US3778567A

US3778567A - Circuit interrupter with interlocking mechanism

Info

Publication number: US3778567A
Application number: US00277954A
Authority: US
Inventors: N Davies
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1972-08-04
Filing date: 1972-08-04
Publication date: 1973-12-11
Anticipated expiration: 1990-12-11
Also published as: CA995719A; JPS5634481Y2; JPS4978771U

Abstract

A circuit interrupter with an interlocking system is provided with stored energy overcenter spring operating means for operating the interrupter between open and closed positions. A latch device latches the operating means in charged positions for the opening and closing operations. An interlocking system provides adequate safety to operating personnel by rendering the latch device inoperable when an enclosure door is opened, or to prevent opening of the door when the interrupter is in the closed position.

Description

United States Patent [1 1 Davies Dec. 11, 1973 I 221 Filed:

[ CIRCUIT INTEIIRUPTER WITH INTERLOCKING MECHANISM [75] inventor: Norman Davies, Trafford, Pa.

[73] Assignee: Westinghouse Electric Corporation,

- Pittsburgh, Pa.

Aug. 4, 1972 21 Appl. No.: 277,954

[52] U.S. Cl 200/50 A [51] Int. Cl. II0lh 9/22 [58] Field of Search 200/50 A, 153 SC [56] References Cited UNITED STATES PATENTS 3,609,261 9/1971 Rys 200/50 A 3,684,848 8/1972 Davies 200/153 SC Primary Examiner.l. R. Scott Atl0rney--A. T. Stratton et al.

[57] ABSTRACT A circuit interrupter with an interlocking system is provided with stored energy overcenter spring operating means for operating the interrupter between open and closed positions. A latch device latches the operating means in charged positions for the opening and closing operations. An interlocking system provides adequate safety to operating personnel by rendering the latch device inoperable when an enclosure door is opened, or to prevent opening of the door when the interrupter is in the closed position.

10 Claims, 12 Drawing Figures PATENTEU M01 1 ms SHEET 1- UF 9 FIG.

SHEET 2 OF 9 -QLI . PAIENIEDBEC 11 I975 FIG. 2

mmmmn ms SHEET 3UP 9 FIG. 3

3778.567 SHEET 6 UF 9 PATENTED HEB 11 I973 minnow i 1 ma SHEET 8 BF 0 mmz CIRCUIT INTERRUPTER WITII INTERLOCKING MECHANISM CROSS-REFERENCE TO RELATED APPLICATIONS Certain parts of the circuit interrupter disclosed herein are disclosed incopending patent application to Norman Davies entitled Circuit Interrupter, Ser. No. 106,328, filed Jan. 14, 1971, now US. Pat. No. 684,848.-

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to circuit interrupters and more particularly to circuit interrupters of the type comprising a stored energy overcenter spring operating means foroperating the circuit interrupter between open and closed positions and comprising an interlock system for providing safety to operating personnel.

2. Description of the Prior Art Circuit interrupters of prior construction, among other things, comprise a stored energy overcenter spring operating means for operating the interrupter between open and closed positions. They also comprise latch means for latching the spring operating means in charged positions for both opening and closing operations.

Most of the circuit interrupters of prior use have been provided with inadequate, if any, safety devices for the protection of operating personnel. More particularly, circuit interrupters of the indoor type are usually enclosed within a housing provided with an enclosure door. When the circuit interrupter is in the closed position, it is normally unsafe to open the door. In addition, when the door is open and the circuit interrupter is in the open position with the stored energy overcenter spring operating means in the charged position, another safety hazard exists. I-Ieretofore, most of the existing safety devices for operating personnel have been inadequate.

