Abstract:
Fuse state indicators include temperature responsive elements adapted to visually display a number of different fuse states. The displays may include distinct colors and markings that are made visible or concealed from view based on temperature ranges that the fuse is exposed to in use. Various temperature sensitive elements and various markings are disclosed to convey at least three distinct fuse states to interested persons at the location of the fuse.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to fuses and, more particularly, to fuses with a fuse state indicator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features and aspects of the invention will be best understood with reference to the following description of certain exemplary embodiments of the invention, when read in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a plan view of a fuse comprising a fuse state indicator that responds to temperature in accordance with an exemplary embodiment; 
         FIG. 2  is a top view of a fuse comprising a fuse state indicator displaying a fuse state in accordance with an exemplary embodiment; 
         FIG. 3A  is a perspective view of a temperature sensitive element showing the light reflectance at one temperature in accordance with an exemplary embodiment; 
         FIG. 3B  is a perspective view of a temperature sensitive element showing the light reflectance at another temperature in accordance with an exemplary embodiment; 
         FIG. 4  is a plan view of a fuse comprising at least one fuse state indicator that responds to temperature in accordance with a second exemplary embodiment; 
         FIG. 5A  is a perspective view of a temperature sensitive element showing a plurality of thermochromic liquid crystals at one temperature in accordance with an exemplary embodiment; 
         FIG. 5B  is a perspective view of a temperature sensitive element showing a plurality of thermochromic liquid crystals at another temperature in accordance with an exemplary embodiment; 
         FIG. 6  is a top view of a fuse comprising a fuse state indicator displaying an off fuse state in accordance with an exemplary embodiment; 
         FIG. 7  is a top view of a fuse comprising a fuse state indicator displaying an on fuse state in accordance with an exemplary embodiment; 
         FIG. 8  is a top view of a fuse comprising a fuse state indicator displaying a too hot fuse state in accordance with an exemplary embodiment; 
         FIG. 9  is a top view of a fuse comprising a fuse state indicator displaying a short circuit and overload fuse state in accordance with an exemplary embodiment; 
         FIG. 10  is a top view of a fuse comprising a fuse state indicator displaying an on fuse state in accordance with an exemplary embodiment; 
         FIG. 11A  is a top view of a fuse comprising a fuse state indicator displaying an off fuse state in accordance with an exemplary embodiment; 
         FIG. 11B  is a top view of a fuse comprising a fuse state indicator displaying an on fuse state in accordance with an exemplary embodiment; 
         FIG. 12  is a plan view of a fuse comprising a fuse state indicator that responds to temperature in accordance with a third exemplary embodiment; and 
         FIG. 13  is a top view of a fuse comprising a fuse state indicator displaying a fuse state in accordance with an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  is a plan view of an exemplary embodiment of a fuse  10  comprising a fuse state indicator  12  that responds to heat being generated from the body of fuse  10 . The fuse  10  includes an insulative (i.e., nonconductive) fuse body  14  and conductive ferrules  16  attached thereto on either end thereof. The fuse state indicator  12  extends on an outer surface  18  of the fuse body  14  between the ferrules  16  and is not electrically connected to the ferrules  16 . The fuse body  14  is elongated in the direction of a longitudinal axis  20  and is generally cylindrical in the illustrated embodiment. It is appreciated that the benefits of the instant invention may also apply to non-cylindrical fuses, including but not limited to rectangular fuses, in alternative embodiments. Further, it is understood that the invention is applicable to a wide variety of fuses intended for a wide variety of applications and having a wide variety of fuse ratings. Therefore, the embodiments of the invention shown and described herein are for illustrative purposes only, and the invention is not intended to be restricted to a particular fuse type, class, or rating. 
     In an exemplary embodiment, the ferrules  16  are generally cylindrical and complementary in shape to the fuse body  14 . It is, however, appreciated that the benefits of the instant invention may also apply to non-cylindrical ferrules, including but not limited to rectangular ferrules, in alternative embodiments. 
