US3501731A

US3501731A - High voltage circuit interrupter

Info

Publication number: US3501731A
Application number: US663019A
Authority: US
Inventors: Calvin C Patterson
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1967-08-24
Filing date: 1967-08-24
Publication date: 1970-03-17
Anticipated expiration: 1987-03-17
Also published as: SE344136B; BE718705A; SE344139B; ES357486A1; FR1578503A; ES357490A1; GB1200705A; FR1577703A; BE719026A; US3401247A; GB1200706A

Description

March 17, 1970 c. c. PATTERSON HIGH VOLTAGE CIRCUIT INTERRUPTER Filed Aug. 24. 1967 FIG. 3.

FIG.|.

United States Patent 3,501,731 HIGH VOLTAGE CIRCUIT IN TERRUPTER Calvin C. Patterson, Bethel Park, Pa., assignor to Westinghouse Electric Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Filed Aug. 24, 1967, Ser. No. 663,019 Int. Cl. H01h 85/02 U.S. Cl. 337203 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates to high voltage circuit interrupters and more particularly, to high voltage fuse structures.

More specifically, a pivotally mounted fuse holder having fusible means disposed therein is normally latched in a closed circuit condition with a pair of spaced, relatively stationary contacts which are mounted on a pair of spaced insulatnig supports. A body of gas evolving arc-extinguishing material is disposed in the fuse holder and during an interrupting operation, gas from saidbody is evolved and exhausted from one end of the holder. In order to prevent axial movement of the holder due to the gas exhausted during an interrupting operation and to insure that both of the insulating supports share the mechanical stresses which result, means are provided on both of the insulating supports which engage the holder to prevent such axial movement and to insure such sharing of mechanical stresses.

In the construction of certain high voltage circuit interrupters, such as power fuses, a problem arises in providing adequate insulating supports for power fuses of the type which are freely vented only at one end thereof. Where the power fuse includes a fuse holder having fusible means and a body of gas evolving material disposed therein, the fuse holder is normally pivotally sup ported adjacent to one end on an associated hinge structure which is mounted on a first insulating support along with a first relatively stationary contact which is adapted to engage a terminal disposed adjacent to one end of the holder. A power fuse of the type described also includes a latching means which is mounted on a second insulating support along with a second relatively stationary contact which is adapted to engage a terminal disposed adjacent to the other end of the associated holder. When such a power fuse blows and exhausts high pressure gas at only one end of the holder, a thrust results which tends to move the holder axially. If only the hinge structure of the power fuse includes means for restraining the axial movement of the holder, the insulating support associated with the hinge structure must withstand substantially all of the stresses due to the axial thrust which results during the operation of the power fuse. It is therefore desirable to provide an improved power fuse structure of the type described which includes means for insuring that both of the insulating supports which form part of the power fuse structure share the mechanical stresses which result when only one end of the power fuse is freely vented.

It is an object of this invention to provide a new and improved high voltage circuit interrupter construction.

Another object of this invention is to provide a power fuse structure of the type which is freely vented at only one end including means for insuring that both of the insulating supports which form part of such a power fuse structure share the mechanical stresses which result during an interrupting operation of the power fuse.

A more specific object of this invention is to provide a high voltage power fuse construction including means for preventing axial movement of the fuse holder at both the hinged end and at the latching end of the power fuse structure.

Other objects of the invention will, in part, be obvious, and will, in part, appear hereinafter.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a side elevational view of a high voltage power fuse structure which embodies the principles of the present invention and which is shown in the closed operating condition;

FIG. 2 is an enlarged, longitudinal, sectional View of a fuse unit which forms part of the power fuse structure shown in FIG. 1 with portions of the end fittings of the fuse unit omitted;

FIG. 3 is an enlarged front elevational view of a portion of the power fuse structure shown in FIG. 1; and

FIG. 4 is an enlarged plan view, in section, of a portion of the power fuse structure shown in FIG. 1 taken along the line IV-IV in FIG. 3.

Referring now to the drawings and FIG. 1 in particular, the structure shown comprises a power fuse structure of the high voltage, drop-out type, the general arrangement of which is set forth more fully in copending application Ser. No. 663,020, filed Aug. 24, 1967, by R. E. Frink and C. T. Walker, which issued May 27, 1969 as U.S. Patent 3,447,114 and which is assigned to the same assignee as the present application. As illustrated in FIG. 1, the power fuse structure 10 includes a base (not shown) formed of sheet metal and a pair of vertically spaced, outwardly extending or projecting insulator supports 272 and 282. The upper insulator support 272 fixedly supports in position a latching assembly 250 which includes a relatively stationary break contact 252, as described in greater detail in the copending application just mentioned. The lower insulator support 282 supports a hinge assembly 260 which, in turn, pivotally supports a fuse unit and which includes a relatively stationary hinge contact 262 and a generally U-shaped hinge member 285 as described in the copending application just mentioned. As illustrated in FIG. 1, the fuse unit 100 serves to electrically bridge the upper break contact 252 and the lower hinge contact 262 so that electric current will normally pass therebetween by wa of terminal pads (not shown) to which an external electrical circuit may be connected.

The fuse unit 100 includes a generally tubular fuse holder or casing 32 which is formed from a suitable weather-proof, electrically insulating material, such as a filament wound, glass epoxy material or the like, and a pair of upper and lower end fittings or

terminals

34 and 36, respectively, which are disposed at or adjacent to the opposite ends of the casing 32 and which are formed from an electrically conducting material, as best shown in FIG. 2. The upper and lower end fittings or

terminals

34 and 36, respectively, are securely fastened to the opposite ends of the associated holder or casing 32 by suitable means, such as cement, and a plurality of pins (not shown) which pass transversely through both the end fittings or terminals '34 and 36 and the associated holder 32. As illustrated, the fuse unit 100 also includes at its upper end a hook-eye 274 which is pivotally mounted on a laterally projecting portion 34A of the upper terminal 34, as shown in FIG. 2, and which may be used for effecting opening and closing movements of the fuse unit 100 by means of a conventional hook-stick, as explained in detail in the copending application previously mentioned. The lower terminal 36 includes a hinge lifting eye 284 which may be formed integrally with the lower terminal 36 and which may be employed in conjunction with a conventional hook-stick to effect physical removal of the fuse unit 100 from the hinge assembly 260 for replacement or insertion of the fuse unit 100. The lower terminal 36 also includes an inwardly projecting flange portion 36B against which the lower end of the holder or casing 32 bears, as shown in FIG. 2.