SUMMARY OF THE INVENTION In accordance with this invention it has been found that the disclosed circuit interrupter with an interlocking system satisfies prior existingproblems by providing a stationary contact and a movable contact, means for opening and closing the contacts including an operating shaft supported for rotation between open and closed positions, an overcenter spring structure operatively connected to the operating shaft, drive means operable from a first position to a second position to move the overcenter spring structure from a spring discharged open position to a spring charged open position, the overcenter spring structure being movable to a spring discharged closed position for driving the operating shaft to the closed position, the drive mechanism being operable from the second position to the first position to move the overcenter spring structure from the spring discharged closed position to the spring discharged open position, the overcenter spring structure being movable to a spring discharged open position for driving the operating shaft to the open position, an enclosure door for access to the operating shaft and the spring discharge structure, means for interlocking the enclosure door and the operating shaft to prevent opening of the door when the stationary contact and the movable contact are in the closed positions, means for blocking the operating shaft from rotating to the closed position when the door is open, and means movably mounted adjacent to the drive means and responsive to the door for blocking discharge of the charged overcenter spring when the door is opened.

The advantage of the device of this invention is that it provides for adequate safety means to operating personnel which means constitute improvement over prior known circuit interrupters.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a side elevational view, with parts broken away, of a circuit interrupter constructed in accordance with the principles of this invention;

FIG. 2 is a front view of the circuit interrupter illustrated in FIG. 1;

FIG. 3 is a sectional view taken generally along the line III-III of FIG. 2;

FIG. 4 is a front view, with parts broken away, illustrating the operating mechanism shown in FIG. 2;

FIG. 5 is a sectional view, taken generally along the line V-V of FIG. 4, with the parts being shown in the spring discharged closed position;

FIG. 6 is a view of certain parts disclosed in FIG. 5, with the parts being shown in the spring-charged closed position;

FIG. 7 is a view similar to FIG. 5 with the parts being shown in the spring discharged open position;

FIG. 8 is a view similar to FIG. 6 with the parts being shown in the spring-charged open position;

FIG. 9 is a vertical sectional view, taken on the line IX--IX of FIG. 2;

FIG. 10 is a vertical sectional view,-taken on the line XX of FIG. 2;

FIG. 11 is an enlarged fragmentary view of a portion ofthe circuit interrupter of FIG. 2 and showing the interlock device of this invention; and

FIG. 12 is a vertical sectional view, taken on the line XII-XII of FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, there is shown, in FIGS. 1 and 2, a circuit interrupter 7 comprising support means 9 and a circuit-interrupter structure 11 supported on the support means 9. The support means 9 comprises backplate means 13 and a pair of side plate means 15, connected to the backplate means 13. A pair of elongated channel members 17 are supported on the side plate means 15 for supporting the terminals of the circuit interrupter.

The circuit interrupter structure 11 comprises three stationary contacts 21 (FIGS. 2 and 3) supported on three spaced insulating members 23 that are supported on one of the back support channel members 17. A separate movable contact arm 25 is provided to cooperate with each of the stationary contacts 21. Each of the contact arms 25 comprises a pair of spaced contact members (FIG. 2) that comprise contact portions that engage the opposite sides of the associated stationary contact 21 in the closed position of the contacts. Each of the contact arms 25 is supported for pivotal movement on a separate conducting terminal 27 by means of a pivot pin 29. Each of the terminals 27 is supported on an insulating support 31 that is, in turn, supported on one of the channel support members 17. In each pole unit a terminal plate 33 is connected to the 3 contact 21 and a terminal plate 35 is connected to the terminal 27 to enable connection of the pole unit in an electric circuit.

In each pole unit, an elongated electrically insulating link 37 (FIG. 3) is pivotally connected at one end thereof to the movable contact arm 25 by means of a pivot pin 39 and at the other end thereof to a member 41 by means of a pivot pin 43. Each of the members 41 is an integral part of an elongated operating shaft 45. As can be understood with reference to FIGS. 2 and 3, the operating shaft 45 is supported on the sideplate means for rotational movement about the elongated axis thereof. The circuit interrupter is shown in full lines in FIG. 3 in the closed position. Upon counterclockwise movement of the operating shaft 45 to the open position shown in broken lines, the three links 37 of the three pole unitsare moved to move the contact arms to the open positions shown in broken lines. Reverse or clockwise movement of the operating shaft from the position shown in broken lines operates through the links 37 to move the three contact arms 25 from the open positions shown in broken lines to the closed position shown in full lines.

