Abstract:
A retainer plate is pivotally mounted on a panelboard cabinet door lock housing, which carries a latch for locking the door. A detent on the plate engages in a rabbet opening to enable limited opening movement of the door in response to the pressure developed by arc gases generated by fault currents passing through a tripped circuit breaker in the panelboard cabinet. For ordinary opening movement, the lock latch is manually operated to pivot the retainer plate and disengage the detent from the rabbet opening.

Description:
FIELD OF THE INVENTION 
     The present invention relates in general to locked enclosures subject to internal gas pressure and more particularly to an improved panelboard vent assembly. 
     SUMMARY OF THE PRIOR ART 
     Panelboard assemblies incorporate a cabinet, which houses a plurality of circuit breakers each connected to a respective bus bar. The circuit breakers are disposed behind an interior trim and for access their handles project through the interior trim. 
     The front of the cabinet including the interior trim is overlapped by an exterior trim or cover. The cover is provided with a door, which is opened to provide access to the circuit breaker handles. The door carries a lock assembly, which may be of the type shown in U.S. Pat. No. 3,402,579 and when the door is closed and locked prevents access by unauthorized persons. 
     The lock assembly incorporates a latch, which is received behind a tang or keeper formed in the door frame to retain the door closed. The tripping of one of the circuit breakers under short circuit fault conditions creates large pressures which are applied against the locked door to open the door since the keeper can yield relatively easily to the pressure. The door may thus blow open with considerable force and injure nearby personnel, while the sudden release of a large volume of hot ionized gas creates a hazard. 
     In view of this situation regulatory and/or testing agencies have instituted a requirement that the panelboard doors open no more than 60°, when subject to the gas pressure occuring from tripping of an enclosed circuit breaker by short circuit fault currents. Holding a panelboard door closed under short circuit fault current conditions can of course result in the warpage and bending of the door and/or associated metal parts. 
     SUMMARY OF THE INVENTION 
     To solve the problem of holding a door from opening fully, when subject to arc gases generates by short circuit fault currents, the present invention employs a retainer plate pivotally carried on the lock assembly to permit a slight opening of the door for the purpose of venting the arc gases. 
     On closure of the door, the retainer plate and the latch element of the lock are both pivoted to respectively move into alignment with a passage in the door frame and past the latch keeper. A bias spring on the retainer plate then pivots the plate back to normal to engage a detent on the retainer plate in the frame passage, while the lock latch simply engages behind its keeper. 
     With the detent of the retainer plate engaged in the frame passage, limited movement of the door is permitted, if the latch keeper gives, since the frame passage is somewhat larger than the detent. 
     On the generation of arc gases, pressure against the door may cause the keeper to bend and allow movement of the door, but the detent then engages the transverse edge on the frame to allow a slight opening of the door for venting the gases. A lip on the detent also engages behind the frame edge, which provides a rigid stable stop, and the lip prevents the detent from slipping past the edge. 
     Thus limited opening movement of the door is permitted to vent the gases but full opening is prevented. 
     For normal opening of the door the lock handle is simply pivoted to withdraw the latch from behind the keeper and the latch plate moves the retainer plate to disengage the retainer detent from the frame passage. The door may then be simply pulled open. 
     Accordingly it is one object of the present invention to provide an improved vent assembly for the enclosure of a circuit interrupting device. 
     It is another object to provide an improved latch assembly for use in venting a panelboard. 
     Other objects and features of the present invention will become apparent on examination of the following specification including the claims and accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of a panelboard incorporating the principles of the present invention. 
     FIG. 2 is an exploded isometric view of the lock assembly incorporating the principles of the present invention. 
     FIG. 3 is a side elevational view of the lock assembly shown in FIGS. 1 and 2. 
     FIG. 4 is a front elevational view of the lock assembly shown in FIGS. 1 and 2. 
     FIG. 5 is a side elevational view of the lock assembly shown in FIGS. 1 and 2. 
     FIG. 6 is a fragmentary view of the door and frame from the inside of the enclosure showing the door in locked condition. 
     FIG. 7 is a sectional taken along the line 7--7 in FIG. 6 and looking in the direction of the arrows. 
     FIG. 8 is a sectional taken along the line 8--8 in FIG. 6. 
     FIG. 9 is a sectional taken along the line 9--9 in FIG. 6. 
     FIG. 10 is a fragmentary view of the door and frame showing the lock and retainer partially disengaged position. 
     FIG. 11 is a fragmentary view showing the door in partially open position. 
     FIG. 12 is a fragmentary view of the door and frame illustrating the latch and retainer plates disengaged from the frame to permit gas venting. 
     FIG. 13 is a sectional view taken along the lines 13--13 in FIG. 12 illustrating the door partially open to vent arc gases. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1 of the drawings a panelboard assembly is indicated by the reference character 10. The panelboard assembly 10 comprises a cabinet 12 having a trim plate or cover 14 with a frame defining an opening 16 adapted to be closed by a door 18 hingedly mounted on the cover 14 for movement to a closed position and to an open position. 
     The door 18 carries a latch assembly 20 of the type mentioned or described in the aforementioned U.S. Pat. No. 3,402,579. The latch assembly 20 includes box like housing 22 carrying a handle 24 pivoted about the axis of pin 25 for controlling a latch or latch element 26 biased by a torsion spring 27 best seen in FIGS. 3 and 8. Latch element 26 is adapted to be translated in a plane parallel to the handle pivot pin 25 to enable one end of latch 26 to be received behind a keeper 28 as best seen in FIGS. 6 and 9, when the door is closed. The keeper 28 is formed as a flat forwardly projecting tang on one portion of the door frame extending parallel to the door in the closed position. 
