US3179774A - Indicating and actuating fuses - Google Patents

Description

April 20, 1965 K. w. SWAIN 3,179,774

INDIGATING AND ACTUATING FUSES Filed Aug. 21. 1961 lzwezzfofl: Kezarzebw Wswaim United States Patent 3,179,774 INDICATING AND ACTUATING FUSES Kenneth W. Swain, Hampton Falls, N.H., assignor to The Chase Shawmut Company, Newburyport, Mass. Filed Aug. 21, 1961, Ser. No. 135,696

4 Claims. (Cl. 200-121) This invention relates to electric indicating and actuating fuses.

It is a general object of this invention to provide improved electric fuses of the above description, or type.

Another object of this invention is to provide indicating and actuating fuses which are normally not intended to carry electric currents and are intended to blow when, due to an abnormal condition, they are caused to carry electric currents. Such indicating and'actuating fuses are generally shunted across power or main fuses normally carrying electric currents, and the former fuses blow in response to blowing of the latter. When blowing, the former fuses indicate the blowing of the power or main fuses which they are shunting, or the former fuses cause some actuation in response to blowing of the power or main fuses.

It is another object of the invention to provide improved indicating and actuating fuses which are particularly adapted to be arranged at points remote from the power or main fuses and lend themselves well to perform either a visual indicating function, or a mechanical operating duty, or any electrical switching duty, as called for by any particular set of circumstances.

Another object of the invention is to provide improved indicating and actuating fuses which are highly flexible or adaptable, i.e. which lend themselves to be adapted by small changes to a number of different, or specialized, applications.

Other objects of the invention are to provide improved indicating and actuating fuses designed to preclude hot products of arcing from escaping from the casings of the fuses and to preclude outer corrosive atmospheres from penetrating into the casings of the fuses, and to thereby damage the fusible restraining wires arranged inside of the casings thereof.

Another object of the invention is to provide improved indicating and actuating fuses which combine a strong mechanical tie between the spring-biased striker pin and the restraining wire for the striker pin with gas-tightness.

A further object of this invention is to provide improved indicating and actuating fuses having casings of insulating materials different from those of prior art fuses.

U.S. Patent 2,794,095 to Frederick J. Kozacka, May 28, 1957, Striker Pin Structures discloses an electric indicating and actuating fuse wherein the restraining wire for the striker pin is soldered to the latter. Such solder connections are not of a permanent nature, i.e. they gradually give by virtue of cold flow of the solder under the continued action of the spring bias to which the striker pin is normally subjected.

It is, therefore, another object of this invention to provide improved indicating and actuating fuses which are not subject to the aforementioned limitation.

U.S. Patent 2,914,636 to Frederick J. Kozacka, Nov. 24, 1959, Miniaturized High Current-Carrying Capacity Current-Limiting Fuses With Built-In Indicating Plungers, and U.S. Patent 2,918,551 to Frederick J. Kozacka, Dec 22, 1959, Fuses With Built-In Indicating Plungers, disclose indicating and actuating fuses wherein the connection between the striker pin and the restraining wire for the latter is of a permanent nature. These fuses call for a looped restraining wire doubling the length thereof, and therefore it is necessary to provide in such fuses a highly effective de-ionizer, or arc-quenching filler such as, for instance, quartz sand. The provision of such a 3,17%,774 Patented Apr. 20,1965

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filler requires, in turn, the provision of relatively expensive casings capable of containing the hot fulgurite resulting from fusion of the tiller on blowing of the fuse.

It is, therefore, another object of this invention to procide improved indicating and actuating fuses which are not subject to the aforementioned limitations.

