside said casing, and means operatively connecting said control member to said air-gap adjusting crossbar whereby adjustment of said control member simultaneously adjusts the spacing between each of said armature members and its associated core member.

3. The multipole electric circuit breaker comprising a molded casing having a plurality of elongated longitudinally side-by-side compartments therein, a pluraltiy of stationary contacts disposed respectively in said compartments, a plurality of elongated contact arms pivotably mounted respectively in said compartments, a plurality of movable contacts disposed respectively in said compartments, each of said movable contacts being secured to a respective one of said contact arms and being engageable with a respective one of said stationary contacts, an elongated contact arm crossbar disposed in said casing and extending transversely of said compartments, means operatively connecting said contact arm crossbar to each of said contact arms, a releasably latchable trip lever pivotably mounted in one of said compartments and releasable from a latched position to effect separation of said movable contacts respectively from said stationary contacts, means in said one compartment operatively connecting said trip lever and said contact arm crossbar, an elongated trip bar mounted in said casing and extending transversely of said compartments, said trip bar normally being effective to maintain said trip lever in a latched position and being pivotable to effect release of said trip lever, a plurality of elongated terminal straps each having an inner end portion disposed in a respective one of said compartments and an Outer end portion extending out of its respective compartment adjacent an end of said casing, a plurality of bimetallic strip members disposed respectively in said compartments, each of said bimetallic strip members having a xed end portion secured to the inner end portion of a respective one of said terminal straps and an opposite free end portion engageable with said trip bar upon sustained flow of moderate overload current through its associated terminal strap to pivot said trip bar and effect release of said trip lever, a plurality of heating strip members disposed respectively in said compartments, each of said heating strip members having a xed end portion secured to the fixed end portion of a respective one of Said bimetallic strip members and an opposite free end portion, and a plurality of flexible conductors disposed respectively in said compartments, each of said flexible conductors electrically connecting the free end portion of a respective one of said heating strip members to a respective one of said contact arms, and each of said bimetallic strip members and its associated heat strip member extending from their fixed end portions generally in the same direction their associated terminal strap extends from its inner end portion, whereby each of said bimetallic strip members has its associated terminal strap disposed relatively closely thereto on one side thereof and has its associated heating strip member disposed relatively closely thereto on the other side thereof so as to be heated along its length relatively rapidly by radiant heat from its associated terminal strap and heating strip member upon sustained flow of moderate overload current therethrough as well as by heat of conduction at its lixed end portion.

4. A multipole electric circuit breaker as claimed in claim 1, including a plurality of pins disposed respectively in said compartments, said contact arms being pivotably mounted on said pins and said pins being carried by said contact arm crossbar,

5. A multipole electric circuit breaker as claimed in claim 2, including a plurality of pins disposed respectively in said compartments, said contact arms being pivotably mounted on said pins and said pins being ca rpied by said contact arm crossbar.

6. A multipole electric circuit breaker as claimed in claim 2, wherein said air-gap adjusting crossbar is pivotably mounted in said casing and wherein said actuating members are movable by said air-gap adjusting crossbar to move said armature members.

References Cited UNITED STATES PATENTS 3/1954 Cole 335-23 5/1966 Gryctko et al 20G-122

