US3467920A - Molded case circuit breaker with sensitive thermal and magnetic trip mechanism - Google Patents

Description

Sept. 16, 1969 J; 5. HALL ETAL 3,467,920

MOLDED CASE CIRCUIT BREAKER WITH SENSITIVE THERMAL AND MAGNETIC TRIP MECHANISM Filed Oct. 24. 1967 JOHN S HALL PETE/i" E 6. CARPENTER United States Patent MOLDED cAsE cIRciJIT BREAKER WITH SENSITIVE THERMAL AND MAGNETIC TRIP MECHANISM John S. Hall, Highworth, and Peter E. G. Carpenter, Newbury, England, assignors to Square D Company, Park Ridge, 111., a corporation of Michigan Filed Oct. 24, 1967, Ser. No. 677,535 Claims priority, application Great Britain, Nov. 5, 1966, 49,691/ 66 Int. Cl. H01h 73/48 U.S. Cl. 335-23 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates generally to automatic electric circuit breakers, and more particularly to a thermally and magnetically responsive circuit breaker of the molded case variety operable to effect the automatic opening of an electric circuit thermally at less than twice the current rating of the circuit and magnetically at as low as 2.4 times the current rating.

Circuit breakers of the general type disclosed in U.S. Patent No. 2,902,560; issued Sept. 1, 1959, are often used to protect relatively low voltage and low power circuits against overload and fault conditions. Basically, such a circuit breaker comprises a pair of separable contacts, a spring-operated mechanism for effecting separation of the contacts, and a trip device that automatically releases the spring-operated mechanism upon the occurrence of predetermined conditions in the circuit in which the circuit breaker is connected.

One form of trip device often utilized in circuit breakers of the general type disclosed in the aforementioned patent comprises a thermally responsive element in the form of an elongated bimetallic strip arranged to carry the current of the circuit to be protected and which, upon continuation of a moderate overload, flexes sufliciently as a result of the heat produced by the overload current to release the spring-operated mechanism. The trip device also includes a magnetic assembly that becomes operative upon the occurrence of a severe overload or a fault condition in the circuit to release the spring-operated mechanism more quickly than can the thermally responsive element. The former circuit breakers operate satisfactorily thermallyupon moderate overloads but the former circuit breakers do not operate magnetically unless the overload or fault current in many times and current rating of the circuit being protected. For use in some relatively low voltage and low power circuits, it is desirable that a molded case circuit breaker be capable of opening the circuit magnetically when the current is as low as 2.4 times the current rating of the circuit.

Such prior molded case circuit breakers are usually mounted in panelboards which have become standardized in design, and thus the exterior dimensions and configuration of the circuit breakers must be such that they can be accepted in the panelboard. Therefore, it is important that any improvement or change in the trip device of a circuit breaker be accomplished without necessitating a change in a critical external dimension or the general configuration of the circuit breaker.

3,467,920 Patented Sept. 16, 1969 Because of cost and insulation space requirements, the electrical spacing between conductive components of prior molded case circuit breakers is at the acceptable minimum and cannot be materially reduced without reducing the rating of the circuit breaker. Therefore, in order to maintain the critical external dimensions, a trip device operable magnetically at lower currents than prior trip devices preferably is of comparable size and has the same general configuration as the prior trip devices.

Accordingly, a principal object of the present invention is to provide a circuit breaker having an improved trip device that is rendered operative magnetically promptly upon flow of relatively low overload or fault currents to open the contacts of the circuit breaker.

Another object is to provide a trip device of increased magnetic sensitivity in a circuit breaker of relatively low current and low voltage rating without requiring a change in a critical external dimension of the circuit breaker, thereby enabling the circuit breaker to be used in the same electrical panelboard as prior circuit breakers of less magnetic sensitivity.

A further object is to provide a circuit breaker having a trip device of the same general configuration as the trip devices of the type described above and usable with the same type of operating mechanism, but having a more sensitive magnetic trip characteristic.

One way of increasing the magnetic sensitivity of a trip device comprising, as the magnetic tripping means, a magnetic core and an associated clapper-type armature is to increase the effective ampere-turns of the magnetic circuit. Since the amount of current is determined by the circuit in which the circuit breaker is used, the eiiec tive ampere-turns can be increased only by increasing the number of turns of the electrical conductor wound about the core. Because the exterior dimensions of the trip device cannot be materially increased, the increased number of turns must be accommodated substantially within the confines of the space occupied by the original trip device.

