Circuit Interrupter Comprising Electromagnetic Opening Means

Abstract

A circuit interrupter is constructed to utilize the electromagnetic forces generated by an overload current condition in order to drive a movable contact arm to open the contacts of the interrupter.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

Circuit interrupters of the type automatically operable to move a contact arm to an open position upon the occurrence of overload current conditions.

2. Description of the Prior Art

It is old in the art to provide a circuit interrupter with stored energy opening means and an electromagnetic trip device operable upon the occurrence of overload current conditions to release the stored energy opening means to thereby effect an opening operation of the circuit interrupter. It is also old in the art to use electromagnetic forces such as the blow-off forces between a pair of contacts or an electromagnetic plunger device in order to open the contacts of a circuit interrupter upon the occurrence of overload current conditions. In the subject invention, a circuit interrupter is constructed such that an overload current in an elongated current carrying contact arm generates electromagnetic forces that operate in a magnetic device to drive the contact arm to an open position at high speed to provide current limiting and to interrupt the overload current.

SUMMARY OF THE INVENTION

A magnetic-drive circuit interrupter is provided comprising an insulating housing and a circuit interrupter structure supported in the housing. The circuit interrupter structure comprises a stationary contact, a movable contact cooperable with the stationary contact, and an elongated generally flat contact arm carrying the movable contact in proximity to one end thereof. The contact arm is supported for pivotal movement in proximity to the other end thereof. An arc-extinguishing structure is supported in the housing in proximity to the cooperable contacts. The elongated contact arm, which carries the current through the breaker, is biased by spring biasing means, into the closed position. A magnetic device, comprising a plurality of plates of magnetic material, is provided with a slot open at one end thereof and closed at the other end thereof. The magnetic device is supported in the housing over the contact arm. The contact arm, in the closed position thereof, is disposed in the slot of the magnetic device in proximity to the open end of the slot. The spring biasing means is strong enough to maintain the contact arm in the closed position under normal current conditions. Upon the occurrence of an overload current above a predetermined value through the contact arm the magnetic flux, that is generated by the overload current, operates in the magnetic device to drive the movable contact arm upward in the slot toward the closed end of the slot to thereby open the contacts at high speed. The arc formed between the contacts during opening operations is extinguished in the arc-extinguishing structure. By using the electromagnetic forces generated by the overload current itself, the contact arm is opened at such high speeds upon the occurrence of fault currents that the circuit interrupter serves as a current limiter as well as a circuit interrupter. The current-limiting action protects the circuit, and the apparatus connected therein, from the destructive effects of the maximum available short-circuit currents. Latch means is provided for latching the contact arm in the open position, and a latch release is provided to release the latch means following an opening operation whereupon the biasing means will return the contact arm to the closed position.

The invention has particular utility in a combination where the magnetic-drive circuit interrupter is supported in an end-to-end series relationship with a standard stored-energy type circuit interrupter. In this combination the magnetic-drive circuit interrupter takes the place of current-limiting fuse means utilized in prior art combinations of the type disclosed in the patent to Dyer U.S. Pat. No. 3,077,525. An advantage of a magnetic-drive circuit interrupter over current limiting fuse means is that the magnetic-drive circuit interrupter can be reset and reused without requiring replacement of fuses.

In another embodiment of the invention, two elongated contact arms are provided. The contact arms are biased toward each other into a closed position. Two magnetic devices of the type previously described are provided, and the contact arms are connected, by gear means, for simultaneous movement in opposite directions. The contact arms are driven in opposite directions toward the open position upon the occurrence of overload current conditions above a predetermined value. Since the contact arms are both moving the contact arms are opened at a higher speed.

In still another embodiment of the invention, the magnetic device is modified in that the slot therein is generally T-shaped, and a flexible current carrying conductor is wound about a part of the magnetic device through the upper arm of the T-shaped slot.

This approach increases the speed of the device by increasing the rate of rise of the flux in the magnetic device which in turn would increase the force. The addition of these turns provides that the magnetic slot motor will open the contacts at a lower level of fault current.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view, with parts broken away, of a circuit interrupting structure constructed in accordance with principles of this invention.

