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BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a door latch system for a door of a switchgear enclosure and more particularly to a door latch system for a door of a switchgear enclosure wherein all the components of the door latch system are located outside the door for ease of repair. 
     2. Description of the Related Art 
     The terms switchgear and switchboard are general terms which cover metal enclosures which house switching and interrupting devices such as fuses, circuit breakers, relays, inner connections and supporting structures, including assemblies of these devices with associated fuses, interconnections and support structures used for the distribution of electric power. 
     Most switchgears presently produced include an exhaust system for venting gas and debris particles generated by an electric arc under arc-fault conditions. During an arc-fault explosion, the temperature and pressure inside the switchgear increase very rapidly and the rapid pressure build-up can damage the switchgear and its components. Exhaust systems such as that disclosed in US Published Patent Applications US 2009/0212022 and 2010/0258532 are designed to vent the gas and debris particles from the switchgear enclosure during an arc-fault explosion. Even though the venting systems of the prior art perform generally satisfactorily, the doors of the switchgear enclosure are subjected to large internal pressures which may cause the doors to “blow” open thereby subjecting workers in the area to possible injury. 
     Door latch systems have been previously provided in an attempt to prevent the enclosure doors from opening during an arc-fault explosion. However, the components of the prior art door latch systems are located within the door or within the enclosure at the inside surface of the door. If one of the components of the prior art door latch system should fail, it is impossible, or very difficult, to open the door to gain access to the failed component. In such a situation, it may be necessary to cut a large hole in the door to gain access to the failed component so that the door may be opened to perform the necessary repairs on the door. 
     SUMMARY OF THE INVENTION 
     This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key aspects or essential aspects of the claimed subject matter. Moreover, this Summary is not intended for use as an aid in determining the scope of the claimed subject matter. 
     A door latch system is provided for the doors of a switchgear enclosure. The doors of the switchgear may be of the walk-in type or the non-walk-in type. The doors of the switchgear enclosure of the non-walk-in type will usually be located in the front panel of the enclosure. If the door or doors are of the walk-in type, the door or doors will usually be located in the rear panel of the enclosure. In the present invention, the only difference between the door latch systems utilized with the walk-in type and the non-walk-in type doors is that in the walk-in type door latch system, a door jamb may be bolted to the rear panel which extends around the door opening. 
     This summary will be directed to the door latch system for the walk-in type door. A door opening is provided in the rear panel of the switchgear enclosure which has an upper edge, a lower edge, a first side edge and a second side edge. An optional jamb is welded to the exterior surface of the rear panel around the door opening and includes an upper jamb member, a lower jamb member, a first side jamb member and a second side jamb member. A door is provided which includes an upper end, a lower end, a first side, a second side, an inner surface and an outer surface. The door in the rear panel will be described as if the optional jamb is not utilized. 
     The first side of the door is hingedly secured to the rear panel adjacent the first side edge of the door opening, about a vertical axis, by a plurality of vertically spaced-apart first hinges. A plurality of externally threaded studs are secured to the rear panel adjacent the second edge of the door opening and extend outwardly therefrom in a vertically spaced-apart manner. A plurality of second hinges are provided each of which includes a first part and a second part which are pivotally secured together by a vertically disposed pivot pin. The first part of each of the second hinges is secured to the outer end of one of the studs which extend from the rear panel adjacent the second side edge of the door opening. The second part of each of the second hinges is secured to an elongated and vertically disposed angle member having first and second walls which are transversely disposed with respect to one another. The second part of each of the second hinges is secured to the first wall of the angle member. The angle member is selectively movable between latched and unlatched positions. 
     A plurality of vertically spaced-apart door latches, having inner and outer ends are secured to the angle member for movement therewith and extend horizontally therefrom. At least one of the door latches has a handle associated therewith. Each of the door latches has a latch pin opening formed therein outwardly of the inner end thereof. 
     A vertically-disposed and generally channel-shaped door latch housing is secured to the outside surface of the door adjacent the second side thereof. The housing defines an interior compartment having upper and lower ends. A latch handle is pivotally mounted on the housing which is movable between latched and unlatched positions. The latch handle includes a shaft which extends into the interior compartment of the housing. The housing has a plurality of vertically spaced-apart and horizontally disposed slots formed therein. 
     A plurality of first latch plate assemblies are secured to the housing in the interior compartment thereof in a vertically spaced-apart manner between the shaft of the latch handle and the upper end of the housing. Each of the first latch plate assemblies includes vertically spaced-apart and horizontally disposed upper and lower latch plates. Each of the upper and lower latch plates of the first latch plate assemblies have first and second openings formed therein. 
