US2234480A - Safety indicator fuse - Google Patents

Description

March ll, 1941,

L SCHMIDT SAFETY INDICATOR FUSE lf'iled March 19, 1938 3 Sheets-Sheet l 4 am H. .mw m wf m .mf @@M m a L March 11, 1941. l. scHMxDT 2,234,480

SAFETY INDICATOR FUSI I Filed llarch 19, 1938 3 Sheets-Sheet 2 Elllil @n-Vg INVENTOR.

' ffm/w@ /u'o ATTORNEY.

'Marh l1, 1941. L. SCHMIDT 2,234,480

SAFETY INDICATOR FUSE Filed March 19, 1938 3 shuts-Sheet 5 Zig. f5.

y0 1N VENTOIL ATTORNEY.

Patented Mar. 11, 1941 UNITED STATES APATENT GFFICE 2,234,480 v SAFETY INDICATOR ruse corporation of Illinois Application March 19, 1938, Serial No. 196,841

1s claims.

The present invention relates to fuses for electrical circuits, and has for an object to provide an improved construction of fuse which will bek more eiiicient in operation and which also may 5 be easily inspected to determine the operative condition of the fuse both when in position for use as also when selecting a new fuse to replace one which has blown out.

Some of the subject matter disclosed, but not claimed herein, is covered by my copending application Serial No. 376,078, filed January 27, 1941.

Cin the fuse and development of plug and cartridge type fuses of this character, inventors l and manufacturers have constantly endeavored to increase the safety in the operation and use of the fuse and have met with three main faults in prior fuse constructions. The rst fault is the possibility of dangerous explosions due to the gases given of! by the burning of the fuse metal when subjected to an excessive current. The second fault is that a continuation of the vburning of the fuse metal takes place, depending on the excess current going through the fuse metal.

The third fault is inadequacy or no indication as to whether the fuse has blown or not.

It is an object of the present invention to improve electricai fuses of the plug and cartridge type along these lines, and to effect, at the 30 enum point of burning of the fuse metal, the

quick separation of the ends of the fuse and the isolation of the parted ends so that the burning would immediately cease and there would be no possible chance for continuedlarcing to form the dangerous gases.

Another object of the invention is to provide a fuse construction which may be quickly and easily inspected to ascertain whether or not the fuse has been blown so that the user will not have to resort to the expedient of trying out different fuses to. determine whether or not they are in operative condition.

Another object of the invention is to maintain a cooling ei'iect on thefuse metal in order to cause a time delay. in that the heat accumulating to burn the-fuse is first absorbed by the cooling member lto a certain extent, and then fuses the link. When 125% of the current goes through the fuse, it will take one hour before the fuse metal link will part, this being permissible by the Underwriters Laboratories.

Another object is to provide means for deadening the spark or arcing at the fusing point of the link.

Another object of ther present invention is to (Cl. 20o-119) prevent a fuse of larger size being used instead oi a permitted fuse, and to provide means to prevent tampering with the fuse, which tampering would close the circuit, even after the fuse is blown. 5

The invention consists in providing a plug or cartridge type fuse in which the fuse link is quickly disrupted when the part intended to be fused is brought vto its fusing point.

Furthermore, the invention consists in sepa- 10 rating the parts of the fuse link after it reaches its fusing point, and maintaining its separated parts distant from each other. An insulated barrier under spring or similar pressure quickly separates the link and acts as a barrier between 15 the broken ends of the link to prevent current from passing from end to end of the link.

The invention consists further in the means for indicating from the outside of the fuse whether the fuse link is in operative or inoper- 20 ative condition.

The invention consists further in disposing at one side of the surface of the link an insulating member of low heat conductivity, so as to absorb heat from the link to a certain extent before the 25 fusing point is reached.

'I'he invention consists further of means in the form of a fuse link cooling member which acts as a spark deadening and gas absorbing member when the fuse point is reached, whereby the arcing is reduced.

'Ihe invention consists further in providing a fuse structure including an adapter, which is securely fastened to the cut out, wherein the current i's-not completed through the fuse until 3 5 the device is completely set up into operative position, the circuit closing being effected by the final movement of the parts into place. This feature of the invention offsets the tampering with the fuse to close the circuit through it, even after the fuse is blown, as a slight amount of foreign material inserted in the adapter will prevent the fuse parts from making the final necessary movement or adjustment to close the circuit.