An operating mechanism 49 (FIGS. 2,4, and 5) is provided for operating the operating shaft 45 between the closed and open positions. The operating mechanism 49 comprises drive means 51, ,an overcenter spring structure 53, a latch linkage 55, a latch structure 57,.and a trip device 59.

The drive means 51 comprises a drive member 61 supported on the operating shaft 45 for rotational movement relative to the, operating shaft 45. The drive member 61 is provided with an opening 63 for receiving a crank rod 65 that can be placed into the opening 63 in order to crank the drive member 61 between the open and closed positions.

The overcenter spring structure 53 comprises an elongated rod 67 that extends at one end thereof through an opening 69 in a stationary plate 71 that is connected on the side plate means 15. A pin 73 and washer 75 are supported on the rod 67. An overcenter spring 77 is supported on the rod 67 between the washer75 and the plate 71. The rod 67 is pivotally connected at the other end thereof to a member 79 by means of a pin 81. As can be understood with reference to FIG. 4, the pin 81 extends out through opposite sides of the member 79. The member 79 is supported on the operating shaft 45 for rotational movement relative to the operating shaft 45. A member 85 is fixedly secured to the operating shaft 45. The member 85 is provided with an extension 87 at one side of the operating shaft and an extension 89 at the other side of the operating shaft 45. The member 85 is also provided with an integral extension or toggle link 91 that serves as one link of a toggle of the latch linkage 55 in a manner to be hereinafter described. The other toggle link is a member 93 that is pivotally connected at one end thereof to the part 91 by means of a pivot pin 95 and at the other end thereof to an elongated link 97 by means of a pivot pin 99.

The link 97 is pivotally supported, intermediate the ends thereof, on a stationary support bracket 101 by means of a pin 103 (FIG. 5). The support bracket 101 is suitably secured to the side plate means 15. The link 97 is provided with a notch 105 at the upper end thereof that engages a roller 107 of a roller latch 109. The roller latch 109 is pivotally supported on the bracket 101 by means of a pin 111. The roller latch 109 is provided with a roller 113 at the other end thereof that engages in a notch 115 of a latch member 117 that is pivotally supported on the bracket 101 by means of a pivot pin 119. A torsion spring 121 biases the roller latch 109 in a clockwise direction to the latching position seen in FIG. 5, and a torsion spring 123 biases the latch 117 in a counterclockwise direction to the latching position seen in FIG. 5. The latch 117 is provided with an extension 127 that can be manually moved to pivot the latch 117 in a clockwise direction in order to operate the interrupter in a manner to be hereinafter described. The extension 127 may also be actuated by the electromagnetic trip 59 that comprises a plunger 129 that is raised when the electromagnet 59 is energized to thereby automatically move the latch 117 in a clockwise (FIG. 5) direction to the actuated position.

The circuit interrupter is shown in the spring discharged closed position in FIGS. 1-5. In order to operate the circuit interrupter to the open position, the crank rod 65 is placed in the opening 63 (FIG. 5) of the drive member 61, and the crank rod 65 is manually cranked from the spring discharged closed position seen in FIG. 5 to the spring charged closed position seen in FIG. 6. During this movement, an extended part 131 of the drive member 61 engaged the pin 81 (FIGS. 4 and 5) to drive the intermediate member 79 and spring rod 67 from the spring discharged closed position seen in FIG. 5 to the overcenter spring charged closed position seen in FIG. 6. During this movement, the spring 77 is charged and near the end of this movement, the spring rod 67 passes overcenter relative to the axis of the operating shaft 45, whereupon the spring 77 starts to discharge driving the pin 81 against the extended part 87 of the member 85 to bias the member 85 and the operating shaft 45, to which the member 85 is secured, in a counterclockwise (FIG. 6) direction toward the open position seen in FIG. 7.

