Patent Publication Number: US-6703917-B2

Title: Resettable fuse/circuit interrupter with visual fault indication

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
    
    
     CROSS REFERENCE TO OTHER PATENT APPLICATIONS 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The present invention relates generally to fuses for circuits. More particularly, this invention relates to a multi-metallic heat reactive strip that snaps when conducting an overloaded current to interrupt a load circuit and turn on an indicator light. 
     (2) Description of the Prior Art 
     Most fuse systems in automotive electrical systems, test instruments, and domestic appliances use miniature fuses that fit into tight spaces. These fuses are partially made of materials that melt and part when they are subjected to overloads of current, and the fuses do not clearly indicate that a circuit has been overloaded and broken at the fuse. Consequently, operators may not be aware of the overloaded and open-circuit condition until sometime much later when some other event develops that will more surely attract their attention. After being overloaded, the fuses with the melted materials cannot be reset and must be replaced with intact units to resume whatever it was that the associated circuits were doing. Sometimes the replacements are not immediately at hand, and the associated circuits might have to be shutdown for a considerable period until replacements are located and installed. 
     Thus, in accordance with this inventive concept, a need has been recognized in the state of the art for a device to interrupt a circuit when subjected to overload current, to provide a clearly visual indication of such overload and interruption, and to have the capability to be reset to reestablish a closed circuit. 
     SUMMARY OF THE INVENTION 
     The first object of the invention is to provide a circuit having a multi-metallic heat reactive strip to interrupt and indicate an overload current. 
     Another object is to provide a circuit having a multi-metallic heat reactive strip to interrupt and indicate an overload current that can be reset after being tripped by the overload current. 
     Another object is to provide a circuit having a multi-metallic heat reactive strip snapped to a lamp to indicate a fault condition. 
     Another object is to provide a circuit having a multi-metallic heat reactive strip responding to overload current with snap action to activate a lamp. 
     Another object is to provide a circuit interrupter device having a multi-metallic heat reactive strip being snapped, or tripped to open a load circuit and close a light emitter circuit that visually indicates current overload and being reset to reestablish a closed circuit. 
     Another object of the invention provides a circuit interrupter including a snap-action multi-metallic heat reactive strip being reset and used in miniature circuitry in confining spaces. 
     Another object of the invention is to provide a circuit interrupter including a temperature-sensitive snap-action multi-metal strip to produce a visual indication of a fault condition by a lamp and being capable of being reset. 
     Another object is to provide a compact circuit interrupter device adaptable to miniaturization and having a multi-metallic heat reactive strip being snapped to open a load circuit and close a light emitter circuit to visually indicate current overload and capable of being reset to reestablish a closed circuit without spring loading structure of present circuit breaker designs. 
     These and other objects of the invention will become more readily apparent from the ensuing specification when taken in conjunction with the appended claims. 
     Accordingly, the present invention is a circuit interrupter for indicating and removing overload current from a load. A snap action multi-metallic heat reactive strip snaps from coupling current to a load circuit to a light emitter circuit when a predetermined magnitude of excessive, or overload current heats the multi-metal heat reactive strip. An indicator lamp in the light emitting circuit provides a visual indication of the overload condition. A manual push button engages the multi-metal heat reactive strip to reset and snap the strip back to coupling power to the load. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A more complete understanding of the invention and many of the attendant advantages thereto will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings wherein like reference numerals refer to like parts and wherein: 
     FIG. 1 is a schematic circuit diagram showing the multi-metallic heat reactive strip of the circuit interrupter device of the invention connecting current to a load during a normal operating condition. 
     FIG. 2 is a schematic circuit diagram showing the multi-metallic heat reactive strip of the circuit interrupter device of the invention connected to an indicator light in a light emitting circuit during a snapped, or tripped condition; and 
     FIGS. 3A,  3 B, and  3 C schematically show side, top, and bottom views of the package of the interrupter circuit device of the invention. 
     FIG. 4 shows side and top views of the multi-metallic heat reactive strip ( 14 ) in a disc shape. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1 and 2 of the drawings, circuit interrupter device  10  of this invention is coupled to a load circuit  20  to conduct current  22  from a source of electrical power  24  through electronic/electrical components and assemblies of a load  26 . Circuit interrupter device  10  prevents excessive, or overload currents in load circuit  20  from damaging the constituents of load  26  and, snaps to a light emitter circuit  30  of circuit interrupter device  10  that gives a visual indication that an overload current condition exists in load circuit  20 . 
     Circuit interrupter device  10  can be made in rectangularly-shaped modularized packages from off-the-shelf components and has elongate electrodes  11  that fit into mating sockets  21  of load circuit  20 . When electrodes  11  are plugged into sockets  21 , a conductor section  12  and a multi-metallic heat reactive strip  14  of circuit interrupter device  10  complete, or close load circuit  20 . 
     Multi-metallic heat reactive strip  14  snaps from one shape to another shape when a current that exceeds a predetermined magnitude is coupled to it and heats it sufficiently to cause its heat stressed condition to snap, or trip it to another shape. Heat reactive strips are well known and some widely used disc shaped strips have been formed into domed-shapes that snap to inverted domed-shaped configurations in response to changes in temperature. The simplicity of discs and their ease of manufacture are contributing factors for their widespread use. Accordingly, a disc-shaped multi-metallic heat reactive strip  14  can be made by pressing a flat disc of multi-metallic heat reactive material between steel dies until it assumes a desired domed configuration as shown in FIGS. 1 and 2. Other shapes for multi-metallic heat reactive strip  14  can be made, such as rectangular or tongue-shaped, for examples, as different applications may require. FIG. 4 shows strip  14  in a disc shape from a top and side view. 
