Current limiting circuit breaker

A molded case current limiting circuit interrupter includes a pair of pivoting contact arms each supporting a contact and being connected to wiring terminals such that current flows through the contact arms in opposite directions. One of the contact arms has a movable pivot point. A magnetic drive slot motor device is provided to generate electrodynamic contact opening force upon the contact arms during short circuit conditions. A high-speed magnetic trip device releases the operating mechanism under short circuit conditions to move the arm pivot point before the contact arms reclose. A spring latch may be provided to latch the upper contact arm in a contact-separated position during short circuit conditions until such time as the overcurrent flow through the breaker operates a thermal and magnetic trip mechanism to move an operating mechanism to the tripped position. Alternatively, a cam may be provided which is connected by a link to the upper contact arm and positioned such that upon short circuit conditions the contact opening motion of the upper contact arm caused by electrodynamic repulsion forces will cause the connecting link to rotate the cam and move the armature of the magnetic trip device to actuate the trip mechanism and release the operating mechanism to the tripped position, thereby preventing reclosing of the contact arms before the operating mechanism is able to trip. The operating mechanism includes a bracket to allow normal contact reset yet provide a positive closed contact indication if the contacts are welded together. An anti-rebound contact arm shock absorber is provided which is made of material having a high mechanical hysteresis loop to provide maximum energy dissipation.

CROSS-REFERENCE TO RELATED APPLICATIONS 
The present invention is related to material disclosed in the following 
copending U.S. Patent Application, assigned to the assignee of the present 
invention: 
Ser. No. 952,035, "Current Limiting Circuit Breaker with High Speed 
Magnetic Trip Device", filed Oct. 16, 1978, by W. E. Beatty and J. A. 
Wafer; and 
Ser. No. 952,036, "Current Limiting Circuit Breaker with Integral Magnetic 
Drive Device Housing and Contact Arm Stop", filed Oct. 16, 1978, by J. A. 
Wafer, R. H. Hill, and W. Stephenson. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates generally to circuit interrupters and, more 
particularly, to circuit interrupters operating under short circuit 
conditions to limit the flow of current through the interrupter to a value 
lower than the available fault current which the circuit is capable of 
supplying. 
2. Description of the Prior Art: 
Circuit breakers are widely used in industrial, residential, and commercial 
installations to provide protection against damage due to overcurrent 
conditions. As the usage of electrical energy has increased, the capacity 
of sources supplying this electrical energy has increased correspondingly. 
Therefore, extremely large currents can flow through distribution circuits 
should a short circuit condition occur. Under these conditions 
conventional circuit interrupters are incapable of preventing severe 
damage to apparatus connected downstream from the interrupter. 
Current limiting circuit interrupters were developed to provide the degree 
of protection necessary on circuits connected to power sources capable of 
supplying very large fault currents. One type of circuit interrupter 
provides such current limiting action by operating to achieve extremely 
rapid separation of the contacts during short circuit conditions. This 
action produces an arc voltage across the contacts which quickly 
approaches the system voltage, thus limiting the current flow between the 
contacts. Although the performance of prior art current limiting circuit 
interrupters of this type was adequate in certain applications, it would 
be desirable to provide a circuit breaker providing an even higher degree 
of current limiting action. Furthermore, prior art current limiting 
circuit interrupters were expensive to manufacture and bulky in size, thus 
limiting their applicability. It would therefore be desirable to provide a 
current limiting circuit interrupter offering increased performance in a 
smaller size at a more economical cost. 
SUMMARY OF THE INVENTION 
In accordance with a preferred embodiment of the present invention, there 
is provided a current limiting circuit interrupter comprising a housing, 
separable contacts disposed in the housing, and a high-speed operating 
mechanism having a carriage and means including a handle adapted for 
manual operation to move the carriage between open and closed positions. 
First and second pivoting contact arms are provided, each supporting one 
of the contacts. The first contact arm is pivotally attached to the 
carriage. Bias means are connected to the first contact arm to urge the 
first contact arm into a first position with respect to the carriage so 
that under normal conditions the attached contact arm and carriage rotate 
as a unit to open and close the separable contacts. During current 
limiting operations, the first contact arm pivots independently with 
respect to the carriage against the action of the bias means to a second 
position. 
Means are provided for generating electrodynamic force upon the contact 
arms, such that under short circuit conditions through the circuit 
breaker, the contact arms are rapidly pivoted in opposite directions to 
separate the contacts thus stretching the arc to provide a high arc 
voltage and current limiting action. 
