Abstract:
An enclosure such as an electrical junction box has fixed clamping flanges exterior to the enclosure, screws rotatable relative to the enclosure and operative for drawing clamping brackets from an initial elevated position towards the clamping flanges for clamping the edges of an opening cut in drywall or the like, thereby to fasten the enclosure inside a wall or ceiling. The clamping brackets are initially retracted in the enclosure and rotation of the screws releases the brackets to an extended clamping position relative to the clamping flanges.

Description:
FIELD 
     This invention relates to junction boxes and housings used in residential and commercial construction to enclose electrical wiring and recessed light fixtures against fire and electrical hazards. 
     BACKGROUND 
     Municipal construction codes generally require that electrical wiring, particularly in-wall wiring, be contained in fire resistant protective conduit, usually metal conduit. Where two or more electrical wires are connected the outer protective conduit must be cut or terminated in order to join the interior electrical conductors to each other. The resulting gap in protective conduit is bridged with a junction box which provides continuity of enclosure between multiple wire conduits. The ends of metal conduits are joined to the walls of the junction box while electrical wires in the conduits enter through openings in the box walls into the junction box where the wires may be interconnected with each other, e.g. with electrical nut fasteners. In the event of an electrical overload, short circuit or similar anomalous condition which causes overheating or sparking, the fire resistant junction box contains and prevents ignition of nearby flammable materials. Construction codes typically require that junction boxes meet a minimum standard of protection, e.g. two hours of protection at a given exterior temperature. 
     With the advent of compact light fixtures based on LED (light emitting diode) technology, it becomes possible to house small compact light fixtures directly in the junction box itself, thereby eliminating the need for the bulky and awkward sheet metal lamp housing. The relatively small junction box serves as a fire resistant enclosure for both the power supply wiring and for the light fixture itself. 
     In new construction, junction boxes are easily fastened to the rigid building frame, such as ceiling joists or wall studs, before drywall or other wall and ceiling material is installed. After the electrical connections are made, the wall or ceiling is then installed over the junction box, with holes cut in the ceiling or wall material for access to the boxes before being fixed into place. 
     In remodel construction requiring installation of junction boxes, however, it is difficult to access the building frame without removing the wall or ceiling surface first, i.e. tearing off dry wall sheet and the like. This is a labor intensive and expensive process. There is a category of junction boxes on the market specifically made for remodel construction that do not require the removal of wall and ceiling to install. These require a hole to be cut in the existing wall or ceiling surface, electrical connections to be made, and then the junction box is installed through the hole from the outside. These junction boxes have a mechanism for attaching the box to the ceiling surface, e.g. to the dry wall sheet covering, instead of to the building frame. 
     These remodel junction boxes typically require either an irregularly shaped hole to be cut, a clamping tab to be manually set into position before installation, a fastener to be applied to the fragile wall surface, or a combination of the these. Many of these products are designed for a single installation, damaging both the wall and the junction box if removed. 
     A continuing need exists for an improved wall clamping junction box. 
     SUMMARY OF THE INVENTION 
     This invention provides an improved electrical junction box and lamp housing which is easier to install in remodel or retrofit work. 
     The improved junction box clamps to a surrounding wall, which is normally surrounding drywall sheet, in a substantially fire resistant joint to provide a continuous protective partition between the interior of the junction box and the ceiling space above the dry wall, while an open bottom of the junction box accessible from beneath the ceiling permits installation and servicing of compact lamp modules and associated wiring. 
     The clamping junction box has a top wall between four or more side walls and an open bottom. A pair of outer flanges extend from the exterior of opposite side walls which also each have a vertical slot between the top wall and the corresponding outer flange. 
     A clamping bracket is slidable in each of the slots and a pair of clamping screws each threaded to one bracket is captive to the box. Each screw is rotatable for drawing a corresponding clamping bracket along its slot from an initial elevated position towards the corresponding outer flange, such that a wall edge adjacent to the box side walls is clamped between the brackets and the outer flanges thereby fastening the box to the wall. 
     The clamping screws are tiltable between an initial inclined position in which the clamping brackets are retracted into the box and an upright position where the brackets are extended from the box. 
