US2210036A - Fusible protective device for electric circuits - Google Patents

Description

Aug. 5, 194%- .J. A. MCENTEE FUSIBLE PROTECTIVE DEVICE FOR ELECTRIC CIRCUITS Filed Jan.

Patented Aug. 6, 1940 UNITED STATES PATENT OFFICE FUSIBLE PROTECTIVE DEVICE Eon ELECTRIC cmcUrrs setts Applicationdanuary 22, 1936, Serial No. 60,239

31 Claims.

This invention relates to fusible protective device for electric circuits.

It is. common practiceto protect electric circuit and the apparatus therein against damage due to overloads by fuses which are in the series with the circuit and are adapted to blow when traversed by a current in substantial excess of their rated continuous carrying capacity. For circuits of moderate current carrying capacity, as say up to and including 30 amperes, the fuses are commonly of the screw plug type. Electric circuits, and many pieces of apparatus operated from the circuits, are able to carry a moderate overload current for a considerable period of time normal current is demanded for a short period of time. For instance, an electric motor that is adapted to be connected directly to the line without the use of a starting impedance draws for a second or so or until the motor comes up to normal speed, a starting current that may be from five to ten times in excess of its normal full load running current.- An electric fuse and particularly one of the plug type, having a capacity suited to the normal current, ordinarily is unable to carry the momentary overload and thus blows and interrupts the circuit needlessly.

.Hence an object of the present invention is the provision of an improved form of a fusible protective device and particularly one of the screw plug characterized by its ability to carry a current that is considerably in excess of its normal rated current for a substantial period of time sufllcient topermit excessive current momentarily to be supplied to the circuit and the apparatus therein and yet to operate tointerruptthe circuit if excessive current flow persists for an unusual time and also if the normal current is exceeded for a longer time.

A further object of the invention is, the provision of an improved form of fusible protective device having means providing for the delayed interruption of the circuit when traversed by a moderate overlo current and the quicker or instant interruptio of the circuit when traversed by a short-circuit current.

The fusible protective device embodying the present invention includes a normally solid mass of readily fusible metal adapted to be heated to the fusing point by an electric resistance element and when solid retaining-therein the spring tensioned end of a movable conducting member and when fused releasing its hold upon the conducting member, thereby permitting the spring to without damage; and inthe operation of many pieces of apparatus a considerably higher than withdraw the ehd of the member from engagement with the fused mass and thereby interrupt the circuit.

An object of the present invention is the provision of novel means for holding the fusible metal mass, the holding means being a part of the heating element.

A yet further object is the provision of holding means for the fusible mass wherein the heating element is a resistance conductor wound in a helix, the fusible mass being contained in one end of the helix by direct engagement with the convolutions thereof.

Another object of the invention is the provision of a fusible protective device of the type above described having a construction wherein the op erative elements can be contained within a screw plug body the dimensions of which, and particularlythe length of which, does not exceed the ,dimensions of the ordinary plug type of fuse so that the device can go in any receptacle and in any installation having a plug fuse, to replace the fuse.

A further object of the invention is the provision of a fusible protective device of the screw plug type having a novel form of spring for mov- ,ing the conductor.out of the fused fusible mass whereby a relatively great separation is provided between the conductor and the metal mass for a smaller movement of the spring and also V wherein the length of the device can be kept and permitting a'long circuit interrupting gap.

Another object is generally to improve the construction and operation of fusible protective de-- vicesv for electric circuits.

- Fig. 1 15.8. side elevation of the fusible protective device embodying the present invention.

Fig, 2 is a sectional elevation of the device'of Fig.1 taken along line 2-4 of Fig. 1.

Fig. 3 is a plan view of the device of Fig. 1 1,

the cap and transparent window being removed.

Fig. 4 is a section taken along the line H of Fig. 2.

Fig. 5 is a sectional detail similar to Fig. 4 but illustrating the operated position of the parts.

Fig. 6 is a sectional detail taken along line 6-6 of Fig. 5.

wardly projecting boss It in which a. center contact 58 is fixed, the stem or shank 2d of the center contact having an internal recess 22.