U.S. Patents 2,794,096 to Frederick J. Kozacka, May 28, 1957, High Interrupting Capacity Current-Limiting Fuses With Striker Pins, and U.S. Patent 2,834,852 to Kenneth W. Swain et al., Plug-In Type Power Fuses, disclose main or power fuses including integrated indicating and actuating fuses whose striker-pin-restraining-wires shunt the ribbon-type fuse links of the main or power fuse. The striker pin is in the shape of a rugged plunger adapted to perform a relatively onerous mechanical duty, particularly that of tripping a circuit breaker. A striker pin intended to perform a switching operation rather than to perform a mechanical duty should preferably be silverplated. The kind of striker pins shown in the above U.S. patents do not lend themselves to silver plating because they are provided with narrow passages for receiving the restraining wire which passages tend to retain highly corrosive plating liquids. Another limitation of the structures disclosed in the above patents consists in that the knotted ends of the restraining wires are exposed to the outer atmosphere which may be damaging if the latter is corrosive. Restraining wires are generally made of steel because they require a high tensile-strength, and may lllllst and be impaired if exposed to a humid or damp atmosp ere.

It is, therefore, another object of the invention to provide indicating and actuating fuses which are not subject to the aforementioned limitations.

The foregoing and other general and special objects of the invention and advantages thereof will more clearly appear from the ensuing particular description of the invention, as illustrated in the accompanying drawing wherein:

FIG. 1 is a longitudinal section of an indicating and actuating fuse embodying the invention;

FIG. 2 is a section taken along 22 of FIG. 1;

FIG. 3 is an end view of the striker pin mechanism;

FIG. 4 shows in longitudinal section a modified detail of the structure of FIG. 1, and

FIG. 5 shows in longitudinal section another modified detail of the structure of FIG. 1.

Referring now to the drawing, numeral 1 has been applied to indicate a tubular casing of insulating material. As a general rule casings of indicating and actuating fuses are made of the same insulating materials as casings of power fuses the condition of which they are to sense. Thermoplastic materials and more particularly thermoplastic synthetic resins are generally deemed unsuitable for casings of power fuses because, in operation, such casings are likely to be subjected to temperatures exceeding the softening temperatures of thermoplastic synthetic resins. I have found that thermoplastic resins are well suited as materials for casings of indicating and actuating fuses which are separate, and arranged remotely from, the power fuses the condition of which they are to sense. This suitability of thermoplastic resins is due to the fact that such indicating and actuating fuses are normally not current carrying and, therefore, normally not subjected to i -r losses and concomitant heat generation. It requires, however, some precautions to be able to provide indicating and actuating fuses with casings of synthetic thermoplastic resins. One of these precautions or requirements is minimizing the length of the fusible element or striker-pin-restraining wire which is arranged inside of the casing, and another of these precautions or requirements is the arrangement of the fusible element or ea /awe striker-pin-restraining wire coextensive with the axis of the casing, as clearly shown in FIG. 1, where reference character 3 has been applied to indicate the fusible element or striker-pin-restraining wire. The latter is made of steel to comply with high tensile strength requirements. Casing 1 may be made of an extruded thermoplastic resin as, for instance, an acrylonitrile-butadiene-styrene copolymer having a high degree of dimensional stability.

A pair of terminal elements or terminal caps 2 is arranged adjacent the ends of casing 1 and closes said ends. Each terminal element or terminal cap has a perforation 2a in the center thereof. Wire 3 is threaded through perforations 2a and tautly stretched along the axis of easing 1 and is conductively interconnecting caps 2 as will be explained below more in detail. An additional pair of caps 6 and 7 is mounted on caps 2. Cap 7 defines jointly with one of caps 2 a chamber 13 for accommodating a striker pin mechanism. The latter is arranged in coaxial relation to casing 1 and includes a substantially cylindrical striker pin 4 having a predetermined diameter, a helical striker-pin-biasing spring and a striker pin support 14 under the bias of spring 5 and formed by a part distinct from striker pin 4. Striker pin support 14 is preferably made of brass. If striker pin 4 is to perform a mechanical duty involving transmission of a relatively high force, pin 4- is preferably made of steel. Striker pin support 14 defines a first relatively narrow axial passage 15 having an entrance at the side of support 14 juxtaposed to casing 1 and support 14 further defines a second axial passage 16 having an entrance 17 at the side of support 14 remote from casing 1. Passage 16 is equal in diameter to the diameter of striker pin 4. One end of restraining wire 3 is threaded through the narrow passage 15 in support 14 and forms a knot 18 at the axially inner end of passage 15. Striker pin 4 is inserted into passage 16 through the entrance 17 thereof and plugs passage 16. Both ends of striker pin 4 are preferably convex. The end of striker pin 4 remote from casing 1 projects through a central opening 7a in cap 7 and is slidably guided in said opening. The end of striker pin 4 juxtaposed to casing 1 engages knot 18 under some pressure, tending to slightly expand knot 18 and thus to prevent the same from slipping through the narrow passage 15 in support 14 through which wire 3 is threaded.