In U.S. Patent No. 3,246,098, there is disclosed a molded case circuit breaker having a trip device in which a thermally responsive conductor and non-thermally responsive conductor are electrically connected in series and are supported in cooperative relation with a magnetic core of a clapper-type magnet to provide a plurality of turns about the core without materially increasing the critical dimensions over those of similar circuit breakers, not having a multi-turn coil, thereby rendering the circuit breaker usable in the same electrical panelboard as the other circuit breakers although being more sensitive magnetically.

An electric circuit breaker in accordance with the present invention comprises a molded case, a stationary contact in the case, a contact arm mounted in the case for pivotal movement between an open position and a closed position, a movable contact secured to the contact arm adjacent a free end thereof and engageable with the stationary contact in the closed position of said contact arm, a releasably latchable trip lever pivotally mounted in the case, an overcenter spring mechanism operativel} connected to the contact arm and trip lever, a coil in the case, and a slidable plunger associated with the coil, the trip lever being releasably latchable adjacent a free end by a latch lever pivoted in the case. In addition, a bimetallic member in the case is electrically connected in series with the coil and contacts and has a free end portion adjacent the plunger. An outer end portion of the plunger is loosely coupled to the latch lever so that movement of the plunger into the coil when the contact arm is in the closed position and the trip lever is latched eifects release of the trip lever and operation of the overcenter mechanism to move the contact arm to the open position. When the coil is sufficiently energized, the plunger is caused to be attracted by magnetic action into the coil, and upon the bimetallic element being sufficiently heated by an overload current, the free end portion thereof pushes the plunger into the coil. Thus the latch lever is moved by either magnetic or thermal action to effect re lease of the trip lever and operation of the overcenter Spring mechanism.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a side elevational view of circuit breaker in accordance with this invention, the mechanism being shown in on" position and the cover of the case having been removed;

FIG. 2 is a sectional view of the magnetic tripping means of the circuit breaker of FIG. 1;

FIG. 3 is a side view of a combination solenoid frame and latch lever support of the circuit breaker of FIG. 1; and

FIG. 4 is a top view of the combination solenoid frame and latch lever support of FIG. 3.

Referring to the drawings, the molded case of the circuit breaker includes a base 20 and a cover (not shown) molded of insulating material and secured together by a plurality of rivets 22. The base and cover are provided with molded recesses and barriers for supporting many of the other parts of the circuit breaker, as will be understood.

A load terminal 25 is provided adjacent one end of the case and is electrically connected to one end portion of a terminal strap 26. A stationary contact 28 is secured to the other end portion of the terminal strap 26 for cooperation with a movable contact 30 secured to the bight portion of a generally U-shaped contact arm 32 pivotally supported, between a pair of inwardly extending spaced handle leg portions 33, on an operating handle 34 which in turn is pivotally supported in the case. A rectangular hole 35 is provided through the handle 34 for the reception of a handle tie bar (not shown) when it is desired to provide a multipole circuit breaker in a manner similar to that shown in U.S. Patent No. 2,889,428, issued June 2, 1959.

A slidable arc shield member 36 formed of insulating material is hooked to the contact arm 32. An overcenter tension spring 38 is hooked at one end to the bight ortion of the contact arm 32 and at the other end to a generally U-shaped releasable trip lever 40 pivotally mounted adjacent one end on a projection 41 of the base 20 between the load terminal 25 and the contact arm 32 and releasably latched at the other end in a window 43 of a latch lever 44 provided with a reversely-bent tail portion 45. The latch lever 44 is made of non-magnetizable material to prevent spurious magnetic paths. The trip lever 40 extends between the leg portions 33 of the handle 34 and carries a reset pin 46 cooperable with the leg portions 33 for resetting or relatching of the trip lever after it has tripped. A hole 48 is provided in the trip lever for the reception of a pin (not shown) cooperable with a common-trip crossbar (not shown) mountable in the base 20 and cover when knockouts (not shown) in the base 20 and cover are removed to provide a multipole circuit breaker similar to that shown in aformentioned Patent No. 2,889,428. The window 43 of the latch lever 44 is provided with a thin generally Z-shaped latch plate 49 shown as being thicker than it is in actual practice due to scale limitations of the drawing.

