US3360751A

US3360751A - Circuit breaker undervoltage trip device with magnet resetting means

Info

Publication number: US3360751A
Application number: US499917A
Authority: US
Inventors: George E Gauthier; Charles L Jencks
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1965-10-21
Filing date: 1965-10-21
Publication date: 1967-12-26
Anticipated expiration: 1984-12-26

Description

Dec. 26, 1967 G. E. GAUTHlER ET AL 3,360,751

CIRCUIT BREAKER UNDERVOLTAGE TRIP DEVICE WITH Filed Oct, 2l, 1965 MAGNET RESETTING MEANS 2 Sheets-Sheet 1 INVENTORS 650/?65 56m/rma?, CHA R455 dfn/ms 15V/IMJ C417 ATTOR/VEY- DCC- 26, 1967 G. E. GAUTHIER ET Al.

CIRCUIT BREAKER UNDERVOLTAGE TRIP DEVICE WIT MAGNET RESETTING MEANS Filed Oct. 2l. 1965 2 Sheets-Sheet 2 mwww 35m mi w V 6 T N A S LM P. R 0 5H 66% Y B United States Patent O 3,360,751 ClRCUlT BREAKER UNDERVOLTAGE TRIP DE- VICE WITH MAGNET RESETTNG MEANS George E. Gauthier, Plaiuville, and' Charles L. Jeudis,

Avon, Conn., assignors to General Electric Company,

a corporation of New York Filed Oct. 21, 1965, Ser. No. 499,917 4 Claims. (Cl. 335-175) ABSTRACT F 'IIrliI DISCLOSURE An undervoltage tripping device for use with an electric circuit breaker, including a spring biased plunger which is normally latched against operation by a roller engaging a 'bevelled shoulder on the plunger; the roller is held in position by the combined force of the holding solenoid and a tension spring. When the holding force of the solenoid decreases, such as due to a drop in voltage, the tripping plunger cams the roller out of its path and causes tripping of the circuit breaker. When the tripping plunger is reset, the tension spring is permitted to act on the solenoid armature to return it to attracted position, ready for a subsequent operation.

The present invention relates to electrical circuit breakers, and more particularly, to electric circuit breaker assemblies loi the type including means for causing automatic opening of the breaker in response to predetermined conditions in the current passing therethrough and also auxiliary means for causing opening in response to other electrical conditions such as a change in the condition of a remote control circuit or a decrease in line voltage.

Electrical circuit breakers commonly have a housing and include manually operable mechanisms for operating relatively movable contacts thereof between open and closed circuit positions and current responsive means for causing automatic opening of the contacts upon the occurrence of certain predetermined conditions in the current passing through the circuit breaker. In certain installations, it is desirable that the circuit breaker also include auxiliary means for causing opening of the contacts of the circuit breaker upon other conditions such as in response to a predetermined drop in the voltage in the circuit.

It is an object of the present invention to provide a novel, extremely compact and highly eiiective auxiliary tripping device for use in association with an electrical circuit breaker.

It is also an object of this invention to provide such an auxiliary tripping device for an electrical circuit breaker that has buzz or chatter control means for the solenoid used therein.

It is a specific object of this invention to provide a novel, compact and highly eective undervoltage tripping device that is adjustable to operate rapidly and eiciently over a wide range of percentage of desired circuit voltage.

It hasv now :been found that the foregoing objects and other advantages can readily be attained in a tripping device for circuit breakers which includes a support for mounting on an associated circuit breaker and mounted on the support is a solenoid which reciprocally engages an armature actuator. A tripping plunger is slidably mounted on the support and is engaged and biased from a latched position to a tripped position for operating a trip unit of the associated circuit breaker, by compression spring means mounted on the support. Pivotably mounted on the support and engaged with the armature actuator for pivotal movement thereby is a latch member which includes rolling means engageable with the tripping ice plunger in the latched position of the plunger. The rolling means and plunger are contigured `for relatively free movement of the plunger relative to the rolling means upon pivoting ofthe latch member while spring means operating between the support and the latched mem-ber bias the latch member toward latching engagement with the tripping plunger in the latched position. A resetting lever pivotably mounted on the support is engageable with the tripping plunger for movement of the tripping plunger to the latched position.

