CA2139024A1 - Current responsive latching apparatus for disconnecting and isolating an electrical device - Google Patents

Abstract

Abstract of the Disclosure A current responsive latching apparatus may be employed in a dropout fuseholder or other electrical component for retaining the component in a current-carrying position and disconnecting and isolating the electrical component upon the occurrence of an overcurrent of a predetermined magnitude. The apparatus includes a current path through the component, including a current-carrying stud or conductor, a portion of which extends outside the component for releasably engaging a support member. A latching apparatus, which may include an actuating member of memory allow or a bimetallic material, engages the conductor to retain the support member in a supporting position beneath the electrical component. The apparatus may further include a heater element in the current path to ensure that the actuation member is heated to the temperature necessary to cause it to change shape and release the conductor upon the presence of an overcurrent.

Description

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CURRENTRESPONSIVE LATCHlNG APPARATUS FOR
DISCO~INECTI~IG A~ll) ISOLAT~IG AN ELECTRICAL l)EVlCE
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The prcsent invendon relates generally to electncal power distribution equipment. More particularly, the invention relates to apparatus for automadcally disconnec~ing electrical `
components from the energized network. Still more particularly, thc invention relates to relcasable latching apparatus which cmploys current rcsponsive demcnts for disconnecdng and isolating an electrical component from an energized conductor upon the occurrence of a fault.

. ' Electrical transmission and distribution networks consist of a staggenng number of transforrners, capacitor banks, reactors, motors, genera~ors and other major pieces of electrical equipment. Such cquipment is extremely expensive. Further, each such piece of equipment typically plays a vit I role in the distribution of power to end users, such that an ouuge caused by the equipment being damaged or taken out of service for repairs, may have exceptionally costly consequences. As a result, such equipment is typically protected from potentially ~;~ 2~3902~ ~
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damaging overvolhges and overeurrents by protectdve components, such as fuses and surge arresters.
A fuse is a current interrupting device which includes a current-responsive element that will melt or fuse open when an overcurrent or short circuit of a predetermined magnitude and duration is condueted through the fuse. After the fuse has operated ~o interrupt the overcurrent, it must be replaeed in ordèr to restore service.
A partieularly convenient and desirable fusing device is a dropout fuseholder. A dropout fuseholder ineludes a pair of terminals for connecting the fuseholder to the circuit ;hat is to be . . .
proteeted, and an aetuadon means for causing the fuseholder to physically drop out of enga8ement with the energized cireuit after the fuse has operated to clear a fault. The drop open feature provides a elear visual indieadon to utility personnel that the fuse has operated. Furtha, the drop o en feature removes the fuseholder from the voltage stress otherwise assoeiated with the ener ized eireuit, eliminadng the possibility of trac ing and ultimate flashover around the fuse.
A typieal prior art dropout fuseholder is diselosed in U.S. Patent No. 3,611,240 (Mikuleeky). Mikuleelcy diseloses a eurrent-limiting dropout fuseholder having a fuDi sange of fault elearing eapabiliity As disclosed in that patent, upon aetuadon of the fuse, an explosive eharge is ignited whieh actuates the dropout meehanism and frees the fuseholder to drop out of engagementiwith the eutout mounting in whieh it is installed. Similarly, U.S. Patent No 3,825,871 (Blewitt) also diseloses a dropout fuseholder whieh employs an explosive charge to initiate dropout.

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.., Although such explosive charges have genera3ly been successfully employed in the industry, it is not uncommon for such a fuse to fail to drop open after clearing a fault due to a failure of the charge to detonate. Such failure is frequent3y due to the powder of the explosive charge absorbing too much moisture to ignite after a prolonged period of service. No matter the reason for such failurcs, the failure of a dropout fuse to drop open after operadon is a source of great frustration and delay to utility personnel who are unable to identify the actuated fuses by visual observation, and must instead resort to more ume consuming and less convenient means for detecting which fi3ses have 07erated. Further, a fuseholder that has failed to drop open rcmains subject to the voltage stress imposed by the energi~ed netvork, making it suscepdble to traclcing and possible flashover.
Acl-ordingly, despite advances made in fi3se technology over the years, further mprovements would be welcomed by the industry. Specifically, there is a need for a mechanically operable dropout mechanism tha~ would retain ~he fuseholder in its current carrying -positdon undl actuation of the fusible element, and would reliably cause the fuse to drop open upon actuation of the fusc. The dropout mechanism should allow the fuse to completely clear the fault before dropout is initiated. Ideally, the device would be simple and inexpensive to manufacture, and would provide dependable operadon without the need to rely upon an cxplosive charge. -~ ;

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,, The present invention provides a current-responsive, releasable latching apparatus useful for retaining an electrical componen~ in electrieal engagement with an energized network and for disconnecting the component from the network when certain predetermined conditions are present. The invention may, for example, be applied in a current-limiting dropout fuseholder - -so as to retain the fuseholder in its current carrying position until actuation of a fusible element, - :" .,: ,:.': :
at whieh time the invention disconneets the fuseholder from its current-carrying position and allows it to drop open so as to isolate the fuseholder from the energized network.
The invention includes an electrical component having a current path through the body of the component. The path includes a conducting pin partially extending outside the body of the electrical eomponent. The eondueting pin is disposed through an aperture in a supporting member adjaeent to the eomponent body, the supporting member being retained in posidon by an actuadng member whieh engages the pin until sueh time as a predetermined current is eonducted through the eleetrical eomponent. Heat generated by the eonduedon of sueh predetermined eurrent causes the actuating member to ehange shape and release the eondueting pin, thereby freeing the suppor~ing member which may then be biased awajfrom the elect~ical ~;
component, allowing it to drop out of engagement with a line-potendal terminal. The actuadng ~nember may eomprise a metallic member made from memory alloy or from a bimetallic material, and includes latching tangs or clamping arms for engaging the conducting pin undl the ;~
actuating member reaches a predetermined temperature.
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To ensure that the actuating member reaches the prede~ermined temperaturc required for it to change shape and release the pin member, the invention may include a heater element in the cunrent path. The heater element may comprise, for example, a silicon carbide ring or a member formed of other material having a high electrical resisunce. The heatcr element is placcd in physical contact with the actuating member such that when cunrent is conducted through the cunrent path, the heat generated by the heater element will be conducted to the actuating member.
In an alternative embodiment, rather than a conducting pin, the current path includes a trigger wire that is disposed through a central aperture in a conducting washer that is disposed ;
within the lower conducting end cap of a fuseholder. The gap between the washer's aperture and the trig~er wire forms a spark gap in the fuseholder. The tngger wire extends outside the lower end cap and is attached to a supporting member rouuble between a nonsuppordng and supporting or latched position beneath the end cap. When fault cunent is conducted through this cunrent path, an arc is developed between the trigger wire and the conducdng washer. The heat of the arc severs the trigger wire thereby releasing the support member and allowing the fuseholder to drop out of engagement with the energized network. , ~
To ensure that the ttigger wire is severed in even the lowest cunrent-rated fuseholders, ~ -the conducdng washer, the t igger wire, or both, may be made of a material generadng an exothermic reacdon when exposed to the heat of the arc, such materials including magnesium, -aluminum or thermite. Heat generated by the oxidadon of these materials when exposed to the heat of the arc (and in some cases by the condnuation of oxidadon after the arc has been ~ `

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-- ~139024 extinguished) will add to the heat produced by the arc to ensure that the trigger wire will be completely severed.
The invention may also include a frangible fastener disposed through a latuh member of a hinge assembly that is used to support an electrical component. The latch member remains in the latched posidon undl current is diverted through an ignidon circuit of an e~plosive charge that is disposed in the frangible fastener. A means is provided for diverdng current conducted through the component into the explosive charge. Ignition o~ the explosive charge causes the frangible fastener to disintegrate, releasing the latch and allowing the component, a fuseholder for example, to drop out of engagement with an energized electrical network.
Thus, the present invendon comprises a combinadon of features and advantages which enable it to substandally advance fuse and other component technology by providing a current-responsive latching apparatus for disconnecdng such devices and isoladng them from an energized network. The invendon provides a mechanical apparatus that will reliably retain the -: . .
component in its normal current-Gurying positdon but permit dropout upon the occurrence of an overcurrent of a predetermined magnitude. These and various other characteristics and advantages of the present invendon will be readily apparent to those skilled in the art upon reading the following detailed description and referring to the accompanying drawings.

