US2884497A - Circuit breaker - Google Patents

Description

April 1959 H. M. STEVEN ETAL 2,884,497

CIRCUIT BREAKER Filed Aug. 22, 195'? 3 Sheets-Sheet 1 INVENTORS HARRY M. STEVEN, RAYMOND W. MARSHALL ATTORNEY Abril 28, 1959 Filed Aug. 22, 1957 H. MIS'FEVEN EI'AL CIRCUIT BREAKER 3 Sheets-Skieet 2 INVENTORS HARRY M. STEVEN,

RAYMoNDW. MARSHALL April 28, 1959 H. M. STEVEN ETAL 12,884,497

CIRCUIT BREAKER Filed Aug. 22, 1957 3 Sheets-Sheet 3 INVENTORS HARRY M. STEVEN, RAYMoNp W. MARSHALL KMJ C 7 ATTORNEY United States Patent CIRCUIT BREAKER Harry M. Steven, Schenectady, and Raymond W. Marshall, Scotia, N.Y., assignors to General Electric Company, a corporation of New York The present invention relates to electric circuit breakers and particularly to circuit breakers of the type including thermal and magnetic tripping means.

Circuit breakers of the type referred to ordinarily include thermal tripping means for causing automatic opening on low and intermediate value overload currents. In addition, magnetic or instantaneous acting tripping means is included for causing automatic opening in response to overload currents of short circuit magnitude, that is, currents in the neighborhood of five or more times the circuit breakers nominal current rating. The particular value at which thermal tripping occurs is pre-set when the breaker is manufactured, and, for safety reasons, should not be changed during use. In the case of the magnetic or instantaneous tripping, how ever, it is desirable that the maximum and minimum instantaneous tripping points be set by the manufacturer, but that a certain latitude of adjustment be permitted the user. Apparatus for permitting such setting of maximum and minimum tripping points and adjustment within this range by the user have in the past been relatively complicated. In addition, such adjustments have not been convenient for the user to use, requiring the use of a screwdriver, etc. It has also been difiicult, with prior art constructions, to set such adjustments accurately and to observe or read the settings.

It is an object of the present invention to provide an electric circuit breaker including magnetic tripping means which is relatively simple and which can be adjusted with a high degree of accuracy.

It is another object of the present invention to provide an electric circuit breaker including magnetic tripping means which is readily accessible for manual operation without the use of tools.

It is another object of our invention to provide an electric circuit breaker including magnetic tripping means having adjusting means the setting of which can be readily determined by observation.

In accordance with the present invention, an electric circuit breaker trip unit is provided including a stationary magnet field piece and a pivotally supported armature movable toward the field piece to cause tripping. The armature includes an extension which is adapted to support one end of a biasing spring biasing the armature to its open or unattracted position. The opposite end of the biasing spring is supported on a pivotally mounted adjusting lever. The adjusting lever, in turn, is supported in such a manner that rotation thereof carries the line of action of the biasing spring closer to or farther away from the pivotal axis of the armature. This varies the effective biasing force of the biasing spring on the armature, substantially without change in its length, thereby varying the amount of 'magnetic pull and the amount of current needed to actuate it.

In accordance with another aspect of the present invention, the trip unit is provided with an insulating housing and the adjusting lever has its outer end brought through a specially formed'slot in the wall of the housing to be accessible for manual movement in such a manner that the slot does not altord a straight-in opening to the interior of the trip unit.

In accordance with another aspect of the present invention, the biasing spring is attached to the adjusting lever by an adjustable connector.

This connector is accessible through the trip unit housing even after assembly of the unit, and serves to adjust the length and pull of the biasing spring. This establishes the maximum and minimum tripping points of the magnetic tripping means.

Additional objects and aspects of the invention will be pointed out in the following detailed description and illustrated in the accompanying drawings and the scope of the invention will be particularly pointed out in the appended claims.