The overcenter spring structure 53 is latched in this spring charged closed position (FIG. 6) by the latch linkage 55 (FIG. 5) which prevents counterclockwise rotation of the operating shaft 45 and by the latch structure 57 which latches the latch linkage 55 in the position seen in FIG. 5. In this position, it is noted that a

toggle

91, 93 of the latch linkage 55 is underset or collapsed in a downward (FIGS. 5 and 6) direction. The parts will remain in the spring charged closed position seen in FIG. 6 until release of the latch linkage 55. Thus, energy is stored for a closing operation.

In order to close the circuit interrupter with the spring 77 in the charged position seen in FIG. 6, the latch member 117 (FIG. 5) is pivoted in a clockwise (FIG. 5) direction manually, by lifting the part 127, or electromagnetically by operation of the electromagnet 59 to move the plunger 129 upward to lift the part 127. During this movement, the latch 117 moves to release the roller 113 from the notch 115, permitting the roller latch 109 to rotate in a counterclockwise (FIG. 5) direction about the pin 111. This movement permits the roller 107 to move out of the notch 105, permitting the elongated link 97 to pivot in a counterclockwise direction about the pivot pin 103. This movement releases the

toggle

91, 93 to release the operating shaft 45, whereupon the charged spring 77 discharges driving the rod 67 from the spring charged closed position seen in FIG. 6 to the spring discharged open position seen in FIG. 7 with the pin 81 (FIGS. 4, 6, and 7) operating against the extended part 87 of the member 85 to drive the member 85, and the operating shaft 45 to which the member 85 is secured, in a counterclockwise direction from the spring charged closed position seen in FIG. 6 to the spring discharged open position seen in FIG. 7.

During that movement, the operating shaft 45 rotates from the closedposition seen in full lines in FIG. 3 to the open position seen in broken lines in FIG. 3 moving the links 37 of the three pole units to the position seen in broken lines in FIG. 3 to thereby move the three contact arms 25' to the open position seen in broken lines in FIG. 3. Upon movement of the parts from the spring charged closed position seen in FIG. 6 to the spring discharged open position seen in FIG. 7, the

toggle

91, 93 is moved from the collapsed or downward underset position seen in FIG. 6 to the collapsed or upward underset position seen in FIG. 7 during which movement the link 97 is movedfirst in a counterclockwise direction as the

toggle

91,93 moves to the erected position and then in a clockwise direction as the

toggle

91, 93 collapses to the upward underset position seen in FIG. 7. This movement automatically resets the toggle link 97 in the position seen in FIG. 7, and the

springs

121, 123 automatically reset the latches 109, 117, respectively, in the latching positions seen in FIG. 7.

In order to manually operate the circuit interrupter from the spring discharged open positionseen in FIG. 7 to the spring discharged closed position seen in FIG. 5, the circuit interrupter is first operated to the spring charged open position seen in FIG. 8. With the circuit interrupter in the position seen in FIG. 7, the crank 65 is moved from the position seen in FIG. 7 to the position seen in FIG. 8. During this movement, the drive member 61 is moved with the projecting portion 133 thereof operating against the-pin 81 (FIGS. 7 and 4) to drive the member 79 and the rod 67 from the spring discharged open position seen in FIG. 7 to the spring charged open position seen in FIG. 8. During this movement, the rod 67 goes overcenter relative to the axis of the operating shaft 45 and the spring 77, which is charged during the early part of this movement, starts to discharge forcing the rod 67 and member 79 in a counterclockwise (FIG. 8) direction. This movement is limited by the engagement of the pin 81 with the projecting part 89 of the member 85, that is secured to the operating shaft 45, and with the latch linkage 55 latched by means of the latch structure 57, the parts are latched in the stored energy spring charged open positions seen in FIG. 8.

