Abstract:
A spring steel spring interlocked with a panelboard assembly door by a pull having a leg projecting through the door to engage a passage edge in the spring. When the pull is rotated to open the door the leg moves the spring to disengage a latch adjacent one end of the spring from behind a detent in a frame latch passage. The detent in the frame passage engages the latch to hold the door from rapid opening, if a circuit breaker trips to generate arc gases which exert pressure against the door, but permits separation of the door from the frame and flexure of the door to vent arc gases.

Description:
FIELD OF THE INVENTION 
     The present invention relates in general to latched door enclosures subject to internal gas pressure and more particularly to an improved panelboard vent assembly for use in economical panelboards. 
     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 their handles project through the interior trim for access thereto. 
     The interior trim is overlapped by a door, which is opened to provide access to the circuit breaker handles. In order to latch the door closed, the more economical panelboard cabinet doors may utilize a single sheet metal spring detent or latch operated by a pull for engagement with and disengagement from an edge of the associated door frame. Latches for panelboard cabinet doors of a similar type are shown in U.S. Pat. Nos. 2,761,716 and 3,334,770. 
     The tripping of one of the circuit breakers in the cabinet may give rise to a volume of hot expanding ionized gas creating pressure against the latched door to open the door since the latch 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 may also create 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 occurring from tripping of an enclosed circuit breaker. Providing a panelboard door with the required variety of functions under these conditions can of course add considerable expense to a panelboard assembly. 
     SUMMARY OF THE INVENTION 
     To solve the problem of holding a door latched closed by an economical latch from opening fully, when subject to arc gas pressure, the present invention employs a simple pair of shoulders on a spring steel latch of a type similar to that used in economical panelboards for engaging a pair of detents formed in a latch passage of the door frame. The shoulders engage the detents in response to opening movement of the door resulting from arc gas pressure to hold the door closed. Some bending or warpage of the light sheet metal door from the frame then permits venting of the gas. 
     Normal opening of the door is provided by a ring like pull that interlocks the latch and door and has a simple leg moving the spring latch to disengage the shoulders from the detents and enable facile movement of the door to an open position. 
     Accordingly it is one object of the present invention to provide a more economical vent assembly for the enclosure of a circuit interrupting device. 
     It is another object to provide an economical panelboard latch assembly enabling for venting of 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 a fragmentary front elevational view of the relevant portion of the panelboard shown in FIG. 1. 
     FIG. 3 is an exploded isometric view of the latch assembly incorporating the principles of the present invention. 
     FIG. 4 is a sectional view taken through the line 4--4 in FIG. 2. 
     FIG. 4a is an isometric view of the latch member. 
     FIG. 5 is a sectional view taken through the line 5--5 in FIG. 4. 
     FIG. 6 is a sectional elevational view taken through the line 6--6 in FIG. 4. 
     FIG. 7 is a sectional view showing the latch assembly in door releasing position, and illustrating by dashed lines, the partially open door, and 
     FIG. 8 is a sectional view illustrating the manner in which the latch assembly responds to elevated internal gas pressure. 
    
    
     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 such as shown in one of the aforementioned patents or as shown in a publication entitled QO Circuit Breakers and Load Centers copyright 1977 by the Square D Company. 
     The cabinet 12 has a trim plate or cover 14 with a recessed portion 16 surrounded by a frame 17 to define an opening. The opening is adapted to be closed by a door 18 hingedly mounted on the cover 14 along one edge when the door closing edge is moved to overlappingly engage the door frame 17. When the door is moved to an open position access is provided to one or more circuit breaker handles extending through the interior trim. 
     The door 18 carries a latch assembly 20. The latch assembly 20 includes an elongate planar spring steel member or latch 22 having an open fold 24 projecting through passage 26 in the door and located adjacent the closing door edge, as may be seen from FIGS. 2, 3, 4, 7 and 8. 
     A pull or handle 28 in the form of a split ring is received between the two arms of the fold 24. The pull 28 extends past opposite edges of passage 26 to overlap the outer face of door 18 and a planar leg 30 at one end of fold 24 engages the inner surface of door 18 to thereby secure the latch assembly 20 to the door. 
     Leg 30 extends in a direction from the adjacent door closing edge toward the door hinged edge for substantially 1/2&#34;. A reverse bend 32 at the end of leg 30 extends the latch member 22 along a main body portion or planar leg 34 toward the door closing edge. An open fold 36 is formed in leg 34 intermediate the ends of leg 34. Fold 36 extends in the opposite direction from fold 24 and is offset from fold 24 in the direction of bend 32 with the open end of fold 36 facing in the direction of the open end of fold 24 to receive a leg 38 projecting through passage 26 from one of the split ends of pull 28. 