In the drawings:

Figure 1 is a side elevation view partly in section, of an electric circuit breaker incorporating the invention;

Figure 2 is a perspective view of a circuit breaker trip unit constructed in accordance with the invention;

Figure 3 is a side elevation view of a portion of the tripping mechanism of the circuit breaker trip unit of Figure 2;

Figure 4 is a fragmentary view of a portion of the mechanism of Figure 3 with the bimetallic strip shown in a heated or defective condition;

Figure 5 is a sectional view taken along the lines 55 of Figure 7;

Figure 6 is a sectional elevation view taken along the lines 66 of Figure 7;

Figure 7 is a side elevation view of the trip unit of Figure 2;

Figure 8 is a sectional view of a portion of the trip unit of Figure 2 taken generally on the line 8-8 of Figure 7;

Figure 9 is an exploded view of the interior parts of the circuit breaker trip unit of Figure 2, with certain parts removed for clarity.

In the drawings, the invention is shown as embodied in a three-pole electric circuit breaker comprising an insulating outer or main casing having a base 10 and a cover 11, and including three load terminals 12 (only one shown) at one end. A removable trip unit 23 is mounted within the main enclosure adjacent the load terminals 12 and is electrically connected to the load terminals 12 by means of conductor straps 24, and to the circuit breaker contacts (not shown) by conductors 22.

The circuit breaker includes an operating mechanism, not shown, which may be of conventional form, and which includes a handle member 32 for moving the contacts between open and closed. circuit positions manually, and a releasable member 31 which is movable to cause automatic opening of the circuit breaker contacts upon the occurrence of predetermined current conditions. The releasable member 31 is normally retained in a predetermined latched position and is released upon the occurrence of predetermined current conditions by means of the trip unit 23. A type of operating mechanism suitable for use with the present invention is shown in application Serial Number 679,607, filed August 22, 1957, by E. B. Judd, et al., assigned to the same assignee as the present invention.

The end of the releasable member 31 is formed to act as a latching element and to engage an intermediate latch member 34 which is pivotally and slidably supported on a pin 35 carried by the mechanism frame, not shown. A biasing spring 34' constantly urges the intermediate latch 34 in a clockwise direction as viewed in Figure 3. By reason of the substantially greater force exerted on it by the releasable member 31, however, the intermediate .and slightly beyond the normal off position.

latch member 34 is biased in a counterclockwise direction when the breaker is latched as shown.

The trip unit 23 includes an insulating housing, to be more fully described, and alatch member. 36 adapted normally .to prevent the intermediate latch member; 34 from rotating in a counterclockwise-direction. The latch member36 is pivotally supported on the tripunit v23 on a pivot pin 37 extending through aligned openingsin a boss 38 molded integral with the housing of the trip unit.

The latch member 36 carries a latch roller 39 supported on a pin 40 extending between opposed spaced 3 apart portions of the latch member 36. The intermediate latch member 34 is provided with a cam surface 41 which, when the breaker is latched, .bears against the roller 39 and biases the latch member 36 in a counterclockwise .direction, that is to the left as viewed in Figure 3.

The latch member36 is prevented from moving to the left by the action of a pair of toggle links 42 and 43 which are interconnected between a relatively stationarypivot pin 44 carried by the trip unit 23 and the pivot pin 40 carried by the latchmember 36. The toggle links 42 and 43 are interconnected and joined by a knee pivot pin 45. The toggle linkage including the links 42 and 43, is biased in an upwardly oroverset directionby means of a spring 46 which surrounds a portion of the pin 40 and has its opposite ends engaging the toggle link 42 and the latch member 36, respectively. The bias of the spring '46 is such as to urge the knee pivot pin 45 upwardly as. viewed in Figure 3; tending to cause collapse upwardly of the toggle linkage 42, 43 and therefore movement ofthe latch 1 member 36 counterclockwise. as viewed in this Figure 3.