Means are provided to prevent a fuse of larger capacity from being used, as this would not be interchangeable with the predetermined sizes of the parts of the adapter. As an embodiment thereof, the adapter has a conical bore which registers only with the fuse member .of the correct diameter, and which acts to impede a fuse of larger capacity from contacting with the parts necessary to complete the circuit.

Furthermore, the fuse structure is provided 55 with means to prevent arcing between the adapter and the cut out, a very serious objection in devices heretofore proposed. The invention embodies means to break the circuit in the fuse member itself before the electrical connection between the adapter and cut out is broken.` In the embodiment, a lighter spring, of delayed action, maintains the velectrical connection until a heavier spring, or one of quicker action, in the fuse member breaks the circuit. Thus, there cannot be an arc between the adapter and cut out.

The invention, as shown y,in the various embodiments, provides for a high degreeof safety, as the tests made have proven the fuse reliable and explosion proof and also non-tamperable.

The invention will be more fully described hereinafter, and will be more particularly pointed out in the claims appended hereto.

In the drawings: f

Figure l is a longitudinal section taken through a modified form of fuse embodying the features of the invention and showing the parts in operative position;

' Figure 2 is a transverse section taken through the same on the line 2-2 of Figure l; y

Figure 3 is a longitudinal section similar to Figure l, but showing the fuse in blown `posi-l tion;

Figure is a transverse section taken through the same, similar to Figure 2, but with the fuse in blown position;

Figure 5 is a longitudinal section taken through one form of fuse embodying the features of the present invention, on the line 5 5 of Figure 6, the plug portion of, the fuse being shown in position ready for insertion in the adapter;

Figure 6 is a top plan viewof the came;

Figure 7 is a bottom plan view of Lie plug portion of the fuse;

Figure 8 is a fragmentary bottom plan view of the adapter, showing the locking lug or prong for holding the adapter from removal from an electrical socket;

Figure 9 is a partial view in section showing the plunger in a position which it occupies after it has separated from each other the two torn ends of the fuse link;

Figure 10 is a side view of a cartridge fuse embodying thisinvention;

Figure l1 is a horizontal section taken on line II-ll of Figure 10, showing the fuse link in operative position and the cartridge ready to be inserted into an electrical circuit;

Figure 12 is a similar section but with the parts shown after the fuse link has reached its fuse point and has been severed; and

Figure 13 is a vertical section taken on line' |3-l3 of Figure 1l. A

Referring now to the construction of the fuse shown in Figures 1 to e, the fuse body is in the comprise a shell portion 41a.of sheet metal, with the ller 41h of other suitable metal in which is embedded one end ofa fuse element 48. The

fuse element 48, which is in the form of a blank thereof, the opposite end of the fuse element be ing carried downwardly through the opposite side oi' the body 45 and turned upwardly against-the exterior of the cap 46. Preferably a piece of insulating material 46h is disposed vor) the member 46, over which piece 46h the fuse link extends. threaded shell 49 is secured to the exterior of the cap 46 by engagement with the threads 49a of the member 46, and is provided with a retaining flange 50 at its lower end-overlapping a shoulder portion of the body 45 to hold the cap 46 and body portion 45 together.

