US3806846A

US3806846A - Pushbutton reset undervoltage release device

Info

Publication number: US3806846A
Application number: US00376459A
Authority: US
Inventors: D Powell
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1973-07-05
Filing date: 1973-07-05
Publication date: 1974-04-23
Anticipated expiration: 1991-04-23

Abstract

An electric circuit breaker is provided with an undervoltage release having a manual reset button independent of the handle used for manually opening and closing the circuits controlled by the circuit breaker. The undervoltage release device includes a solenoid plunger movable between a seated position and a released position and a tripping member movable into and out of a tripping position in response to the movement of the plunger. The reset button operates on an actuator lever operatively associated with the separate tripping member and plunger so that upon actuation of the button the tripping member is urged toward a tripping position and the plunger is urged toward the seated position.

Description

United States Patent Powell [451 Apr. 23, 1974 PUSHBUTTON RESET UNDERVOLTAGE RELEASE DEVICE David B. Powell, Bristol, Conn.

General Electric Company, New York, N.Y.

Filed: July 5, 1973 Appl. No.: 376,459

Inventor:

Assignee:

US. Cl. 335/20, 335/166 Int. Cl. H0lh 83/12 Field of Search 335/20, 27, 26, 166

References Cited UNITED STATES PATENTS 9/1966 Franz 335/166 12/1966 Kiesel et a1. 335/20 6/1969 Murphy, Jr. et al. 335/166 Primary Examinerl-larold Broome Attorney, Agent, or FirmRobert A. Cahill; Philip L. Schlamp; Frank L. Neuhauser [57] ABSTRACT An electric circuit breaker is provided with an undervoltage release having a manual reset button independent of the handle used for manually opening and closing the circuits controlled by the circuit breaker.

The undervoltage release device includes a solenoid plunger movable between a seated position and a released position and a tripping member movable into and out of a tripping position in response to the movement of the plunger. The reset button operates on an actuator lever operatively associated with the separate tripping member and plunger so that upon' actuation of the button the tripping member is urged .toward a tripping position and the plunger is urged toward the seated position.

15 Claims, 6 Drawing Figures PATENTEDAPR 23 m4 3,806; 846 m 1 [IF 2 FIG.

PUSI-IBUTTON RESET UNDERVOLTAGE RELEASE DEVICE BACKGROUND AND SUMMARY OF THE INVENTION The present invention relates generally to electric circuit breakers. More particularly is is concerned with a new and improved electric circuit breaker having an undervoltage release type device responsive to a decrease in line voltage within a circuit controlled by the breaker.

Undervoltage release type devices utilized heretofore have commonly employed a solenoid retained actuator or plunger that is held by the solenoid during normal operation and is released in response to a predetermined drop in the line voltage. Typically the plunger is reseated or reset by the opening or tripping movement of some part of the breaker mechanism. As a result a common problem has existed with undervoltage release devices; namely, the reversal of this tripping motion or a release of the reseated plunger must take place before the undervoltage release device can trip the breaker latch. Consequently, if an undervoltage condition persists and the circuit breaker is moved to its ON position, a race occurs between latch release by the undervoltage release device and movement of the contacts toward their closed circuit positions. This becomes particularly critical in mining use applications. Under such use it is extremely important for safety reasons that there be no re-energization of the cable which originally signaled the undervoltage release device until that cable has been repaired.

Although many different approaches have been used in solving this problem, none has been completely satisfactory. According to one approach, a fine adjustment of the mechanism makes it possible to cause latch release and therefore tripping early enough to prevent the contacts from re-energizing the line. However, such an adjustment puts a heavy strain on the mechanism since maximum energy is imparted to the links and pivots of the mechanism by such an adjustment.

According to another method, the reset motion of the breaker handle between the OFF and RESET positions is utilized to provide the work necessary to reset or reseat the solenoid plunger. While this is more practical in some breakers than others, it also requires accurate parts and fine controls and further requires interphase mechanical connections. Additionally, electrical reset schemes have been tried with or without switching but these techniques have also encountered difficulty for various reasons.

Accordingly, it is an object of the present invention to provide a new and improved electric circuit breaker having an undervoltage tripping device that prevents resetting or reseating of the undervoltage release while the undervoltage condition persists. Included in this object is the provision for a new and improved undervoltage trip control device that requires a separate and distinct resetting action not associated with the main ONI- OFF handle of the circuit breaker.