The plug body is provided with an internal open-top chamber 2% in which the operative parts of the device are located; The top of the body is provided with a peripherally outstanding flange 25. An electrically insulating transparent disc 28 of suitable material, as mica, overlies the top of the body and is seated upon the flange 2S and constitutes a closure for the open end offthe chamber 2d. A metal disc-retaining cap 38 has its topwall 32 overlying and seated upon the transparent disc 28 and its side wall 3% engaged with the outer face of the flange 28 and the end of the side wall turned in under the flange andthereby permanently retained tightly engaged (with the plug body. The top wall 32 of the cap is provided with an opening or window 36 through which a view of the interior of the plug chamber can behad. The plug body so far described is essentially the body of a plug type of fuse and has the same dimensions.

A' combined holder and heating element for a mass of readily fusible metal is located in the .bottom part of the chamber 25. Said holder and heating element comprises a helix 38 of resistance wire 60, thelower end $2 of the resistance wire being extended parallel with the axis of the helix and located in the recess 22 of the shank of the end cap where it is permanently retained by a mass of solder having a melting point sufliciently high to remain solid at any temperature sumcient to melt the readily fusible metal and cause the operation of the. device.

The uppermost two or three turns 36 of the helix are in substantial contact or at least are sufiiciently close to one another to form a cup to retain a mass 58 of readily fusible metal. The cupis provided with a bottom by a plate dd of suitable heat resistant sheet material, asmica, for instance, which is inserted between and is gripped by the convolutions under the fusible mass. The convolutions below the cup are separated and constitute a heating coil which when traversed by sufiicient current heats the readily fusible metal mass 48 in the cup and ultimately causes it to melt or fuse.

' While the bottom plate 59, as above described,

is intended to be a permanent part of the cup,

its presence in the completed device is not essential. The plate may be retained in place while the molten metal is poured into the cup and until the metal mass has solidified. It can then be removed. Such a construction is illustratedin Fig. 7. For this purpose the plate can be of mica, aluminum or other sheet material not harmed by the heat of the molten metal mass or adapted tobond therewith. t

The fusible metal mass is normally connected to the terminal shell id through a flexible conducting strip 5% which preferably is composed of copper although it can be composed of fuse link material, usually zinc. The inner end 56 of the strip is imbedded in the normally solid metal mass 448 and is thereby held in electrical and mechanical engagement'with the metal mass. and is anchored thereby. The outer end 55 of the strip islocated in a channel 58 formed in the I &

wall o the body it and is imbedded in a mass 66 of solder by which it is connected electrically with the terminal shell 5. The strip is thus of looped or inverted U formation. The strip is under spring tension acting in such manner as 10 to constantly act upon the inner end .55 of the strip to pull it upwardly out of engagement with the fusible metal mass 68 when said mass be; comes fused.

The spring tension is provided with a how 15 spring 62 consisting of a normally straight helix of spring wire wound in close convolutions. The spring helix is extended transversely across the chamber 2% of the plug body under the conducting strip 52, and the ends of the spring helix 20 are receivedin notches 5d formed in'the side wall of the plug body immediately under the transparent cover 253. Barriers 56 integral with the plug body traverse the ends of the notches to isolate the ends of the spring helix from the 25 metal cap 3!). The diameter of the spring helix and the depth of the notches 56, however, preferably is such that the'helix projects slightly above the tops of the notches so that the mica disc 28 is pressed firmly thereagainst by the 30 metal cap whereby to grip the ends of the spring helix between the mica disc and the bottoms of the slots so asto prevent endwise movements of the spring.

The conducting strip 52 is looped over thejg middle part of thespring helix and the length of the strip is such that in the normal condition of the device the spring helix is bowed downwardly by a substantial amount as indicated in Figs. 2 and 4, thereby placing the conducting strip (30 under a tension in a direction to withdraw the inner end of the strip out of the fusible metal In the assembly of the device the following procedure is convenient. The ends of the conducting strip are secured to the solder masses 58 and fifl'with the strip forming an u standing loop, as shown. A curved wire or nee e is then run through the initially straight spring 62,

thereby forming it into the bow shape illustrated.

