US3214535A

US3214535A - Electric circuit breaker with positive tripping means

Info

Publication number: US3214535A
Application number: US261345A
Authority: US
Inventors: Martin F Koenig; Alexander J Pastene; Lloyd D Williams
Original assignee: Cutler Hammer Inc
Current assignee: Cutler Hammer Inc
Priority date: 1963-02-27
Filing date: 1963-02-27
Publication date: 1965-10-26
Anticipated expiration: 1982-10-26
Also published as: SE301927B

Description

Oct. 26, 1965 M. F. KOENlG ETAL 3,214,535

ELECTRIC CIRCUIT BREAKER WITH POSITIVE TRIPPING MEANS Filed Feb. 27, 1963 2 She ets-Sheet 1 Oct. 26, 1965 M. F. KOENIG ETAL 3,214,535

ELECTRIC CIRCUIT BREAKER WITH POSITIVE TRIPPING MEANS Filed Feb. 27, 1963 2 Sheets-Sheet 2 United States Patent 3,214,535 ELECTRIC CIRCUIT BREAKER WITH POSKTIVE TRIPPING MEANS Martin F. Koenig and Alexander J. Pastene, Milwaukee, and Lloyd D. Williams, Waukesha, Wis., assignors to Cutler-Hammer, Inc., Milwaukee, Wis., a corporation of Delaware Filed Feb. 27, 1963, Ser. No. 261,345 11 Claims. (Cl. 200-458) This invention relates to electric circuit breakers and more particularly to electric circuit breakers of the thermal and magnetic trip type.

This invention, although not limited thereto, is especially applicable to circuit breakers of the type having an overcenter spring mechanism for tripping the breaker to open-circuit condition and having a latch which is held in engagement with the overcenter spring mechanism and which is disengaged to trip the breaker in response to an abnormal electrical condition, such as disclosed in Martin F. Koenig, Alexander J. Paste-x1e and Lloyd D. Williams copending application Serial No. 1,073, filed January 7, 1960, Patent -No. 3,081,386, dated March 12, 1963, and assigned to the assignee of this invention.

An object of the invention is to provide an improved circuit breaker.

A more specific object of the invention is to provide an improved tripping mechanism for a circuit breaker of the thermal and magnetic trip type.

Another specific object or the invention is to provide a circuit breaker with improved means for positively causing tripping thereof in response to an abnormal or excessive current condition.

Another object of the invention is to provide a circuit breaker with improved operating mechanism which allows use of less expensive material particularly for the latch parts because mechanical deterioration or corrosion products occurring over a period or time will not affect the operating characteristics thereof.

Other objects and advantages of the invention will hereinafter appear.

According to the invention, there are provided improvements to a circuit breaker of the type disclosed in the aforementioned Koenig et .al. patent whereby the breaker is positively caused to trip to open-circuit condition when an abnormal current condition occurs. 'These improvements comprise the addition of a latch hook whereby the latch is positively or forcibly separated from the catch under excessive thermal or magnetic action. This latch hook is secured to the armature and moves therewith to pull the latch away from the catch. These improvements also comprise lateral slots forming a pair of inwardly directed projections on the slide plate confining the end of the armature so that when the electro-responsive thermal element bends and moves the slide plate, the latter forcibly moves the armature to .cause tripping of the breaker. Since the latch is actually pulled away from the catch to trip the circuit breaker, corrosion on the catch will not alfect or change the operating characteristics over a period of time.

7 These and other objects and advantages of the invention and the manner of obtaining them will best be understood by reference to the following detailed description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIGURE 1 is a fragmentary front elevational view with the cover removed of a circuit breaker constructed in accordance with the invention and showing the breaker mechanism in its on condition;

FIG. 2 is :an isometric view of the armature assembly and slide plate of the breaker of FIG. 1;

FIG. 3 is a front elevational view like FIG. 1 but showing the breaker mechanism in its tripped or off condition; and

FIG. 4 is a front elevational view like FIGS. 1 and 3 but showing the breaker mechanism in a transistory condition following tripping but before resetting of the latch.