Movement of the knee of the toggle linkage I42, 43 upwardly is limited byits engagement with. the toggle adjusting screw 47 carried by an integral boss 43 on the trip bar 49. The trip bar 49 is, in turn, prevented from rotating in a counterclockwise direction by its engagement with a trip .bar adjusting screw 50. The parts aretherefore. retained normallyin the condition shown in Figure 3 and in Figure l.

The trip bar 49 is pivotally supported in the trip unit housing on an axis coaxial with the pin 44. Clockwise rotation of the trip bar 49 by the current responsive. means in a manner to be described :causes the toggle adjusting screw 47 to move the knee of the toggle to and through the dead center position until the toggle collapses downwardly. At' the same time, thelatch 36 moves to the left, carrying the latch roller 39, and allowing theintermediate latch member 34 to rotate-counterclockwise and to release the member31, with consequent openingof the contacts.

Following such release, the intermediate. latch is urged clockwise by its bias spring 34', against a stop portion of the frame, not shown. This permits the trip toggle'4243 to resetitself due to the action of the bias spring 46, these parts returning, aftercooling of the bimetallic strip, substantially to thecondition'of Figure 3.

In order to relatch the breaker following atripping operation, .the handle 32 is moved manually to the left to During this movement, a portion of the handle engages the carrier 31 and rotates it counterclockwise. 'When the latch tip of the carrier-31 engages the surface 345 of the intermediate latch 34, further counterclockwise movement of the carrier causes theintermediate latch34 to move to the. left,.as.viewed, with a combined pivoting andsliding action, as permitted by the elongated pivot notch 34N. The ends of thebias spring 34'also are adapted to slide along the inner surface f the portion 348 to permit this sliding retracting action. The latch tip of the carrier'31 finally clears the latch surface of the intermediate. latch,

. andthe. intermediate latch is returned to its normal position by the action of the spring 34', thereby relatching the breaker.

.Certain aspects of the trip 'unit mechanism disclosed herein'form apart of the subjectmatter disclosed'and brating screw '52- at its'opposite end. In order to prevent accidental alteration'of'the calibration such as by vibration," the. calibrating screw is" mounted in a'lock-nut 53 which is, in turn, carriedby the bimetallic strip 51.

In order to heat the bimetallic strip 51 in accordance with current passing through the circuit breaker, an intermediate portion 54 of the conductor is provided between the terminals 22 and 24 comprising a heater portion. As will-be observed from Figure 9, the heater portion 54 is of reduced cross section thereby-increasing the resistance of this .portiom of the conductor and concentrating the r able means suchas by screws 74 and 75.

heating therein. Current does not pass through the bimetallicstripmember. .Instead, the bimetallic member is mounted closely adjacent and preferably against the heater portion 54 of the conductor. .The terminals 22 and 24, together with. the intermediate heater portion 54, comprise a single continuous conductor .56 of relatively rigid nonlaminatedmaterial which is fastened to the base by suit- The terminal portions 22 and 24 are therefore adapted to .serve as mounting supports for the trip unit, and, since theyv are relatively heavyand inflexible, are. adapted to prevent movement onmisalignment of thetrip unit with respect to, the circuit breaker mechanism. which might cause a change in calibration of the breaker.

-Magnetic orinstantaneous tripping action is provided by means 10f arelatively stationary magnet .55 surrounding the conductor56sand mounted on the trip unit housing by suitable means such as by screws 57. The magnet 55 is generally U-shaped and surrounds the heater portion '54, whereby the current passing through the heater portion also serves to create a magnetic field in the magnet 55. Magnetic armatures58 are provided, one for each pole, pivotallysupported with respect to the magnet member; 0n the. same pivotal axis as the trip bar 49. Each of thearmatures :58 includes :upwardly bent portions '58 having aligned holes therein adapted to receive one of the" pivot pins 44.

' Upon the.occurrenceiofexcessive overloads or short circuit currents, the magnet'SS attracts the armature 58 causing it to strike a projection on the trip bar49, rotating the trip bat- 49 clockwise, collapsing the toggle linkage and tripping the cireuit'breaker.