Within the upper e'nd of the body 45 is disposed a plunger 5l of non-conducting-material of inverted U shape, which has a spring 52 seated on an insulating disc 153A in the bottom in the body 45 and which spring urges the plunger 5i upwardly against the underside of the fuse strip i8 at its portion resting on the plunger El. The upper end ofthe plunger 5l may be provided with a suitable indicator. such asa portion of a red color, as shown by Ela in Figure 4. or other suitable means to indicate that the uppere'nd oi the plunger 55 is entirely exposed when the fuse lstrip da is disrupted. The plunger covering por tion of the fuse strip 8 is provided with an asbestos disc or layer 5d adapted to bear the data relating to the character of the fuse, such as shown in Figure 2 indicating that the fuse is capable of sustaining l0 amperes with a current of volts. This asbestos layer may be in disc form, and is disposed over the fuse strip i5 and the upper end ofthe plunger 5l. The disc 55 is made up of two halves, separated by the. line 55a, and each piece is pasted on the fuse strip. so that the halves abut. When the fuse strip 65 is fused and disrupted, the action takes place at the upper end Iof the plunger, so that the asbestos strip is disruptedwith the fuse strip and the plunger 5I is projected by its spring 53 against the fuse strip to eilect the quick vseparation of its fusing portion when weakened sufciently to be disrupted by the action of the spring 52. As shown in Figure 3, the plunger 5I noty only quickly separates the disrupted ends of the fuse strip, but also forces the ends apart to a considerable distance and serves as au insulator between the ends of thefuse strip to separate the same. The asbestos disc absorbs certain of the gases, and also dampens the arcing, if any. The quick rupture prevents arcing. At the sanie time, the asbestos covering the strip is disrupted and moved aside by the plunger, and the indicating upper end 5Ia, of the plunger 5l is brought into the upper end of the cap 46. As the cap d6 is of glass or other suitable transparent material, the upper end 5Ia of the plunger is readily exposed to view so as to determine the operative condition of the fuse.

Referringnow to Figures 5 to 9. the fuse link rupture mechanism shown in Figure 5 is substantially like that of lFigure l. this i'use rupture mechanism, this fuse of Figure 5 has a fuse structure embodying an adapter i5 of suitable insulating material enclosed within a conductor shell I6, the exterior portion of which is provided with coarse screw threads adapted to t into the usual fuse socket. The bottom or lower end of the shell I6. is' turned inwardly to provide a flange I1 for holding the shell to the body i5 and also for holding an insulating disc I8 seated in the bottom of the body I5. 'I'he bottom of the body I5 is of considerable thickness and is provided with an opening I9 centrally,

In. addition to 2,234,480 therethrough which flares at opposite sides to.

ward the disc i8 and into the interiorfoi the body I5.

'Ihe inner wall of the body I5 is provided with coarse screw threads 20 adapted to receive in threaded. engagement therein the threaded plug 2I of the fuse body. A contact stud 2| is slidably mounted in the opening I9 and has an intermediate shoulder 22 disposed in the lower ilaring portion of the opening I9 and .adapted to seat inthe opening to limit the upward or inward movement ofthe stud 2I'. The upper portion of the stud 2l may be rounded and is of less height than the upper ilaring portion I9a of the opening I9, so that to engage the stud it is essential to project a contact or the like a short distance downwardly into the opening I9c before the stud 2|.; can |be moved. If such a contact is too large, it will be blocked by the conical walls of the bore Isa. Such an operative contact ts uponthe ball 2Ia. A helical spring 23, or the like, is disposed about the stud 2l' between the disc i8 and the shoulder 22 for normally urging the stud into retracted position, and the lower end of the stud is of such length that it normally is disposed in retracted position inwardly of the bottom face of the disc I8, and the latter is provided with a central opening I8a, forming a guide for the lower end of the stud and through which the latter may project to engage the central contact of the usual No claim is made thereto.

The upper or outer end of the adapter is provided at its inner wall with a contact ring 25v held withinrthe socket lby overturned iianges on the upper ends of the ring and the shell i6.

The upperend ci the fuse plug 2i is enlarged and chambered and is closed at its upper outer end by a transparent disc 2B of mica or the like which may be held in place by a flanged ring 2l secured about the upper shouldered end of the plug 2l. Within the upper end of the plug 2i is disposed a fuse element 28 which is looped upwardly within the plug and has one end 28a anchored through the bottom wall oi the chamber against a contact brush 29 which is exposed at the upper end of the threaded portion of the plug and extends downwardly through the bottom oi the chambered portion of the plug.l 'Ihe brush.