Claims

2. A MULTIPOLE ELECTRIC CIRCUIT BREAKER COMPRISING A MOLDED CASING HAVING A PLURALITY OF ELONGATED LONGITUDINALLY SIDE-BY-SIDE COMPARTMENTS THEREIN, A PLURALITY OF STATIONARY CONTACTS DISPOSED RESPECTIVELY IN SAID COMPARTMENTS, A PLURALITY OF ELONGATED CONTACT ARMS PIVOTALLY MOUNTED RESPECTIVELY IN SAID COMPARTMENTS, A PLURALITY OF MOVABLE CONTACTS DISPOSED RESPECTIVELY IN SAID COMPARTMENTS, EACH OF SAID MOVABLE CONTACTS BEING SECURED TO A RESPECTIVE ONE OF SAID CONTACT ARMS AND BEING ENGAGEABLE WITH A RESPECTIVE ONE OF SAID STATIONARY CONTACTS, AN ELONGATED CONTACT ARM CROSSBAR DISPOSED IN SAID CASING AND EXTENDING TRANSVERSELY OF SAID COMPARTMENTS, MEANS OPERATIVELY CONNECTING SAID CONTACT ARM CROSSBAR TO EACH OF SAID CONTACT ARMS, A RELEASABLY LATCHABLE TRIP LEVER PIVOTALLY MOUNTED IN ONE OF SAID COMPARTMENTS AND RELEASABLE FROM A LATCHED POSITION TO EFFECT SEPARATION OF SAID MOVABLE CONTACTS RESPECTIVELY FROM SAID STATIONARY CONTACTS, MEANS IN SAID ONE COMPARTMENT OPERATIVELY CONNECTING SAID TRIP LEVER AND SAID CONTACT ARM CROSSBAR, AN ELONGATED TRIP BAR MOUNTED IN SAID CASING AND EXTENDING TRANSVERSELY OF SAID COMPARTMENTS, SAID TRIP BAR NORMALLY BEING EFFECTIVE TO MAINTAIN SAID TRIP LEVER IN A LATCHED POSITION AND BEING PIVOTABLE TO EFFECT RELEASE OF SAID TRIP LEVER, A PLURALITY OF ELONGATED TERMINAL STRAPS EACH HAVING AN INNER END PORTION DISPOSED IN A RESPECTIVE ONE OF SAID COMPARTMENTS AND AN OUTER END PORTION EXTENDNG OUT OF ITS RESPECTIVE COMPARTMENT ADJACENT AN END OF SAID CASING, A PLURALITY OF MAGNETIZABLE CORE MEMBERS DISPOSED RESPECTIVELY IN SAID COMPARTMENTS IN ELECTROMAGNETIC RELATIONSHIP RESPECTIVELY WITH SAID TERMINAL STRAPS WHEREBY FLOW OF CURRENT THROUGH EACH OF SAID TERMINAL STRAPS ESTABLISHES MAGNETIC FLUX IN ITS ASSOCIATED CORE MEMBER, A PLURALITY OF ARMATURE MEMBERS DISPOSED RESPECTIVELY IN SAID COMPARTMENTS IN SPACED RELATIONSHIP RESPECTIVELY TO SAID CORE MEMBERS, EACH OF SAID ARMATURE MEMBERS BEING BIASED AWAY FROM ITS ASSOCIATED CORE MEMBER AND BEING ATTRACTABLE THERETO UPON FLOW OF SEVERE OVERLOAD CURRENT THROUGH ITS ASSOCIATED TERMINAL STRAP, A PLURALITY OF ACTUATING MEMBERS DISPOSED RESPECTIVELY IN SAID COMPARTMENTS, MEANS OPERATIVELY CONNECTING SAID ACTUATING MEMBERS RESPECTIVELY TO SAID ARMATURE MEMBERS, EACH OF SAID ACTUATING MEMBERS BEING ENGAGEABLE WITH SAID TRIP BAR UPON BEING ATTACTED TOWARD ITS ASSOCIATED CORE MEMBER TO PIVOT SAID TRIP BAR AND EFFECT RELEASE OF SAID TRIP LEVER, A MOVABLE ELONGATED AIR-GAP ADJUSTING CROSSBAR DISPOSED IN SAID CASING AND EXTENDING TRANSVERSELY OF SAID COMPARTMENTS, MEANS OPERATIVELY CONNECTING SAID AIR-GAP ADJUSTING CROSSBAR TO EACH OF SAID ARMATURE MEMBERS, AN ADJUSTABLE AIR-GAP CONTROL MEMBER DISPOSED IN SAID CASING, SAID CASING HAVING AN APERTURE THEREIN PROVIDING ACCESS TO SAID CONTROL MEMBER FROM OUTSIDE SAID CASING, AND MEANS OPERATIVELY CONNECTING SAID CONTROL MEMBER TO SAID AIR-GAP ADJUSTING CROSSBAR WHEREBY ADJUSTMENT OF SAID CONTROL MEMBER SIMULTANEOUSLY ADJUSTS THE SPACING BETWEEN EACH OF SAID ARMATURE MEMBERS AND ITS ASSOCIATED CORE MEMBER.