     The housing 22 of the latch assembly 20 has a pair of ears at opposite ends mounted on the rear surface of door 18 by means of a pair of spaced shouldered studs or posts 30 having threaded ends received by nuts 31 secured to the door. A retainer or retainer plate 32 having a pair of spaced passages 34 and 36 each receiving a respective post 30 is located behind the door 18 and the latch housing 22. 
     The passage 36 pivotally receive the corresponding post 30 and a U-shaped bend at the corresponding end of plate 32 abuts one of the housing ears and has an aligned semi-circular passage 38 engaging the respective post so that passages 36 and 38 provide spaced bearing or journal areas. 
     Passage 34 of plate 32 comprises a slot receiving the respective post 30 to enable limited pivotable movement of the retainer plate 32 about the axis of passages 36 and 38 toward and from a rabbet 39 on the cover 14 and forming a transverse portion of the door frame forming opening 16 as best seen in FIGS. 6-11. 
     An arm 40 is formed along one edge of plate 32 in alignment with latch 26 for engagement by the latch 26, when the latch element is withdrawn from the keeper 28 to pivot the plate 32 clockwise, as viewed in FIGS. 2 and 4. 
     The opposite edge of plate 32 is provided with an L shaped detent 42. The detent 42 projects toward the door edge with one leg of the detent extending in the direction of housing 22 to form a lip 43, generally aligned with the one end of latch 26 engaging keeper 28 and displaced upwardly therefrom. The L-shaped detent 42 is adapted to be received in an opening or passage 44 of the door frame or rabbet 39 so as to be located behind a transverse edge of the rabbet when the door 18 is closed as best seen from FIGS. 6, 7 and 9. 
     A cam 46 is also formed on the upper edge of plate 32. Element 46 is provided with a cam surface 48 terminating in the plane of the lip 43 and generally aligned with a cam surface of a toothed member 50 in the lock assembly 20, best spaced forwardly thereof. Cam surface 48 engages the door frame for opening 16 and pivots the retainer plate from the opening or frame edge on closing movement of the door. 
     The retainer plate 32 is biased toward the frame edge by a spiral or torsion spring 52 wrapped about the lower post 30 with one end of the spring engaged by the retainer plate 32 and the other end of the spring engaged with the lock housing 22. The plate 32 is thus normally biased into parallel alignment with the housing as the upper post 30 engages one edge of slot 34 to form one limit position for the plate 32. The detent 42 is then generally aligned with one end of the latch 26 under the bias of the respective springs 52 and 27. 
     To close the door 18, the door is simply pivoted toward a closing position and the cam surface 48 of cam 46 engages the door frame to pivot the retainer plate 32 from the frame against the bias of spring 52. Thereafter the cam surface of toothed element 50 engages the frame and it translates the latch 26 to the right as seen in FIGS. 2 and 4. Alternatively handle 24 is pivoted clockwise, as viewed in FIGS. 2 and 3, about the axis of pin 25 to pivot a cam 54, which pivots toothed member 50 to engage teeth along the top surface of latch 26. Latch 26 moves to the right as seen in 2 and 4 to engage arm 40 of plate 32 and pivot the plate clockwise as seen in FIGS. 2 and 4 so that latch 26 and lip 43 clear the door frame. 
     When the detent 42 and cam surface 48 are aligned with opening 44 in rabbet 39 the pressure on plate 42 is relieved either by release of handle 24 or by the position of latch 26 behind keeper 28, and the spring 52 pivots the plate 32 to engage detent 42 in the opening 44 behind a transverse edge of the rabbet 39. As the cam surface on element 50 and latch 26 have moved past the keeper 28, the pressure applied against the bias of spring 27 is relieved and the spring 27 moves the latch element 26 behind the keeper, whereafter the lock assembly may be key locked in position at the key cylinder 56. 
     If a circuit breaker indicated at 58, one or more of which are normally located behind the interior trim indicated generally at 60 in FIG. 1, should trip in response to a fault current, the arc gasses may generate considerable pressure against the door 18. The keeper 28, which is generally a simple flat tang formed from the outwardly facing surface of the rabbet may easily bend in response to the pressure applied against door 18 to release the latch 26. However the detent 42 being located behind an edge of rabbet 39 whose major cross sectional dimension is transverse to the opening direction of movement engages that relatively rigid edge, after the door moves or pivots a short distance about its hinges so that the door is held from further opening movement. Thus in the opening movement of the door, it may separate substantially 0.25&#34; from the frame, as the passage 44 is larger than the detent 42 to provide a sufficiently large passage to vent the gases without creating a hazard for nearby personnel, since far less than a 60 degree movement is permitted. The projecting portion or lip 43 of detent 42 engaging behind the rabbet locks the retainer plate 22 against release by bending of the rabbet or by movement by the latch element 26 to pivot the plate 32. 
     To open the door 18 normally, the lock handle 24 is pivoted about the axis of pin 25 to engage cam 54. Cam 54 pivots into the plane of the paper as seen in FIG. 4 to in turn pivot the element 50 against the bias of spring 27 and withdraw the latch element 26 from behind the keeper 28. 
     As the latch element 26 travels to the right as seen in FIG. 4, it engages arm 40 to pivot the plate 32 against the bias of spring 52 and withdraw the detent 42, from passage 44, as best seen in FIGS. 10 and 11. The door may now be simply pivoted to an open position. As will be appreciated the door may be closed in a manner similar to that explained for opening. 
     The foregoing is a description of an improved panelboard door lock assembly, whose inventive concepts are believed set forth in the accompanying claims.