Abstract:
A plastic mounting plate closes a electrical box which delivers wires to an alarm unit or emergency light or the like. The alarm unit is mounted to the mounting plate by a snap connection and a tab-in-slot connection, without requiring the use of a tool. The mounting plate is connected to the electrical box by screws which engage threaded holes provided by the electrical box. The mounting plate can be mounted to either a single-wide electrical box or a double-wide (4×4) electrical box and provides corresponding holes for connection to either box. An alternate mounting plate for a single-wide electrical box is also provided.

Description:
This application is a continuation-in-part of U.S. Ser. No. 08/953,122, filed Oct. 17, 1997, now U.S. Pat. No. 6,133,843. 

   FIELD OF THE INVENTION 
   The present invention relates to alarm units and associated devices which mount to electrical boxes. More particularly, the present invention relates to a mounting plate for attaching an alarm unit module to either a recessed or a surface mounted electrical box. 
   BACKGROUND OF THE INVENTION 
   For purposes of safety and security, alarm or security related electric devices can be positioned throughout a building or structure. The devices can constitute detectors such as smoke detectors, or can be annunciators such as audible fire and security alarms, or can include emergency lights. 
   The detectors can include motion detectors or other intruder alarms. Additionally, other local area monitoring devices which sense an ambient condition or provide a local alarm can be mounted at locations throughout a building or other structure. 
   In the case of a building having unfinished walls, such as a warehouse, such devices are typically attached to surface mounted electric wire electrical boxes or junction boxes. These boxes are connected by surface mounted conduits to a central location. The conduits carry signal wires between the central location and the local electrical device, such as the alarm unit or detector. 
   The alarm units are typically installed by two screws which engage standard screw holes provided on top and bottom sides of the open face of a respective electrical box. 
   Although such mounting may be adequate to support the alarm unit, it would be desirable to provide a mounting plate which integrates the alarm unit and the respective electrical box into a unitary appearing mounting configuration. It would be desirable to provide a mounting plate which, by its presence on the electrical box, designates the electrical box as being dedicated to a particular safety or security system. It would be desirable to provide a mounting plate which quickly and easily attaches an alarm unit thereto. It would also be desirable to provide a mounting plate which is installable at either a single or double wide (4×4) electrical box without leaving gaps between the mounting plate and the electrical box. 
   SUMMARY OF THE INVENTION 
   The mounting plate of the present invention is attachable to a wall recessed electrical box or a surface mounted electrical box. The mounting plate provides an easy mounting arrangement for an alarm unit or module or other electrical device to be attached thereto. The mounting plate and associated alarm units or module include snap engagement parts which allow the alarm unit or module to be attached to the mounting plate without any need for fasteners or tools. 
   The mounting plate can include a snap lever arrangement for attachment of a compatibly fashioned unit or module which provides a snap stop arranged to engage the snap lever. The mounting plate can also include a slot and the unit or module can include a tab for insertion into the slot, for an additional engagement between the mounting plate and the module or unit. 
   The arrangement of the invention provides for a quick and easy installation or exchange of an alarm unit, emergency light or other electrical device onto a pre-installed mounting plate. 
   The mounting plate can be provided in alternate embodiments including a larger version for covering either a single or double wide (4×4) electrical box. A smaller mounting plate is particularly suited for a single wide electrical box. The mounting plates can be significantly oversized when compared to an open face of either electrical box. 
   When mounted to a recessed electrical box, the electrical box is effectively concealed. Additionally, the screws which connect the mounting plate to the electrical box can be covered by the respective alarm unit, or emergency light, thereby improving the overall appearance of the assembly. 
   An attachment arrangement incorporating screws or other fasteners is provided for connecting the mounting plate to the standard mounting screw holes available in a electrical box. 
   The mounting plate is advantageously designed to mount an alarm unit, or other electrical device onto the electrical box and to present a unitary appearance therewith. When so mounted onto a wall recessed electrical box, the electrical box is not visible. 