29, as shown in Figures 5 and '1, is anchored at one end 'to the end 28a of the @fuse element 2l, and at its other end extends circumferentially in a slot 3i! provided in the upper threaded portion of the plug and in line with the contact ring 25 oi the adapter so that when the plug is turned into the adapter the iinal turning of the plug brings the brush 29 into electrical contact' with the ring( 25 to complete one side of the circuit from the fuse element 28 through the exterior shell I5 of the adapter and to the shell of the socket. Y The fuse element 28 is of any suitable fusing metal of the required resistance of the plug, .and has lateral notches as shown in Figure 2, as known. A contact cup or guide cylinder 34 is secured at its closed end to the lower end of the stud 32 and receives therein a. plunger having anY upper insulating portion Il and a lower contact portion I8 mounted upon a central contact stem 21, the upper end oi.' which is substantially flush with the insulating portion I5 and adapted to engage the stud 32 when the plunger is moved upwardly in the guide cylinder 3l. The lower contact portion of the plunger is also adapted, upon the upward movement of the plunger, to engage the side walls `of the guide cylinder I4 for completing that portion of the circuit. The stem 31 may be threaded and the plunger sections 35 and 36 may be in the form oi nuts which are threaded in locked relation upon the stem. The stem 31 has an intermediate enlarged cylindrical portion 38 slidable through the lower portion of the plug 2l, and carries at its upper end a stop disc 38 seating in the bottom of the plug cavity and held thereto by the plunger sections 35 and 3B. The lower extremity of the plug 2l is recessed to provide an annular space lila about the enlarged Iportion 38 oi' the stem to accommodate a coil spring 40 seating within the lower end of the plug at one end and at its other end engaging in a guide cap 4I slidably disposed in the recess of the plug and normally urged outwardly or downwardly therefrom by the spring IIL The lower end o! the guide cap 4I is provided with a contact projection I2 which may be suitably recessed, as shown by 12a, to engage with the upper end oi.' the stud 2Ia in the bottom of the adapter so as to project the stud 2|' sufficiently through the opening I8a to engage the socket contact as the plug 2l is finally seated in the adapter. The circuit is thus closed through the stud 2l' making electrical contact with the cut out. In the drawings, projection 42 is separate from cap 4i secured thereto by solder or fusing, making it for all purposes integral in action. In Figure 6 is shown the end Sii oi' the fuse member which has diametrically disposed ridges 8l, which cooperate with the wall $2 of the adaptor. 0n rotation of the fuse member, the ridges 9| clean the wall 82. As shown in Fig. 5 one oi the ridges Si is indicated in dotted lines.

In operation, the adapter i5 is screwed into a fuse socket orvcut out, not shown, as well known, and is held locked therein by the prong 2l. A fuse member in accordance with the foregoing invention is selected and is screwed into the adapter with the result that the plunger` structure of the fuse is retracted after engagement with the stud 2|' and the latter is projected to close the circuit through the central contact ci' the fuse socket. During the iinal stages of turning the plug into the adapter, the contact brush 2l is brought into engagement with the contact ring 25 so as to complete the circuit through the shell portion oi' the fuse socket. Upon the short .circuiting or overloading oi' the circuit, the fuse vportions and prevented from contacting with each other. This quick action of the spring pressedplunger ll prevents arcing of the current between the free ends o! the disrupted fuse. and Il consequently prevents the slow burning of the fuse end and the generation or the gases which create explosions and thus become dangerous in the use of the fuse.

In Figures l to 13, embodiments of my invention as applied to a cartridge fuse are shown.

In Figure the exterior of the cartridge aD- 63 having a shoulder ed and a stem 65 extending inwardly of thecartridge iii. This 'stern @El has a covering sleeve G6.

Surrounding the stern @5 and its covering sleeve Bda helical spring 6l is provided which seats upon the plate E53 at one end thereof, and which has its other end seat/ed at the inside of a tubular recess @tl in a plunger l@ of insulating material. This plunger l@ has a lateral slot or recess 'll and also a hook-shaped portion lil. lhis hookshaped portion i2 engages the hookshaped por tion'l'l of an electrical conductor lf3 which is bent at l5 and terminates at llt at the lother cap il of the cartridge where the electrical' con-fV lcluctor it is upset, as shown by lil.

'i'hjs electrical conductor l! is rigid and is silbstantially of rectangular cross section, as shown in Figure 13. |This electrical conductor 'lll serves to conduct the current from one end oi' the cartridge fuse to the other when the inse link itself is in proper position. .d further iunction'oi this member i4 is to hold the end of the inse link .on to the plunger.` A third function of this member l0 is to provide a barrier to the further movenient of the plunger lil, as shown in Figure ll, the bent portion la acting as a barrier.