In accordance with general construction, the electrical circuit breaker used herewith is a multi-pole, molded case type having at least two elongated chambers therein each containing parts with relatively movable contacts providing one current path or pole of the circuit breaker, and current responsive principal tripping means for causing automatic opening of all poles simultaneously. The principal tripping means includes a trip member which is movable to cause automatic opening of the contacts and which is operable by movement of the tripping plunger of the auxiliary tripping device to operate the circuit breaker.

The auxiliary tripping device may be installed in a cir* cuit breaker to provide automatic undervoltage tripping such as when a loss of power occurs or when there is a voltage dip of predetermined magnitude, More particularly, the auxiliary tripping device has a solenoid magnet with a moving armature affixed to a spring loaded latch for restraining a spring-biased tripping plunger in a latched position. When released, the plunger moves the circuit breaker trip unit to trip the circuit breaker. As long as the voltage connected to the solenoid is normal, the solenoid magnetic force and the spring force on the latch restrain the plunger from acting on the trip unit. If the voltage dips to a predetermined percentage of rates voltage, the solenoid magnetic force is reduced and the tripping plunger is unlatched to operate the tripping unit to trip the breaker. Unless the required voltage is restored to the solenoid, the Ibreaker will again be tripped if an attempt is made to close it. When normal voltage has been restored, manual closing lof the operating mechanism of the circuit breaker will rotate the resetting lever which moves the tripping plunger into engagement with the latch member and the armature is again positioned for magnetic engagement by the solenoid.

An auxiliary tripping device for use as an undervoltage tripping device is provided with a tension spring and a solenoid which both bias the latch member into the latched position. The tension spring acts to hold the latch member in the tripped position and also to rotate the latch member into this position. The latch member has a roller member engageable with a shoulder on the tripping plunger adapted to restrain the tripping plunger in the latched position but the force of the tension spring alone acting on the latch member is insuilicient to hold the rolling member in engagement with the shoulder oi the tripping plunger. Accordingly, the t-ripping plunger will be held in the latched position only when the latch member is subjected to the force of both the spring and the solenoid. When the force of the solenoid restraining the latch member is removed, the rolling member is forced to roll ofi the cam surfaced shoulder of the tripping member onto the main body portion thereof which causes rotation of the latch member and the tripping plunger is released for movement to the tripped position by the force of the helical compression spring. Thus by providing the rolling member on the latch member and the camsurfaced shoulder on the tripping plunger, it is unnecessary to have an independent means for moving the latch member from engagement with the tripping plunger when the force applied by the solenoid is reduced or removed.

The rotatable resetting lever has a portion on one side of its pivotal mounting engaged with the tripping plunger and other portion on the same side of the pivotal mounting engaged with the trip unit so that when the tripping plunger is released by the latched member, it eng-ages a portion of the resetting lever which is thereby rotated toward the trip unit which is actuated by engagement with a portion of the resetting lever. The auxiliary tripping device is moved to the latched position by engagement -of the operating mechanism of the circuit breaker with another portion of the resetting lever on the opposite side of the pivotal mounting whereby the resetting lever is rotated and the tripping plunger is moved to the latched position by engagement with an end portion of the resetting lever. When the tripping plunger has been moved to the latched position with the cam-surfaced shoulder in engagement with the rolling member, overtravel of the tripping plunger beyond this position merely causes the rolling member to roll on the tripping plunger until the tripping plunger is allowed to return to its normal latched position.

The invention will be more fully understood from the following detailed description and its scope will be pointed out in the appended claims.