"Thearmature 58 is biased at all times in a counterclockwise direction against an adjustable stop screw 59 (Figure 6). For'thispurpose, a tension spring 60 is provided having-one-end thereof connected-to the armature v58 at the'upwardlybent portions 58, and the other end connected to an adjustinglever 61. The adjusting lever 61 is pivotally supported in an elongated recess or notch 61N inthe trip unit housing, being held there by the bias of. the spring60. As the adjusting lever 61 is moved from itsupper to its lower position, as indicated in Fig- .ure.6,. the line ofactionof .theadjusting spring 60 is moved: closer -to thepivot point of the armature 58, and

vice versa. This changesthe'lefiective-bias of the spring .60u0nf'the. magneticarmature-and-varies the amount of ":current5required to causemagnetic' actuation.

.The trip.. barr49- is :provided with spaced deeply cut notches 49' extending therewithinto a point past the-axial center- 0f the pivot'pins 44.for the purpose of providing clearance for the adjusting lever61,whereby the levers 61 I 'may move the-springs 60rto a position substantially in linewith' the pivotal axis of the -tn'pbar 49 when in'the fully depressed condition such for instance as shown in dotted lines in Figure 6.

A fiat spring member 62 is attached to the lever 61 and has its outer end return-bent. This provides a rounded cam surface adapted to ride against the cam surfaces 63 formed in the trip unit housing. The action of this spring 62 in moving over the cam surfaces 63 aifords a step-bystep adjusting action for the lever 61.

Adjustment of the maximum and minimum magnetic tripping values is achieved by an adjustable mounting of the spring 60 on the lever 61. This adjustable mounting includes a short mounting lever 64 pivoted on the lever 61 at 65, and carrying the end of the spring 60 at its outer end. The mounting lever 64 includes an offset portion 66 which bears against an adjusting screw 67 carried by the main adjusting lever 61. As the adjusting screw 67 is turned inwardly, the lever 64 is rotated clockwise as viewed in Figure 6, stretching the tension spring 60, and increasing the bias on the magnetic armature 58. Thus the length of the spring 60 is varied without moving the lever 61.

The trip unit housing includes two mating molded parts 68 and 68, the part 68 being larger and serving as a base for supporting the various parts of the trip mechanism. The part 68' serves as a cover and also supports some of the parts. The two portions 68 and 68' of the trip unit 23 are adapted to be fastened together by suitable means such as by bolts and nuts 88, arranged to be insulated and made substantially non-removable by filling over the ends thereof with a suitable material such as a potting compound or cement. Other fastening means such as spun-over tubular rivets may of course be used instead of bolts.

In order to enclose the adjusting means for the armatures 58 without unduly enlarging the trip unit housing, the cover member 68 is provided with projecting portions or chambers 76 at corresponding points.

The trip unit casing part 68 includes an arcuate boss 69 for each pole of the circuit breaker, each arcuate boss having an elongated slot 70 through which the outer portion of the adjusting lever 61 projects. Each slot 70 also preferably includes a shield portion 71 at right angles to the general direction of the adjusting lever 61, the adjusting lever 61 having an offset integral portion 72 passing through the slot. Each of the slots 70 therefore does not afford a direct opening to the interior of the trip unit.

Initial assembly of the adjusting lever 61 into the slot 70 is accomplished by providing each slot 70 with a portion 73 at one end wherein the shield 71 is omitted to admit the outer end of the adjusting lever 61 including the offset portion 72.

Each of the magnets 55 preferably has two auxiliary pole members 77, each comprising an elongated strip of magnetic material projecting beyond the pole faces of the magnet 55 and having its outward end upwardly bent to extend close-1y adjacent to the armature 58 when they are in their unattracted position. The auxiliary pole members 77 maintain a relatively small backward pull on the armatures 58 during normal currents and minor overload currents. On the occurrence of relatively large overcurents, however, the intermediate portions of the auxiliary pole member 77 become saturated and the pull of the main pole portions of the magnet 55 greatly exceeds the backward pull of the auxiliary poles 77. The net effect of this action is to cause the armatures 58 to move to closed position with what may be termed a snap action. The auxiliary pole members 77 may be and preferably are,

omitted in forms of the invention used for lower ampere rated circuits, such for instance at 125-300 amperes.