The fuse link il@ has the usuel out out portion, as shown in the other embodiments, this cut out portion Gi being placed directly on the u1-n. of the curved plunger iii, and one end of the fuse link extends downwardly over the plunger and is secured to the plunger by the pressure the member lll when its hook-shaped portion ll engages the hook-shaped portion l2 oi the'plunger. The other end of the fuse link is provided with an opening, and this opening is passed through by the portion G3 before it has been upset upon the cap and the fuse link .es a goed electrical connection between the shoulder 55 Sii of the member and'also the cap 62,' and thenthe fuse link @El extends along the side oi the insulated plunger l@ until, as before stated, it reaches its summit. When the parts are locked in the position shown in Figure ll, the fuse cartridge is ready to be inserted in an electrical circuit and is ready for use. Should an electrical current pass through the fuse link of such an en; cessive amount as to cause the fuse link at 5l to reach the fuse point, the pressure of the spring 6l will immediately tear .the two parts of the fuse link apart and separate the same, Figure l2 showing the two separated ends 85 and 88 of the easiest reaches its melting or fusing point, the action of the spring will tear the two lparts of the fuse link apart, and the spring will press the plunger l0 until the plunger strikes the bent portion l5 of the member ld, asshown in Figure 12.

-t will be thus seen that in the various forms of the invention, a member is yieldingly urged against one sideof a fuse strip and' that as soon as the inse strip is weakened suciently by fuslly in the cartridge 6| ing, the insulator effects the quick disruption of the fuse strip and quickly separates the disrupted ends apart to odset arcing. Also, the fuse link, in contacting before rupture with. the inof an electrical circuit and having an opening therein, a piston or plunger 5l of insulating material tting into said opening andbiased in'one direction in said opening by a springl 52, a fuse link 38 having a'portion Gila oi reduced section adjacent the piston or plunger 5l. and extending from said contact il over the end of the piston 5i tosubiect-ie link lil to the Apressure of the spring S2 on the piston 5l and hold the piston iii in said opening, said link it being anchored to means is exterior or theimdy portion l5 to io a second contact o the electrical circuit, and e hollow cap 66 fitting over the body portion l5 to provide a closed chamber lila of predeterruined volume over the ends of the body portion and piston El wit which the piston 5i may move upon rupture of'y the fuse link d8, the end wall oi the hollow canl (i6 being spaced from the piston Eli and ruse link di? whereby excessive heating ojffthe fuse link il@ enables the spring pressed piston iii to rupture the link i8 and En another aspect, the present invention includes a fuse having a body 2l of insulating material which has exterior threads, exterior electrical contact means 2Q anda central opening therein, a stationary central contact 3Q mounted in said opening within ther body 2l, a movable central contact il@ and Sl carried in said opening by the body 2l and movable into and out of engagement with the stationary central contact 3d, said movable contact SS and 3l havingan exposed contact portion 52 exposed at the end of said opening, a Vspring d@ normally biasing the movable contact llt and 3l away from the stationary central contact tl to prevent electrical 'contact between the stationary central contact is and-the movable contact 3S and 3l until the movable contact 36 and 3l has been moved a oi the spring 49. A fusible element 2B electrically connects the exterior electrical contact 29 and the central stationary contact 3l.. In the disclosure of Fig-5, an adapter i5 has an outer contact 25 adapted to cooperate with the contact 29 and a central contact 2l adapted to cooperate with the central contact l2. This adapter is provided insizes dependent upon the current rating. oi. the /fuse and thereby prevents a fuse of the wrong size from being utilized in a particular socket.

It is obvious that various changes and modiilpredetermined distance against the biasing force cations may be made in the details of construction and design of the above speciilcally described embodiment of this invention without departing from the spirit thereof, such changes and modications being restricted only by the scope of the following claims:

What is claimed is:

1. A fuse comprising a body portion having a hollow upper end and a screw threaded lower end, an adapter adapted to be seated in a fuse socket and having a threaded opening for receiving the threaded end of the fuse body, a yielding contact carried by the fuse body vportion for engagement ,in the adapter to close one side of the circuit therethrough with the fuse socket, cooperating contact elements carried by the upper portion of the fuse body and the adapter for closing the other side of the circuit as the fuse body is turned into full operative position within the adapter, and a tensioned fuse strip mounted in the hollow upper portion of the body between the opposite sides of the circuit for quick disruption and spacing apart of the ends of the fuse strip when weakened sufficiently by fusing.