     The fuse state indicator  12  comprises at least one temperature sensitive element  22  capable of undergoing a visible change upon being subjected to various temperature ranges. The temperature sensitive element  22  is adapted to visibly indicate the state of fuse  10 . The state of fuse  10  may be indicated as inoperable due to the fuse  10  not being installed properly or the circuit being off, operable within normal temperature limits, operable but exceeding normal temperature limits, and/or open fuse due to a short circuit or an overload. Other fuse states and other descriptions for the fuse states may be used in alternative embodiments without departing from the scope and spirit of the exemplary embodiment. The temperature sensitive element  22  may be employed as part of the fuse state indicator  12  coupled to the outer surface  18  of the fuse  10  or the temperature sensitive element  22  may be employed independently. The temperature sensitive element  22  is coupled to the outer surface  18  of the fuse body  14  between the ferrules  16  and is not electrically connected to the ferrules  16 . 
       FIG. 2  is a top view of a fuse  10  comprising a fuse state indicator  12  displaying a fuse state in accordance with an exemplary embodiment. As illustrated here, the fuse state indicator  12  comprises the temperature sensitive element  22 , which is capable of undergoing a visible change upon being subjected to various temperature ranges. In an exemplary embodiment, the visible change the temperature sensitive element  22  experiences comprises a plurality of color changes. These plurality of color changes are dependent upon the temperature ranges the temperature sensitive element  22  is exposed to. 
       FIG. 3A  is a perspective view of a temperature sensitive element  22  showing the light reflectance at one temperature in accordance with an exemplary embodiment. As illustrated here, the temperature sensitive element  22  comprises a transparent lens  30 , a plurality of thermochromic liquid crystals  32  adjacent to the transparent lens  30  and a backing layer  34  adjacent to the plurality of thermochromic liquid crystals  32 . 
     These thermochromic liquid crystals  32  are liquid crystals capable of displaying different colors at different temperature ranges. This color change is dependent on selective reflection of certain wavelengths by the crystallic structure of the material. This selective reflection occurs as the material changes between the low-temperature crystallic phase, through the anisotropic chiral or twisted nematic phase, to the high-temperature isotropic liquid phase. However, only the nematic mesophase has thermochromic properties, thereby restricting the effective operating temperature range of the material for experiencing a plurality of color changes. It is understood that the effective operating temperature range of the material may vary depending upon the type of thermochromic liquid crystal  32  selected. 
     The twisted nematic phase has the molecules oriented in layers with regularly changing orientation, which gives them periodic spacing. The light passing through the crystal undergoes Bragg diffraction on these layers, and the wavelength with the greatest constructive interference is reflected back. This reflected wavelength of light is perceived as a spectral color. 
     In  FIG. 3A , the thermochromic liquid crystals  32  are oriented in a first crystallic structure  35  according to the temperature the thermochromic liquid crystals  32  are experiencing. A light  36  is shown to pass through the first crystallic structure  35 , wherein a first reflected wavelength of light  38  is reflected back. Thus, the first reflected wavelength of light  38  experiences the greatest constructive interference. The first reflected wavelength of light  38  is associated with a viewer visualizing a first color that is associated with a fuse state. 
       FIG. 3B  is a perspective view of a temperature sensitive element  22  showing the light reflectance at another temperature in accordance with an exemplary embodiment. As the thermochromic liquid crystals  32  undergo changes in temperature, thermal expansion occurs, resulting in change of spacing between the layers, and therefore a change in the reflected wavelength of light. As illustrated here, the thermochromic liquid crystals  32  are oriented in a second crystallic structure  37  according to the temperature the thermochromic liquid crystals  32  are experiencing. A light  36  is shown to pass through the second crystallic structure  37 , wherein a second reflected wavelength of light  39  is reflected back. Thus, the second reflected wavelength of light  39  experiences the greatest constructive interference. The second reflected wavelength of light  39  is associated with a viewer visualizing a second color that is associated with another fuse state. 
     The color of the thermochromic liquid crystals  32  may therefore continuously range from black through the spectral colors to black again, depending on the temperature. A few examples of thermochromic liquid crystals include, but are not limited to, cholesteryl nonanoate and cyanobiphenyls. 
