GB2040610A - Fuse - Google Patents

Abstract

A cartridge fuse link has a ceramic barrel 1 closed by end cap assemblies, each assembly consisting of a dished inner end cap 3 with an outer end cap 4 overlying it, the spaces between the outer end caps and the dished parts of the inner end caps being filled with particulate arc- quenching material, e.g. silica sand 9. This material may also fill the barrel interior. Fuse elements 2 are located within the barrel, pass through holes 8 in the inner end caps and are soldered thereto. <IMAGE>

Description

SPECIFICATION Fuse This invention relates to a cartridge fuse, particularly, but not exclusively, of the type known as "high rupturing capacity cartridge fuse links".

More particularly, the invention is concerned with a cartridge fuse link of the type comprising an insulating barrel enclosing a fuse element or elements connected to inner end caps which are located on the ends of the barrel and each of which is overlaid by an outer end cap. Such a fuse link will be referred to hereinafter and in the appended claims as "a cartridge fuse link of the type described". In known cartridge fuse links an asbestos pad is placed between each inner end cap and its outer end cap. The asbestos pads are provided, firstly, to form a heat-resisting barrier between the fuse elements and the outer cap, secondly to prevent the hot products of the fusion of the elements when fusion occurs from reaching the outer cap, and, thirdly to avoid puncturing of the outer end caps when the elements fuse. The barrels are usually ceramic and the fuse element or elements silver.Fixing tags, if provided, are attached to the outer end caps.

The handling of asbestos can involve a health risk, and an aim of the present invention is to provide a design of cartridge fuse link which avoids the need for asbestos pads.

The present invention resides in a cartridge fuse link of the type described, in which each of the inner end caps is dished away from its outer end cap to form a central gap between the two caps for the reception of arc-quenching material. The need for asbestos pads is then avoided, the arcquenching material being, for example, silica sand.

As the fuse element, or each such element, is connected between the dished parts of the inner end caps, the dishing results in a reduction of the length of the fuse element or each such element, and hence in a cost saving and in a reduction in the ohmic resistance of the fuse element, with resulting cooler operation.

The invention will be more readily understood by way of example from the following description of a high rupturing capacity cartridge fuse link of the type described, reference being made to the accompanying drawing, in which Figures 1 and 2 are respectively an end view and a sectional view of an inner end cap of the fuse link, and Figure 3 is a part-sectional view of the entire fuse link.

Apart from the construction of the end cap assemblies, the fuse link is generally of known form, and comprises a ceramic tube or barrel 1 (Figure 3) within which are arranged a number of fuse elements 2 of known construction including a solder addition 2A. The number of fuse elements employed depends on the rating of the fuse links; for some low rated fuse links a single fuse element is used. Each end of the ceramic barrel is closed by an end cap assembly.

Each end cap assembly comprises an inner end cap 3, which is also shown in Figure 1 and 2, and an outer end cap 4. As shown in Figures 1 and 2, the inner end cap is of integral construction and comprises an end plate 5 and a cylindrical skirt 6.

The end plate 5 is centrally dished at 7 and fuse element receiving holes 8 are formed in the dished part corresponding in number to the number of fuse elements employed. The inner end caps are forced with an interference fit over the ends of the barrel 1 so that the dishing enters the barrel and the fuse elements are passed through the holes 8 and the ends attached to the inner end caps by soldiering.

Each of the outer end caps 4 is similar to an inner end cap, except that it is not dished and the diameter of the skirt portion is sufficiently great to enable the skirt 6 of the inner cap to be received within it, again with an interference fit. Each outer end cap 4 is pushed on to an inner end cap 3, so that the two are in electrical contact and a central gap is formed between the end plate of the outer cap and the dished part 7 of the inner end cap.

The fuse link is assembled by pressing the inner end caps 3 on to the barrel 1, and passing the fuse elements 2 through the holes 8 and soldering their ends to the caps 3. One outer end cap 4 is then pressed into place and the assembly mounted with that outer end cap down most. Silica sand 9 is introduced through the holes 8 of the upper inner end cap 3 and compacted within the fuse link so that it fills the gap between the end caps at the bottom of the assembly, the space within the barrel about the fuse elements 2, and the dished part of the upper inner end cap 3. Finally the second outer end cap is pressed on to the upper inner end cap.

Coventional fixing tags 10, if provided, are attached to the outer end caps 4, preferably before location on the inner end caps 3.

A secondary advantage of the fuse link construction as described above is that it enables the length of the fuse elements 2 to be standardised for fuse links within a range of current ratings. High rupturing capacity cartridge fuse links are normally made with fixed overall axial lengths which vary with the current ratings of the fuse links; in the past, using undished inner end caps, that has required the fuse elements to be made to a variety of lengths. In the present construction, the lengths of the fuse elements can be the same for a range of overall axial lengths by appropriate alteration of the depth of dishing of the inner end caps. For example, the depth of dishing may be varied between 2 mm and 6mm, giving overall axial lengths varying by 8 mm for the same separation of the dished parts of the inner end caps and therefore for the same length of the fuse elements. The making of fuse elements to a constant length for a wide range of current ratings is a considerable manufacturing advantage.

In addition, the dishing of the inner end caps reduces the length of the fuse elements and hence, as those elements are usually made of pure silver, the cost.

Claims (6)

1. A cartridge fuse link of the type described, in which each of the inner end caps is dished away from its outer end cap to form a central gap between the two caps for the reception of arcquenching material.

2. A cartridge fuse link according to claim 1, in which particulate arc-quenching material fills the central gap.

3. A cartridge fuse link according to claim 2, in which the arc-quenching material is silica sand.

4. A cartridge fuse link according to claim 2 or claim 3, in which the arc-quenching material also fills the interior of the barrel and surrounds the fuse element or elements.

5. A cartridge fuse link according to any one of the preceding claims, in which the dished part of each inner end cap has at least one hole through which the fuse element or elements pass before being secured to the inner end caps, and by which arc-quenching material is introduced into the barrel.

6. A cartridge fuse link of the type described substantially as herein described with reference to the accompanying drawings.