Abstract:
A latch for an electrical device enclosure, wherein the latch comprises a moveable member operable in response to high pressure conditions inside the enclosure, and is configured to prevent opening of the enclosure in the event of high pressure conditions inside the enclosure.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The field of the present invention relates to a door latch for an electrical equipment enclosure generally, and more particularly to a door latch which can prevent the door of an electrical equipment enclosure from being forced open during a short circuit over current condition without requiring bolts within the latch, of which the following is a specification, reference being had to the drawings accompanying and forming a part of the same. 
     2. Description of the Related Art 
     In conventional electrical distribution and control systems, electrical switching devices are often enclosed in a housing having an openable cover or door. Conventional electrical equipment enclosures such as those containing, for example, a motor starter, electric switch, or circuit breaker require durable latches to prevent the enclosure door from blowing open under the arc gas pressure generated upon occurrence of a short-circuit overcurrent condition within any of the enclosed electric equipment. 
     In  FIG. 1 , a conventional switch device enclosure  100  is having a switching device (not shown), such as a circuit breaker or switch installed therein. A hinged cover or door  104  is openable via at least one hinge  133  to provide access to the interior of enclosure  100 . When closed, the door  104  prevents direct operative access to the enclosed switch (not shown). An operating handle  102  mounted external to the enclosure  100  and movable in the directions indicated by arrow  119  is configured to drive a mechanism (not shown), which in turn acts to toggle the switch (not shown) from a power ON position to a power OFF position. Labels having text such as “ON” and “OFF”, are positioned on enclosure  100  to correspond to operating handle  102  positions that likewise correspond to, and thus indicate, the state of the enclosed switch (not shown). The door  104  is retained in a closed position by at least one releasable door-latching mechanism  128  ( FIG. 2A ) having a releasable pawl or latch member  108  ( FIG. 2A ) comprising a tab  118  extending therefrom. 
     Referring to  FIG. 2A , a cut-away side view of the interior of the enclosure of  FIG. 1  is shown in the vicinity of the latch mechanism  128 . A conventional latch member  108  is rotatably mounted to enclosure  100  by a rivet or pin  138  which provides an axis of rotation A 1  for latch  108 . A center line C L1  through the center axis of rotation pin  138  and generally orthogonal to the surface of door  104  is shown in  FIG. 2A  for reference. Latch member  108  comprises a tab  118  having a latching surface  119  configured to latchably cooperate with a latching portion  134  the outer surface of door  104 . When enclosure door  104  is closed, an aperture or slot  114  disposed in the door  104  is configured to allow tab  118  to protrude through to the exterior of enclosure  100 . To secure the door  104  in a closed position, a bias spring  120  is anchored between latch member  108  and enclosure  100  and disposed to apply a bias force F 1  in a first latching direction D 1  to maintain at least a portion of latching surface  119  proximal to a latching portion  134  of the outer surface of door  104 . Generally, a small air gap  137  is provided between latching surface  119  and latching portion  134 . The latching portion  134  of the outer surface of door  104  is conventionally disposed, with respect to the centerline C L1  of the axis of rotation A 1 , in first latching direction D 1 . In this way, the latching surface  119  of tab  118  interferes with the surface of door  104  to prevent inadvertant opening of door  104 . 
     To allow the door  104  to open, the latch member  108  is unlatched by manually applying a force F 2  to latch member  108  in a second de-latching direction D 2  generally opposite to the first latching direction D 1 , sufficient to cause latch member  108  to rotate in a second de-latching direction D 2  around the axis of rotation A 1  and allow tab  118  to pass through slot  114 . 
     Latch member  108  is provided with an aperture  112  configured to receive a locking member (not shown) such as the hasp of a lock (not shown) for locking the cover  104  closed. 
     As shown in  FIG. 2B , in the event of a high-pressure condition in enclosure  100 , for example, if the switching device (not shown) in the enclosure  100  experiences a short circuit fault, a relatively high instantaneous pressure is generated inside the enclosure  100 . Under such a high internal pressure, a resultant expansive force vector F e  is applied generally orthogonal to the enclosure door  104  which causes the door  104  to deflect or move in an outward direction. The door  104 , at latching portion  134 , in turn contacts the latching surface  119  of tab  118 , thus applying the expansive force vector F e  to tab  118 . The latching surface  119  of tab  118  is conventionally configured to create a moment arm of length R 1  in the first latching direction D 1 , between the centerline C L1  of the axis of rotation A 1  and the latching surface  119  of tab  118 . It will be appreciated that, in the event of a high expansive force F e  applied to the latching surface  119  in a direction generally orthogonal to the interior of enclosure door  104 , a rotational force, or torque, T R1 , is developed in a second de-latching direction D 2 , is applied to latch member  108  having a magnitude that is the product of the expansive force F e  and moment arm R 1 , such that T R1 =F e ×R 1 . The rotational force T R1  biases the latch  108  in the second de-latching direction D 2 , and, if of sufficient magnitude, for example greater than the force applied by bias spring  120 , results in the rotation of latch  108 . 
     As shown in  FIG. 2C , and as discussed above, in the event of a high-pressure condition in enclosure  100 , the conventional latch  108  may unlatch or move out of position, and allow the door  104  to open, thus releasing hot gasses and debris. 