     A plurality of second latch plate assemblies are secured to the housing in the interior compartment thereof in a vertically spaced-apart manner between the shaft of the latch handle and the lower end of the housing. Each of the second latch plate assemblies includes vertically spaced-apart and horizontally disposed upper and lower latch plates. Each of the upper and lower latch plates of the second latch plate assemblies have first and second openings formed therein. 
     A first elongated actuator rod, having upper and lower ends, has its lower end coupled to the shaft of the latch handle and extends upwardly therefrom through the first openings in the upper and lower latch plates of the first latch plate assemblies. A second elongated actuator rod, having upper and lower ends, has its upper end coupled to the shaft of the latch handle and extends downwardly therefrom through the first openings in the upper and lower latch plates of the second latch plate assemblies. The pivotal movement of the latch handle from its unlatched position to its latched position causes the first actuator rod to move upwardly and causes the second actuator rod to move downwardly. The pivotal movement of the latch handle from its latched position to its unlatched position causes the first actuator rod to move downwardly and causes the second actuator rod to move upwardly. 
     A plurality of first latch pin assemblies are mounted on the first actuator rod in a vertically spaced-apart manner with each of the first latch pin assemblies having a latch pin extending vertically upwardly therefrom. The movement of the latch handle from its unlatched position to its latched position causes the latch pins of the first latch pin assemblies to move upwardly with the first actuator rod so as to be received by the second openings in the upper and lower latch plates of the first latch plate assemblies. 
     A plurality of second latch pin assemblies are mounted on the second actuator rod in a vertically spaced-apart manner with each of the second latch pin assemblies having a latch pin extending vertically downwardly therefrom. The movement of the latch handle from its unlatched position to its latched position causes the latch pins of the second latch pin assemblies to move downwardly with the second actuator rod so as to be received by the second openings in the upper and lower latch plates of the second latch plate assemblies. 
     The door may be moved to its closed position when the angle member is in its unlatched position. The latch handle is then moved to its unlatched position if not already done so. The angle member is then moved to its latched position which causes the latches secured thereto to move into the interior compartment by way of the slots formed in the housing. The latch pin openings of the latches are then vertically aligned with the latch pins of the first and second latch pin assemblies. At that time, the second wall of the angle member is pressed against the outside surface of the door. The latch handle is then moved to its latched position which causes the latch pins to be moved into the second openings of the upper and lower latch plates of the first and second latch plate assemblies to securely latch the door in its closed and latched position. 
     During use, if any of the components of the door latching system should fail and require repair while the door is closed, the components are easily reached since all components are located at the outer side of the door. 
     It is a principal object of the invention to provide an improved switchgear door latch system. 
     A further object of the invention is to provide a switchgear door latching system which locks the door of the switchgear enclosure from the outer side thereof. 
     A further object of the invention is to provide a switchgear door latch system wherein all of the components of the system are located at the outer side of the door. 
     A further object of the invention is to provide a switchgear door latch system which will prevent the door of the switchgear enclosure from opening during an arc-fault explosion. 
     A further object of the invention is to provide a switchgear door latch system which may be used with practically any size door. 
     A further object of the invention is to provide a switchgear door latch system which is durable in use. 
     These and other objects will be apparent to those skilled in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Non-limiting and non-exhaustive embodiments of the present invention are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified. 
         FIG. 1  is a front perspective view of a switchgear enclosure; 
         FIG. 2  is a perspective view of a support which extends around the door opening; 
         FIG. 3  is a perspective view of the door latch system of this invention associated with a door in the rear panel of the switchgear enclosure; 
         FIG. 4  is a perspective view of one of the latches of this invention which has a handle associated therewith; 
         FIG. 5  is a perspective view of a latch utilized in the system; 
         FIG. 6  is a partial exploded perspective view of a portion of the door latch system; 
         FIG. 7  is a perspective view of the door latch system; 
         FIG. 8  is a partial elevational view of the inside of the housing portion of the door latch system and a portion of the latching mechanism therein; 
         FIG. 9  is a partial perspective view of the lower portion of the housing positioned at the outside surface of the door; 
         FIG. 10  is a partial perspective view of the portion of the housing and associated latching structure; and 
         FIG. 11  is a partial sectional view illustrating the manner in which the door latch system functions. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Embodiments are described more fully below with reference to the accompanying figures, which form a part thereof and show, by way of illustration, specific exemplary embodiments. These embodiments are disclosed in sufficient detail to enable those skilled in the art to practice the invention. However, embodiments may be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. The following detailed description is, therefore, not to be taken in a limiting sense in that the scope of the present invention is defined only by the appended claims. 
