US3248500A

US3248500A - Multipole circuit interrupting device having a removable fuse unit with a common unitary tripping bar

Info

Publication number: US3248500A
Application number: US215858A
Authority: US
Inventors: Albert R Cellerini; Majcher John
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1962-08-09
Filing date: 1962-08-09
Publication date: 1966-04-26
Anticipated expiration: 1983-04-26
Also published as: ES289594A1; DE1229631B; CH403036A; FR1383781A

Description

April 1966 A. R. CELLERINI ETAL 3,

MULTIPOLE CIRCUIT INTERRUPTING DEVICE HAVING A REMOVABLE FUSE UNIT WITH A COMMON UNITARY TRIPPING BAR Filed Aug. 9, 1962 5 Sheets-Sheet 1 III Fig.l.

April 1966 A. R. CELLERINI ETAL 3, 48,500

MULTIPOLE- CIRCUIT INTERRUPTING DEVICE HAVING A REMOVABLE FUSE UNIT WITH A COMMON UNITARY TRIPPING BAR 5 Sheets-Sheet 2 Filed Aug. 9

April 1966 A R. CELLERINI ETAL 3,248,500

MULTIPOLE CIRCUIT IN TERRUPTING DEVICE HAVING A REMOVABLE FUSE UNIT WITH A COMMON UNITARY TRIPPING BAR Filed Aug. 9, 1962 3 Sheets-Sheet 5 [5' 'III'IIIIIIIII WITNESSES: INVENTOR Albert R Cellerini a a 8 John Mojcher.

ATTORNEY MULTIPOLE CIRCUIT INTERRUPTING DEVICE HAVING A REMOVABLE FUSE UNIT WITH A COMMON UNITARY TRIPPING BAR Albert R. Celleriui, Beaver, and John Majcher, Chippewa Township, Beaver County, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa. a corporation of Pennsylvania Filed Aug. 9, 1962, Ser. No. 215,858 2 Claims. (Cl. 200-114) This invention relates generally to circuit interrupters and more particularly to circuit interrupters of the type comprising a low'cost circuit breaker and a fuse unit electrically connected in series'relation with the circuit breaker to interrupt fault currents that exceed the interrupting capacity of the circuit breaker.

An object of this invention is to provide an improved compactly constructed circuit interrupter comprising a circuit breaker and a fuse unit connected in electrical series with the circuit breaker.

Another object of this invention is to provide an improved multi-pole circuit interrupter comprising a multipole circuit breaker and a multi-pole fuse unit removably mounted on the circiut breaker and connected in electrical series with the circuit breaker, with means for tripping the circuit breaker upon removal of the fuse unit and means for tripping the circuit breaker when one of the fuses of the fuse unit blows.

A more general object of this invention is to provide an improved circuit interrupter which largely retains the advantages of circuit breakers over fuses and at the same time embodies the desirable current-limiting function of current-limiting fuses when there is a heavy short circuit, without requiring the use of an expensive circuit breaker of high interrupting capacity.

The invention, both as to structure and operation, together with additional objects and advantages thereof, will be best understood from the following detailed description when read in conjunction with the accompanying drawings.

In said drawings:

FIGURE 1 is a top plan View, with parts broken away, of a circuit interrupter embodying principles of this invention; I

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

FIG. 3 is a top plan view, with parts broken away, of the removable trip unit seen in FIGS. 1 and 2;

FIG. 4 is a sectional view taken generally along the line lV--IV of FIG. 3, with the trip unit cover seen in FIG. 3 removed;

FIG. 5 is a bottom plan view of the removable fuse unit seen in FIGS. 1 and 2; and

FIG. 6 is a sectional view taken generally along the line VIVI of FIG. 5.

' Referring to the drawings, and particularly to FIGS. 1

and 2, there is shown therein a circuit interrupter 3 com- Serial No. 819,268, filed June 10, 1959, and assigned to the assignee of the instant application. For this reason, only a brief description of the circuit breaker 5 will be given herein.

Each pole unit of the circuit interrupter 3 comprises a line terminal conductor 15 and a load terminal conductor 17. A solderless terminal connector 19 of a type well United States Patent 0 3,248,500 Patented Apr. 26, 1966 "Ice known in the art is connected at the outer end of each of the terminal conductors 15, 17 to enable connection of the circuit interrupter in an electrical circuit.

'switch arm 31- for the center pole unit.