The circuit breaker includes a high speed releasable operating mechanism 
for moving the carriage from the closed to the open position. High speed 
trip means responsive to current flow through the contacts are provided, 
an overcurrent condition through the contacts causing the trip means to 
release the operating mechanism and move the carriage to a tripped 
position to separate the contacts. 
An extreme overcurrent condition through the circuit breaker generates 
electrodynamic force upon the contact arms sufficient to rapidly pivot 
them in opposite directions to separate the contacts, thus stretching the 
arc to provide a high arc voltage and current limiting action. The trip 
means then rapidly releases the operating mechanism to move the carriage 
to the tripped position before the first contact arm, under influence of 
the bias means, can return to the first position, thereby preventing 
reignition of the arc. 
An anti-rebound spring latch may be provided for certain ratings to 
maintain the contact arm in the second position until the operating 
mechanism arrives at the tripped position. Alternatively, a cam-link 
arrangement may be provided so that movement of the contact arm to the 
second position initiates a tripping operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, in which like reference characters refer to 
corresponding members, FIG. 1 shows a three pole circuit breaker 3 
comprising an insulating housing 5 and a high-speed circuit breaker 
mechanism 7 supported in the housing 5. The housing 5 comprises an 
insulating base 9 having a generally planar back, and an insulating front 
cover 11 secured to the base 9. The housing 5 comprises insulating 
barriers separating the housing into three adjacent side-by-side pole unit 
compartments in a manner well known in the art. 
The circuit breaker mechanism 7 comprises a single operating mechanism 13 
and a single latch mechanism 15 mounted on the center pole unit. The 
circuit breaker mechanism 7 also comprises, in each of the three pole 
units, a separate thermal trip device 16 and a high-speed electromagnetic 
trip device 17. The high-speed electromagnetic trip device is more 
completely described in the aforementioned copending U.S. patent 
application Ser. No. 952,035. 
A pair of separable contacts 19 and 21 attached to upper and lower pivoting 
contact arms 20 and 22, respectively, are provided in each pole unit of 
the breaker. An arc extinguishing unit 23 is also provided in each pole 
unit. The upper contact 19 is electrically connected, through the upper 
contact arm 20 (constructed of conducting material), to a shunt 24 which 
is in turn connected through a conducting strip 25 and the thermal and 
magnetic trip devices 16 and 17 to a terminal connector 26. The lower 
contact 21 is connected through the lower contact arm 22, also constructed 
of conducting material, through a shunt 27 and conducting strip 28 to a 
similar terminal connector 29. With the circuit breaker 3 in the closed 
position as is shown in FIG. 1, an electrical circuit thus exists from the 
terminal 26 through the conducting strips 25, the shunt 24, the upper 
contact arm 20, the upper contact 19, the lower contact 21, the lower arm 
22, the shunt 27, and the conducting strip 28 to the terminal connector 
29. 
The upper contact arm 20 is pivotally connected at the point 30 to a 
rotating carriage 32, which is fixedly secured to an insulating rotatable 
tie bar 35 by a staple 34. A tension spring 36 connected between the left 
end of the upper contact arm 20 and a bracket 37 attached to the carriage 
32 serves to maintain the upper contact arm 20 in the position shown in 
FIG. 1, with respect to the carriage 32. The upper contact arm 20 and 
carriage 32 thus rotate as a unit with the crossbar 35 during normal 
current conditions through the circuit breaker 3. 
The single operating mechanism 13 is positioned in the center pole unit of 
the three pole circuit breaker and is supported on a pair of spaced 
metallic rigid supporting plates 41 that are fixedly secured to the base 9 
in the center pole unit of the breaker. An inverted U-shaped operating 
lever 43 is pivotally supported on the spaced plates 41 with the ends of 
the legs of the lever 43 positioned in U-shaped notches 56 of the plates 
41. 
The U-shaped operating lever 43 includes a member 44 extending through a 
hole in a slide plate 46. The slide plate 46 is slidingly attached to the 
cover 11 by a support plate 47, and includes a member 48 seated in a 
molded handle member 49. 