     The numeral  10  refers to a conventional switchgear including an enclosure  12  having an upper end  14 , lower end  16 , front panel  18 , side panels  20  and  22 , and rear panel  24 . The numeral  26  refers to doors of non-walk-in type which are normally hingedly mounted on the front panel  18  and which may have various dimensions. Each of the doors  26  extend over a door opening  27  formed in front panel  18 . The numeral  28  refers to a door of the walk-in type which is normally utilized on the rear panel  24  to close the door opening formed therein. Each of the doors  26  and  28  have the door latch system of this invention associated therewith which is referred to by the reference numeral  30 . As seen in the drawings, the doors  26  may have the door latch system mounted at either the right side of the door or the left side of the door opposite to the supporting hinges of the door. For illustration purposes, the door  26 A at the upper right side of front panel  18  will be described in detail. 
     For purposes of description, the door opening  27 , which is closed by door  26 A, will be described as having an upper edge  32 , lower edge  34 , first side edge  36  and second side edge  38 . Preferably, a metal support or lip  40  extends from panel  18  around door opening  27  as seen in  FIG. 2 . A resilient seal  42  is mounted on the lip  40  as seen in  FIG. 11  and extends completely therearound. 
     Preferably, the upper, lower and side edges of door  26 A are provided with an inwardly directed flange  44  as seen in  FIG. 11 . For purposes of description, the doors  26  will be described as having an upper end  46 , lower end  48 , first side  50 , second side  52 , inner surface  54  and outer surface  56 . 
     Door  26  is hingedly secured at its first side  50  to the outer surface  56  thereof by a plurality of vertically spaced-apart hinges  58 . The hinges  58  have one part thereof screwed or bolted to panel  18  and the other part thereof screwed or bolted to door  26 A at side  50  thereof about vertical axes in conventional fashion. The doors  26  are movable between open and closed positions. 
     A plurality of threaded studs  60  are secured to and extend from panel  18  in a vertically spaced and horizontally disposed manner and have lock nuts  62  threadably mounted thereon. The numeral  64  refers to a hinge which is secured to each of the studs  60 . Each of the hinges  64  include a bearing-like part  66  which is threadably secured to the outer end of the associated stud  60  and has a vertically disposed opening  68  extending therethrough. Hinge  64  also includes a part  70  having a head  72  and a stud  74  extending therefrom. Head  72  has an opening extending upwardly thereinto from the lower side thereof. Hinge  64  further includes a part  70 ′ which is identical to part  70 . Part  70 ′ includes a head  72 ′ and a stud  74 ′. Head  70 ′ has an opening  76 ′ formed therein which partially extends into head  72 ′. Parts  70  and  70 ′ are identical but are reversed with respect to one another. A washer  78  is positioned on the upper side of part  66  of said washer  80  and is positioned at the underside of part  66 . Pivot or hinge pin  82  is positioned in opening  68  of part  66 . Part  70  is positioned so that the upper end of hinge  82  is rotatably received by the opening in the underside of head  72  of part  70 . Part  70 ′ is positioned so that the lower end of hinge pin  82  is rotatably received by openings  76 ′ in head  72 ′ of part  70 ′. The parts of the hinges  64  are held together by the fact that the studs  74  and  74 ′ are received by openings  84  and  86  formed in an elongated angle member  88  and held therein by nuts  87  and  89  respectively. Angle member  88  will be described as having an upper end  90  and a lower end  92  with transversely disposed walls  94  and  96 . A plurality of horizontally disposed latches  98  are secured to angle member  88  by welding or the like in a vertically spaced-apart manner. Each of the latches  98  have an elongated latch pin opening  100  formed therein. One of the latches  98  has a handle  102  extending therefrom. 
     The numeral  104  refers to a channel-shaped latch housing having flanges  106  and  108  extending therefrom which have vertically spaced-apart openings  110  and  112  formed therein respectively. For purposes of description, housing  104  will be described as having an upper end  114  and a lower end  116 . Housing  104  defines an interior compartment  118  at its inner side. A plurality of vertically spaced-apart and horizontally disposed slots  120  are formed in housing  120  as seen in  FIG. 7  which are adapted to receive the latches  98 . The handle  102  is not received by a slot  120 . 
     A latch handle  122  is rotatably mounted on housing between latched and unlatched positions and has a shaft  124  secured thereto which extends inwardly into compartment  118  of housing  104 . Shaft  124  is coupled to a conventional crank mechanism  126 . The lower end of an elongated actuator rod  128  is coupled to crank mechanism  126  and extends upwardly therefrom in compartment  118 . The upper end of an elongated actuator rod  130  is coupled to crank mechanism  126  and extends downwardly therefrom in compartment  118 . When latch handle  122  is moved from its unlatched position to its latched position, crank mechanism  126  causes actuator rod  128  to move upwardly and causes actuator rod  130  to move downwardly. Conversely, when latch handle  122  is moved from its latched position to its unlatched position, crank mechanism  126  causes actuator rod  128  to move downwardly and causes actuator rod  130  to move upwardly. 