The circuit breaker 5 is of the three-pole type, only the center pole being shown in FIG. 2. An operating mechanism 20, common to all of the poles, is disposed in the center pole compartment. A stationary contact 22 is rigidly mounted on the inner end of each of the terminal conductors 17. A movable contact 23 is provided to cooperate with each of the stationary contacts 22. Each of the movable contacts 23 is secured to a movable contact arm 25 that is movably mounted, by securing means 29, on a switch arm 31. The switch arms 31 for the three pole units are secured to a common insulating tie bar 35 that is rotatably supported in the

circuit breaker housing

11, 13. Springs 36 are provided to bias the contact arms 25 clockwise about the switch arms 31 to provide contact pressure in the closed position of the contact arms.

The operating mechanism 20 is disposed in the center pole unit and it comprises a generally U-shaped operating lever 41 having its inner end portions pivoted on a suitable frame 42 that is mounted on the base 11. The operating lever 41 has an arcuate insulating shield 47 mounted on the outer end thereof. A handle portion 49 extends out from the shield 47 through an opening 51 in the cover 13. The switch arm 31 for the center pole unit is connected, by means of a toggle comprising links 53 and 55, to a releasable trip member or cradle 57 that is pivotally mounted on the frame 42 by means of a pin 59. The toggle links 53 and 55 are pivotally connected together by a knee pivot pin 61. The toggle link 53 is pivotally connected to the releasable trip member 57 by means of a pin 63, and the toggle link 55 is pivotally connected by means of a pin 65 to an extension of the Over center springs 67 (only one spring being shown in FIG. 2) are connected under tension between the knee pivot pin 61 of the toggle 53, 55 and the bight portion of the U-shaped operating lever 41.

The contacts for all of the poles are manually closed and opened in a well-known manner by movement of the operating lever 41 to the on and off positions. Movement of the lever 41 to the on position moves the springs 67 over center to straighten the toggle 53, 55 to thereby move the switch arm 31 for the center pole unit to the closed position. Since the switch arm 31. for the center pole unit is connected to the tie bar 35, this movement rotates the tie bar 35 clockwise (FIG. 2) to simultaneously move all of the switch arms 31 to the closed position. Reverse movement of the operating lever 41 to the oil position moves the springs 67 over center to cause collapse ofthe toggle 53, 55. This movement rotates the tie bar 35' counterclockwise to move all of the switch arms 31 to the open position seen in FIG. 2.

The releasable member 57 is held in the latching position seen in FIG. 2 by means of a latch 71 that is part of a multi-pole trip unit 73, which trip unit is removably mounted in the

circuit breaker housing

11, 13. The trip unit 73 :(FIGS. 3 and 4) comprises an insulating base 75 on which is mounted a trip-unit mechanism, and an insulating two-part cover 77 that cooperates with the base 75 to enclose the trip-unit mechanism in the same general manner as that described in the copending application of Robert H. Hill et 211., Serial No. 846,980, filed October 16, 1959, and assigned to the assignee'of the instant application. A conductor 79 is provided for each pole unit to enable connection of the trip unit 73 in the circuit interrupter 3. As can be seen in FIG. 4, each of the conductors 79 passes through a generally U-shaped magnetic yoke 81 that is suitably mounted on the trip unit base 75. An armature 83 is pivotally supported on one leg of each of the magnetic yokes 81 and is biased to the open position seen in FIG. 4 by means of a spring 85. The opening movement of each of the armatures 83 is limited by engagement thereof with an adjusting screw 87 that is mounted on one end of a lever 89, which lever is pivoted, intermediate its ends, by means of a pin 91 on a bracket 93. The other end of each of the levers 89 engages a cam 95 (seen in only the center-pole unit of FIG. 4) that is supported on the bracket 93 and rotatable by operation of a knob 96. The knob 96 is rotated to rotate the cam 95, which movement pivots the lever 89 to adjust the air gap between the armature 83 and the associated magnet yoke 81. Each of the pole units of the trip device 73 also comprises a rod 97 that is pivotally attached at one end to the associated armature 83. A head portion 99 on the other end of each of the rods 97 is provided to engage an insulating trip bar 101 that is common to all of the pole units of the trip unit 73 and is rotatably supported on the base 75 by means of two pivot pins 103 (only one of the pivot pins being shown in FIG. 4).

