US2183728A

US2183728A - Fuse

Info

Publication number: US2183728A
Application number: US85700A
Authority: US
Inventors: Hugh A Triplett
Original assignee: Schweitzer & Conrad Inc
Current assignee: Schweitzer & Conrad Inc
Priority date: 1936-06-17
Filing date: 1936-06-17
Publication date: 1939-12-19
Anticipated expiration: 1956-12-19

Description

Dec. 19, 1939.

H. A. TRIPLETT FUSE . Original Filed June 17, 1936 Patented Dec. 19, 19.39

Y i UNITED STATES alsa-12s FUSE Hugh A. Triplett, Wilmette, Ill., assigner to Schweitzer: & Conrad, Inc., Chicago, Ill., a corporation of Delaware Application June 17,

1936, Seal N0. 85,700

Renewed October 17, 1938 42 Claims.

My invention relates generally to electric clr- I cuit interrupters and it has particular relation to fuses.

It is now Well known to those skilled in the art that an arc drawn between the separable terminals of a circuit interrupter within a body of arc extinguishing material, such as magnesium hydroxide or b'oric acid, may be extingished by the vapor which is evolved from this l material Vdue to the heat o the arc. Circuit interrupters have been constructed in which the arc extinguishing material is provided with two longitudinal bores, one a main and centrally located bore and the other an auxiliary bore ci V smaller diameter than and positioned parallel` to the main bore. An arcing terminal is provided in the main bore which may be retracted :from the adjacent end terminal oi the circuit inter- .rupter or fuse by a spring when the fusible element connecting these terminals melts. l'i the current is relatively small, an.l arc is established in the auxiliary bore where 'a conductor is positioned having one end connected to the arcing terminal and the other end disposed in such rela-` tion to the adjacent end terminal as to 'iorm a small gap therebetween. This gap is broken down on *the formation of an arc caused by the blowing of the fusible member or element and, as a result, no arc is required to be extinguished in the :lO-main bore under certain conditions.

However, ii the current causing the fusible element to melt is relatively great, such as that which ows on short circuit, an arc will persist in the main bore. Since the arcing terminal will now have traveled a considerable distance, the arc path in the main bore will be lengthened and, due toths'fcondition and the vapor which is evolved from the arc extinguishing material, the

arc willbe extinguished with a. minimum of disy theforce exerted by the spring is relatively great, a considerable stress is imposed upon the fusible element. This is undesirable particularly in the lower ratings of fuses, since the' time-current 'pharacteristic of the fuse cannot be predeterminedwith 'the desired degree of accuracy. It is, therefore, preferable to -relieve the fusible elerment'ofjall tension stress, and to design it solely "with` regard to its time-current function and `55 without consideration to stress requirements.

tweenth'e arcing terminal and the adjacent end "'45 terminal of the fuse or circuit interrupter. Since (Cl. 20o-117) Fusible element assemblies applied in fuses of the assignees previous designs have consisted' of two elements which were electrically connected in parallel. One element consisted of a high con- Y ductivity, low resistance, metallic section which 5 was proportioned to lcarry the major portion oi' the current and calibrated to give the desired time current characteristics. The second element consisted of a high strength, high resistance, metallic member, the principal function o'f 1li which was to relieve'said rst element o mechanical stresses. When such a fusible assembly is blown by overload or short circuit currents, the low resistance portion fuses, shunting the current to the strain element which then fuses l5 and an arc forms between the severed ends of the strain element.

In fuses in which a solid arc Jextinguishing material is applied, the interrupting capacity of the bore, through which the arc is lengthened 2@ following fusion. of the'usible section, varies with` the diameter of the bore. For a bore of given diameter and length, there will be a certain minimum value of current which can be promptly cleared and also a maximum' value of current 25 which can be cleared without rupture oi the ruse container. It is necessary in most cases to have two bores in such fuses, one or which is relied upon to interrupt low faultA current, and the other bore of larger diameter which is relied upon to 3@ interrupt the possible short circuit current. These bores are proportioned so that the maximum interruptingcapacity of the small bore 'exceeds the minimum interrupting capacity of the larger bore. 35

It is therefore an object of my invention, generally stated, to provide a fuse or circuit interrupter which shall be simple and efficient l throughout its range of operation and which may be readily and economically manufactured and 40 installed.

An important object of my invention is to provide for supporting the arcing terminal of a fuse of the solid arc extinguishing material typeA against the retractile force of its spring independently of the fusible element interconnecting the arcing terminal and the adjacent terminal, thereby permitting the fusible element to be constructed solely with regard to its time-current. characteristics. l

Another important object of my invention is to provide for combining the features of the parallel conductor and strain wire in a fuse of the solid arc extinguishing material type into a single element whereby no mechanical stress will be applied to the main fusible element and small curent arcs will be extinguished in the auxiliary ore.

Still another important object of my invention is to provide for definitely transferring the current path in a fuse of the solid arc extinguishing material type from the main bore to the auxiliary bore to initiate the arcing in the auxiliary bore when the fusible element in the main bore melts.