In the drawings:

FIGURE 1 is al side elevational view of a circuit breaker assembly incorporating the auxiliary tripping device of this invention with the casing partially broken away to reveal internal construction;

FIGURE 2 is a fragmentary side elevational view of an enlarged scale of a portion of the circuit breaker assembly of FIGURE 1 showing the auxiliary tripping device and a portion of the circuit breaker component partially broken4 away and partially in section for clarity of illustration with parts thereof illustrated in the on position in solid line and in the olf position in phantom line;

FIGURE 3 is a fragmentary plan view of the Iauxiliary tripping device illustrated in -t-he tripped position and with parts ofthe circuit breaker component in section and in phantom line for clarity of illustration;

FIGURE 4 is a similar view with the device illustrated in the on or latched condition; and

FIGURE 5 is a fragmentary perspective View to an enlarged scale of the auxiliary tripping device.

Referring now in detail to the attached drawings, an undervoltage tripping device embodying the present invention is shown in FIGURE 1 in assembly with a circuit breaker having a generally rectangular insulating casing with a base and a cover I2. A stationary contact 14 in the base 10 is connected to a line terminal (not shown) mounted on the base 10 and a movable contact 16 is connected to a load terminal (not shown) also mounted on the base 18. The movable contact 16 is carried by a contact arm 18 which is pivotably supported on the base 10 by shaft 20 mounted thereon and is connected to Ia contact cross arm 22. In actuality, the circuit breaker illustratedis a three-pole circuit breaker with three elongated chambers or poles, each of which contains current carrying parts `and cont-acts similar to those described hereinbefore.

An operating mechanism (only partially illustrated) is also mounted on the base 10 for operating the contact cross arm 22 and the associated contact `arms 18 of the pole chambers between open and closed circuit positions by means of a manually operable handle 24. For general operation, the cross arm 22 is considered to be a part of the operating mechanism of the circuit breaker. The operating mechanism referred to includes a normally restrained but releasable member or cradle (not shown) which is adapted to be releasably held by a pivotable trip member 26 mounted in suitable latch means (not shown) carried by the trip unit generally designated by the numeral 28 and adapted to be released thereby upon the occurrence of predetermined current conditions. An exemplary electrical circuit breaker mechanism of the type described is shown and more fully described in United States Patent No. 3,155,803, granted on Nov. 3, 1964, to Kline and Powell, and assigned to the same assignee as the present invention. The trip unit 28 includes a boxlike insulating enclosure 30 and may be of `any suitable type having a trip member 26 which is movable to cause the breaker to trip. A trip unit of the type described is shown in United States Patent No. 3,116,388, granted on Dec. 3l, 1963, to C. F. Hobson, Ir., and assigned to the same assignee as the present invention.

For the purpose of initiating tripping operation of the trip unit 28 upon the occurrence of a predetermined decrease in voltage in a selected cir-cuit as the circuit breaker provides a current path through the stationary and moving

contacts

14 and 16 described above, there is incorporated an undervoltage tripping device embodying the present invention generally designated by the numeral 40; Referring particularly to FIGURES 2-5, the undervoltage tripping device 40 comprises a generally at sheet metal support frame or support generally designated by the numeral 42 and having upwardly extending bentover end or

side wall portions

44, 46, and 48. The side wall portion 44 abuts against a wall portion 50 of the trip unit 28 and is secured thereto by means of fastener 51 disposed in an aperture 53 therein. The frame 42 also has depending

leg portions

52 and 54, and a transverse support member 56 is attached to the depending leg portion 54 by suitable means such as rivet 57 and is supported in suitable notches 58 in the base 10.

A tripping plunger, generally designated by the numeral 60, is slidably supported in a suitable aperture (not shown) in the side wall portion 48 and in the aperture 61 in side wall portion 46 of the frame 42. The tripping plunger 60 has a body portion 62 and a trip actuating portion 64 of reduced cross section which extends through the aperture 61 land beyond the side wall portion 46. The shoulder 66 between the body portion 62 and the portion of reduced cross section 64 is provided with a cam surface inclined outwardly toward the body portion for a purpose to be described more fully hereinafter. Encircling the tripping plunger 60 is a helical compression spring 68 which is retained between the side wall portion 48 and a washer 70 fixed to the tripping plunger and providing a radially outwardly extending shoulder so that the spring 60 biases the tripping plunger 78V toward the trip unit 28.