     Since fuses come in different sizes and have a variety of ratings, temperature ranges for the various states of fuse  10  may differ from one type of fuse to another. For example, one fuse may have a lower normal operating temperature range than another. Similarly, one fuse may have a lower short circuit or overload temperature range than another fuse. Thus, the type of thermochromic liquid crystal  32  that is used may depend upon the size and rating of the fuse. 
     Referring back to  FIG. 2 , the temperature element  22  may turn a first color during a first temperature range indicating that the fuse  10  is inoperable due to the fuse  10  not being installed properly or the circuit being off. When the temperature sensitive element  22  experiences a temperature falling within the first temperature range, the color change of the temperature sensitive element  22  may be reversible. The temperature element may change to a second color during a second temperature range indicating that the fuse  10  is operating within normal temperature limits. When the temperature sensitive element  22  experiences a temperature falling within the second temperature range, the color change of the temperature sensitive element  22  may be reversible. Additionally, the temperature element  22  may change to a third color during a third temperature range indicating that the fuse  10  is operating but exceeding normal temperature limits. When the temperature sensitive element  22  experiences a temperature falling within the third temperature range, the color change of the temperature sensitive element  22  may be reversible. Furthermore, the temperature element  22  may change to a fourth color during a fourth temperature range indicating that the fuse  10  is open due to a short circuit or an overload. When the temperature sensitive element  22  experiences a temperature falling within the fourth temperature range, the color change of the temperature sensitive element  22  may be irreversible. 
     Although only one color change per temperature range has been illustrated, other embodiments may include multiple color changes within a temperature range associated with one status of the fuse  10  without departing from the scope and spirit of the exemplary embodiment. 
     The fuse state indicator  12  may comprise lettering to describe the fuse  10  and the states of the fuse. The fuse state indicator  12  may also comprise a color chart for assisting an operator in identifying the meaning of the plurality of color changes. To further assist operators in analyzing the state of the fuse  10 , pocket cards comprising color charts may be provided to the operators. 
     Additionally, although the exemplary embodiment described above illustrates the fuse  10  comprising one temperature sensitive element  22 , multiple temperature sensitive elements  22  may be utilized without departing from the scope and spirit of the exemplary embodiment. 
       FIG. 4  is a plan view of a fuse comprising at least one fuse state indicator that responds to temperature in accordance with a second exemplary embodiment. The fuse  40  includes an insulative (i.e., nonconductive) fuse body  44  and conductive ferrules  46  attached thereto on either end thereof. The fuse state indicator  42  extends on an outer surface  48  of the fuse body  44  between the ferrules  46  and is not electrically connected to the ferrules  46 . The fuse body  44  is elongated in the direction of a longitudinal axis  50  and is generally cylindrical in the illustrated embodiment. It is appreciated that the benefits of the instant invention may also apply to non-cylindrical fuses, including but not limited to rectangular fuses, in alternative embodiments. Further, it is understood that the invention is applicable to a wide variety of fuses intended for a wide variety of applications and having a wide variety of fuse ratings. Therefore, the embodiments of the invention shown and described herein are for illustrative purposes only, and the invention is not intended to be restricted to a particular fuse type, class, or rating. 
     In an exemplary embodiment, the ferrules  46  are generally cylindrical and complementary in shape to the fuse body  44 . It is, however, appreciated that the benefits of the instant invention may also apply to non-cylindrical ferrules, including but not limited to rectangular ferrules, in alternative embodiments. 
     The fuse state indicator  42  comprises at least one temperature sensitive element  52  capable of undergoing a visible change upon being subjected to a particular temperature range. The temperature sensitive element  52  is adapted to visibly indicate the state of fuse  40 . The state of fuse  40  may be indicated as inoperable due to the fuse  40  not being installed properly or the circuit being off, operable within normal temperature limits, operable but exceeding normal temperature limits, and/or open fuse due to a short circuit or an overload. The temperature sensitive element  52  may be employed as part of the fuse state indicator  42  coupled to the outer surface  48  of the fuse  40  or the temperature sensitive element  52  may be employed independently. The temperature sensitive element  52  is coupled to the outer surface  48  of the fuse body  44  between the ferrules  46  and is not electrically connected to the ferrules  46 . 