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Figure 1 is a side elevadonal view of a current limidng dropou~ fuseholder including the latching apparatus of the present invendon, the fuseholder being shown mounted in a convendonal interchangeable cutout mounting;

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Figure 2 is a cross-sectional view of the fuse body of the current limidng fuseholder shown in Figure l;

Figure 3 is a side elevadonal view of the latching apparatus of the presen~ invendon and -~
the lower cap and hinge assembly of the fuseholder shown in Figure 1; :,' ~ `,'. ." .'"
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/ , ., ..,.. ;-Figure 4 is a top view of the connecdve member of the lower cap and hinge assembly ~ ,;~ ;~ ' . ',''' '' `' shown in Figure 3; ;', -~
~ "~ ~ ~, ", Figure 5 is a side view of the connecdve member shown in Figure 4; ~ ,~ ;,; ,~ , .:: . . .
Figure 6 is a top view of the hing,e member of the lowcr cap and hinge assembly shown ~; in Figure 3;
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Figure 8 is a side elevadonal view, partly in cross-section, of the sleeve for the lower cap and hinge assembly shown in Figure 3;

Figure 9 is a side view of the latch member of the latching apparatus shown in Figure 3;

Figure 10 is a top view of the latch member shown in Figure 9;

Figure 11 is a side elevadonal view of the la~ch plate member of the lower cap and hinge assembly shown in Figure 3; ~ :~

Figure 12 is a perspecdve view of the current interchange of the lower cap and hinge -~
assembly shown in Figure 3;

Figure 13 is a partial cross-sectional view of an alternative embodiment of the latchir.g ~ ; ... ~
apparatus of the present invendon as applied to a current limiting dropout fuseholder;

Figux 14 is a top view of the actuating member of the latching apparatus shown in iigure 13; .-Figure 15 is a side view of the actuating member of the latching apparatus shown in Figure 13 showing the tangs of the actuation member in their retracted positdon; .
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Figure 16 is a partial cross-sectional view of another alternadve embodiment of the latching apparatus of the present invention employed in a current-limiting dropou~ fuseholder; ; :

Figure 17 is a cross-sectional view of the latching apparatus taken along line I~ in Figure 16; ~ ~ .
" '' ,~ ~ ' :' Figure 18 is a partial cross-sectdonal view of still another alternative embodiment of the latching apparatus of the present invention applied to a current limidng dropout fuseholder;

Figure 19 is a partial cross-sectional view of another alternadve embodiment of the latching apparatus of the present invention applied to a current limiting dropout fuseholder;
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'"',;' Figure 20 is a partial cross-secdonal view of the explosive squib of the latching apparatus : '~ . . : , :- -shown in Figure 19. ; .; .;

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A variety of types of costly electrical equipment must be protected from potendally damaging overcurrents and overvoltages. A common type of overcurrent protectdon is the .
dropout fusekolder which protects the downstream equipment from fault currents and which, :.
after actuation, drops out of engagement from its cutout moundng to provide a visual indicadon ;.
that the fuse has operated. The present invention provides a latching apparatus to maintain the ;:

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fuseholder in its current carrying position within the cutout mounting, but which releases thc fuseholder and allows drop open movement to occur after the fuse has interrupted the flow of fault current; however, the invendon is believed to have a much broader application beyond current limidng fuseholders. Accordingly, for purposes of example only, and not by way of limiting tho present invention in any way, the invention will be described with reference to its use in a current limiting dropout fuseholder, it being understood tha~ the invendon may also be employed with any of a variety of other electrical components where a means for disconnecting and isolatdng the çomponent from an energized conductor is desirable.
Re~erring inidally to Figure 1, the latching apparatus I of the present invention is shown employed in current limidng dropout fuseholder 50. Fuseholder 50 is shown installed in a convendonally known interchangeable cutout mounting 10.
Cutout mounting 10 generally comprises insulator 12 and upper and lower terminal assemblies 16 and 18, respecdvely, which are mounted on opposite ends of insulator 12 on upper and lower tern ina support members 17 and 34. Upper ~ermina assembly 16 genera y includes t~rminal pad 42, for receiving and clamping an electrical line conductor (not shown), conducting strap 28 and a cup contact 26 which is integrally formed in conducting strap 28.
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Conducting strap 28 electrically interconnects cup contact 26 and terminal pad 42 through ~ -terminal shunt 29. Lower terminal assembly 18 generally includes terminal pad 44, current shunt 47 and molmdng hinge 35. Mounting hinge 35 includes a pair of hanger arrns 36 and is . ~ .
formed of brass or another electrically conducdng material. Formed within arms 36 are U- ;

shaped elbows 40 for supporting fuseholder 50. Attached to upper surface 41 of moundng hinge . ' 13902~

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35 are conducting spring clips 45 biased against the hinge assembly of the fuseholder 50 to insure ~ood electrical conuct. Terrninal pad 44 is provided for recdving and clamping an electrical line conducsor (not shown). Lower current shunt 47 provides good electrical contact between moundng hinge 35 and lower terminal pad 44.
Ln the preferred embodiment, fuseholder 50 comprises a full range, current-limiting dropout fuseholder, similar to that described and claimed in copending U.S. Patent Application, Serial No. 07/946,961, filed September 17, 1992, the entire disclosure of which is incorporated herein by reference.

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Fuseholder 50 generally comprises fuse body 52 having upper cap assembly 54 and lower ~ ;-; ~;
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cap and hinge assembly 58. Upper cap assembly 54 includes a top conuct 56. Lower cap and hinge assembly 58 includes latching apparatus I and a conducting hinge member 60 which, as ~ - ~
described below, is electrically interconnected through fuse body 52 with top conuct 56. Top ~ ;-contact 56 is disposed within the recess of cup contac~ 26, and hinge member 60 is engaged by hanger arms 36 of cutout mounting 10. :-" .,, Rcfemng now to Figure 2, fuse body 52 includes an insuladve fuse tube 70 disposed ..
about longitudinal fuse axis 51. A high cutTent fusible element 78 and a low curTe~t fusible element 80 are housed in fuse tube 70 and arc connected in series between upper and lower element te~minations 84, 86 respecdvely. Fuse tube 70 is a generally tubular member which is closed at its ends by upper,and lower closures 72, 74, respectively. Fuse body 52 houses an insuladve suppordng structure known as a spider 76 which supports fusible elements 78 and 80.
High purity silica sand 82 or other materials having suitable interrupting and insulation .:

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characterisdcs surrounds spider ~6 and fusible elements 78, 80 and fills the unused volume within fuse body 52. Spider 76 is made of an inorganic mica and it includes four arms 100 ~ ~ ' radiadng from the longitudinal axis 51, threc of arms 100 being visible in Figure 2. Evenly ' ~
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spaced along the length of each arrn 100 are element support surfaces 102. ,' -... . ......
Uppcr and lower element terminations 84, 86 respectively are formed of a conducting '' ~
matcrial, prcferably coppcr, and scrvc as supports for arms 100 of spider 76 and as landings and ~,,, ,' ,,, terrnination points for fusible elcmcnts 78, 80 and for the upper end of auxiliary wire 1~0, as ,, ' ''''` 1 ~ ~
described below. Element tcrminadons 84, 86 include angular tabs 209 for maintaining the '~ '"~ ',", separadon between spider arms 100. The upper end of ribbon 90 is soldercd to conducting tab - ', ', "~, 156 on upper element terminadon 84. ' ' ' ',~ "' ' ',, - .: .::, . :: :
,High current fusible element 78 comprises a ribbon element 90 made of silver or other ~; ", ' - , `,' cleetrieally eondueting material. Ribbon element 90 includes an array of redueed area portions : , ,: .:
92 whieh eomprise holes that are formed through thc thieh)ess of ribbon 90. As alternadves ' ~"' ~', to holes, notches may be formed along the edges of ribbon 90, or combinadons of holcs and ' ' ~
notehes may be used to reduee the cross sccdonal area of ribbon 90. Ribbon 90, with its '' '' ~' ' ,, ~
rcdueed arca portions 92, is helieally wound on the clement support surfaecs 102 of spidcr arms :, . - . . , `~ ~ 100. , ~
Rcferring sdll to Figurc 2, connectcd in serics with high current fusible elemcnt 78 is low ~ ~ - ' ~ ' ';;
` current fusible,clemcnt 80. I'rheisericsiconnector between fusible eleshents 78 and 80 is formed by copper conducting strap 79 which is supported on spider 76. Low current fusible elcment 80 is designed to operate at a prcdetcrrnined current level below that level at which high current ', ' 12 ",''' ' ', ~ . ~.'.'' ;,` ,;': :','.' ' : ~ : ''' '. '. '.'' ,, ,; . . " ,., ~..