For the purpose of releasably holding the tripping plunger 60 against movement toward the trip unit due to the biasing pressure of the compression spring 68, a latch member generally designated by the numeral 76 is pivotably supported on a shaft or pivot pin 78 which extends generally perpendicularly to the axis of the tripping plunger 60 and is rigidly mounted on base portion 43 of the frame 42. A solenoid 80 is also rigidly mounted on the base portion 43 by suitable means and has an actuating armature 82 reciprocally disposed in the core thereof. One end of the latch member 76 is pivotally connected to the actuating armature 82 by means of a pin 84 which is disposed in an aperture (not shown) in the latch member 76.

Constantly biasing the latch member 76 in a clockwise direction as viewed in FIGURE 4 is a helical tension spring 86 threadably mounted on one end to the threaded member or screw 88 which is disposed in an aperture (not shown) in the side wall 48. The pitch of the screw 88 is the same as the pitch of the helix of the tension spring 86 so that the length of the spring 86 may be adjusted by threading the spring S6 on the shank of the screw 88. The opposite end portion of the spring 86 is hooked into an aperture 90 in the latch member 76 between the pivot pin 78 and the pin 84 connecting the actuating armature 82 to the latch member 76 so that the spring 86 biases the latch member 76 toward the solenoid 80. The tension or biasing force acting on the latch member 76 may be adjusted by turning the screw 88 to release or take up a portion of the tension spring on the threaded shank of the screw 88. Thus, both the magnetic force of the solenoid acting on the armature 82 and the adjustable force of the tension spring 86 tend to move the latch member 76 toward the latched position illustrated in FIGURE 4.

The tripping plunger 60 is held in the latched position by a cylindrically-shaped roller member 94 mounted on a shaft or pin 92 extending normally to the pivotal plane of the body of the latch member 76 and is restrained from axial movement by lip portion 96 of the shaft member 92. The roller member 94 is positioned for engagement with the cam-surfaced shoulder 66 of the triping plunger 60 so that when the latch member 76 is held in the latched position by the magnetic force of the solenoid acting on the armature 35 and by the tension spring 86, the tripping plunger 60 is restrained from movement toward the tripping unit 28. The camsurtaced shoulder 66 is conligured to a suitable angle so that the roller member 94 is able to restrain the tripping plunger 60 from movement when the force of both the solenoid 80 and spring 86 act upon latch member 76.

When the voltage energizing the solenoid 80 falls below the predetermined percentage of the rated voltage, the holding force of the solenoid -80 on armature 82 decreases to the point where the force applied by compression spring 68 on the tripping plunger 60 is suicient to overcome the force of the tension spring 86 and the solenoid 80. The roller member 94 then rolls up the cam-surfaced shoulder 66 on the tripping plunger 60 so that the latch member 76 is rotated away from the latched position. The force of the tension spring 86 acting alone on latch member 76 is adjusted to be insucient to restrain the tripping plunger 60 from movement toward the tripped position illustrated in FIGURE 3 and to require a predetermined magnetic force. Accordingly, when the solenoid 80 decreases its holding force on the armature 82 past a predetermined point, the rolling member 94 rolls ol the cam-surfaced shoulder 66 onto the body portion 62 and allows the tripping plunger 60 to be moved by the force of compression spring 86 to the tripped position.

