US3012238A - Circuit breaker - Google Patents

Description

Dec. 5, 1961 w. H. NASH ErAL 3,012,238

CIRCUIT BREAKER Filed Aug. 3, 1959 3 Sheets-Sheet 1 B ,a 45 JM LUM ittorngy Dec. 5, 1961 w. H. NASH ETAL 3,012,238

CIRCUIT BREAKER Filed Aug. 3, 1959 3 Sheets-Sheet 2 wtzorfiay/ Dec. 5, 1961 w. H. NASH ErAL CIRCUIT BREAKER 3 Sheets-Sheet 3 Filed Aug. 3, 1959 ttormyf United States Patent f! 3,912,238 CIRCUIT BREAKER William H. Nash and Edward W. Kaminsky, South Milwaukee, Wis., assignors to McGraw-Edison Company, Milwaukee, Wis., a corporation of Delaware Filed Aug. 3, 1959, Ser. No. 831,424 11 Claims. .(Cl. 340-253) This invention relates to circuit breakers and more particularly to circuit breakers which have particular but not exclusive application to the protection of electrical apparatus such as transformers.

Distribution class transformers are often provided with circuit breakers which open the secondary circuit upon the occurrence of a short circuit across the secondary leads or when long, continued overloads heat the transformer to a point where there is a likelihood that its insulation will fail. For'this purpose, therefore, circuit breakers of this type are provided with thermal and overcurrent responsive elements adapted to open the circuit breaker contacts upon the occurrence of such overloads. In addition, such devices may also include a signal light assembly for giving an external indication that the device being protected has been subjected to an overload.

It is an object of the invention to provide a new and improved circuit breaker for use in an oil immersed transformer which is responsive both to the temperature of the transformer oil and to short circuit currents in the secondary leads. j

` It is another object of the invention to provide a circuit breaker having a new and improved operating mechanism. It is a further object of the invention to provide an overload responsive circuit breaker with new and improved means for adjusting its minimum trip current.

It is a still further object of the invention to provide a circuit breaker for use with a distribution type transformer which has a new and improved signal light assembly.

Yet another object of the invention'is to provide a new and improved contact assembly for such circuit breakers.

These and other objects of the invention will become apparent from the detailed description of the invention taken in view of the accompanying drawings in which:

FIG. l is a vertical elevational view of the circuit 4breaker according to the instant invention with parts broken away;

FIG. 2 is a top plan view of the circuit breaker shown in FIG. l;

FIG. 3 shows a circuit breaker operating mechanism when it is unlatched and the main contacts are open;

FIG. 4 shows the circuit breaker operating mechanism when it is latched and the main contacts are open;

FIG. 5 Shows the circuit breaker operating mechanism when it is latched and the main contacts are closed;

FIG. 6 shows a front view of the circuit breaker operating 'mechanism lwhen it is in the position shown in v FIG. 5;

FIG. 7 shows the signal light operating assembly;

FIG. 8 shows a portion of the circuit breaker operating mechanism;

FIG. 9 is a partial sectional view 9-9 of FIG. 2; and

FIG. 10 is a partial sectional view 10-10 of FIG. 9.

The invention comprises a 'two-pole automatictripfree circuit breaker mounted on a suitable base 10 of molded .insulating material. Each pole includes a con- Vtact assembly 12 and an overcurrent responsive assembly 14. A common operating and latch assembly 16 holds each of the contact assemblies 12 in closed position and is operable to release said contact assemblies upon the taken along lines taken along lines actuation of either of the overcurrent responsive assemblies 14. Prior to the release of the operating and latch assembly 16 and the consequent opening of the contact assembly 12, the overcurrent responsive assembly 14 actuates a signal light mechanism 18 so that an external signal is given that the system or device being protected has been subject to an overload. An overcurrent responsive quick adjusting means 20 is provided so that the magnitude of the overcurrent necessary to cause tripping may be adjusted from a remote point.

