Electricity: electrical systems and devices – Safety and protection of systems and devices – Circuit interruption by thermal sensing
Reexamination Certificate
1999-09-09
2001-07-03
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Circuit interruption by thermal sensing
C361S093100, C361S103000, C361S115000
Reexamination Certificate
active
06256183
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to electric fuses, and more particularly, to a time delay fuse.
BACKGROUND OF THE INVENTION
A time delay fuse is a type of fuse that is designed to allow temporary and harmless currents to pass therethrough without triggering (i.e. opening) the fuse. The fuse is nevertheless operable to open if subjected to sustained overloads or excessive short circuit conditions. Time delay fuses are typically used in circuits subject to temporary transients such as motor starting currents.
The present invention relates to an improved time delay fuse having indicator/actuator means for indicating a triggered (open) fuse.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided an electric fuse comprised of a tubular casing formed of an electric insulating material. A first conductive ferrule is attached to a first end of the casing. A second conductive ferrule is attached to a second end of the casing, the second conductive ferrule having an opening therethrough. A first fusible element within the casing is electrically connected to the first conductive ferrule. A trigger mechanism is electrically connected in series to the fusible element and the second conductive ferrule. The trigger mechanism is comprised of a first conductive sleeve electrically connected to the second conductive ferrule. A conductive plunger is within the first conductive sleeve in electrical contact therewith. The plunger is biased away from the fusible element. A second conductive sleeve is electrically connected to the second ferrule. A conductive striker is disposed within the second sleeve in electrical contact therewith, the striker being biased along an axis through the opening in the second ferrule. Thermal solder maintains the plunger in a first position in electrical contact with the fusible element. A second fusible element is electrically connected in series between the first ferrule and the striker. The second fusible element is dimensioned to maintain the striker in a retracted position substantially within the casing. The second fusible element has a current carrying capacity less than the first fusible element.
In accordance with another aspect of the present invention, there is provided an electric fuse comprised of a tubular casing formed of an electric insulating material. A first conductive ferrule is attached to a first end of the casing. A second conductive ferrule is attached to a second end of the casing, the second conductive ferrule having an opening therethrough. A first conductive path is defined between the first ferrule and the second ferrule. The first conductive path is comprised of a first fusible element having a first current carrying capacity, a first stationary contact element and a movable contact element. A thermal element maintains the movable contact element in a first position in electrical contact with the first fusible element and the stationary contact element. A first biasing element biases the movable element to a second position destroying the first conductive path. A second conductive path is defined between the first ferrule and the second ferrule. The second conductive path is comprised of a second stationary contact element and an indicator movable along a path through the opening in the second ferrule from a first position wherein the indicator is substantially within the casing to a second position wherein a substantial portion of the indicator is outside the casing. A second biasing element biases the indicator from the first position to the second position. A second fusible element has a second current carrying capacity that is less than the first current carrying capacity. The second fusible element maintaining the indicator in the first position.
In accordance with another aspect of the present invention, there is provided a fuse comprising a tubular fuse casing and first and second conductive ferrules located on the exterior of the casing at opposite ends thereof. The second ferrule has an opening therethrough. A first short circuit fusible element is attached to the first ferrule, and a heater is attached to the second ferrule. A time delay over-current trigger mechanism electrically connects the first fusible element and the heater to each other in series in an electrical path between the conductive ferrules. The mechanism is connected to receive heat from the heater and to mechanically interrupt the electrical path when the heater heats up under low over-current conditions. An indicator mechanism is provided for indicating when the electrical path between the conductive ferrules is interrupted. The indicator mechanism is comprised of an indicator movable from a first position wherein the indicator is substantially within the casing to a second position wherein a substantial portion of the indicator is outside the casing. An indicator-biasing element biases the indicator toward the second position. A second short circuit fusible element maintains the indicator in the first position. The second fusible element is electrically connected between the first and second ferrules in parallel within the first fusible element. The second fusible element has a current carrying capacity below said low over-current conditions.
It is an object of the present invention to provide a time delay fuse having a mechanical trigger assembly for indicating when the fuse has blown.
Another object of the present invention is to provide a time delay fuse as described above that is operable to actuate an external device such as an electrical switch.
Another object of the present invention is to provide a time delay fuse as described above having a fusible element that is not influenced by a biasing device.
Another object of the present invention is to provide a time delay fuse as described above that contains an arc-quenching material that does not interfere with the mechanical trigger assembly.
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Ferraz Shawmut Inc.
Jackson Stephen W.
Kusner Mark
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