AU639994B2 - Circuit breaker with positive indication of welded contacts - Google Patents

Description

_j 9994 s P/00/011 Form PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE Short Title: Int. Cl: Application Number: Lodged: domplete Specification-Lodged: Accepted: Lapsed: Published: Priority: Related Art: TO BE COMPLETED BY APPLICANT SName of Applicant: ,Adcdress of Applicant: Actual Inventor: Address for Service: WESTINGHOUSE ELECTRIC CORPORATION 1310 Beulah Road, Churchill, Pittsburgh, Pennsylvania 15235, United States of America ROBERT JOSEPH TEDESCO PHILLIP LLOYD ULERICH Peter Maxwell Associates Blaxland House Ross Street NORTH PARRAMATTA NSW 2151 Complete Specification for the invention entitled: CIRCUIT BREAKER WITH POSITIVE INDICATION OF WELDED CONTACTS The following statement is a full description of this invention, including the best method of performing it known to me:-' 'Note: The description is to be typed in double spacing, pica type face, in an area not exceeding 250 mm in depth and 160 mm in width, on tough white paper of good quality and it is to be inserted inside this form.

14599/78- L Printed by C. J. THONMPSON, Commonwealth Government Printer, Canberra

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This invention relates to circuit breakers having handles for manual operation and for providing an indication of the open, closed or tripped state of the s electrical contacts within the circuit breaker. More 5 particularly, it relates to such a circuit breaker in which the handle is prevented from being moved to the off position when the contacts are welded closed.

In circuit breakers of the type disclosed in the specification of U.S. Patent No. 4,642,431, a fixed electrical contact and a movable electric contact mounted on a movable contact arm are closed and opened by rotating a handle, which forms part of an operating member, to an on or off position, respectively. A latchable cradle connected to the movable contact arm by a spring operated actuating device is held in a latched position by a trip mechanism. In response to predetermined current overload conditions in the circuit breaker, the trip mechanism unlatches the latchable cradle and the spring operated actuating assembly rotates the movable contact arm to open the contacts. When the circuit breaker is tripped in this manner, the spring operated actuating assembly also moves the handle to a trip position intermediate the on and off positions. Thus, the handle provides a visual indication of the state of the circuit breaker. The circuit breaker is reset by moving the handle slightly past the off position to relatch the latchable cradle and then to the on position to reclose the contacts.

r -L I- It is possible under some overload conditions for the contacts of a circuit breaker to become welded closed. Under these circumstances, the trip mechanism of the circuit breaker disclosed in the specification of U.S.

Patent No. 4,642,431 can respond to the overload condition by unlatching the latchable cradle. If the weld has sufficient strength, the contact arm can not be rotated and the contacts remain closed. However, it is possible to rotate the handle to the off position to relatch the cradle.

Several remedies for this condition have been proposed. In the specification of U.S. Patent No.

3,525,959, the cradle may be latched by a latch member which is engaged by the trip mechanism. To reset a tripped circuit breaker of this type, the knee pivot of a toggle which forms part of a spring loaded operating mechanism which trips the breaker engages the latch member as the handle is moved to the off position to relatch the cradle. When the breaker is tripped, but the contacts are welded closed, the toggle remains erected and does not engage the latch member to relatch the cradle when the handle is moved to the off position. Thus, the cradle cannot be reset and the springs of the actuating mechanism maintain the handle in the on position when released indicating the true condition of the contacts.

In the specification of U.S. Patent No.

3,614,685 is disclosed a blocking member on the movable contact arm structure prevents the cradle from moving to a position at which it can be relatched by the trip mechanism when the handle is moved to the off position following a trip with the contacts welded closed. In another embodiment of this circuit breaker, a latch on the cradle engages a stationary part to prevent rotation of the cradle to the relatch position following a trip with the contacts welded closed. In both embodiments, the springs bias the handle to the on position under these conditions to indicate the real position of the welded contacts.

_rX While the circuit breakers as disclosed in the specification of U.S. Patent Nos. 3,525,959 and 3,614,685 are arranged to prevent relrtching of the cradle following a trip with the contacts welded closed, and bias the handle to the on position to show that the contacts remain closed, the handle can still be moved to the off position. In some applications, circuit breakers are operated remotely by a motor operator. If the handle can be moved to the off position even though biased to the on position, the motor operator could hold the handle in the off position providing an indication that he contacts of the circuit breaker were open when in fact they were welded closed. In addition, in some installations, the circuit breaker is mounted in a cabinet with a handle mechanism extending through the cabinet door or wall for external operation. It is possible for such a handle mechanism to have sufficient friction that the handle could remain in the off position despite the spring bias in the circuit breaker to the open position when the contacts we-e welded closed.