     Referring now to  FIGS. 5A and 5B , the temperature sensitive element is illustrated and its operation is described hereinbelow in accordance with an exemplary embodiment.  FIG. 5A  is a perspective view of a temperature sensitive element  52  showing a plurality of thermochromic liquid crystals  54  at one temperature in accordance with an exemplary embodiment.  FIG. 5B  is a perspective view of a temperature sensitive element showing a plurality of thermochromic liquid crystals at another temperature in accordance with an exemplary embodiment. As illustrated in these Figures, the temperature sensitive element  52  comprises a transparent lens  53 , a plurality of thermochromic liquid crystals  54  adjacent to the transparent lens  53  and a backing layer  55  adjacent to the plurality of thermochromic liquid crystals  54 . 
     These thermochromic liquid crystals  54  are liquid crystals capable of changing its orientation from a first orientation  56 , wherein a substantial portion of the light does not pass through the layer of thermochromic liquid crystals  54 , to a second orientation  58 , wherein a substantial portion of the light passes through the layer of thermochromic liquid crystals  54 , and possibly back to the first orientation  56  upon exposure to various temperature ranges. When the thermochromic liquid crystals  54  are positioned in the second orientation  58 , the molecules are pointed mostly in the same direction. These orientational changes may be reversible or irreversible depending upon the thermochromic liquid crystals  54  used and/or the temperature ranges the thermochromic liquid crystals  54  are exposed to. 
     Referring now to  FIGS. 6-9 , the various states of the fuse  60  are illustrated. In the embodiment shown in  FIGS. 6-9 , a fuse state indicator  62  comprising four (4) temperature sensitive elements, an off status temperature sensitive element  64 , an on status temperature sensitive element  66 , a too hot status temperature sensitive element  68 , and a short circuit and overload status temperature sensitive element  70 , are illustrated. 
     Similar to the temperature sensitive element  52  illustrated in  FIGS. 5A and 5B , the off status temperature sensitive element  64  of  FIGS. 6-9  comprises a transparent lens  53 , a plurality of thermochromic liquid crystals  54  adjacent to the transparent lens  53 , a backing layer  55  adjacent to the plurality of thermochromic liquid crystals  54  and a first marking  65  coupled to the backing layer  55 , wherein the first marking  65  indicates that the fuse  60  is not installed properly or the circuit is off. Although this embodiment uses the word “off” as the first marking  65 , any marking may be used, including a particular color, e.g. black dot or square, or any other marking associated with an off status, without departing from the scope and spirit of the exemplary embodiment. The first marking  65  may be marked on the surface of the backing layer  55  or may be marked on a material directly or indirectly coupled to the backing layer  55 . 
     Similar to the temperature sensitive element  52  illustrated in  FIGS. 5A and 5B , the on status temperature sensitive element  66 , of  FIGS. 6-9 , comprises a transparent lens  53 , a plurality of thermochromic liquid crystals  54  adjacent to the transparent lens  53 , a backing layer  55  adjacent to the plurality of thermochromic liquid crystals  54  and a second marking  67  coupled to the backing layer  55 , wherein the second marking  67  indicates that the fuse  60  is in normal operation. Although this embodiment uses the word “on” as the second marking  67 , any marking may be used, including a particular color, e.g. green dot or square, or any other marking associated with an on status, without departing from the scope and spirit of the exemplary embodiment. The second marking  67  may be marked on the surface of the backing layer  55  or may be marked on a material directly or indirectly coupled to the backing layer  55 . 
     Similar to the temperature sensitive element  52  illustrated in  FIGS. 5A and 5B , the too hot status temperature sensitive element  68 , of  FIGS. 6-9 , comprises a transparent lens  53 , a plurality of thermochromic liquid crystals  54  adjacent to the transparent lens  53 , a backing layer  55  adjacent to the plurality of thermochromic liquid crystals  54  and a third marking  69  coupled to the backing layer  55 , wherein the third marking  69  indicates that the fuse  60  is operating at a temperature exceeding the temperature range of normal operation. Although this embodiment uses the word “too hot” as the third marking  69 , any marking may be used, including a particular color, e.g. red dot or square, or any other marking associated with a too hot status, without departing from the scope and spirit of the exemplary embodiment. The third marking  69  may be marked on the surface of the backing layer  55  or may be marked on a material directly or indirectly coupled to the backing layer  55 . 