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fusible element 78 is designed to operate. Depending on the current radng of the fuseholder 50, low current fusible element 80 is comprised of one or more parallel connected conducting wires 110 (one shown in Figurc 2), which are preferably forrned of silver or other good electrically conductive material and insulated in silicone rubber coverings 114. The covered wire 110 is then helically wrapped about the lower section of spider 76. One end of wire 110 is attached ;
to conducting strap 79 at termination point 116 by soldering. The other end of wire 110 is -... .. : .. ... .
conductively attached to tab 211 of lower element termination 86 also by soldering.
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Wire 110 of fusible element 80 is made from two approximately equal lengths of wire that are soldered together as at juncdon 112 with a solder having a substantially lower melting temperature than that of wire 110. The electrically conductive material used for wire 110 or the solder used at junction 112 has thermal characteristics causing it to melt at a temperature consistent with the time-current characteristic requirements of the fuse. Although junctions 112 are completely insulated by covering 114, for clarity, wire 110 is depicted in Figure 2 with a portion of covering 114 cut away.
Also disposed within fuse body 52 is auxiliary wire 120. Preferably, auxiliary wire 120 is formed of silver for higher currenl ra~ed fuses and a conductor of higher resistivity such as nichrome for lower current rated fuses. Auxiliary wire 120 is helically wound about spider 76 so as to be concentrically disposed wi~hin the helix formed by ribbon 90 and wire 110. ln this fashion, auxiliary wire 120 does not icontact ribbon 90 or wire 110 except, as described below, near its upper point of terminadon. The lower segment 121 of auxiliary wire 120 is insulated in a siliconc rubber coveting as it enters the space occupied by the helix formed by low current - - ~ . ; ,: -~: .
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: ~ -fusible element 80. The upper end of auxiliary wire 120 is soldered to tab 156 of upper element termination 84. The lower end of auxiliary wire 120 terminates on flanged receptacle 186 which is made of brass or other conducting material and retained in a centIal recess 185 formed along fuse axis 51 in the lower end of spider 16. A conducting insert 188, preferably made of brass, is inserted into bore 187 of receptacle 186 and is electrieally conneeted to a trigger wire 204 whieh preferably is made of high strength and high eleetrical resistance nichrome. Trig8er wire 204 forms a part of latehing apparatus I and extends outside of fuse body 52 through lower closure 14. Conducting receptacle 186, insert 188 and trigger wire 204 are all electrically insulated from lower closure 14.
Upper cap assembly 54 generally comprises top contact 56, pull ring 132, top end cap 138 and upper element termination 84, all of which are attached and their positions relative to one another maintained by the use of a single fastener, stud 134. An o-ring seal 136 is disposed about stud 134 betwoen top contact 56 and end cap 138. Stud 134 includes a central longitudinal bore (not shown) to permit filling of fuse tube 10 with sand 82 upon assembly of fuseholder 50.
Lower closure 14 generally comprises bottom end cap 180, lower element termination 86, seial member 182, positioner 184, conductive washer 116 and insulative spacer 174. Bottom end eap 180 is formed of copper alloy or other conducting materiial and generally includes a eylindrieal body portion 190 disposed about fuse tube 70 and a generally cylindrical redueed .
diameter e~tension 194 attached to and extending from the center of cylindrieal body portion 190 , ..,:'~ ;,-,, thereby forming an interior recess within extension 194. Extension 194 and bady 190 are ,; , , ,;:
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generally coaxially aligned with fuse axis 51. An aperture 196 is formed substandally in the center of lower surface 195 of extension 194 at the intersection with axis 51.
Lower element terminadon 86 includes central aperture 214 which is substan~ially aligned with fuse axis 51, and funher includes conducting tab 211 which serves as a landing and terminadon point for wire 110 of low current fusible elemen~ 80 as shown in Figure 2. Lower element terminadon 86 is electrically connected to bottom end cap 180 by means of conducdng tab 192. Tab 192 is formed on and extends from element termination 86 through hole 193 formed in bottom end cap 180. The portion of tab 192 extending through end cap 180 is bent over and soldered to cap 180.
Coa~tially disposed within the central recess of end cap extension 194 are insulative spacer 174, conducdve washer 176, wire posidoner 184 and seal member 182. Seal member 182 comprises a rubber washer having central aperture 200. Wire posidoner 184 comprises an insuladve washer made of mica or nylon or other insulating material and includes central aperture 202. Washer 176 is made of an electrically conducdve material and includes a central .- '" , . , ":
aperture 178 and an outer edge surface 177 which engages the walls of extension 194 so as to create a current path therethrough. Insuladve spacer 174, which may be rnade of rubber or : ,.:, . ....
nylon, for example, includes a central aperture 175. Trig8er wire 204 is brazed cr soldered to - ,:
conducdng insert 188. Insert 188 includes flange 189 which is disposed between seal member 182 and positdoner 184. Aperture 202 of wire posidoner 184 has a diameter that is smaller than . ...
the diameter of aperture 178 of conducdng washer 176 so as to centrally posidon trigger wire 204 in aperture 178.
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Receptacle 186, adapted to receive and electrically engage insert 188, is disposed through central hole 214 in lower elemen~ termination 86 and is reuined in central recess 185 in thc lower end of spider 76. Receptacle 186 is atuchod to, and in conducting engagement vith, auxiliary wire 120 as previously describod, but does not contact element termination 86.
Conducdng insert 188 is inserted into bore 187 of conducting receptacle 186 through hole 214 of lower element terminadon 86 during assembly of fuse body 52 with trigger wire 204 extending out of fuse body 52 through aperture 196 in end cap 180, passing through apertures 175, 178, 202, 200 of spacer 174, conducting washer 176, positioner 184, and seal 182, respectively. Tho lower segmen~ 121 of auxiliary wire 120, recepucle 186, insert 188 and trigger wire 204 are all clectrically insulated from lower cap and hinge assembly 58. A spark gap 210, which preferably is approximately 0.040 inches for all voluge and current ratings for fuseholder 50, is thus formed between trigger wire 204 and washer 176 and itseLf forms part of latching apparatus 1.
Referring now to Figures 3 - 5, lower cap and hinge assembly 58 of fuseholder 50 genera~y includ latching apparaNs 1, hinge member 60, and connoctive member 64. ~st shown in Figures 4 and 5, connecdve member 64 functions lilce a clamp and generally includes ;
a strap portion 215 and a pair of hinge supporting members 217 attached thereto. The ends 216 of hinge supporting members 217 are bent toward one another and formed at substantially right ;
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angles to hinge supports ,217. Two pairs of aligned holes 218,, 220 are formed! in hinge supporting members 217. As best shown in Figure 3, fastener 225 is disposed through aiigned - -16 - ~-,~, , ,,., ,,,. . ~ " ~... ..

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holes 220 in order to draw together hinge supporting members 217 and to secure and clamp strap portion 215 of connective member 64 about bottom end cap 180.
Refesring to Figures 3, 6 and 7, hinge member 60 generally comprises base por~ion 232 and a pair of outwardly extending side members 234. Side members 234 include tapered edge 240, shoulder 244 and two pairs of aligned holes 236, 250. Holes 236 are formed through side members 234 adjacent tapered edge 240. Shoulder portions 244 have ~nions 246 extending outwardly therefrom and include cam-like electrical conuct surfaces 248 adapted for electrical engagement with conducting spring clips 45 of moundng hinge 35 shown in Figure 1. Holes 250 are formed in side members 234 between holes 236 and shoulders 244. Base 232 extends between sidc members 234 and includes slot 254. Slot 254 generally bisects base 232 forming a pair of leg portions 256. Legs 256 include ends 258 which extend outwardly from base 232 -, : .- -: :
at an angle which is substandally equal to 45 and form a shoulder which engages and supports one end of thc curren~ interchange 68, best shown in Figure 3. '~ ~
Rcferring now to Figures 3 and 8, cap and hingc assembly 58 further includes sleeve 69. - : .
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Sleeve 69 gencrally comprises a cylindrical body æ2 having reduced diameter portions 224 at each end, forming shouldeK 228. A central bore 226 is longitudinally forrned through sleeve 69. Reduced diameter portions æ4 are disposed in holes 218 of hinge supporting members 217 ~ - .
af connecdve member 64 ~Figure 4) such that members 217 abut shoulders 228. Sleeve 69 provides a spacing means t,o maintain, the proper separation between hinge supporting members ~ -217 and provides a bearing mcans for a pin 230, which is disposed through central bore 226 and .
which supports hinge member 60 (Figure 3).