Each of the contact assemblies 12 includes a movable contact member 22 and a cooperating fixed contact 24 which is mounted on the base 10. A U-shaped metallic frame member 26 is rigidly secured to the base 10 and has a transverse pivot pin 27 mounted near its lower extremity for pivotally supporting a contact carrier member 28 formed of a suitable molded insulating material and which carries each of the movable contact members 22 in a contact shell 290 disposed at each of the opposite ends of a transverse connecting portion 29 so that the movable contact members 22 are operated in unison.

As shown in FIGS. 9 and 10 each shell'290 has a central cavity 292 for receiving the movable contact assembly which includes a compression spring 31 for resiliently urging movable contact 22 into engagement with fixed contact 24 and a self locking spring retaining clip 30 having an inverted U-shaped central portion 3014 and an upwardly extending locking tip 302 integral with the end of each of the legs of said central portion. -In assembly, the contact tips 302 are forced into cavity 292 between inwardly extending shoulders 293 whereupon the resilience of clip 30 forces said tips into a locked position beneath shoulders 293. As can be seen in FIG. 9, when the movable contact assembly is in open position, a conductive member 91 secured to movable contact 22 engages the upper end of a slot 294 formed in the upper end of shell 298 to prevent spring 31 from forcing movable contact 22 out of cavity 292.

Each lof the overcurrent responsive assemblies 14 includes a pair of parallel bimetallic elements 32 and 33 (as seen in FIG. 2) and each element has one end aixed to the rear of base 10 by rivets 34, and each pair is electrically and mechanically connected at their free ends by a conductive metallic member 36. An upwardly extending angular insulating link 38 is rigidly connected to each of the conductive members 36 and each carries a rearwardly extending trip bracket 39 at its upper end. An adjusting and trip pin 40 is threadably received in the free end of each trip bracket 39 and each engages the upper surface of a latch plate 42 which is pivotally mounted at 43 on the frame 26. The latch plate 42 has a depressed central portion 45 which carries an L-shaped latch member 46.

Referring now in particular to FIGS. 3, 4, 5 and 6, the operating and latch assembly 16 is shown to include an inverted U-shaped operating member 50 having an oiset transverse connecting portion 51 at its upper end and whose lower ends 52 are pivotally received in suitable recesses 53 formedl in the base member 10.

A latching mechanism 55 is disposed between the legs of operating member 50 and includes a latch arm 57 which carries a latch tip 58 at one end and which is pivoted at its other end .around a fixed axis by means of a transverse pin 69 extending between the upright portions of frame 26. An arc shaped link 62 is pivotally connected at one end to latch arm 57 and at its other end to an inverted L-shaped holding element 64 which is pivotally mounted on a transverse pin 65 fixed in frame 26. Holding element 64 is connected to movable contact carrier 28 by means of a toggle linkage 67 comprising a pair of parallel upper toggle links 68 which are pivotally connected at 69 to the midpoint of holding element 64 and a lower .toggle link 71 pivotally connected to movabe contact 3 carrier 28 at 72. The other ends of these toggle links are pivotally connected together by a knee pin 74. A pair of parallel overcenter springs 76 are connected at one end to knee pin 74 and at their other end to the transverse portion 51 of operating member 50.

Operation of the latching mechanism will now be discussed in relation to FIGS. 1 3, 4, 5 and 6. As shown in FIG. l, the arm 78 of an operating crank 79 is adapted to be rotated in the plane of the drawing Vby an operating handle (not shown) disposed on the exterior of the apparatus being protected. Arm 78 is connected to operating member 50 by means of an operating rod 80 and an operating link 82 which threadably receives the lower end of operating rod 80 in one end and which is pivotally connected at its other end to the transverse connecting portion 51 by means of a U-shaped bracket 83 and a pin 84.