In order to release the stored energy and close the circuit breaker, the part 127 of the latch member 117 is lifted, either manually or electromagnetically, to rotate the latch 117 in a counterclockwise direction to release the roller 113 from the notch 115 to release the roller latch member 109, permitting counterclockwise movement of the roller latch member 109. Upon release of the roller latch member 109 the roller 107 moves out of the notch 105 of the link 97 to permit counterclockwise movement of the link 97. This movement permits the

toggle

91, 93 to move from the upward underset position seen in FIG. 7 to thereby permit clockwise movement of the operating shaft 45. The spring 77 discharges and moves the rod 67 from the spring charged open position seen in FIG. 8 to the spring discharged closed position seen in FIG. 5. During this movement, the pin 81, operating against the part 89 of the member 85, drives the member and operating shaft 45 from the spring charged open position seen in FIG. 8 to the spring discharged closed position seen in FIG. 5. During this movement, the operating shaft 45 rotates in a clockwise (FIG. 3) direction to move the links 37 and the three contact arms 25 from the open position seen in broken lines in FIG. 3 to the closed position seen in full lines in FIG. 3. During this movement to the closed position, the movement of the operating shaft 45, operating through the

toggle

91, 93, first moves the link 97 in a counterclockwise direction as the

toggle

91, 93 moves to the erected position and then the link 97 is moved in a clockwise direction as the

toggle

91, 93 moves to the downward underset position seen in FIG. 5. This movement moves the link 97 to the latching position seen in FIG. 5, and the

springs

121, 123 operate to automatically reset the roller latch member 109 and latch member 117 in the latched position seen in FIG. 5. The circuit interrupter may then be operated to the spring charged closed position seen in FIG. 6 and to the springdischarged open position seen in FIG. 7 in the same manner as was hereinbefore described.

In accordance with this invention in order to provide adequate safety protection to operating personnel the disconnect or circuit interrupter 7 is provided, with an interlocking system as shown in FIGS. 9 to 12. The system comprises three interlocking structures that provide cooperating safety means responsive to varying conditions of the circuit interrupter 7.

The circuit interrupter 7 is usually disposed within an enclosure (not shown) having a door 135 as shown in FIGS. 1, 9, 10, and 12. In order to prevent access to the circuit interrupter 7 when the

contacts

21 and 25 are in the closed position as shown in FIG. 3, the door is locked in the closed position as shown more particularly in FIG. 9. For that purpose, an apertured lug or eye 137 is mounted on the inner surface of the door 135 in a suitable manner such as by a weld (not shown). In addition, an eye-engaging hook 139 is mounted on the operating shaft 45 in a suitable manner such as by a weld (not shown). Accordingly, when the shaft is in the contact closed position, the hook 139 engages the eye 137, thereby preventing opening of the door 135. When, however, the shaft 45 is in the contact open position, the hook 139 is in a retracted (broken line) position as shown in FIG. 9 which position is substantially counterclockwise from the contact closed position. In the alternative, it is understood that the hook and eye may be interposed in such a manner that the hook 139 may be mounted on the door with the outer end turned down and the eye 137 mounted on the shaft 45 so that rotation of the shaft would bring the eye into and out of engagement with the hook. Accordingly, when the interrupter 7 is in the contact closed position as shown in FIG. 3, the door 135 is locked to prevent operating personnel from having access to the interrupter.

When the door 135 is open, other potentially unsafe conditions may exist which should be guarded against. For example, when the door is open and the interrupter 7 is in the spring charged position with the contacts open, such as shown in FIG. 8, it is necessary to provide an additional interlock to block the shaft 45 from rotating in the event that the operating mechanism 49 is inadvertently actuated to trigger the spring closing structure 53. For that purpose, as shown in FIG. 10, an interlock structure 141 is provided. It consists of a U-shaped bar 143 and a projection or lug 145. The lug 145 is mounted on the shaft 45 and is movable between the solid and broken line positions of the lugs 145 as shown by the arrow 147. In the solid position of the lug 145, the shaft 45 is in the open position and in the broken line position, the shaft is in the closed position of the contacts.