FIG. 2 is a sectional view taken generally along the line II--II of FIG. 1;

FIG. 3 is a sectional view of one pole unit of the magnetic-drive circuit interrupter seen in FIG. 2 and taken along the line III--III of FIG. 2;

FIG. 4 is a side sectional view, with parts broken away, illustrating another magnetic-drive circuit interrupter constructed in accordance with the principles of this invention;

FIG. 5 is a sectional view, taken generally along the line V--V of FIG. 4;

FIG. 6 is a partial side sectional view, with parts broken away, illustrating another embodiment of the invention; and

FIG. 7 is a sectional view taken generally along the line VII--VII of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, there is shown, in FIGS. 1 and 2, a three pole circuit interrupting device 5 comprising a stored-energy type circuit interrupter or circuit breaker 7 and a magnetic-drive circuit interrupter 9 connected in electrical series with the circuit interrupter 7 in an end-to-end relationship.

The stored energy circuit interrupter 7 is of the type that is more specifically described in the patent to Nick Yorgin et al., U.S. Pat. No. 3,462,716 issued Aug. 19, 1969. Thus, only a brief description of the circuit interrupter 7 is given herein.

Referring to FIGS. 1 and 2, the stored energy circuit interrupter 7 is a three-pole circuit interrupter comprising an insulating housing 11 and a circuit-interrupter mechanism 13 supported in the housing 11. The housing 11 comprises a back insulating housing base 15 and a front insulating housing cover 17 cooperating with the base 15 to enclose the circuit-interrupter mechanism. The housing 11 comprises suitable insulating barrier means separating the housing into three internal compartments for housing the three-pole units of the circuit interrupter. The circuit interrupter mechanism 13 comprises an operating mechanism 19, a latch mechanism 2 and a thermal and magnetic trip device 23.

A stationary contact 25, a movable contact 27 and an arc-extinguishing structure 29 are provided for each pole unit of the stored-energy circuit interrupter 7. The stationary contact 25 for each pole unit is fixedly mounted on the inner end of a conducting strip 31 that extends outward to an external cavity where a well-known type of solderless terminal connector 33 is secured to the end of the conductor 31. The movable contact 27, for each pole unit, is mounted on a contact arm 35 that is mounted on a switch arm 37 that is fixedly secured to a common insulating tie bar 39. The switch arms 37 for the three-pole units are secured to the common tie bar 39, and the tie bar 39 is mounted for pivotal movement between open and closed positions.

The operating mechanism 19 comprises an inverted generally U-shaped operating lever 41, an overcenter spring means 43 and a toggle 45. An insulating handle 47 is connected to the lever 41, with the handle 47 protruding through a suitable opening in the front of the housing 11. The lever 41 is mounted for pivotal movement about the inner ends of the legs thereof. The toggle 45 is pivotally connected at one end thereof to a trip member 49 and at the other end thereof to the switch arm 37 of the center pole unit. The toggle 45 comprises two links pivotally connected together at a knee pivot 50.

The contacts are manually opened by movement of the handle 47 from the "on" or closed position to the "off" or open position. This movement moves the lines of action of the overcenter springs 43 to cause collapse of the toggle 45 to thereby cause opening movement of the switch arm 37 in the center pole unit. Since all three switch arms are connected to the tie bar 39 for simultaneous movement, this movement simultaneously moves the three switch arms 37 to the open position. The contacts are manually closed by reverse movement of the handle 47 from the "off" to the "on" position, which movement moves the line of action of the overcenter springs 43 to erect the toggle 45 to thereby move the center pole switch arm 37, and therefore all the switch arms 37, to the closed position seen in FIG. 2.