     Similar to the temperature sensitive element  52  illustrated in  FIGS. 5A and 5B , the short circuit and overload status temperature sensitive element  70 , of  FIGS. 6-9 , comprises a transparent lens  53 , a plurality of thermochromic liquid crystals  54  adjacent to the transparent lens  53 , a backing layer  55  adjacent to the plurality of thermochromic liquid crystals  54  and a fourth marking  71  coupled to the backing layer  55 , wherein the fourth marking  71  indicates that the fuse  60  has experienced a short circuit or an overload. Although this embodiment uses a black dot as the fourth marking  71 , any marking may be used, including words, e.g. failed, or any other marking associated with a short circuit or overload status, without departing from the scope and spirit of the exemplary embodiment. The fourth marking  69  may be marked on the surface of the backing layer  55  or may be marked on a material directly or indirectly coupled to the backing layer  55 . 
       FIG. 6  is a top view of a fuse comprising a fuse state indicator displaying an off fuse state in accordance with an exemplary embodiment. When the fuse  60  is experiencing a temperature within a first temperature range, the thermochromic liquid crystals within the off status temperature sensitive element  64  orient to the second position, which is when the molecules point in mostly the same direction and allow the operator to view the first marking  65 . The thermochromic liquid crystals within the on status temperature sensitive element  66 , the too hot status temperature sensitive element  68 , and the short circuit and overload status temperature sensitive element  70  remain oriented in the first position, which prevents the operator from viewing the respective associated markings  67 ,  69 ,  71 . The orientation of the thermochromic liquid crystals of the off status temperature sensitive element  64  may be reversible when the temperature rises above the first temperature range. The fuse state indicator  62  registers the first marking  65 , which is “OFF” in this embodiment, when the fuse temperature falls below the minimum operating temperature. 
       FIG. 7  is a top view of a fuse comprising a fuse state indicator displaying an on fuse state in accordance with an exemplary embodiment. When the fuse  60  is experiencing a temperature within a second temperature range, the thermochromic liquid crystals within the on status temperature sensitive element  66  orient to the second position, which is when the molecules point in mostly the same direction and allow the operator to view the second marking  67 . The thermochromic liquid crystals within the off status temperature sensitive element  64 , the too hot status temperature sensitive element  68 , and the short circuit and overload status temperature sensitive element  70  remain oriented in the first position, which prevents the operator from viewing the respective associated markings  65 ,  69 ,  71 . The orientation of the thermochromic liquid crystals of the on status temperature sensitive element  66  may be reversible when the temperature rises above the second temperature range or falls below the second temperature range. The fuse state indicator  62  registers the second marking  67 , which is “ON” in this embodiment, when the fuse temperature is within normal operating temperature range. 
       FIG. 8  is a top view of a fuse comprising a fuse state indicator displaying a too hot fuse state in accordance with an exemplary embodiment. When the fuse  60  is experiencing a temperature within a third temperature range, the thermochromic liquid crystals within the too hot status temperature sensitive element  68  orient to the second position, which is when the molecules point in mostly the same direction and allow the operator to view the third marking  69 . The thermochromic liquid crystals within the off status temperature sensitive element  64 , the on status temperature sensitive element  66 , and the short circuit and overload status temperature sensitive element  70  remain oriented in the first position, which prevents the operator from viewing the respective associated markings  65 ,  67 ,  71 . The orientation of the thermochromic liquid crystals of the too hot status temperature sensitive element  68  may be reversible when the temperature rises above the third temperature range or falls below the third temperature range. The fuse state indicator  62  registers the third marking  69 , which is “TOO HOT” in this embodiment, when the fuse temperature has elevated above normal operating temperature but below short circuit and overload temperature range. The third marking  69  registering would warn of possible upcoming failure to the fuse  60  due to extended thermal stress. 