     BRIEF SUMMARY OF THE INVENTION 
     In view of the foregoing, there is a need to provide a durable latch that is relatively simple in construction, using a minimum number of parts that prevents the enclosure door from opening during a short circuit fault. It would be desirable to provide a simple latch for an electrical equipment enclosure that increases the latching force exerted on the door in the event of a short circuit fault. 
     In an embodiment, an enclosure for mounting a switching device. The enclosure comprises a simple latch assembly that is configured to prevent opening of the enclosure in the event of high pressure conditions inside the enclosure. 
     In another embodiment, a latch for an enclosure having a door is provided. The latch comprises a moveable member operable in response to high pressure conditions inside the enclosure, and configured to prevent opening of the enclosure in the event of high pressure conditions inside the enclosure. 
     Other features and advantages of the disclosure will become apparent by reference to the following description taken in connection with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Although specific features of the invention are shown in some drawings and not in others, this is for convenience only as one or more of the features of any drawing may be combined with any or all of the other features of one or more of the remaining drawings in accordance with one or more embodiments of the invention. 
       The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate a presently preferred embodiment of the invention, in which: 
         FIG. 1  illustrates a perspective view of a prior art enclosure having a door secured by a conventional latch; 
         FIG. 2A  illustrates a side view of the prior art latch of  FIG. 1  under a low-pressure condition; 
         FIG. 2B  illustrates the forces applied to the prior art latch of  FIG. 2A  under a high-pressure condition; 
         FIG. 2C  illustrates the prior art latch of  FIG. 2B  in an unlatched state; 
         FIG. 3  illustrates a perspective view of an embodiment of an enclosure of the present invention; 
         FIG. 4A  illustrates a side view of an embodiment under a low-pressure condition; 
         FIG. 4B  illustrates the forces applied to the embodiment of  FIG. 4A  under a high-pressure condition; and 
         FIG. 4C  illustrates embodiment of  FIG. 4B  in a fully latched state under the high-pressure condition of  FIG. 4B . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As used herein, an element or function recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or functions, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the claimed invention should not be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
     In  FIG. 3 , a housing  300  configured to enclose a conventional switching device such as a conventional circuit breaker (not shown), installed therein is shown. A cover or door  304  having a first interior surface  354  and a second exterior surface  366  is openable to provide access to the interior of the housing  300 . The door  304  is retained in a closed position by at least one releasable door-latching mechanism  328  having a biased releasable pawl or latch member  308  having a tab  318  extending therefrom. 
     As shown in  FIG. 4A , a conventional latch member  308  is rotatably mounted to enclosure  300  by a rivet or pin  338  which provides an axis of rotation A 2  for latch  308 . A center line C L2  through the center axis of rotation pin  338  and generally orthogonal to the surface of door  304  is shown in  FIG. 3A  for reference. Latch member  308  comprises a tab  318  having a latching surface  319  configured to latchably cooperate with a latching portion  334  the outer surface of door  304 . When enclosure door  304  is closed, an aperture or slot  314  disposed in the door  304  is configured to allow tab  318  to protrude through to the exterior of enclosure  300 . To secure the door  304  in a closed position, a bias spring  320  is anchored between latch member  308  and enclosure  300  and disposed to apply a bias force F 1  in a first latching direction D 1  to maintain at least a portion of latching surface  319  proximal to a latching portion  334  of the outer surface of door  304 . The latching portion  334  of the outer surface of door  304  is disposed, with respect to the centerline C L2  of the axis of rotation A 2 , in a second de-latching direction D 2  generally opposite to the first latching direction D 1 . In this way, the latching surface  319  interferes with the opening of door  304 . 
     To allow the door  304  to open, the latch member  308  is unlatched by manually applying a force F 2  in the second de-latching direction D 2 , sufficient to overcome the biasing force of spring  320 . The unlatching force F 2  rotates latch member  308  in the second de-latching direction D 2  around the axis of rotation A 2  and allows tab  318  to pass through slot  314 . 
     As shown in  FIG. 4B , in the event of a high-pressure condition in enclosure  300 , if the switching device (not shown) in the enclosure  300  experiences a short circuit fault, a relatively high instantaneous pressure is generated inside the enclosure  300 . Under such high internal pressure, an expansive force vector F e  is applied generally orthogonal to the enclosure door  304  which causes the door  304  to deflect or move in an outward direction. The door  304 , at latching portion  334 , in turn contacts the latching surface  319  of tab  318 , thus applying force vector F e  to tab  318 . The latching surface  319  of tab  318  is configured to create a moment arm of length R 2  in the second de-latching direction D 2 , between the centerline C L2  of the axis of rotation A 2  and the latching surface  319  of tab  318 . In the event of a high expansive force F e  applied to the latching surface  319  in a direction generally orthogonal to the interior of enclosure door  304 , a rotational force T R2 , is developed in the first latching direction D 1 , is applied to latch member  308  having a magnitude that is the product of the expansive force F e  and moment arm R 2 , such that T R2 =F e ×R 2 . In this way, in the event of a high pressure condition, latch  308  acts to retain the door in a closed position 
     With respect to the above description, it should be realized that the optimum dimensional relationships for the parts of the invention, to include variations in size, form function and manner of operation, assembly and use, are deemed readily apparent and illustrated in the drawings and described in the specification are intended to be encompassed only by the scope of appended claims. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.