Referring to FIG. 1, there is shown one pole of a plural pole circuit breaker having a shallow insulating housing 2 provided with an open front which may be closed by a cover. Housing 2 is provided at its top with an aperture 2a through which extends the handle portion 4a of an operating lever 4. The operating lever is provided with a pair of cylindrical projections 4b integral therewith and laterally extending therefrom in opposite directions whereby the operating lever is journaled in the housing .and cover for rotation through a limited arc. 'llhe midportion 4c of the operating lever is enlarged and partially rounded so that as the handle is rotated from its extreme counterclockwise on position shown in FIG. 1 to its extreme clockwise off or tripped position shown in FIG. 3, such enlarged midp-ort-ion maintains aperture 2a closed at all times.

The lower portion 4d of the operating lever is enlarged .and divided into two leg portions to provide space for pivotal excursion of a trip lever or latch lever 6 therebetween and to provide for pivotal suspension of a latch 8 and a movable contact 10 therefrom.

Latch lever 6 is generally of inverted U-shaped configuration and is pivoted at the lower end of the left depending leg thereof at a fixed point in a recess in housing 2. An over-center tension spring 12 has one end h-ook connected in a hole in the yoke portion intermediate the legs of the latch lever. The other end hook of overcenter spring 12 is connected in a hole in the lower end of movable contact carrier or finger 10 having a contact 10a thereon. The upper end of movable contact finger 10 is bifurcated and the bifurcated ends 10b are bent outwardly in opposite directions and extend into holes in the divided lower portions 4d of the operating lever to pivot the movable contact finger on the operating lever. *It will be apparent from the foregoing description that Whenever the operating lever moves the movable contact finger pivot and the center line or line of action of the overcenter spring across one another, the movable contact finger will snap open or closed relative to stationary contact 14 depending upon the direction of movement. Also, when latch lever 6 is released to move the upper end of the overcenter spring past the movable contact finger pivot, the movable contact finger will snap open relative to the stationary contact.

A tension spring 16 has one end hook connected in a hole in the left depending leg of latch lever 6 and has its other end hook connected to a stationary projection 18 molded integrally in the housing. Spring 16 is a resetting spring which rotates the latch lever counterclockwise whenever overcenter spring 12 is relaxed and does not overpower the same. A connector 14a is connected to the stationary contact and extends through an aperture in the lower portion of the housing to afford electrical connection of the breaker to an external circuit. A common trip lever 20 is journaled in holes extending through the housing and cover below the right-hand depending leg of latch lever 6 to cause tripping of a second, adjacent breaker when the first breaker trips. Latch 8 is U-shaped and the upper ends 8a of the side portions thereof are bent outwardly in opposite directions and are journaled in alined holes in the divided portions 4d of the operating lever to freely pivot the latch on the operating lever. The lower yoke portion of latch 8 is provided with aflat upper surface 811 inclined at a small angle to the left for engagement on a catch 6a provided on the right-hand'depending I 3 leg portion of latch lever 6, this catch being most clearly shown in FIG. 4.

A slide plate 22 is slidably accommodated in horizontal slots in the housing and cover and is biased in the lefthand direction by a helical compression spring 24 positioned between a Wall of the housing and the right-hand end portion of the slide plate. To maintain spring 24 in registration with the slide plate, the latter is provided with spaced notches providing a tongue 22a therebetween as shown in FIG. '2. As shown in FIG. 1, the opposite sides of spring 24 are in these notches and tongue 22a extends into the left-hand end of the spring to maintain the slide plate in engagement with the spring.