Upon the occurrence of an overload current above a predetermined value through the conductor 79 for any of the pole units of the trip unit 73, the associated magnet yoke 81 is energized sufficiently to draw the armature 83 into engagement with the one leg of the magnet yoke 81 pulling the rod 97 downward (FIG. 4) to rotate the trip bar 101. This effects movement of the latch 71 (FIGS. 2 and 3) to release the releasable member or cradle 57, whereupon the member 57 is rotated clockwise about the .pivot 59 by means of the springs 67 to cause collapse of the toggle 53, 55. This movement rotates the tie bar 35 counterclockwise (FIG. 2) to open all of the contacts 22, 23.

The circuit breaker is trip-free in that the mechanism will operate to open the contacts when a tripping overload occurs oven if the handle 49 is held in the closed position.

Upon the occurrence of a low persistent overload current below a predetermined value in any of the pole units, a bimetal member (not shown) in the overloaded pole unit is heated and flexes to rotate the trip bar 101 to trip the circuit breaker after a time delay in a manner specifically described in the aforementioned patent application of Glen R. Thomas, Serial No. 819,268, filed June 10, 1959.

Before the breaker contacts can be closed following an automatic opening or tripping operation, it is necessary to reset and relatch the mechanism. This is accomplished by moving the handle 49 clockwise to the full off position. During this movement, a projection 107 on the operating lever 41 engages a shoulder 109 on the releasable member 57 to move the member 57 counterclockwise about its pivot 59. Near the end of this movement, the lower free end of the member 57 engages under the latch 71 to be held in the operative latched position seen in FIG. 2. Thereafter, the contacts can be closed and opened by operation of the handle 49 in the same manner previously described.

Referring to FIG. 2, it can be seen that the removable trip unit 73 is mounted in the circuit breaker by means of a bolt 113 for each pole unit that secures the one end of the conductor 79 to a terminal strip 115, and a bolt 117 for each pole unit that secures the other end of the conductor 79 to a terminal strip 119.

The multi-pole fuse unit 7 (FIGS. 1, 2, 5 and 6) comprises a housing 131 of molded insulating material having barriers 132 that divide the housing into three separate compartments. A fuse 133 is removably mounted in each of the compartments and is secured therein by a removable insulating securing plate 134. Each of the fuses 133 has a conductor 135 connected to one end thereof and a conductor 137 connected to the fuse near the other end. A plug-in type connector 139 is connected to the conductor 135, and a plug-in type connector 141 is connected to the conductor 137. A spring-loaded plunger or actuator 145 is disposed at one end of each of the fuses 133, and it passes through a suitable opening in the associated conductor 135. Each of the plungers is biased to move outward and away from the fuse 133 when the fuse blows. This plunger and biasing means for operating it may be in one of the forms disclosed, for example, in the patent to Rawlins et al., Patent No. 2,435,844, issued February 10, 1948.

The fuse unit 7 also comprises a tripping bar structure 147 that is rotatably supported in the fuse unit housing 131 by means of barriers 148. The tripping bar structure 147 is common to all three poles of the fuse unit. The tripping bar structure 147 comprises an insulating tripping bar 149 having three insulating arm portions 151 molded integral therewith, each of which arm portions 151 is positioned adjacent one of the plungers 145 of one of the fuses 13 3. A single elongated actuating arm 153 is riveted to the trip bar 149 in a position that will be adjacent an elongated rod (FIG. 2) when the fuse unit 7 is mounted on the circuit breaker 5. As is seen in FIG. 6, a spring 157 is positioned between the housing 131 and a support 158 that is riveted to the trip bar 149, to bias the trip bar into a position wherein the arms 151 thereof engage the plungers 145.

When the fuse unit 7 is in place (FIG. 2) and the contacts 22, 23 of the circuit interrupter 3 are in the closed position, the circuit through each pole unit of the multipole circuit interrupter 3 extends from the line terminal 15, through a tulip-type connector 163 that is mounted on the terminal 15, the plug-in type connector 139, the conductor 135 (FIG. 6), the fuse 133, the conductor 137, the plug-in type connector 141, a tulip-type connector 165 (FIG. 2) that is mounted on the terminal conductor 115, the trip-unit conductor 79, the conducting strip 119, through a flexible conductor 167 that is secured at one end to the conductor 119 and at the other end to the associated contact arm 25, the contact arm 25, the contacts 23, 22 to the load terminal conductor 17.