The spring on the needle is then passed under the looped strip 52 and theends of the spring located in the. notches E i. The needle is then withdrawn out of the spring and thespring flexes upwardly somewhat and applies tension 55 on the strip 52, the ends of the spring bearing downwardly on the bottoms of the notches and projecting upwardly partly above the top face of the plug body Hi. The mica disc 28and end 'cap 30 are then applied, bending the upstanding spring ends downwardly andclamping them in place. The clamping action is desirablefor preventing endwise movement-of the spring especially if the walls of the notches are omitted but is not necessary merely to retain the spring 65 ends in the notches. 4

Y Under normal conditions of service, where the device is traversed by not more than the'current which it can carry continuously-the parts re main in the aforesaid relation. When, however,

the device is subjected for a sufficient period of time to an excessive current the heat generated by the heating element 38 raises the temperature of the readily fusible metal mass tdthe melting point thereof.v The metal mass thus becomes fluid and no longer can retain its grip on the inner end of the conducting strip 52. The inner end of the strip is thereupon pulled rapidly upward out of the fusible mass by the tension of the bow spring 62, thereby interrupting the circuit, the bow spring usually assuming a straight horizontal position as illustrated in Fig. 5.

Due to the arrangement of the spring under and in engagement with the looped portion of the conducting strip and to the fact that there is a relative-movement between the strip and the spring in the direction of the length of the strip,

the upward movement of the inner end of the conducting strip is twice that of the upward movement of the spring, per se. Due also to the inherent rigidity of the free end of the conducting strip said end is moved upwardly into a position where it lies against the inner face of the mica disc 28 as illustrated in Fig. 6. Thus a very large distance of separation between the strip and the fusible metal mass is attained without the necessity for a long length of enclosing casing.

The conducting strip 52 is preferably provided with a more readily fusible portion, or fusing zone by having a part of reduced cross-section as made by the perforation 68 located in the inner end of the conducting strip in'a position to be out of the mass of readily fusible metal when the device is in service condition. They can-vaporize more or less completely without the generation of harmful gas pressures within the enclosing casing. For currents of lesser magnitude but still sufficient to fuse the strip before the readily fusible metal 'melts, the strip will fuse at its portion of highest temperature, usually betweenthe spring 62 and the mass of fusible metal 48, which portion is thus the equivalent of the more readily fusible portion provided by' the perforation.

I claim:

1..A fusible protective device comprising a. fusible mass, heating means for melting said mass, a fusible conductor having an end engaged with and anchored by said mass and adapted to be released upon the fusing of said mass, terminals, said conductor, heating means and fusible mass being in series with said terminals, said conductor having a part adapted to fusewhen traversed by a dangerous current,

and spring means operatively excluded from the circuit between said terminals tensioning said conductor at said fusible mass and also at said fusing part.

- 21. A fusible protective device comprising a fusible mass, heating means therefor, a fusible conductor having one anchored end and its other end engaged with and anchored by said mass, terminals between which said mass, heating means and conductor areconnected in series, said conductor having a fusing section, and spring means operatively excluded from the circuit between said terminals engaged with and acting on said condubtor intermediate its ends in a direc: tion that tensions said conductor at said fusible mass a d also at said fusing section.

3. In a fusible protective device having a fusible mass, a conductor engaged with and anchored by said fusible mass, and spring means to withdraw said conductor from the molten fusible mass, the combination therewith of a holder for the fusible mass comprising a helix having convolutions directly engaged with and within which the fusible mass is disposed,

4. In a fusible protective device having a fusiblemass, a conductor engaged with and anchored by said fusible mass, spring means to withdraw said conductor from the molten fusible mass, the combination therewith of a holder for the fusible mass comprising a helix having close convolutions directly engaged with and within which the fusible mass is disposed.

5. In a fusible protective device having a fusible mass, aconductor engaged with and anchored by said fusible mass, spring means to withdraw said conductor from the molten fusible mass, the combination therewith'of a holder for the fusible mass comprising a helix having close convolutions directly engaged with and within which the fusible mass is disposed, and a bottom closure member traversing the helix under said fusiconvolutions directly engaged with and within which the fusible mass is disposed, and a bottom closure member traversing the helix under sai I fusible mass and located between the convolu tions of the helix, the convolutions on opposite sides of said closure member being in pressure engagement therewith. 7. In a fusible protective device having a fusible mass, a conductor engaged with and anchored heating coil for said fusible mass having some of its convolutions surrounding and directly engaged with said fusible mass and forming a retaining cup therefor.