As shown in FIG. 2, the left-hand end of slide plate 22 is provided with a slot 22b for accommodating the lower free end of a thermal element such as bimetal element 26. The upper end of bimetal element 26 is rigidly secured as by welding to the upper end of an electrical connector member 28. Connector member 28 is held in a slot in the housing formed partly by the right-hand Wall portions of the housing and is held in position by an adjusting screw 30. Screw 30 extends from the exterior of the housing through a slot in the right-hand wall thereof through a hole in connector member 28 into threaded engagement with a tapped hole in a pole piece hereinafter described. The right-hand wall of the housing above and below screw 30 is provided with an undercut portion 2b to afford adjustment of the position of bimetal element 26 by bending connector member 28 when screw 30 is turned in while the head of the screw bears against the exterior wall of the housing. The lower end of connector member 28 extends through an aperture in the righthand wall of the housing and is provided with a screw type connector or the like to afford connection thereof to an external circuit.

An elongated fiat armature 32 is provided at its upper end portion with rearwardly and forwardly projecting ears 32a shown in FIG. 2 for pivotally supporting the armature in depressions in the housing and cover as shown in FIG. 1. The rearward and forward edges of slot 22b in slide plate 22 are provided with laterally alined slots 220 for accommodating the lower end portion of armature 32. As a result of the force of spring 24 acting through slide plate 22, the lower end of armature 32 is biased in the left-hand direction and is moved in the right-hand direction by projections 22d on slide plate 22 when bimetal element 26 bends.

A compensating bimetal element 34 is rigidly secured as 'by welding at its lower end portion to the left-hand surface of the lower end portion of armature 32. The upper portion of compensating bimetal element 34 diverges from armature 32 into engagement with the lower end portion of latch 8 so as to normally press latch 8 into engagement with catch 6a on the latch lever. A latch hook 36 preferably of resilient spring wire but which could be rigid is rigidly secured as by welding at its upper end portion to the left-hand surface of the upper portion of armature 32. Latch hook 36 extends at an angle from the armature in the left-hand downward direction and its lower end portion is bent downwardly into engagement with and overlapping the upper tip portion of compensating bimetal element 34. The lower end of latch hook 36 is arranged so that when the breaker is turned from its 01f position shown in FIG. 3 to its on position shown in FIG. 1, the lower yoke portion of U-shaped latch 8 enters between compensating bimetal element 34 and latch hook 36 and separates the latter from the former against the spring bias of the latch hook. As shown in FIG. 2, latch hook 36 is positioned and secured off-center relative to the upper end of compensating bimetal element 34 and armature 32 so that it can enter on one side of the right-hand depending leg of latch lever 6 and will not interfere with movement of the latch lever.

A magnetiza'ble pole piece 38 of generally rectangular block configuration is positioned on the right-hand side of bimetal element 26 for magnetically attracting armature 32 which is positioned on the left-hand side of bimetal element 26 substantially parallel to the latter. Pole piece 38 is provided with a tapped hole into which the extreme end portion of adjusting screw 30 is threaded to maintain the pole piece at a downwardly diverging angle to bimetal element 26 whereby to afford space for the lower end of bimetal element 26 to bend in the right-hand direction. The right-hand surface of pole piece 38 is provided with a pair of elongated extrusions 38a, one on each side of the adjusting screw hole therein which bear against connector member 28 to space the remainder of the pole piece from the latter. An L-shaped insulating strip 40 has one angular portion anchored between connector 14a and a horizontal wall of the housing by way of a hole in such strip and a projection 20 molded in such wall of the housing. The other angular portion of the insulating strip extends upwardly to provide effective dielectric protection of contact finger 10 from the left-hand depending leg of latch lever 6. A pair of electrical conductors 42 connect the lower end portion of bimetal element 26 to movable contact finger 10.