       FIG. 9  is a top view of a fuse comprising a fuse state indicator displaying a short circuit and overload fuse state in accordance with an exemplary embodiment. When the fuse  60  is experiencing a temperature within a fourth temperature range, the thermochromic liquid crystals within the short circuit and overload status temperature sensitive element  70  orient to the second position, which is when the molecules point in mostly the same direction and allow the operator to view the fourth marking  71 . The thermochromic liquid crystals within the off status temperature sensitive element  64 , the on status temperature sensitive element  66 , and the too hot status temperature sensitive element  68  remain oriented in the first position, which prevents the operator from viewing the respective associated markings  65 ,  67 ,  69 . The orientation of the thermochromic liquid crystals of the short circuit and overload status temperature sensitive element  70  may be irreversible once the temperature falls within the fourth temperature range. Additionally, once the fuse  60  experiences a short circuit or overload status, the fuse  60  eventually cools to a temperature within the first temperature range, resulting in the thermochromic liquid crystals within the off status temperature sensitive element  64  orienting to the second position, which allows the operator to view the first marking  65 . The fuse state indicator  62  registers the fourth marking  71 , which is “a black dot” in this embodiment, when the fuse temperature has elevated to within the short circuit or overload temperature range. Thus, once the fuse  60  experiences a short circuit or an overload and after a period of time has elapsed for the fuse  60  to cool down, the fuse state indicator  62  registers the first marking  65  and the fourth marking  71 . 
       FIG. 10  is a top view of a fuse comprising a fuse state indicator displaying an on fuse state in accordance with an exemplary embodiment. The embodiment shown here is similar to the embodiments illustrated in  FIGS. 4-9 , except that the positioning of the off status temperature sensitive element  64 , the on status temperature sensitive element  66 , and the too hot status temperature sensitive element  68  is vertical, instead of horizontal. It should be understood that the position of the temperature sensitive elements may be in any position, including, but not limited to, horizontal, vertical, diagonal, zigzag, staggered or any other position, which is capable of being viewed by an operator once installed without departing from the scope and spirit of the exemplary embodiment. 
     Referring now to  FIGS. 11A and 11B , a top view of a fuse comprising a fuse state indicator displaying a fuse state is described hereinbelow.  FIG. 11A  is a top view of a fuse comprising a fuse state indicator displaying an off fuse state in accordance with an exemplary embodiment.  FIG. 11B  is a top view of a fuse comprising a fuse state indicator displaying an on fuse state in accordance with an exemplary embodiment. This embodiment may only indicate an on status and an off status. 
     The thermochromic liquid crystals used in this embodiment operate similarly to the thermochromic liquid crystals used in the embodiments illustrated in  FIGS. 4-10 . The fuse  110  comprises a fuse state indicator  112  comprising a temperature sensitive element  114  capable of undergoing a visible change upon being subjected to a particular temperature range. The temperature sensitive element  114  is adapted to visibly indicate the state of fuse  110 . In this embodiment, the state of fuse  110  may be indicated as inoperable or operable. The temperature sensitive element  114  may be employed as part of the fuse state indicator  112  coupled to an outer surface  118  of the fuse  110  or the temperature sensitive element  114  may be employed independently. The temperature sensitive element  114  is coupled to the outer surface  118  of the fuse  110  between the ferrules  116  and is not electrically connected to the ferrules  116 . 
     Similar to the temperature sensitive element  52  illustrated in  FIGS. 5A and 5B , the temperature sensitive element  114 , illustrated in  FIGS. 11A and 11B , comprises a transparent lens  53 , a plurality of thermochromic liquid crystals  54  adjacent to the transparent lens  53 , a backing layer  55  adjacent to the plurality of thermochromic liquid crystals  54  and a fifth marking  119  coupled to the backing layer  55 , wherein the fifth marking  119  indicates that the fuse  110  is operational. Although this embodiment uses the word “on” as the fifth marking  119 , any marking may be used, including a particular color, e.g. green dot or square, or any other marking associated with an on status, without departing from the scope and spirit of the exemplary embodiment. The fifth marking  119  may be marked on the surface of the backing layer  55  or may be marked on a material directly or indirectly coupled to the backing layer  55 . 