In accordance with this invention, a combination solenoid frame and latch lever support 53 (see FIGS. 3 and 4) is provided. The support 53 has a relatively large generally U-shaped solenoid frame portion 54 at its lower end, a smaller generally U-shaped latch lever support portion 55 at its upper end, and a flat connecting portion 56 connecting the bight portion of the solenoid frame portion 54 with a leg portion of the latch lever support portion .4 55. The connecting portion 56 is positioned against a side wall of the base 20 and a cylindrical projection 58 on the base 20 is received in an opening partly in the connection portion 56 and partly in the adjoining leg portion of the support portion 55. A downwardly opening slot 59 in the bight portion of the solenoid frame portion 54 receives a boss 59a on the base 20. Thus the solenoid frame and latch lever support 53 is held in position on the base 20 when the cover is in place.

The solenoid frame portion 54 has one leg portion 54a adjacent an end wall of the base 20. Extending inwardly from the leg portion 54a is a projection 54b (FIG. 2) and an opposite leg portion 540 has an aligned circular opening 54d. A tube 61 of non-magnetizable material, such as brass, is snugly fitted over the projection 54!) and extends through the opening 54d. The tube 61 preferably has a longitudinally disposed slit along its entire length to reduce eddy currents. A cylindrical slug or plunger 60 of. magnetizable material is disposed within the tube 61 with clearance to provide easy linear movement longitudinally thereof. The plunger 60 has a protruding end portion comprising a spherically rounded tip portion 60a positioned outwardly of a reduced diameter portion 60b.

The latch lever 44 is pivotally supported on the support portion 55 by means of a pair of ears 44a received in complementary slots in respective leg portions of the support portion and is biased clockwise as viewed in FIG. 1 by a helical compression spring 62 seated in an upper wall portion of the base 20. The tail portion 45 of the latch lever 44 has an end portion received in the reduced diameter portion 60b of the plunger 60.

A line terminal 64 is provided adjacent the other end of the case from the load terminal 25. In the embodiment shown, the line terminal 64 is generally U-shaped to provide a pair of plug-in type terminal jaws. A conductive wire 66 is electrically connected at one end to the line terminal 64 and is wound several times around the tube 61 forming a solenoid coil 67 and is electrically connected at the other end to one end of a mounting bracket 68 held in position, as by an adjustment screw 69, against a pair of rounded raised bearing portions 71 and 73 formed on the base 20. A bimetallic member 70 is secured at one end to the upper end of the bracket 68 and extends between the latch lever 44 and the rounded tip 60a of the plunger 60. The bracket 68 is resiliently deformable by rotation of the screw 69 to vary the position of the free end of the bimetallic member 70 with respect to the tip portion 60a of the plunger 60 thus to calibrate the thermal tripping point of the circuit breaker. A flexible braided wire conductor or cable 72 is electrically connected at one end to the free end of the bimetallic member 70 and is secured at the other end to the contact arm 32.

An arc chute assembly including a plurality of deionizing plates (not shown) held in spaced relationship to each other in a formed insulating fiberboard enclosure 75 is provided for the separable contacts 28 and 30. The base 20 is provided with a pair of vent passages 76 and 77 extending from opposite sides of the arc chute assembly, the passage 77 venting between the jaws of the line terminal 64. A mechanical mounting clip 78 is provided adjacent the other end of the case from the line terminal 64.

Movement of the handle 34 clockwise from the position shown in FIG. 1 shifts the pivot point of the contact arm 32 across the line of action of the spring 38 and causes the spring to pivot the contact arm to the ofl? position, and conversely, movement of the handle back to the position of FIG. 1 causes the spring to pivot the contact arm back to the on position.

Pivoting the latch lever 44 counterclockwise as viewed in FIG. 1 unlatches the trip lever 40 and causes the spring 38 to pivot the contact arm 32, handle 34, and trip lever 40 to their tripped positions. Movement of the handle 34 clockwise toward the oil? position from the tripped position causes the leg portions 33 to engage the reset pin 46 thereby to move the trip lever 40 counterclockwise about the projection 41 to reset or relatch the trip lever.

The unlatching of the trip lever 40 from the latch plate 49 in the window 43 of the latch lever 44 is caused thermally upon sustained moderate overloads of approximately twice the normal current rating of the circuit by engagement of the free end of the bimetallic member 70 with the plunger tip 60a upon fiexure of the bimetallic member as a result of an increase in its temperature. This forces the plunger 60 to the right, as viewed in FIG. 1, so that the tail portion 45 of the latch lever 44 is engaged by the tip 60a thereby to swing the latch lever counterclockwise against the bias of the spring 62 to effect release of the trip lever 40.