     A spring on each screw urges the screw towards the upright condition and the corresponding clamping bracket toward an initial elevated position against an upper end of the corresponding slot. A detent on the bracket engages the side wall to keep the bracket in its retracted position and the screw in the tilted position. 
     The detent releases when the screw is turned to move the bracket down along the screw, freeing the screw which is righted from the tilted position by the spring, thereby extending the bracket out of the box through the slot in the side wall from its retracted position. 
     These and other improvements, features and advantages of this invention will be better understood by reference to the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top side perspective view of a clamping junction box according to this invention, shown with the clamping brackets held retracted into the box and the clamping screws tilted; 
         FIG. 2  is a view as in  FIG. 1  with the clamping brackets extended from the box and the clamping screws in upright position; 
         FIG. 3A  is a side elevational section taken along line  3 A- 3 A in  FIG. 1  showing the box in initial condition for installation with clamping brackets retracted and clamping screws tilted as in  FIG. 1 , with the box inserted for installation in an opening cut in a sheet of dry wall; 
         FIG. 3B  is a side elevational view of the junction box of  FIG. 3A  showing the exterior end of a clamping bracket retracted against a side wall of the junction box in the condition also shown in  FIG. 3A ; 
         FIG. 3C  is a side elevational section taken along line  3 C- 3 C in  FIG. 2  showing the clamping brackets released to an extended position and lowered along corresponding slots into clamping engagement with the sheet of dry wall, and the clamping screws righted to an upright position by the compressed coil spring on each screw; 
         FIG. 3D  is a side elevational view of the junction box of  FIG. 3C  showing the exterior end of a clamping bracket lowered along its slot into clamping engagement with the sheet of dry wall as also shown in  FIG. 3C ; 
         FIG. 4  shows in perspective view a junction box housing and a clamping bracket disassembled from the junction box housing; and 
         FIG. 5  shows in perspective view how the junction box of this invention is advanced into an installation opening cut in a wall or ceiling covering such as a sheet of dry wall material. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With reference to the accompanying drawings wherein like elements are designated by like numerals,  FIG. 1  shows a wall clamping junction box generally designated by numeral  10  which has a rectangular top wall  12  and four side walls  14  defining a generally rectangular enclosure  16  with an open bottom  18  bounded by the four side walls  14 . The enclosure  16  may be of sheet metal similar to electrical junction boxes currently in general use. A number of knockout openings  22  are provided in top wall  12  and side walls  14 , which may be individually opened as needed to receive electrical conduit and admit electrical conductors into box  10 . 
     A pair of rigid clamping flanges  20  extend horizontally away from lower edges  24  of opposite side walls  14 . A pair of screw bearing flanges  26  are supported in diagonally opposed corners between contiguous side walls  14 . Each screw bearing flange  26  is perforated with a screw hole  28  sized to loosely pass the threaded shaft  32  of a machine screw  30  upward into box enclosure  16  while making an interference fit with screw head  34  of screw  30  against the underside of flange  26 . The two screws  30  are loosely held in in screw holes  28  of respective flanges  26 , where each screw  30  is free to rotate and move axially through flange  26  and each screw  30  is free to tilt away from the vertical in box enclosure  16 . 
     Two vertical slots  38  are cut in the two opposite side walls  14  which carry the clamping flanges  20 . Each slot  38  is generally parallel and adjacent to one of the two screws  30 . A pair of clamping brackets  40  each have an inner portion  42  with a screw hole  42   a  through which is threaded shaft  32  of each screw  30  and a mid-portion  44  slidable between upper slot end  38   a  and lower slot end  38   b  in a corresponding slot  38 . Bracket midportion  44  extends to the exterior of box enclosure  16  through slot  38  and terminates in an end portion  46  shaped to interfere with passage through slot  38  into enclosure  16 . As shown in  FIG. 1 , end portion  46  is bent transversely to mid-portion  44  and lies flat against the outside of side wall  14  in the maximally retracted position of bracket  40  into box enclosure  16 , preventing further entry of the bracket into the enclosure, and limiting tilting of the screw  30 . In this position bracket  40  also supports screw  30  in a maximally tilted position away from the vertical, as shown in the same  FIG. 1 . 