The operating mechanism 19 comprises the trip member 49 that is latched by means of a latch device 21. In each pole unit, the trip device 23 comprises a bimetal 51, a magnetic yoke 53 and a magnetic armature 55. Upon the occurrence of an overload above a first predetermined value, the bimetal 51 is heated and flexes to the right with a time delay whereupon an adjusting screw 57 engages a common trip bar 59 to move the trip bar 59 to a releasing position to release a latch 61 which then releases the trip member 49. In the latched and closed position seen in FIG. 2, the springs 43 are in a stored energy charged condition. Thus, upon release of the trip member 49, the springs 43 operate to move the trip member 49 in a clockwise direction about the pivot 60 to thereby effect collapse of the toggle 45 and opening movement of the switch arms 37 in a well-known manner. Following a thermal tripping operation, the circuit breaker is reset and relatched by movement of the handle 47 to the full "off" position whereupon a part 62 of the lever 41 engages a shoulder 63 of the trip member 49 to move the trip member 49 back to the latched position. When the stored energy circuit interrupter 7 is subjected to an overload above a second predetermined value higher than the first predetermined value, the armature 55 is instantaneously attracted to the yoke 53 pivoting about a pivot 64 in a clockwise direction whereupon an upper portion of the armature 55 engages the trip bar 59 to move the trip bar 59 to the tripped position to effect a tripping operation in the same manner as was hereinbefore described with regard to the thermal tripping operation.

Referring to FIG. 2, the circuit through each pole unit of the stored energy circuit interrupter 7 extends from a generally L-shaped conductor 65 through a flexible conductor 67, the bimetal 51, a flexible conductor 71, the contact arm 35, the movable contact 27, the stationary contact 25, the conductor 31, to the solderless terminal connector 33. As can be understood with reference to FIGS. 1 and 2, there is in each pole unit a pair of cavities at the opposite ends of the housing. The conductor 33 is supported in the cavity on the right and the conductor 65 extends into the cavity on the left. In each pole unit the conductor 65 is positioned to be connected to one of the terminals of the magnetic-drive circuit interrupter 9 in a manner to be hereinafter more specifically described.

Referring to FIGS. 1 and 2, the magnetic-drive circuit interrupter 9 comprises three pole units 77 supported in a side-by-side relationship to each other and in an end-to-end relationship with the three pole units of the stored energy type circuit interrupter 7. Since the three pole units are of identical construction, only one of the pole units will be specifically described herein. The pole unit comprises an insulating housing 78 comprising an insulating base 79 and an insulating cover 81 secured to the base 79. A stationary contact 83 is supported on a terminal 85 that extends out through an opening in the housing 78 and that is provided with an opening therein for receiving a screw 87 that secures the terminal conductor 85 to the associated conductor 65 of the stored energy circuit interrupter 7. A movable contact 91 is supported on one end of an elongated flat current carrying contact arm 93 that is supported for movement between open and closed positions about a pivot pin 95. The contact arm 93 is provided with a latch extension 97 that cooperates with a latch 99 in a manner to be hereinafter described. A compression coil spring 101 is supported between the insulating material of the base 79 and the latch extension 97 to bias the contact arm 93 in a clockwise direction to the closed position seen in FIG. 2. The latch 99 is supported for movement on a pivot pin 105 and biased toward the latching position seen in FIG. 2 by means of a coil spring 107. An insulating plunger 111, which extends out through a suitable opening in the housing 78, is biased to the inoperative position seen in FIG. 2 by means of a spring 113. A solderless terminal connector 115 is supported on a conductor 117 that is secured to the insulating base 78 by means of a screw 119. A flexible conductor 121 is connected at one end thereof to the conductor 117 and at the other end thereof to the contact arm 93. As can be seen in FIG. 2, there is an end opening 125 in the housing 78 to receive a conducting line that would be brought in through the opening 125 to be connected to the solderless terminal connector 115. In the housing 78 there is a front opening 127 to receive a tool that may be used to work a screw connector 129 to secure a conducting line to the solderless terminal connector 115. As can be understood with reference to FIG. 2, there is insulating material between the cavity in which the solderless terminal connector 115 is located and the compartment where the arcs will be drawn during circuit interruption. A magnetic device 133 is supported on the housing 78 by means of the molded insulating housing and also by means of an elongated pin 134 that extends through the magnetic device 133 and is secured in suitable slots in the housing 78. The magnetic device 133 comprises a plurality of laminations of relatively thin generally U-shaped plates 135 of soft magnetic material, such as iron, that are secured together in a face-to-face relationship. A thin insulation coating is provided over the surface area of the magnetic device 133. As can be understood with reference to FIG. 3, each of the plates 135 is formed as an inverted generally U-shaped plate to provide a slot 137 in the magnetic device 133 for receiving the contact arm 93. As can be understood with reference to FIGS. 2 and 3, the slot 137 starts at the left with a small height dimension, which height dimension increases going to the right so that the slot 137 can receive the pivoted contact arm 93 in the fully open position. As can be understood with reference to FIGS. 2 and 3, the slot 137 is a relatively narrow slot that is open at the bottom and closed at the top of the magnetic device 133.