Another object of the present invention is to provide a new and improved electric circuit breaker of the type described including an undervoltage trip control device constructed so as to make it impossible to reset the trip latch of the circuit breaker while the solenoid is in a low voltage or de-energized condition.

Still, anotherobject of the present invention is to provide an undervoltage trip control device that requires the operator of the breaker to supply a separate resetting force while at the same time preventing any attempts to defeat the undervoltage release function of the unit.

A further object of the present invention is to provide a new and improved circuit breaker of the type described including an undervoltage trip control device that has no interphase mechanical connections yet permits tripping of the breaker from the ON or OFF positions with the solenoid energized.

A still further object of the present invention is to provide a new and improved electric circuit breaker and undervoltage trip control device of the type described that indicates a breaker tripping condition by means of a separate button position.

Still another object of the present invention is to provide a new and improved electric circuit breaker and undervoltage trip control device of the type described which is compact, efficient, simple and relatively trouble free.

Other objects will be in part obvious and in part pointed out in more detail hereinafter.

These and related objects are accomplished in accordance with the present invention by providing an electric circuit breaker of the type described having a casing, a handle extending through the casing for manually opening and closing the circuit controlled by the circuit breaker, a trip unit in the casing operable to effect automatic opening of the circuits and a trip control unit adjacent the trip unit for controlling the tripping operation of the trip unit. The trip control unit includes a tripping member movable toward a tripping position for tripping the trip unit. An automatic trip actuator is movable between an electrically responsive seated position and a released position and is operable upon movement toward its released position to cause movement of the tripping member toward its tripping position. The actuator in its released position is operative to prevent movement of the tripping member out of its tripping position. A manual reset operator extends through the casing independent of the handle and is movable between a rest position and an operating position and is operative upon movement toward said operating position to urge the tripping member toward its tripping position and the actuator towards its seated position. v

A better understanding of the invention will be obtained from the following detailed description and the accompanying drawings which set forth an illustrative embodiment indicative of the way in which the principles of the invention are employed.

A BRIEF DESCRIPTION OF THE DRAWING In the drawing:

FIG. 1 is a side elevation view partially broken away and partially in section of a molded case circuit breaker incorporating the undervoltage release device of the present invention;

FIG 2 is a partial top view of the circuit breaker of FIG. 1 showing the location of the independent reset button for manual actuation of the release device;

FIG. 3 is an enlarged top view of the undervoltage release device of the present invention;

FIG. 4 is a side view of the undervoltage release device of FIG. 3 showing the device during normal closed circuit operation of the breaker;

FIG. 5 is a view similar to FIG. 4 showing'the undervoltage trip control device in its fully tripped condition.

in response to a low voltage or no voltage condition; and

FIG. 6 is a view similar to FIG. 4 showing the undervoltage trip control device upon manual actuation of the device's reset button.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawing in greater detail wherein like reference numerals indicate like parts throughout the several figures, the invention is shown as incorporated in an electric circuit breaker including a generally rectangular insulating case comprised of a base portion 10 and a cover portion 12. The particular circuit breaker illustrated is a three pole circuit breaker and comprises three elongated chambers or current paths each of which contain separable contacts (not shown) of a conventional type. The operating mechanism which controls movement of the separable contacts between open and closed circuit positions is controlled by a manually operated handle 14 projecting centrally from the top of cover 12 for movement between its ON and OFF positions. The operating mechanism includes a trip unit 16 such as that described and illustrated in U.S. Pat. No. 3,162,740, the disclosure of which is incorporated herein by reference, and a normally restrained but releasable member (not shown) which is adapted to be releasably held by a trip bar 18 housed within unit 16. The bar 18 extends fully across the circuit breaker and is mounted for pivotal movement between a latched position and a tripped position where it effects simultaneous opening of all three current paths controlled by the circuit breaker.

For the purpose of initiating a tripping operation of the trip unit upon the occurence of a predetermined decrease in voltage in a selected circuit controlled by the breaker, an undervoltage trip control device is provided as indicated generally in FIG. 1 by the numeral 20. The undervoltage release device 20 is enclosed within the casing and is operatively associated with a reset button 22 that projects upwardly through an aperture 24 in the casing cover 12 intermediate the manual handle 14 and the side of the casing. In the embodiment illustrated the protruding portion of button 22 is enclosed by a deformable dust cap 26 attached to a cylindrical sleeve or guide 28 secured to the cover 12 at the aperture 24.