As described in greater detail in the copending application previously mentioned, the hinge member 285 of the hinge assembly 260 includes a pair of laterally spaced side wall portions, as indicated at 289 in FIG. 1. The side wall portions 289 of the hinge member 285 include slots which are adapted to receive a pair of trunnions as indicated at 293 in FIG. 1 which may be formed integrally with or mounted on the lower terminal 36 of the fuse unit 100. In order to assist in guiding the rotational travel of the fuse unit 100 during at least part of its movement, the lower terminal 36 also includes a pair of laterally projecting cylindrical portions as indicated at 287 in FIG. 1, which engage and bear against the cam surfaces provided on the side wall portions 289 of the hinge member 285, as indicated at 291. The projecting portions 287 also cooperate with the side wall portions 289 of the hinge member 285 to assist in preventing axial movement of the fuse unit 100 during an interrupting operation of the fuse unit 100, as will be explained more fully hereinafter.

As also described in greater detail in the copending applicaton previously mentioned, the latching assembly 250 is provided to releasably latch the fuse unit 100 in the closed circuit position shown in FIG. 1 and to provide the necessary means for transferring electrical current between an external circuit to which the fuse structure may be electrically connected and the upper end of the fuse unit 100 at the upper terminal 34. In addition, the latching assembly 250 may include means for automatically actuating the drop-out movement of the fuse unit 100 from the position shown in FIG. 1 to an open circuit position which is angularly displaced from that shown in FIG. 1 by an angle of substantially 180 upon the operation of the fusible means which forms part of the fuse unit'100 following the interruption of the are which normally results within the fuse unit 100. More specifically, the latching assembly 250 includes a generally rectangular enclosing housing or hood 310 as shown in FIGS. 3 and 4 which is formed from an electrically conducting material and which is secured to the upper insulator support 272 by a suitable means, such as bolts (not shown). As shown in FIG. 3, the enclsoing housing 310 includes a pair of laterally spaced

side wall portions

314 and 316 which are interconnected by a rear wall portion 315 and a top wall portion 312. In order to facilitate the entrance of the upper end of the fuse unit 100 during opening and closing movements of the fuse unit 100, the enclosing housing or hood 310 includes a front opening in the path of movement of the upper end of the fuse unit 100.

In order to assist in preventing axial movement of the fuse unit 100 during an interrupting operation of the fuse unit 100, the

side wall portions

314 and 316 of the enclosing housing or hood 310 include the

stop members

322 and 324 as shown in FIG. 3, which may be mounted on or formed integrally with the associated side wall portions and which project laterally inwardly toward each other to provide the stop surfaces as indicated at 322A and 324A, respectively, at the lower end of the

stop members

322 and 324, respectively. As shown in FIGS. 3 and 4, when the fuse unit 100 is in the closed position shown in FIG. 1, the

stop surfaces

322A and 324A engage or bear against the top of the upper terminal 34 at the opposite sides at the upper end of the fuse unit 100 to prevent axial movement of the fuse unit 100 in an upward direction, as viewed in FIGS. 1 and 3, during an interrupting operation of the fuse unit 100. It is important to note that by providing the stop means 322 and 324 as part of the latching assembly 250, the upper insulator support 272 will be forced to share with the lower insulator support 282 the mechanical stresses which result from the upward thrust which is exerted on the fuse unit 100 during an interrupting operation when the lower end of the fuse unit 100 only is freely vented.

The fuse unit further includes a renewable or refillable unit 20 which is mounted or disposed within the holder structure which includes the casing 32 and the upper and

lower terminals

32 and 36, respectively. The renewable unit 20 includes its own supporting tube or insulating casing which is formed from a suitable electrically insulating material having sufiicient strength to withstand the internal gas pressures and intense heat which results during an interrupting operation of the fuse unit 100, such as a filament wound, glass-epoxy material. A body of gas evolving, arc-extinguishing material, such as boric acid, is disposed inside the casing 110 and axially spaced from the ends thereof. As shown in FIG. 2, the body of gas evolving material may include a plurality of generally

annular blocks

122, 124, 126 and 128, each of which includes a relatively larger central opening and a relatively smaer opening at one side thereof, both of the openings in each block extending axially through the respective blocks. When the

blocks

122, 124, 126 and 128 are stacked axially in end-to-end relation, as shown in FIG. 2, with the respective larger and smaller openings thereof substantially aligned, a main bore 130 is formed through the body of gas evolving, arc-extinguishing material which includes said blocks and a relatively smaller auxiliary bore 192 is formed through the body of gas evolving material.

In order to prevent the travel of ionized gases between the main bore 130 and the auxiliary bore 192 during an interrupting operation of the fuse unit 100 as described in greater detail in copending application Ser. No. 663,- 018, filed Aug. 24, 1967, by C. W. Upton, Jr. and J. A. Sensue which is assigned to the same assignee as the present application, the meeting surfaces of the

blocks

122, 124, 126 and 128 are structurally joined to one another around the relatively smaller openings in said blocks which form the auxiliary bore 192 by a sealing and bonding material having a relatively high dielectric strength, such as an epoxy resin. More specifically, as explained in the copending application just mentioned, the meeting surfaces of the

blocks

122, 124, 126 and 128 each includes a recess or groove which extends substantially around the relatively smaller opening in each of said blocks and forms with the adjacent block a combined passageway which is substantially filled with the sealing and bonding material, as indicated at 132 in FIG. 2. It is to be noted that the manner in which the block-s 122, 124, 126 and 128 are bonded to one another around the auxiliary bore 192 substantially prevents the entrance of the sealing and bonding material into either the auxiliary bore 192 or into the main bore 130.

In order to limit the gas pressures which result during an interrupting operation of the fuse unit 100 inside the casing 110 to a value within the rupture strength of the casing 110, as described in greater detail in my copending application Ser. No. 663,126, which is assigned to the same assignee as the present application, each of the

blocks

126 and 128 includes a generally C-shaped recess, as indicated at 129 in FIG. 2, which extends axially from one end of each of said blocks to an axial position which is adjacent to and axially spaced from the other end of the respective blocks, with each of the recesses terminating peripherally short of the portion of each of said blocks which includes the relatively smaller openings which form part of the auxiliary bore 192. Each of the

blocks

126 and 128 therefore includes around the major portion of its inner periphery a frangible inner wall, as indicated at 126A and 128A, respectively, which is arranged to break up or' disintegrate when the fuse unit 100 is called upon to interrupt relatively large currents and when intense heat results within the main bore 130 and the gas pressure within the main bore 130 exceeds a predetermined value. During such an interrupting operation, the size or volume of the main bore 130 through the

blocks

126 and 128 is effectively increased by the breaking up of the

inner walls

126A and 128A of the

blocks

126 and 128, respectively, to thereby increase the size or volume of the gas space inside the casing 110 and to decrease or limit the gas pressure which would otherwise result.