A resetting lever generally designated by the numeral 100 is provided to reset the undervoltage tripping device 40 into the latched position and to actuate the trip unit 28 when the tripping plunger 60 moves to the tripped position. The resetting lever 100 is mounted on the depending leg portion 52 of the frame 42 by means of a pivot pin 102 and has a bentover engaging portion 104 on one side of the pivot pin 102 which is slidably engaged with the cross arm 22 of the operating mechanism of the circuit breaker. On the other side of the pivot pin 102, the resetting lever 100 has a portion 105 engaged with the trip actuating portion 64 of the tripping plunger 60 and a portion 106 which engages a spring-biased tripping rod 107 slidably supported in an aperture 108 in the side wall 50 of the trip unit 28. The tripping rod 107 extends through the wall 50 of the trip unit 28 and is biased toward the trip actuating portion 64 by the spring 110 to engage the trip member 26. Thus, the tripping plunger 60 may actuate the tripping unit 28 by engaging the portion 105 of the resetting lever 100' to elect pivoting thereof so that the portion 106 moves into engagement with the tripping rod 107 which thereby is moved into engagement with the trip member 26 to trip the circuit breaker.

The undervoltage tripping device is reset to the latched position by movement of the cross arm 22 of the operating mechanism of the circuit breaker from the on position illustrated in solid line in FIGURE 2 to the oi position illustrated in phantom line. Movement of the contact arm 18 about shaft 20 causes the cross arm 22 to engage the portion 105 of the resetting lever 100 which is thereby rotated in a clockwise direction. This movement of the cross arm 22 which in turn causes the portion 106 thereof to move the tripping plunger 60 to the latched position where it is engaged by the roller member 94 on the latch member 76. If the circuit voltage is normal, the solenoid will magnetically engage the armature 84 and, in cooperation with the tension spring 86, will exert sufficient force to restrain the tripping plunger 60 in the latched position with the rolling member 92 of the latch member 76 engaged with the cam-surfaced shoulder 66 of the tripping plunger 60.

The solenoid -80 is provided with a buzz or chatter reducing or control member 120 similar to that described in Patent No. 3,117,257 issued to Richard S. Stone on Ian. 7, 1964. The drop-out voltage of the solenoid may be set to the desired percentage of rated voltage by the adjusting screw 88 and buzzing or chattering in the solenoid 80 at the selected voltage may be reduced by rotating the buzz control member 120. Thus, an undervoltage tripping device is provided that may be set to operate at a high percentage of rated voltage where buzzing and chattering frequently occur, and which may be easily and conveniently removed by adjusting the buzz control member 120. The reference voltage is supplied to the solenoid 80 by means of the wires 81.

Operation In FIGURES l, 4, and 5 the parts of tripping device 40 are shown in the position which they occupy during normal operation of the circuit breaker. In this position, the tripping plunger 60 is held in the latched position by the action of the magnetic eld produced by the solenoid 80 when energized by a reference Voltage of predetermined magnitude which holds the armature 82 and the latch member 76 in the latched position cooperating with the tension spring 86. In this position, the rolling member 94 is engaged with the cam-surfaced shoulder 66 of the tripping plunger 60, restraining the tripping plunger 60 from movement toward the trip unit 28. If the voltage applied to the solenoid 80 decreases a predetermined amount, the magnetic eld acting upon the armature 82 will be reduced sufliciently so that the latch member 76 will be pivoted from engagement with the tripping plunger 60 by the force of the helical compression spring 68 acting upon the cam-surfaced shoulder 66 acting on the roller member 94. As the latch member 76 is pivoted, the roller member 94 rolls over the camsurfaced shoulder 66 onto the body portion 62 of the tripping plunger 60, thus permitting the tripping plunger 60 to move toward the trip unit 28 and the trip actuating portion 64 to engage portion 106 of the resetting lever and thereby to pivot the resetting lever 100 in a counterclockwise direction as viewed in FIGURE 2. As the resetting lever 100 is moved in a counterclockwise direction, the portion 106 engages the tripping rod 107 which moves inwardly against the bias of the spring 110 and actuates the trip member 26, thereby initiating tripping action of the circuit breaker.

