Abstract:
An electrical box support is provided having a set of struts telescoping one within the other to accommodate the length for attachment to studs of different spacings. Each strut has a face suited for mounting an electrical box and has a series of inwardly directed, uniformly and relatively closely spaced detents. The detents serve both for releasably locking the length of the support and for guiding the entry of screws used to attach the box to the support. Each strut has an end tab adapted for bending to mount to the studs in a position established so that a mounted electrical box appropriately meets the surface of a wall board to be installed. Bending in a controlled straight line is accomplished by the formation of discontinuous score lines. 
     A second embodiment of the invention is formed with two struts having end tabs and a third strut having no end tabs and engaging the other two struts. Either one or both of the struts with end tabs can be moved to change the length of the assembly. The assembly length is releasably locked by a series of mating detents.

Description:
FIELD OF INVENTION 
     This invention relates to an electrical box support constructed of telescoping struts having means to releasably lock the struts and at an outer end of each strut a studengaging tab that can be bent to conform to different box depths. 
     BACKGROUND OF THE INVENTION 
     The terms “box” and “electrical box” as used herein are intended to refer to a junction box, receptacle box, switch box, terminal box, connector box or the like as are known in the electrical trade. The teachings of the patents described below are given for background and are deemed to be incorporated herein by reference. 
     U.S. Pat. No. 1,506,330 issued in 1924 recognized the need for an electrical box support capable of accommodating an electrical box of a known depth and studs of different spacing. The &#39;330 patent teaches the practice of forming an electrical box support from a pair of telescoping, channel formed struts, each having a face to which the box could be attached. The &#39;330 patent also teaches bending the ends of the support to form right angled tabs for mounting the box support to and between adjacent studs. The &#39;330 patent box support however required that adjustments for boxes of different depths be made by locating the bent ends of the box support at different locations on the sides of the studs. 
     U.S. Pat. No. 1,789,124 issued in 1931 also recognized the need for adjusting the length of an electrical box support by bending the ends of the support to accommodate to studs of different spacing. 
     U.S. Pat. No. 2,233,334 issued in 1941 also recognized the need for an electrical box support capable of accommodating electrical boxes of different depth and mounting to studs of different spacing. The &#39;334 patent teaches the practice of forming an electrical box support from a single bar having a face to which the box could be attached. The &#39;334 patent also teaches bending the ends of the support to form right angled tabs for mounting the box support between and to adjacent studs. The electrical box support of the &#39;334 patent however was not adjustable lengthwise and also required that adjustments for boxes of different depths be made by locating the bent ends of the box support at different locations on the sides of the studs. 
     U.S. Pat. No. 2,788,188 issued in 1957 illustrates in one embodiment an electrical box support constructed of a pair of struts which telescope within each other so as to be able to adjust to different spacings between the studs and providing a face to which the box could be attached. In the mentioned embodiment, the &#39;188 patent also illustrates the practice of prebending the ends of the telescoping struts to form tabs useful for attaching the box support to and between adjacent studs. In another embodiment, the &#39;188 patent illustrates an electrical box support formed from a single flat sheet with bendable tabs at each end each having a plurality of grooved, embossed or etched lines at different locations along which each tab can be bent in the field to form a flange at right angles to the plane of the sheet. Thus, the &#39;188 patent can also be construed to teach the practice of being able to form an electrical box support either with prebent tabs or with flat tabs adapted to be bent in the field. 
     With regard to the practice of providing lines of weakened metal, bend points, a line of holes or the like in an electrical box support, to facilitate bending or breaking of the metal along a particular line, reference is also made to U.S. Pat. No. 4,399,922, issued in 1983, for an electrical outlet box support. The &#39;922 patent illustrates a pair of weakening lines used to facilitate bending of a portion of the support; U.S. Pat. No. 4,483,453, issued in 1984, also illustrates an electrical box support in which a plurality of parallel lines of holes are used to facilitate breaking of excess metal; and U.S. Pat. No. 4,673,235, issued in 1987, also describes an electrical receptacle subplate having two pairs of such bend lines. 
     U.S. Pat. No. 1,800,813, issued in 1931, illustrates use of a lengthwise V-groove in the strut of an electrical box support and of a series of preformed holes to facilitate insertion of nails, screws or the like. U.S. Pat. No. 4,967,990, issued in 1990, recognizes use of pilot holes to facilitate the starting and use of metal screws for securing the box to a face on one of the telescoping struts. The electrical box support described in the &#39;990 patent comprises a pair of telescoping struts adapted to be mounted between two spaced-apart wall studs. Each strut comprises an elongate web of sheet metal forming a front face of the strut, a pair of side walls extending rearwardly from the side edges of the web, and a channel formed inwardly of the web running substantially the full length of the web between the side edges of the web. Inwardly turned flanges connect to the side walls and define the bottom of the channel. Pilot holes are spaced along the web at relatively closely spaced and regular intervals whereby an electrical box may be attached to the strut in a selected position lengthwise of the strut by placing the back wall of the box flush against the front face of the web over the channel and then fastening the box to the strut by using screws threaded through selected pilot holes. 