Furthermore, the specification of U.S. Patent No. 3,849,747 discloses a miniature circuit breaker with a latchable cradle which is connected by a spring to a movable contact arm which in turn is connected to a handle. Since the handle is connected directly to the contact arm, it can not be moved to the off position if the contacts are welded closed, and correspondingly, the cradle can not be relatched.

There remains a need in circuit breakers where the handle is connected to the movable contact arm through a spring operated actuating assembly to prevent movement of the handle to the off position when the contacts are welded closed.

According to the present invention, an electrical circuit breaker comprises a fixed contact, a movable contact, a movable contact arm structure carrying said movable contact and movable between open and closed positions to open and close said contacts, an operating mechanism including a latchable cradle, a trip device latching said latchable cradle in a latched position and unlatching said latchable cradle in response to predetermined current overload conditions, spring operated actuating means connected to said latchable cradle and said movable contact arm structure moving said movable contact arm structure to the open position to open said contacts when said cradle is unlatched by said trip delce ehn:* an operating member incorporating a handle to which said spring operated actuating means is connected manually movable to an on position to move said movable contact arm structure to the closed position to close said contacts and provide a positive indication that the contacts are closed, is manually movable to an off position to move said movable contact arm structure to the open position to open said contacts and provide a positive indication that said contacts are open, is movable to an intermed 4 .ate position by the spring operated actuating means when said cradle is unlatched by the tripAmzthan-car.

to provide a positive indication that the circuit breaker has been tripped, said latchable cradle only being relatched by movement of said operating member incorporating said handle adjacent said off position, said circuit breaker including interference "'ins by which said movable contact arm structure engages caid operating member so as to prevent the operating member incorporating said handle from being moved to said off position when said contacts are welded closed, and a pair of sideplates spaced a distance apart, with said movable contact arm structure having a crossbar member journalled in said sideplates for rotation and a contact arm carrying said movable contact and mounted on the crossbar member for rotation therewith between said sideplates in which said interference means comprises projection means on at least one of said crossbar member and operating member which contacts t' other member to prevent said operating member from moving to the off position when said contacts are welded in the closed position.

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%r Conveniently, the operating member includes a Ushaped yoke having a pair of spaced apart arms joined by a web and the interference means comprise axial projections on the crossbar which engage the arms of the yoke to prevent movement of the handle to the off position if the contacts are welded closed and the crossbar cannot rotate.

It is further preferred that the arms of the yoke are seated in arcuate recesses in spaced apart side plates which support the crossbar and the cradle, and that the projections on the crossbar comprise opposite ends of a pin which project into the common planes of the yoke arms and side plates. The ends of the pin ride in arcuate slots in the side plates when the crossbar rotates.

The pin is mounted in a boss integrally molded on the molded crossbar. In an alternate embodiment of the invention, the pin is spring biased in a slot in the boss radially outward into alignment with the arcuate slots in the side plates. However, when the contacts are welded closed, the metal arms of the yoke deflect the metal pin out of alignment with the arcuate slots and instead jam the pin against the metal side plates to provide metal-tometal contact preventing the handle from being moved to the off position.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is a top plan view of a circuit breaker.

Figure 2 is a vertical section taken along the line 2-2 of the circuit breaker of Figure 1.

Figure 3 is a fragmentary sectional view taken along the line 3-3 in Figure 4 of the circuit breaker in the on position.

Figure 4 is a fragmentary transverse sectional view taken along the line 4--4 of the circuit breaker as shown in Figure 2.

i Figure 5 is a fragmentary longitudinal sectional similar to Figure 3 showing the circuit breaker in the off position.

Figure 6 is a fragmentary longitudinal sectional view similar to Figure 3 showing the circuit breaker in the tripped position.

Figure 7 is a fragmentary longitudinal sectional view similar to Figure 3 showing the circuit breaker in the tripped condition with the contacts welded closed.

Figure 8 is a cross-section in enlarged scale of a modified form of a cross-bar which forms part of the circuit breaker of the invention.