The upper contact arm 20 for the center pole unit is operatively connected 
by means of a toggle comprising an upper toggle link 53 and a lower toggle 
link 55 to a releasable cradle member 57 that is pivotally supported on 
the plates 41 by means of a pin 59. The toggle links 53 and 55 are 
pivotally connected by means of a knee pivot pin 61. The lower toggle link 
55 is pivotally connected to the carriage 32 of the center pole unit by 
means of a pin 65 and the upper toggle link 53 is pivotally connected to 
the releasable cradle member 57 by means of a pin 63. Overcenter operating 
springs 67 are connected under tension between the knee pivot pin 61 and 
the bight portion of the operating lever 43. The lower contact arm 22 is 
pivotally mounted at the point 18 to the base 9. 
A leaf spring 31 urges the lower contact arm 22 in a counterclockwise 
direction about the pivot point 18, the counterclockwise travel of the 
lower contact arm 22 being limited by a pin 40. Since the clockwise force 
upon the upper arm 20 in the closed position is greater than the 
counterclockwise force on the lower arm 22, a degree of overtravel is 
provided from the first point of contact between the arms until the fully 
closed position. This allows for the effect of contact wear. 
The contacts 19 and 21 are manually opened by movement of the handle 49 in 
a leftward direction as seen in FIG. 1 from the ON position to the OFF 
position. This movement causes the slide plate 46 to rotate the operating 
lever 43 in a counterclockwise direction. The rotating movement of the 
operating lever carries the line of action of the overcenter operating 
springs 67 to the left causing collapse, to the left, of the toggle 
linkage 53, 55 to thereby rotate the crossbar 35 in a counterclockwise 
direction to simultaneously move the upper contact arms 20 of the three 
pole units to the open position, opening the contacts of the three pole 
units. The operating mechanism 13 is then in the position shown in dashed 
lines in FIG. 1. 
The contacts are manually closed by reverse movement of the handle 49 from 
the OFF to the ON position, which movement moves the line of action of the 
overcenter springs 67 to the right to move the toggle linkage 53, 55 to 
the position shown in FIG. 1. This movement rotates the crossbar 35 in a 
clockwise direction to move the upper contact arms 19 of the three pole 
units to the closed position. 
The releasable cradle 57 is latched in the position shown in FIG. 1 by 
means of the latch mechanism 15. The latch mechanism 15 comprises a 
primary latch member 71 and an insulating trip bar 73 pivoted at the point 
70. The primary latch member 71 comprises a generally U-shaped latch lever 
75 and a roller member 77 movably supported for limited travel in a pair 
of slots 78 in opposite legs of the lever 75. A torsion spring 81 biases 
the roller member 77 to one end of the slots. The primary latch member 71 
is pivotally supported on the supporting plates 41 by means of a pin 83. 
The free end of the cradle 57 moves within a slot in the bight portion of 
the lever 75. 
The trip bar 73 is a molded insulating member pivotally supported in the 
support plates 41, and is provided with a secondary latch member 89 for 
engaging the bight portion of the latch lever 75 of the primary latch 
member 71 to latch the primary latch member 71 in the position seen in 
FIG. 1. The releasable cradle 57 is provided with a hook portion 58 
serving as a primary latching surface for engaging the roller 77 to latch 
the cradle 57 in the position seen in FIG. 1. 
The primary latch member 71 includes a bias spring 72 secured at the upper 
end thereof, the other end of the bias spring 72 being seated against the 
trip bar 73. The bias spring 72, in compression, urges the primary latch 
member 71 in a clockwise direction about its pivot point 83. Thus, as soon 
as the trip bar 73 is rotated in the counterclockwise direction raising 
the secondary latch 89 away from the top of the latch lever 75, the bias 
spring 72 will rotate the primary latch member 71 in a clockwise direction 
allowing the cradle 57 to be released from the roller 77. The action of 
the bias spring 72 is overcome during a resetting operation as will be 
described hereinafter. 
There is a separate high-speed electromagnetic trip device 17 in each pole 
unit. Each of the electromagnetic trip devices 17 comprises a generally 
U-shaped pole piece 95, the legs of which extend around the conducting 
member 25. An armature structure 97 is pivotally supported in the housing 
5 and includes a laminated magnetic clapper 101 and an actuating member 
103. 
A separate thermal trip device 16 is also included in each pole unit. The 
thermal device 16 includes a bimetal element 105 welded to the conducting 
strip 25. The upper end of the bimetal element 105 includes an adjusting 
screw 107 threaded therein. 