In order to retain the

blocks

122, 124, 126 and 128 in assembled relationship with the associated tube or casing 110 as shown in FIG. 2, the outer surfaces of said blocks may be coated with a suitable cement, such as an epoxy bonding material, prior to the assembly of the blocks inside the casing 110, said cement serving to bond said blocks to the casing 110. In addition, a generally annular retaining member or plug member 189 may be disposed at the upper end of the

blocks

122, 124, 126 and 128 with the major portion of the retaining member 189 extending axially inside the casing 110, as shown in FIG. 2. The retaining member 189 may be formed or molded from a suitable electrically insulating material having sufficient strength to assist in retaining said blocks in assembled relationship with the casing 110 during an interrupting operation of the fuse unit 100, such as a glasspolyester material. A washer 183 formed from similar material may be disposed between the retaining member 189 and the uppermost block 122, as viewed in FIG. 2, and may be employed during the assembly and bonding of said blocks together prior to the assembly of said blocks inside the casing 110. It is to be noted that the retaining member 189, as well as the washer 183, includes a relatively larger central opening which forms an extension of the main bore 130 and a relatively smaller opening which forms an extension of the auxiliary bore 192. In order to assist in retaining the member 189 in assembled relation with the associated casing 110 during an interrupting operation of the fuse unit 100, the outer surface of the retaining member 18 9 and the inner surface of the tube or casing 110 at the upper end of said casing include adjacent helical grooves which together form a passageway in which a helical wire 181 is disposed to firmly secure the retaining member 189 in assembled relation with the casing 110. The retaining member 189 may be assembled with the upper end of the casing 110 by first assembling the helical wire 181 in the groove around the outer surface of the retaining member 189 and then screwing the retaining member 189 into the upper end of the casing 100 to the final position shown in FIG. 2.

In order to substantially prevent the escape of ionized gases from the upper end of the refillable or renewable unit 20 around the elongated conducting member 83 which extends through the main bore 130, a generally tubular member 185 is disposed in concentric or nested relation with the retaining member 189, as shown in FIG. 2, and is preferably formed from an electrically insulating material having a relatively low coefficient of friction, such as polytetrafluoroethylene which is sold under the trademark Teflon. A shoulder portion 185A is provided at the upper end of the tubular member 185 and includes an opening of reduced cross-section or size through which the conducting member 83 passes and which forms a substantially gas-tight seal with the conducting member 83 during an interrupting operation of the fuse unit 100 when the conducting member is actuated to move axially upwardly, as viewed in FIG. 2. The tubular member 185 also acts as a bearing to guide the axial movement of the conducting member 83. In order to prevent the tubular member 185 from being blown out of the upper end of the tube 108 during an interrupting operation of the fuse unit 100, the retaining member 189 includes an inner shoulder portion against which the upper end of the tubular member 185 bears, as shown in FIG. 2. The escape of ionized gases from the upper end of the renewable unit 20 from the auxiliary bore 192 may be adequately prevented by reducing the size of the relatively smaller opening through the retaining member 189 through which the auxiliary conductor 182 passes so that the cross-section of the auxiliary conductor182 substantially fills the relatively smaller opening through the retaining member 189.

In order to further assist in retaining the

blocks

122, 124, 126 and 128 in assembled relationship with the casing 110 during an interrupting operation of the fuse unit 100, a generally tubular or annular retaining member 142 is disposed inside the casing 110 at the lower end of the

blocks

122, 124, 126 and 128, as shown in FIG. 2, and is formed or molded from an electrically insulating material having sufficient strength to assist in retaining the blocks 122 through 128 inside the casing 110 during such an interrupting operation, such as a glass-polyester material. The outer surface of the retaining member 142 is preferably coated with a suitable cement or bonding material, such as an epoxy bonding material, prior to the assembly of the retaining member 142 inside the casing 110. This bonding material serves to bond the retaining member 142 to the inside of the easing 110. The retaining member 142 includes a relatively larger opening which extends axially therethrough, as

indicated at 142A, into which the lower end of the main bore 130 opens and which may serve as an exhaust passageway for high pressue gases which result during the operation of the fuse unit 100. The opening 142A also serves as a chamber in which the fusible means 160 is disposed. The retaining member 1 42 also includes a relatively smaller opening 142B which extends axially therethrough. The lower end of the auxiliary bore 192 opens into the opening 142B and the lower end 'of the auxiliary conductor 182 projects in the same opening. The insulating wall or partition 142C which is formed integrally with the retaining member 142 around the relatively smaller opening 142B through the retaining member 142 assists in preventing certain are products which may result during the operation of the fuse unit 100 in the relatively smaller opening 142B of the retaining member 142 from being deflected into the relatively larger opening 142A of the retaining member 142 and impinging on parts of the fusible means 160. The retaining member 142 also includes an upportion 142D by a flexible bonding material, such as silicone rubber. This joint between the retaining member 142 and the block 128 around the auxiliary bore 192 assists in preventing the travel or escape of ionized gases between the auxiliary bore 192 and the main bore 130 and between the auxiliary bore 192 and the relatively larger opening 142 through the retaining member 142 during an interrupting operation of the fuse unit 100.

The elongated conducting member or rod 83 of the refillable unit 20 is normally disposed, as shown in FIG. 2, to extend through the main bore 130 with the upper end of the conducting rod 83 projecting axially beyond the upper end of the casing 110 and with the upper portion of the conducting rod being externally threaded, as indicated at 83A. The conducting rod 83 is normally held in the position shown in FIG. 2 by a connection through the fusible means 160 to the generally annular or tubular lower conducting member or contact 150.

More specifically, the fusible means 160 comprises a strain element 162 and a fusible element or link 164.