The bar 143 is mounted on a C-shaped mounting bracket 149 which in turn is attached to a support channel 151 (FIG. 2) so that upper and lower portions of the U-shaped bar are supported in similar apertures 153 in the bracket where the bar is slidably mounted. A spring 155 is disposed between the mounting bracket 149 and a pin 157 for holding the bar 143 in the solid line position (FIG.-) with the upper end 143a of the bar in the position shown. A pair of wheels 159 is mounted on the end 143a of the bar for engagement with the inner surface of the door 143. The lower end 143b of the bar is then disposed in the solid line position and in the'path of movement of the lug 145. Accordingly, if the operating mechanism 49 is inadvertently actuated to release the spring charged structure 43, the operating shaft 45 is prevented from moving to the closed position by the lug 145 coming into contact with the end portion l43b of the bar 143. In that manner, when the door 135 is open, the spring 155 thrusts or actuates the bar 143 to the left as shown in FIG. 10 in order to move the lower end 143 of the bar into a blocking position with the lug 145, thereby providing a safety interlock for operating personnel.

When the door 135 is closed in the position shown in FIG. 10, the bar 143 is disposed in the broken line position against the spring 155, whereby the lower end 143b of the bar is retracted to the right and out of the path of movement of the lug 45. In that condition, with the door 135 closed, the operating shaft 45 is free to rotate to the closed position when the operating mechanism 49 is released.

In addition to the foregoing to provide adequate safety to operating personnel, it is necessary to make or render the interrupter or disconnect 7 inoperable when the enclosure door 135 is in the open position. This is achieved by providing the operating mechanism 49 with suitable interlock device, as shown in FIGS. 11 and 12. As was set forth above, the crank 65 (FIG. 7) is rotated clockwise about the shaft 45 to the position shown in FIG. 8 in order to move the pin 81 to the overset position of FIG. 8, thereby charging the spring 77. The drive member 61 which is rotatably mounted on the shaft 45 includes a pair of members 161 which extend substantially radially from the axis of the shaft 45. To prevent the operating mechanism 49 from being charged when the door 135 is open, the handle or crank 65 is restricted from rotation by an interlock structure 163 (FIGS. 11 and 12). The structure 163 comprises a lever or bellcrank 165 which is pivotally mounted on a pin 167 which, in turn, is mounted on a channel frame member 169. The structure also includes biasing means, such as a coil spring 171 and a camming member 173. A blocking pin 175 extends from one side of the bellcrank 165 and a camming pin 177 extends from the other side thereof, as shown in FIG. 11. The spring 171 having one end attached to the frame member 169 and the other end attached to the bellcrank 165 operates to pull the bellcrank 165 upwardly to the broken line position (FIG. 12), whereby the blocking 10 is disposed in the path of movement of the locking lug 161 when the door is open. When the door 135 is closed, the camming member 173, being suitably mounted on the inner surface of the door such as by a weld (not shown) and having a camming surface 179, holds the camming pin 177 downwardly against the pressure of the spring 171, whereby the blocking pin 175 is out of the path of movement of the locking lug 161. Thus, when the door 135 is open, the bellcrank 165 being in the upper position prevents rotation of the drive member 61; but when the door is closed, the bellcrank 165 is inoperative and the drive member 61 may be rotated in order to charge the spring 77.

Accordingly, the circuit interrupter with the interlocking system of the present invention provides adequate safety to operating personnel when operating enclosed load break disconnects or circuit interrupters fitted with stored energy overcenter spring operating means.

What is claimed is:

1. A circuit interrupter with an interlocking system comprising a stationary contact and a movable contact, an operating shaft supported for rotation between open and closed positions to move the movable contact between open and closed positions relative to the stationary contact, a contact arm supporting the movable contact at one end and being attached to the operating shaft at the other end, an overcenter spring structure operatively connected to the operating shaft, drive means operable from a first position to a second position to move the overcenter spring structure from a spring discharged open position to a spring charged open position, the overcenter spring structure being movable to a spring discharged closed position, the drive means being operable from the second position to the first position to move the overcenter spring structure from the spring discharged closed position, the overcenter spring structure being movable to a spring discharged open position for driving the operating shaft to the open position, an enclosure containing the circuit interrupter, an enclosure door for access to the operating shaft and the spring discharge structure, means for interlocking the enclosure door and the operating shaft to prevent opening of the door when the stationary contact and the movable contact are in the closed position, means for blocking the operating shaft from rotating to the closed position when the door is open and comprising cooperating interlocking structures that are movable between blocking and nonblocking positions with respect to each other when the door is open and closed respectively.

