A fuse

Abstract: A fuse having a fuse element extending tautly between two terminals in a housing, said element including at least two parallel connected conductors (9,10,11) and at least a core of insulating material. At least one of the parallel connected conductors has the form of a metal coating (11) on or a metallization of the or a core of insulating material (12). The number of conductors, the material of the conductors and the number of cores of insulating material is chosen in such a manner that the fuse has the desired rated current and the desired fusing characteristic.

Description: The present invention relates to a fuse comprising a fuse element extending tautly between two terminals in a housing, said fuse element including at least two parallel connected conductors and comprising at least a core of insulating material. Such a fuse is known from EP-A-0 141 344. The fuse disclosed in this publication comprises a fuse element consisting of a core of insulating material, one or more straight fuse filaments extending parallel to said insulating core and a longer fuse filament being spirally wrapped around said system of core and straight fuse filament(s). The straight filament(s) and the spirally wrapped filament are mechanically and electrically connected at their respective ends so that all fuse filaments are electrically parallel. Thus a suitable time-delay fuse is constructed. In Dutch Patent 165.879 a fuse is disclosed comprising a fuse element consisting of a core formed by a straight wire or band of metal wound with a thin metal wire. The metal wire of the winding consists substantially of the same metal as the metal of the core. By means of such construction, it is possible to accurately control the fusing characteristic of the fuse. Variation in the fusing characteristics and the rate current can be achieved by variation in the wire thickness of the winding and within narrower limits also by variation in the winding pitch. As regards miniature fuses, I.E.C. has issued a directive (No. 127). This IEC directive 127 gives specifications for such fuses to a number of 25 values of the rated current. Many manufacturers manufacture besides this series of 25 different miniature fuses, also some fuses having rated current values deviating from the IEC directive. The complete series of fuses of a manufacturer, consequently, comprises mostly 30 or more rated current values. Each rated current requires a different fuse element. Besides, the users require fusing characteristics differing at a given rated current (slow-blow or less slow-blow characteristics), which wish is met by the manufacturers. Thus, the variety of fuse elements exceeds by far the above mentioned thirty or more. Such a large variety can be realized by means of the known construction by using a great many different wire diameters and wire materials for core wire and winding wire. Naturally, this creates problems in connection with the manufacture, quality guarantee and in particular the economy of the manufacture. It is an object of the present invention to provide a fuse whose fuse element is constructed in such a manner that by means of a relatively small number of starting materials, a great many different fuses with the required large number of rated currents and with the desired fusing characteristics can be realized. The object according to the present invention is achieved with a fuse in which at least one of the parallel connected conductors has the form of a metal coating on or a metallization of the or a core of insulating material, while the number of conductors, the material and diameters of the conductors and the number of cores of insulating material are chosen such that the fuse has the desired rated current and the desired fusing characteristics. It has to be noted that a fuse in which the fusible element comprises a conductor having the form of a metal coating on a core is known from US-A-4,293,836. In the fuse according to said document the single conductor consists of a monofilament of quartz glass fiber coated with an alloy composed of silver, copper, tin and antimony. On application according to the present invention of a fuse element comprising at least two conductors and at least one insulating core, it is possible by a suitable choice of the number of conductors, the number of cores and, possibly, using different conductors, to realize such a number of combinations that as a result the entire desired range of rated currents can be covered, while moreover, depending on the choice of material, the fuse can have fast or slow blowing characteristics. In a suitable embodiment of the fuse according to the present invention the fuse element includes a bundle of at least two conductors having the form of a core of insulating fibrous material with a metal coating, which bundle has been twisted together at relatively large pitch and suitably sized. Furthermore, the bundle of metallized fibres may be wrapped with one or more conductors having the form of a solid metal wire. The conductors of the fuse according to the present invention may all consist of the same material, and have mutually differing sizes. For instance, wires of the same material having mutually differing diameters. However, the conductors may all have the same diameter, but consist of mutually differing material. For a good variation possibility, even as far as fusing characteristics is concerned, it is of relevance that always at least one insulating core is present. As observed, the at least one