The upper end of the strain element 162 is secured by suitable means, such as brazing, to the lower end of the conducting rod 83, while the other end of the strain element 162 is secured by suitable means, such as brazing, to the connecting conductor or terminal 156 which is of the flat strip type. The connecting conductor 156 is secured in turn to the lower contact 150 adjacent to the upper end of the lower contact 150 by suitable means, such as brazing. Similarly, the upper end of the fusible element or link 164 is secured to the lower end of the conducting rod 83 by usitable means, such as brazing, while the lower end of the fusible element or link is secured to the lower contact 150 adjacent to the upper end of the lower contact 150 by suitable means, such as brazing. It is to be noted that the strain element 162 and the fusible element 164 are electrically connected in parallel between the lower end of the conducting rod 83 and the lower contact 150 of the renewable unit 20.

Similarly, the auxiliary conductor 182 which is of a relatively smaller cross-section or size than the conducting rod 83 normally extends through the auxiliary bore 1'92 with the upper end of the auxiliary conductor 182 extending axially beyond the upper end of the auxiliary bore 192 and being both mechanically and electrically connected to the upper portion of the conducting rod 83 by a transversely extending spring pin 184. The pin 184 is disposed in a transversely extending recess or opening provided at the upper end of the retaining member 189' to prevent rotation of the conducting rod 83 after assembly of the rod 83 in the renewable unit 20. The upper end of the auxiliary conductor 182 may be formed as a loop which is assembled over the conducting spring pin 184 and retained thereon by the head 186 of the spring pin 184. The lower end of the auxiliary conductor 182 extends or projects into the relatively smaller opening 142B of the retaining member 142, as shown in FIG. 2, and is electrically connected through a helical conducting wire of reduced cross-section, as indicated at 194, to an angle-shaped auxiliary stationary terminal 157 which is secured to the tubular conducting member 150 adjacent to the upper end of the member 150 by suitable means, such as brazing. The upper end of the helical wire 194 which is disposed inside the relatively smaller opening 142B of the retaining member 142 is secured to the lower end of the auxiliary conductor 182 by suitable means, such as brazing, and the lower end of the helical wire 194 is secured to the auxiliary terminal 157 by suitable means, such as crimping or brazing, as disclosed in greater detail in copending application Ser. No. 663,029, filed Aug. 24, 1967, by F. L. Cameron, now Patent 3,401,243, issued Sept. 10, 1968, which is assigned to the same assignee as the present application.

The lower contact or conducting member 150 also includes an elongated arcing terminal 158, as disclosed in the copending application just mentioned, which projects upwardly from the upper end of the contact 150 into the relatively smaller opening 142B of the retaining member 142 to axially overlap the lower end of the auxiliary conducting member 182 with the lower portion of the arcing terminal 158 being disposed adjacent to and generally parallel to the axis of the helical wire 194. The arcing terminal 158 is electrically insulated along its length by a coating or film of electrical insulating material, such as an insulating enamel, which is provided on the arcing terminal 158 to prevent the electrical shorting out of the helical wire 194. The arcing terminal 158 which is formed from an electrically conducting material may be structurally secured to the upper end of the lower contact 150 at the inner periphery thereof by suitable means, such as brazing, or may be formed integrally therewith in a particular application. It is to be noted that the auxiliary current path which extends from the upper portion of the conducting rod 83, through the cross pin 184, the auxiliary conductor 182 and the helical wire 194 to the auxiliary terminal 157 on the lower contact 150 is also electrically connected in parallel with the conducting paths which include, respectively, the strain element 162 and the fusible element 164.

In order to assist in retaining the

blocks

122 and 128 and the retaining member 142 in assembled relationship inside the casing 110, as well as for another important purpose during an interrupting operation of the fuse unit 100 as described in copending application Ser. No. 663,029, mentioned previously, the lower tubular conducting member or contact 150 includes a main portion 152 which extends axially inwardly from the lower end of the casing to bear against the lower end of the retaining member 142. The lower contact also includes a flange portion 154 at the lower end thereof against which the lower end of the casing 110 bears when the conducting member 150 is assembled with the casing 110.

In order to retain the lower contact 150, as well as other parts of the renewable unit 20, in assembled relationship with the casing 110 during an interrupting operation of the fuse unit 100, a generally tubular external terminal member or ferrule 172 is disposed to telescope over the lower end of the casing 110. In order to firmly secure the external terminal member 172 to the lower end of the casing 110, the internal surface of the external terminal member 172 and the external surface of the portion of the casing 110 adjacent to the member 172 include adjacent helical grooves which, when the parts are assembled, form a combined helical passageway in which a helical wire 173 is disposed. In the assembly of the external terminal member 172 on the lower end of the casing 110, the helical wire 173 may be first assembled in the helical groove on the lower end of the casing 110 and the external terminal member 172 may then be screwed onto the lower end of the casing 110 until the parts reach their final positions, as shown in FIG. 2. In order to additionally assist in retaining the external terminal member 172 on the lower end of the casing 110, the outer surface of the casing 110 and the inner surface of the external terminal member 172 may be coated with a cement or bonding material, such as an epoxy bonding material, prior to the assembly of the external terminal member 172 on the lower end of the casing 110. It is to be noted that the external terminal member 172 also includes an inwardly projecting flange portion 172A around a central opening 172B which bears against the adjacent flange portion 154 of the tubular conducting member 150 to assist in retaining the tubular conducting member 150 in assembled relation with the other parts of the renewable unit 20.

In order to form a current conducting path which extends between the lower end fitting 36 and the lower contact 150 of the renewable unit 20, the external terminal member 172 also includes an external flange portion 172C which bears against the inwardly projecting flange portion 36B of the lower end fitting 36. The electrically conducting path thus formed extends from the lower contact 150 through the inwardly projecting flange portion 172A of the external terminal 172 and through the externally projecting flange portion 172C to the inwardly projecting flange portion 36C of the lower end fitting 36. The area of the current transfer paths between the external terminal member 172 of the renewable unit 20 and the lower end fitting 36 may also be augmented by the contact ring which may be formed of electrically conducting material and which is disposed to threadedly engage the internally threaded opening at the lower end of the fitting 36 and bear against the external terminal member 172 of the renewable unit 20, as shown in FIG. 2.

It is important to note that in order to prevent the concentration of relatively high potential stresses adjacent to the external terminal member 172 during an interrupting operation of the fuse unit 100* at relatively high voltages, the upper end of the lower contact 150 extends axially beyond the upper end of the external terminal member 172 toward the other end of the casing 110 a minimum distance to prevent such a concentration of relatively high potential stresses externally of the casing 100 adjacent to the external terminal member 172, as disclosed in great er detail in copending application Ser. No. 663,029, filed Aug. 24, 1967, by F. L. Cameron.

