Circuit breaker with improved latch mechanism

A three pole molded case circuit breaker including a push-to-trip button, a flux transfer shunt trip mechanism, an undervoltage trip mechanism, and an improved latch mechanism. The latch mechanism comprises a metal trip bar covered with insulating tubing and adapted for translational movement to actuate the latch mechanism and trip the contacts. Contact carrier movement during the tripping operation serves to reset the latch mechanism.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The invention relates to electrical apparatus, and more particularly, to 
circuit breakers having a releasable latch mechanism to provide shunt 
tripping operation. 
2. Description of the Prior Art 
Circuit breakers are widely used in industrial, commercial, and residential 
applications to provide protection for electrical apparatus and 
distribution circuits. Upon overcurrent conditions through a connected 
electrical circuit, the circuit breaker will automatically open to 
interrupt electric current flow through the circuit. Some circuit breakers 
utilize direct tripping operation wherein the circuit current flowing 
through the breaker also flows through a device such as a bimetal element 
or an electromagnet to directly actuate a latch mechanism. In multiple 
circuit breakers employing direct tripping operation, a separate trip 
mechanism is often employed for each pole. Overcurrent conditions through 
any pole of the circuit breaker will thus cause its associated trip device 
to function, effecting separation of the contacts of that pole. Since it 
is generally desirable to have all poles of the circuit breaker trip at 
the same time, such circuit breakers employ a trip bar or other means 
connecting the various poles of the circuit breaker to provide 
simultaneous tripping operation of all poles. 
Other circuit breakers employ shunt tripping operation wherein a sensing 
device such as a current transformer is used to monitor the current flow 
through each pole of the circuit breaker and generate a tripping signal 
upon overcurrent conditions. Tripping signals from any pole can then in 
turn actuate a single latch mechanism to effect automatic separation of 
the contacts. A trip bar is also required on shunt tripping circuit 
breakers which employ multiple tripping modes, such as manual push-to-trip 
and undervoltage trip capabilities. 
In order to provide isolation between the various poles of the circuit 
breaker, the trip bar must be insulated therefrom. Prior art circuit 
breakers have employed trip bars of molded insulating material which are 
rotated by the tripping action of any one pole or tripping device, thereby 
causing the other associated poles or tripping devices to also operate. A 
circuit breaker employing such a molded insulating rotating trip bar is 
described in U.S. Pat. No. 3,422,381 issued Jan. 14, 1969 to Julius Toth 
and assigned to the assignee of the present invention. Such an arrangement 
generally provides excellent service. However, under certain conditions 
problems can develop with rotating trip bars of molded insulating 
material, such as warping or breakage. It would therefore be desirable to 
provide a circuit breaker employing a metal trip bar. 
Prior art circuit interrupters employing trip bars also lacked features 
which are advantageous for certain applications. For example, some circuit 
breakers in the prior art have required separate operations to reset the 
latch mechanism following a tripping operation. It would be desirable to 
provide a circuit breaker employing a self-resetting latch mechanism. It 
would also be desirable to provide a mechanism for releasing the latch of 
the circuit breaker without moving the trip bar. 
In addition, for circuit breakers employing separate latch release 
mechanisms, trip mechanisms, and undervoltage trip mechanisms, it is 
desirable to provide means for automatically resetting all such 
mechanisms. 
SUMMARY OF THE INVENTION 
In accordance with a preferred embodiment of the invention, there is 
provided a circuit breaker comprising separable contacts, an operating 
mechanism for moving the contacts between open and close positions, the 
operating mechanism comprising a cradle releasable to effect automatic 
separation of the contacts, and a latch mechanism operable upon actuation 
to release the cradle. The latch mechanism comprises a releasable latch 
member cooperating with the cradle to maintain the cradle in the latched 
position, trip lever means for releasing the latch member, and a movable 
trip bar adapted for translational movement to operate the trip lever to 
release the cradle. The circuit interrupter further comprises trip means 
for causing translational movement of the trip bar to actuate the latch 
mechanism and release the cradle and effect automatic separation of the 
contacts.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings, wherein like reference characters refer to 
like members, there is shown in FIG. 1 a molded case circuit breaker 10 
comprising an insulating housing 12. The circuit breaker 10 is of the type 
more specifically described in U.S. Pat. No. 3,585,329 issued June 15, 
1971 to Eugene J. Walker, James P. Ellsworth, and Alfred E. Maier. Thus, 
only a brief description of the circuit breaker is given herein. The 
housing 12 is separated into three adjacent compartments containing three 
pole units of the multi-pole circuit breaker in a manner well known in the 
art. In each pole unit, a pair of solderless terminals 14 and 16 are 
provided at opposite ends of the compartment to enable connection of the 
circuit breaker in an electric circuit. 
In each of the pole unit compartments a rigid stationary conductor 18 feeds 
through a current transformer 20. A mounting screw 22 extends through a 
latch mechanism 24 and into the housing 12. The mounting screw 22 also 
serves to connect the rigid conductor 18 to a flexible shunt 26 which is 
in turn connected to a contact carrier 29 supporting a movable contact. 