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Latching apparatus 1 includes, in addidon to sparlc gap 210 and trigger wire 204, latch 62, spring 63 and latch plate 66. As best shown in Figures 3, 9 and 10, latch 62 generally comprises base 260, side members 262, and fuse restraining end 268. Side members 262 are attached to, and extend substantially perpendicularly from, base 260. Side members 262 include ears 264 having aligned holes 266 formed therein. Pin 252 (Figure 3) is disposed through aligned holes 266 such that latch 62 is rotatably mounted about pin 252. Spring 63 is also mounted around pin 252 between side members 262 to bias latch 62 to rotate about pin 252 in a clocl~wise direction as viewed in Figure 3. Base 260 of latch 62 includes latching surface 267 extending between sides 262 for engaging latch plate 66 as described in more detail below. A
notch 269 is formed in latching surface 267 for receiving spring arm 65 of spring 63, best shown ~ ;
in Figure 3. The free end of latch 62 comprises fuse retaining end 268 which includes an elongate aperture 272. Latch 62 is preferably made of stainless steel, although any conductive ~ ~ .
or insulative material having sufficient rigidity and strength may be employed.
Referring again ~o Figures 2 and 3, latching apparatus 1 further includes a bobbin 124. -Bobbin 124 is made of nylon or other insula~ive material and generally comprises a spool-shaped body 126 and an annular extension 128 attached to body 126. A central aperture 129 is formed :
through body 126 and extension 128. Upon assembly of fuseholder 50, fuse retaining end 268 of latch 62 is rotated into a latched or supponing position against extension 194 of bottom end cap 180. Aperture 272 in retaining jend 268 of latch 62 is preferably a slot ~o allow annular extension 128 of bobbin 124 to properly a~ign with fuse axis 51. Annular extension 128 of bobbin 124 is disposed through aperlure 272 in latch 62 and the end of trigger wire 204 Ai ~ ' ---' 213902~

extending from fuseholder 52 is disposed through central bore 129 of bobbin 124. Trig8er wirc 204 is then bent and pressed into a radially formed groove 12 7 in lower surface of spool body 126 and held in place against the sides of body 126 by clamping band 130. When so attached, latch surface 267 of latch 62 engages projecdng latch surface 276 of la~ch plate 66 (described below) to retain hinge membcr 60 and connective member 64 in fixed angular reladonship to one another in a ~contracted" and ~charged~ position, and prevent rotadon about the joint means, i.e. pin 230 and sleeve 69. , -Now with reference to Figures 3 and 11, latch plate 66 is a generally flat metal plate ~
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having a projecdng latch surface 276 for engaging latching surface 267 of latch 62 (Figure 10).
Latch plate 66 further includes a notch 278 for receiving fastener 225 of connecdve member 64, a key way 280 for use in installing and removing fuseholder 50 by "hot sdck," and an aperture ~ -,: . . .: . .
284 for recciving pin 290 shown in Figure 3. Latch plate 66 furdter includes aperture 282 for - `~
=iving body 222 of sleeve 69 which, as previously described, is disposed between hinge suppordng members 217 of connecdve member 64. Pin 230 is disposed through central bore 226 of sleeve 69 and through holes 236 of hinge member 60. Latch plate 66 is received in slot 254 of hinge member 60 (Figure 6) and includes a stop shoulder 227 for limidng its rotadon on pin 230 through engagement with pin 252. The rotatable moundng of connecdve member 64 and latch plate 56 about sleeve 69, together with the inter-engagement of the fastener 225 within the notch 278 cause latch p!ate 66 to ,be non-rotatably anchored to connecdve member 64. This connecdon means causes latch plate 66 and connecdve member 64 to always ro~ate as a single unit along with fuse body 52 about the join~ means, i.e. pin 230 and sleeve 69. ~

'i','':','"' :'.
:'. ''~ ,, ' ;,' .: '~ : ' ': ~- :

~13902~

Current interchange 68 is bes~ shown in Figures 3 and 12. As shown, pin 290 is disposed through aperture 284 of latch plate 66 and provides support for current interchange 68.
Current interchange 68 is preferably formed of phosphor bronze, a good electrical conducting material that is also suitable for use as a spring. Current interchange 68 includes a pair of U-shaped legs 292, 293 separated by slot 294 and connected by segment 296. Current interchange 68 comprises a means for conducdng current between bottom cnd cap 180 of fuse body 52 and hinge member 60. Legs 292, 293 straddle latch plate 66, and are supported on pin 290 which -: : :.:
projects from latch plate 66. Connecting segment 296 electrically engages bottom end cap 180 while ends 298 of legs 292, 293 electrically engage the ends 258 of legs 256 of hinge member -.
60. When engaged bet~voen fuse body 52 and hingc 60, current interchange 68 acts as a spring ~ :.
and imparts approximately 12 inch-pounds of torque betwoen hinge 60 and fuse body 52 which ~ ~:
assists hinge member 60 to rotatc to its extended posidon to allow fuseholder 50 to drop out of engagement with cutout moundng 10. : , Fuseholder 50 is shown in Figures I and 3 with hinge member 60 and connective member 64 in their cont~acted and charged posidon, and with latch 62 and latch plate 66 la~ched.
So latched, fuseholder S0 is in its exunded posidon and current is conducted from upper terminal 16 of cutout mounting 10 through fuseholder 50 to lower terminal assembly 18 by means of bottom end cap 180, current interchange 68, hinge membcr 60 and conducting spring clips 45 to mounting hinge 35 of lower urminal assembly 18.
Referring to Figures 1-3, when current limidng fuseholder 50 experiences an overcurrent of a predeterrnined magnitude and duradon, fusible element 78 or 80 will fuse opein. For an ; ': -21 3902~

instant after this occurs, the overcurrent is conducted through fuseholder S0 ~o bottom end cap . -.
180 via auxiliary wire 120, trigger wire 204, spark gap 210 and conducting washer 1~6.
Trigger wire 204 has a high resistance, and the high I~R headng, coupled with the heat genera~ed ~ -by the arc across gap 210 will sever triggcr wirc 204, thaeby acting as a release means for ~ -releasing and freeing latch 62 from retainment by trigger wire 204 and bobbin 124. When this ~ - ~
occurs, fuse restraining end 268 of latch 62, no longer held in contact with bottom end cap 180, ; ~ .-is biased away from end cap 180 by spring 63. The weight of fuseholder 50 and the forces ; . :. ; .
imparted thereon by top terminal assembly 16 and conducting spring clips 45 of interchangeable - ~ ~-cutout mounting 10 and thc spring force from current interchange 68 will cause the lower cap and hinge assembly 58 to begin to collapse about pin 230 to an exundcd posidon and causc the . . ,--~.,: :.:
upper cap assembly 54 of fuse body 52 to drop out of engagement with top terminal assembly 16. When this occurs, fuse body 52 and lower cap and hingc assembly 58 will begin to rotate ~ ~ ~
abou~ trunion 246 in a clockwise direcdon as viewed in Figure 3 until the fuseholder 50 reaches . .; . ~.
the dropout posidon and comes to rest supported by hanger arsns 36 of interchangeable cutout 10. ' ~' " . ~ ' The dropout posidon that results provides a clear and highly visible indlcation to linemen . ~:
that the fuse has operated. Addidonally, by causing the fuseholder 50 to drop out of engagement with interchangeable cutout moundng 10 upon the occurrence of an overcurrent, voltage strcss . .. .:
is thus removed from the a;~ctuated fuSe.; This voltage stress could otherwisc eventually lead to ~ . .
tsacldng along the outer surface of the fuseholder 50, and possible ultimate flashover betwccn the upper and lower tersninal assemblies 16 and 18 of interchangeable cutout moundng 10.