2. A fuse comprising an adapterhaving an insulated body portion with a central movable contact and an outer shell contact for permanent engagement in a cut-out, a plug having an insulatedl threaded portion for engagement in the adapter and provided with a central contact to make connection with the movable contact of the adapter, an opposite side contact carried by the plug for engagement with the threaded shell yportion of the adapter when the plug is turned completely into position, a movable plunger for the central contact of the plug, a xed contact, a inseA connected at one end with the fixed contact and at the other end with the side contact, said movable plunger adapted to engage and disengage 19g-.said fixed 'contact for closing and opening the circuit, and a spring disposed between plug contact and the plug to normally move the plunger into circuitbreaking position, wherebywhen `the plug is screwed into the adapter, the central adapter contact, plug contact and fixed contact are electrically in circuit, and when the plug is partially unscrewecl,V the spring holds the plug contact in engagement with the centraladapter contact and disconnects the plunger from the .fixed contact, to break the circuit prior to the breaking of the connections between central and plug contacts and opposite side contacts.

3. A fuse comprising an adapter having exterior threads for engagement in a cut out, and having interior threads, a spring actuated central contact mounted in the bottom of the adapterY and normally closing an opening in the bottom wall thereof away from the exterior surface of the bottom wall, a fuse body having lan insulated exterior threaded plug portion for engaging the interior threads in the adapter, said plug portion having a contact to contact with the contact of the adapter and move the latter contact exterior of the adapter to close one side of the circuit with the cut out contact to which the adapter is permanently secured, a fuse strip mounted in the upper end of the fuse body and having its first end electrically connected with the plug contact, a brush 'connected with the other end of the fuse strip, avcontact ring carried upon the upper end of the adapter for receivlng said brush thereagainst and `connected to the exterior threads of the adapter or completing the other side of the circuit when the plug is turned fully into position into the adapter, and

a spring for said plug contact, stronger than the adapter contact spring, for moving the plug contact out of electrical connection with the fuse strip upon the unscrewing of the plug in the adapter, whereby the circuit is opened in the fuse body before its opening at the adapter contact, thereby preventing arcing between the adapter andcut out contact.

4. A fuse, comprising an insulating body open at its top and having a central contact in its lower end, a fuse strip connected at one end to the contact ,and extending over the open top of the body, a transparent cap tted over the body and having an exterior contact shell connected to the other end of the fuse strip and adapted for insertion into the usual fuse socket, a frangible cover carried by the fuse strip over the open top of the body, and a spring pressed plunger in the body normally urged through the open top thereof against thefuse strip disrupting the same when weakened by fusing and for quickly spreading apart the ends ci the fuse strip to prevent arcing. said plunger having an indieating upper end normally covered by the cover and adapted te be exposed in the cap when the fuse strip is disrupted.

5. In a fuse, the combination of an adapter having a conical bore, a spring pressed member movable in said bore, and having a curved surface of deilnite curvature, said member adapted to extend through an opening in the adapter when pressed against the action oi the spring, and to extend exterior to the exterior surface of the adapter when so pressed, with a yieldablc contact member ci substantially the same curvature as the spring-pressed member and oi a certain diameter and adapted to fit over the spring pressed member and push the same, without said yieldable member contacting with the conical bore whereby when yieldable contact members of different larger diameters are attempted to be used to operate the spring-pressed member, implngement oi the sides with the conical bore takes place.

6. In a fuse, the combination of an adapter having a movable contact and a bore having a conical wall surrounding the contact, and a fuse plug having a contact for contacting with the adapter contact for moving the same to complete the circuit with the contact in the cut out, without the plug contact contacting with said conical Wall; said conical wall obstructing any larger-sized contact of a different load fuse plug from moving the contact oi the adapter.

7. In a fuse, a ruse plug having a screw threaded extension with an. exposed face, projections upon said exposed face, and an adapter having a screw threaded socket engaging the screw threads of a plug, and having a flat surface engaged by said projections whereby rotary move-V ment of the projections upon the rotation of the plug cleans said flat surface of the adapter of any foreign material thereon.