The trip unit housing members 68 and 68' have matching cut-away portions which provide openings or windows in the top wall thereof adapted to permit access to the adjusting screws 67. Following adjustment of the screws 67, the apertures are closed by relatively thin fiber insulating' members 78, which are snapped in place, being trapped therein under tapered ledge retaining portions 78'. The trip unit base 68 also has apertures 79 which are aligned with calibrating screws 52, and through which the calibrating screws 52 may be adjusted from outside the unit casing after the casing is completely assembled.

In order to facilitate testing of the mechanical operation of the trip unit when installed in a circuit breaker, means is provided for tripping the trip unit manually when desired. For this purpose, a plunger 80 is mounted in a recess in the trip unit base 68 and has a reduced portion extending through the trip unit wall, with the inner end adjacent the trip bar 49. A biasing spring 80', under the head of the plunger 80, biases it outwardly away from the trip bar, outward travel being limited by a retaining clip or washer on the inner end of the plunger. An inward force on the plunger 80 against the force of a bias spring 80, causes the inner end of the plunger to engage the trip bar 49 rotating it in a tripping direction.

The trip unit cover 68 supports the parts relating to the tripping toggle and also supports a bracket member 81 (Figure 2) adapted to interengage with a portion of the side frames of the mechanism proper, to prevent any relative movement between the two members.

Certain aspects of the circuit breaker and trip unit enclosure construction disclosed herein form a part of the subject matter disclosed and claimed in application Serial Number 679,589, filed August 22, 1957, by R. W. Dunham and C. L. Jencks and assigned to the same assignee as the present invention.

It Will be observed that the trip mechanism of the trip unit 23, including the thermal and magnetic tripping elements have been provided with a number of independently manipulatable adjustments as indicated particularly in Figure 3. Adjustment and calibration of the circuit breaker is carried out using these adjustments, in the following manner. Initially, before the trip unit is mounted in the circuit breaker, all adjusting screws are retracted. With no current passing through the breaker, the armature adjusting screw 59 is turned in until the armature touches magnet 55 (closed position). The screw 59 is then retracted a predetermined small amount such as one turn, establishing a first position of the armature short of the closed position. With the parts in this condition, the toggle adjusting screw 47 is turned inwardly sufiiciently to cause the toggle links 42, 43 to move to collapsed position. This assures that when the armature has reached its first position short of closing, the trip toggle will have been broken. Following this, the screw 59 is then turned outwardly an additional predetermined amount such as 3 /2 turns to establish a desired initial air gap, set in accordance with the current at which tripping is desired. The trip bar adjusting screw 50 is then turned in sufficiently to contact the trip bar 49, thereby establishing the normal position of the trip bar. Following the preliminary adjustments, the trip unit is mounted Within the circuit breaker proper and the breaker is placed in the on position. With the breaker in this condition, the trip toggle adjusting screw 47, which is accessible through the central opening in the top of the trip unit leasing, is given a final adjustment. As mentioned above, a component of the main operating spring force trying to move the carrier 31 upwardly, is transmitted, through the intermediate latch 34, to the toggle 4243. The proportion of such force which is transmitted can be varied in a particular design in a number of ways, but most easily by varying the steepness of the latch angle of the cam surface 41.

It will also be observed that regardless of the latch angle, the amount of force required to force the trip toggle over-center can be varied by varying the amount of over-set of the toggle. Thus the greater the over-set, the greater the force required to move the toggle back through dead center, and vice versa. We have found that the best results are obtained as to stability, uniformity of calibration and dependability, when the over-set is assess? suchas. torequire aiforce'ofi%-lbi to 1 lb. force on the trip bar at a point adjacent the endof the calibrating screw 52 to initiate movement and cause tripping. Following such force'calibration of the toggle, the adjusting screw 52'for the thermal element 51 is adjusted in accordance with the predetermined current conditions to cause thermal trippingasdesired.