Referring now to FIGS. 36, the undervoltage trip control or release device is shown as comprised of a generally flat sheet metal supporting frame having a central planar portion 30 with an enlarged circular aperture 32 adjacent one end thereof for registry with the reset button aperture 24 in the cover of the circuit breakers casing. The support includes front and

rear end walls

34, 36 respectively that are bent in opposite directions at approximately 90 to the central planar portion 30 and provide appropriate means for mounting the entire undervoltage trip control unit within the circuit breaker. In this connection, the front bent-up end wall 34 is preferably mounted on the trip unit 16 of the circuit breaker and secured thereto by means of a suitable threaded connector 38.

Side flanges

42, 44

depend downwardly from the central planar portion 30 of the support and provide means for mounting the movable components of the trip control unit.

A tripping lever 46 is pivotally mounted on the depending side flange 42 adjacent the upstanding front wall 34 by means of fixed pin 48 and in turn is pivotally connected by pin 50 to a flat sheet metal slide member 52. In the embodiment illustrated the member 52 is provided with an elongated tripping plunger portion 54 adapted to extend into the trip unit 16 for tripping contact with the trip bar 18. As best shown in FIGS. 46, the tripping lever 46 is a generally triangular member with the aforementioned pivotal connections at two of its three corners and the free corner 56 thereof positioned remotely from front wall 34 in such a manner that pivotal movement of the tripping lever 46 about the fixed pivot pin 48 in a counterclockwise direction as viewed in FIG. 4 will drive the slide member 52 to the left as viewed in FIG. 4 so as to bring the plunger portion 52 into engagement with the trip bar 18. As shown, the slide member 52 is also provided with a linear elongated slot or guideway 58 within which is positioned a laterally extending guide tab 60 located generally within the plane of the main body portion 30 of the support and extending laterally therefrom. In this man ner, the slide 52 is restrained to travel along a reciprocally linear path during movement between its retracted and advanced positions in response to the pivotal movement of the tripping lever 46.

A solenoid 62 is positioned in operative alignment with the elongated slide member 52 and is rigidly mounted on the support adjacent the rear depending wall 36 by threaded connectors 64. The solenoid is provided with a generally cylindrical plunger 66 fixedly mounting a flat guide plate 68 on its free end for restrainably confining a plunger drive spring 70 coiled around the plunger between the plate 68 and the solenoid 62. The guide plate 68 is provided with topand bottom notches 72 and the reciprocating slide member 52 is provided with an enlarged recess 74 adjacent its rearward end and above guideway 58 so that the slide 52 and the plate 68 on the solenoid plunger interfit for relative sliding movement while cooperating to provide coaxial alignment therebetween.

A tripping plunger return spring 76 is connected at one end to the guide plate 68 and at its opposite end to the pivot pin 50 interconnecting the guide plate 68 with the slide member 52. Thus, as will be appreciated, the slide member and the solenoid plunger may move independently or in unison between their respective extended or retracted positions. However, when the solenoid plunger is in its retracted or seated position and the slide member is in its extended or tripping position, the tripping plunger return spring 76 will be in its extended or loaded condition. Accordingly, unless the slide 52 is restrained, the return spring 76 will bias the slide toward the solenoid plunger after the latter has moved to its seated position. Therefore, as the solenoid plunger is moved under the influence of its drive spring 70 out of its seated position toward its extended position, the guide plate 68 will drivably move the slide member 52 to the left as viewed in FIG. 4 toward its extended or tripping position shown in FIG. 5.

Also pivotably mounted on the support is the mechanism employed in resetting or reseating the solenoid plunger 66 after it has been released by an undervoltage condition. As mentionedhereinbefore, the resetting mechanism includes a reset button 22 extending through a reset aperture 24 in the cover 12 of the casing intermediate the manual ON/OFF lever 14 and side wall of the casing. The aperture 24 in the cover is preferably provided with a tubular guideway 28 supportably mounted on the cover 12 and enclosed by a resilient dust cover or cap 26 that lockably interfits over the tubular guideway 28. The reset button 22 of rod-like construction is slideably mounted within the guide 28 and extends into the interior of the circuit breaker so as to pass through the circular opening 32 in the central planar portion 30 of the support for the undervoltage trip device.