     A coil spring  46  lies coaxially along each screw shaft  32  in axial compression between bearing flange  26  and inner portion  42  of bracket  40 . The length of coil spring  46  is such as to remain in compression when bracket inner portion  42  is in an initial maximally elevated position on screw shaft  32  as shown in  FIG. 1 , with an upper edge  44   a  of the bracket mid-portion  44  abutting against the upper end  38   a  of slot  38 . The force of spring  46  holds the screw head  34  in interference against the underside of flange  26  and keeps the screw shaft  32  above flange  26  in box enclosure  16 . 
     The compressed spring  46  normally urges the shaft  32  towards an upright, vertical position because tilting of the screw shaft tends to further compress the coil spring  46  between the flat surfaces presented by flange  26  and bracket inner portion  42 . One side of the lower end of spring  46  is pressed against flange  26  and pushed upwards along screw shaft  32  when screw  30  is tilted relative to flange  26 . The spring seeks to minimize its compression by righting the screw shaft towards the vertical relative to the horizontal top surface  26   a  of flange  26 , and consequently normally urges screw  30  towards a vertical position substantially parallel to side walls  14 . This tendency of compressed spring  46  is opposed by a detent in the form of detent tab  48  which rises from the upper edge  44   a  of bracket mid-portion  44 . With bracket  40  maximally elevated in slot  38 , detent tab  48  rises above the upper end  38   a  of the slot and prevents bracket  40  from moving outwardly through slot  38 . Detent tab  48  is held in engagement with the upper end  38   a  of slot  38  by the force of compressed spring  46  which urges screw  30  upwards through its hole  28  in flange  26  and lifts bracket  40  against slot upper end  38   a , thereby holding bracket  40  in the retracted position shown in  FIGS. 3A and 3B . 
     Bracket  40  is released from its maximally retracted position of  FIGS. 1, 3A and 3B  by turning screw  30  so as to draw inner portion  42  of bracket  40  down along screw shaft  32 . This action brings detent tab  48  below the upper end  38   a  of slot  38 , allowing the bracket mid-portion  44  to move outwardly through slot  38  under urging of spring  46  until stopped by stop face  42   b  of bracket inner portion  42  abutting against the inner surface of side wall  14 , a condition illustrated in  FIGS. 2, 3C and 3D . In this maximally extended position brackets  40  may be drawn down along screw shafts  32  and along slots  38  towards the underlying clamping flanges  20  by further turning of screws  30 . 
     Junction box  10  is installed in a wall or ceiling by first cutting a rectangular opening O in the exterior dry wall sheet W, or other wall or ceiling surface covering, as illustrated in  FIG. 5 . Opening O is made slightly oversized to the rectangular perimeter side walls  14  of enclosure  16 , with a small allowance for passing the thickness of outer portions  46  of the two clamping brackets  40 . The edges of the wall opening O may be four straight edges in a rectangle slightly greater than top wall  12  of the junction box. The junction box  10  is installed with brackets  40  in the initial retracted condition shown in  FIGS. 1, 3A and 3B . Box  10  is introduced into the wall or ceiling interior by advancing top wall  12  into the wall opening O until clamping flanges  20  abut against the outer surface T of the dry wall sheet W and the clamping flanges  20  lie against edge portions of the drywall adjacent to side walls  14 , as seen in  FIG. 3A . 
     Screws  30  are then turned to release brackets  40  from their initial retracted position of  FIG. 1 , and further turned to draw down the clamping brackets  40  along screw shafts  32  towards the inner surface of the drywall sheet W until the preferably serrated lower edges  40   b  of brackets  40  press and bite into the inside surface P of dry wall sheet W, as seen in  FIG. 3C , clamping the dry wall sheet W between the flanges  20  and brackets  40 . Preferably, screws  30  are tightened sufficiently until edges  40   b  of brackets  40  cut and press somewhat into the dry wall surface P to secure box  10  against possible displacement relative to the wall or ceiling. 
     The clamping mechanism described herein is not limited to application in electrical junction boxes but may be incorporated in a variety of boxes, housings, enclosures and other structures intended for mounting inside walls or ceilings. 
     While a presently preferred embodiment of the invention has been described and illustrated for purposes of clarity and example it must be understood that various changes, modifications and substitutions to the described embodiment will be apparent to those having no more than ordinary skill in the art without departing from the scope of this invention as defined by the following claims.