A specific object of my invention is to provide a strain wire in theauxiliary bore of a fuse of the solid arc extinguishing material type for relieving the main fusible element of the retractile stress that would otherwise be imposed by the spring and for causing small current arcs to be extinguished in the auxiliary bore. L

Other objects of my invention'will in part be obvious and in part appear hereinafter.

My invention, accordingly, is disclosed in the embodiments hereof shown in the accompanying drawing and it comprises the features of construction, combination of elements and arrangenient of parts which will be exemplified in the constructions hereinafter set forth and the scope of the application ofwhich will be indicated in the appended claims.

For a more complete understanding of` the nature and scope of my invention reference may be had to the following detailed description taken in connection with the accompanying drawing in which: v

Figure 1 is a view, partly in side elevation and partly in section, illustrating one embodiment y of my invention, the fuse housing or tube being composed of glass;

Figure 2 is a perspective view on an enlarged scale of the strain wire assembly shown in Figure 1;

Figure 3 is a perspective view at an enlarged scale of the strain wire pin shown'in Figure 1; and

Figure 4 is a viewsimilar to Figure 1 showing the construction of a fuse provided with a housing formed of a phenolic condensation product which may be .purchased under the name of' "Bakelite.

According to my invention I have provided a fuse having a body of arc extinguishing material such as magnesium hydroxide or boric acid in one end of the housingI while a tension spring is positioned in the other end of the housing. The body of-arc extinguishing material is provided with va centrally located main bore and an auxiliary bore of smaller diameter disposed parallel to the main bare. An arcing terminal, inthe form of a rod, is mounted in the vmain bore and is arranged to ,be retracted bythe spring. fusible element, such as A.a silver wire is interconnected between the arcing terminal and the adjacent end terminal of the fuse. In order to hold the arcing terminal against the retractile for'ce of the spring and to relieve the main fusible element of this duty a strain wire is provided fwhich is fconnectedl in parallel.A with the main fusible element.

Since it is desirable to form the small current arc in the auxiliary bore and .further since it has been the practice in the past to position a conductor in this bore,4 which will not 'be fused at low current values up tovalues that are greater than the main current that can be extinguished in the main bore, advantageis taken oflthese requirements to position the strain wire in the `auxiliary bore. In other words advantage,I is `taken of the current transfer which occurs from A main` the main bore to the auxiliary bore to place the strain wire in the auxiliary bore where, following fusion, it will be effective in low current interruption. In thisv position it serves not only to relieve the main fuse element of the retractile force of the spring but it also provides the shunt conducting path in the small bore for the formation therein of low current arcs. The strain wire assembly is so constructed that the strain wire will fuse at the arcing end of the arc extinguishing material with the result that the arc is drawn into the'smaller auxiliary bore and is there extinguished. A flexible cable, connected to the outer end of the strain wire, is provided for sliding engagement therewith to maintain a metallic circuit'throughthe fuse until the terminal in the main bore has been withdrawn an appreciable distance. The flexible cable is insulated, as by enameling, so that it does not shunt the fusible section of the strain wire until after this section has parted. The insulation of thelcable is then broken down and the conducting path therethrough is then formed. The arcing terminal, arc extinguishing material and the strain wire assembly are arranged in cartridge form so that the fuse housing or tube maybe refused after the fuse blows. The construction is such that the blown cartridge may be readily removed and a new one inserted.

Referring now particularly to the embodiment of the invention shown in Figure l, it will be observed that a fuse or circuit interrupter, shown generally at I0, is there illustrated. The fuse III comprises a housing or fuse tube II, in this embodiment composed of glass, having an upper ferrule I2 with which a cooperating ferrule contact I3 is disposed and a lowersferrule I4. The

ferrules I2 and I4 may be secured in position on the ends of the fuse tube II by cement, as illustrated. The ferrule contact I3 is provided with a plurality of upstanding spring fingers, the function of whichwill be set forth hereinafter. For the purposes of illustrationv and description the fuse I0 isshown with the ferrule I 2 atthe top and the ferrule I4 at the bottom. It will be understood, however,that the fuse l0 is mounted in a reverse position with the ferrule,l2 at the bottom andthe ferrulerl 4 at the top.