Figure 9 is a fragmentary side view of the cross-bar of Figure 8.

Figure 10 is a fragmentary view similar to that of Figure 3 illustrating the modified circuit breaker of Figure 8 in the tripped position when the contacts are welded closed.

Referring to the drawings is circuit breaker 1 similar to as disclosed in the specification of U.S.

Patent No. 4,642,431.

While the invention is shown as applied to a three-phase circuit breaker, it is suitable for single phase or other multiphase circuit breakers, including three-phase circuit breakers with a neutral line.

Figure 1 shows the circuit breaker 1 that has a molded, electrically insulating enclosure 3 comprisi.ng a base 5 (see Figure 2) and removable cover 7. A set of input terminals 9a, 9b and 9c, one for each pole, and a set of output terminals lla, llb and lic are provided to connect the circuit breaker 1 into, in this instance, a three-phase electrical system to be protected by the circuit breaker. A handle 13 for manually opening and closing the circuit breaker, and for indicating the state of the circuit breaker as will be seen, extends through an opening 15 in the cover 7.

Figure 2 is a cross-section through the center pole, the circuit breaker 1 includes for each pole a lower 7 contact structure 17, a movable contact structure 19, an arc chute 21 to aid in extinguishing the electrical arc created by interrupting current through the pole, and a slot motor 23 to aid in accelerating interruption of the current. The major components of the circuit breaker 1 also include a common latchable cradle 25, an operating mechanism 27, an operating member 29 and a i.p mechanism 31 which is responsive to predetermined overcurrent conditions in each pole.

The lower contact structure 17 includes a stationary conducting member 33, the outer end of which constitutes the input terminal 9 for the respective pole.

The fixed contact structure 17 further includes a lower contact arm 35 connected to the member 33 and which carries a fixed electrical contact 37.

The movable contact structure 19 includes a movable contact arm 39 carrying at its outer end a movable electrical contact 41. Each of the movable contact arms 39 is mounted on a common transverse cross-bar 43 for simultaneous rotational movement between a closed position shown in full line in Figure 2 and an open position shown in phantom. The fixed electrical contact 37 and the movable electric contact 41 form a set of contacts which are closed to complete an electrical circuit through the circuit breaker when the contact arm is in the closed position and to interrupt current through the respective pole of the circuit breaker when the contact arm is in the open position. A flexible conductor 47 is connected between the movable contact arm 39 in each pole and a stationary member 49, the outer extremity of which forms the respective output terminal 11.

Figure 4 shows the common cross-bar 43 is journalled for rotation in aperture 51 in spaced apart side plates 53 secured in partitions 55 in the molded base 5 of the circuit breaker. Axial movement of the cross-bar 43 is restrained by integral flanges -7 which are engaged by grooves 59 in the partitions 55. Insulating panels 61 electrically isolate the poles of the circuit breaker i.

L The latchable cradle 25 is mounted for rotation about one end by a cradle pin 63 supported by the side plates 53. The free end of the latchable cradle 23 has a latching surface 65, which in the on position of the circuit breaker illustrated in Figure 2, engages a trip bar 67 which forms part of the trip mechanism 31.

The operating member 29 includes a U-shaped yoke 69 having a pair of spaced apart parallel arms 71 joined by a web 73. The arms 71 of the yoke 69 are spaced apart the same distance, and therefore lie in a common plane with, the side plates 53. As best seen in Figures 3 and through 7, arcuate free ends 75 of the arms 71 are received in and rotate in arcuate recesses 77 in tne side plates 53. The operating member 29 includes the handle 13 S having an integrally molded base 79 which is secured to the yoke 69. The handle 13, and with it the yoke 69 are movable between the on position shown in Figures 2 and 3 and an off position shown in Figure 5. They are also positionable to a tripped position shown in Figure 6 which is intermediate the on and off positions.

The spring operated actuating mechanism 27 includes a toggle device 81 and a pair of helical tension springs 83. The toggle device 81 includes a pair of lower toggle arms 85 straddling the movable contact arm 39 of the center pole pivotally connected thereto by a lower toggle pin 87. The toggle device 81 further includes a pair of uppe;r toggle arms 89 straddling the latchable cradle 25 and connected thereto by upper toggle pin 91.

The upper and lower pairs of toggle arms 89 and 85 are pivotally connected together by a toggle knee pin 93. The helical tension springs 83 are stretched between the web 73 of yoke 69 and t.le toggle knee pin 93 outside of the upper toggle arms 89.