When a fuse 133 in any of the poles blows in response to a severe overload current, biasing means (not shown) within the fuse operates to move the plunger 145 outward against the associated arm 151 (FIG. 6) to rotatethe tripping bar 149 in a tripping direction against the bias of the spring 157. During this movement, the arm 153, that is attached to the tripping bar 149, engages the elongated rod 150 (FIGS. 2 and3) moving the rod rectilinearly inwardly against the bias of a spring 171. The spring 171 is positioned over the rod 150 and is supported between the cover 77 of the trip unit 73 and a bracket 173 that is attached to the outside of the cover 77 to support the rod 150. As the rod 150 is moved inward, it engages and rotates the trip bar 101 (FIGS. 3 and 4) to effect release of the member 57 and tripping of the circuit breaker in the same manner hereinbefore described. The plunger or actuator 145 of the blown fuse 133 will remain in the position holding the tripping bar 149 of the fuse unit 7 in the tripped position to thereby hold the trip bar 101 of the trip unit 73 in the tripped position to prevent relatching of the circuit breaker. Thus the circuit breaker cannot be operated while the fuse unit, with the blown fuse therein, is in the connected position.

Referring to FIG. 3, it will be, seen that an elongated rod 183 is operatively connected to the trip bar 10 1 by means of a supporting plate 185. The supporting plate 185 is attached to the trip bar 101 by means of two screws 187 that pass through an elongated slot in the plate 185. The plate 185 is mounted for limited vertical movement (FIG. 4) relative to the trip bar 101 to permit assembly of the cover 77 over the knobs 97 with the rod 183 passing through an opening in the cover 77. A compression spring 189 (FIG. 3) is placed over the rod 183 and supported between the trip unit base 75 and a shoulder portion 191 on the rod 183-. A bracket 193, having an opening therein to receive the rod 183, is suitably secured to the trip unit cover 77 to support the outer end of the rod 183 for generally rectilinear reciprocal movement.

- 3,24s,5oo

When the fuse unit 7 is placed in the connected position (FIG. 2) on the circuit breaker 5, a cam surface 195, that is molded integral with the fuse unit housing 131, engages the rod 183 moving the rod 183 inward to charge the spring 189 (FIG. 3), and to permit the trip bar 101 to assume the normal latching position. The trip bar 101 is biased to the normal latching position by means of two springs; one on each side of the trip bar. A spring 196 is positioned between the trip unit base 75 and the trip bar 101 on the lower (FIG. 4) side of the trip bar 101 to bias the trip bar in one direction, and an adjustable spring 197 is positioned between the bracket 93 and the trip bar 101 on the lower side of the pivot of the trip bar 101 to bias the trip bar in the opposite direction.

The shock-proof type biasing action of these springs maintains the trip bar in latching position under normal current conditions. When the fuse unit 7 is removed from the circuit interrupter, the charged spring 189 operates against the shoulder portion 191 (FIG. 3) of the rod 183 to move the rod 183 outwardly. During this movement the shoulder 191 of the rod 183 engages the plate 185 to rotate the trip bar 101 in a tripping direction. This moves the'latch 71 to effect release of the releasable member 5'7 and opening of all of the circuit breaker contacts 22, 23 if the contacts are closed when the fuse unit is removed. If the contacts are open when the fuse unit is removed, the rod 183 will move the trip bar 101 to the tripping position to prevent relatching of the cradle or releasable member 57 to thereby provide that the circuit breaker cannot be operated when the fuse unit 7 is not in place.

If the fuse unit 7 should be placed in position on the interrupter with a blown fuse still in the holder, the plunger oractuator 145 (FIGS. 5 and 6) would hold the tripping bar 149 in the tripping position, and a lower cam portion 194 (FIG. 6) on the arm 153 would engage the elongated rod 150 (FIG. 3) to cam the rod 150 inwardly to maintain the trip bar 101 in the tripped position and prevent resetting of the circuit breaker 5. Thus, when the fuse unit 7 is placed in position, as the elongated rod 183 is cammed to a position to no longer maintain the trip bar 101 in the tripping position, the elongated rod 150, by virtue of the blown fuse, is cammed to a position to maintain the trip bar 101 in the tripping position. Thus, the circuit interrupter cannot be operated when the fuse unit is replaced if the blown fuse is still in the fuse unit.

From the foregoing, it will be understood that there is provided by this invention an improved compactly constructed multi-pole circuit interrupting device comprising a manually and automatically operable circuit breaker and a removable fuse unit connected in electrical series with the breaker. The operating characteristics of the two devices are such that the circuit breaker functions in a conventional manner to interrupt fault currents within its interrupting capacity and the fuses become effective to interrupt fault currents greater than those which the circuit breaker can safely interrupt. The advantages of this general type of circuit interrupting device are more thoroughly explained, for example, in the patent to H. E. Reichert et al., Patent No. 3,009,035.

