Electricity: measuring and testing – Fault detecting in electric circuits and of electric components – Of individual circuit component or element
Reexamination Certificate
2000-06-09
2002-09-10
Sherry, Michael (Department: 2829)
Electricity: measuring and testing
Fault detecting in electric circuits and of electric components
Of individual circuit component or element
C337S194000, C337S198000, C361S835000, C439S620180, C340S639000
Reexamination Certificate
active
06448785
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to high power electrical components and more particularly to a fuse puller for a cartridge type fuse in an electrical device, which puller includes a continuity indicator for indicating the condition of the fuse.
BACKGROUND OF THE INVENTION
Large cylindrical cartridge fuses are widely used in high power electrical contactors, switches, and similar electrical devices. Such fuses may have cylindrical or flat ends adapted to engage a fuse holder for creating a secure mechanical connection and a low resistance electrical connection. Because of the large current carried by such fuses, a substantial contact area is required between the fuse and the fuse holder. Substantial pressure is exerted by the fuse holder on the contact surfaces of the fuse, which although it holds the fuse securely in position and reduces the resistance between the fuse and the holder, thereby reducing the tendency of the fuse to arc and increasing the current carrying capacity, makes it difficult to remove and replace the fuse. Moreover, fuse holders are oftentimes positioned close together when multiple phases are fused, and this makes removing and replacing the fuses even more difficult.
Heretofore, there have been a number of approaches to providing apparatus for assisting a user in removing and replacing a fuse. Fuse grippers have long been known that are configured generally like pliers, but have jaws with cylindrical openings adapted to engage a fuse to pull it from the fuse holder, and replace it as required. More recently, flexible plastic fuse holders have been employed that extend under the body of the fuse to allow the fuse to be lifted with a finger of a user, for example, and withdrawn from the fuse holder.
Although such fuse extractors are more or less effective, they do not assist the user in replacing a blown fuse with a substitute fuse, since for the most part they cannot be used to exert downward pressure on a fuse.
Before now, when a failure such as an overload, a short-circuit, or another failure, occurred, that resulted in a fuse blowing, it had been necessary to shut down the power to the device and identify the blown fuse. The blown fuse would be identified with a continuity tester or the like, remove the fuse from the fuse block and replace it with a new fuse. Because of the high currents involved in circuits of the type to which this invention relates, the fuse box and fuses have physically large contacts and substantial pressures exist between the fuse contacts and the retaining clips of the fuse block. While this provides low resistance electrical connections to the fuses and reduces heating losses, it makes the fuses physically difficult to extract from the fuse block. Various devices have been employed to extract and replace fuses, but there is a need for a more convenient method.
Fuse blocks are also known that include integral mechanisms for mechanically detaching the fuses from the fuse holders. One such fuse block is manufactured by the Gould Corporation under the catalog number US3J31. This combination of fuse block and extractor retains the fuses in a pivotal assembly that includes an operating lever for mechanically removing a fuse from the fuse block connectors, and inserting a new fuse. However, while this device is relatively convenient to use, it does not address the problem of removing and replacing fuses from existing fuse blocks. This is because using it would require that the entire fuse block be replaced, and the device is physically somewhat larger than a conventional fuse block and therefore may not be useable in existing equipment where there is insufficient space to mount it.
Moreover, the device is relatively expensive compared to a basic fuse block, and cost considerations may prevent its use except in certain applications.
Another problem with cartridge fuses of the type to which this invention is addressed, is that a blown fuse looks identical to a good fuse. In cases where multiple fuses are used to protect multiple phases, it is usually impossible to determine by observation alone which fuse of a plurality of fuses is blown. While a blown fuse can easily be detected with an electrical multi-meter, this requires additional equipment that may not be handy when the time comes to identify and replace a blown fuse.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a fuse puller that can be used both to extract and replace high current fuses from fuse blocks.
It is another object of this invention to provide a fuse puller having a built in fuse integrity indicator for assisting in the identification of blown fuses.
Briefly stated, and in accordance with a presently preferred embodiment of the invention, a fuse puller includes a generally cylindrical fuse receiving portion, a lifting and inserting tower attached to the cylindrical fuse receiving portion, and a gripping head attached to the tower.
In accordance with another aspect of the invention, the tower portion of a fuse extractor and replaced in accordance with this invention is hollow and incorporates a continuity detector having an indicator for indicating the condition of a fuse.
In accordance with another aspect of the invention, a fuse extractor and puller includes first and second spring contacts attached to the continuity checker, and adapted to contact the electrical terminals of a fuse positioned within the extractor and puller.
In accordance with another aspect of the invention, the tower includes a spring clip for resiliently holding the continuity detector within the fuse extractor.
In accordance with another embodiment of the invention, the fuse continuity indicator comprises a light extending through the top of the gripping portion for easy visibility.
In accordance with another aspect of the invention, the light may be pressed downwardly against the gripping portion; the stress created thereby being absorbed by the resilient mounting for the indicator board, thereby preventing damage.
REFERENCES:
patent: 4475283 (1984-10-01), Olson
patent: 5488345 (1996-01-01), Yoshinobu
patent: 5662496 (1997-09-01), Kanamori
patent: 5751208 (1998-05-01), Martinez
Livingston Thomas J.
Rohmer Richard
Nguyen Trung
Pass & Seymour, Inc.
Sherry Michael
Wall Marjama & Bilinski LLP
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