     The dome-shaped multi-metallic heat reactive strip  14  of circuit interrupter device  10  along with conductor section  12  normally completes a closed circuit for current  22  from electrical power source  24  through electronic/electrical components and assemblies that make up load  26 . This is the normal operating condition shown in FIG.  1 . 
     When, however, dome-shaped multi-metallic heat reactive strip  14  becomes heated by current  22  that increases to excessive, or overload levels for one reason or another, multi-metallic heat reactive strip  14  is quickly stressed by the heat generated. The stresses generated by heating multi-metallic heat reactive strip  14  to the heated condition by currents that exceed a predetermined overload magnitude create the only forces used to snap multi-metallic heat reactive strip  14  into an inverted dome shape. The stressed multi-metallic heat reactive strip  14  that has snapped to the inverted dome shape opens load circuit  20  and virtually simultaneously closes light emitter circuit  30 , see FIG.  2 . Since the now-closed light emitter circuit  30  has an indicator lamp  32  serially connected to a current limiting resistor  34 , indicator lamp  32  provides an immediate visual indication that an overload condition has been created in load circuit  20  and that load circuit  20  is open. 
     Circuit interrupter device  10  provides a fusing function as described above that is clearly, visually indicated for appropriate action. However, circuit interrupter device  10  of this invention has a reset capability after cooling from its heated condition for reactivation of load circuit  20  with acceptable levels of current  22 . In other words, the light radiating from indicator lamp  32  will draw an operator&#39;s attention to load circuit  20  and appropriate action will be taken in regard to correcting or ignoring the excessive levels of current. Ignoring and resetting may be the right procedure, when, for example, a non-damaging, isolated stray transient current may have been created by a single isolated, non-repeatable incident. 
     After circuit interrupter  10  has cooled below the snap-action temperature of its heated condition, an operator pushes-in a push-button  16  of a reset push button mechanism  18  of circuit interrupter device  10  in the indicated arrow direction  18   a  to reset it. This reset is accomplished by displacing the inverted dome shape of multi-metallic heat reactive strip  14  via push button  16  until multi-metallic heat reactive strip  14  snaps to its previous dome shape as shown in FIG.  1 . The snapped multi-metallic heat reactive strip  14  opens light emitter circuit  30  to extinguish indicator lamp  32  by isolating it from power source  24  and virtually simultaneously closes load circuit  20  to permit its reactivation. 
     Under normal conditions, current  22  is within acceptable limits and circuit interrupter device  10  allows current  22  to flow through load  26 , and light emitter circuit  30  is isolated from power source  24 . When multi-metallic heat reactive strip  14  is tripped by increased overload levels of current  22 , it snaps quickly to open load circuit  20 , close light emitter circuit  30  through current limiting resistor  34  and light indicator lamp  32 . Once tripped, multi-metallic heat reactive strip  14  remains in the tripped condition due to its physical properties. Manually depressing push button  16  of push button mechanism  18  is required to return multi-metallic heat reactive strip  14  to its normal operating condition. 
     Circuit interrupter device  10  usually is reset by pressing and releasing reset push button  16  once multi-metallic heat reactive strip  14  has cooled below its snap action temperature. Optionally, multi-metallic heat reactive strip  14  can be reset in place as circuit interrupter device  10  is connected to load circuit  20 , or circuit interrupter device  10  can be removed from load circuit  20  by pulling electrodes  11  from sockets  21 , and strip  14  is reset. Then, circuit interrupter device  10  is returned and plugged into sockets  21  when the overload condition that caused the trip has been fixed. 
     Circuit interrupter device  10  can be modularized and miniaturized by current technologies in a compact environmentally resistant housing  40  as depicted in the side, top, and bottom views depicted in FIGS. 3A,  3 B, and  3 C, respectively. First and second electrodes  11  extend from the bottom of housing  40  and manual push button  16  of reset push button mechanism  18  and indicator lamp  32  of light emitter circuit  30  are prominently located to extend outwardly from the top surface. Selection of components from among contemporary fast acting miniature multi-metallic strips, miniature light emitting devices, and other constituents and interfacing them in compact rugged modular housing  40  for a job at hand can be readily done without requiring anything beyond ordinary skill. 
     Circuit interrupter device  10  of this invention can be fabricated compact enough to be used in many miniature circuit applications such as those found in automobile electrical systems, test instruments, domestic appliances and many other electronic/electrical circuits. Circuit interrupter device  10  answers the need for miniature fusing in tight, confining spaces and/or assemblies that have unusual shapes that restrict access. It also greatly reduces the problems inherent in the circuit breakers and fuse arrangements of the prior art that are associated with identifying overloaded circuits and tripped fusing devices in crowded, tight, or hard-to-get-at fuse panels, particularly under low light conditions. Additional benefits from using multi-metallic heat reactive strips  14  of the invention of circuit interrupter device  10  are that the fusing, status indicating, and resetting functions are performed without reliance on complicated and bulky spring loading structures like those used in many contemporary circuit breaker designs. Thus, circuit interrupter device  10  can be made more compactly and is further capable of miniaturization to help assure higher reliability for more of the tighter arrangements of electronic/electrical components and assemblies. 
     The disclosed components and their arrangements as disclosed herein all contribute to the novel features of this invention. Circuit interrupter device  10  of this invention provides a reliable and cost-effective means to improve the reliability and responsive operation of many electronic and electrical assemblies. Therefore, circuit interrupter device  10  as disclosed herein is not to be construed as limiting, but rather, is intended to be demonstrative of this inventive concept. 
     It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.