21 .
' -`-" 2139024 .,, ,-Thus, the latching apparatus 1 offers a mechanicaUy operable dropout mechanism that provides - ~:
for dependable operadon upon actuation of the fuse. The latching apparatus 1 is reladvely -; -;
inexpensive to produce and provides increased reliability over prior fuseholders which relied upon explosive charges to initiate drop open movement. - ;; -As apparent from the description above, dropout of fuseholder 50 is dependent upon the ~ ~ -shiftdng of thc fault current from a first current path including fusible clements 78, 80 into a second currcnt path ineluding auxiliary wire 120 and trigger wire 204, such that trigger wire 204 ~ ~
is severed by the heat generated from the arc that is formed across spark gap 210. Thus it is - - - `
-- . . ...
important from the standpoint of causing fuseholder 50 to drop open, that auxiliary wire 120 not ~ ~
melt and forec the current to transfer back to the first current path of fusiblc elcments 78, 80 ~ -too quiekly, but instead rcmain conducdng long enough for the areing aeross gap 210 to sever trigg wirc 2a4. On the othcr hand, thc dropout funedon is of secondary importanee to the abil;q of fuseholdcr 50 to interrupt ~he flow of fault current and to do so before the dropout aetdon of fuscholder 50 causcs any significant separadon betwcen thc uppcr conuct asscmbly 54 , of fuschold 50 and thc cup contact 26 of cutout mounting 10. As the current ratings of fuseholder 50 deereasc, thc level of current that thc fuse must be capable of ~terrupting and thc allowablc la through current (la thorough PT) during interrupdons at all fault currcnt Icvcls -, :: i .. .
` deercase aeeordingly. Thc size of auxiliary wires 120 used in highcr currcnt rated fuses can be ~ ~ ~
. ~-, -,: .
reladvely large without having any adverse affect on sueh fuses' intcrrupting performance. On the other than, thc size of thc auxiliary wires 120 normally used in high current rated fuses can approaeh thc size of the high currcnt fusible element 78 used in lower current rated fuses and, :'~"'' , ,, ~ ;,.

;',, ''.~"..:' ~"

::: :: :". ,; ,!;

`,':, :. .'` " "` .:~

9., ~ 2139~24 ;~

if used in such lower current ra~ed fuses, can adversely affect the interrupting performance by causing excessive let through I'T for these lower current rated fuseholders 50. Also, even at the lowest level of current that these lower current rated fuseholders 50 must interrupt, the trigger wire 204 will be severed within several 60 Hz cycles after the current is shifted to the second current path which includes auxiliary wire 120. In these cases, the auxiliary wire 120 must be smaU enough that it can melt and interrupt these low level currents within the nex~
several cycles of 60 Hz current flow. If the interruption is not accomplished within this time frame, an arc will develop between the separating upper contact assembly 54 of fuseholder 50 ~ ~ ~
and the cup contact 26 of cutout mounting 10. This arc can cause the cutout mounting to ~ ; -flashover. - -The requirements that dictate the size of the auxiliary wire 120 can be conflicting. On one hand, the wire must be large enough to allow completion of t'ne severing of the trigga wire 204, while on the other hand the wire 120 must be small enough thu it does not impede ~ ;
successful fault current interruption by the fuse. Difficulties in satisfying both requirements increase with lower current rated fuses since mechanical requirements for the trigger wire 204 do not allow the size of trigger wire 204 to be reduced accordingly. In hi~gher curren~-rated fuseholders~such as those rated 18 amps and above, no tension exists between the requirement that auxiliary wire 120 melt soon enough to interrupt the fault current and the desire to have spar~ gap 210 conduct long enough ~o sever tngger wire 204. On lower current-rated fuses, however, such as those rated less than 18 amps, the auxiliary wir~ 120 sdected to properly interrupt aU the various magnitudes of fàult currents that may be experienced by fuseholder 50 23 . --- 213902~ ~

must be relatively small. So constrained, wire 120 may melt too quiclcly, causing conduction across gap 210 to cease before trigger wire 204 is severed. In this instance, although the fuse would perform its primary function of clearing the fault, the fuseholder would not drop open and provide the convenient indication means so valuable to udlity personnel. This may cause considcrable delays while utility personnel search to find the fuses which have operated to open a c~rcult.
To provide additional heating to insure that the trigger wire 204 is severed in lower current-ratcd fuses, conducdng washer 176 may alternatively be made of a metal which undergoes an exothermic reaction under the heat of an arc. For example, conducting washer 176 may be made of or coated with magnesium, aluminum or thermite. Once an arc is formed between the trigger wire 204 and such a conducting washer 176, the heat generated by the oxidadon of the aluminum, magnesium or thermite structure when exposed to the heat of the arc (and in some cases thc condnuation of the oxidadon of the process after the arc has subsided) will add to the heat generated by the arc. Thus, a current flowing across the gap 210 of even a short duradon, in conjunction with the heat provided by the burning metal, will cause the ,, :::
trigger wire 204 to be severed and release the latch 62, allowing dropout to occur.
Altetnadvely, the trigger wire 204 itself may be manufacNred of aluminum, magnesium or thermite instead of, or in addidon to, using such material for the conducdng washer 176.
In Figures 13-20, a number of other ~lternadve embodiments of the present invendon are shown which include alternadve means for retaining latch 62 in the suppordng posidon beneath fuseholder 50 prior to acNadon of fusi~le elements 78 or BO, and for releasing the latch 62 upon .:'-,,''~''~ ~".

2~3902~

actuadon of either of the fusible elemcnts. These alternative embodiments employ many elements that are identical to those previously shown and described. Accordingly, where like elements are shown and described, the identical reference number may be used.
Referring now to Figure 13, there is shown a releasable latching apparatus 300 as applied to current-limidng fuseholder 50. Fuseholder 50 includes high current and low current fusible elements 78, 80, fuse tube 70, spider 76, upper and lower element terminadons 84, 86, lower ~, end cap 180, latch 62 and auxiliary wire 120, all as previously described with reference to Figures 1-12. Latching apparatus 300 generally comprises conducdng receptacle 312, pin member 310, actuadng member 308 and heat transfer ring 306. Conducting receptacle 312, preferably made of brass, is retained in spider 76 and includes a flange 315 and a central bore 314 generally aligned coaxially with the fuse axis 51. The receptacle 312 extends beyond the lower most edge of the lower termination member 86 and is centered within extension end cap 194 by annular spacer member 316 which preferably is made of nylon or rubber or another insuladve material. Receptacle 312 is disposed through a central aperture formed in spacer member 316. Flange 315 on receptacle 312 retains spacer 316 in position between lower element terminadon 86 and receptacle 312. ' ~~
Stacked in columnar fashion with annular spacer 316 within end cap extension 194 are lower annular seal 318, heat transfer ring 306, actuadng member 308 and spacer 320. In the preferred embodiment, heat transfer ring 306 is comprised of silicon carbide, conductive rubber, - ~: ~
or another material having a high electrical resistance. Heat transfer ring 306 includes a central ~ ~ -aperture 326 generally aligned with the fuse axis 51 and includes an outer edge surface 328 .i. .~ ' :, ;, .

'~

.~ . .

~ 2139024 which engages the inner surface of end cap extension 194 so as to create a current path therethrough. Disposed between heat transfer ring 306 and the bottom of end cap extension 194 is seal member 318. Seal 318 is preferably made of rubber and also inc~udes a central aperture 319 generally aligned with the fuse axis 51.
Referring to Figures 13 and 14, acmating member 308 is a washer-like member having a circular base pordon 322 and a pair of latching tangs 324 integrally formed on base portion 322 and extending upwardly from the base and toward the fuse axis 51. Base 3æ has an outer diameter less than the inside diameter of end cap extension 194 to ensure that base 322 does not engage end cap 180 when positioned in end cap extension 194. The base 3æ of actuadng member 308 is disposed against and physically and electrically engages heat transfer ring 306.
Actuating member 308 is preferably made of a memory alloy such as the nickel-titanium shape-memory alloy known as Nidnol. Nitinol, its properties and physical characteristics are discussed in the article entitled "Shape-Memory Wires, ' authored by S.M. Tuominen and R.J. Biermann :: , , :~ , :- , which was published in the February 1988 edidon of Joun~al of Merals, incorporated herein by this reference. Alternatively, actuadng member 308 may be made from a bimetallic material, `
: . , " ,., ,-" ~
such as thin layers of NiFe and NiCrFe bonded together. As known to those s~lled in the art, .. f',;:
memory alloy will rapidly deform or change shape when a particular threshold temperature is - ~;-reached. Bimetallic materials can also be made to undergo a rapid change in shape when a threshold temperature is reached if tbe material is loaded while, in an over center position.
Heating will bias the material toward the position opposite its inidal over cenur posidon until a threshold temperature is reached, at which time the material will snap to the opposite position. ~ - ;
, . ~