' The circuit interrupting device of this invention is provided with a removable separately enclosed trip unit that can be mounted in assembled condition in the interrupting device; The trip unit comprises a first generally rectilinearly movable rod that extends out through an opening in the trip-unit housing. The removable fuse unit comprises a common tripping bar structure that is rotated when any one of the fuses blows to engage and move the first rod to trip the breaker. The trip unit also comprises a second generally rectilinearly movable rod that extends out through another opening in the trip unit housing. The fuse unit is provided with a cam surface molded integral with the fuse unit housing, which surface engages the second rod when the fuse unit is moved into operative position to cam the second rod to an inoperative position. This cam surface is rigid and unyielding to provide a definite camming action against the second rod. When the fuse unit is removed, the second rod is released whereupon biasing means operates to move the second rod to trip the breaker. Since both of the rods that are mounted on the trip unit move generally rectilinearly, they substantially close the openings, in the trip unit cover, through whichthey protrude, thereby making it more difficult for anyone to tamper with the internal mechanism of the enclosed trip unit.

While the invention has been described in accordance with the provisions of the patent statutes, it is to be understood that various changes and modifications may be made in the structural details disclosed and in the arrangement of parts without departing from the spirit and scope of the invention.

We claim as our invention:

I. A multi-ipole circuit interrupting device comprising.

in combination, a circuit breaker comprising a first housing, a multi-pole circuit breaker mechanism disposed generally within said first housing and comprising separable contact means for each pole, a removable multi-pole trip unit com-prising a second housing and a trip unit mechanism disposed generally within said second housing, said trip unit mechanism comprising a trip device for each pole and a tripbar common to all of said poles, said trip bar being movable to open all of said contact means, a first member mounted on said trip unit and extending out from said second housing, a second member mounted on said trip unit and extending out from said second housing, a multi pole fuse unit supported adjacent said trip unit, said fuse unit comprising a third housing, fuse unit means supported on said third housing and comprising a fuse for each pole of said circuit breaker and a common tripping 'bar structure, each of said fuses comprising means operable upon the occurrence of certain current conditions to move said common tripping bar structure to thereby move said first member to move said trip .bar to open all of said contact means, connecting means removably connecting said fuse unit to said circuit breaker, said connecting means comprising plug-in type terminal means connecting said fuses in electrical series with said contacts, said fuse unit being removed by removal of said third housing during which removal said plug-in type terminal means is automatically disconnected and during which removal said fuses which are supported on said third housing and said common tripping bar structure which is supported on said third housing are removed with said third housing, said fuse unit comprising fixed means on said third housing holding said second member in an inoperative position when said fuse unit is mounted on said circuit breaker, upon removal of said fuse unit said second member being released by said fixed means on said third housing whereupon said second member automatically moves said trip bar to open all of said contact-s, and said fixed means on said third housing operating to move said second member to an inoperative position when said fuse unit is moved into operative position.

2-. A multi-pole circuit interrupting device comprising, in combination, a circuit breaker com-prising a first housing, a multi-pole circuit breaker mechanism disposed generally within said first housing and comprising separable contact means for each pole, a removable multipole trip unit comprising a second housing, said second housing comprising an insulating trip unit base and insulating trip unit cover means removably secured to said base, trip unit means supported generally within said second housing and comprising a trip device for each pole unit, each of said trip devices being mounted on trip unit cover means and extending out from said sec- 0nd housing, a second elongated member operatively connected to said trip bar and extending out from said housing, said second elongated member being supported for generally rectilinear longitudinal movement, fuse unit means removably mounted in said circuit interrupting device adjacent said trip unit, plug-in type terminal means connecting said fuse unit means in electrical series with said contact means, said fuse unit means comprising a third housing and a fuse for each pole of said circuit breaker mounted on said third housing, a common unitary tripping bar structure mounted on said third housing and having an arm portion adjacent each of said fuses, an actuating arm on said common tripping bar structure, each of said fuses comprising means operable upon the occurrence of certain current conditions to engage the associated arm portion of said common tripping bar structure and move said common tripping bar structure whereupon said actuating arm engages said first elongated member to move said first elongated member and said common trip bar structure to open all of said contact means, said fuse unit being removed by removal of said third housing during which removal said \plug-in ty-pe terminal means is automatically disconnected and during which removal said fuses which are supported on said third housing and said common tripping bar structure which is supported on said third housing are removed with said third housing, said third housing com-prising, cam means formed integral therewith, said cam means engaging and holding said second elongated member in an inoperative position when said fuse unit is mounted in operative position, and upon removal of said fuse unit said cam means being moved to permit said second elongated member to automatically move said common trip bar and effect opening of all of said contact means, said cam means operating when said fuse unit is moved into operative position to cam said second elongated member to an inoperative position.