8. In a fusible protective device having a fusible mass, a conductor engaged with and anchored by said fusible mass, and spring means to withdraw said conductor from the molten fusible mass, the combination therewith of a holder and electric heating element for said fusible mass comprising a resistance helix having said fusible mass retained therein by direct engagement with convolutions-of said helix which form a retaining cup for said fusible mass.

9. In a fusible'protective device having a fusible mass, a conductor engaged with and anchored by said fusible mass, and spring means to withdraw said conductor from the molten fusibleby said fusible mass, spring means to vvitluirawv said conductor from the molten fusible mass, the

combination therewith 'of a holder and electric heating element for said. fusible mass comprising plug body having a center contact. a screwa resistance helixhaving -a series of open convolutions and a series of close convolutions, said fusible mass being contained within and engaged with said close convolutions, and a closure-member traversing said helix under said fusible mass.

11. A fusible protective device comprising an electric resistance helix, a fusible mass contained in one end of said helix and retained-therein by ing close convolutions at one end surrounding and directly engaging said fusible mass, and a closure plate-traversing said helix under said fusiblemass. 4

13; A fusible protective device comprising a threaded shell and an internal chamber, a heating element comprising a resistance helix in said chamber having an end connected with said center contact, a fusible mass retained in the other end of said helix by direct engagement with convolutions thereof, a conductor having one end engaged with and anchored by said fusible mass and its other end connected with said shell, and spring means for withdrawing said conductor from said fusible mass;

14. A fusible protective device comprising a fusible mass, a conductor forming a part of the circuit through said device engaged with and anchored by said fusible mass,spring means for withdrawing said conductor from said fusible mass, 7 and means for supporting said spring means for flexure transversely of its length; said spring means bearing on and disposed with its length transversely of the length'of said conductor. r

15. A fusible protective device comprising a fusiblemass, a conductor forming a part of the circuit through said device engaged with and anchored by said fusible mass, and ineans including a bow spring acting o said'conductor for withdrawing it from said sible mass.

16. A fusible protective device comprising a] fusible mass, a conductor engaged with and'anchored by saidfusible mass, and means having a determined distance of action for withdrawing said conductor a greater distance from said fusible mass.

17. A fusible protective device comprising a fusible mass, aconductor forming a part of the circuit through said device engaged with and anchored by saidfusible mass, and a bow spring for withdrawing said conductor from said fusible mass, said bow springv being disposed cross-wise ofsaid conductor in engagement therewith.

18. A fusible protective device comprising a fusible mass, a conductor having a fixed endand an end anchored by said fusible mass, and a bow spring disposed-cross-wise of said conductor and acting thereon intermediate the ends thereof.

19. A fusible protective device comprising a fusible mass, a conductor having a fixed end and an end anchored by said fusible mass, and a bow spring comprising a springhelix disposed crosswise of said conductor and acting thereon intermediate the ends thereof. I

. 20. A fusible protective device comprising a fusible mass, a conductor having a fixed end and an end anchored by said fusible mass, a bow spring comprising a spring helix disposed crosswise of said conductor and acting thereon intermediate the ends thereof, and a support for the ends of said helix.

.21. A fusible protective device comprising a fusible mass, a looped conductor having a fixed end and an end anchored by said fusible mass, and a spring helix disposed cross-wise of said conductor in the loop thereof and bearing there? against.

22. A fusible protective device comprising a fusible mass, a looped conductor having a fixed end and an end anchored by said fusible mass, a spring having a part disposed cross-wise of said conductor in the loop thereof and bearing thereagainst, and an anchorage for said spring.