Referring now to FIG. 3, which shows the operating mechanism in its unlatched position with the circuit breaker contacts open, it can be seen that the righthand edge ofthe transverse portion 51 of operating member 50 bears against the upper edge of holding element 64. In order to operate the mechanism to the latched position Ishown in FIG. 4, arm 78 is rotated in a clockwise direction thereby pivoting the operating member 50 in a clockwise direction within recesses 53. As operating member 50 pivots, its transverse portion 51 forces holding element 64 to rotate about pin 65 so that its upper end is Vmoved downwardly and to the right as viewed in FIGS. 3 and 4. This movement of holding element 64 is transmitted to latch arm 57 by link 62 whereby said latch arm is rotated in a clockwise direction around pivot pin 60. As latch arm 57 rotates, latch tip 58 engages latch 46 torotate latch plate 42 in a counterclockwise direction around its pivot point 43. After latch tip 58 has cleared latch 46, the latter is returned to its position shown in FIG. 4 by a signal light biasing, spring 86, shown in FIGS. 1 and 7, and an adjusting spring 87 shown in FIG. 2. The mannerV in whichv these springs bias latch plate 42 will be more clearly indicated when these portions of the device are discussed in detail. Thereturn of latch plate 42 toV its position shown in FIG. 4 secures the latching assembly in a latched position with the contacts open.

In order to close the contact assembly 12 after the latching assembly has Ibeen made rigid, operating arm 78 is rotated in a counterclockwise direction to pivot operating member 50 in a counterclockwise direction in recesses S3. As operating member 50 rotates the upper ends of overcenter springs 76 are moved to the left as viewed in FIG. 4,'by transverse portion S1, while the lower ends of said springs momentarily remain stationary. Because the upper ends of overcenter springs 76 are rotating in an are whose radius is longer than the length of e the springs themselves, they will be extended as a result of this rotation so that energy will be availableto rapidly close the contacts and to separate them rapidly upon tripping. When the line of action of springs 76 pass the upper pivot Ypoint 69 of toggle link 68, they will become overcentered causing pin 74 to snap from its position shown in FIG. 4 to the position shown in FIG. 5. This brings lower link 71'into toggle with the upper link 68 which snaps movable contact carrier 28 in a counterclockwise direction about pivot pin 27 thereby closing movable contact 22 as shown in FIG. 5. It will be appreciated 4that because the movement of pin 74 to the right somewhat shortens overcenter springs 76, a portion of their stored energy is utilized in the closing of the contact assembly 12.

l The operating sequence during manual opening of the main contacts is thev directropposite of the closing operation just explained; Here the operating arm 78 is pivoted in a clockwise direction thereby moving the upper end of operating member 50 to the right as viewed'in 4, tion shown in FIG. 4. Latch arm S7, however, will remain latched as shown in FIG. 4.

Referring now to FIGS. l and 2, the electrical current path through each pole of the device is from a first conductive member secured to xed contact 24; through the xed and movable contacts 24 and 22; through the second conductive member 91 secured to movable contact 22; through a flexible conductive member 92 secured at the one end to conductive member 91 and at its other end to a third conductive member 93 affixed to bimetallic element 32; through conductive member 36 and bimetallic member 33 and then out through a fourth conductive member 95 connected to second bimetallc element 33. If the device is used to protect a distribution transformer, it is normally mounted below the oil level by means of a bracket member 96 secured to the underside of base member 10. As a result, the bimetallic elements 32 and 33 are subjected to heating as `a result of the ow of load current therethrough and due to the ternperature of the ambient oil. Should a high magnitude overcurrent heat the bimetallic elements as a result of the 12R losses therein, or should the bimetallic elements be heated by a low magnitude overcurrent in the transformer windings which heats the surrounding oil, or should a combination of both cause the lefthand end of the bimetallic elements, 32 as viewed in FIG. 1, to deect downardly, the consequent downward movement of trip pin 40 will rotate latch plate 42 in a counterclockwise direction. As a result, latch arm 57 is released so that overcenter springs 76 are free to contract, moving knee pin 74 from its position shown in FIG.`5 to its position in FIG. 3 and thereby breaking the toggle linkage 67. This rotates the movable contact carrier 28 in a clockwise direction from its position shown in FIG. 5 to its position shown in FIG. 3 whereby the main contacts are opened and the circuit is interrupted. The movement of knee pin 74 also rotates holding elemnt 64 in aclockwise direction which motion is transmitted to latch arm 57 by link 62 whereby it is also rotated in a counterclockwise direction. It can be seen therefore Vthat this tripping action returns each of the members of the operating assembly 16 from their positions shown in FIG. 5 to theirr original positions shown in FIG. 3. Y