When the circuit breaker is in the latched position as seen in FIG. 1, the 
springs 67 operate through the toggle link 53 and pivot 63 to bias the 
cradle 57 in a clockwise direction about the pivot point 59. Clockwise 
movement of the cradle member 57 is restrained by engagement of the 
latching surface of the hook portion 58 under the roller 77 of the primary 
latch member 71, with the cradle member 57 pulling the primary latch 
member 71 in a clockwise direction about the pivot 83. Clockwise movement 
of the primary latch member 71 about the pivot 83 is restrained by 
engagement of the primary latch member with the secondary latch part 89 on 
the trip bar 73. The force of the primary latch member 71 against the 
secondary latch 89 of the trip bar 73 operates through the axis of the 
pivot 70 of the trip bar 73 so that clockwise movement of the primary 
latch member 71 is restrained by the trip bar 73 without tending to move 
the trip bar 73 about its axis. Thus, the trip bar 73 is in a neutral or 
latching position latching the primary latch member 71 and cradle member 
57 in the latched position as seen in FIG. 1. 
The circuit breaker is shown in the closed and reset position in FIG. 1. 
Upon occurrence of a high overload current above a predetermined value in 
any of the pole units, the clapper 101 is attracted toward the associated 
pole piece 95 whereupon the armature structure 97 pivots in a clockwise 
direction closing the air gap between the pole piece 95 and clapper 101 
and pivoting the armature actuating member 103 in a clockwise direction 
against the member 79 of the trip bar 73. This causes rotation of the trip 
bar 73 in a counterclockwise direction moving the secondary latch 89 of 
the trip bar 73 out of engagement with the latch lever 75. The upward 
force of the cradle member 57 upon the roller 77 now rotates the primary 
latch member 71 in a clockwise direction, releasing the hook portion 58 of 
the cradle member 57. The force of the operating springs 67 upon the knee 
pin 61 is transmitted through the upper toggle link 53 to cause the cradle 
member 57 to rotate in a clockwise direction about the point 59. Continued 
rotation of the cradle member moves the upper toggle pin 65 to the right 
of the line of action of the operating springs 67, causing collapse of the 
toggle linkage 53, 55 to rotate the carriage 32 and the attached crossbar 
35 in a counterclockwise direction and move all three upper contact arms 
20 in a counterclockwise direction to simultaneously open the contacts of 
the three pole units. During this movement, the handle 49 is moved to a 
TRIP position between the OFF and ON positions in a well-known manner to 
provide a visual indication that the circuit breaker has been tripped. 
Before the circuit breaker can be manually operated after an automatic 
tripping operation as shown in FIG. 3, the circuit breaker mechanism must 
be reset and latched. This resetting operation is effected by movement of 
the handle 49 from the intermediate TRIP position to the left to the full 
OFF position. During this movement, the slide plate 46 acts upon the 
member 44 of the operating lever 43 to rotate the operating lever 43 in a 
counterclockwise direction about the pivot point at the notch 56 in the 
support plates 41. A lower extending member 45 of the operating lever 43 
engages a corresponding surface 54 of the cradle member 57 to move the 
cradle member 57 from the position shown in FIG. 3 in a counterclockwise 
direction about the point 59. 
During this movement, the hook portion 58 of the cradle member 57 moves 
down in the slot in the bight portion of the latch lever 75 of the primary 
latch member 71 and the hook portion 58 of the cradle member 57 comes in 
contact with the roller 77 to move the roller 77 to the right in the slots 
and wipe past the roller 77. When the hook portion 58 of the cradle member 
57 passes the roller 77, the spring 81 snaps the roller 77 back to the 
position seen in FIG. 1. As the primary latch member 71 reaches the 
position seen in FIG. 1, a part of the member 71 clears the latch part 89 
of the trip bar 73, whereupon the spring 72 biases the latch part 89 into 
latching engagement with the primary latch member 71 to latch the primary 
latch member 71 in the position seen in FIG. 1. Thereafter, upon release 
of the handle 49 by the operator, the springs 67 again act upon the toggle 
link 55 to bias the cradle member 57 in a clockwise direction to move the 
hook portion 58 up to engage the roller 77 in the latched position seen in 
FIG. 1. The handle 49 can then be manually moved back and forth between 
the ON and OFF positions to close and open the contacts. 
With the circuit breaker in the closed and latched position as seen in FIG. 