     The temperature sensitive element  114  operates similarly to the temperature sensitive element of  FIGS. 5A and 5B . However, in this embodiment the thermochromic liquid crystals are positioned in the first orientation, wherein a substantial portion of the light does not pass through the layer of thermochromic liquid crystals, when exposed to a first temperature range. Furthermore, the thermochromic liquid crystals are positioned in the second orientation, wherein a substantial portion of the light does pass through the layer of thermochromic liquid crystals, when exposed to a temperature range other than the first temperature range. The orientation of the thermochromic liquid crystals of the temperature sensitive element  114  may be reversible. 
     In an alternate embodiment of that described in  FIGS. 4-10 , the thermochromic liquid crystals described in  FIGS. 1-3  may be used in lieu of the thermochromic liquid crystals used in  FIGS. 4-10 . In certain alternative embodiments, four (4) distinct kinds of thermochromic liquid crystal may be used for each of the four (4) temperature sensitive elements. A first thermochromic liquid crystal may be used for the off status temperature sensitive element  64 , wherein the first thermochromic liquid crystal changes color only when exposed to the first temperature range. A second thermochromic liquid crystal may be used for the on status temperature sensitive element  66 , wherein the second thermochromic liquid crystal changes color only when exposed to the second temperature range. A third thermochromic liquid crystal may be used for the too hot status temperature sensitive element  68 , wherein the third thermochromic liquid crystal changes color only when exposed to the third temperature range. The color changes associated with the off status temperature sensitive element  64 , the on status temperature sensitive element  66 , and the too hot status temperature sensitive element  68  may be reversible when the temperature sensitive elements  64 ,  66 ,  68  fall outside of the first temperature range, the second temperature range, and the third temperature range, respectively. Furthermore, a fourth thermochromic liquid crystal may be used for the short circuit and overload status temperature sensitive element  70 , wherein the fourth thermochromic liquid crystal changes color only when exposed to the fourth temperature range. The color change associated with the short circuit and overload status temperature sensitive element  70  may be irreversible once the short circuit and overload status temperature sensitive element  70  is exposed to the fourth temperature range. 
       FIG. 12  is a plan view of a fuse  120  comprising a fuse state indicator  122  that responds to temperature in accordance with a third exemplary embodiment. The fuse  120  includes an insulative (i.e., nonconductive) fuse body  124  and conductive ferrules  126  attached thereto on either end thereof. The fuse state indicator  122  extends on an outer surface  128  of the fuse body  124  between the ferrules  126  and is not electrically connected to the ferrules  126 . The fuse body  124  is elongated in the direction of a longitudinal axis  130  and is generally cylindrical in the illustrated embodiment. It is appreciated that the benefits of the instant invention may also apply to non-cylindrical fuses, including but not limited to rectangular fuses, in alternative embodiments. Further, it is understood that the invention is applicable to a wide variety of fuses intended for a wide variety of applications and having a wide variety of fuse ratings. Therefore, the embodiments of the invention shown and described herein are for illustrative purposes only, and the invention is not intended to be restricted to a particular fuse type, class, or rating. 
     In an exemplary embodiment, the ferrules  126  are generally cylindrical and complementary in shape to the fuse body  124 . It is, however, appreciated that the benefits of the instant invention may also apply to non-cylindrical ferrules, including but not limited to rectangular ferrules, in alternative embodiments. 
     The fuse state indicator  122  comprises at least one temperature sensitive element  132  capable of undergoing a visible change upon being subjected to a particular temperature range. The temperature sensitive element  132  is adapted to visibly indicate the state of fuse  120 . The state of fuse  120  may be indicated as inoperable, operable and/or open fuse due to short circuit or overload. The temperature sensitive element  132  may be employed as part of the fuse state indicator  122  coupled to the outer surface  128  of the fuse  120  or the temperature sensitive element  132  may be employed independently. The temperature sensitive element  132  is coupled to the outer surface  128  of the fuse body  124  between the ferrules  126  and is not electrically connected to the ferrules  126 . 