   The mounting plate of the present invention is formed as a one-piece, molded plastic structure. The mounting plate can be color coded for type of service, such as a very visible red or yellow fire-alarm color for fire protection or alarm devices. Additionally, different colors can represent different emergency situations. For example, red alarm mounting plates can be allocated for fire alarms, green alarm mounting plates can be allocated for tornado warnings, and blue alarm mounting plates can be allocated for a “take cover immediately” warning. Other colors can be allocated for warning of the presence of excessive concentrations of toxic or explosive gas, or other emergency situations. 
   The invention also encompasses a mounting plate which can interchangeably receive either an audible alarm unit or an emergency strobe light, or a combination of the two services. Alternate types of modules can also be attached. 
   In addition to being architecturally appealing, the mounting plate is also functional. When the alarm unit or emergency light is removed from the mounting plate, the mounting plate provides an enclosure and protection to signal wires located within the otherwise open electrical box. 
   Also, unlike the relatively smaller electrical box, the mounting plate provides a mounting surface which is larger than the alarm unit mounted thereto which provides a stable and secure mounting arrangement. Once installed onto the mounting plate, no portions of the alarm unit overhang the mounting plate. This arrangement avoids an exposed edge vulnerable to prying the alarm unit off the electrical box by vandals. 
   When installed onto a recessed electrical box the relatively oversized mounting plate covers a greater expanse of wall so that a rougher and larger wall opening around the electrical box can be covered. This is particularly advantageous for retrofitting walls with electrical boxes for alarm service. 
   While the alarm unit or emergency light is being exchanged, tested, or during construction, the conduit and electrical box is clearly designated as dedicated to signal wires for alarms to reduce any confusion between signal conduits and signal electrical boxes and electrical power conduits and electrical power electrical boxes. In this way, the alarm system components can be more clearly demarcated. 
   In addition to screws, in an alternate embodiment, the mounting plate can be attached using other types of fasteners. In this regard, snap-fit fasteners can be used. 
   Other features and advantages of the present invention will become readily apparent from the following detailed description, the accompanying drawings, and the appended claims. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a mounting plate installed on a wall recessed electrical box; 
       FIG. 2  is an exploded perspective view of the mounting plate to be assembled on the wall recessed electrical box; 
       FIG. 3  is a fragmentary perspective view of a portion of the mounting plate shown in  FIG. 2 ; 
       FIG. 4  is a front elevational view of the mounting plate shown in  FIG. 1 ; 
       FIG. 5  is a sectional view taken generally along lines  5 — 5  of  FIG. 4 ; and 
       FIG. 6  is a front elevational view of an alternate mounting plate. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   While the present invention is susceptible of embodiment in various forms, there is shown in the drawings and will hereinafter be described a presently preferred embodiment, with the understanding that the present disclosure is to be considered as an exemplification of the invention, and is not intended to limit the invention to the specific embodiment illustrated. 
   The present invention is an improvement to the mounting plate and module system described in U.S. Ser. No. 08/953,122, filed Oct. 17, 1997 and herein incorporated by reference. 
     FIG. 1  illustrates an alarm unit assembly  10  installed onto an electrical box  12  (shown in  FIG. 2 ) which is recessed into a wall  13  from a wall surface  14 . 
   A mounting plate  17  is connected to the electrical box. The mounting plate has a surrounding edge  19  which is adjacent to the wall surface  14 . 
   A strobe light alarm unit  20  is mounted to the mounting plate  17 . The alarm unit includes a lens  21  covering a lamp  22 . In the illustrated embodiment, the strobe light alarm unit also includes an audible alarm  20   a , in addition to the strobe light lamp  22 , for audible signaling of an alarm condition. The alarm unit  20  includes a disengagement slot  24  used for removal of the unit  20  from the plate  17 , as described below. 