2. The circuit interrupter of claim 1 in which the means for interlocking the enclosure door and the operating shaft comprise interengaging members on the door and the shaft, and the interengaging member on the shaft being movable to a disengaged position when the shaft is in the open position.

3. The circuit interrupter of claim 2 in which the interengaging members include a hook on one of the door and shaft and an eye on the other of the door and shaft.

4. The circuit interrupter of claim 3 in which the hook is on the shaft and the eye is on the door, and in which the hook engages the eye when the shaft is in the open position.

5. The circuit interrupter of claim 1 in which the interlock structure comprises a projection on the shaft and a bar movably mounted between the door and the path of movement of the projection, and a portion of the bar being movable into and out of the path of movement of the projection when the door is open and closed respectively.

6. The circuit interrupter of claim 5 in which there are biasing means for moving the bar into the path of movement of the projection when the door is opened, and the bar being retained out of said path against the biasing means when the door is closed.

7. A circuit interrupter with an interlocking system comprising a stationary contact and a movable contact, an operating shaft supported for rotation between open and closed positions to move the movable contact between open and closed positions relative to the stationary contact, a contact arm supporting the movable contact at one end and being attached to the operating shaft at the other end, an overcenter spring structure operatively connected to the operating shaft, drive means operable from a first position to a second position to move the overcenter spring structure from a spring discharged open position to a spring charged open position, the overcenter spring structure being movable to a spring discharged closed position for driving the operating shaft to the closed position, the drive means being operable from the second position to the first position to move the overcenter spring structure from the spring discharged closed position to a spring charged closed position, the overcenter spring structure being movable to a spring discharged open position for driving the operating shaft to the open position, an enclosure containing the circuit interrupter, an enclosure door for access to the operating shaft and the spring discharge structure, the drive means comprising a member rotatably mounted on the operating shaft and operatively connected to the overcenter spring structure and including a second arm extending outwardly from the member, the second arm being operable from a first position to a second position, an interlock structure movably mounted adjacent to said member between positions within and retracted from the path of movement of the second arm, the interlock structure being within the path of movement of the second arm when the door is open, and a cam on the door to hold the interlock structure in the position retracted from the path of movement of the member when the door is closed.

8. The circuit interrupter of claim 7 in which there is biasing means for biasing the interlock structure within said path of movement of the arm.

9. The circuit interrupter of claim 7 in which the interlock structure comprises a lever and a latch pin on the lever, and the pin being movable into the path of movement of the arm when the door is open.

10. A circuit interrupter with an interlocking system comprising a stationary contact and a movable contact, an operating shaft supported for rotation between open and closed positions to move the movable contact between open and closed positions relative to the stationary contact, a contact arm supporting the movable contact at one end and being attached to the operating shaft at the other end, an overcenter spring structure operatively connected to the operating shaft, drive means operable from a first position to a second position to move the overcenter spring structure from a spring discharged open position to a spring charged open position, the overcenter spring structure being movable to a spring discharged closed position for driving the operating shaft to the closed position, the drive means being operable from the second position to the first position to move the overcenter spring structure from the spring discharged closed position to a spring charged closed position, the overcenter spring structure being movable to a spring discharged open position for driving the operating shaft to the open position, an enclosure containing the circuit interrupter, an enclosure door for access to the operating shaft and the spring discharge structure, means for interlocking the enclosure door and the operating shaft to prevent opening of the door when the stationary contact and the movable contact are in the closed position, and means for blocking the operating shaft from rotating to the closed position when the door is open and comprising an interlock structure which is inoperative when the door is closed, and means movably mounted adjacent to the drive means and responsive to the door for blocking discharge of the charged overcenter spring when the door is open.