1, a low current overload condition will generate heat in the conductor 
member 25 and cause the upper end of the bimetal member 105 to flex to the 
right as seen in FIG. 1. The adjusting screw 107 impinges on the armature 
actuating member 103 of the armature structure 97. This causes 
counterclockwise rotation of the trip bar 73 to initiate a tripping action 
and achieve automatic separation of the contacts in all three pole units 
as hereinbefore described with regard to a magnetic trip. 
As can be seen in FIGS. 1, 2 and 3, the circuit breaker also includes a 
slotted magnetic drive device 110. The magnetic drive device 110 includes 
a housing 112 having a slot 18 within which are disposed the upper and 
lower contact arms 20 and 22. The magnetic drive device 110 is described 
more completely in the aforementioned U.S. patent application Ser. No. 
952,036. 
A bumper member 120 is provided to limit the travel of the upper contact 
arm 20 during current limiting operations as will be described 
hereinafter. The bumper member 120 is composed of shock absorbing material 
such as polyurethane or butyl plastic. This type of material has a very 
large mechanical hysteresis loop, thus absorbing a maximum amount of 
energy and minimizing rebound. A similar member 121 mounted to the base 9 
is provided for the lower arm 22. 
Under short circuit conditions, extremely high levels of overload current 
flow through the circuit breaker 3. The current flow through the conductor 
member 28 and lower contact arm 22 generates a large amount of magnetic 
flux in the slotted magnetic drive device 110. This flux and the current 
flow through the lower contact arm 22 produces a high electrodynamic force 
upon the lower contact arm 22, tending to drive the arm 22 from the closed 
position shown in dashed lines in FIG. 4 toward the bottom of the slot 
118. In addition, the current flow through the contact arms 20 and 22 in 
opposite directions generates a high electrodynamic repulsion force 
between the arms 20 and 22. This force builds up extremely rapidly upon 
occurrence of a short circuit condition, causing the upper contact arm 20 
to pivot in a counterclockwise direction about the pin 30, acting against 
the tension force of the spring 36, from the closed position shown in 
dashed lines in FIG. 4 to the current limiting position shown in solid 
lines. The upper contact arm 20 is thus driven with great force into the 
bumper member 120, which is designed so as to minimize the amount of 
rebound of the upper contact arm 20. This rebound is undesirable since the 
established arc which has been extinguished by the arc extinguishing 
device 23 may restrike if the contacts 19 and 21 return to close 
proximity. The high-speed magnetic trip device 17 is therefore designed to 
operate the latch mechanism 15 to release the operating mechanism 13 
before the arms 20 and 22 can reclose. As the operating mechanism 13 moves 
from the closed positon shown in FIG. 4, to the tripped position shown in 
FIG. 3, the carriage 32 rotates in a counterclockwise direction to raise 
the pivot point 30 of the upper contact arm 20 before the tension spring 
36 returns the upper contact arm 20 to the first position with respect to 
the carriage 32 as shown in FIG. 1. 
The initial high opening acceleration of the contact arms produces a high 
arc voltage resulting in extremely effective current limiting action. The 
combination of the high speed electromagnetic trip device and high speed 
operating mechanism assures that the contacts will remain separated to 
prevent re-establishment of the arc after it is extinguished. 
An alternative embodiment suitable for higher rating circuit breakers is 
shown in FIG. 5. An arm latch , or restraining means, 122 is secured to 
the base 9 by a rivet 124. A latching surface 126 is provided on the end 
of the upper contact arm 20. Under short circuit conditions when the arm 
20 is rotated counterclockwise about the pivot point 30, the latch 122 
engages the surface 126 to lock the arm 20. This prevents return rotation 
of the arm in the clockwise direction about the point 30 as the 
electrodynamic repulsion forces reduce due to the approach toward current 
zero of the fault current waveform. The arm 20 remains in this position 
with respect to the carriage 32 until the trip mechanism 17 releases the 
latch and operating mechanism 13 to move the carriage 32 and pivot point 
30, thus releasing the surface 126 from the latch 124. 
Another alternative construction of the current limiting circuit 3 is shown 
in FIG. 6. This alternative is also suitable for higher rating circuit 
breakers. A cam member 128 including a cam surface 134 is pivotally 
connected at the point 129 to the bracket 37 of the carriage 32. A rigid 
link 130 is connected between a pin 132 on the cam 128 and the left-hand 
end of the upper contact arm 20. 