     FIG. 2  illustrates the assembly  10  in an exploded view. The assembly  10  (components of which are described below) is installed over and onto a front face of the wall recessed electrical box  12  which is installed to be recessed from the wall surface  14  (portions of the wall shown broken away). The surface  14  can be on a vertical wall as shown, or on a column, or a ceiling, or on any exposed surface. 
   The electrical box  12  is connected by at least the one conduit  16  such as being connected to a top panel  23  of the electrical box  12 . The conduit  16  carries signal wires into the electrical box. 
   The conduit  16 , as shown, is connected to the top panel  23  by way of a conventional, threaded two-piece conduit connector  34 . Also, the box  12  provides bent-tabs  38 ,  40  which provide threaded screw holes  38   a ,  40   a , therethrough, for receiving screws. 
   Mounted to and covering an open front face of the electrical box  12  is the mounting plate  17 . The mounting plate  17  has a front side  50 , and a back side  52 . The mounting plate is preferably a one-piece, molded plastic, color coded structure. 
   The front side  50  includes a recessed central region  62  having four offset, smaller supplemental recesses  66 ,  68 ,  70 ,  72 . The recesses  66 ,  68 ,  70 ,  72  are arranged in a rectangular pattern and are open to the recessed region  62 . The recesses  66 ,  68 ,  70 ,  72  are arranged recessed into a surrounding rim  74 . 
   Screw supporting cylinders  78 ,  80  with through-holes  78   a ,  80   a , respectively, are arranged extending through the recessed region  62 . The holes  78   a ,  80   a  are aligned with the screw holes  38   a ,  40   a  of the electrical box  12 . 
   Screws  81 ,  82  can extend through the holes  78   a ,  80   a  which have plain bores. They can be screwed into the screw holes  38   a ,  40   a  to mount the mounting plate  17  to the electrical box  12 . Other types of fasteners could be used for this purpose. For example, snap-fit fasteners each of which include resilient members such as ridges, or hooks, or ribs, or similar formation, can be inserted into the screw holes  39   a ,  40   a  to engage therewith. 
   A snap lever  84  extends outwardly from within the recessed region  62 . The snap lever  84  engages the alarm unit  20 , as described below. 
   The mounting plate  17  further provides a slot  102  formed through the recessed region  62 , and also into the rim  74  in a direction generally parallel to a front surface  62   a  of the recessed region  62 . The slot  102  receives a tab  106  of the strobe light unit  20 . A front portion  74   a  of the rim  74  thus retains the tab  106  from frontward movement. The strobe light unit  20  can be easily and quickly installed to the mounting plate by sliding the tab  106  into the slot  102  at a slight angle, pivoting the unit  20  toward the mounting plate, and engaging the snap lever  84  to the unit  20  as described below. 
   The unit  20  further provides extending tab portions  110  which are arranged to inter-fit into the smaller recesses  66 ,  68 ,  70 ,  72  to cover oblong screw-receiving bores  112 ,  114 ,  116 ,  118 . These bores provide an alternate means of mounting the mounting plate to a 4×4 electrical box. 
   The mounting plate  17  provides a convenient mounting for a plurality of different types of alarm units.  FIG. 2  also illustrates an audible alarm unit  119  which is mounted in an identical fashion. The alarm unit  119  includes a horn or audible signal generator  119   a  within the unit  119 . 
   Either of the alarm units  20 ,  119 , can be attached by using the tab-in-slot and snap connection components. 
   The mounting plate  17  further includes a central opening  130  through the recessed region  62  which allows the connection of wires from the unit  20 , or the unit  119 , to wires within the electrical box  12  from the conduit  16 . The opening  130  can be made smaller than an open face of the electrical box, so that if a unit  20 ,  119  is removed from the mounting plate, loose wires can be retained within the electrical box by the mounting plate. 