The amount of downard deflection of the bimetallic elements and hence, the magnitude ofthe overcurrent necessary to trip the device may be adjusted by varying the initial rotation of latch plate 42 through the agency of the threaded trip pins 40. It can be seen that by suitably turning trip pins 40 so that latch plate 42 is allowed to be rotated through a slight clockwise angle as viewed in FIG. 1 under the influence of biasing springs-86 and 87, the contact between latch tip 58 and latch 48 will be increased and hence thev downward deection of bimetallic elements 32 and 33 necesary to cause tripping, will be increased. Conversely, `by turning adjustable trip pins 40 to increase the initial counterclockwise rotation of latch plate 42, the deflection of the bimetallic elements, and hence the amount of load current necessary to cause tripping will beY decreased. Y

In addition, overcurrent responsive adjusting assembly 20 allows the rapid adjustment from a remote point of sides of pin 99 which are selectively registrable with one.

pair of four corresponding indentations 105Y in V,frame member and which are disposed in spaced apart relation at 90. Biasing spring 87 extends between tabs 107 and 109 extending upwardly from adjusting plate 98 and trip plate 42 respectively. It can be seen, therefore, that counterclockwise rotation of adjusting plate 98 as viewed in FIG.- 2, will move stop 101 into engagement with ear 103 `and indentations 104 into register with the corresponding depressions 105 in frame member 100 whereupon they are seated by a spring 106 surrounding the lower end of pin 99, as seen in FIG. 8. This moves tab 107 from its position shown by full lines in FIG. 8 to the position shown by dashed lines so that adjusting spring 87 is extended to place an initial force on latch plate 42 in opposition to that exerted by bimetallic elements 32 and 33. As a result, a greater magnitude of overload current will be necessary to cause tripping of the device. Such rotation of adjusting plate 98 is accomplished by moving an adjusting link 108 upwardly, as viewed in FIG. 2, by means of an operating handle (not shown) on the exterior of the device being protected. If, on the other hand, adjusting plate 98 is rotated in an opposite direction until stop 192 is engaged, spring 87 will be relaxed as shown by the full lines in FIG. 8 thereby decreasing the magnitude of the overload current necessary to trip the device.

The signal light assembly 18 as shown in FIGS. 1, 2 and 7 is provided to give an external indication that the device being protected has been overloaded and includes a movable contact and latch member 110 and a stationary contact member 111and normally is adapted to be tripped upon the occurrence of an overload current less than that necessary to cause tripping ofl the circuit breaker itself.` Suitable insulation 112 electrically insulates stationary contact member 111 from the metallic components of the circuit breakers frame. Movable contact 110 is rotatably mounted at 113 on an adjusting bar 114 and includes aV latch tip 116 adapted to engage one end of a trip bar 117 which is mounted for rotation at 118 on frame member 119 and carries a roller 120 at its other end which rides on the upper surface of latch plate 42. Adjusting bar 114 is pivotally mounted at one end on frame 110 and isvthreadably engaged at its other end by adjusting screw 122 which extends through a suitable opening in frame member 124 and is surrounded by a biasing spring 126 disposed between frame member 124 and adjusting bar 114 so that the lefthand end of said adjusting bar is urged downwardly as viewed in FIG. 7. It can be seen that by suitable adjustment of screw 122 pivot pin 113 of Contact member 110 may be moved downwardly or upwardly to increase or decrease the overlap between latch tip 116 and trip bar 117 so that the amount of rotation of trip bar 117 necessary to release said contact member is correspondingly varied.

'It will be recalled that heating of the bimetallic elements will cause trip plate 42 to be rotated in a counterclockwise direction about its pivot point 43. This will in turn rotate latch bar 117 in a clockwise direction about its pivot point 118 tending to release latch tip 115 and allow movable contact 110 to rotate in a clockwise direction under the inuence of biasing spring S6 which extends between ear 127 onvlatch bar 117-and ear 128 on movable contact 110. Such rotation will cause contact tip 130 of movable contact 110,` whichis grounded to the frame through its pivotal connection 113, adjusting bar 1.14 and pivot 121, to engage stationary contact 111 and complete the circuit through current transformer 132 and signal light 133 whereby the latter is energized.