In order to actuate the axial movement of the conducting rod 83 as well as that of the auxiliary conductor 182 during an interrupting operation of the fuse unit 100 and to electrically connect the renewable or refillable unit just described to the upper end fitting or terminal 34, a spring and cable assembly 30 is disposed inside the outer tube 32 between the renewable unit 20 and the upper end fitting 34, as disclosed and claimed in my copending application Ser. No. 663,021, filed Aug. 24, 1967, which is assigned to the same assignee as the present application. The spring and cable assembly 30 includes at its lower end a generally tubular conducting member or socket 84 having an internally threaded central opening, as indicated at 84A, to receive the upper threaded end 83A of the conducting rod 83'. A lower spring seat member 86 is fixedly mounted on the socket 84 for movement therewith by assembling the spring seat 86 over the outer periphery of the socket 84 with the lower end of the spring seat 96 bearing against a shoulder provided on the outer periphery of the socket 84 and with the upper end of the spring seat 86 being engaged by a plurality of portions of the socket 84 at the upper end of the socket 84 which serve to stake or secure the spring seat 86 on the socket 84. The spring and cable assembly 30 also includes an upper spring seat 74 which is slidably disposed over the lower portion 60A of a generally cylindrical conducting member 60 whose integral upper portion 60B extends axially through an opening 34B in the upper end fitting 34 and is externally threaded at the upper end thereof, as indicated at 60C. As illustrated, the generally cylindrical conducting member 60 may be secured to the upper end fitting 34 by an internally threaded end cap 44 which may be screwed down on the upper threaded portion 60C of the conducting member '60 until the flange portion 44A of the end cap 44 bears against the upper end fitting 34 around a flange or shoulder portion, as indicated at 34C in FIG. 2. A helical tension spring 76 is secured at its upper end to the externally helically threaded portion of the upper spring seat 74, while the lower end of the spring 76 is secured to the externally helically threaded portion of the lower spring seat '86 to bias the conducting rod 83, as well as the auxiliary conductor 182, in a generally upward direction, as viewed in FIG. 2, away from the lower contact 150. It is important to note that the turns of the spring 76 are generally rectangular or square in crosssection to substantially prevent any overlapping of the turns 76 and the consequent damage to the spring 76 that might otherwise result during an interrupting operation of the fuse unit 100, as explained in greater detail in copending application Ser. No. 663,021, just mentioned.

In order to electrically connect the renewable unit 20 and more specifically the conducting rod 83 to the upper end fitting 34 both prior to and during an interrupting operation of the fuse unit 100, a plurality of helically coiled flexible cables or conductors 82 are electrically and structurally connected at the bottom ends thereof to the conducting socket 84 into separate openings (not shown) provided in the socket 84 by suitable means, such as brazing or by staking, and at the upper ends thereof are secured to the conducting member 60 in separate openings provided in the conducting member 60' by suitable means, such as brazing or staking. In order to increase the effective current transfer area between the conducting member 60 and the upper end fitting 34, a washer 54 formed of electrically conducting material may be disposed between the shoulder which is formed at the intersection of the upper and

lower portions

60A and 60B, respectively, of

the conducting member 60 and the shoulder which is formed inside the upper end fitting 34, as indicated at 34D around the central opening 34B.

In order to facilitate the assembly of the renewable unit 20 and the associated spring and cable assembly 30 inside the outer holder 32 as will be explained hereinafter, a pair of spring pins 5 8 may be disposed in associated openings provided at the opposite sides of the upper portion 60B of the conducting member '60 to be positioned finally within an enlarged central opening or recess 34E in the upper end fitting 34, as shown in FIG. 2.

In order to actuate the release of the latching assembly 250 shown in FIG. 1 following an interrupting operation by the fuse unit 100, as disclosed and claimed in copending application Ser. No. 663,021, previously mentioned, a tripping rod or member 52 is slidably disposed inside a central opening or passageway 72 which is provided in the conducting member 60 with the upper end of the tripping rod 52 being normally positioned below the top of the end cap 44, as shown in FIG. 2. The lower end of the tripping rod 52 is fixedly coupled to the upper spring seat 74 for axial movement therewith by the cross pin 56 which passes laterally through aligned transverse openings in the tripping rod 52 and the upper spring seat 74 and through a pair of elongated'slots 62 provided at the opposite sides of the conducting member 60 with the cross pin 56 being normally positioned at the lower end of the slots 62, as shown in FIG. 2. In order to permit the axial movement of the tripping rod=52 upwar-dly through the end cap 44 following an interrupting operation of the fuse unit 100, the top of the end cap 44 includes a central opening 46 through which the tripping rod 52 may pass to actuate the release of the latching assembly 250 as shown in FIG. 1. When the latching assembly 250 is released by the movement of the tripping rod 52, the upper end of the fuse unit will be actuated to rotate in a clockwise direction, as viewed in FIG. 1, about the lower hinge assembly 260 to thereby provide an electrically insulaing gap between the upper break contact 252 and the lower stationary hinge contact 62 by such drop-out action.

In order to assemble the renewable unit 20- and the associated spring and cable assembly 30 into the outer holder 32, the. threaded end of the conducting rod 83 is first screwed into the socket 84 at the lower end of the spring and cable assembly 30. A refill fusing tool (not shown) is then screwed into the internally threaded central opening or passageway 72 at the other end of the spring and cable assembly 30. The spring and cable assembly 30 is then inserted into the outer holder 32 with the upper end of the spring and cable assembly 30 being inserted first into the lower end of the outer holder 32, as viewed in FIG. 2, until the refill tool (not shown) passes through the central opening 34B of the upper end fitting 34. By use of the refill tool, the spring 76 is stretched and placed in tension until the cross pins 58 mounted at the sides of the conducting member 60- are drawn upwardly through a pair of radial slots (not shown) provided in the upper end fitting 34 around the central opening 34B. The upper conducting member 60 and the spring and cable assembly 30 are then rotated until the pins 58 rest on the shoulder provided at the bottom of the enlarged opening 34E in the upper end fitting 34. The end cap 44 may then be screwed down on the upper threaded portion 60C of the conducting member 60 to further stretch the spring 76 to the final condition or position shown in FIG. 2 in which the cross pin 58 are drawn upwardly away from the shoulder in the upper end fitting 34 at the bottom of the enlarged opening 34E. It is to be noted that when the spring and cable assembly 30 and the renewable unit 20 are assembled inside the outer holder 32, as just described, the cross pin 56 which couples the upper spring seat 74 to the tripping rod 52 is disposed at the bottom of the. slots 62 at the opposite sides of the conducting member 60 to permit limited upward travel of the upper spring seat 74 along with the cross pin 56 and the tripping rod 52 to a final position of the tripping rod 52 in which the tripping rod 52 projects beyond the end cap 44 axially to release the latching assembly 250, as previously mentioned. The. washer 54 also acts as a stop surface against which the upper end of the spring seat 74 bears to limit the upward travel of the tripping rod 52, the cross pin 56 and the spring seat 74.