FIG. 3 shows the breaker in its tripped or 01f condition. When the manual operating lever is rotated in the counterclockwise direction, the upper pivot of contact finger 10 at the lower left-hand portion of the operating lever is moved in the right-hand direction toward the center line or line of action of overcenter spring 12. At the same time, the lower right-hand portion of the operating lever raises latch 8 so that the lower horizontal yoke portion of the latch engages catch 6a on the latch lever. Following engagement of the catch by the latch, further rotation of the operating lever causes latch 8 to rotate latch lever 6 counterclockwise. As a result, the latch lever moves the upper end of spring 12 and the line of action of this spring in the left-hand direction. When the contact finger pivot and the line of action of the overcenter spring pass one another, the overcenter spring causes the contact finger to pivot whereby to snap the movable contact into engagement with the stationary con tact as shown in FIG. 1. In this position of the breaker, the lower horizontal portion 8b of latch 8 has entered between latch hook 36 and compensating bimetal element 34 and has separated the latch hook from the latter.

In the closed condition of the breaker shown in FIG. 1, compression spring 24 biases slide plate 22 in the left-hand direction. The slide plate acts upon the lower end portion of armature 32 to cause the upper end of compensating bimetal element 34 to apply a force against the lower end of latch 8 whereby the latch is maintained in engagement with the catch on the latch lever. Latch hook 36 is preferably made of spring metal rather than being stiff so that the lower end thereof will be in engagement with the latch to eliminate lost motion in its action described below and will return into engagement with the upper end of compensating bimetal element 34 when the breaker is tripped as shown in FIG. 3. In the closed condition of the breaker, a circuit is established for current flow in a path extending from connectormember 28 through bimetal element 26, conductors 42, contact finger 10, movable contact 10a and stationary contact 14 to connector 14a.

To prevent ambient temperature variation from affecting the tripping point of the breaker for electrical conditions, element 34 is provided. For example, if the ambient temperature increases and causes bimetal element 26 to bend to the right, compensating bimetal element 34 correspondingly bends to the left to compensate for any movement of armature 32. In this manner, the thermal and magnetic conditions caused by current flow which are required to trip the breaker will remain constant even it the surrounding temperature changes.

When excessive current flows through the breaker such as to cause thermal tripping, bimetal element 26 bends. The lower end of such bimetal element bears against the bottom of slot 22b to move slide plate 22 in the righthand direction against the force of spring 24. Such movement of the slide plate causes the projections 22d on the left-hand sides of slots 22c, FIG. 2, to move the lower end of armature 32 in the right-hand direction. Armature 32 carries compensating bimetal element 34 with it to reduce the force applied to latch 8. And latch hook 36 positively pulls latch 8 in the right-hand direction to separate the latch from the catch. Because latch hook 36 biases latch 8 against the upper end portion of compensating bimetal member 34 and because slide plate 22 pulls armature 32 in the right-hand direction, the latch will release latch lever 6 when bimetal element 26 has bent the proper amount from an initial position as set by adjusting screw 30.

When suddent excessive current flows through the breaker such as to cause magnetic tripping, the high current flow through bimetal element 26 induces a magnetic field whereby stationary polepiece 38 attracts armature 32 thereto. As the armature is so attracted, it pushes slide plate 22 and compresses spring 24. There is suificient space in slot 22b in the slide plate between the armature and bimetal element 26 so that the latter will not be bent by such movement of the armature. When the armature is attracted as aforesaid, it carries compensating bimetal element 34 with it to decrease the force on the latch and carries latch hook 36 with it to pull latch 8 from catch 8b whereby to release latch lever 6.

When latch lever 6 is released due to either thermal or magnetic tripping as aforesaid, Overcenter spring 12 pivots it clockwise. As a result, the line of action of overcenter spring 12 is moved to the right past the pivot of contact finger 10 whereupon the Overcenter spring snaps the contacts open as shown in FIG. 4. The lower end of the right-hand depending leg of latch lever 6 strikes the cam surface of common trip lever 20 to rotate the common trip lever clockwise. This common trip lever is rigidly coupled or connected to a like common trip lever in the adjacent breaker to rotate it in unison. In such adjacent breaker, the common trip lever moves the compensating bimetal element, latch hook and armature assembly to the right to trip the adjacent breaker.