The reset mechanism of the trip control device includes a sheet metal accelerator plate 80 pivotably mounted on a pin 82 extending between the depending

flanges

42, 44 of the support so that the free end of the plate underlies the aperture 32 and is engaged by the reset button 22. A flat sheet metal resetting lever 84 is also mounted on the pin 82 for pivotable movement and includes a first uppermost leg portion 86 which extends upwardly from the pin 82 for engagement by its free end with the guide plate 68. A second leg portion 88 of the resetting lever 84 extends downwardly at an angle slightly greater than 90 relative to the first leg portion and is pivotably connected by pin 90 at its end to a spaced actuating lever 92 having an elongated slot 94 therein through which passes the mounting pin 82. The flat sheet actuator lever 92 is disposed so as to be contacted by the free end of the accelerator plate 80 at the end 96 of the actuator remote from the elongated slot 94. The opposite end of the actuator lever, that is, the end adjacent the elongated slot 94 and remote from the pin 90 is provided with a drive dog 98 adapted to contact the free corner 56 of the triangular tripping lever 46 to effect counterclockwise pivotable movement of the tripping lever toward its tripping position.

In FIG. 4 the parts are shown in the positions which they occupy during normal operation of the circuit breaker. In this condition the solenoid plunger 66 is held in its retracted or seated position within the solenoid 62 while it is energized by the operating referenced voltage. The slide member 52 and its associated elongated tripping plunger portion 54 is held in its retracted position by the biasing action of the trip return spring 76 and the tripping lever 46 is positioned so that the free corner 56 thereof bears against the dog 98 of the actuating lever 92. Additionally in this condition the reset button 22 rests on accelerator plate 80 and tends to hold the leg 86 of reset lever 84 against guide plate 68.

If the voltage applied to the solenoid decreases a predetermined amount, such as to a level of about 60 percent of its referenced voltage, the plunger 66 will fall out, that is, will be driven outwardly from its seated position by the driving action of thedrive spring 70. The guide plate 68 will bear against the coaxially aligned slide member 52, driving the member 52 to the left as viewed in FIG. 4 and simultaneously rotating the tripping lever 46 counterclockwise as viewed in FIG. 4 causing the tripping plunger 54 to operate against the trip bar 18 and'effect tripping of the circuit breaker. At the same time, the guide plate 68 drives the arm 86 of the reset lever 84 counterclockwise as viewed in FIG. 4 about its fixed pivot pin 82. The simultaneous pivotal movement of the tripping lever 46 and reset lever 84 elevates the actuator lever 92 as well as the accelerator plate 80 and reset button 22. As a result, the undervoltage trip control device 20 assumes the position shown in FIG. 5 when the circuit breaker is in its trip condition and the reset button indicates the tripped condition by its elevated position. Since the solenoid plunger drive spring will continue to urge the tripping plunger 54 toward its tripped position until the plunger 66 is reseated, movement of the manually operated handle 14 between its ON and OFF positions will be ineffective to close the contacts of the circuit breaker. Thus the operator is required to perform the positive act of pushing the reset button in order to reset or reseat the plunger prior to turning the manual handle 14 of the circuit breaker to its ON position.

The separate and distinct reset action required in the circuit breaker of the present invention can be effected by depressing the reset button 22 to drive the accelerator plate clockwise about its pivot pin 82 thereby simultaneously driving the free end 96 of the actuating lever 92 downwardly or clockwise as viewed in FIG. 5. As will be appreciated, the dog 98 on the end of the actuating lever 92 firmly engages the free corner 56 of the tripping lever 46 to assure that the tripping plunger 54 is held in its tripping position during the resetting operation. Additionally, the clockwise movement of the actuator lever 92 will impart clockwise movement to the resetting lever 84 causing the uppermost leg 86 thereof to bear against the guide plate 68 driving it rearwardly against the bias of its drive spring 70 toward its seated position. This will also load the slide member return spring 76 since the dog end 98 of the actuator lever 92 will continue to retain the tripping plunger 54 and pin 50 in their tripped position.

So long as the undervoltage condition persists, the solenoid will be ineffective in retaining the plunger 66 in its seated position and release of the reset button 22 will permit the plunger drive spring 70 to drivably return the plunger to its extended position. Once the undervoltage condition is corrected, the trip control unit 20 can be reset by depressing the reset button 22 to drive the plunger to its reset or reseated position and load the tripping plunger return spring 76. This condition of the device is shown in FIG. 6.