In considering the operation of the fuse unit 100, it is to be noted first that the current paths which include,

respectively, the strain element 162, the fusible element 164 and the helical wire 194, which are connected in series with the auxiliary conductor 182, are all electrically connected in parallel between the upper end of the conducting rod 83 and the lower contact 150 at the lower end of the renewable unit 20. The resistance of the current path which includes the fusible element 164 and which is calibrated to have predetermined time-current characteristics is arranged to be relatively much less than the resistance of either the path which includes the the strain element 162 or the path which includes the helical wire 194 so that normally most of the current which flows through the fuse unit 100 is carried by the fusible element 164. Although the resistance of the current path which includes the strain element 162 is relatively greater than the resistance of the path which includes the fusible member 164, the resistance of the path which includes the strain element 162 is relatively less than that of the path which includes the helical wire 194 so that when the fusible element 164 melts or blows, most of the current which was formerly carried by the fusible element 164 is then transferred to the strain element 162. In other words, when the current which is flowing through the fuse unit 100 increases to a value which is of suificient magnitude and duration to melt or blow the fuse element 164, most of the current which is flowing through the fuse unit 100 then transfers to the strain element 162. When the current which is transferred to the strain element 162 following the melting of the fusible element 164 has passed through the strain element a sufficient period of time to melt or blow the strain element 162, the current which was previously carried by the strain element 162 is .finally transferred to the current path through the auxiliary bore 192 which includes the auxiliary conductor 182 and the helical wire 194. No arcing occurs as these

elements

162 and 164 melt because of the parallel elec trical path through the helical wire 194. When the strain element 162 melts or blows, the conducting rod 83 is no longer restrained from upward movement under the influence of the biasing spring 76 and the conducting rod 83 and the auxiliary conductor 182 will start to move upwardly under the influence of the spring 76 to thereby stretch the helical wire 194 which is electrically connected to the bottom of the auxiliary conductor 182. It is to be noted that the stretching of the helical wire 194 permits limited travel of both the conducting rod 83 and the auxiliary conductor 182 while maintaining a continuous electrical circuit through the. auxiliary bore 192 and that as long as the current path which includes the auxiliary conductor 182 and the helical wire 194 is intact, no arcing will take place in either the main bore 130 or in the auxiliary bore 192. In other words, the stretching of the helical wire 194 during the initial movement of the conducting rod 83 and the auxiliary condu ctor 182 following the melting or blowing of the fusible element 164 and the strain element 162 will permit the formation of an electrically insulating gap in the main bore 130, while initially maintaining a conductive path and delaying the formation of an insulating gap in the auxialiary bore 192.

After the strain element 162 melts or blows as just described, and the conducting rod 83 and the auxiliary conductor 182 begin to move upwardly to thereby stretch the helical wire 194, the helical wire 194 will either fracture mechanically when stretched to its limit or the current transferred to the current path which includes the auxiliary conductor 182 and the helical wire 194 will be suflicient to melt or blow the helical wire 194 which is of reduced cross-section compared with that of the auxiliary conductor or rod 182. After the helical Wire 194 is melted or otherwise broken, an arc will be initiated between the retreating end of either the broken helical wire 194 or the auxiliary conductor 182 and the arcing terminal 158 which axially overlaps the lower end of the auxiliary conductor 182 to thereby burn through the electrical insulation on the arcing terminal 158. Even after the wire 194 melts or is broken, the formation of a significant electrical insulating gap in the auxiliary bore 192 is further delayed by the axial overlapping of the auxiliary conductor 182 by the arcing terminal 158 until the retreating free end of either the wire 194 or the conductor 182 passes the upper end of the arcing terminal 158 whose insulation will have burned through by this time. It is important to note that the insulating gap in the main bore 130 between the separated ends of the conducting parts will increase at a faster rate than the formation of an insulating gap in the auxiliary bore 192 due to both the delay in the formation of an arc in the auxiliary bore 192 because of the presence of the helical Wire 194 and due to the overlapping of the auxiliary conductor 182 by the arcing terminal 158. It is also important to note that the arcing which takes place in the fuse unit during an interrupting operation will always take place initially in the auxiliary bore 192, as just explained. When the retreating end of either the helical wire 194 or the auxiliary conductor 182 passes the upper end of the arcing terminal 158, the arcing which takes place initially in the auxiliary bore 192 will cause gases to be evolved from the gas evolving material around the auxiliary bore 192 which will be un-ionized.

When the current to be interrupted by the fuse unit 100 is relatively low, such as 1000 amperes or less, and when the gas pressure of the evolved gases in the auxiliary bore 192 increases to thereby increase the dielectric strength in the auxiliary bore 192, the insulating gap which is formed in the auxiliary bore 192, along with the corresponding increased dielectric strength, will be sufiicient to interrupt the alternating current following a particular current zero in the auxiliary bore 192. The insulating gap which is formed simultaneously in the main gap 132 of the fuse unit 100' at a relatively faster rate will have suflicient dielectric strength considering the instantaneous potential dilference between the separating conducting parts in the main bore of the fuse unit 100 to prevent a restrike of the arc in the main bore 130 for such relatively low fault currents. In other words, when any fault current is interrupted by the fuse unit 100, as just described, arcing will always be initiated in the auxiliary bore 192 and for relatively small fault currents, the arcing which results will be finally interrupted in the auxiliary bore 192. One important reason for this is that the relative dielectric strength of the main bore 130 at the time that the arc is finally interrupted in the auxiliary bore 192 will be relatively higher than that in the auxiliary bore 192 to prevent a restrike or breakdown of the main bore 130 due to the potential difference which results between the separated conducting parts in the main bore 130.