It will be apparent from FIGS. 1 and 4 that tripping of the breaker and clockwise rotation of latch lever 6 caused resetting spring 16 to stretch. In the transistory condition shown in FIG. 4, overcent'er spring 12 is under tension whereby it'causes the operating lever to rotate clockwise from the on position shown in FIG. 1 toward the off position shown in FIG. 3. Overcenter spring 12 becomes completely constricted before the operating lever moves all the Way off. Thereafter, resetting spring 16 returns latch lever 6 counterclockwise. Latch lever 6 carries spring 12 with it which in turn carries contact finger with it to complete the clockwise rotation of the operating lever to its fully ofi? position shown in FIG. 3. It will be apparent that during the transitory condition shown in FIG. 4, catch 6a is below the lower end of latch 8. However, the resetting operation just described causes catch 6a to be raised and concurrently causes latch 8 to be lowered below the catch as shown in FIG. 3. In this position, the latch is in condition to engage the catch when the operating lever is moved back to its on position provided the bimetal element 26 has cooled.

Whilethe apparatus hereinbefore described is effectively adapted to fulfill the objects stated, it is to be understood that we do not intend to confine our invention to the particular preferred embodiment of electric circuit breaker disclosed, inasmuch as it is susceptible of various modifications without departing from the scope of the appendedclaims.

We claim:

1. In a circuit breaker having a spring-loaded latch tripped operating mechanism mounted in an insulating housing and an operating lever extending from said housing'for actuating said operating mechanism between circuit-closed and circuit-open conditions:

(a) means for maintaining said operating mechanism in circuit-closed condition when actuated thereto and for reliably tripping the same to circuit-open condition in response to a predetermined electrical condition comprising:

(b) latch means for said operating mechanism requiring application of a force to maintain it latched;

(c) means for applying said force to said latch means to maintain said operating mechanism in circuitclosed condition;

(d) biasing means for applying an increasing counter force to said latch means to effect positive release of said operating mechanism when said maintaining force is decreased; 7

(e) and means responsive to an abnormal electrical condition for decreasing said maintaining force to cause tripping of said operating mechanism to circuit-open condition;

(f) said maintaining force applying means comprising and armature assembly pivoted in said housing;

(g) a slide plate engaging a first portion of said arma ture and being slidable in said housing;

(h) a spring compressed between said slide plate and a Wall of said housing to cause another portion of said armature assembly to apply said force to said latch means;

(i) and electro-responsive means for sliding said plate against the force of said spring to cause said plate to pull said armature assembly away from said latch means to decrease said maintaining force.

2. The inventiondefined in claim 1, wherein:

(a) said biasing means comprises a resilient member rigidly secured at one end to the armature assembly and having another end extending to the other side of said latch means to separate the latter from said operating mechanism when the armature assembly is pulled away.

3. In a circuit breaker having a spring-loaded latchtripped operating mechanism and an operating lever for actuating said operating mechanism between circuitclosed and circuit-open conditions:

(a) means for maintaining said operating mechanism in circuit-closed condition and for electrically tripping the same to circuit-open condition comprising:

(b) latch means requiring application of a force thereto to maintain it in latching engagement with said operating mechanism;

(d) biasing means for applying a counter force to said latch means which is less than said maintaining force whereby said operating mechanism remains latched under normal electrical conditions;

(e) and means responsive to' an abnormal electrical condition for decreasing said maintaining force and for creating and simultaneously and proportionally increasing said counter force to positively separate said latch means from said operating mechanism to trip the latter to its circuit-open condition.

4. The invention defined in claim 1 wherein:

(a) said slide plate is provided with a slot opposite said spring having one portion for pushing said armature assembly toward said latch means;

(b) and another portion of said slot engaging the other side of said armature assembly for pulling it away from said latch means under the force of said electro-responsive means.