The lower'V ferrule I4 is provided with a ferrule cap I5 and it hasconnected thereto cables Il,

formed preferably of iiexible conductors, and a tension spring I1 by means of a spring and cable fastener I8. The spring and cable fastener Il is provided with a threaded stud I! for threaded engagement with the ferrule cap I5 as illustrated. The cables I8 are secured in a suitable groove in the spring and cable fastener I8 by means of a clamp washer 20 that is held in place by screws 2|, only one of which is shown. The end convolutions of the spring I1 are secured in suitable helical grooves in` the outer periphery of the spring and cable fastener I8. The upper ends of the cablesv It and the upper end of the spring I1 are secured to a spring and cable fastener Il which is similar in construction to the spring and cable fastener Il.,

The portion of the fuse I0 that has just been described in detail constitutes .the part there-"af vwhich is notreplaced on theoperation of the fuse. The parts which will presently be described rial, lat the upper end of which is positioned a gg aisance cartridge ferrule 23 having a shoulder nut 29 threaded on the end thereof. Within the cartridge tube 21 a body of arc extenguishing material 3l is provided. This material may either be 5 in the form of a continuous cylinder or it may be sectionalized as indicated. The arc extinguish-Y ing material may comprise magnesium hydroxide or horic acid or other like material which will evolve a vapor in the presence of an are that will assist in extinguishing the arc with a minimum of disturba-nce. 'I'he body of arc extinguishing material 30 may be termed an arcing tube-and it has positioned therein amain bore 3| centrally .located and extending longitudinally therev through and'an auxiliary bore 32 of smaller diameter and disposed parallel to the main bore. The arcing tube 30 is secured in position within the cartridge tube 21 by means of a cartridge .washer 33 at the lower end and a threaded clamp zofring 34, as illustrated. c Atthe upper end a retaining ringl 35 of insulation is provided, the internal section of which is. outwardly flared to form an arcing chamber. f

An arcing terminal or plunger 38 is slidably 25 mounted in the main borerll of the arcingtube 3 6 and is secured to the spring and cable fastener l 22 by4 threaded engagement therewith. At the lower end of the arcing terminal 36, which is rodllke in form and which may be composed of copper, an arcing terminal pin 39 is provided extending transversely through the arcing terminal 33 and into a transverse slot in the lower end of the cartridge tube 2l. One of the functions of the arcing terminal pin 39 is to prevent the arcing 35 terminal 38 from turning relative to the cartridge tube 2l when the refusing operation takes place. The upper end of the arcing terminal 38 is connected by a fusible element 40, formed preferably of a silver wire, to the cartridge ferrule n 28. One end of the fusible element 40 is secured in a suitable slot, not shown, in the upper end of the arcing terminal 38 while the o`ther end is disposed in a transverse opening 4I in the side ,wall of the cartridge ferrule 23 and is secured therein by frictional engagement with a contact bushing 42 that is preferably formed of annealed copper and driven into position.

'In order to relieve the fusible element 40 of the retractile force that would be otherwise exerted G thereon by the spring I1, a strainfwire assembly.

shown generally at 44, and positioned ln the auxiliary bore 32, is provided. The upper endof the strain wire assembly 44 is connected to a strain wire pin 45, Figure 3, which is positioned in a suitable opening in the wall of the cartridge fer- -rule'23 while its lower end is secured to the arcingterminal pin 39. The construction of the strain wire assembly is shown more clearly in Figure 2. As there shown, the strain wire asn sembly 44 comprises a strain wire 4 6 the lower end f which is waved and has mounted thereon a strain wire terminal 41 of such mass that it is relatively infusible as compared to the strain wire 46. The terminal 41 is formed preferably of a 55 soft copper tube which may be readily attened out and compressed upon the waved lower end oi the strain wire 46. A suitable opening is provided Ain the strain wire terminal 41 through Which the arcing terminal pin 39 may project.

0 It is desirable that the strain wire 46 be melted at its upper end in the l.vicinity of. the arcing Chamber formed by the retaining ring 35. ,A

strain wire tube 43 is provided surrounding the Strain wire 46 forl accomplishing this result as/ well as for another purpose which will be presently set forth. The'tube 43 may be formed of ducting path through the strain wire assembly \44 will be at a minimum at the upper end of the strain wire 46, it will be readily understood that it will fuse in this portion.

' The upper end. of the strain wire 46 is also waved and has pinched thereon a strain wire ter- Slnce minal 49 which also is formed preferably of soft copper tubing and, like terminal 49, is also relatively infusible. As illustrated, the upper end of the strain wire terminal 49 is pinched in a plane at right angles to the' lower portion for( the purpose of intertting in a slot-5li formed in` the upper surface of a pair of projecting fingers 5I from the strain wire pin 45, Figure 3.

With a view to maintaining a conducting path through the auxiliary bore 32 after the strain wire 46 has'parted, a cable 52 is provided which is preferably formed of a plurality of strands of copper wire having an enameled coating thereon. It will be understood that other suitable forms of insulation may be employed as desired. One end of the cable 52 has pinched thereon the upper portion'of the-strain wire terminal 49 and the other end of the cable 52 is arranged to be disposed along the tube 4B inside ofthe auxiliary bore 32. Since the strands of the cable 52 are provided with an insulating coating, the fusible portion of the strain wire 46 is not shunted. However, after the strain wire 46 has parted, the

insulated coating of the cable 52 is broken down l and a conducting path is formed between it and the tube 48 as will be readily understood.