References Qited by the Examiner UNITED STATES PATENTS 2,824,929 2/ 1950 Bdmunds 20046 3,009,035 11/1961 Reichert et a1 2001 14 3,009,037 111/1961 Jones et a1. 200-416 X 3,116,385 12/1963 Scott 200-114 BERNARD A. GILHEANY, Primary Examiner. ROBERT K. SCHAEF-ER, Examiner.

Claims

1. A MULTI-POLE CIRCUIT INTERRUPTING DEVICE COMPRISING IN COMBINATION, A CIRCUIT BREAKER COMPRISING A FIRST HOUSING, A MULTI-POLE CIRCUIT BREAKER MECHANISM DISPOSED GENERALLY WITHIN SAID FIRST HOUSING AND COMPRISING SEPARABLE CONTACT MEANS FOR EACH POLE, A REMOVABLE MULTI-POLE TRIP UNIT COMPRISING A SECOND HOUSING AND A TRIP UNIT MECHANISM DISPOSED GENERALLY WITHIN SAID SECOND HOUSING, SAID TRIP UNIT MECHANISM COMPRISING A TRIP DEVICE FOR EACH POLE AND A TRIP BAR COMMON TO ALL OF SAID POLES, SAID TRIP BAR BEING MOVABLE TO OPEN ALL OF SAID CONTACT MEANS, A FIRST MEMBER MOUNTED ON SAID TRIP UNIT AND EXTENDING OUT FROM SAID SECOND HOUSING, A SECOND MEMBER MOUNTED ON SAID TRIP UNIT AND EXTENDING OUT FROM SAID SECOND HOUSING, A MULTI-POLE FUSE UNIT SUPPORTED ADJACENT SAID TRIP UNIT, SAID FUSE UNIT COMPRISING A THIRD HOUSING, FUSE UNIT MEANS SUPPORTED ON SAID THIRD HOUSING AND COMPRISING A FUSE FOR EACH POLE OF SAID CIRCUIT BREAKER AND A COMMON TRIPPING BAR STRUCTURE, EACH OF SAID FUSES COMPRISING MEANS OPERABLE UPON THE OCCURRENCE OF CERTAIN CURRENT CONDITIONS TO MOVE SAID COMMON TRIPPING BAR STRUCTURE TO THEREBY MOVE SAID FIRST MEMBER TO MOVE SAID TRIP BAR TO OPEN ALL OF SAID CONTACT MEANS, CONNECTING MEANS REMOVABLY CONNECTING SAID FUSE UNIT TO SAID CIRCUIT BREAKER, SAID CONNECTING MEANS COMPRISING PLUG-IN TYPE TERMINAL MEANS CONNECTING SAID FUSE IN ELECTRICAL SERIES WITH SAID CONTACTS, SAID FUSE UNIT BEING REMOVED BY REMOVAL OF SAID THIRD HOUSING DURING WHICH REMOVAL SAID PLUG-IN TYPE TERMINAL MEANS IS AUTOMATICALLY DISCONNECTED AND DURING WHICH REMOVAL SAID FUSES WHICH ARE SUPPORTED ON SAID THIRD HOUSING AND SAID COMMON TRIPPING BAR STRUCTURE WHICH IS SUPPORTED ON SAID THIRD HOUSING ARE REMOVED WITH SAID HOUSING, SAID FUSE UNIT COMPRISING FIXED MEANS ON SAID THIRD HOUSING HOLDING SAID SECOND MEMBER IN INOPERATIVE POSITION WHEN SAID FUSE UNIT IS MOUNTED ON SAID CIRCUIT BREAKER, UPON REMOVAL OF SAID FUSE UNIT SAID SECOND MEMBER BEING RELEASED BY SAID FIXED MEMBER ON SAID THIRD HOUSING WHEREUPON SAID SECOND MEMBER AUTOMATICALLY MOVES SAID TRIP BAR TO OPEN ALL OF SAID CONTACTS, AND SAID FIXED MEANS ON SAID THIRD HOUSING OPERATING TO MOVE SAID SECOND MEMBER TO AN INOPERATIVE POSITION WHEN SAID FUSE UNIT IS MOVED INTO OPERATIVE POSITION.