Upon short circuit conditions with the circuit breaker 3 in the closed 
position as shown in FIG. 6, the upper contact arm 20 will rapidly rotate 
in a counterclockwise direction about the point 30 with respect to the 
carriage 32. The link member 130 will thus move to the right, causing 
counterclockwise rotation of the cam member 128 about the pin 129. The cam 
surface 134 of the cam member 128 will strike the clapper 101 of the 
magnetic trip device 17, causing release of the latch mechanism 15 in the 
manner hereinbefore described with regard to a magnetic tripping 
operation. The latch mechanism is thus released causing collapse of the 
operating mechanism 13 in a shorter interval following counterclockwise 
pivoting of the upper contact arm 20 than is the case for a current 
limiting circuit breaker not including the cam member 128 and link 130. 
The cam 128 and link 130 are provided in current limiting circuit breakers 
designed for applications having high available fault currents. During 
short circuit conditions in such a circuit breaker, the contact arms 20 
and 22 are separated extremely rapidly. For some ratings of breakers, the 
magnetic force upon the clapper 101 is not sufficient to overcome the 
inertia thereof, preventing sufficiently rapid initiation of a tripping 
operation. Using the cam-link arrangement as shown in FIG. 6 provides a 
circuit breaker which will initiate a tripping operation concurrent with 
separation of the contact arms 20 and 22. Accordingly, the operating 
mechanism 13 is released in a sufficiently short time to prevent contact 
restrike. 
As can be seen in FIGS. 6 and 7, the latch lever 75 may include an L-shaped 
reset bracket 135 welded thereto. Following a tripping operation, the 
operating mechanism 13 is reset by sliding the handle 19 from the TRIP 
position, midway between the ON and OFF positions, to the OFF position. 
This rotates the operating lever 43 in a counterclockwise direction about 
the pivot point in the notch 56 of the support plates 41. The knee pin 61 
of the toggle linkage contacts the reset bracket 135, rotating the primary 
latch member 71 in a counterclockwise direction against the action of the 
bias spring 72 until the end of the latch lever 75 is below the secondary 
latch 89. Concurrent with this operation, the cradle 57 is also being 
rotated in a counterclockwise position (by the action of the member 45 
against the surface 54), with the hook portion 58 wiping past the roller 
77, to move the roller 77 to the right in its slots against the action of 
the spring 81 until the hook portion 58 is below the roller 77. Roller 77 
then snaps into the position shown in FIG. 6 to secure the cradle 57 in 
the latched position. The contacts 19 and 21 may then be moved to the 
closed position by sliding the handle from the OFF to the ON position. 
In the event that the contacts 19 and 21 become welded together due to 
extreme overcurrent conditions, the latch mechanism 15 will be released by 
the magnetic trip device 17. The contact arms 20 and 22 will rotate in a 
counterclockwise direction until the pin 40 reaches the stop 39 (FIG. 6) 
on the slot motor housing 112. If an attempt is then made to reset the 
circuit breaker, the handle 49 will be moved to the left toward the OFF 
position. This will rotate the operating lever 43 and the cradle 57 in a 
counterclockwise direction. The hook portion 58 will be moved below the 
level of the roller 77. However, because the upper contact arm 20 (which 
is connected to the toggle linkage through the carriage 32) is welded to 
the lower contact arm, it is not possible to move the knee pin 61 far 
enough to the left to contact the reset bracket 135. Thus, the bias spring 
72 maintains the primary latch member 71 in a state of clockwise rotation 
such that the roller 77 remains to the right of the hook portion 58. The 
cradle 57 will not be secured in the latched position. When pressure is 
released from the handle 49, the force of the operating springs 67 will 
move the handle back to the ON position, thus indicating the true state of 
the contacts 19 and 21. This "positive-on" feature is very important, 
since it is desirable that an operator have knowledge that the contacts 
are indeed welded in the closed position despite the attempt to open or 
reset the circuit breaker. 
A circuit breaker having a pair of pivoting contact arms, one of which has 
a movable pivot point, and a high speed magnetic trip device as described 
herein provides extremely rapid contact separation and current limiting 
action. In addition, the features including the slotted magnetic drive 
device, the spring latch member, the cam link arrangement, the reset 
bracket, and shock absorber aid in providing a current limiting circuit 
breaker which is not subject to restrike or reclosure and includes a 
positive indication of a contact closure state. In summary, it can be seen 
that the present invention provides a current limiting circuit breaker 
exhibiting superior performance over the prior art.