When-the fusible element and the strain wire assembly 4H are blown on operation o the fuse, portions thereof are expelled through the opening in the cartridge ierrule 2t. In order to readily permit the expulsion of these parts and still prevent extraneous matter from entering the interior of theiuse before it has operated, a mica disc 53 is provided, as illustrated, for covering the opening in the cartridge ferrule 28 and it may be secured in position by a retaining ring 5d in the form of Ve. split spring wire.

A pull-up pin 55 is provided in a suitable opening 56 in the wall o the cartridge ferrule 28 to which a suitable pull-up device, not shown, may be attached for placing the cartridge 26 in operative position in the fuse IB.

In assembling the fuse I0 the cables I6 and the spring 11 are connectedto the spring and cable fasteners I3 and 22. The spring and cable fastener I8 is then threaded into the ferrule cap I5. The cartridge 26 is then placed in position by threading the arcing terminal 38 into the spring and cable fastener 22. The assembly may then be positioned in the fuse tube II from its lower end. In this condition the tension spring I1 is retracted and the cartridge 26 is positioned well within the fuse tube Ii. Afsuitable pull-up device, such as a strap, is now connected to the pun-up pin ss and thecartridgezs ispdrawn upwardly. thereby stressing the tension spring I1. The cartridge 2 6 is drawn upwardly until the shouldernut 29 passes beyond the spring fingers of the ferrule contact I3, whereby the cartridge 26 will be locked and prevented from moving inwardly under the'iniiuence-of the spring I1. A clamp nut 51 may then be screwed onto the upper vierrule I2 to secure the spring fingers of the ferrule contact I3 in engagement with the outer periphery of the cartridge ferrule 28.

It will now be observed that the retractile force of the spring i1 tending to move the arcing terminal 38 downwardly is entirely taken up by the strain wire assembly 44 which is connected between the arcing terminal pin 38 and the strain wire pin 45. Thus the fusible element 40 is entirely' relieved of any tensile stress and may be designed with reference solely to the desired timecurrent characteristic.

In operation, when the current flow through the fusible element 40 is such that it is melted, the current flow is then transferred to the strain 5 wire 46 and it melts in the. arcing chamber formed by theretaining ring 35, the upper end of theterminal 38, and disc 5 31or in the bore in the ring 35 through which it extends and releases the spring l1. The strain wire 48 fuses in the reduced sction between the strain wire tube 48 and the terminal 49 forming an arc and releasing the arcing 'terminal 38 for movement inwardly through the bore 3| underthe influencelof `the spring l1. The arc thus formed destroys the insulation on the flexible cable 52 'and insures the maintenance of the arc in the small bore 32 until the end of the strain wire tube 48 passes the end of the flexible cable 52. The arc is then interrupted in the small bore and the movement of the arcing terminal38, which has taken place in the' large bore 3| during the above operation, will be suiiicient to prevent restriking of the arc therein.

D'uring a short circuit, the current transfers from the main current carrying element to the 35 strain element in the saine manner. However, under this condition, the ventire section of the strain element may fuse and reestablish the arc in the main bore before any appreciable move-v nent of .the arcing terminal 38 has taken place n it.

In the low current fuse ratings, such as 1 to 5 amperes if it is desired 4to insure that no current is conducted by the strain wire 48 until after" the main fuse element 40 blows, the strain wire terminal 41 may be insulated from the arcing terminal pin 39 as by the provision of an insulating` sleeve 58 thereon. 'I'he insulating lsleeve 58 should be relativelythin, thereby permittin the gap formed between the strain wire termina `4'I and the arcing terminal pin 3.8 to bel readily broken down for completing the circuit through the strain wire 48. In this construction the arc would first `strike in the main bore 3| and at current lzero the recovery voltage breaks down theinsulatlng sleeve 88 to establish the -circuit through the strain wire 4,8. The sequence of operationl wm then be as described above. The fuse vshown-generally vat 88 in Figure 41s similar in construction to the fuse I8 described wv .hereinbefore. The distinction resides in the construction of the housing 8| which may be formed of an opaque material such as Bakelite or any similar material. At eachend of the fuse tube housing 8| athreadedsnapring82isdisposedin` a suitable circumferentialgroove onto which ferrules 88 and 84 may be threaded, as illustrated. Since the construction and functioning of the remaining elements of the -fuse 88 are identical with those set forth in connection with the de- 70 -scription of the fuse I8 shown in lfigure l of the -drawing,afurtherdcscription ofthefuse 88will not be set forth herein.

'l .Sinceccrtainfurtherchangesmaybemadein theforegoing constructions and diflerent' em-Y n bodimentsoftheinventionmaybemadewithout.-

"forlocaliaingthepartofaidstrain departing from the .scope thereof, it will be understood that all matter shown in the accompanying drawing or described hereinbefore shall be interpreted as illustrative and not in a limiting sense.