Each pole unit of the circuit breaker 10 also includes a rigid conductor 
30 connected at one end to the terminal 16 and supporting at the other end 
thereof a fixed contact 32 cooperating with the movable contact 28. 
A single operating mechanism 34 for controlling all three circuit poles is 
mounted in the center pole unit of the circuit breaker. The operating 
mechanism 34 comprises a frame 36 including spaced supporting plate parts 
mounted on the base of the housing 12, a pivoted forked operating lever 
38, upper and lower toggle links 40, 42 which are pivotally connected by 
means of a knee pin 44, a pair of tension springs 46, and a movable 
insulating handle 48. The upper toggle link 40 is pivotally connected to a 
movable releasable arm or cradle 50 by means of a pin 52. The releasable 
cradle 50 is pivotally supported on the frame 36 by means of a pivot pin 
54. The other end of the releasable cradle 50 includes a latch surface 56 
which is held in a latched position by a primary latch member, or roller, 
59. The roller 59 is part of the latch mechanism 24, as shown more clearly 
in FIG. 2. 
In operation, connection is made to an electrical circuit at the terminals 
14 and 16. The current path through the circuit breaker thus flows from 
the terminal 14 through the stationary conductor 18, the flexible shunt 
26, the contact carrier 29, the movable contact 28, the fixed contact 32, 
and the stationary conductor 18 to the terminal 16. Operation of the 
handle 48 is operable to move the contact carrier 29 and open and close 
the contacts 28, 32 in a well known manner. The contact carrier 29 
includes a staple 31 which is secured about a molded insulating cross arm 
33, connecting the contact carriers of each pole unit. 
The current transformer 20 is connected to solidstate electronic circuitry, 
not shown, which is in turn connected to a flux transfer trip mechanism 58 
mounted within one of the outside pole unit compartments, as shown in FIG. 
6. The flux transfer trip mechanism 58 is of the type described more 
completely in U.S. Pat. No. 3,783,423 issued Jan. 1, 1974 to Alfred E. 
Maier et al. Overcurrent conditions through any of the pole units will be 
detected by the corresponding current transformer 20, the output signal of 
which is then processed by the electronic circuitry to activate the flux 
transfer trip mechanism 58. This causes a plunger 60 in the mechanism 58 
to move to the left as shown in FIG. 6, moving a trip bar 62 to the left 
and actuating the latch release mechanism 24 in a manner to be described 
more completely. 
The circuit breaker 10 may also include an undervoltage release mechanism 
64 mounted in the outside pole unit compartment opposite the flux transfer 
trip mechanism 58. The undervoltage mechanism 64 can be actuated in any 
well known manner to move a plunger 66 to the left as shown in FIG. 6, 
thus operating the trip bar 62 in a manner similar to that described above 
with regard to the flux transfer trip mechanism 58. 
The latch mechanism 24, shown in more detail in FIG. 2, comprises a 
generally U-shaped frame member having two symmetrical side plates 68 
connected by a base member 70. The base member 70 is secured to the 
housing 12 by means of the mounting screw 22. The roller 59 is movably 
mounted within slots 76 in a roller lever 72, the roller lever 72 being 
pivotally supported between the side plates 68 by means of a pivot pin 74. 
The roller 59 is biased to the right as shown in FIG. 2 by means of spring 
78 surrounding the pivot pin 74. Reset springs 75 are provided to maintain 
the roller lever 72 in the tripped position until the cross bar staple 31 
rotates counterclockwise to reset the lever 72 by pushing on the springs 
78. Thus, if the contacts are welded closed, the lever 72 is not reset and 
the breaker cannot be latched. This assures that the handle 48 will remain 
in the ON position, providing a positive indication of the ON status of 
the contacts, despite the occurrence of a tripping operation. 
The trip bar 62 is supported by a generally U-shaped bar lever 80 which is 
in turn pivotally supported between the side plates 68 by means of a pivot 
rod 82. Reset ears 84 are also pivotally supported upon the rod 82 to the 
outside of the side plates 68 and are connected to the trip bar 62. Also 
pivotally supported upon the pivot rod 82 and independent of the bar lever 
80 is a trip lever 86 including an extending arm having a catch surface 88 
to form a notched slot 90. A secondary latch member, or pin lever, 92 is 
pivotally supported between the side plates 68 at the point 94 and 
includes an upward extending L-shaped arm 95 (FIG. 5) which cooperates 
with the notched slot 90 of the trip lever 86. A spring 96 biases the trip 
lever 86 and pin lever 92 in a clockwise direction. The pin lever 92 
includes a restraining pin 100 which cooperates with an extending ear 102 
of the roller lever 72 to maintain the roller lever 72 in the position 
shown in FIG. 2. 
As can be seen in FIG. 2, the latch surface 56 of the cradle 50 rests upon 
the lower surface of the roller 59 and is thereby restrained from rotating 
in a clockwise direction. Thus, the circuit breaker 10 is in an untripped 
condition, and the handle 48 is operable to move the contacts 28, 32 
between open and closed positions. 