After the breaker has been tripped due to the actuation of the undervoltage tripping device 40, the circuit breaker may be reset by movement of the cross arm 22 of the operating mechanism of the circuit breaker through movement of the handle 24 to the olf position. As the cross arm 22 and the contact arm 18 rotate in a counterclockwise direction as seen in FIGURE 2 from the on position shown in solid line to the olf position illustrated in phantom line, the cross arm 22 engages the portion of the resetting lever 100 and pivots -it in a clockwise direction from the position illustrated in solid line to the position illustrated in phantom line in FIGURE 2. As the resetting lever 100 is pivoted, the portion 106 engages the trip actuating portion 64 of the tripping plunger 60 and the roller member 94 rolls on body portion 62 onto the cam-surfaced shoulder 66 and is free to roll on the trip actuating portion 64 when there is overtravel of the tripping plunger 60. If the reference voltage applied to the solenoid 80 is of a predetermined value, the armature 82 will be held by the `action of the solenoid 80 and the spring 86, and the latch member 76 will retain the tripping plunger 60 in the latched position ready for subsequent operation, and the handle 24 then may be turned to the on position.

If the handle 24 is moved to the on position before the voltage applied to the solenoid 80 has returned to the predetermined required value, the tripping plunger 60 again will trip the breaker in the manner described above because the cross arm 22 no longer restrains the resetting lever 100, and the torce of tension spring 86 and the reduced force of solenoid Si) are not suicient to retain rolling member 94 in engagement with the cam-surfaced shoulder 66 against the bias of helical compression spring 88.

It can be seen that the circuit breaker and undervoltage tripping device 4i) are both designed to cooperate in .such a way that the device 4? can be securely mounted within the insulating casing of the circuit breaker with `a minimum of fastening elements. v

Accordingly, there is provided by this invention an auxiliary tripping device which is novel, extremely compact and highly effective for use in association with an electrical circuit breaker. The auxiliary tripping device is provided with a buzz or chatter control means so that the solenoid may be adjusted to drop out at a wide range of predetermined percentage of rated voltage which may be effected by conveniently turning a screw to set the device at the desired dropout point. The use of the rolling member makes it unnecessary to have a biasing means to move the latch from engagement with the tripping plunger.

While we have disclosed only certain embodiments of the invention, it will be readily appreciated that many modiiications thereof may be made. We therefore intend by the appended claims to cover all such modifications as fall Within the true spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

il. A circuit breaker undervoltage trip device comprising:

(a) a support for mounting in an associated circuit breaker;

(b) a solenoid mounted on said support, said solenoid including a winding and a movable armature movable between attracted and a released position with respect to said winding;

(c) a tripping member mounted on said support, said tripping member being movable between latched and tripping positions;

(d) first spring means biasing said tripping member from said latched toward said tripping position for operating a trip member of said circuit breaker;

(e) latch means connected to said armature, said latch means having a latch portion engaging a portion of said tripping member when said latch means is in latching position and said tripping member is in said latched position and holding said tripping member in said latched position against the bias of said rst spring means;

(f) said portion of said tripping member acting on said latch portion of said latch means under the bias of said first spring means so as to urge said latch means out of the path of movement of said tripping means;

(g) second spring means acting on said latch means and biasing said latch means toward said latching position with a predetermined force when said latch means is in said latched position;

(h) said solenoid Winding when energized by `a predetermined voltage exerting a predetermined holding force on said armature in said attracted position;

(i) said predetermined force of said second spring means being insufficient to hold said latch means in said latching position against the bias of said irst spring means, but said predetermined force of said second spring means and said predetermined holding force of said solenoid together being sufficient to hold said latch means in said latching position;

(j) resetting means for resetting said tripping membei from said tripping position to said latched position;

(k) said second spring means acting on said armature to move said armature from said released to said attracted position when said tripping member is reset to said latched position.

2. A circuit breaker undervoltage trip device as set forth in claim 1 wherein said latch means comprises a member pivotally mounted on said support at a predetermined pivot point and connected to said armature at a point remote from said pivot point; said portion of said latch means engaging said tripping member being substantially closer to said pivot point than said point connected to said armature.