Depending upon the particular application of the device a striker pin 4a of insulating material as shown in FIG. 4 may be substituted for the striker pin 4 of metal shown in FIG. 1. If the striker pin is of metal and intended to establish an electrical contact with some other cooperating part, the striker pin should preferably be silver plated, or silver surfaced by any other desired silver surfacing method. The support 14 for the striker pin 4 does not lend itself to silver electroplating and does not need to be silver plated. Silver plating of a metallic striker pin as shown in FIG. 1 is conducive to establishing a good electrical contact in such instances where the striker pin cooperates with another contact not covered with an oxide or similar film whose conductivity is low. Applying the modification of the striker pin 4b shown in FIG. 5 is indicated where the striker pin is intended to cooperate with a contact of copper, eg a copper bus, having an oxide film which is a poor conductor of electricity. According to FIG. 5 the end of striker pin 4b remote from casing 1 defines a sharp point adapted to pierce a copper oxide layer having a small conductivity and, by so doing, to establish a contact of low resistance in spite of the presence of such a layer.

It will thus be apparent that the fact that pin 4 and support 14 are formed by two distinct parts imparts a great flexibility and/ or adaptability to indicating and actuating fuses embodying the present invention.

Referring now again to FIG. 1, an eyelet 12 is inserted into the center perforation in the inner cap 2 at the right hand end of easing 1. Eyelet 12 forms a bushing for the passage of steel wire 3 from the inside of casing 1 to the outside thereof. Eyelet 12 and the convex surface of the cap 2 on the right hand end of casing 1 are filled with soft solder, thus afiixing the right end of wire 3 to said cap. After wire 3 has been soldered to the right inner cap 2 the loose end of Wire 3 is bent around the top of said cap and its end cut off at point 20 after the right outer cap 6 is fully seated. A center perforated washer 9 of fiber is preferably arranged inside the right inner cap 2. Where it is desirable to achieve a high degree of tightness a rubber seal 21 may be inserted between the axially outer surface of left cap 2 and the axially inner surface of support 14. Such a seal frictionally engages wire 3 and is being slightly compressed between parts 14 and 2.

A pulverulent arc-quenching filler inside casing 1 may be dispensed With as long as the circuit voltage is relatively low, i.e. in the order of volt. For higher circuit voltages a pulverulent arc-quenching filler must be placed into casing 1. If casing 1 is made of thermoplastic extruded tubing the pulverulent arc-quenching filler must be compatible with such casing materials. Gypsum powder has been found to be a compatible pulverulent arc-quenching filler, and quartz sand has been found to be an incompatible pulverulent arc-quenching filler.

The structure of FIG. 1 is intended to be used in an appropriate fuse holder having spaced contact clips supporting the outer caps or ferrules 6 and 7. The current path through the device is as follows: left outer cap 7, left inner cap 2, support 14, wire 3, right inner cap 2, right outer cap 6.

When restraining wire 3 is caused to carry an electric current, though even of relatively small magnitude, wire 3 melts, thus releasing striker pin support 14. Now support 14 and striker pin 4 are jointly propelled by spring 5 to the left from their respective position shown in FIG. 1.

Having disclosed a preferred embodiment of my invention it is desired that the same be not limited to the particular structure disclosed. It will be obvious to any person skilled in the art that many modifications and changes may be made without departing from the broad spirit of the invention. Therefore it is desired that the invention be interpreted broadly, and that it be limited only as required by the prior state of the art.