As an independent adjustment, the adjusting screw 67 for the armature bias spring may be adjusted to determine the maximum and minimum amount of current required to cause magnetic tripping. 3 By way of further adjustment, it is possible to replace the spring 60 with other springs of differing strength.

The trip unit 23 is also-provided with a bracket 86 (Figure 1) attached thereto by suitable means such as by rivets and having an intermediate portion thereof spaced away from the top wall-of the trip unit to provide a convenient means forlifting the-trip unit out of the circuit breaker. The bracket 36 also includes a further offset portion 86A which is adapted to extend within an opening 87 in the top wall ofthe circuit breaker cover 11 to provide a marking or indication of the circuit breaker current rating.

While we have shown one specific embodiment of our invention, it will be appreciated that many variations thereof may readily be made 'by those skilled in the art, and we therefore intend by-theappended claims to cover all such variations as fall within the true spirit and scope of our invention.

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

1. An electric circuit breaker comprising a pair of relatively movable contacts movable between open and closed circuit positions, atrip member movable to cause automatic opening of said contacts, a magnetic armature pivotally supported in said circuit breaker and including means engageable withsaid trip member to cause tripping movement thereof upon pivotal movement of said armature in a first direction,-an insulating housing for said circuit breaker, an adjustinglever pivotally supported in said housing and including a portion projecting outside of said housing for manual operation, and biasing spring means connected between an intermediate point of said adjusting lever and a point on said armature eccentric to the pivotal axis of said armature and adapted to bias said armature for pivotal movement in a direction opposite to said first direction, said adjusting lever being movable along a predetermined path to move the line of action of said biasing spring means relative to the pivotal axis of said armature whereby to vary biasing component of said biasing means.

2. An electric circuit breaker comprising a pair of relatively movable contacts movable between open and closed circuit positions, a trip member movable to cause automatic opening of said contacts, a magnetic armature pivotally supported in said circuit breaker and including means engageable with said trip member to cause tripping movement thereof upon pivotal movement of said armature in a first direction, an insulating enclosure, an adjusting lever pivotally supported in said enclosure, biasing spring means interconnected between an outer portion of said adjusting lever and a point on said magnetic armature eccentric to the pivotal axis thereof to bias said armature for pivotal movement in a direction opposite to said first direction, said adju-sting'lever being movable about its pivotal axis to move the line of action of said biasing spring to alter the distance between the line of action of said tension spring and the pivotal axis of said armature whereby to vary the biasing component of said force, said enclosure having a plurality of notches in a wall thereof and means carried by said adjusting lever adapted to cooperate with said notches in said enclosure to provide a plurality of predetermined positions of said adjusting lever.

3.'An electric circuitbreaker comprising a pair of relatively movable contactsmovable-between openand closed circuit positions, a trip member movable to cause automatic opening of saidcontacts, a magnetic. armature pivotally supported in said circuit-breaker and including means engageable with said trip member to cause tripping movement thereof upon pivotal movement of said armature in a first direction, an insulating-housing, an adjusting lever pivotally supported in said insulating housing, tension spring means interconnected between an intermediate point of said adjusting lever and a point on said armature eccentric to'the'pivotal axis ofusaid armature to bias said armature for pivotal movement. in a direction opposite to said first direction, said tension spring means being attached to said'adjusting lever by means which is adjustable to vary .the length of said tension spring means.

