Abstract:
An apparatus for indicating the proper seating of a high voltage fuse in its mounting assembly in connection with electrical switchgear utlilizes a spring loaded flag positioned adjacent a latching protrusion for engagement by the latch of the mounting assembly such that the flag is moved from an obscured position to an visible position only when the latch is in its affirmatively locked position.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This patent application is based on U.S. provisional patent application No. 60/500,891, that was filed on Sep. 5, 2003.  
         [0002]     The present invention relates to the field of electrical switchgear and more particularly to the field of switchgear fuses. In even greater particularity the present invention relates to an indicator mounted on a fuse housing body to give a visual indication that the fuse has been properly latched into the fuse mounting structure.  
         [0003]     Fuses for electrical switchgear are typically attached to fuse handling hardware including an interrupter body at a first end and a pull ring assembly a the opposite end. The hardware is configured to positively support the fuse on a fuse mounting assembly which is often times pivotally mounted on a door or carrier such as within the switchgear housing. The interrupter body is generally configured to engage a latching mechanism which is part of the fuse mounting assembly. A set of “ears” are formed on the outside of the interrupter body and have a cam like surface inclined away from the axis of the fuse and body. The fuse and interrupter body are generally pivotally mounted within the mounting assembly such that as the interrupter body pivots to move the fuse into its proper position a spring loaded latch moves up the cam surface until the surface abruptly ends at a shoulder extending outwardly from the body, whereupon the latch is urged and against the interrupter body and helps to secure the fuse in the mounting assembly such that the entire assembly may be rotated into position to complete the electrical connection. The manipulation of the fuse is often accomplished with hotsticks or insulated gear as a safety precaution.  
         [0004]     Occasionally the fuse and interrupter are not actually moved to a latched position in as much as the pull ring end of the fuse also engages an electrical contact and some times the fuse only appears to be latched in the mounting assembly due to frictional resistance of the latch or at the pull ring end. Improper seating of the fuse can lead to fuse failure and failure of the phase of the switchgear associated with the fuse. Accordingly, a need exists for an indicator that will visibly identify the fuse as being properly seated in the fuse mounting assembly.  
       SUMMARY OF THE PRESENT INVENTION  
       [0005]     It is the object of this invention to improve the reliability of fuses used in electrical switchgear.  
         [0006]     Another object of the present invention is to give a person installing a fuse in electrical switchgear an indication that the fuse is affirmatively latched into place.  
         [0007]     Yet another object of the invention is to provide a visual cue that the latching mechanism has engaged when a switchgear fuse is installed.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]     Apparatus embodying features of the present invention are depicted in the accompanying drawings which form a portion of this disclosure and where in:  
         [0009]      FIG. 1  is a perspective view showing a fuse holder body with a visual indicator mounted there to.  
         [0010]      FIG. 2  is a second perspective view of a fuse holder body with a visual indicator mounted thereto.  
         [0011]      FIG. 3  is a detailed view of the indicator mounted to the fuse holder body.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0012]     Referring to the drawings for a clearer understanding of the invention, it may be seen that the present invention finds its application in conjunction with a fuse  11  of the type used in high-voltage switchgear. As is well known in the art the fuse  11  is a replaceable unit which is mated to a reusable end piece  12  and a reusable fuse holder body  13 . The end-piece  12  provides electrical connection between the fuse and a mounting bracket connected to the high-voltage circuit. The fuse holder  13 , is the primary mounting structure for securing the fuse  11  in a fuse mounting bracket  14  as a part of a fuse mounting assembly  16 . The fuse mounting assembly  16  is preferentially on a hinged door  17  that allows the mounting assembly and fuse to be moved as a unit into and out of engagement with the protected electrical circuit.  
         [0013]     Fuse holder  13  is made from a molded polyester and typically includes a body  21  closed at one end  22  and tapped at that end for appropriate electrical connections. The other end is open and receives the fuse  11  therein. A radially extending annular flange  23  circumscribes the open end, however, one side of the body  21  is slotted from the open end to near the closed end  22 . Adjacent the slot are a pair of protrusions  24  formed to cooperatively engage a latch  25  included in mounting assembly  16 . The protrusions  24  form an inclined face  26  which flares outwardly from the body  21  away from flange  23  and terminates in a face  28 , which is normal to body  21 . In practice the resiliently mounted latch  25  of the fuse mounting assembly is cammed outwardly by relative motion between itself and inclined surface  26  until the latch  25  passes over protrusion  24  to latch behind normal face  28 . The present invention is intended to provide a visible indication that such latching actually occurs and that the latch  25  is not left engaging only inclined face  26 .  
         [0014]     An aperture is formed in normal face  28  and a thermo-bonded threaded insert  32  is affixed into the aperture. A threaded fastner  34  with a torsion spring  36  coaxially placed thereon passes through a link  38  and threadedly engaged in insert  32 . Link  38  is thus mounted for rotation about an axis parallel to the central axis of fuse holder  13  and has a first end  41  which extends beyond the normal face  28  of protrusion  24 . A second end  43  of link  38  is shorter as measured from the pivot axis and moves in an arc across normal surface  28 . Spring  36  biases the link  38  such that first end  41  is biased toward the body  21  of fuse holder  13 . Accordingly first end  38  is behind flange  23  in its biased position. Preferentially first end  41  will carry an extension  45  which is perpendicular to link  38  and has a colored face or flag  47  having a dimension such that the flag is obscured by flange  23  when link  38  is biased toward the body  21  by spring  36 .  
         [0015]     In operation when the latch  25  is cammed over protrusion  24  and falls behind normal surface  36 , it displaces second end  43  against the bias of the spring  36  such that first end  41  is pivoted away from body  21  and the flag  47  is moved outwardly from body  21  beyond flange  23  such that it becomes visible by the worker installing the fuse.  
         [0016]     In an alternative embodiment, the presence of flange  23  is irrelevant, rather a fan shaped indicator  51  is pivotally attached to normal surface  36  near the apex of indicator  51 . Indicator  51  has an outer edge  53  and an inner edge  54  which are separated by an internal arc of nearly 90°. Spring  35  biases the indicator  51  such that inner edge  54  is urged toward the intersection of normal surface  28  and inclined surface  26 , thus outer edge  53  is aligned with or just inside the outer edge of normal surface  28  and therefore. Indicator  51  is the same color as holder  13  over the surfaces thereiof other than the face abutting and adjacent normal surface  28  which is distinctly colored to serve as a flag  57 . Thus when the inner edge is biased toward the inclined face and the outer edge in inward of the edge of normal surface  28 , there is no contrast of color visible. When latch  25  is properly seated behind normal surface  28 , it abuts inner edge  54  and urges it away from the junction of the normal and inclined surfaces, thereby causing outer edge  56  to extend beyond the lateral edge of normal surface  28  and exposing distinctively colored flag  57  to be exposed to the view of the worker installing the fuse. As may be seen, this embodiment may be used on fuse holders where flange  23  is too narrow or not present or does not provide adequate obscuration of flag  47 .  
         [0017]     The invention has been described with reference to two embodiments by way of illustration and not limitation, rathter the invention is limited only by the scope of the appended claims.