For relatively higher fault currents, the arcing which is initiated in the fuse unit 100 will still be initiated in the auxiliary bore 192 in the manner just described. For such relatively higher current faults however, the gas pressure which builds up in the auxiliary bore 192 during an interrupting operation and the burning back of the separated conducting parts in the auxiliary bore 192 will result in a relatively higher dielectric strength in the auxiliary bore 192 compared with that in the main bore 130 between the separated conducting parts in the main bore 130. If the instantaneous potential difference between the separated ends of the conducting parts in the main bore 130 is sufficient when the dielectric strength of the main bore 130 becomes relatively less than that of the auxiliary bore 192, the arc will restrike in the main bore 130 to thereby cause the evolution of un-ionized gases in the main bore 130 to thereby increase the gas pressure in the main bore 130, as well as the corresponding dielectric strength in the main bore 130. The are which restrikes in the main bore 130 will be elongated both by the upward movement of'the conducting rod 83 and by the burning back of the separated conducting parts in the main bore to thereby increase the quantity of unionized gases evolved from the gas evolving material around the main bore 130. The arc in the main bore 130 will :be finally interrupted following a particular current zero in the alternating current which is being interrupted when the insulating gap and the corresponding dielectric strength in the main bore 130 is suflicient to withstand the instantaneous potential difference between the separated conducting parts in the main bore 130.

If the fault current which is being interrupted by the fuse unit 100 is of a relatively still higher magnitude or value, the gas pressure in the main bore 130 along with the intense heat which results will be suflicient to break up or disintegrate the frangible

inner walls

126A and 128A of the

blocks

126 and 128, respectively, to thereby limit the gas pressure of evolved gases because of the increase in the size or volume of the gas passageway or volume of the gas spaced inside the refillable unit 20 to thereby limit the gas pressure of the evolved gases to a value within the rupture strength of the casing 110 as previously explained. It is to be noted that when the

inner walls

126A and 128A break up during the operating condition just mentioned, the outer walls of the

blocks

126 and 128 will then be exposed to the arc being interrupted and will continue to evolve gases which will aid in arc extinction of the relatively higher currents which result in such an interrupting operation. As mentioned previously, the

inner walls

126A and 128A will remain intact when the fuse unit 100 is interrupting relatively lower currents to thereby assist in confining the arc by maintaining a normal size opening of the main bore 130 to more effectively aid in arc extinction.

When the arc is interrupted in the main bore 130 of the fuse 100 or in the main bore 130, as enlarged by the breaking up of the

inner walls

126A and 128A of the

blocks

126 and 128, respectively, as just described to thereby cause the evolution of gas from the gas evolving material in the

blocks

122, 124, 126 and 128 which surround the main bore 130, the upward movement of the conducting rod 83 along with the upward movement of the auxiliary conductor 182 will be additionally accelerated by the force of the gas pressure of such evolved gases in the main bore 130 along with the force exerted on the conducting rod 83 by the biasing force of the spring 76.

During an interrupting operation of the fuse unit 100 as just described, when the conducting rod 83 is released and moved upwardly under the influence of the spring 76- or under the influence of both the spring 76 and the gas pressure of the evolved gases inside the renewable unit 20, the turns of the spring 76 which are normally held in tension will partially collapse toward a compressed condition but after the turns .of the spring 76 collapse to a certain extent, the upper spring seat 74 will slide axially on the lower portion of the conducting member 60 until the upper end of the spring seat 74 impacts or bears against the Washer 54 to thereby drive or actuate the tripping rod 52 in an upward direction as viewed in FIG. 2. The tripping rod 52 will then be actuated from the position shown in FIG. 2 until the upper end of the tripping rod 52 actuates the release of the latching means 250 as described in the copending application Ser. No. 663,020 previously mentioned and in US. Patent No. 2,403,121 which issued July 2, 1946, to H. L. Rawlins et al. It is to be noted that the upward movement of the conducting rod 83 and the auxiliary conductor 182 will establish the insulating gaps previously described between the separated ends of the conducting parts inside the renewable unit 20 following an interrupting operation. In addition, the fuse unit 100 Will be actuated by the release of the latching means 250 by the tripping rod 52 to rotate in a clockwise direction, as viewed in FIG. 1, about the lower hinge assembly 260 in a drop-out movement to establish a longer or greater insulating gap between the break contact 252 and the lower stationary hinge contact 262 of the fuse structure 10.

It is important to note that during an interrupting operation of the fuse unit as previously described for either relatively low fault currents or for relatively high currents, the gas seal and joint structure between the

successive blocks

122, 124 and 126, as previously described, substantially prevents the escape of ionized gases from the auxiliary bore 192 in which all arcing initially takes place to the main bore along the meeting surfaces of the successive blocks in the renewable unit 20. As previously mentioned, if such ionized gases were permitted to escape to the main bore 130, a restrike might result when the fuse unit 100 is called upon to interrupt relatively low fault currents and the restrike of an arc in the main bore 130 would result in an arcing condition which the fuse unit 100 is incapable of interrupting in the main bore 130 for such relatively low fault currents. This is because for such relatively low fault currents, the quantity of gas evolved in the main bore 130 is not sufficient to establish a dielectric strength in the main bore 130 which would be great enough to interrupt the are which results for such relatively low fault currents in the main bore 130.

It is important to note that in the operation of the fuse unit 100 as just described in detail, the gases which are evolved from the body of arc-extinguishing material which includes the

blocks

122, 124, 126 and 128 are exhausted or freely vented at only the lower end of the fuse unit 100, as shown in FIG. 2 of the drawing. The exhausting or venting of the high pressure gases from only the lower end of the fuse unit 100 results in an upward force or thrust on the fuse unit 100' which tends to cause the fuse unit 100 to move axially in an upward direction. The projecting portions 287 on the lower terminal 36 of the fuse unit 100 bear against the cam surfaces 281 on the side wall portions 289 of the hinge member 285 of the hinge assembly 260 to assist in preventing such axial movement and force the lower insulator support 282 at least to share in the mechanical stresses which result when such an upward thrust is exerted on the fuse unit 100. If the latching means 250 did not include some means for insuring that the upper insulator support 272 share the mechanical stresses which result when high pressure gas is exhausted from only the lower end of the fuse unit 100 as viewed in FIG. 1, the lower insulator support 292 would be called upon to carry substantially all of the mechanical stresses which result due to the upward thrust produced by said gas pressure and the lower insulator support 282 might be stressed beyond the limits of its mechanical strength and either break or mechanically fail, particularly when the fuse unit 100 is called upon to interrupt relatively high fault currents and when a relatively high rate of rise of recovery voltage is involved in the interrupting operation.