     Applicant&#39;s prior U.S. Pat. No. 5,405,111, issued in 1995 for a Bracket For Anchoring Apparatus Between Wall Studs, also illustrates a feature of interest to the present invention, namely, the use and advantage of detents. As disclosed in the &#39;111 patent, detents are used rather than holes to facilitate installation of self drilling sheet metal screws for attaching apparatus to the bracket. So far as applicant is aware, the &#39;111 patent is the only known prior art reference which illustrates the use and advantage of detents in an electrical box support though it has been known to use a series of holes to facilitate insertion of nails, screws and the like as seen for example in the aforementioned U.S. Pat. No. 1,800,813, issued in 1931 and U.S. Pat. No. 4,967,990, issued in 1990. 
     With the above as background, it is to be noted that use of the telescoping type electrical box support has introduced a problem in that the known struts which telescope one within the another often come loose before being installed because of the typical free-sliding fit between the telescoping struts of the support. Thus, if an installer, for example, is on a ladder and is in the process of installing a telescoping type electrical box support of conventional construction, the typical telescoping struts particularly when held vertically because of their relatively loose sliding fit are apt to separate and permit one of the struts to fall, thus risking harm to both people and objects below. 
     With regard to the need for establishing a relatively tight fit between struts of a telescoping type electrical box support, U.S. Pat. No. 2,788,188, issued in 1957 describes a telescoping type electrical box support but specifically refers to the sections of the support being “relatively slidable.” U.S. Pat. No. 2,809,002, issued in 1957, refers to the relation between two struts forming a telescoping type electrical box support as permitting “relatively free-sliding movement.” U.S. Pat. No. 5,386,959, issued in 1995, describes a telescoping type electrical box support in which mention is made of the two sections of the support “not being readily separable”. The &#39;959 patent however does not show nor do any of the other mentioned patents show, any kind of releasable locking mechanism which would permit telescoping struts once assembled to be held vertically without separating and yet be readily adjustable lengthwise by manual pressure applied to the struts. In dealing with this same problem, B-Line Systems, Inc. has recently started marketing a telescoping type electrical box support formed with inner and outer sections and with pilot holes in each section such as shown in B-Line&#39;s Patent 5,209,444, issued in 1993, and a resilient finger (not shown in the &#39;444 patent) formed intermediate the length of the outer section and having a protrusion which resiliently engages and slides on an opposite surface of the inner section apparently for the purpose of reducing any tendency of one section to slide on the other. However, the sections are never releasably locked as with the present invention. 
     The term “stud” as used herein is intended to include structural members in a building surface, including wall studs, joists, rafters, etc. The term “wall” as used herein is intended to include ceiling surfaces as well as vertical walls. 
     Therefore, the object of the invention is to provide a further improved telescoping type electrical box support which accommodates and can be field bent to accommodate boxes of different depths, can be adjusted to different stud spacings, and, of particular importance to the invention can while being installed, maintain a relatively tight but releasably locked engagement between the telescoping struts. Other objects will become apparent as the description proceeds. 
     SUMMARY OF THE INVENTION 
     The improved electrical box support of the invention comprises in a first embodiment at least two and in a second embodiment three struts that are assembled in telescoping relation to accommodate different stud spacings and also having means to accommodate different depths of electrical boxes. The box support assembly of the invention is formed of outer and inner struts with a series of interengaging detents, i.e. conical or hemispherical shaped depressions, so that the struts can be moved to relative positions in which the outer strut detents engage and nest into opposed inner strut detents to releasably lock the struts comprising the two-strut assembly together at some selected length. The outer strut can be manually moved relative to the inner strut to temporarily disengage the detents and change the releasably locked length of the box support assembly. One end of the outer strut and an opposed end of the inner strut are formed with a tab that is adapted to be bent for mounting to adjacent building studs at a depth appropriate to accommodate an electrical box to be mounted thereto. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a perspective illustration of a first embodiment of the adjustable electrical box support of the invention made up of two releasably engaged struts and showing the front surfaces of the end tabs before the end tabs thereof have been bent in the field for attachment to adjacent wall studs and to accommodate to a particular depth of electrical box. 