       FIG. 13  is a top view of a fuse  120  comprising a fuse state indicator  122  displaying a fuse state in accordance with an exemplary embodiment. As illustrated here, the fuse state indicator  122  comprises the temperature sensitive element  132 , which is capable of undergoing a visible change upon being subjected to a particular temperature range. The temperature sensitive element may comprise at least one material selected from a group consisting of thermochromic liquid crystals, thermochromic ink, thermochromic paint, thermal paper, thermal calibrated wax, mercury thermometer, and infrared technology, which are capable of indicating a fuse state upon exposure to a particular temperature range. 
     Thermochromic inks or dyes are temperature sensitive compounds that temporarily change color with exposure to heat. When using the thermochromic inks or dyes, the color of the ink may change when exposed to the heat generated from the fuse  120  while the fuse  120  is operating. However, when the fuse  120  is not operating, either due to an open fuse, a fuse that has been installed improperly or an open circuit, the color of the ink may be its original color. This color change may be reversible and may allow an operator to easily diagnose the state of the fuse  120 . 
     Thermochromic paints are temperature sensitive pigments that temporarily change color with exposure to heat. After absorbing a certain amount of light or heat, the crystallic or molecular structure of the pigment reversibly changes in such a way that it absorbs and emits light at a different wavelength than at lower temperatures. When using the thermochromic paints, the color of the paint may change when exposed to the heat generated from the fuse  120  while the fuse  120  is operating. However, when the fuse  120  is not operating, either due to an open fuse, a fuse that has been installed improperly or an open circuit, the color of the paint may be its original color. This color change may be reversible and may allow an operator to easily diagnose the state of the fuse  120 . 
     Thermal papers comprise temperature sensitive chemical that change color with exposure to heat. One example of a thermal paper includes paper impregnated with a solid mixture of a fluoran dye with octadecylphosphonic acid. This mixture is stable in solid phase. However, when the octadecylphosphonic acid is melted, the dye undergoes chemical reaction in the liquid phase, and assumes the protonated colored form. Since this color change may not be reversible, the thermal paper may be used to indicate a short circuit or an overload. There may be some color change during normal operation, but the intensity of the color change may increase as the temperature rises into the temperature range associated with a short circuit or an overload. 
     The fuse state indicator  122  may comprise lettering to describe the fusel  20  and the fuse states. The fuse state indicator  122  may also comprise a color chart for assisting a user in identifying the meaning of the color change. To further assist operators in analyzing the status of the fuse  120 , pocket cards comprising color charts may be provided to the operators. 
     Additionally, although the exemplary embodiment described above illustrates the fuse  120  comprising one temperature sensitive element  132 , multiple temperature sensitive elements  132  may be utilized without departing from the scope and spirit of the exemplary embodiment. 
     Furthermore, although some exemplary embodiments have been described above, it is envisioned that the various temperature sensitive elements that have been described may be used alternatively in lieu of one another or in combination with each other without departing from the scope and spirit of the invention. 
     In an exemplary embodiment, the 80% current fuse tube temperatures may range from about 35° C. to about 65° C. depending upon the location of the measurement. Additionally, the 500% overload fuse tube temperatures may range from about 45° C. to about 90° C. depending upon the location of the measurement. However, at a particular location, e.g. location of the temperature sensitive element, the temperatures may be more consistent. It should be understood that these ranges may differ among different fuse types, classes and ratings without departing from the scope and spirit of the exemplary embodiment. 
     In some embodiments, the temperature sensitive element may change colors from green to black at the set temperature point and may remain black when the temperature increases beyond the set temperature point. However, it should be understood that the temperature sensitive element may change colors from any color to any other color without departing from the scope and spirit of the exemplary embodiment. 
     Although the invention has been described with reference to specific embodiments, these descriptions are not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention will become apparent to persons skilled in the art upon reference to the description of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiments disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. It is therefore, contemplated that the claims will cover any such modifications or embodiments that fall within the scope of the invention.