With the handle 13 in the on position, the line of action of the springs 83 is to the left of the upper toggle pin 91 as viewed in Figure 2 to rotate the toggle knee pin 93 in the counterclockwise direction. With the latching cradle 25 engaged by the trip bar 67, the lower

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9 toggle arms 85 are rotated in a counterclockwise direction to rotate the crossbar 43, and therefore each of the movable contact arms 39, in the counterclockwise direction to the closed position wherein the electrica. contacts are closed.

Upon the occurrence of predetermined overcurrent conditions in one of the poles of the circuit breaker 1, the trip mechanism 31 is operated to rotate the trip bar 67 out of engagement with a latching surface 65 on the latching latchable cradle 25. With the cradle 25 unlatched, the springs 83 acting through the -toggle knee pin 93, upper toggle arms 89 and upper toggle pin 91, rapidly accelerate the latchable cradle 25 in the counterclockwise direction as viewed in Figure 2. The upper toggle armsA-8 follow the counterclockwise rotation of the latchable cradle 25 thereby raising the toggle knee pin 93, and through the lower toggle arms 85, the lower toggle pin 87. Raising of the lower toggle pin 87 rotates the crossbar 43 in the clockwise direction thereby raising all of the movable contact arms 39 to s,.multaneously open the sets of contacts 45 for each pole of the circuit breaker.

As this occurs, any electrical arcs struck across the sets of contacts 45 are extinguished by the arc chute 21, As the contact arms 39 are raised, the toggle device breaks as the upper toggle arms 89 rotate counterclockwise and the lower toggle arms 85 rotate clockwise. The yoke 69 carrying the handle 13 moves to the intermediate position shown in Figure 6. This positioning of the handle between the off and the on positions provides a visual indication 30 that the circuit breaker has tripped.

To reset the circuit breaker, the handle 13 is moved toward, and slightly past the off, or full right position, as viewed in Figures 3 and 5 through 7. As the handle is brought to this position, a cam pin 95 connected between the arms 71 of the yoke 69 (see Figure 2) bears against a camnming surface 97 on the latchable cradle 25 to rotate the cradle clockwise until the latching surface Sengages the trip bar 67 of the trip mechanism 31 as shown in Figure 5. Moving the handle to this position causes the line of action of the springs 83 to move to the right of the upper toggle pin 91 so that the handle remains in the off position.

To again close the circuit breaker, the handle 13 is moved from the off position shown in Figure 4 to the on position shown in Figures 2 and 3. When the line of action of this springs 83 passes to the left of the upper toggle pin 91, the toggle device 81 is erected and the crossbar 43 is rotated counterclockwise to close the sets of electrical contacts 45 as previously described.

If the set of contacts 45 of any one of the poles of the circuit breaker 1 is welded closed, the crossbar 43 and therefore n-ne of the movable curontact arms 39 can be rotated. Thus, the contacts for all of the poles remain closed. In the case of a trip, even though 6-7, the latchable cradle 25 is released by the trip bar the handle 13 remains in the on position because the toggle knee pin 91 is prevented from rising by the welded 2j contacts. Without the present invention, however, it would still be possible to move the handle 13 to the off position, although it would spring back to the on position whrn released since the line of action of the springs 83 could not be moved to the right of the upper toggle pin 91. As previously mentioned, however, this is not a satisfactory condition where the handle 13 is operated remotely by a motor driven operator, or by a handle extension when the circuit breaker is mounted within a enclosure.

J 30 A boss 99 is integrally molded onto the center section of the crossbar 43. An interference pin 101 mounted in a bore 103 through the boss 99 projects laterally from the axially ends of the boss 99 into the common plane of the sideplates 53 and arms 71 of the yoke 69. The side plate 53 are provided with arcuate grooves 105 in which the ends of the interference pin 101 ride as the crossbar is rotated in the clockwise direction as shown in Figures 2 and 3 through 6. As can be appreciated I ~I from Figure 5, when the handle 13 is moved to the off position causing the crossbar 43 to rotate clockwise carrying with it the movable contact arms 39 to open the electrical contacts, the interference pin 101 rotates into the arcuate grooves 105 and the arms 71 of thie yoke 69 are free to rotate clockwise until they are adjacent the edges 107 of the sideplates. Similarly, as is evident from Figure 6, the ends of the interference pin 101 rotate into the grooves 105 of the side'?lates 53 when the contacts of the circuit breaker are tripped open and the yoke 69 moves to the position shown in Figure 6.