5. In a combined thermal and magnetic trip mechanism for an electric circuit breaker; the combination comprising:

(a) an insulating housing;

(b) a stationary contact mounted in said housing and a movable contact for engaging said stationary contact;

(c) an operating lever pivotally supported in said hous- (d) a spring biased trip mechanism comprising a movable contact carrying finger pivoted on said operating lever, a latch lever pivoted in said housing and an overcenter spring connected between said movable contact carrying finger and said latch lever;

I (e) a catch on said latch lever;

(f) a latch member pivoted on said operating lever for engaging said catch;

(g) a spring biased armature assembly for applying a force on said latch member to maintain engagement with said catch and to maintain said contacts closed;

(h) combined electro-thermal and electromagnetic means for withdrawing said armature assembly to reduce the force applied to said latch member;

(i) and a latch hook on said armature assembly for pulling said latch member from said catch when said armature is withdrawn to trip the contacts open.

6. In a trip mechanism for an electric circuit breaker;

the combination comprising:

(a) an insulating housing having a stationary contact mounted therein and a movable contact for engaging said stationary contact;

(b) a spring biased trip mechanism comprising a latch lever pivoted in said housing and a movable contact carrying finger connected by an overcenter tension spring to said latch lever for opening and closing said contacts;

(c) an operating lever for actuating said trip mechanism;

(d) a catch on said latch lever;

(e) a latch member pivoted on said operating lever for engaging said catch;

(f) spring biased means in said housing comprising a compensating bimetal member for applying a force on said latch memberto maintain engagement with said catch and to maintain said trip mechanism in contact-closed position;

(g) a resilient member mounted on said spring biased means for biasing said latch against said compensating bimetal member;

(h) and means responsive to an abnormal electrical condition for counteracting said spring biased means whereby said resilient member pulls said latch member from said catch to release said latch lever and to trip the contacts open.

7. In a circuit breaker, the combination of:

(a) a manual operating lever pivotally mounted in an insulating housing;

(b) a stationary contact in said housing;

(c) a movable contact carrier pivoted on said lever;

(d) a trip lever pivoted at a fixed point in said housing;

(e) an overcenter tension spring connected between said contact carrier and said trip lever;

(f) means mounted in said housing for holding said trip lever in unoperated position when said manual lever is in its on position to cause said overcenter spring to hold said contact carrier in contact-closed position; said means being responsive to movement of said manual lever to its off position to allow pivotal movement of said trip lever thereby to carry the line of action of said overcenter spring and the pivot of said contact carrier across one another and to cause said overcenter spring to move said contact carrier to contact-open position, said means comprising:

(g) a pivoted latch member for holding said trip lever 8. in unoperated position when a force is applied to said latch member;

(h) spring biased means for applying a force to said latch member;

(i) means responsive to an excessive electrical con-' 8. In combination with a circuit breaker having an operating mechanism for operating the breaker between circuit-closed and circuit-open conditions:

(a) an operating lever for actuating said operating mechanism;

(b) a catch on said operating mechanism;

(c) a movable latch for engaging said catch to maintain the breaker in circuit-closed condition and being separable from said catch to allow said operating mechanism to trip the breaker to circuit-open condition;

(d) means for applying a force to said latch to maintain it in engagement with said catch;

(e) means movable responsive to an abnormal current condition for increasingly opposing the force of said force applying means as said movable means moves to reduce the force of said latch;

(f) and resilient means movable in response to movement of said movable means when said force is reduced for positively separating said latch from said catch to cause tripping of the breaker.