The magnetic-drive circuit interrupter 9 is shown in the closed position in FIG. 2. In this position, a circuit extends from the solderless terminal connector 115 through the conductor 117, flexible conductor 121, elongated current carrying contact arm 93, movable contact 91, stationary contact 83, conductor 85, to the associated conductor 65 of the associated pole unit of the stored energy circuit interrupter 7. As can be seen in FIGS. 1 and 2, the contacts 91, 93 are disposed in an arc-extinguishing structure 141. The arc-extinguishing structure 141 comprises an insulating wrapper or support 143 and a plurality of flat, generally U-shaped plates 145 of magnetic material. The magnetic plates 145 are supported in a stacked spaced face-to-face relationship with the slots thereof aligned so that the one end of the movable contact arm 93 moves within the slots in moving to the open position.

The magnetic flux generated by the current in the contact arm 137 operates in the magnetic device 133 in a magnetic flux path indicated by the arrows in FIG. 3. Upon the occurrence of normal current conditions and overload current conditions, up to a third predetermined value higher than the second predetermined value, the spring 101 (FIG. 2) has a force that overcomes the electromagnetic forces so that the contact arm 93 remains in the closed position. Upon the occurrence of a heavy overload current above the third predetermined value higher than said second predetermined value, the electromagnetic forces are sufficient to overcome the bias of the spring 101 and rapidly drive the contact arm 93 in a counterclockwise (FIG. 2) direction about the pivot 95 to an open position determined by the engagement of the contact arm 93 with a stop surface 146. The high current conditions under the severe overload or short circuit, generate large magnetic forces on the contact arm 93 so that the contact 93 is moved to the open position at a very high speed, limiting the severe overload or fault current to a more tolerable value to provide a current limiting action. During the opening of the contact arm 93, an arc is drawn between the contacts 91, 83, and the arc is magnetically drawn into the bight portions of the spaced magnetic plates 145 where it is broken up into a plurality of serially related arcs to be extinguished in a well-known manner. During the opening operation of the contact arm 93, the let-through current is sufficient to start the magnetic armature 55 of the circuit interrupter 7 in a tripping direction and the inertia of this moving part causes the armature to continue in motion after the current is interrupted with the result that the trip member 59 is unlatched and the contacts of all three pole units are opened by the tripping of the circuit interrupter 7.

The magnetic force which drives the contact arm at high speed under fault conditions is powered by the fault current itself. The driving force on the contact arm results from the interaction of the current in the contact arm and the self-induced magnetic flux pattern in the surrounding soft magnetic yoke and across the gap where the contact arm is located. This force causes the conductor to be pulled deeper into the slot in the same manner that the windings of a motor are pulled into their slots during the passage of a high current. The force which pulls a conductor into a slot is given approximately by the equation:

F = 14.1 (LI.sup.2 /l) .times. 10.sup.-.sup.8 lbs.

where

L = length of the yoke in ins

I = current in amps

l = slot width in ins.

This equation is for a conductor in an infinitely deep, parallel sided slot in a mass of infinitely permeable iron. In practice of course the iron saturates and the above equation is really a special case of the more general equation:

F = 0.572 BIL .times. 10.sup.-.sup.6 ins.

where B is the flux density in the gap where the conductor is located, in gauss.

This is the well known equation for the force on a conductor in a magnetic field. Now if we assume that the yoke saturates at about 18 kilogauss this shows that for a 2 ins long contact arm in a 2 inch long yoke with a 0.16 inch, slot that a force of approximately 200 lbs. can be obtained at 10,000 amps and 400 lbs, at 20,000 amps. Consequently, large forces are available during faults of this magnitude to drive the contact arms with large accelerations thereby providing rapid contact separation. It is the rapid contact separation together with the driving of the arc into the deion plates that creates the rapid rise of arc voltage which results in current limitation. The more rapid the initial rate of rise of arc voltage the better is the resulting current limitation.