     FIG. 3  illustrates the snap lever  84  and associated structure in more detail. The snap lever  84  is a substantially L shaped member. The snap lever  84  extends from a base end  84   a  to a free end  84   b , toward the front surface  62   a  of the recessed region  62 . 
   The base end  84   a  is formed onto a rectangular base member  302  that extends perpendicularly from the surface  62   a . Lateral wall members  304 ,  306  extend perpendicularly from both the base member  302  and the surface  62   a  and stiffen the base member  302 . 
   The surface  62   a  includes a rectangular opening  308  which is present to allow injection molding of the snap lever  84  unitarily with the recessed region  62  in a simple two-piece separable mold. A substantially horizontal leg  84   c  of the snap lever  84  is angled upwardly toward the surface  62   a . 
     FIG. 4  illustrates the alarm unit  20  and the disengagement slot  24 . The slot  24  is sized to receive a screw driver blade to disengage the snap lever  84  from the unit  20 . 
     FIG. 5  illustrates the unit  20  includes a snap stop  85  which engages the distal end  84   b  of the snap lever  84 . A guiding wall  322  is adjacent the slot  24 . For disengaging the unit  20  from the plate  17 , the guiding wall  322  acts to guide the screw driver blade onto a top surface of the leg  84   c  of the snap lever  84 , to depress downwardly the leg  84   c  to disengage the free end  84   b  from the snap stop  85 . The snap stop  85  is a short, inwardly directed vertical wall portion of top wall  20   b  of the alarm unit  20 . 
   The attachment components of the alarm unit  119  (shown in  FIG. 2 ) to the plate  17  are identical to those of the alarm unit  20 , and need not be described in detail. 
     FIG. 6  illustrates an alternate mounting plate  417  of the present invention. This mounting plate  417  is particularly suited for a single-wide electrical box and includes the snap lever  84  and associated structure as previously described, for holding the electronic unit, such as a strobe light  20  or the audible alarm  119 , to the plate  417 . 
   A slot  422  arranged on the bottom end of the plate  417  receives a tab  106  of the electronic unit as previously described. The plate  417  includes a recessed region  430  for slidingly receiving an alarm unit. The recessed region  430  is surrounded by a rim  432 . 
   Located in a central region of the recessed region  430  is an aperture  440  for passing wires between the mounted electronic unit  20 ,  199  and the electrical box. Located between the screw-receiving cylinder  420  and the slot  422  are oval cylinders  444 ,  446 . 
   The cylinders  444 ,  446  each receive a screw which connects to the fixture-receiving holes of the electrical box, such as  38   a ,  40   a , as shown in FIG.  2 . The oval shape of the cylinders  444 ,  446  allows for some adjustment of verticality of the mounting plate  417  with respect to the electrical box, particularly for aesthetic appearance. The sectional views of the plate  417  are as described in U.S. Ser. No. 08/953,122, except as modified by the above description. 
   The alternate embodiment of  FIG. 6  can be used with the alarm units as shown in  FIG. 2 , the strobe light  20  and the audible alarm  119 . For use with these alarms, the tabs  110  on the alarm units can be broken off easily, as described in U.S. Ser. No. 08/953,122. The alarm units thus modified have a rounded rectangular profile to fit snugly within the recessed area  430 . 
   The present invention provides a system of attaching alarm units  20 ,  119  to mounting plates such as plates  17 ,  417  that requires no tools for attachment and only requires a screw driver for detachment of the alarm units from the plates. The system allows alarm units to be quickly and securely installed onto mounting plates. The system provides for a lower parts and manufacturing cost by eliminating metallic fasteners, as well as a lower installation cost by reducing the time required to install each unit to its mounting plate. 
   From the foregoing, it will be observed that numerous modifications and variations can be effected without departing from the true spirit and scope of the novel concept of the present invention. It is to be understood that no limitation with respect to the specific embodiment illustrated herein is intended or should be inferred. The disclosure is intended to cover, by the appended claims, all such modifications as fall within the scope of the claims.