9. In combination with a circuit breaker of the type having a circuit breaker operating mechanism for operating the breaker between circuit-closed and circuit-open conditions:

(a) an operating lever for actuating said operating mechanism;

(b) said operating mechanism comprising a catch thereon;

(c) a movable latch engaging said catch to maintain said breaker in circuit-closed condition and being separable from said catch to allow said operating mechanism to trip said breaker to circuit-open condition;

(d) means for applying a force to said latch to maintain the same in engagement with said catch;

(e) means responsive to an abnormal current condition for opposing said force applying means;

(f) and resilient means effective when said force is opposed sufiiciently for positively separating said latch from said catch to cause tripping of the breaker;

(g) said resilient means comprising a spring wire secured at one end to said force applying means and extending to the other side of said latch to pull said latch from said catch.

10. In a circuit breaker of the type having a circuit breaker operating mechanism for operating the breaker between circuit-closed and circuit-open conditions:

(a) an operating lever for actuating the breaker operating mechanism;

(b) an overcenter mechanism comprising a latch lever, means providing a fixed pivot for said latch lever, a movable contact finger pivoted on said operating lever, an overcenter spring connected between said latch lever and said contact finger, and a latch pivoted on said operating lever for engaging said latch lever;

(c) said latch and said contact finger being responsive to movement of said operating lever for moving said latch lever and the pivot of said contact finger relative to one another against the force of said overcenter spring whereby said over-center mechanism moves through its dead center position to cause said contact finger to snap into circuit-closed condition.

(d) a trip mechanism responsive to an abnormal electrical condition for causing separation of said latch from said latch lever to cause tripping of the contact finger to circuit-open condition;

(e) and said trip mechanism comprising means to positively pull the latch from the latch lever to release the latter.

11. In a circuit breaker having a spring-loaded latchtripped operating mechanism and an operating lever for actuating said operating mechanism between circuitclosed and circuit-open conditions:

(a) means for maintaining said operating mechanism in circuit-closed condition when actuated thereto and for positively tripping the same to circuit-open condition in response to an abnormal electrical condition comprising:

(b) freely pivoted latch means for said operating mechanism requiring application of a force to maintain it latched;

(0) means for applying said force to said latch means to maintain said operating mechanism in circuitclosed condition;

open condition.

References Cited by the Examiner UNITED STATES PATENTS Gano et a1 20088 Dorfman 20088 Dorfman et al 200116 Jennings 20088 Casey 20088 Norden 20088 Coleman 200106 20 BERNARD A. GILHEANY, Primary Examiner.

ROBERT K. SCHAEFER, Examiner.

Claims

1. IN A CIRCUIT BREAKER HAVING A SPRING-LOADED LATCHTRIPPED OPERATING MECHANISM MOUNTED IN AN INSULATING HOUSING AND AN OPERATING LEVER EXTENDING FROM SAID HOUSING FOR ACTUATING SAID OPERATING MECHANISM BETWEEN CIRCUIT-CLOSED AND CIRCUIT-OPEN CONDITIONS: (A) MEANS FOR MAINTAINING SAID OPERATING MECHANISM IN CIRCUIT-CLOSED CONDITION WHEN ACTUATED THERETO AND FOR RELIABLY TRIPPING THE SAME TO CIRCUIT-OPEN CONDITION IN RESPONSE TO A PREDETERMINED ELECTRICAL CONDITION COMPRISING: (B) LATCH MEANS FOR SAID OPERATING MECHANISM REQUIRING APPLICATION OF A FORCE TO MAINTAIN IT LATCHED; (C) MEANS FOR APPLYING SAID FORCE TO SAID LATCH MEANS TO MAINTAIN SAID OPERATING MECHANISM IN CIRCUITCLOSED CONDITION; (D) BIASING MEANS FOR APPLYING AN INCREASING COUNTER FORCE TO SAID LATCH MEANS TO EFFECT POSITIVE RELEASE OF SAID OPERATING MECHANISM WHEN SAID MAINTAINING FORCE IS DECREASED; (E) AND MEANS RESPONSIVE TO AN ABNORMAL ELECTRICAL CONDITION FOR DECREASING SAID MAINTAINING FORCE TO