However, if the contacts 45 of any one of the poles of the circuit breaker 1 are welded closed, the crossbar 43 does not rotate if the trip mechanism is actuated to release the cradle 25. With the crossbar 43 remaining in the position shown in Figure 7 when the circuit breaker is tripped with the contacts welded closed, the yoke cannot be moved to the off position as shown in Figure 7 because it is blocked from reaching this position by the interference pin 101. Thus, the motor operator or the handle extension will not be able to move the handle to the off position, let alone maintain it in the off position. If the contacts are lightly welded, application of force on the handle 13 which is transmitted through contact between the arm 71 and the interference pin 101 may be sufficient to break the weld, in which case a spring action would rotate the crossbar 43 and theretore the movable contact arms 39 in the manner described above.

Otherwise, the motor operator will stall or the handle extension will not be able to be moved to the off position which will provide an indication that the co-tacts have not opened.

Figures 8 through 10 illustrate an alternate embodiment of the invention. The sideplates 53, the yoke 69 and the interference pin 101 are made of metal, while the integral boss on the crossbar 43 is preferably made of a molded resin. While currently available resins are very strong, it may be desired in certain applications to have 12 a metal to metal contact preventing movement of the handle to the off position when the contacts are welded closed.

The embodiment of the invention shown in Figures 8 through provide such a feature. In this embodiment, the interference pin 101 is inserted in a radially extending slot 109 in a boss 111 integrally molded on top of the crossbar 43'. A leaf spring 113 seated in a recess 115 in the boss 111 biases the interference pin 101 radially outward into alignment with the arcuate grooves 105 in the sideplates 53.

Operation of the this embodiment of the invention is the same as that shown in Figures 2 through 7 when the sets of electrical contacts 45 are not wela.-d closed.

That is, when the contacts are tripped open or the handle 13 is moved to the off position,, the interference pin 101 rides in the arcuate grooves 105. However, when the contacts 45 of any pole are welded closed so that the crossbar 43' cannot rotate, rotation of the yoke 69 clockwise toward the off position causes camming surfaces 117 on the arms 71 to apply forces to the ends of the interference pin 101 having a radially inward component which forces the interference pin 101 radially inward within the slot 109 against the bias of the leaf spring 113 so that the ends of the pins 101 are no longer aligned with the grooves 105 in the sideplates 53 but are jammed against the sideplate at 119 adjacent the grooves 105.

This provides a metal to metal contact between the arm 71 of the yoke 69, the interference pin 101 and the sideplates 53 to assure that the handle cannot be moved to the off position with the contacts welded closed.

Claims (14)

1. An electrical circuit breaker comprising a fixed contact, a movable contact, a movable contact arm structure carrying said movable contact and movable between open and closed positions to open and close said contacts, an opernting mechanism including a latchable cradle, a trip device latching said latchable cradle in a latched position and unlatching said latchable cradle in response to predetermined current overload conditions, spring operated actuating means connected to said latchable cradle and said movable contact arm structure moving said movable contact arm structure to the open position to open said contacts when said cradle is unlatched by said trip device, an operating member incorporating a handle to which said spring operated actuating means is connected manually movable to an on position to move said movable contact arm structure to the closed position to close said contacts and provide a positive indication that the contacts are closed, is manually movable to an off position to move said movable contact arm structure to the open position to open said contacts and provide a positive indication that said contacts are open, is movable to an intermediate position by the spring operated actuating means when said cradle is unlatched by the trip device to provide a positive indication that the circuit breaker has been tripped, said latchable cradle only being relatched by movement of said operating member incorporating said handle adjacent said off position, said circuit breaker including interference means by which said movable contact arm I 'j; 1 -14- structure engages said operating member so as to prevent the operating member incorporating said handle from being moved to said off position when said contacts are welded closed, and a pair of sideplates spaced a distance apart, with said movable contact arm structure having a crossbar member journalled in said sideplates for rotation and a contact arm carrying said movable contact and mounted on the crossbar member for rotation therewith between said sideplates in which said interferen -e means comprises projection means on at least one of said crossbar member and operating member which contacts the other member to prevent said operating member from moving to the off position when said contacts are welded in the closed position.