     The leg 38 projects at an angle of substantially 60° from the plane of the ring forming pull 28 and when the pull projects toward the door closing edge, the leg 38 extends in the direction of fold 36. A passage 40 located in the rear leg of fold 36 serves to facilitate spring flexure in the area. A passage 42 is also provided in the front leg of fold 36 to accommodate the leg 38 in response to rotation of the pull 28 and passage 42 extends into the planar portion of leg 34 to provide an end edge 44 transverse or perpendicular to the rotational path of leg 38, for rotating the latch to move the leg 34 together with a detent or main latch portion 46 of member 22 towards the door closing edge or frame as may be best seen from FIG. 3, 4, 7 and 8. 
     The leg 34 extends through a passage 48 in an offset portion 50 of the door. A reduced section reverse bend 52 at the free end of leg 34 passes through a reduced section passage 53 formed in the edge of a planar closing edge portion of door 18 to interlock the door and latch assembly against movement in one direction perpendicular to the longitudinal axis of leg 34. The reduced section 52 resiliently connects the body portion 34 to latch portion 46 A leg 54 is formed at the free end of bend 52 and is offset from leg 34 in the direction of frame 17 and main latch portion 46 is formed on the free end of leg 54. Latch portion 46 extends transverse to the leg 54 in the direction of frame 17 and has a bent cam or nose 56 for registry and receipt in a wide portion of a keeper or latch passage 58 formed in frame 17. 
     The keeper passage 58 has a pair of shoulders or detents 60 extending therein to form a narrow passage portion 62 located in the portion of passage 58 extending in the direction of the door hinge edge. The shoulders 60 have one edge for engaging nose 56 to cam the latch portion 46 to interlockingly engage with a respective shoulder 64 formed by a reduced section portion between leg 54 and latch portion 46. 
     The member 22 is assembled to the door by moving fold 24 through passage 26 after passing leg 34 through passage 48 and then bend 52 is engaged with reduced section passage 53. Leg 38 of pull 28 is forced under the free end of fold 24 against the pressure of bend 32 with the leg 38 directed toward passage 42 to enable the split segment of pull 28 to be received between the arms of fold 24. At that time the pull 28 extends toward the door closing edge and leg 38 is pivoted into position adjacent passage 40 while reverse bend 32 applies pressure against the inner surface of door 18 to move fold 24 toward passage 26 and hold the split segment on leg of pull 28 against the door outer surface to interlock the member 22 with the pull 28 and the door. 
     To close the door 18, the door is simply pivoted toward a closing position and the nose 56 of latch 46 engages the edge of detents 60 in the door frame 17 to move the latch through passage 58 until the door is closed, at which time the detents 60 are received between leg 54 and shoulders 64. This interlocks the latch and frame for holding the door closed. A pair of short ears 68 extend from the reduced section between leg 54 and shoulders 64 in a direction transverse to the plane of shoulders 64 to aid engagement in the event of misalignment. 
     If a circuit breaker in the cabinet 12 and located behind the interior trim or frame indicated generally at 16 in FIG. 3, should trip in response to a fault current, the arc gasses may generate considerable pressure against the door 18. As the door 18 pivots about its hinges indicated at 70 in FIG. 1, the shoulders 64 on the latch portion 46 attempt to move therewith, but engage the detents 60, which limit the opening movement of the door, as may best be seen in FIG. 8. Since the spring 22 flexes at the reduced section 52 some opening movement occurs and space is provided between the door and frame to vent the gas in addition to any venting provided by the normal flexure of the light sheet metal door from the frame between shoulders 64 and the hinges under the applied pressure. 
     To open the door 18 normally, the pull 28 is pivoted about the axis of the ring segment in fold 24 to engage leg 38 with the edge 44 of passage 42 as best seen in FIG. 7 to move leg 34 to the left as the bend 32 and fold 36 flex to accommodate the pressure against edge 44. As leg 34 moves toward the passage 58, shoulders 64 on the latch portion are disengaged from behind detents 60 and are aligned with passage 58 to permit the latch portion to be disengaged from the frame 17 and the door opened as indicated by the dashed lines in FIG. 7. The door may now be simply pivoted to an open position. It will be appreciated that the pull 28 is operated in a similar fashion on a closing operation if desired. 
     The member 22 is formed of spring steel substantially 0.035&#34; thick and 0.62 wide so that while the material is capable of the necessary flexure, sufficient rigidity is provided at shoulders 64 to resist opening pressure of the arc gasses. Leg 38 is substantially 0.5&#34; long while the opposing segment of pull 28, which is manually grasped, is substantially 1&#34; from the segment passing through fold 24 to thereby provide a desirable mechanical advantage when leg 38 engages edge 44. 
     The foregoing is a description of an improved panelboard door lock assembly, whose inventive concepts are believed set forth in the accompanying claims.