insulating core forms part of one or more conductors, since as conductor are used metallized fibres of synthetic resin or glass or ceramic material. Instead of metal-coated insulating fibres, however, also strip-shaped or ribbon-shaped metallized fabrics or metallized synthetic resin foils can be used as conductor. Some embodiments of the fuse according to the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is a side view of an embodiment of the fuse according to the present invention; Fig. 2 is a cross-sectional view of an other embodiment of the fuse according to the present invention; and Fig. 3 is a side view of a portion of an embodiment of a fuse element for the fuse according to the present invention. In the figures corresponding parts have the same reference numerals. Fig. 1 shows the cylindrical housing 1 including two end caps 2 slid thereon at the ends. Housing 1 includes e.g. a tube of glass or quartz, the end caps 2 consist of a suitable metal, e.g. nickle-plated brass. A fuse element is disposed in the housing between the end caps. The fuse element according to the present invention includes at least three separate conductors, each having electrical properties differing from the other conductors. The fuse element shown in Fig. 1 includes three conductors 3, 4 and 5. Conductors 3, 4 and 5 are basically metallized insulating fibres arranged in parallel and adjacent relationship and which are held together e.g. by a suitable size. Conductors 3, 4 and 5 may be insulating fibres having a coating of the same metal but of mutually different thickness or may be fibres having the same thickness but with mutually different metal. Naturally, also filaments of mutually different material and with mutually different thickness may be employed. The filaments may be solid, i.e. consist entirely of a given metal, but they may also consist of metallized fibres of glass or synthetic resin. Fig. 2 shows a cross-section of a fuse having a fuse element including three separate conductors 6, 7 and 8 twisted together. The resulting fuse element, as shown, is clamped on both ends between the housing 1 and the respective end cap 2. Conductors 6, 7 and 8 may be metallized fibres of the same type as mentioned in the above for conductors 3, 4 and 5 of the fuse shown in Fig. 1. Fig. 3 is a view of a portion of a fuse element of the type employed in the fuse shown in Fig. 2. The fuse element shown includes three twisted conductors 9, 10 and 11. Of these conductors, conductors 9 and 10 have the same diameter and consist of the same metal. Conductor 11 is a metallized insulating fibre. The insulating core is indicated at 12. Naturally, it is also possible that conductors 9 and 10 are also metallized insulating fibres. In that case, the construction shown in Fig. 3 may be wrapped with solid metal wire in order to attain other values of the rated current. Rated current Characteristic I Characteristic II Characteristic III 32 mA 2 x A 40 mA 3 x A 50 mA 4 x A 63 mA 5 x A 80 mA 6 x A 3 x A + B 100 mA 8 x A 4 x A + B 125 mA 4 x C 6 x A + B 2A + C 160 mA 6 x C or 4C + 4A 6 x A + 2 x B 5 x A + C 200 mA 8 x C or 6C + 4A 8 x A + 2 x B 8 x A + C 250 mA 9 x C 6 x C + D 8 x A + C + D 315 mA 12 x C 6 x C + 2 x D 8 x C + 2 x B 400 mA 17 x C 8 x C + 2 x D 10 x C + 3 x B Table A indicates how a great many fuses of different values of the rated current can be obtained with only a few different wire types. In the table, four different conductors are included: Conductor A - glass fibre having a diameter of 18 µm, having a tin coating of 0.2 µm. Conductor B - solid round copper wire, diameter 15 µm. Conductor C - glass fibre having a diameter of 50 µm, having a tin coating of 0.5 µm. Conductor D - solid round copper wire, diameter 25 µm. The fuses in the column under characteristic I are fast-blow, fast-acting fuses obtained by twisting the numbers of conductors A, and C, respectively, mentioned in the column, at a large pitch and sizing the same in a suitable manner, consequently, a construction as shown in Fig. 3. The fuses in the columns under characteristic II, and III, respectively, are slow-blow, time-delay fuses obtained by wrapping bundles of the numbers of conductors A, and C, respectively, mentioned in the column whether or not twisted, with one or more of conductors B or D, as indicated in the column.

Claims: A fuse comprising a fuse element extending tautly between two terminals in a housing, said fuse element including at least two parallel connected conductors and comprising at least a core of insulating material, characterized in that at least one of the parallel connected conductors has the form of a metal coating on or a metallization of the or a core of insulating material, while the number of conductors, the material and diameters of the conductors and the number of cores of insulating material are chosen such that the fuse has the desired rated current and the desired fusing characteristics. A fuse according to claim 1, characterized in that the fuse element includes a bundle of at least two conductors having the form of a core of insulating fibrous material with a metal coating, which bundle is twisted together at relatively large pitch and is suitably sized. A fuse according to claim 2, characterized in that the bundle of metallized fibres is wrapped with one or more conductors having the form of a solid metal wire.

Inventors: VERMIJ LEENDERT, VERMIJ, LEENDERT
Applicants: LITTELFUSE BV, LITTELFUSE B.V.
Application year: 1985
Main classification: H01H85
IPC codes: H01H85, H01H37