I claim as my invention:

1. In combination a housing having xed terminals, a tension spring in one endv of the housing, a body of arc extinguishing material in the other end ofthe housing having a main bore and' 10 a separate parallel auxiliary bore, a rod-like terminal in the main bore connected to the tension spring, a main fusible element connected between the rod-like terminal and the adjacent fixed terminal, and an auxiliary 'fusible e ent of less 15 current carrying capacity than said main fusible element disposed in theauxiliary bore, said main fusible element being free of thetension of said tension spring. 2. Ina circuit interrupter the 'combination 01,20 means providing a main bore andan auxiliary bore of smaller size than the main bore and disposedin parallel therewith, said means under the iniiuence of an arc in a bore causing a ow of a gaseous arc extinguishing medium through such 25 bore, a pair of separable arcing terminals for the main bore, meanstending to separate said terminals, and a conductor means in said auxiliary bore for restraining said pair of arcing terminals from separating, said conductor means including 30 a relatively small current carrying section.

3. In a circuit interrupter the combination of a housing containing a spring, a body of solid arc extinguishing material having two parallel bores therethrough comprising a main bore and an 35 auxiliary bore, a retractile plunger in said main bore operatively connected to said spring and constituting a niain arcing terminal of large current carrying capacity, a high tensile vstrength conductor of small current carryingJcapacity dls- 40 posed in said auxiliary boregandadapted to hold the plunger against retraction by said spring.

4. In combination a housing having fixed ter-A minals, a tension spring in one end of the housing, a body of arc extinguishing: material in the other end of the housing, said body having a main longitudinal bore and a separate auxiliary longitudinal bore in parallel with the main bore, a. rod-like terminal in the main bore adapted to be retracted by the spring, a fusible conductor auxiliary bore and mechanically holding said sion spring `in one vengl-of said' housing, a body of arc extinguishingmaterial in the other end of .said housing having a main bore and a parallel on auxiliarylv bore, an arcing terminal in said main bore disposed te be retracted by. said spring, e yt main fusible element connecting said arcing minal andthe adjacent'nxed terminal, a strain wire disposedin saidauxiliary boro" holding said arcing terminal against theI tile force of said spring, said. strain disposed to be fusedatter said maint ment is -i'usedto release saidspring,

t 6. A circuit interruptor comprising, nationpa housing having fixed terminal sionsspringinoneendofsaidhml arc extinguishing material in the oth.'

aisance f 'f 5 said housing having a main bore and a parallel auxiliary bore, an arcing terminal in said main,

bore disposed to be retracted by said` spring,I a main fusible element connecting said arcing terminal and the adjacent'llxed terminal, a fusible strain wire disposed in said auxiliary, bore for holding said arcing terminal against the retrac- `tile forceof said spring, said strain wire being disposed to be fused Vafter said main fusible element is fused to release said spring, and a conductor connected in parallel with a portion of said strain wire for effecting fusion along a limited portion thereof.

7. A circuit interrupter comprising, in, combinatioma housing having fixed terminals, a tension spring in one end of said housing, a body of arc extinguishingmaterial in the other end of said .housing having a'main bore and a parallel auxiliary bore, an arcing terminal in said main bore disposed to be retracted by said spring, a main fusible element connecting said arcing terminal and the adjacent fixed terminal, a fusible strain wire disposed insaid auxiliary bore for holding said arcing terminal lagainst the retractile force' of said spring, said strain wire being disposed to be fused after said main fusible element is fused to release said spring, and a `metal lic tube surrounding said strain wire along a por- -tion thereof and having itsendspinched thereon '3o for localizing the part of said strain wire that is fused.'

S. A circuit interrupter comprising, in combination, a housing having fixed terminals, a tension spring in one end of saidf'houslng, a body of 3g arc extinguishing material in the other end of said housing having a main bore and a parallel auxiliary bore, an arcing terminal in said main bore disposed to be retracted byV saidspring, a main fusible element connecting said arcing terw minal and the adjacent dxed terminal, a fusible strain Wire disposed in said auxiliary bore for holding said arcing terminal against the retractile force of said spring, said strain Wire being disposed to be fused after said main fusible element is iused to release said spring, a pair oi tuhuiar terminals pinched onto the ends of said strain wir-e for securing it in position, and a metallic tube surrounding said strain wire, said metallic tube being secured at one end to one oi said tubuiar tenais and the other end being pinched onto said strain wire in'spaced relation to said other tubular terminal. 9. il circuit interrupter comprising, in combination, a housing having nxed terminals, a tension spring in one end of said housing'a body oi arc extinguishing material in the other end ofi said housing having a main bore and a parallel auxiliary bore, an arcing terminal in said main bore disposed to be retracted by said' spring, a

o@ main fusible element connecting said arcing terminal and the adjacent fixed terminal, a fusible strain Wire disposed in said'aumliary bore for holding said arcing terminal against the retrac- V tile force cfsaid spring, said strain wire being @5 disposed to be fused after said main fusible element is fused to release said spring, and -means for maintaining a metallic conducting path through said auxiliary bore after said strain wire is fused.