Since the latching means 250 as previously described does also include means for assisting in preventing axial movement of the fuse unit 100 when the gases which result during an interrupting operation are exhausted from only the lower end of the fuse unit 100 as viewed in FIGS. 1 and 2, the upper insulator support 272 is forced to share the mechanical stresses which result due to the upward thrust exerted on the fuse unit 100 and the stresses on the lower insulator support 282 may be limited to a value within the limits of the mechanical strength of the lower insulator support 282 to prevent the mechanical failure of the lower insulator support 282 which might otherwise result. More specifically, the latching means 250 includes the pair of stop means 322 and 324 which bearagainst the top of the upper terminal 34 on the fuse unit 100 at the opposite sides thereof to prevent the upward axial movement of the fuse unit 100 in cooperation with the means previously described which form part of the hinge assembly 260 to insure that the upper insulator support 272 at least shares the mechanical stresses which result from the upward thrust due to the force exerted on the fuse unit 100 because of the exhausting or venting of the gases which are evolved from the body of arc-extinguishing material inside the fuse unit 100 during an interrupting operation, particularly as relatively high fault currents. It is important to note that the construction disclosed by the applicant to insure the sharing of stresses by the upper insulator support 272 does not interfere with the operation of the means included as part of the latching assembly 250 which actuates the drop-out movement of the fuse unit 100 follow ing the interruption of the arc which normally results inside the fuse unit 100 upon the blowing or fusing of the fusible means which is disposed inside the fuse unit 100'. In other words, the stop means 322 and 324 which are provided at the opposite sides of the upper end of the terminal 34 at the upper end of the fuse unit 100 assist in preventing axial movement of the fuse unit 100 during an interrupting operation and also in insuring that the upper insulator support 272 share the mechanical stresses which result due to the upward thrust exerted On the fuse unit 100 while not interfering with the actuating operation of the latching means 250 which actuates the drop-out movement of the fuse unit 100 following the interruption of the arc whichresults' when the fusible means disposed inside the fuse unit 100 blows or fuses as described in detail in copending application Ser. No. 663,020 previously mentioned.

It is to be understood that the teachings of the applicants invention may be applied to power fuses for high voltage applications which are not of the drop-out type as disclosed in my copending application Ser. No. 663,021 filed Aug. 24, 1967 which is assigned to the same assignee as the present application. It is also to be understood that the teachings of the applicants invention may be applied to power fuses for high voltage applications which do not include a tubular conducting member or shield, such as the lower contact 150 shown in FIG. 2 but which instead employs a lower contact ring of the type disclosed in detail in copending application Ser. No. 663,127 filed Aug. 24, 1967, by C. W. Upton, C. C. Patterson and F. L. Cameron which is assigned to the same assignee as the present application.

The apparatus embodying the teachings of this invention have several advantages. For example, a power fuse structure as disclosed including a hinge assembly and a latching assembly which both include means for insuring that the associated upper and lower insulator supports share the mechanical stresses which result from the upward thrust exerted on the associated fuse unit when only one end of the fuse unit is freely vented prevents the mechanical failure which might otherwise resultif only one of the insulator supports were subjected to all of the mechanical stresses which result in such an operation. In addition, the applicants construction avoids the requirement for providing an oversized insulator support for the insulator support which is required to carry all of the mechanical stresses which result from such an upward thrust exerted on the fuse unit in a construction in which only either the hinge assembly or the latching assembly includes means for preventing axial movement of the associated fuse unit under such circumstances. Finally, in a power fuse structure disclosed by the applicant the sharing of mechanical stresses by the spaced insulator supports is insured without interfering with the operation of the means which is provided to actuate the drop-out movement of the associated fuse units in power fuse structures of the drop-out type.

Since numerous changes may be made in the abovedescribed apparatus and different embodiments of the invention may be made Without departing from the spirit and scope thereof, it is intended that all the matter contained in the foregoing description or shown in the ac companying drawings shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. A circuit interrupter comprising a tubular insulating holder, a body of gas evolving, arc-extinguishing material disposed in the holder and including at least one passageway extending axially therethrough, separable conducting means including fusible means disposed in the holder and connected between a pair of terminals mounted adjacent to the opposite ends of the holder, 9. pair of spaced, relatively stationary contacts, means for pivotally supporting the holder adjacent one end near one of the stationary contacts to permit movement of the terminals on the holder into and out of engagement with the respective stationary contacts, means disposed adjacent to the other stationary contact for releasably latching the terminal on the holder adjacent the other end of the holder into engagement with the other stationary contact, said supporting means including relatively stationary means for bearing against a portion of the adjacent terminal to assist in preventing axial movement of the holder upon fusing of the fusible means when gas from the body of arc-extinguishing material is exhausted from only one end of the holder, said latching means including relatively stationary means for bearing against a portion of the adjacent terminal on the holder to further assist in preventing axial movement of the holder upon fusing of the fusible means when gas from the body of arc-extinguishing material is exhausted from one end of the holder to thereby insure that both the latching means and the supporting means share the stresses which result when the holder tends to move axially under the influence of the gas which exhausts from only one end of the holder.

2. The combination as claimed in claim 1 wherein the latching means includes an enclosing hood mounted on an electrically insulating support to at least partially enclose the other stationary contact, the relatively stationary means of the latching means comprising a pair of spaced stops formed integrally with the enclosing hood to bear against a portion of the adjacent terminal on the holder when the terminal engages the other contact.

3. The combination as claimed in claim 1 wherein an axially movable member is provided in the holder to project axially from the holder upon the fusion of the fusible means and the latching means includes means actuated by the axially movable member for actuating the holder to rotate about the pivotally supporting means to an open position.

4. The combination as claimed in claim 1 when an additional means is disposed in the holder for actuating the separable conducting means to separate upon the fusing of the fusible means,

5. The combination as claimed in claim 2 wherein the spaced stops on the enclosing hood bear axially against one end of the associated holder through the terminal disposed at that end of the holder.

6. The combination as claimed in claim 3 wherein a releasable means is provided inside the holder for biasing the axially movable member to move axially and project axially out of the holder upon the fusion of the fusible means.

References Cited UNITED STATES PATENTS 2,305,996 12/1942 Schultz et al. 337176 X 2,328,818 9/1943 Lindell et al. 337-176 2,750,469 6/1956 Baker 337178 X 3,002,070 9/1961 Bronikowski et al. 337-177 3,048,680 8/1962 McCloud 337177 BERNARD A. GILHEANY, Primary Examiner H. B. GILSON, Assistant Examiner U.S Cl. X,R. 337177, 186