:: . , . ,: . .: . ~, :,: .-.~ .:
' '.' "'.'''' '...~'.":
: ::':'-:' '., -- 213902~

Actuating member 308 of ~he present invention is configured as shown in Figures 13 and 14 under normal operadng condidons where the normal system current is flowing through fuseholder 50. These temperatures, under normal condidons, vill not exceed 100C.
Disposed between actuadng member 308 and annular spacer 316 is another annular spacer 320. Upon assembly of fuseholder 50, base 322 of actuadng member 308 is disposed between annular spacer 320 and heat transfer ring 306.
Retaining pin 310 of latching apparalus 300 includes a conducting insert or stud 336 and an insuladve retainer 338 fastened to the lower end of slud 336. The retainer 338 may be fastened by adhesive or, as shown in Figure 13, by a pin 340. Retainer 338 includes an annular ex ension or collar 342 disposed about a portion of stud 336 to insulate the stud 336 from end cap 194 after assembly. The stud 336 includes recesses which, in the preferred embodiment, comprise an annular groove 344 formed about the circumference of stud 336.
Upon assembly of fuseholder 50, latch 62 is rotated into the latched or suppordng posidon beneath lower end cap 180 such that latch surface 267 of latch 62 engages projecting latch surface n6 of latch plate 66 to maintain hinge assembly 58 in its contracted posidon. Stud 336 of pin 310 is disposed through aperture 272 of latch 62 and through aperture 196 in ,: - , :
extension 194 and is received in and engages bore 314 of receptacle 312. During inserdon of stud 336 into end cap 180, tangs 324 of actuadng member 308 are biased radially outwardly by conducdng stud 336. As the stud 336 is further inserted, the tangs 324 snap radially inwardly into groove 344. This effecdvely locks the retaining pin 310 and prevents it from being : ~ ....
withdrawn from fuseholder 50 undl tangs 324 release stud 336. -~

. : ,, ,,,~. ,, :. .~ 1 . .-.:
, :,: .,~., ..: ,..
.: .~ ," ..............

, . -; . . . ~ ~ . , . . : : : -,,........ .. , , j. ".. , , . , ,., i : ; - ., , 213902~

As is apparent, a first current path exists in fuseholder 50 and includes the series combinadon of high and low current fusible elements 78, 80, lower termination 86, and lower end cap 180. A second current path, in parallel with the first, comprises the path formed by auxiliary wire 120, receptacle 312, stud 336, actuating member 308, heat transfer ring 306 and lower end cap 180. The separadon of base 322 of actuadng member 308 from end cap 180 prevents current flowing in the second path from bypassing heat transfer ring 306. Similarly, the insulative collar 342 on retainer 338 insulates stud 336 from latch 62, again ensuring current flow through heat transfer ring 306.
In operation, the normal system current is conducted through the first current path which , " .;..,:.;,;;: ,:
includes fusible elements 78, 80 due to the relatively high resistance of heat transfer ring 306.
When fuseholder 50 experiences an overcurrent of a predetermined magnitude and duration, the high or low current fusible clements 78, 80 will fuse open. During this process, thc overcurrent will then shift and be conducted through the fuseholder 50 to lower end cap 180 via the auxiliary wirc 120, receptacle 312, stud 336, acNadng member 308 and heat transfer ring 306 of the second current path. As the overcurrent continues to flow through heat transfer ring 306, the temperature of the silicon carbide ring will increase. With actuating mernber 308 physically engaging heat transfer ring 306, the heat generated by ring 306 will be conducted to actuadng ~nember 308. When the temperature of actuating member 308 reaches a predetermined magnitude, sucb as approximately 15QC, the tangs 324 of actua,ting member 308 will snap radially outwardly out of engagement with the stud 336 of retaining pin 310. Upon actuation, the tangs 324 will take the shape as shown in Figure 15.

.: ,.,, ~':';'~:, - -, :; ,: ,, , .;:
", ,. ' , ~:~
' ~ : " .
,., . -,, .. .. . . .

~ ~139~2~ ~ ;

With the release of retaining pin 310 by actuating member 308, graviy, as well as tne spring and other forces imposed on latch 62, will cause latch 62 to route out of the latched or supporting position beneath fuseholder 50, in a cloc'kwise direction as viewed in Figure 13.
Such rotation releases projecting atch surface 2;'6 of latch plate 66 and allows hinge assembly 58 to collapse to an extended posidon and, in turn, allows fuseholder 50 to drop out of engagement with cup contact 26 of cutout mounting 10.
RefetTing now to Figures 16 and 17, there is shown another alternative embodiment of the present invention including releasable latching apparatus 350 suitable for use with current~
limiting dropout fuseholder 50. Latehing apparatus 350 genera ly includes conducting receptaele 312, heat ttansfer ring 306, lower annular seal 318 and retaining pin 310, all as previously described with referenee to Figure 13. Latching apparatus 350 further ineludes spacer 316 with annular insulating extension 317 and an aetuating member 352, whieh comprises locking ring 354 preferably fotmed of a memory alloy sueh as Nitinol. As best shown in Figure 17, the loeking rdng 354 generally eomprises a paur of arms 356 and 357 that are connected to a eentral : :, . , ~;, lobe 358. Locking dng 354 is disposed in extension 194 of end eap 180 where it is placed in - ~ ~
; "~
eontaet with heat transfer ring 30;6 of silieon carbide or otner similar mateTial having a high electrical resisunce. Insulating extension 317 of spaeer 316 is disposed between the wa~ of end .. . :,.~, ., ,,, ~;, .,,:;
cap extension 194 and loeking ring 354. Arms 356, 357 of locking ring 354 are disposed about -stud 336 and engage groove 344 when the stud 336 is insened through the lateh 62 and into lower end eap 180. Seal 318 is disposed between heat transfer ring 306 and bottom 195 of end cap extension 194 and seals between end cap 180 and extension or collar 342 of retainer 338.

'Z13902~ :
,",',''~
.. :- ~, , .,, :
When an overcurrent of sufficient magnitude to melt fusible element ~8 or 80 is conducted through fuseholder 50, the current will be diverted to the secondary current path formed by auxiliary wire 120, receptacle 312, stud 336, locking ring 354 and heat transfer ring ~ :
..
306 to bottom end cap 180. During such a fault condition, the current conducted through the : :
high electrical resistance of heat transfer ring 306 will cause the ring to heat to an elevated " , , temperature. In turn, the heat will be transferred to locking ring 354. When locking ring 354 reaches a temperature of approximately 150C, ring 354 will change shape almost instantaneously and assume the configuration represented by the dashed lines shown in Figure 17. This thermally induced change in shape causes arms 356, 357 to release retaining pin 310, thereby again permitting the latch 62 to rotate out of engagement with projecting latch surface 276 of latch plate 66, and permitting the fuseholder 50 to drop out of engagement with the ~, , "~ ., ,,, ,::
cutout mounting 10.
Referring again to Figure 16, it is evident that if only one of the arms 356, 357 moved . ; i :,:~ :, . ., ::':
out of engagement with groove 344 of stud 336, retaining pin 310 would still be retained by the ~:
remaining arm of locking ring 354. Accordingly, latching apparatus 350 would continue to .
maintain ~tch 62 in a supporting position beneath fuseholder 50. Accordingly, it is important :, ,: ~ ,,, :: :, to the operation of latching apparatus 350 that both arms 356, 357 move radially outwardly to . :-~:~ the actuated posidon shown by the dashed lines in Figure 17. To ensure that both anns of - ' locking ring 354 clear groove 341 upon actuation of the fusible elements in fuseholder 50, -:; . `, . .
Iocl~ing ring 354 is dimensioned such that upon actuation, locking ring 354 takes a generally . : :
, . .
: , ,, ~, ::, : ,' ;., ::':, :.
-'~13902~