The correction of the undervoltage condition permits the solenoid to retain the plunger in its seated position so that the release of the reset button 22 permits clockwise movement of the tripping lever 46 as the slide member 52 is drawn to the right as viewed in FIG. 6 under the driving action of theloaded tripping plunger return spring 76. The withdrawal of the tripping plunger 54 will permit resetting of the trip bar 18 thereby enabling the operator to manually operate the ON/OFF handle 14 to the ON position.

It is an advantageous feature of the present invention that the separate reset button described herein will permit tripping of the circuit breaker from either an ON or OFF position with the solenoid energized. Thus, if the undervoltage trip control device is in the position shown in FIG.4 with the solenoid in an energized condition and the plunger 66 held in its seated position, an operator may trip the circuit breaker by simply depressing the reset button 22. Since the reset lever 84 is restrained against clockwise movement by the contact of its upper leg 86 with the guide plate 68, the actuator lever 92 will pivot about the pivotal connection so that the dog end 98 of the'actuator lever may travel clockwise bearing against the free corner 56 of the tripping lever 46 to move the tripping lever counterclockwise against the bias of the tripping plunger return spring 76. This in turn will drive the slide member 52 to the left as viewed in FIG. 4 until it reaches its tripping position and the mechanism assumes the position shown in FIG. 6. In this connection it will be noted that this positioning of the parts of the device is substantially the same as during the resetting operation. Thereafter, release of the reset button 22 will permit the slide member return spring 76 to return the tripping plunger 54 to its retracted position in substantially the same manner as it returns after a resetting operation.

As can be seen from the foregoing detailed description the undervoltage release device of the present invention advantageously prevents resetting of the device while an undervoltage condition persists or while the solenoid actuator is in a de-energized condition. Additionally, the device requires a separate and distinct resetting action not associated with the main ON/OFF handle of the circuit breaker, requiring the operator of the breaker to supply a said independent resetting force thereto. At the same time the independent undervoltage tripping device of the present invention prevents any attempt to defeat the undervoltage release function of the unit. An added feature of the device is its ability to permit the operator to trip the circuit breaker from an ON or OFF position with the solenoid energized and further permits an operator familiar with the device to detect a breaker trip condition by means of the position of the reset button. Further, as is evident from the drawing and description, all of these advantages are achieved within a device that is compact, efficient, simple and relatively trouble free.

As will be apparent to persons skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the teachings of the present invention.

I claim: 7

1. An electric circuit breaker comprising a casing, a handle extending through the casing for manually opening and closing the circuits controlled by the circuit breaker, a trip unit in the casing operable to effect automatic opening of said circuits, a trip control unit adjacent the trip unit for controlling the tripping operation of the trip unit including a tripping member movable toward a tripping position for tripping the trip unit, an automatic trip actuator movable between an electrically responsive seated position and a released position and operable upon movement toward its released position to cause movement of the tripping member toward its tripping position, said trip actuator in its released position being operative to prevent movement of the tripping member out of its tripping position, and a reset operator independent of the handle and movable between a reset position and an operating position and operative upon movement toward said operating position to urge the tripping member toward its tripping position and the actuator toward its seated position.

2. The circuit breaker of claim 1 wherein the trip control unit includes a solenoid operative upon energization to a predetermined level to retain the trip actuator in its seated position and actuator drive means effective upon a predetermined reduction in the level of said energization to drive the actuator out of its seated position toward its released position to trip the circuit breaker.

3. The circuit breaker of claim 1 wherein the reset operator includes a reset button operative upon actuation to prevent movement of the tripping member out of its tripping position and to drive the trip actuator into its seated position to effect resetting of the trip control unit.

4. The circuit breaker of claim 1 wherein the reset operator includes a reset button operative upon actuation to drive the tripping member toward its tripping position while the trip actuator is in its seated position.

5. The circuit breaker of claim 1 including actuator drive means operative on the trip actuator for driving the actuator toward its released position and tripping member drive means interconnecting the tripping member and the actuator for driving the tripping member out of its tripping position toward a retracted position upon movement of the actuator to its seated position.

6. The circuit breaker of claim I including a reset lever operatively connected with the reset operator and responsive to movement of the trip actuator toward its released position to change the position of the reset operator for indicating the tripped condition of the circuit breaker.