The trip bar 62 comprises a rod of steel, aluminum, or other metal which is 
covered by insulating tubes 104 of phenolic or other suitable insulating 
material. The insulating tubes 104 serve to electrically isolate the three 
poles of the circuit breaker 10. When the trip bar 62 is translated to the 
left by either the flux transfer trip mechanism 58 or the undervoltage 
mechanism 64, as described above, the bar lever 80 rotates in a 
counterclockwise direction about the pivot rod 82. The trip bar 62 
contacts the trip lever 86 at the point 98, causing the trip lever 86 to 
rotate in a counterclockwise direction against the action of the bias 
spring 96 about the pivot rod 82. A small amount of rotation of the trip 
lever 86 causes the surface 88 of the notched slot 90 to disengage itself 
from the L-shaped extending arm 95 of the pin lever 92. The upward force 
exerted upon the roller 59 causes the roller lever 72 to exert a downward 
counterclockwise rotating force upon the pin lever 92 through the action 
of the ear 102 upon the restraining pin 100. When the surface 88 is 
sufficiently rotated to allow the upstanding L-shaped arm 95 to become 
free of the slotted notch 90 the pin lever 92 will rotate under the 
influence of the transmitted cradle force to the dashed line position of 
FIG. 3, moving the pin 100 out of the path of movement of the ear 102, 
thereby allowing the roller lever 72 to rotate in a counterclockwise 
direction to the dashed line position of FIG. 3, moving the roller 59 to 
the left and allowing the cradle 50 to rotate in a clockwise direction. 
Freeing of the cradle 50 allows the toggle links 40, 42, to collapse in a 
well known manner. 
As soon as the ear 102 of the roller lever 72 has rotated out of the 
influence of the pin 100, the bias spring 96 causes the pin lever 92 to 
quickly rotate in a clockwise direction, allowing the L-shaped arm 95 to 
return to the notched slot 90. At this point, the trip lever 86 is still 
in a counterclockwise rotated position as shown in FIG. 3. As the contact 
carrier 29 rapidly rotates in a counterclockwise direction, the staple 31 
comes in contact with the reset springs 78. This causes the roller lever 
72 to rotate in a clockwise direction about the pin 74 and return to its 
original position. In doing so, the ear 102 contacts the lower side of the 
pin 100 and, since the trip lever 86 is still depressed at this time, the 
pin lever 92 is free to momentarily rotate in a counterclockwise direction 
and allow the ear 102 to pass. The roller lever 72 then moves from the 
dashed line position of FIG. 3 to assume its original position. When the 
trip lever 86 is allowed to rotate in a clockwise direction (due to the 
action of the spring 96) the surface 88 once again captures the L-shaped 
arm 95 of the pin lever 92. At this time the latch mechanism 24 is 
completely reset and is in the position shown in FIG. 4. 
In order to reset the operating mechanism 34, the handle 48 is operated in 
a counterclockwise direction to the left as shown in FIG. 1 to rotate the 
cradle 50 in a counterclockwise direction and reset the operating 
mechanism 34 in a well known manner. The roller 59 operates in the slots 
76 to allow the cradle 50 to slip under the roller 59 when the operating 
mechanism 34 is reset. Since the trip lever 86 is independently pivoted 
upon the pin 82, it is possible for the latch mechanism 24 to be released 
without the trip bar 62 moving. This is an advantage since it allows the 
undervoltage mechanism and shunt trip mechanism to be reset by the handle 
48 operating the trip bar 62 through the ears 84, while at the same time 
allowing a rating plug interlock to function through the trip lever 86, 
releasing the cradle. Thus the latch mechanism 24 can be released before 
the handle has moved a distance sufficient to charge the springs 46. This 
prevents the large shock to which the mechanism 34 would be subjected 
should the springs 46 become highly charged before the cradle 50 were 
released. 
A shoulder 49 of the handle contacts the ears 84 attached to the pin 82, 
causing the ears 84 and the trip lever 62 to which they are attached to 
rotate in a clockwise direction about the pin 82. As the trip bar 62 moves 
to the right as shown in FIG. 1, the flux transfer trip mechanism 58 and 
the undervoltage release mechanism 64 are both reset. 
In summary, it can be seen that the present invention provides a circuit 
breaker having an improved latch mechanism and trip bar. Problems of 
warping and breaking which occasionally occurred with molded rotating trip 
bars are eliminated with the use of the metallic trip bar in the present 
invention. Providing a trip bar which translates rather than rotates 
allows the elimination of trip bar levers at each independent pole. 
Furthermore, the trip bar of the present invention can be used to reset 
the undervoltage mechanism and the flux transfer trip mechanism. The metal 
trip bar of standard rod stock and the simple stamped sheet metal bar 
lever is lower in cost than the prior art molded insulating trip bars. It 
can be seen therefore that the present invention provides improved 
performance with a reduction in cost.