When the contact arm 93 reaches the open position, the latch 97, which cams past the latch 99, is engaged and latched in the open position by the latch 99. Suitable stop means, such as the surface 146 stops movement of the contact arm 93 in the open position. In order to reset the circuit interrupter 9, the plunger 111 is depressed, moving the latch 99 in a clockwise releasing direction to release the latch 97 whreupon the spring 101 returns the contact arm 93 to the closed position seen in FIG. 2. The circuit interrupter 7 is relatched following a tripping operation in the same manner as was hereinbefore described. As can be understood with reference to FIG. 3, the flat contact arm 93 moves in the relatively narrow slot 137 in an endwise direction which is along the planes of the generally flat sides thereof.

Another embodiment of the invention is illustrated in FIGS. 4 and 5 wherein parts similar to the parts of the first embodiment are identified with reference characters that are primed. The circuit interrupter 9' of FIGS. 4 and 5 would be mounted in a series relationship with a stored energy type circuit breaker of the type disclosed in FIG. 2 in a manner similar to that disclosed in FIG. 2 and the flexible conductor 155 would be extended to be connected to a terminal similar to the terminal 85 of FIG. 2 that would in turn be connected to the terminal 65 of FIG. 2. An additional flexible conductor 157 (FIG. 4) would be connected to a solderless terminal connector similar to the solderless terminal connector 115 of FIG. 2. As can be understood with reference to FIGS. 4 and 5, two elongated current carrying generally flat contact arms 93' are supported on pivots 95' within the insulating housing 78'. Each of the contact arms 93' carries a movable contact 91' at the free end thereof, and springs 101' bias the contact arms 93' in opposite directions to the closed position seen in FIG. 4 wherein the contacts 91' are engaged. An arc-extinguishing structure 141', comprising a plurality of spaced generally U-shaped magnetic plates 145', is supported in proximity to the free ends of the contact arms 93' and the contact arms move to an open position in the aligned slots of the magnetic plates 145'. A pair of magnetic devices 133' are supported in the housing by means of the pins 135', and the contact arms 93' move within the slots 137' of the respective magnetic devices 133'. Each of the contact arms 93' is provided with a gear part 161 at the pivoted end thereof, and the gear parts 161 mesh to provide for simultaneous movement of the contact arm 93' in opposite directions. The circuit through the circuit interrupter 9' extends from a solderless terminal connector similar to the terminal connector 115 of FIG. 2, through the flexible conductor 157, the upper contact arm 93', the movable contacts 91', the lower contact arm 93', the flexible conductor 155 to a terminal similar to the terminal 85 of FIG. 2. Upon the occurrence of current conditions less than the third predetermined value, the biasing force of the springs 101' is sufficient to maintain the contact arms 93' in the closed position seen in FIGS. 4 and 5. As can be understood with reference to FIG. 5, the current through the contact arms 93' generates magnetic flux which operates in the associated magnetic devices 133' along the flux paths indicated by the arrows in FIG. 5. Upon the occurrence of a severe overload above the third predetermined value, the electromagnetic forces generated by the current in the contact arms 93' overcome the bias of the springs 101' and move the contact arms 93' in opposite directions (the upper contact arm 93' moving counterclockwise and the lower contact arm 93' moving clockwise in FIG. 4) to the open position at high speed under the large electromagnetic forces. The gear 161 serves to provide for simultaneous opening movement of the contact arms 93'. As the contacts 91' separate, an arc is drawn between the contacts which is then drawn into the bight portions of the plates 145' where the arc is broken up into a plurality of serially related arcs which are extinguished in a wellknown manner. The latch part 97' of the upper contact arm 93' cooperates with a defeatable latch structure similar to the latch structure in FIG. 2 so that the contacts will remain in the open position until defeat of the latch structure by depression of a plunger similar to the plunger 111 in FIG. 2 whereupon the springs 101' will return the contact arms 93' to the closed position. As was the case with the circuit interrupter 9 disclosed in the first embodiment, the contact arms 93' move at high speed to provide current limiting action during the interruption of the circuit.