3. A circuit breaker undervoltage trip device as set forth in claim 1 wherein said latch portion of said latch means and said portion of said tripping member engaged by said latch portion comprise cam and cam follower means.

4. A circuit breaker undervoltage trip device `as set forth in claim '1 wherein said latch portion of said latch means comprises a roller member and said portion of said tripping member engaged by said latch portion comprises a cam surface.

References Cited UNITED STATES PATENTS 3,174,010 3/1965 Bottonari et al. 335-175 X 3,293,577 12/1966 lKiesel et al. a 335-20 BERNARD A. GILHEANY, Primary Examinar.

R. N. ENVALL, IR., Assistant Examiner.

Claims

1. A CIRCUIT BREAKER UNDERVOLTAGE TRIP DEVICE COMPRISING: (A) A SUPPORT FOR MOUNTING IN AN ASSOCIATED CIRCUIT BREAKER; (B) A SOLENOID MOUNTED ON SAID SUPPORT, SAID SOLENOID INCLUDING A WINDING AND A MOVABLE ARMATURE MOVABLE BETWEEN ATTRACTED AND A RELEASED POSITION WITH RESPECT TO SAID WINDING; (C) A TRIPPING MEMBER MOUNTED ON SAID SUPPORT, SAID TRIPPING MEMBER BEING MOVABLE BETWEEN LATCHED AND TRIPPING POSITIONS; (D) FIRST SPRING MEANS BIASING SAID TRIPPING MEMBER FROM SAID LATCHED TOWARD SAID TRIPPING POSITION FOR OPERATING A TRIP MEMBER OF SAID CIRCUIT BREAKER; (E) LATCH MEANS CONNECTED TO SAID ARMATURE, SAID LATCH MEANS HAVING A LATCH PORTION ENGAGING A PORTION OF SAID TRIPPING MEMBER WHEN SAID LATCH MEANS IS IN LATCHING POSITION AND SAID TRIPPING MEMBER IS IN SAID LATCHED POSITION AND HOLDING SAID TRIPPING MEMBER IN SAID LATCHED POSITION AGAINST THE BIAS OF SAID FIRST SPRING MEANS; (F) SAID PORTION OF SAID TRIPPING MEMBER ACTING ON SAID LATCH PORTION OF SAID LATCH MEANS UNDER THE BIAS OF SAID FIRST SPRING MEANS SO AS TO URGE SAID LATCH MEANS OUT OF THE PATH OF MOVEMENT OF SAID TRIPPING MEANS; (G) SECOND SPRING MEANS ACTING ON SAID LATCH MEANS AND BIASING SAID LATCH MEANS TOWARD SAID LATCHING POSITION WITH A PREDETERMINED FORCE WHEN SAID LATCH MEANS IS IN SAID LATCHED POSITION; (H) SAID SOLENOID WINDING WHEN ENERGIZED BY A PREDETERMINED VOLTAGE EXERTING A PREDETERMINED HOLDING FORCE ON SAID ARMATURE IN SAID ATTRACTED POSITION; (I) SAID PREDETERMINED FORCE OF SAID SECOND SPRING MEANS BEING INSUFFICIENT TO HOLD SAID LATCH MEANS IN SAID LATCHING POSITION AGAINST THE BIAS OF SAID FIRST SPRING MEANS, BUT SAID PREDETERMINED FORCE OF SAID SECOND SPRING MEANS AND SAID PREDETERMINED HOLDING FORCE OF SAID SOLENOID TOGETHER BEING SUFFICIENT TO HOLD SAID LATCH MEANS IN SAID LATCHING POSITION; (J) RESETTING MEANS FOR RESETTING SAID TRIPPING MEMBER FROM SAID TRIPPING POSITION TO SAID LATCHED POSITION; (K) SAID SECOND SPRING MEANS ACTING ON SAID ARMATURE TO MOVE SAID ARMATURE FROM SAID RELEASED TO SAID ATTRACTED POSITION WHEN SAID TRIPPING MEMBER IS RESET TO SAID LATCHED POSITION.