semi-circular shape having an outside diameter substantially equal to the inside diameter of annular extension 317 of spacer 316.
Still another altesnative embodiment of the prescnt invention is shown in Figure 18. As shown, rcleasable latching apparatus 380 retains latch 62 in the latched and suppor~ing position beneath fuseholder 50 until an overcurrent of a predetermined magnitude and duration causes latching apparatus 380 to release. Latching apparatus 380 "enerally comprises heat transfer ring 306 and actuating member 308, both as previously described with reference to Figures 13-15.
Alternadvely, actuating member 308 may comprise a locking ring made of memory metal or a bimetallic material such as, for example, rin, 354 which was described above with reference to Figures 16 and 17. Latching apparatus 380 further comprises pin member 382. Pin member 382 comprises a conducting stud having an annular groove 388 formed adjacent to lower end 390.
Upon assembly of fuseholder 50, upper end 392 of pin member 382 is seated within recess 185 form~d along fuse axis 51 in spider 76. End 392 of pin member 382 is soldered or otherwise elec ica Iy connected to auxiliary wire 120 shown at 393. An insulati~e nylon washer 394 and annular rubber seal 396 are disposed between bottom 195 of end cap extension 194 and Iower element termination 86. Pin member 382 is disposed through the central apertures of washer 394 and scal 396. Lower end 390 of pin 382 extends outside end cap extension 194 through aperture 196. In th;is embodiment, aperture 196 is made large enough to ensure that the air gap 395 between extension 194 and pin 382 is too large to permit conduction across the gap Pin member 382 is fixed in this position by any suitable manner, such as by pin 389 which is 31 .. , 13902~

, ' ,: -, :
disposed through pin 382 and into insulating washer 394 such ~hat the ends of pin 389 remain electrically insulated from the walls of lower end cap extension 194.
Referring still to Figure 18, latching apparatus 380 further comprises a shallow annular recess 398 formed in the lower surface of latch 62. To complete the assembly of fuscholder 50, latch 62 is routed into its latched or supporting position beneath lower end cap 180 with latching surface 267 engaging projecting latching surface 276 of latch plate 66. Lower end 390 of pin ~ :
member 382 is disposed through aperture 272 centrally formed through annular recess 398 of . :~
latch 62. Heat transfer ring 306 is placed about end 390 and seated within annular recess 398. : ; ;
Actuating member 308 is next disposed about end 390 of pin member 382 such that base 322 : . :~
engages heat transfer ring 306, while tangs 324 engage pin member 382 in groove 388 so as to secure retaining end 268 of latch 62 between end cap extension 194 and heat transfer ring 306. - . -Because in rhis embodiment heat transfer ring 306 does not physically contact end cap extension 194, latch 62 is made of stainless steel or another conducting material so as to complete the . ,-,... :-, :,:. .
second current path through fuseholder 50. :: -Upon the occurrence of a fault of sufficient magnitude and duration, fusible elements ~8, .
80 will melt and the current will be transferred from that current path into-the second path within fuseholder 50, the second cumnt path including auxiliary wire 120 and pin member 382.
The second current path to hinge 60 is completed by means of actuating member 308, heat transfer ring 306 and latch 62. As shown in Figure 18, pin member 382 is insulated from bott~m end cap 180 by seal 396, washer 394 and an air gap 395. Similarly, pin 382 is insulated from conducting latch 62 by air gap 402 formed between pin 382 and the edges of aperture 2~6.
: -, - ::
~ ' .'; ' .'.

;- 213902~

When a fault current of prede~ermined magnitude is thus conducted through pin 382, actuating member 308 and heat transfer ring 306, the heat generated by the high electrical resistance ring 306 will cause actuating member 308 to heat to a predetermined temperature that will cause tangs 324 to snap apart and release pin 382. Thereafter, the spring force applied to latch 62 by spring 63 (Figure 3) will cause latch 62 to rotate in a cloclcwise direction as viewed in Figure - ~ -18, and actuatdng member 308 and heat transfer ring 306 will slide off end 390 of pin 382, ~ -: -:
allowing latch 62 to rotate free from engagement with fuseholder 50. As previously described, when this occurs, fuseholder 50 will then be permitted to drop out of engagement with cutout mounting 10.
In higher current-rated fuses, such as those rated 18 amps and above, conduction of fault current through the actuadng member may itself be sufficient ~o heat the actuadng member to the temperature necessary to cause it to release the pin me:nbcr. Accordingly, as an alternadve .~ " . ,-.
embodiment to those described with reference to Figures 13-18, for the higher current-rated fuseholders, the latching apparatus may not require a heat transfer element. Thus, in the embodiments of Figures 13, 16 and 18, the heat transfer ring 306 may be replaced with a simple washer of a conductdng material, such as brass.
Another alternadve embodiment of the releasable latching apparatus of the present invention is shown in Figures 19-20. The embodiment of Figures 19-20 employs an explosive charge, commonly known as a squibs Upon actuation of the fusible elements 78, 80 and the subsequent inidadon of current flow through the auxiliary wire 120 and series-connected heater wire 416, the squib will explode to cause release of la~ch 62 as described more thoroughly :. , ...: :. ~ ..
: ,: . , , . ..:
:. . :. :, ., r ~13902~

below. Although the latching apparatus described with reference to Figures 1-18 may be more desirable from a COSI, reliability and safety standpoint, the embodiment of Figures 19-20 employing the explosive charge may be convenient to manufacture given that squibs are presently widely used and readily available.
Referring momentarily to Figure 20, a squib 410 generally comprises an outer casing 412, typically of brass, a powder charge 414 and a heater element 416 in contact with primer 415 which is embedded in powder charge 414 and surrounds heater element 416. A pair of lead ,.. . . . .
wires 417, 418 are connected to the heater element 416 and are disposed through a rubber plug 413 which retains the powder inside casing 412. Lead wires 417, 418 are reladvely sdff, bare wires, preferably 16 gauge or larger. As shown in Figure 19, the segment of lead 417 adjacent to the upper end of casing 412 is covered with insulating sleeve 419. Insulating sleeve 41g extends into bore 187 of receptacle 186 posidoning the bare segment of lead 417 from the wall of receptacle 186, thereby forming an arc gap 421 therebetween. Alternatively, the arc gap may be formed a~ the upper end oî fuseholder 50 between conducting tab 156 of dement termination 84 and the upper end of auxiliary wire 120. In such an alternadve embodiment, sleeve 419 may be omitted and lead 417 may conuct conducdng receptacle 186; however, in ai'ly design, an arc gap is required at some locadon along the current path which includes auxiliary wire 120 to ptevent ignition of the squib 410 by the milliamps of current which may be conducted through auxiliary wire 120 during nonfault conditions.
Referring sill to Figure 19, the latching apparatus 420 generally comprises two subassemblies 4æ, 424 which are inu:rconnected to retain latch 62 in the latched posidon ~ :. ;.:. .' -.
':, ,. ,' ': ' . ' ., .Z. ', ',,.,' ~""
. .: ~, .
' .' ''"" ' -', , . . ~ :

::.:,~,: .

--- 2~9~24 beneath fuseholder 50. The first subassembly 422 generally comprises end cap 180, squib 410, annular scal membcr 426, and conducting recepucle 186. As describcd with reference to Figure 2, recepucle 186 electrically engages and is physically atuchcd to auxiliary wire 120. Thc receptacle 186 includcs a central bore 187 generally aligned with fuse axis 51 and sized so as to receive a portion of insulating slccve 419 and a bare segment of lcad wire 417 of squib 410.
The casing 412 of squib 410 is disposed through a central bore in scal mcmber 426, and thc second Iead 418 of thc squib is retained betwcen lower element termination 86 and lower end cap 180. An o-ring seal 434 is disposed within end cap extension 194 and sized so as to receive second subasscmbly 424.
The second subassembly 424 comprises a plastic frangible plug 430 and a sleeve member 432. The frangible plug 430 includcs a body 431 having a central bore 436 sized so as to slidingly receive thc lower portion of squib casing 412. Plug 430 further includes a lower flange 432 having a diamctcr that is larger than the diameter of body portion 431 and larger than thc diametcr of aperturc 272 of latch 62. Disposcd about body 431 of plug 430 is sleeve mcmbcr 433 which includcs two or morc outwardly extending tangs 438. Prcferably, slceve 433 is made of brass and is adhesively bonded to plug 430. llle outside diametcr of slecve member 433 is smaller than the diameter of apcrture 196 in end cap 180 and smaller than the aperture 27'' in latch 62.
During manufacturc, plug ,body 431 and attached slecve 433 are disposed through apcrture 272 in latch 62 and through aperture 196 in end cap 180. Tangs 438 are depresscd radially inwardly as they are disposcd through apertures 272, 196. As plug body 431 is inscrted ~ 213902~