30 l0. A circuit interrupter comprising, in comblnation, a housing having fixed terminals, a tension spring in one end of said housing, a body of arc extinguishing material-in the other end of said housing having a main bore and a parallel V75 auxiliary bore, an arcing terminal in aid main bore disposed to be retracted' by said spring, a main fusible element connecting said arcing terv minal and the adjacent xed terminal, a fusible strain Wire disposed in said auxiliary bore for holding s aid arcing terminal against the retracy A5 tile force of said sprng,J said strain wire being disposed to be fused after said vmain fusible element is fused to release said spring, and conductor means connecting the end of said strain wire away from said spring with the end adjacent 10 said spring after said strain wire is fused.

l1. A circuit interrupter comprising, in combi- Y nation, a housing having fixed terminals, a ten--v sion spring in one end of said housing, a body of `arc extinguishing material in the other end of 15 said .auxiliary bore between the ends of said strain Wire after it is fused, and means for insulating said cable from said strain Wire.

12. A circuit interrupter comprising, in combination, a housing having fixed terminals, a ter1'y sion spring in one end of said housing, a body of arc extinguishing material in the other end of said housing having a main bore and a parallel auxiliary `lbore, an arcing terminal in said main bore disposed to be retracted byr'said spring, a main fusible element connectingsaid arcing ter:- rninal and the adjacent nxed terminal, a fusible strain Wire disposed in said auxiliary bore for` holding said arcing terminal against the retractile 40 force of said spring, said strain wire being disposedto ber'used after said main fusible element is fused to release said spring, a pairof tubular terminals pinched onto the ends of said strain. wire for securing it in position, and a conductor connected to one of said tubular terminais and extending in insulated relation along said strain nire to provide a conducting path through said auxiliary bore after said strain wire is fused.

i3. A circuit interrupter comprising, in com hination, a housing having fixed terminals, a

ltension, spring in one end of said housing, a "cody or arc extinguishing material in the other end ci said housing having a main bore and a parallel auxiliary here, an arcing terminalfin said main 55. bore disposed to be retracted by said spring, av main fusible element connecting said arcing terminal and the adjacent nxed terminal, e fusible strain wire disposed in said auxiliary bore for holding said arcing terminal against the retracso tile force of said' spring, said strain Wire being disposed to be fused after said main fusible element is fused to release said spring, a pair of tudbular terminals pinched onto the ends of said strain Wire for securing it in position, a metallic e5 tube surrounding said strain wire, said metallic tube being secured at one end to one of said tubular terminals and the other end being pinched on 14. A strain element for a fuse comprising a Strain wire, terminals at the ends o1'- said strain 75 wire. and a conducting member connected in parallel with the strain wire along a portion of its length and' to one of said terminals for deterxnining the fusing portion thereof.

15. A strain element for a fuse comprising a strain wire, terminalsat the ends of the strain wire, and a conducting tube surrounding the strain wire 'and secured at one end to one of said terminals, the other end of thetube being pinched on the strain wire at a position spaced from the other of said terminals.

16. A strain element for a fuse comprising a strain wire, a tubular terminal pinched onto each end of the strain wire, and a metallic tube surrounding the strain wire throughout a portion of its length, one end of the metallictube being pinched coniointly with one of said tubular terminals on one end of the strain wire and the other end being pinched onto the strain wire.

17. A strain element for a fuse comprising a strain wire, a tubular terminal pinched onto each end of the strain wire, a metallic tube surrounding the strain wire throughout a portion of its length, one end of the metallic tube being pinched conjointly with one of said tubular terminals on one end of the strain' wire and the other end being pinched onto the strain wire, and a flexible insulated 'conductor connected to lthe other of said tubular terminals by being pinched thereby and disposed to be positioned along the adjacent end of said metallic tubeto provide a conducting path between said terminals after the strain wire is fused.

18. In a fuse device. a stationary terminal. a relatively movable rod-like terminal, a fusible element interconnecting said stationary terminal and one end of said rod-like terminal. and a strain element interconnecting said stationary terminal andsaid rod-like terminal. said strain element lbeing connected to said rod-like terminal at a point remote from said one end thereof.

19. A strain element having its endsattached tothe separable terminals of a fuse comprising a strain wire. means for determining the location of melting of said strain wire. and means for determining the extent of relative movement of theends of said strain wire before the arc formed therebetween is extinguished.

20. In a fuse having separable terminals. a

. fusible element, a strain element mountedindependently of and disposed to beconnected in parallel with said fusible element between said separable terminals. relatively infusible terminal members secured to the ends of said strain ele- :.ment., conductor means extending from each of said terminal members toward the other in overlapping` relation. and means for insulating the overlapping. portionsv of said conductor means from each other as long as said strain element l'remains intact. said insulating means being broken down on meltingv of said strain element to determine the extent of relative 'movement of the ends of said strain element before the arc formed on melting thereof is extinguished.