8. In a fuse, a cap member having a transparent wall, a spring-pressed plunger enclosed by said cap member and having an indicating surface visible through the transparent wall when said surface is pressed against the wall, and a. fuse link passing over the plunger and its indicating surface and holding the plunger against. its spring pressure, the severance of the fuse link by excess heat and by the movement of the plunger under its spring pressure separating I 9. In a fuse, the combination of a cap member, a spring-pressed plunger, a iiat fuse link having a portion likely to break first on fusing passing over said plunger, and a ilat asbestos disc indicative of the load of the fuse, formed of abutting semi-circular portions, disposed over said portion of the fuse link at its said fusing point, the semi-circular portions separating from each other upon the fuse being ruptured by excess heat and the spring pressure of the plunger.

10. In a fuse comprising a body portion having a contact for one end of the circuit, and having a cylindrically bored portion, a spring-pressed cylindrical'piston within said bore and 'having a surface extending beyond the bore, a fuse link extending from the iirst contact of t'he circuit over the ends of the cylindrically bored portion' and. over the extended surface of the piston therein to subject the link to the pressure of the piston, said link extending exterior of the body.

portion to form the second contact of the circuit, the combination therewith of a closed cap having an interior top wall to enable the cylindrical- Y ly bored portion, piston and fuse passing over the saine to iit therein, the interior top vvall being spaced from the fuse link passing over the ex- Atended end oi' the piston, to permit when the excess heat reducesthe cohesion of the link, they piston to move against the interior top wall and separate the ends oi the ruptured link and iorm a central barrier dividing said space into a circular compartment with the ruptured ends in diametrically opposed ends or said compartment.

1i.. In a time delay fuse comprising a body portion having a contactior one end of the circuit, and having a cylindrically bored portion, a cylindrical piston ci insulating material within said bore and having a curved surface, a spring for said piston, a fuse link extending from the first contact of the circuit over the ends 'oi the cylindrically bored portion and over the curved surface of the piston therein, and extending exterior or' the body portion to form the second contact of the circuit, the heat or the fuse link when subjected towards the ,fusing point being absorbed by the insulatingmember to permit excess current to pass through the fuse link before reaching its fusing point, the combination therewith of a closed cap having a transparent top with an inner wall, and an interior bore to enable the cylindrically bored portion and the piston to t therein, the interior of the cap and the 'fuse link passing over the bored portion and piston and forming a space in which the distance between the inner Wall and that part of theuse is such that when the piston has separated the ends of the ruptured link, the piston under its spring pressure forms a central barrier between the ruptured ends of the fuse and a circular compartment around said barrier, in which the ruptured ends of the fuse are enclosed diametrically ,opposite to each other.

12. A fuse comprising an adapter having enterior ferrule threads for engagement in a cutout, and having interior insulated threads, a spring actuated central contact mounted in an opening in the bottom of the adapter and normally closing the opening, a fuse bodyhaving an exterior threaded insulated plug portion for engaging the interior insulated threads in.' the adapter, a central contact carried by the threaded plug portion of the fuse body for engagement with the spring actuated contact inthe bottom wall of the adapter to advance the latter contact into position protruding through the opening of the adapter to engage a center contact of the cut-out to complete one side of the circuit through the contacts, a spring actuated plunger for. said central plug contact for normally moving said contact to the adapter contact when the fuse plug is turned fully into posiand having an' opening, therein, a spring-prsent' piston oi insulating material siidabiy htting into said opening, a fuse link having a portion or reduced section adjacent the piston and extending from said contact over the end oi the piston to subject the link to the pressure oi the spring- I.

pressed piston and hold the piston in the said opening, said link being anchored to means eirteror of the body portion to form a second contact of the electrical' circuit, and a hollow capv tting over the body portion to provide a closed chamber of predetermined volume over the ends of the body portion andl piston Within which the piston may move upon rupture of the iuse link, the end wall oi the hollow cap being spaced from the piston and fuse-link whereby excessive heating of the fuse link enables the spring-pressed piston to rupture the link and separate the ends thereof and to form an insulating barrier between the ruptured link ends.

LAR/BERT

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