7. The circuit breaker of claim 1 including a reset lever in driving engagement with the trip actuator, an actuating lever interconnecting the reset operator with the reset lever' and the tripping member, and spring means biasing the tripping member toward the trip actuator, said actuating lever being operative to restrain movement of the tripping member out of its tripping position upon movement of the reset operator toward its operating position and to impart a driving force to the reset lever to cause the reset lever to drive the trip actuator toward its seated position against the bias of said spring means to effect resetting of the trip control unit.

8. The circuit breaker of claim 1 wherein the tripping member is in axial alignment with the trip actuator and is operable between a tripping position and a retracted position, said actuator being operative during movement toward its released position to drivably engage said tripping member and drive said member toward its tripping position, said unit including a tripping lever connected to said tripping member for driving said member toward its tripping position independently of said actuator.

9. The circuit breaker of claim 8 including an actuating lever operatively interconnecting the reset operator and the tripping lever for driving the tripping lever to effect tripping upon movement of the reset operator to its operating position.

10. The circuit breaker of claim 1 wherein the reset operator is a manually operated member protruding through the casing at a location spaced from the handle.

11. For use with an electric circuit breaker having an ON/OFF handle for opening and closing the circuits controlled by the circuit breaker and a trip unit for effecting automatic opening of said circuits, an electrically responsive trip control unit for controlling the tripping operation of the trip unit including a tripping member movable toward a tripping position for tripping the trip unit, an automatic trip actuator including a plunger movable between an electrically responsive seated position and a released position and operable upon movement toward its released position to cause movement of the tripping member toward its tripping position, said plunger in its released position being operative to prevent movement of the tripping'member out of its tripping position, and a reset operator independent of the handle and movable between a reset position and an operating position and operative upon movement toward said operating position to urge the tripping member toward its tripping position and the plunger toward its seated position.

12. The trip control unit of claim 11 wherein the automatic trip actuator includes drive means for driving the plunger toward its released position, and a solenoid operative on said plunger for retaining said plunger in its seated position against the driving action of said drive means, said solenoid being ineffective in retaining said plunger upon the occurrence of a predetermined drop in the voltage applied to the solenoid.

13. The trip control unit of claim 11 including a reset lever operatively connecting the plunger and the reset operator and a plunger drive spring for driving the plunger toward its released position, said reset lever being responsive to movement of the reset operator toward its operating position to drive the plunger toward its seated position against the bias of the plunger drive spring for resetting the trip control unit.

14. The trip control unit of claim 11 including a tripping lever connected to the tripping member for movement therewith, an actuating lever drivably connecting the tripping lever and the reset operator and a tripping member return spring biasing the tripping member toward the plunger, said actuating lever being responsive to movement of the reset operator toward its operating position to drive the tripping lever and tripping member away from the plunger against the bias of said return spring.

15. The trip control unit of claim 11 wherein the reset operator is a manually operated button accessable from the exterior of the circuit breaker and spaced from the ON/OFF handle.

Claims

6. The circuit breaker of claim 1 including a reset lever operatively connected with the reset operator and responsive to movement of the trip actuator toward its released position to change the position of the reset operator for indicating the tripped condition of the circuit breaker.

7. The circuit breaker of claim 1 including a reset lever in driving engagement with the trip actuator, an actuating lever interconnecting the reset operator with the reset lever and the tripping member, and spring means biasing the tripping member toward the trip actuator, said actuating lever being operative to restrain movement of the tripping member out of its tripping position upon movement of the reset operator toward its operating position and to impart a driving force to the reset lever to cause the reset lever to drive the trip actuator toward its seated position against the bias of said spring means to effect resetting of the trip control unit.

11. For use with an electric circuit breaker having an ON/OFF handle for opening and closing the circuits controlled by the circuit breaker and a trip unit for effecting automatic opening of said circuits, an electrically responsive trip control unit for controlling the tripping operation of the trip unit including a tripping member movable toward a tripping position for tripping the trip unit, an automatic trip actuator including a plunger movable between an electrically responsive seated position and a released position and operable upon movement toward its released position to cause movement of the tripping member toward its tripping position, said plunger in its released position being operative to prevent movement of the tripping member out of its tripping position, and a reset operator independent of the handle and movable between a reset position and an operating position and operative upon movement toward said operating position to urge the tripping member toward its tripping position and the plunger toward its seated position.