' ' ' '. -:

." , into end cap 180, the squib casing 412 is received within the bore 436 of plug body 431. Once the tangs 438 clear the aperture 196 in end cap 180, they will spring radially outward and ;
prevent plug 430 from being withdrawn. Flange 432 is larger than aperture 272 and thus secures latch 62 in a latched and supporting position beneath fuseholder 50.
When an overcurrent of a predeterrnined magnitude and duration is conducted through fuseholder 50, the high or low current fusible element 78, 80 will actuate, causing the fault current to be diverted to the current path including auxiliary wire 120. When this occurs, the current is conducted via receptacle 186 and lead wire 417 through the heater element 416 of the squib 410, thereby igniting the primer 415 which in turn ignites powder charge 414. The resulting explosion will sever the retaining plug 430 and release latch 62 allowing it to rotate away from fuseholder 50 in a clockwise direction as viewed from Figure 19. When this occurs, the fuseholder 50 will drop out of engagement with the cutout mounting 10.
,, ~,:: .,: ,:
While the preferred embodiments of the invendon have been shown and described, modifiations thereof can be made by one skilled in the art without departing from the spirit and .:. . - -~ . ,.
teachings of the invention. The embodiments described herein are exemplary only, and are not ~-limiting. Many variations and modifications of the invention and apparatus disclosed herein are - ~
possible and are within the scope of tne invention. Accordingly, the scope of protection is not - - , limited by the description set out above, but is only limited by the claims which follow, that ; ; ;
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Claims (38)

1. An electrical component comprising:
a body;
a current path through said body;
a support member disposed adjacent to said body;
a conducting pin member extending from said body and releasably attached to said supporting member, said pin member forming a portion of said current path;
means for causing said pin member to release said support member when a current of a predetermined magnitude is conducted through said body.

2. The electrical component of claim 1 wherein said causing means comprises an actuating member engaging said pin.

3. The electrical component of claim 2 wherein said actuating member changes shape when it is heated to a predeterrnined temperature.

4. The electrical component of claim 3 wherein said actuating member comprises at least one latching extension, said extension engaging said actuating member pin when said is below said predetermined temperature and releasing said pin when said actuating member reaches said predetermined temperature.

5. The electrical component of claim 4 wherein said actuating member is made of a memory alloy.

6. The electrical component of claim 4 wherein said actuating member is made of a bimetallic material.

7. The electrical component of claim 4 wherein said actuating member comprises a washer having inwardly disposed latching tangs and wherein said pin is disposed through said washer.

8. The electrical component of claim 4 wherein said actuating member comprises a clamping ring having a pair of arms disposed about said pin.

9. The electrical component of claim 3 further comprising a heater element in said current path for causing said actuating member to reach said predetermined temperature when a current of a predetermined magnitude is conducted through said body.

10. The electrical component of claim 3 wherein said actuating member is disposed inside said body.

11. The electrical component of claim 3 wherein said actuating member is disposed outside said body.

12. The electrical component of claim 4 wherein said pin includes at least one recess for engagement with said latching extensions of said actuating member.

13. A dropout fuseholder comprising:
an insulative body;
first and second terminal assemblies on said body;
first and second current paths between said terminals, said paths electrically and parallel;
wherein said first current path includes a fusible element; and wherein said second current path comprises:
a conducting pin having a portion extending out of said insulative body;
and a heat-responsive latching member releasably engaging said pin member.

14. The fuseholder of claim 13 wherein said second current path further comprises a resistive element for heating said latching member when current is conducted through said second current path.

15. The dropout fuseholder of claim 13 wherein said latching member is formed from a memory alloy and wherein said latching member releases said pin when said latching member is heated to a predetermined temperature.

16. The dropout fuseholder of claim 13 wherein said latching member is formed from a bimetallic material and wherein said latching member releases said pin when said latching member is heated to a predetermined temperature.

17. The dropout fuseholder of claim 14 wherein said resistive element is formed of silicon carbide.

18. The dropout fuseholder of claim 13 wherein said latching member comprises a base portion having an aperture formed therethrough and at least one latching tang attached to said base portion; and wherein said pin member is disposed through said aperture of said latching member, said latching tang of said latching member engaging said pin.

19. The dropout fuseholder of claim 18 wherein said pin includes an annular recess and wherein said latching tang engages said pin in said recess.

20. The dropout fuseholder of claim 13 wherein said latching member comprises a clamping ring having a first retaining and a second retaining arm disposed about said pin, said retaining arms releasing said pin when said clamping ring is heated to a predetermined temperature.

21. The dropout fuseholder of claim 14 wherein said latching member in said resistive element are disposed within said insulative body.

22. The dropout fuseholder of claim 14 wherein said latching member and said resistive element are disposed outside said insulative body.

23. The dropout fuseholder of claim 13 wherein said second terminal assembly comprises a conductive end cap and a hinge assembly attached to said end cap; and wherein said hinge includes a latch member having a free end rotatable between a nonsupporting and a supporting position beneath said end cap, said free end of said latch member having an aperture therethrough; and wherein said pin is disposed through said aperture of said latch member.

24. The dropout fuseholder of claim 22 wherein said pin includes a retaining head attached to said portion of said pin that extends outside said insulative body, such free end of said latch member disposed between said conductive cap assembly and said retaining head of said pin.

25. A dropout style fuseholder comprising:
a fuse body including first and second conductive terminals on said body;
a first current path between said first and second terminals, said first current path including at least one fusible element;
a second current path between said first and second terminals, said first and second current paths electrically in parallel;
a conductive washer in said fuse body, said washer having an aperture therethrough and being in electrical engagement with said second terminal;
a support member disposed adjacent to said second terminal;
a trigger wire extending from said fuse body and attached to said support member, said trigger wire forming a portion of said second current path and being insulated from said second terminal;
wherein said trigger wire is disposed through said aperture in said washer, said trigger wire and said washer forming a spark gap therebetween.

26. The dropout fuseholder of claim 25 further comprising a wire positioner for centrally positioning said trigger wire within said aperture of said conductive washer.

27. The dropout fuseholder of claim 25 wherein said conducive washer comprises a material undergoing an exothermic reaction once conduction occurs across said spark gap of said second current path.

28. The fuseholder of claim 27 wherein said conducive washer is formed of magnesium.

29. The fuseholder of claim 27 wherein said conductive washer is formed of thermite.

30. The fuseholder of claim 27 wherein said conductive washer is formed of aluminum.

31. The fuseholder of claim 25 wherein said trigger wire is formed of thermite.

32. The fuseholder of claim 25 further comprising an insulative bobbin for retaining said support member adjacent to said second terminal, said bobbin comprising a body portion having a central aperture; wherein said trigger wire is disposed through said central aperture and is attached to said body of said bobbin.

33. The fuseholder of claim 32 wherein said second terminal comprises a conductive end cap and wherein said bobbin and annular extension attach to said body; and wherein said annular extension is disposed through said support member and said end cap, said extension insulating said trigger wire from said end cap and said support member.

34. An electrical component comprising:
a component body;
first and second terminals disposed on said body;
a first current path between said terminals, said first current path comprising at least one fusible element;
a supporting member adjacent said second terminal of said body;
a frangible plug member disposed through said support member and into said component body for connecting said component body to said support member;
an explosive charge in said body for fracturing said plug member upon ignition of said charge; and means for igniting said charge when a charge of a predetermined magnitude is conducted through said first current path.

35. The apparatus of claim 34 further comprising a second current path electrically in parallel with said first current path; and whereas said ignition means comprises a portion of said second current path in contact with said explosive charge.

36. The apparatus of claim 34 wherein said explosive charge is disposed within a bore formed in said frangible plug.

37. The apparatus of claim 34 wherein said component body and said support include aligned apertures for receiving said frangible plug; and wherein said frangible plug comprising a body portion for receiving said explosive charge and a flange for retaining said support adjacent to said body, said flange connected to said body portion by an interconnecting stem;
wherein said apertures in said support in said component body are sized so as to receive said body portion of said frangible plug therethrough; and wherein said flange on said frangible plug is larger than said aperture in said support member.

38. The apparatus of claim 37 wherein said support member includes a supporting end rotatable between a nonsupporting position and supporting position beneath said component body; and further comprising means for biasing said support from said supporting to said nonsupporting position upon the fracturing of said frangible plug by said explosive charge.