I claim as my invention:

1. An indicating and actuating fuse which is normally not current-carrying and which becomes current-carrying upon blowing of a main fuse by which it is normally shunted, said indicating and actuating fuse comprising a tubular casing of insulating material; a pair of terminal caps arranged adjacent the ends of said casing and closing said ends, each of said pair of caps having a perforation in the center thereof; a striker pin mechanism arranged in coaxial relation to and supported by said casing, said mechanism including a striker pin of predetermined diameter having a smooth lateral surface, a striker-pinbiasing spring and a striker pin support under the action of said spring and formed by a solid of revolution separate and distinct from said striker pin and support defining a first relatively narrow axial passage having an entrance at the side ofsaid support juxtaposed to said casing and said support further defining a second axial passage having a smooth lateral surface and having an entrance at the side of said support remote from said casing and being conical at the end thereof adjacent said casing, said second passage being equal in diameter to said predetermined diameter of said striker pin and said second passage being shorter than said striker pin; a striker-pinrestraining wire of steel arranged inside said casing in coaxial relation thereto exceeding the length of said casing and tautly stretched along the axis thereof and threaded through said perforation in each of said pair of terminal caps and conductively interconnecting said pair of terminal caps, one end of said wire being threaded through said first passage into said conical end of said second passage and aflixed in said second passage to said support; said striker pin being axially driven into said second passage through said entrance thereof and press-fitted into and plugging said second passage, and the end of said striker pin adjacent said support directly engaging the end of said wire inside of said second passage and clamping said end of said wire against the surface of said second passage.

2. An indicating and actuating fuse which is normally not current-carrying and which becomes current-carrying upon blowing of a main fuse by which it is normally shunted, said indicating and actuating fuse comprising a tubular casing of insulating material; a pair of terminal elements arranged adjacent the ends of said casing and closing said ends, each of said pair of terminal elements having a perforation in the center thereof; a striker pin mechanism arranged in coaxial relation to said casing, said mechanism including a silver surfaced striker pin 'having a predetermined diameter, a striker-pin biasing spring and a striker pin support under the bias of said spring formed by a part distinct from said striker pin and having a bare surface, said support defining a first relatively narrow axial passage having an entrance at the side of said support juxtaposed to said casing and said support further defining a second axial passage having an entrance at the side of said support remote from said casing, said secondpassage being equal in diameter to said predetermined diameter of said striker pin and said second passage being shorter than said striker pin; a striker-pinrestraining wire of steel inside of said casing exceeding the length of said casing and tautly stretched along the axis thereof and threaded through said perforation in each of said pair of terminal elements and conductively interconnecting said pair of terminal elements, one end of said wire being threaded through said first passage and forming a knot at the axially inner end of said first passage; and said striker pin being inserted into said second passage through said entrance thereof and plugging said second passage.

3. An indicating and actuating fuse which is normally not current-carrying and which becomes current-carrying upon blowing of a main fuse by which it is normally shunted, said indicating and actuating fuse comprising a tubular casing of insulating material; a pair of terminal caps each mounted on one of the ends of said casing and closing said ends, each of said pair of caps having a perforation in the center thereof; a striker pin mechanism arranged in coaxial relation to said casing and including a cylindrical striker pin having a predetermined diameter, a smooth lateral surface and being semispherical at least at one end thereof, a striker-pin-biasing spring and a striker pin support under the bias of said spring and formed by a part distinct from said striker pin, said support defining a first relatively narrow axial passage having an entrance at the side thereof juxtaposed to said casing and said support further defining a second axial passage having an entrance at the side thereof remote from said casing and being smooth at the lateral sides thereof and conical at the end thereof adjacent to said casing, said second passage being equal in diameter to said predetermined diameter of said striker pin and said second passage being shorter than said striker pin; a striker-pin-restraining wire of steel inside said casing tautly stretched along the axis thereof and threaded through said perforation in each of said pair of caps and conductively interconnecting said pair of caps, one end of said wire being threaded through said first passage and forming a knot at said conical end of said second passage, and said striker pin being pressfitted into said entrance of said second passage plugging said second passage and engaging said knot under pressure with a semispherical end, thereof and thereby compressing said knot. 4. An indicating and actuating fuse which is normally not current-carrying and which becomes current-carrying upon blowing of a main fuse .by which it is normally shunted, said indicating and actuating fuse comprising a tubular casing of insulating material; a pair of terminal caps arranged adjacent the ends of said casing and closing said ends, each of said pair of terminal caps having a perforation in the center thereof; a striker pin mechanism arranged in coaxial relation to said casing, said mechanism including a cylindrical striker pin of insulating material having a predetermined diameter and a smooth lateral surface, a striker pin biasing spring and a metallic striker pin support under the bias of said spring, said support defining a first relatively narrow axial passage having an entrance at the side of said support juxtaposed to said casing and said support further defining a second axial cylindrical passage having a smooth lateral surface, an entrance at the side of said support remote from said casing and a conical end adjacent said casing, said second passage being equal in diameter to said predetermined diameter of said striker pin and said second passage being shorter than said striker pin; a striker-pin-restraining wire of steel inside said casing tautly stretched along the axis thereof and threaded through said perforation in each of said pair of terminal elements and conductively interconnecting said pair of terminal elements, one end of said wire being threaded through said first passage and forming a knot at said conical end of said second passage, and said striker pin being pressfitted into said second passage through said entrance thereof and plugging said second passage.