2. A circuit breaker as claimed in claim 1 wherein said at least one of said crossbar member and operating member is said crossbar member and in which said projection means comprises a pin projecting axially from the crossbar member into a path followed by said operating member.

3. A circuit breaker as claimed in claim 2 wherein said operating member includes a U-shaped yoke comprising a web joining spaced apart, parallel arm members, said projection means including means engaging both parallel arm members.

4. A circuit breaker as claimed in claim 3 wherein said parallel arm members of said yoke are spaced apart the same distance as said sideplates and terminate in arcuate ends, said sideplates having arcuate recesses in which said arcuate ends of the parallel arm members of said yoke are seated for rotation in common planes with said sideplates in an arc IB ii between the open and closed positions of said operating member.

A circuit breaker as claimed in claim 4 wherein said projection means comprises first and second projections on said crossbar member, each of which engages one of said parallel arm members.

6. A circuit breaker as claimed in claim 5 wherein said first and second projections extend laterally into the common planes of said parallel arm members and sideplates, said sideplates having arcuate grooves in which said first and second lateral projections rotate when said contacts move to said open position.

7. A circuit breaker as claimed in claim 6 wherein said first and second projections comprise opposite ends of a pin extending axially through said crossbar member.

8. A circuit breaker as claimed in claim 6 or 7 including means mounting said first and second projections for movement radially on said crossbar member, spring means biasing said first and second projections radially into alignment with said arcuate grooves in said sideplates, and engagement means on said parallel arm members of said yoke deflecting said first and second projection means out of alignment with said arcuate grooves in said side plates to jam said first and second projections against the sideplate prevent said operating member from moving to the off position when said contacts are welded closed and said crossbar member cannot rotate.

9. A circuit breaker as claimed in claim 8 wherein said L. -16- sideplates, said parallel arm members of said yoke and said first and second projection means are all made of metal, so that there is metal to metal contact to prevent said operating means from rotating to the open position when said electrical contacts are welded closed.

A circuit breaker as claimed in claim 9 wherein said first and second projection means comprise opposite ends of a metal pin.

11. A circuit breaker as claimed in any one of claims 1 to wherein a multiphase circuit breaker is provided for interrupting a multiphase current having a separate fixed contact and a separate moveable contact forming a separate pole for each phase of the multiphase current, said contact arm structure includes a separate moveable contact arm for each pole carrying the moveable contact for that pole, and a common crossbar member to which each of said contact arms is connected for movement as a unit, said trip mechanism unlatching said latchable cradle in response to said predetermined current overload conditions in any phase of said multiphase current, and said interference means being mounted on said common crossbar member to prevent the operating member from being moved to the off position when the contacts of any pole or poles are welded closed.

12. A circuit breaker as claimed in claim 11 including a pair of side plates spaced a distance apart on either side of one of said moveable contact arms with said common crossbar journalled for rotation in an aperture in said sidepJatz, with said operating member including a U-shared yoke 1 I ii -17- comprising a web joining parallel arms spaced apart the same distance as said sideplates and having arcuate ends, said sideplates ha-'ing arcuate recesses in which said arcuate ends of the parallel arms of said yoke are seated for rotation in an arc between the open and closed position of said operating member, said interference means comprising means projecting from said crossbar axially into common planes formed by each sideplate and one of the parallel arms, and said sideplates including arcuate grooves in which said pin moves when said crossbar rotates for opening said contacts when the contacts are not welded.

13. A circuit breaker ae claimed in claim 12 wherein said projections on said crossbar comprise opposite ends of a pin carried by and extending axially along said crossbar.

14. A circuit breaker as claimed in claim 13 wherein said sideplates, said parallel arms of said yoke and said pin are all made of metal including means mounting said pin for radially movement on said crossbar and means biasing said pin radially into alignment with said arcuate grooves on the sideplates, said parallel arms of said yoke including means radially deflecting said pin out of alignment with said arcuate grooves in said sideplate to jam the pin against the sideplates in metal to metal contact when any of said contacts are welded closed. -18- An electrical circuit breaker, constructed and adapted for use, substantially as hereinbefore described and illustrated with reference to the accompanying drawings. Dated this 4th day of June, 1993 WESTINGHOUSE ELECTRIC CORPORATION By their Patent Attorneys PETER MAXWELL ASSOCIATES -1