4. An electric circuit breaker comprising a pair of relatively movable contacts movable between openJand closed circuit positions, a trip member movable to cause automatic opening of said contacts, a magnetic-armature pivotally supported in said circuit breaker and including means engageable with said trip member .to cause tripping movement thereof upon pivotal movement of said armature in a first direction, aninsul-ating enclosure, an adjusting lever pivotally supported in said enclosure, spring anchoring means carried by the outer portion of said adjusting lever, tension spring means connected between said spring anchoring means and a point on said armature eccentric to the pivotal axis of said armature to bias said armature for pivotal movement in a direction opposite to said first direction, said spring anchoring means being adjustable to vary the length of saidtension spring means without movement of said adjusting .lever, and said adjusting lever being movable to vary the distance between the line ofaction of said tension spring means and the pivotal axis of said armature whereby to vary the biasing component of said biasing spring means substantially without change in the length of said spring.

5. An electric circuit breaker comprising a pair of relatively movable contacts movable between open and closed circuit positions, a trip member movable to cause automatic opening of said contacts, a magnetic armature pivotally supported in said circuit breaker and including means engageable with said trip member to cause tripping movement thereof uponpivotal movement of said armature in a first direction, an insulating enclosure, an adjusting lever pivotally supported in said insulating enclosure, a secondary adjusting lever carried by a portion of said adjusting lever remote from said pivotally supported portion, biasing spring means interconnected between a point on said secondary'adjusting lever and a point on said magnetic armature eccentric to the pivotal axis thereof to bias said armature for pivotal movement in a direction opposite to saidifirst direction, and means for adjusting the normal position ofsaid secondary adjusting lever on said adjusting lever whereby to vary the force of said biasing spring means Without movement of said adjusting lever.

6. An electric circuit breaker comprising a pair of relatively movable contacts, a member movable to cause automatic opening of said contacts, an insulating enclosure, an armature member pivotally mounted in said insulating enclosure, a first adjusting lever pivotally moimted in said enclosure at one end thereof, spring means having one end thereof attached to said armature member and having the otherend thereof attached to said adjusting lever at a point remote from the pivotally supported end, said enclosure having an elongatedslot therein, said adjusting lever including a portion projecting through said elongated slot and accessiblefor operation from outside said trip unit housing, said adjusting lever including an intermediate portion extending substantially at right angles to the major portion thereof and said enclosure including an'arcuate shield adjacent said elongated slot adapted to prevent direct access to the interior of said enclosure through said slot.

7. A multipole electric circuit breaker comprising a plurality of pairs of relatively movable contacts, a member movable to cause automatic opening of said contacts, an insulating base, an armature member pivotally mounted on said base, an adjusting lever pivotally supported on said insulating base at one end thereof, a tension spring having one end thereof connected to said armature member and having the other end thereof connected to a point on said adjusting lever remote from said piv otally supported end, a common trip bar extending across all poles of said multipole circuit breaker, said armature member being pivotally supported coaxially with said common trip bar, said common trip bar including an intermediate portion having a notch therein extending substantially to the pivotal axis thereof to permit movement of said adjusting tension spring to a point where the line of action of said spring extends substantially through the center of said axis of said common trip bar.

8. An electric circuit breaker comprising an enclosure, a pair of relatively movable contacts movable between open and closed circuit positions, a trip member movable to cause automatic opening of said contacts, a magnetic armature pivotally supported in said enclosure and ineluding means engageable with said trip member to cause tripping movement thereof upon pivotal movement of said armature in a first direction, an adjusting lever having a bearing portion at one end thereof, biasing spring means interconnected between a portion of said adjusting lever remote from said bearing portion and a point on said magnetic armature eccentric to the pivotal axis of said armature to bias said armature for pivotal movement in a direction opposite to said first direction, said enclosure including a bearing recess adapted to receive the said bearing portion of said adjusting lever, said biasing spring being adapted to hold said adjusting lever in said bearing recess.

References Cited in the file of this patent UNITED STATES PATENTS 2,069,305 Frank Feb. 2, 1937 2,486,300 Lindstrom Oct. 25, 1949 2,491,959 Dyer Dec. 20, 1949 2,547,131 Lewis Apr. 3, 1951 2,574,093 Edmunds Nov. 6, 1951 2,686,278 Baston Aug. 10, 1954

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