     A plurality of vertically spaced-apart latch plate assemblies  132  are secured to housing  104  in compartment  118  by welding or the like with each assembly  132  including an upper latch plate  134  and a lower latch plate  136  which are vertically spaced apart. As seen in  FIG. 9 , upper latch plate  134  is positioned above the associated slot  120  and lower latch plate  136  is positioned below the associated slot  120 . Each of the latch plates  134  in each of the latch plate assemblies  132  have a first opening  140  and a second opening  142  formed therein. Each of the latch plates  136  in each of the latch plate assemblies  132  have a first opening  144  and a second opening  146  formed therein. Openings  140  and  144  are vertically aligned and openings  142  and  146  are vertically aligned. 
     Actuator rod  128  movably extends through the openings  140  and  144  in those latch plate assemblies  132  which are positioned above crank mechanism  126  and actuator rod  130  movably extends through the openings  140  and  144  in those latch plate assemblies  132  which are positioned below crank mechanism  126 . 
     A plurality of latch pin assemblies  148  are secured to actuator rod  128  in a vertically spaced-apart manner and have latch pins  150  extending upwardly therefrom which are received by the openings  146  and  142  of those latch pin assemblies  132  which are positioned above crank mechanism  126  when a latch handle  122  is moved from its unlatched position to its latched position. 
     A plurality of latch pin assemblies  148 ′ are secured to actuator rod  130  in a vertically spaced-apart manner and have latch pins  150 ′ extending downwardly therefrom which are received by the openings  142  and  146  of those latch pin assemblies  132  which are positioned below crank mechanism  126  when the latch handle  122  is moved from its unlatched position to its latched position. When the latches  98  are in their latched positions, the latch pins  150  and  150 ′ also extend through the openings  100  in the latches  98  when the latch handle  122  is moved from its unlatched position to its latched position since the latches  98  are positioned between the upper and lower latch plates of the latch plate assemblies and the openings  100  are vertically aligned with the openings  142  and  146  of the latch plates  134  and  136  respectively. 
     The switchgear door latch system of this invention functions as follows. Assuming that the door  26  is in the open position and assuming that the angle member  88  with the latches  98  attached thereto is in the open or unlatched position and the latch handle  122  is in the unlatched position, the following steps take place. The door  26  is then moved from its open position to its closed position to close the door opening  27 . The angle member  88  is then moved from its unlatched position to its latched position wherein the wall  90  of angle member  88  will be moved into engagement with the outside surface of the door  26 , as illustrated in  FIG. 11  which will cause the door  26  to move into engagement with the seal  42 . At that time, the latches  98  have been received by the slots  120  in the housing  104 . The latch handle  122  is then rotatably moved from its unlatched position to its latched position which will cause the actuator rod  128  to move upwardly so that the latch pins  150  will extend upwardly through the opening  146  in latch plate  136 , through opening  100  in the associated latch  98  and through the opening  142  in the latch plate  132 . At the same time, the actuator rod  130  will longitudinally moved downwardly so that the latch pins  150 ′ extend downwardly through the openings  142  in the latch plates  134 , extend through the opening  100  in the associated latch  98  and through the openings  150 ′ in the latch plates  136 . At that time, the door  26  will be latched in place and will prevent the door from moving to its open position should an arc-fault explosion occur within the enclosure. When one of the components of the system fails, it is not necessary to cut a hole in the door to repair the same since all the components of the system are located at the exterior side of the door  26 . For example, if there should be a problem within the housing  104 , the housing  104  may be removed from the door without the need of opening the door. The engagement of the latch pins with the latches and the engagement of the angle member  88  with the outer surface of the door ensures that the door will not open upon an arc-fault explosion occurring. 
     It can therefore be seen that a unique switchgear door latch system has been provided which accomplishes at least all of its stated objectives. 
     Although the invention has been described in language that is specific to certain structures and methodological steps, it is to be understood that the invention defined in the appended claims is not necessarily limited to the specific structures and/or steps described. Rather, the specific aspects and steps are described as forms of implementing the claimed invention. Since many embodiments of the invention can be practiced without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended.

Summary:
A switchgear door latch system is provided which prevents a door of a switchgear enclosure from opening should an arc-fault explosion occur within the enclosure. The door of the enclosure is latched from the exterior side of the door rather than on the inside of the door as is true in the prior at designs. All of the components of the latch system are located at the exterior side of the enclosure which facilitates repair of the same without cutting a hole in the door.