Electricity: electrothermally or thermally actuated switches – Electrothermally actuated switches – Fusible element actuated
Patent
1987-03-03
1988-07-26
Broome, H.
Electricity: electrothermally or thermally actuated switches
Electrothermally actuated switches
Fusible element actuated
337265, H01H 8530
Patent
active
047603674
DESCRIPTION:
BRIEF SUMMARY
This invention relates to electric fuse links, in particular to cartridge fuse links, comprising one or more fuse elements enclosed in a cartridge filled with an arc extinguishing medium such as sand. However, the invention is applicable to fuse links other than the cartridge type.
Fuse links of the cartridge type, for example as used in domestic mains plugs in Great Britain, are thrown away from the fuse element has melted, and replaced with a fresh fuse link. A common difficulty is in knowing whether a particular fuse link has blown. Many attempts have been made to solve this problem, and many different `indicators` have been developed, as evidenced, for example, by British Patent Specifications Nos. 1093428, 542059, 582594, 1415581 and 1549360, only some being directed to use with miniature cartridge fuse links. For various reasons, these different indicators have either not appealed to manufacturers or do not work. For example, those based on colour change of a pigment are extremely unreliable because the temperature change caused simply by the melting of a fuse link is usually quite small while the operating temperature of the fuse link is variable within much greater limits. Those involving explosives, spring release and others are expensive and notoriously unreliable.
Thus the common problem remains that of knowing whether a fuse link is still usable. The present invention aims to provide a fuse indicator which is reliable in operation, cheap to implement, and which can be applied to existing cartridge or other types of fuse link with little or no modification.
Accordingly, the invention proposes an electric fuse link comprising a fuse element and means for indicating burning out of the fuse element, wherein the indicating means comprises a conductive deposit which forms a conductive path in parallel with the fuse element of the fuse link but of higher resistance.
The deposit is preferably at least partly covered by a second non-conductive layer in order to prevent arcing and to render more visible the burn out of the conductive deposit.
According to a further feature of the invention there is provided a method of manufacturing an electric fuse link having a fuse element within a ceramic body, with metal end caps providing contacts with the fuse element characterised by the step of depositing on the outside of the ceramic body a conductive deposit which forms, or will form, a conductive path in parallel with the fuse element betwen the end caps.
In order that the invention shall be clearly understood, exemplary embodiments thereof will now be described, in conjunction with the accompanying drawings, in which:
FIG. 1 shows a first embodiment of an electric fuse link according to the invention; and
FIG. 2 shows a second embodiment.
FIG. 3 shows an enlarged view of a modified form of deposit.
For a cartridge fuse link, apart from the many physical characteristics, there are a number of main electrical criteria which must be met. These are:
1. The time taken to produce disconnection at given overcurrents must be less than a specified maximum; and greater than a specified minimum;
2. The total energy (usually expressed as I.sup.2 t) passed by the fuse link during operation must be within specified limits;
3. The electrical resistance of the fuse link after operation must be greater than a specified minimum;
4. In normal running, the fuse link must not dissipate too much energy (e.g. for a fuselink within BS 1362, the maximum specified is 1 watt at rated current).
Because of the different running conditions, and the different possible faults which can lead to fuse operation, the achievement of all these and other criteria, particularly in miniature cartridge fuse links, is difficult. The invention therefore aims to adopt the already well-developed cartridge fuse links on the market, which already meet these criteria, and to provide the necessary indicator without deleteriously disturbing the other characteristics.
FIG. 1 shows the simplest form of the invention. A cartridge fuse link 10 for a British dome
REFERENCES:
patent: 1514642 (1924-11-01), Werden
patent: 2737552 (1956-03-01), Hitchcock
patent: 3182153 (1965-05-01), Postal
patent: 4308516 (1981-12-01), Shimada et al.
Broome H.
Cranmer Projects Limited
LandOfFree
Electric fuses does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electric fuses, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electric fuses will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-260075