This invention relates to a fuse for connection in and protection of an electrical circuit.
Various fuse devices have been developed for connection into an electrical circuit to open the circuit in response to abnormal current conditions. The fuse elements may include a current conductor which will carry normal current. Preselected abnormal currents result in heating of the element to a fusing level which results in disruption of element and opening of the circuit. This of course is desirable to protect the electrical devices in the circuit. A visual indicator identifying a particular actuated fuse unit is, of course, also often desirable. Various indicating systems have also been suggested. For example, U.S. Pat. No. 2,165,636 which issued July 11, 1939 for an electric fuse, discloses an end-mounted spring element secured to the exterior end of an elongated fuse and interconnected to a fusible element. Abnormal current disrupts and opens the fuse element, releasing the spring structure which then falls from the fuse to provide an indication of the fuse response. An external coil spring includes one end connected to the fuse element by two or three turns of the spring thereon and the opposite end provided with an integral guide for guiding of the fuse element back through the opening into and through the housing. The fuse wire extends from the spring member and is affixed to the terminal external to the housing and spring structure. When the fuse burns open, the spring expands and also drops down such that the hanging unit provides a visual indication of the fuse disruption. Another elongated fuse structure having a special indicator is shown in a more recently issued U.S. Pat. No. 4,023,877 which issued June 28, 1977 and is assigned to the same assignee as the present application. The fuse structure shown therein is a cartridge type adapted to be inserted in a fuse clip assembly. The fuse structure includes an elongated housing having cup-shaped end terminals. A fuse unit within the housing is connected between the end terminals, and in particular includes a relatively heavy rod-like non-fusible element. The one end of the non-fusible element is secured to the one end contact by a fusible material. The rod extends through the housing and terminates in spaced relation to the second contact. A coil spring encircles the rod and acts between a central abutment and the end of the rod. Abnormal current flow disrupts the fusible material and releases the connection to the rod. This releases the spring which expands and carries the indicator rod outwardly, with the total expansion being selected to move the head outwardly of the housing. Thus, both ends of the housing define an indicator of the fuse response. Thus, the one end provides a distinct opening while the opposite end had the solid rod projecting outwardly.
Although various prior art devices have been suggested, there is a need for a relatively reliable but inexpensive fuse indicator structure for elongated tubular fuse elements.