23. A fusible protective device comprising an enclosing casing having terminals, 2. fusible mass connected with one terminal, a conductor con-=- nected between said fusible mass and said other terminal, and a spring helix extended cross-wise of and'bearing against said conductor between the ends thereof;

24. A fusible protective device comprising a plug body having a center contact and ascreivthreaded'shell, a fusible mass connected with said center contact, a loop conductor having one end releasabl'y anchored by said fusible mass and its other end connected-with said shell, and a spring having a part extended transversely of said conductorand hearing on the loop part thereof.

25. A fusible protective device comprising a plug body having acenter contact'and a screwthreaded shell, a fusible mass connected with said center contact, a, looped conductor having] one end releasably anchored by said fusible mass and its other end connected with said shell, and a tensioned spring helix disposed cross-wise of said 5 conductor and bearing on the loop thereof.

26. A fusible protective device comprising a fusible mass, a conductor having a fixed end, and

an end releasably anchored by said fusible ma and spring means having a part extended transversely of and bearing on said conductor and tensioning the entire conductor between its ends.-

27. A fusible protective device comprising a casing having a-chainber, a spring helix travers-= ing said chamber and having its ends supported by the wall of said chamber, a conductor extended across said helix and bearing thereagainst, and

a fusible -mass relea'sably anchoring the end of said conductor.

28. A fusible protective device comprising-a cas-.

ing having a chamber, a center contact and a screw-threaded shell carried by said casing, a.

spring helix traversing said chamber and having its ends supported by said casing, a conductor having'an end connected to said shell and extended across 'and'bearing against said helix,

and a fusible mass connected with said center contact and releasably retaining'the other end of said conductor. I

- 29..A fusible protective device comprising a casing havingaan open ended chamber, a transparent insulating member traversing the open end of said chamber,.means for retaining said transparent member in place, a center contact at the bottom of said 0, a screw-threaded shell.-

surrounding said casing, a spring helix extended across said chamber under said transparent member and having its ends supported by said casing, a conductor having an end connected with said shell and extended across and bearing against said helix, and a fusible mass connected with said center contact releasably retaining the other end of said conductor.

30. A fusible protective device comprising a resistanse heating element having a supported end and a free end, a fusible mass carried by one end of said element, a terminal connected with the other end of said element, a conductor having one end releasably'anchored by said fusible mass and having a fusing part, a second terminal connected with the other end of said conductor, and spring means exerting tension on said conductor and said fusing part thereof.

31. A fusible protective device comprising an r enclosing casing having a window, a fusible mass 5 within said casing, current responsive means for fusing said mass, a flexible conductor engaged with and normally anchored by said mass in a position remote from said window, and means under said conductor for withdrawing said conductor from the fused mass and for flexing it into position displaying the freed end thereof closely adjacent said window.

JAMES A. MCENTEE.

e CERTIFICATE OF comc'rion. Potent no. "2,210,05 6.

. August 6, 191m. JAHES-A.-H0EN1EE.

It ro er 2y certified that error appears in the printed apecf Lfication or the above numberedpatent requiring correction as follows: Page 1, first column, line 52', after the word "plug'insert "type"; and second column, line 52, after the wordandperi od "down," begin a new paragraph; page L, second column, line 514., claim 21+, for "loop" read "looped"; line 58, same 'claimrror "hearing" read '-'--bear11 1g and that'the eaid Letters Patent should be read with this correction therein that the same may conform to the record or the. case in the Patent Office.

si ned and sealed this men-ga of September, A. D. 191m.

Henry Von Arsdale, (Seal) Acting Commissioner -of Patents.

. I CERTIFICATE OF CORRECTIION. Patent na.'2,210,o36. August 6, 194

JAMES- A. mm;

It is neaoy certified that error appears in the printed spemi ficationvor the above numbered patent requiring correction as follows: Pa'g'e 1, first column, line 52', after the word "plug" insert --type--; and second column, line 32, atter tna wordandperiod "down." pe in a new paragraph; page LL, second column, line 3b., claim 21 for p" d "looped"; line 58, same c1aim, or"'hearing" read '-'-bearing and that'the said Letters Patent should be read with this' correction therein that the same may' conform to the record 61' the case in the- Patent Office. a Signed and sealed this zhtn'aa of September, A. D. 19!;0.

Henry Van Arsdale, (Seal) Acting Commissioner -of Patents.

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