Signal light assembly 18 is also provided with a resetting bar 135 having a first transversely projecting portion 137 which engages a resetting 4finger 138 on movablecontact 110 and a second transversely extendingportion 140 which engages operating member 50. y n

The signal light assembly will normally be set to trip upon the occurrence of a smaller `overload current necessary to trip the breaker itself. In operation, therefore, a predetermined overload current will trip the signal light assembly thereby energizing the signal light, while the main contacts remain closed. Should the overload current thereafter increase a sufficient amount, the main contacts will then be tripped open.

If the signal light assembly 18 has been tripped by an overload current which is insutlicient to trip the circuit breaker itself, it can be reset by rotating the end 78 of operating handle 79 in a counterclockwise direction as seen in FIG. 1 thereby forcing operating member 50 in a counterclockwise direction from its position shown by dashed lines in FIG. 7 to the position shown by full lines. This shifts resetting bar to the left as viewed in FIG. 7 so that projection 137 will engage resetting linger 138 to rotate movable contact 110 in a counterclockwise direction until latch tip 116 engages the end of trip bar 117. Movement of resetting bar 135 is opposed by a biasing spring 142 which extends between projection 137 and frame member 124. It can be seen that in the resetting of signal light assembly 18 operating member 50 is moved in the opposite direction from that during the manual tripping operation previously described, so that resetting of the signal light assembly cannot cause accidental tripping of the device. In the event that the signal light assembly has been tripped by an overload current which is also suiicient to trip the circuit breaker itself, the signal light assembly will be reset when the main contact assembly 12 is closed by the action of operating handle 79 in moving the latching mechanism 55 from its position shown in FIG. 4 to its position shown in FIG. 5.

Biasing spring 142 performs the additional function of a signal light assembly test contact. In order to determine whether signal light 133 is operable, operating handle 78 is rotated in the same manner as in the resetting operation of the signal light assembly thereby moving operating membert) from its position shown by dashed lines to that shown by full lines in FIG. 7. This brings the end of biasing spring 142 into engagement with stationary contact 128. Since biasing spring 142 is grounded to the frame, the circuit through signal light 133 is thus completed and if operating properly, it will light.

While only a single embodiment of the invention is shown and described, it is intended to cover in the appended claims all modifications which fall Within the scope thereof.

We claim:

l. A circuit interruptor for protecting an electrical system comprising, a base, switch means, operating means movable to close said switch means, electrical signal means' having a xed and a movable contact mounted on said base, latch means connected to said operating means for latching said movable contact in open position upon movement of said operating means in a switch closing direction, condition responsive means in circuit with said system and operable upon the occurrence of a predetermined circuit condition to open said switch means and unlatch said movable contact allowing it to engage said hxed contact, and biasing spring means connected to said operating means for opposing the latching of said movable contact, said spring means being in circuit with said movable contact and engageable with said fixed contact to complete the circuit through said signal means upon movement of said operating means in a switch closing direction whereby said signal means may be tested without opening said switch means.

2.r A circuit interruptor for protecting an electrical system comprising, a base, switch means, operating means movable to close said switch means, electrical signal means having a stationary contact and a movable contact rotatably mounted on said base and including a latch portion a'n'd a resetting arm integral therewith, a latching member for holding said movable contact in open position, spring means biasing said movable contact toward engagement with said rixed contact, a resetting member connecting said operating means with said resetting arm so that said movable contact is rotated toward latched position when said operating means is moved in a switch closing direction, condition responsive means 1n circuit amazes 7 with said system and operable upon the occurrence of a predetermined circuit condition to Vopen said switch means and to release said movable contact member.