     FIG. 1B is a perspective illustration of the rear surface of one end tab of the preferred embodiment before it has been bent to accommodate to a particular depth of electrical box. 
     FIG. 2A is a cross sectional view of the adjustable electrical box support of the invention as shown in FIG.  1 A and as taken along line  2 — 2  of FIG.  1 A and with the detents engaged. 
     FIG. 2B is a cross sectional view of the adjustable electrical box support of the invention as shown in FIG. 2A but with the struts moved to cause the detents to be disengaged. 
     FIG. 3 is a perspective illustration of the adjustable electrical box support of the invention as shown in FIG. 1A after the end tabs thereof have been bent to accommodate to a particular depth of box and in a form suitable to being attached to a pair of spaced apart wall studs. 
     FIG. 4 is a perspective illustration of the adjustable electrical box support of the invention as shown in FIG. 1A after being attached to a pair of adjacent wall studs with an electrical box of a particular depth mounted thereto. 
     FIG. 5 is a top plan view of the adjustable electrical box support of the invention as shown in FIG. 4 mounted to a pair of adjacent wall studs and with an electrical box of particular depth mounted and with a sheetrock wall shown in dashed lines. 
     FIG. 6 is a top plan view of a second embodiment of the adjustable electrical box support of the invention made up of three releasably locking struts and showing the end tabs thereof bent prior to being shipped. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with the objects described above, and in reference to FIG. 1A, the adjustable electrical box support  10  is illustrated as comprising inner strut  12  and outer strut  14 . Inner strut  12  and outer strut  14  are formed as elongate channels that are sized to telescopically nest. Inner strut  12  slidingly resides within outer strut  14  to allow a user to telescopically adjust the overall support length X shown in FIG.  1 A. Struts  12  and  14  of support  10  are preferably formed with a channel-shaped cross section to provide stiffness and maintain secure engagement of the mating struts. Struts  12  and  14  are preferably formed of galvanized sheet steel, as is known in the electrical trade, of appropriate gauge and of channel dimensions to provide sufficiently stiff support for securely mounting one or more electrical boxes or other devices thereon. For example, 24 gauge (0.6 mm; 0.025 inch thick) sheet steel has been found to be a satisfactory material for the support of the invention. 
     Inner strut  12  terminates with tab  18  that essentially is an extension of web  12   f . A pair of minimal notches or cuts  16  are formed on opposite edges of tab  18  at its juncture to the inner strut web  12   f  to provide stress relief during the cutting and bending operation. A pair of discontinuous score lines  20  are formed in the front surface of tab  18  substantially perpendicular to axis L of inner strut  12  and at selected distances D, D′ from notches  16 , leaving some additional length of tab  18  extending beyond. As used herein, a discontinuous score line is understood to be formed by a linear series of spaced apart indentations in the metal surface, e.g. dashes or points, and which tend to make the metal relatively thin where the indentations are made. That is the indentations only partially penetrate the thickness of the metal but are deep enough to facilitate bending of the metal along the score lines. For example, in FIG. 1A, when the strut is made of 24 gauge sheet steel and the tabs are 1¾ inches in width, the depicted score lines  28  can be ⅝ inch in length and approximately between 0.006-0.020 inches in depth. 
     Distance D is preferably determined to allow a standard 1½ inches (38 mm) deep electrical box, when mounted to support  10  and extending outwardly therefrom (see FIG.  5 ), to be flush with the inner surface of a wall subsequently assembled to the wall studs S and S′. Distance D′ is located similarly for a standard electrical box that is 2⅛ inches (54 mm) deep. In other words, distance D or distance D′ is substantially equal to the depth of the electrical box being mounted. 
     Outer strut  14  has tab  26  with notches  24 , similar to the previously described notches  16 , and discontinuous score lines  28  to bend tab  26  in right angular relation as described above in relation to tab  18  of inner strut  12 . A further discontinuous score line (not shown) is formed on the back surface of tab  26 . 
     FIG. 1B shows a discontinuous score line  22  formed on the back surface of tab  18  and substantially aligned with notches  16 . Positioning discontinuous score line lines  20  on one surface of tab  18  and discontinuous score lines  22  on an opposite surface of tab  18  recognizes that tab  18  is intended to be bent in a direction to open score lines  20 ,  22  for optimum control of bending for straightness, position, and orientation normal to the length of strut  12 . It has been discovered that a discontinuous score line made up of a linear series of spaced apart indentations of appropriate depth and length, while providing for a controlled bend in a selected location retains a substantial portion of the metal&#39;s resiliency to withstand multiple bend cycles without fracture. The depth and length of the segments of the score lines are thus chosen with this object in mind. 