21. For combination in a fuse. a strainl wire. metallic terminals secured to the ends of and electrically in contact with said strain wire. support means for each of lsaid terminals. and means for insulating at least one of saidterminals from the support means-individual thereto.

22. A strainelement for a circuitintermpter comprising a strainwire, a first conducting nieansJ connected between one end of said strain wire and a point intermediate itsends to determine the fusing portion of said wire. and a second conducting means connected to the other end of said strain Wire and extending along said first conducting means, said conducting `means being insulated from each other.

23. A strain element for a circuit interrupter comprising a strain wire, terminals secured to the ends of said strain wire, a first conductor connected between one of said terminals and said strain wire at a point intermediate said terminals' for determining the fusing portion of said strain wire, and a second conductor connected to the other of said terminals and extending along said rst conductor, said conductors being insulated from each other.

24. In a circuit interrupter the combination of means providing a main bore and an auxiliary bore of smaller size than the main bore and disposed in parallel relation therewith, said means under the influence of an arc in a bore causing a flow oi gaseous arc extinguishing medium through such bore, a pair of separable arcing terminals for the main bore, a conductor of relatively small current -carrying capacityI in said auxiliary bore for restraining said pair of arcing terminals from separating, and. means insulating said conductor from at least one of said arcing terminals. 25. In -a circuit interrupter the combination of means providing a main bore and an auxiliary bore of smaller size than the main-bore-and disposed in parallel relation therewith, said .means under the inuence oi an arc in a bore causing a flow of gaseous arc extinguishing medium through such bore, a pair of separable arcing terminals for the' main bore, one of said arcing terminals being arranged'and adapted'to be moved through the main bore to extinguish the arc drawn therein between it and the other arc` ing-terminal, a conductorin said auxiliary bore connected electrically at one end to said other arcing terminal, and means insulating the other end of said conductor from said one arcing terl minal 26. A terminal for a fusible element arranged to withstand tension stress comprising a tubular member flattened at one end onto the fusible element, the other end of the tubularmember being flattened at'rlghtanglesto the, one end to provide shoulders-for supporting the same.

27. In a'fuse device, in combination, a haus;- ing, a terminal at one end of said housing. a support pin carried by said terminal, a pair of lingers carried by said pin having a transverse slot acrossl the upper sides of said fingers, and a terminal for a fusible element arranged to withstand tension stress land to be carried by said support pin, said last named terminal 'comprising a tubular member flattenedatA one end onto the fusible nement and disposed tosnterst between said fingers. the other end of said tubular member being flattened at right angles to the one end to provide shoulders for interntting with said slot. A

28. In a circuit interrupter,- in combination. a body of arc` exti ng material havinga relatively long bore therethrough, va stationary terminal at one end of said bore and a movable terminal at thel other end of said bore,a spring biasing said -terminals apart, conductor means withinsaid bore forinterconnecting said terminals and restraining said spring from moving them apart. said conductor means on fusing forming an arc in said bore, means for determining the portion of said bore in which the arc is formed. andmean's within-said bore for determining the distance through which said movable Vvterminal moves before current flow is interrupted in said bore.

29. In a circuit interrupter, in combination, a pair of separable terminals between which an arc is adapted to be formed, means biasing said terminals apart to extend the arc formed therebetween on separation thereof, a body of arc extinguishing material having a relatively long bore therethrough, conductor means within said bore arranged and adapted to interconnect said terminals and to restrain movement thereof apart, said conductor means on fusing forming i like terminal in said bore mechanically connected,

Y to said spring and electrically connected to one of said ilxed terminals, a fusible element electrically interconnecting said rod-like terminal and the other of said xed terminals, and strain means disposed exteriorly of said bore for relieving said fusible element of the tension of said spring, said strain means being arranged and adapted to be released on Yblowing of said fusible element to permit said rod-lilreterminal to be retracted in said bore by said spring.

3l. In a circuit interruptor the combination of insulated support means carrying a spring, a body oi solid arc extinguishing material carried by said support means and having two parallel bores therethrough comprising a main bore and an auxiliary bore, a' retractile plungerA in said main bore operatively connected'to said spring and constituting a :nain arcing terminal of large current carrying capacity, and a high tensile strength conductor of small current carrying capacity disposed in said auxiliary bore and adapted to hold theplunger against retraction by said spring.

32. ln combination, a pair ci' line terminals disposed in insulated spaced relation,' spring means reacting against one line terminal, a bocljV of arc extinguishing material secured to the other line terminal, said body having a main to be fused after said main fusible element is fused to release said spring, and means for maintaining a metallic conducting path through said auxiliary bore after said strainelement is fused. 34. In combination, insulated support means, line terminals in spaced relation on said support means, a body of solid arc extinguishing material carried by said support means and having at least one longitudinal bore therethrough, a rodlike terminal in said bore electrically connected to one line terminal, a fusible element electrically l interconnecting said rod-like terminal and the longitudinal bore and aseparate auxiliary lonen'- tudinal bore in parallel with the main here, a rod-liire terminal in the main bore adapted to be retracted by said spring means, a i 'ble conductor connecting said. rod-like terminal and said other line terminal, and a parallel conductor of small current carrying capacity in said auxil-r iary bore mechanically holding said plunger against retraction by said spring means.