A third embodiment of the invention is disclosed in FIGS. 6 and 7. Referring to FIGS. 6 and 7, a circuit interrupter 165 comprises a housing 167 that comprises an insulating base 169 and an insulating cover 171 secured to the base 169. A stationary contact 173 is supported on a conducting terminal 175, and a movable contact 177 is supported at the free end of an elongated flat current carrying contact arm 179 that is supported for pivotal movement about the pivot 181. An arc-extinguishing structure 183, similar to that disclosed at 141 in FIG. 2, is supported in the housing to interrupt arcs drawn between the separating contacts 177, 173. A magnetic device 187, comprising a plurality of plates 189 of magnetic material, is supported in the housing by means of the molded insulating housing and a supporting pin 191 that is secured to the housing. As can be understood with reference to FIG. 7, the plates 189 are slotted so that the magnetic device 187 is formed with a generally T-shaped slot 193 therein. A flexible conductor 195 extends from the left (FIG. 6) and is formed to provide a plurality of turns about the upper part of the magnetic device 187 with the conductor extending through the upper portion of the T-shaped slot 193 in the manner disclosed in FIGS. 6 and 7. The one end of the conductor 195 is secured to the contact arm 179. The circuit through the circuit interrupter 165 extends through the conductor 195 from the left (FIG. 6) through the coil portion of the conductor 195, the contact arm 179, the contacts 177, 173 to the conductor 175. Terminals (not shown) are provided at opposite ends of the circuit interrupter 165 to enable connection of the circuit interrupter in an electric circuit. The magnetic flux generated by the current in the conductor 195 and the elongated contact arm 179 operates in the magnetic device 187 in a path indicated by the arrows in FIG. 7. Biasing means (not shown) biases the contact arm 179 to the closed position seen in FIG. 6. Upon the occurrence of a severe overload above the third predetermined value through the circuit interrupter 165, the magnetic flux generated by the current in the conductor 195 and contact arm 179 overcomes the biasing force of the biasing means whereupon the electromagnetic forces drive the contact arm 179 upward in the slot 193 to the open position, with the contact arm 179 moving counterclockwise (FIG. 6). The contact arm 179 is driven to the open position at high speed to limit the current during circuit interruption. The arc drawn between the contacts 173, 177 is drawn into the magnetic plates 184 of the arc-extinguishing structure 183 to be broken up into a plurality of serially related arcs and extinguished in a well known manner.

Claims

I claim as my invention:

1. A circuit interrupter comprising a housing, a circuit interrupter structure supported in said housing, said circuit interrupter structure comprising a stationary contact, a movable contact cooperable with said stationary contact, a contact arm carrying said movable contact, means supporting said contact arm for movement between closed and open positions, means biasing said contact arm into the closed position, a magnetic drive structure comprising a magnetic device of magnetic material having an open slot therein open at one end thereof and closed at the other end thereof, said contact arm being positioned in said slot in proximity to the open end of said slot, the circuit through said circuit interrupter passing through said contact arm and said contacts in the closed position of said contact arm, upon the occurrence of an overload current above a predetermined value through said contact arm the magnetic flux generated by said current in said contact arm operating in said magnetic device to drive said contact arm into said slot toward the closed end of said slot to thereby open said contacts.

2. A circuit interrupter according to claim 1, and an arc-extinguishing structure supported in said housing in proximity to said contacts to effect extinction of arcs drawn between said contacts during opening operations of said circuit interrupter.

3. A circuit interrupter according to claim 2, said circuit interrupter comprising a first terminal means at one end thereof and a second terminal means at the other end thereof to enable connection of said circuit interrupter in an electric circuit.

4. A circuit interrupter according to claim 1, said contact arm being an elongated contact arm, said magnetic device comprising a plurality of laminations of plates of magnetic material with said slot being an elongated slot elongated in the direction of elongation of said contact arm, and said elongated contact arm in the closed position thereof extending lengthwise through said elongated slot in proximity to the open end of said elongated slot.

5. A circuit interrupter according to claim 4, said contact arm being a generally flat contact arm positioned to move in said slot along planes coexistent with the planes of the flat sides of said contact arm.