     As discussed above, while the principle of providing an adjustable length electrical box support has previously been recognized, the prior art adjustable components, with the exception of the previously discussed B-Line support having a frictionally engaged finger, are relatively loosely fitted together, and can readily fall apart particularly after being assembled and when held in a vertical position. None of the known prior art struts can be releasably locked together. By contrast, in the support made according to the invention, the telescoping members of support  10  are releasably locked in relation to each other at some desired overall length X. Length X of support  10 , once selected, is releasably locked by a series of detents  32  that are formed in web  12   f  of inner strut  12  and that can be moved to engage detents  34  that are formed in web  14   f  of outer strut  14  to releasably lock struts  12  and  14  as depicted in FIG.  2 A. Alternatively, struts  12  and  14  can be moved to disengage detents  32  from detents  34  as illustrated in FIG.  2 B. Detents  32  are formed as depressions in web  12   f  of inner strut  12  and effectively appear as dimples. Detents  32  may be round, square, or oval in cross section, for example, resulting in a hemispherical, rounded pyramid, or elliposid-shaped indentation. In the preferred embodiment, detents  32  are substantially hemispherical. Detents  32  are formed on inner strut  12  along a substantially straight, centrally located, axis L that is substantially parallel to the length of inner strut  12 . 
     The series of detents  34  are formed on web  14   f  of outer strut  14  in the manner described above with reference to detents  32  and reside along a central axis L′ which resides parallel to axis L of inner strut  12  when inner and outer struts  12  and  14  are assembled in sliding and releasably locked relation to each other as for example in FIG.  1 A. Detents  32  of inner strut  12  are preferably made slightly larger in diameter and depth than detents  34  of outer strut  14 , to nest snugly together. Detents  32 ,  34  are positioned equidistant from each other along inner and outer struts  12  and  14  so that multiple detents when in the releasably locked position of FIG. 2A nest simultaneously to obtain maximum engagement and security in maintaining the selected length X of support  10 . However, when length adjustments are necessary, the detents can be disengaged as in FIG.  2 B and the struts moved in the appropriate direction during which detents  34  of strut  14  slide on the surface  12 ( f ) of strut  12 . As will be understood by those skilled in the art, detents  32  and  34  are fundamentally a linear series of protrusions formed on a surface of a first strut that are oriented to nest into a mating linear series of depressions in a second strut when the first and second struts are releasably locked together. 
     In the interest of improving the efficiency of field installation, end tabs  18 ,  26  may be preformed (not shown) at a right angle to the length of electrical box support  10  at the factory and shipped in this form. When this is done, the installer only has to make a single bend at each end, cutting the required number of bends for this field-bending operation in half. 
     Referring now to FIGS. 2A and 2B, the releasable engagement and disengagement of inner strut  12  and outer strut  14  is illustrated, especially with respect to detents  32  and  34 . The channel shape of struts  12  and  14 , when assembled into a telescoping bar, has outer rims  38 ,  38 ′ on strut  14  that wrap substantially around inner rims  40 ,  40 ′ on strut  12  to keep the two channels engaged. When so engaged as in FIG. 2A, outer detent  34 , formed in outer strut  14  is pressed into inner detent  32  of inner strut  12 . Outer detent  34  is formed with depth d′, as measured from the front face of web  14   f  to the bottom apex of detent  34 . Inner detent  32  has a depth d″, as measured from the back surface of web  12   f  to the bottom apex of detent  32 . Inner detent  32  and outer detent  34  are preferably formed with the radius and depth of outer detent  34  being incrementally less than the depth of inner detent  32  to facilitate nesting together. Rims  38 ,  40 ,  38 ′, and  40 ′ keep struts  12  and  14  from separating and keep detents  32  and  34  in firm contact. When so engaged, detents  32  and  34  securely maintain the relative positions of struts  12  and  14  and hold the selected length X (see FIG. 1A) of electrical box support  10 . Length X is adjusted to equal the distance between two adjacent wall studs in a wall construction of a building, e.g. 36.8 cm (14.5 inches). When it is necessary to extend or compress the working length X of electrical box support  10 , the user pulls apart or pushes together outer strut  14  and inner strut  12  which causes each outer strut detent  34  to move out of the corresponding inner strut detent  32  as in FIG.  2 B and slide over the planar portion  12   f  of inner strut  12  between adjacent detents  32  and settle into the next inner strut detent  32  once other detents  32 ,  34  become aligned and when the desired length X has been obtained. 