33. A circuit interruptor comprising, in combination, a pair of line terminals disposed in insulated spaced relation, spring means reacting against one line terminal, a body of arc extinguishing material secured to the other line terminal and having a main bore and a parallel auxiliary bore, an arcing terminal in said main bore disposed to be retracted by saidi spring, a main fusible element connecting said arcing terminal and said other line terminal, a fusible strain element disposed in said auxiliary bore for holding Said arcing terminal against the retractile force 'I5 of said spring, said strain element being disposed other line terminal, spring means biasing said' rod-like terminal for movement relative to said bce, and strain means disposed exteriorly of said bore for relieving said fusible element of the biasing force of said Vspring means, said strain means vbeing arranged and adapted to be released on blowing of said fusible element to permit relative movement between said rod-like terminal and said bore. c

35. In combination, insulated support means, line terminals in spaced relation on said support means, a body oi solid arc extinguishing material carried by said support means having main and auxiliary parallel longitudinal bores, a rodlike terminal in said main bore electrically connested to one line terminal, a fusible element electrically interconnecting said rod-like terminal and the other line terminal, spring means bias-l ing said rod-like terminal for movement relative to said here, and strain means in said auxiliary bore for relieving said fusible element of the biasing force of said spring means, said strain. means being arranged and adapted to be released on blowing oi said fusible element to permit relative movement between said rod-like ter-- Initial and said body of solid are extinguishing material.

36. In a circuit interruptor, in combination, a body ci solid arc extinguishing material having main and auxiliary parallel longitudinal bores, a stationary terminal at one end of said main bore, a rod-like terminal movable in said main bore and projecting out oi its other end, a fusible element interconnecting said terminals, and a strain means said auxiliary bore secured at one end to the projecting end of said rod-like terminal and at the other end to said stationary terminal, said strain means characterized by prmiding a predeterndned denite distance between its points ci attachment to said terminals.

37. In replaceable unit for a circuit interrunter comprising, in combination, a body of solid are extinguishing material having main and auxiliary parallel longitudinal bores, a plunger in Said main bore constituting a main arcing terminal or large current carrying capacity and adapted to be retracted therethrough, and a high tensile strength strain element of'small current carrying capacity in said auxiliary bore adapted to hold said plunger against retraction through said bore.

38. A replaceable iuse cartridge comprising, in combination, a body of solid are extinguishing material having main and auxiliary parallel longitudinal bores, a terminal at one end of said body, a rod-like Aterminal in said main bore adapted to be retracted therethrough, a fusible element interconnecting said terminals, and a. high tensile strength strain element in said auxiliary bore also interconnecting said terminals and relieving said fusible element of strain resulting from stress tending to separate said terminals.

39. A replaceable fuse cartridge comprising, in combination, a body of solid arc extinguishing material having main and auxiliary parallel longitudinal bores, a. terminal at one end oi' said body, a rod-like terminal in Fsaid main bore adapted to be retracted therethrough, a fusible element interconnecting said terminals, a high tensile strength strain element in said auxiliary bore also interconnecting said terminals and relieving said fusible element of strain resulting from stress tending to separate said terminals. a portion of said strain element being fused after said fusible element is fused to release said rodlike terminalfor movement through said main bore, and means for maintaining a metallic conducting path through said auxiliary bore after said portion of said strain element is fused.

40. In a fuse device, in combination, a housing, a terminal at one end of said housing, a support pin carried by said terminal and projecting radially inwardly therefrom, the outer end of said pin being bifurcated, and ya. terminal for a fusible element arranged to withstand tension stress and to be carried by said support pin, said last-named terminal comprising a tubular member attened at one end onto the fusible element and disposed to t in the bifurcated end of said support pin,

the other end of said tubular member being fiattened at right angles to theI one end to provide shoulders lfor bearing against one side of thel bifurcated` end of said support pin.

41. In circuit interrupting apparatus, in combination, arc extinguishing material providing parallel main and auxiliary bores having respectively large and small cross-sectional areas, a stationary terminal at one end of said bores, and main and auxiliary relatively infusible terminals in said main and auxiliary boies respectively adapted on being moved away from said stationary terminal to draw an arc :first in an auxiliary bore and subsequently in the main bore if the arc in they auxiliary bore is not extinguished.

42. In circuit interrupting apparatus, in combination, aro extinguishing material providing main and auxiliary bores, a terminal at one end of said bores, main and auxiliary arcing terminals in said main and auxiliary bores respectively connected together at the opposite end of said bores, a fusible element interconnecting said tierminal and said main arcing'terminal, and a strain elementinterconneeting said terminal and u said auxiliary arcing terminal.

HUGH A. TRIPLETI.