6. A circuit interrupter according to claim 4, latch means automatically latching said contact arm in the open position, and latch release means releasable to unlatch said contact arm whereupon said biasing means automatically moves said contact arm to the closed position.

7. A circuit interrupter according to claim 6, pivot support means supporting said elongated contact arm in proximity to one end of said elongated contact arm for pivotal movement about a fixed pivot, said pivot support means being disposed at one end of said magnetic device, said contact arm carrying said movable contact thereon at the opposite end of said contact arm and at the opposite end of said magnetic device, and said slot means in said magnetic device having a reduced height dimension in proximity to said pivot support means and an increased height dimension in proximity to said movable contact.

8. A circuit interrupter according to claim 1, said magnetic device being formed with said slot therein such that in the cross section of said magnetic device said slot is a generally T-shaped slot, a main conductor for carrying current in said circuit interrupter, said main conductor forming a plurality of turns around a portion of said magnetic device with said turns going over the top of said magnetic device and through the upper arm of said T-shaped slot and with said main conductor being connected to one end of said contact arm such that the current through said circuit interrupter extends in series relation through said turns of said main conductor and said elongated contact arm whereby the current through said turns of said main conductor and said elongated contact arm generates magnetic flux in said magnetic device to force said contact arm rapidly to the open position upon the occurrence of said overload current above said predetermined value.

9. A circuit interrupter according to claim 8, and an arc-extinguishing structure supported in said housing in proximity to said contacts to effect extinction of arcs drawn between said contacts during opening operations of said circuit interrupter.

10. A circuit interrupter according to claim 9, said contact arm being a generally flat contact arm positioned to move in said slot along planes coexistent with the planes of the flat sides of said contact arm.

11. A circuit interrupter according to claim 10, said circuit interrupter comprising a first terminal means at one end thereof and a second terminal means at the other end thereof to enable connection of said circuit interrupter in an electric circuit.

12. A circuit interrupter comprising a housing, a circuit interrupter structure supported in said housing, said circuit interrupter structure comprising a pair of elongated contact arms, a separate movable contact supported on each of said elongated contact arms, means supporting said contact arms for movement toward each other to a closed position wherein said movable contacts are engaged and for movement away from each other toward an open position wherein said movable contacts are disengaged, means biasing said contact arms into the closed position, a separate magnetic drive structure for each of said movable contact arms each of said magnetic drive structures comprising a magnetic device of magnetic material having an open slot therein open at one end thereof and closed at the other end thereof, each of said contact arms being positioned in the slot of the associated magnetic device in proximity to the open end of the slot of the associated magnetic device in the closed position of said contacts, the circuit through said circuit interrupter passing first through one of said contact arms then through the engaged movable contacts and then through the other of said contact arms, upon the occurrence of an overload current above a predetermined value through said contact arms the magnetic flux generated by said current operating in said magnetic devices to drive said contact arms in opposite directions into the slots of the associated magnetic devices to thereby open said contacts.

13. A circuit interrupter according to claim 12, and an arc-extinguishing structure supported in said housing in proximity to said contacts to effect extinction of arcs drawn between said contacts during opening operations of said circuit interrupter.

14. A circuit interrupter according to claim 13, each of said contact arms being an elongated contact arm, each of said magnetic devices comprising a plurality of laminations of generally flat magnetic plates of magnetic material supported in a face-to-face relationship with the associated slot extending from one end thereof to the other end and with the associated elongated contact arm extending lengthwise in the associated slot.

15. A circuit interrupter according to claim 14, each of said contact arms being a generally flat contact arm positioned to move in the associated slot along planes coexistent with the planes of the flat sides thereof.

16. A circuit interrupter according to claim 15, and a separate pivot support means for each of said contact arms pivotally supporting the associated contact arm for a pivotal movement about a fixed pivot.

17. A circuit interrupter according to claim 16, and a gear means in proximity to the pivoted ends of said contact arms connecting said contact arms for simultaneous movement between open and closed positions.

18. A circuit interrupter according to claim 17, releasable latch means automatically operable to latch said contact arms in the open position, and manually operable latch release means operable to release said latch means whereupon said biasing means automatically biases said contact arms back to the closed position following opening operations of said circuit interrupter.