3. A circuit interrupter for protecting an electrical systern comprising, a'base, switch means, a collapsible main latch means for holding said switch means in a closed position, operating means movable in a first direction to place said latch means in rigid condition and also movable in a second direction when said latch means is rigid to close said switch means, electrical signal means having a stationary contact and a movable contact rotatably mounted on said base and including a latch portion and a resetting arm integral therewith, a latching member for holding said movable contact in open position, spring means biasing said movable Contact toward engagement with said fixed contact, a resetting member connecting said operating means with said resettingarm so that said movable contact is rotated toward latched position when said operating means is moved in its second direction,

n condition responsive means in circuit with said system and operable upon the occurrence of a predetermined circuit condition to release said main latch means and allow said switch means to open and also operable to release said movable contact and allow said movable contact to close, and biasing spring means connected to said resetting member for opposing the movement thereof by said operating means, said spring means being in electrical circuit with said movable contact and engageable With said fixed contact to complete the circuit through said signal means upon movement of said operating means in its second direction so that said signal means may be tested without opening said switch means.

4. AV circuit interrupter for protecting an electrica] system comprising, a base, switch means, a collapsible main latch means including a first pivotal latching member for holding said switch means in a closed position, operating means movable in a first direction to place said main latch means in rigid condition and movable in a second direction when said main latch means is rigid to close said switch means, electrical signal means having a stationary contact and a movable contact rotatably mounted on said base and including a latch portion and a resetting arm integral therewith, a second pivotal latching member for holding said movable contact in open position and having one end engaging said first pivotal latching member, spring means extending between said movable contact and the other end of said second latching means for biasing said movable contact toward engagement with said fixed contact and for biasing said first and second pivotal latching members toward latched position, a resetting member connectingY A circuit interrupter for protecting an electrical' system comprising, a base, switch means, a collapsible main latch means including a first pivotal latching member for holding said switch means in a closed position, operating means movable in a first direction to place said main latch means in rigid condition and movable in a second directionY when said main latch means is rigid to close said switch means, electrical signal means having a stationary contact and a movable contact rotatably mounted on said base and including a latch portion, a second pivotal latchingl member for holding said Ymovable contact in open position and lhaving one end engaging said first pivotal latching member, spring means extending between said movable contact and the other endof said second latching means for biasing saidl movthe occurrence of a predetermined circuit condition to rotate said first and second latching members against the action of said biasing spring means to open said switch means and release said movable contact.

6. A circuit interrupter for protecting an electrical system the combination of, a base, switch means, a collapsible main latch means for holding said switch means in a closed position and including a first pivotal latching member and a latch arm engageable with said latch member on one side of its pivotal axis, operating means movable to place said main latch means in rigid condition and to close said switch means, electrical signal means having a stationary contact and a movable contact rotatably mounted on said base and including a latch portion, a second pivotal latching member engageable on one side of its pivotal axis with said movable contact for holding the same in open position, said first and second latching members being in engagement on the other sides of their pivotal axes so that they will rotate in unison in an nnlatching direction, spring means extending between said movable contact and said second latching means on the side of its pivotal axis that engages` said movable contact for biasing said movable contact toward engagement with said fixed contact and for biasing said first and second pivotal latching members toward latched position, and bimetallic condition responsive means engaging said first pivotal latch member and in circuit with said system and operable upon the occurrence of a predetermined circuit condition to rotate said firstand second latching members against the action of said biasing spring means to open said switch means and release said movable contact.

7. A circuit interrupter comprising, a base, switch means, a collapsible main latch means including a first pivotal latching member for holding said switch means in a closed position, operating means movable in a first direction to place said main latch means in rigid condition and movable in a second direction when said main latch means is rigid to close said switch means, electrical signal means having a stationary contact and a movable contact rotatably mounted on said base and including a latch portion and a resetting arm integral therewith, a second pivotal latching member for holding said movable contact open and having one end engaging said first pivotallatching member, spring means extending between said movable contact and the other end of said second latching means for biasing said movable Ycontact toward engagement with said fixed contact and for biasing said first and second pivotal latching members toward latched` position, a resetting member connecting said operating means with said resetting arm so that said movable contact is rotated toward a latched position when said operating means is moved in its second direction, condition responsive means inA circuit with said system and operable upon the occurrence of a predetermined circuit condition to rotate said first and second latching members against the action of said biasing spring means and to open said switch means and release'said movable contact, and biasing spring means connected to said resetting member and to said base and in electrical circuit with said fixed Contact for opposing the movement thereof by said operating means, the end of said spring means connected to said resetting member being disposed adjacent said fixed'contact so that said spring means is stretched to engage said fixed contact and complete the circuit through said signal means upon movement of said operating means in its second direction.