References Cited by the Examiner UNITED STATES PATENTS 2,026,381 12/35 Fiedler 200121 2,794,095 5/57 Kozacka 200l21 2,794,096 5/57 Kozacka 200121 2,854,549 9/58 Duerkob 200-121 3,010,000 11/61 Swain et a1 200-13l 3,094,600 6/63 Kozacka 200-432 I FOREIGN PATENTS 724,830 11/43 Germany.

BERNARD A. GILHEANY, Primary Examiner.

Claims (1)

1. AN INDICATING AND ACTUATING FUSE WHICH IS NORMALLY NOT CURRENT-CARRYING AND WHICH BECOMES CURRENT-CARRYING UPON BLOWING OF A MAIN FUSE BY WHICH IT IS NORMALLY SHUNTED, SAID INDICATING AND ACTUATING FUSE COMPRISING A TUBULAR CASING OF INSULATING MATERIAL; A PAIR OF TERMINAL CAPS ARRANGED ADJACENT THE ENDS OF SAID CASING AND CLOSING SAID ENDS, EACH OF SAID PAIR OF CAPS HAVING A PERFORATION IN THE CENTER THEREOF; A STRIKER PIN MECHANISM ARRANGED IN COAXIAL RELATION TO AND SUPPORTED BY SAID CASING, SAID MECHANISM INCLUDING A STRIKER PIN OF PREDETERMINED DIAMETER HAVING A SMOOTH LATERAL SURFACE, A STRIKER-PINBIASING SPRING AND A STRIKER PIN SUPPORT UNDER THE ACTION OF SAID SPRING AND FORMED BY A SOLID FOR REVOLUTION SEPARATE AND DISTINCT FROM SAID STRIKER PIN AND SUPPORT DEFINING A FIRST RELATIVELY NARROW AXIAL PASSAGE HAVING AN ENTRANCE AT THE SIDE OF SAID SUPPORT JUXTAPOSED TO SAID CASING AND SAID SUPPORT FURTHER DEFINING A SECOND AXIAL PASSAGE HAVING A SMOOTH LATERAL SURFACE AND HAVING AN ENTRANCE AT THE SIDE OF SAID SUPPORT REMOTE FROM SAID CASING AND BEING CONICAL AT THE END THEREOF ADJACENT SAID CASING, SAID SECOND PASSAGE BEING EQUAL IN DIAMETER TO SAID PREDETERMINED DIAMETER OF SAID STRIKER PIN AND SAID SECOND PASSAGE BEING SHORTER THAN SAID STRIKER PIN; A STRIKER-PINRESTRAINING WIRE OF STEEL ARRANGED INSIDE SAID CASING IN COAXIAL RELATION THERETO EXCEEDING THE LENGTH OF SAID CASING AND TAUTLY STRETCHED ALONG THE AXIS THEREOF AND THREADED THROUGH SAID PERFORATION IN EACH OF SAID PAIR OF TERMINAL

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