The unlatching of the trip lever 40 from the latch plate 49 is caused magnetically promptly upon flow of a fault current or an overload current having a minimum value slightly in excess of twice the normal current rating by movement of the plunger 60 to the right by magnetic attraction by the coil 67. The magnetic action becomes operative to release the trip lever 40 much more quickly than can the thermally responsive action. The magnetic responsive action is obtained by sufficient energization of the coil 67 to cause the plunger tip 60a, which is in engagement with the tail portion 45, to move the latch lever 44 thereby to effect release of the trip lever 40.

The thermal and magnetic tripping unit herein disclosed lends itself very readily to production of circuit breakers of various current ratings. Thus, for the lowest rating, a relatively large number of turns may be provided in the winding of the conductor 66 to form the solenoid coil 67 to produce sufficient magnetic flux to trip the circuit breaker upon occurrence of relatively low overload or fault currents, and the conductor 66 may be made of nickel-chromium or other high resistance wire to produce additional heat for activating the bimetallic member 70 upon relatively low sustained overload currents. For higher trip ratings, fewer turns may be provided in the solenoid 67, and the material thereof may be changed to copper to reduce the heat input to the bimetallic member 70.

The distance between the line terminal 64 and the mounting clip 78 has been maintained the same as in the circuit breaker of the aforementioned patents, and the distance between the handle 34 and the line terminal 64 and the mounting clip 78 has also been maintained the same as in the aforementioned patents although the line terminal and mounting clip have been reversed from their position in Patent No. 2,902,560 relative to each other. Thus, the circuit breaker of this invention and that of the aforementioned patents can be mounted in the same panelboard.

We claim:

1. An electric circuit breaker comprising a molded case, a pair of separable contacts in the case, a releasably latchable trip lever pivotally mounted in the case, means in the case rendered operative to eifect separation of the contacts upon release of the trip lever, a latch lever pivotally mounted in the case, the latch lever normally releasably latching the trip lever and being movable in one direction to effect release thereof, a magnetic tripping device in the case including a coil electrically connected in series with the contacts and a plunger reciprocably mounted in the coil, the plunger having an outer end portion connected to the latch lever and being attractable into the coil to a retracted position upon predetermined energization of the coil to move the latch lever in said one direction toward the coil to effect release of the trip lever, and a bimetallic member in the case adjacent said outer end portion of the plunger, the bimetallic member being electrically connected in series with the contacts and the coil and being deflectable upon heating to move the plunger toward its retracted position in the coil.

.2. An electric circuit breaker as claimed in claim 1 wherein biasing means is provided which biases the latch lever in a direction opposite said one direction and biases the plunger outwardly of the coil.

3. An electric circuit breaker as claimed in claim 1 wherein a slot is provided in the outer end portion of the plunger and a free end portion of the latch lever is received in the slot.

4. An electric circuit breaker as claimed in claim 3 wherein the plunger is cylindrical and the slot is a peripheral slot extending around the outer end portion of the plunger.

5. An electric circuit breaker as claimed in claim 1 wherein a free end portion of the bimetallic member is positioned adjacent an outer end face of the plunger with the low expansion side of the bimetal facing the outer end face of the plunger.

6. An electric circuit breaker as claimed in claim 1 wherein a spring is provided to bias the latch lever in a direction opposite said one direction, a free end of the latch lever has a reversely bent portion, a slot is provided in the outer end portion of the plunger, a free end portion of the reversely bent portion is received in the slot so that the plunger is biased outwardly of the coil by the spring, and the bimetallic member extends generally parallel to a main body portion of the latch lever and has a free end portion between the main body portion and the reversely bent portion of the latch lever and adjacent an outer end face of the plunger with the low expansion side of the bimetal facing the outer end face of the plunger.

References Cited UNITED STATES PATENTS 2,154,237 4/1939 Frank 337-71 3,023,288- 2/ 1962 Bodenschatz 337- 3,116,388 12/1963 Hobson 33770 3,246,098 4/ 1966 Hall 335--35 BERNARD A. GILHEANY, Primary Examiner H. BROOME, Assistant Examiner US. Cl. X.R. 337-7l g UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 57,9 0 Dated September 16, 1969 Inventor(s) John s. Hall and Peter E. G. Carpenter identified patent It is certified that error appears in the aboveshown below:

and that said Letters Patent are hereby corrected as Column 1, line 58, change "in" to is change "and" to the olhmtU MW SEALED (SEAL) Attest:

00 mm1ss1oner of Patents WILLIAM E- 'SClHUYLER, JR.

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