8. A circuit interrupter having a base, movable contact means, holding means pivotally mounted on said base, overcenter means connecting said movable contact means and holding means, operating means .'pivotally mounted on said base for movement in a iirst and a second direction, movement of said operating means in its lirst direction when said holding means is in an initial position electing movement thereof to la iinal position, a latch arm pivotally mounted on said base and having a latch portion, latch means mounted on said base in the path of pivotal movement of said latch portion for engagement therewith, a link interconnecting said holding means and said latch arm so that said latch portion is pivoted into engagement with said latch means when said holding means is moved to its final position, said overcenter means being moved overcenter into rigid condition to close said movable contact means upon movement of said operating member in its second direction following the engagement of said latch member, said overcenter means being moved overcenter into relaxed condition to open said movable contact upon movement of said operating member to said second position when said movable contact is closed.

9. A circuit interrupter comprising a base, movable contact means, a holding element mounted at one end on said base, an operating member pivotally mounted on said base and having a portion slidably engaging said holding element near its free end when said holding element and said operating member are in an initial position so that when the latter is pivoted in a first direction said holding element will be rotated toward a tinal position, toggle linkage means connected at one end to said movable contact means and at the other end to said holding element at a point intermediate its ends, said toggle linkage including overcenter spring means connected to the free end of said operating member, a latch arm pivotally mounted at one end on said base and having a latch tip near its other end, latch means disposed in the path of pivotal movement of -said latch tip and engageable therewith, a link interconnecting the free end of said operating member to said latch arm at a point intermediate is ends so that said latch arm is pivoted into engaged position when the operating member is moved to said second position, said overcenter spring operable to move said toggle linkage into a rigid position thereby closing said movable contact upon movement of said operating member toward said first position when said latch arm is engaged, movement of said operating member to said second position when said movable contact is in its closed position breaking said toggle linkage to open said movable contact.

10. A circuit nterrupter for protecting an electrical system comprising, a base, movable contact means, latch means for latching said movable contact means in closed position and including a pivotally mounted latch arm Iand a latch plate pivotally mounted on said base, operating means connected to said latch arm and operable to rotate the same into engagement with said latch plate, current responsive means in circuit with said electrical system and engaging said latch plate for rotating it out of engagement with said latch arm to release said movable contact means upon the occurrence of a predetermined overcurrent, an adjusting plate mounted on said base for rotation between rst and second positions, said base having a plurality of indentations formed therein and disposed adjacent said adjusting plate, said adjusting plate having an indentation formed therein and registerable with one of an indentation in said base member when said adjusting plate is in each of its rst and second positions, resilient means biasing said adjusting plate against said base member so that said indentations will positively engage, and spring means extending lbetween said adjusting plate and said latch plate for opposing the action of said current responsive means, movement of said adjusting plate from its lirst to its second position increasing the opposition of said latch plate to said current responsive means so that the magnitude of the current necessary to cause the release of said latch arm is increased.

1l. A contact assembly comprising iiXed and movable contact means, said movable contact means including an insulating shell portion mounted for movement toward said fixed contact means and having an axial passage therethrough, one end of said passage being adjacent said fixed contact when said movable contact is closed, a conductive contact member disposed near the one end of said passage, coil spring means disposed in said passage and having one end in engagement with said conductive member for urging it toward said fixed contact, retaining means engaging said insulating shell means and said conductive member for limiting movement of the latter in said passage, said insulating shell having shoulder means disposed at the upper end of said passage and extending toward the center thereof, self locking spring clip means having a central portion engaging the other end of said coil spring means and having a leg portion extending from each of the opposite sides of said central portion toward the interior of said passage and an upwardly extending locking portion disposed at the end of each leg portion and resiliently engaging the sides of said passage beneath said shoulder portion.

References Cited in the file of this patent UNITED STATES PATENTS 2,259,097 Anderson Oct. 14, 1941 2.757,360 Dripps July 31, 1956 2,698,429 Treanor Dec. 28, 1954

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