     It should of course be understood that the struts  12  and  14  are formed to permit a snug sliding fit when the detents are disengaged so as to permit the surfaces  14   f  and  12   f  to slightly bend to permit the detents  34  to slide on surface  12   f  when being moved. 
     FIG. 3 shows support  10  after tab  18  and tab  26  have each been bent to form a pair of sequential right angles for installation between a pair of adjacent studs. Tab  18 , by way of example, is bent at score line  22  (FIG. 1B) in a first bend direction and at one of score lines  20  in a second bend direction. After bending tabs  18  and  26 , the assembled inner strut  12  and outer strut  14  are telescoped to adjust length X of support  10  in the direction shown by arrow A to fit the stud separation distance required. Because of the snug nesting of inner strut  12  in outer strut  14 , if the distance between a pair of adjacent wall studs were such that detents  32  and  34  did not engage one another, the pressure and frictional engagement of outer detents  34  against web  12   f  would, nonetheless, prevent unwanted sliding. In this manner, struts  12  and  14  would not tend to separate accidentally and particularly when held vertically by the installer of the support. 
     Referring now to FIG. 4, electrical box support  10  is shown after it has been adjusted in length and fixedly attached to adjacent studs S and S′ with detents  32  and  34  releasably locking the support length X during attachment. As noted above, length X of support  10 , when assembled, is substantially equal to the spacing between adjacent studs S, S′. Tabs  18  and  26  may be pre-punched with holes  19  to accept fasteners (as illustrated in FIGS. 1A and 3) or the needed holes may be formed during installation. Fasteners F for attaching electrical box support  10  to studs S and S′ may be of any convenient type, e.g. self-drilling sheet-metal screws. Fasteners F may be installed into the front or side face of studs S and S′. Next, electrical box B is mounted to support  10  in a selected position therealong. Since the holes formed in standard electrical boxes are spaced from one another at known distances, by forming detents  32  and  34  at appropriate intervals, the fasteners passed through the box holes will find the detents. An interval between adjacent detents that is appropriate to match the holes in commercial electrical boxes is 6 mm (¼ inch). A plurality of fasteners F′ are inserted through appropriate holes that are pre-formed in the base plate of electrical box B to nest respectively into detents  32  or  34 . As will be understood, the alignment of the holes in electrical box B with detents  34  assures that electrical box B will be mounted with its top and bottom surfaces TS and BS (FIG. 4) parallel to surfaces S- 1  and S- 2  of electrical box support  10 . According to the teaching in applicant&#39;s prior U.S. Pat. No. 5,405,111, engagement of screw fasteners through a formed detent improves the connective security. 
     FIG. 5 is a plan view of the adjustable electrical box support  10  of the invention, with end tab  18  and end tab  26  bent to engage adjacent wall studs S and S′. The length X of support  10  is adjusted to fill the space between studs S and S′, with tabs  18  and  26  bent respectively at discontinuous score lines  20  and  28 . In this configuration, support  10  mounts to studs S and S′ at a depth D 2  so that the outer edge of electrical box B will be substantially flush with an inner surface of a wall board W (shown in dashed lines) when mounted thereto. 
     FIG. 6 illustrates a further embodiment of the present invention in which electrical box support  50  comprises an assembly having three telescoping channel-shaped components, outer strut  54 , middle strut  56 , and inner strut  58 . Inner strut  58  fits slidingly within middle strut  56  which fits slidingly within outer strut  54 . Middle strut  56  is a channel without end tabs and with a series of detents along substantially its entire length and formed in the manner previously explained. Outer strut  54  has end tab  60 , and inner strut  58  has end tab  62 . This further embodiment functions similarly to the embodiment shown in FIGS. 1-5 and permits a greater range of length adjustability. For example, with two struts (according to the first preferred embodiment) of 25 cm (12 inches) length each, the overall span could be adjusted from a minimum of 25 cm (12 inches) to a maximum of 45 cm (17.7 inches); with three 25 cm (12 inches) long struts, an overall span of from 25 cm (12 inches) to 65 cm (25.6 inches) is possible. It is further recognized that with three struts slideably engaged, it is not possible to predict where the middle strut resides. Thus, in order to prevent middle strut  56  from becoming disengaged from one of the outer struts  54  or  58 , a stop (not shown) is provided in the nested channels to prevent this from happening. 
     The above detailed description of a preferred embodiment of the invention sets forth the best mode contemplated by the inventor for carrying out the invention at the time of filing this application and is provided by way of example and not as a limitation. Accordingly, various modifications and variations obvious to a person of ordinary skill in the art to which it pertains are deemed to lie within the scope and spirit of the invention as set forth in the following claims.