Abstract:
A removable reducer bushing is carried in a threaded port of an outlet box for coupling with a small threaded conduit and electively removable for coupling with a large threaded conduit thereby permitting a single box to handle multiple conduit sizes without separately procured parts. The bushing includes a deformable thread interruption resisting bushing rotation during removal of the small threaded conduit and frontal slots for manual removal of the bushing with a screwdriver against the resistance of the thread interruption.

Description:
FIELD OF THE INVENTION 
     The present invention relates to weatherproof electrical systems and, in particular, to a weatherproof outlet box having a removable reducer bushing for adapting differing electrical conduits without supplemental parts and with simple tools. 
     BACKGROUND OF THE INVENTION 
     Outdoor electrical systems need to conform with regulatory provisions to ensure safe and reliable operation in the presence of inclement weather. The outlet boxes and junctions and outlets are particularly prone to moisture conditions, and great care is taken to provide sealed construction. Gasketed cover plates are provided to seal the box cavity. Threaded ports receive rigid threaded conduits to protect against moisture entry at the electrical lines. Currently, commercially available boxes for outdoor use are provided for accepting only a single threaded conduit size. This presents problems for both the supplier and installer. The supplier must carry inventory and devote space for each size. The installer must carry both sizes inasmuch as the complete details of a job might not be fully defined at time of purchase. There are also situations, where due to design conditions or revisions, multiple conduit sizes are presented at a junction or outlet. If a larger conduit is required, the outlet box must be replaced. Where a smaller conduit is required, separately procured reducer bushings are available to handle the size reduction. This provides versatility for the installer, but further complicates supplier inventory. 
     Available reducer bushings are cylindrical sleeves provided with internal and exterior threads. For assembly, the installer manually threads the bushing into the outlet port, and thereafter threads the conduit into the bushing. To ensure a tight fitting, the installer often uses a wrench for final tightening resulting in a tightly seated condition with the bushing. Should the conduit need to be removed for repair or system modification, difficulties can arise. The breakaway torque at the conduit/bushing interface due to excessive installation force may be greater than the breakaway torque at the bushing/outlet box interface. Accordingly, the bushing rotates with the conduit, and remains attached after conduit removal. Removal of the bushing requires a wrench, which can damage the threads and prevent reuse of the bushing, and in practice both the conduit and bushing are discarded requiring new materials for completing the modification. 
     SUMMARY OF INVENTION 
     The present invention provides a weatherproof outlet box that overcomes the above mentioned problems for both the supplier and installer. The outlet box is provided with removable reducer bushings, requiring the stocking of only the large size box to the benefit of the supplier. In addition to the conventional inner and outer threads, the reducer bushings are provided with front slots to facilitate removal and reinstallation with a simple screwdriver. The outer threads include an enlarged thread discontinuity in the form of a radial cylindrical sleeve integral with the threads that swages and deforms during bushing insertion, to provide an increased breakaway torque at the outlet box that enables removal of the conduit without bushing rotation. This breakaway torque, however, may be overcome by a screwdriver at the slots to allow removal and reuse of the bushing. Thus a single outlet box can handle in varying commercial box configurations multiple conduit sizes without separately purchased parts. 
     Accordingly, it is an object of the invention to provide a weatherproof outlet box that can accommodate differing conduit sizes without supplemental parts. 
     Another object is to provide a reducer bushing for outlet boxes that resists concurrent rotation when removing an installed conduit. 
     A further object of the invention is to provide an outlet box containing all necessary components to allow a supplier to stock a single design for multiple applications and allow a user to procure a single design for variable field conditions. 
    
    
     
       DESCRIPTION OF DRAWINGS 
       The above and other objects and advantages of the present invention will become apparent upon reading the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a top perspective view of an outlet box provided with reducer bushings in accordance with an embodiment of the invention; 
         FIG. 2  is an enlarged fragmentary front perspective view of the outlet box and reducer bushing of  FIG. 1 ; 
         FIG. 3  is a perspective view of the reducer bushing of  FIG. 1 ; 
         FIG. 4  is an enlarged fragmentary perspective view of the circled area of  FIG. 3  showing the interruption on the outer thread of the reducer bushing; 
         FIG. 5  is a front view of the reducer bushing; 
         FIG. 6  is a side view of the reducer bushing; 
         FIG. 7  is a cross sectional view taken along line  7 — 7  in  FIG. 5 ; 
         FIG. 8  is a rear view of the reducer bushing; 
         FIG. 9  is an enlarged fragmentary cross sectional of the thread interruption; 
         FIG. 10  is a fragmentary cross sectional view showing the outlet box without the reducer bushing for direct connection with a rigid conduit; and 
         FIG. 11  is a fragmentary cross sectional view showing the outlet box with the reducer bushing for connection with a smaller rigid conduit. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the  FIG. 1 , a weatherproof electrical outlet box  10  is provided with removable reducer bushings  12  for allowing an installer, without accessing separate components, to establish on-site connection with conventional threaded rigid conduit and/or connectors of varying sizes using conventionally available tools. 
     The outlet box may be a single gang, double gang, round, extension or any box or enclosure approved by electrical codes for outdoor use box configuration of the types conventionally used in weather proof installations. As shown, a single gang unit with three port openings is provided, one on either side or one on the bottom. A suitable outlet box for use with the reducer bushings is product no. 11053 available from Sigma Electric Manufacturing Corp., assignee of the present invention. 
     As shown in  FIG. 10 , the outlet box  10  with the reducer bushing  12  removed is adapted to directly receive the pipe threaded end  14  of a rigid conduit  16  of a first size. As shown in  FIG. 11 , with the bushing  12  inserted the pipe threaded end  17  of a rigid conduit  18  of a smaller second size is coupled. In the present embodiment, the referenced outlet box is adapted to handle ½ in. and ¾ in. threaded conduit and with be described with reference thereto. The threaded connections are provided with 14 NPSM (American Standard Straight Mechanical Pipe Thread) pipe threads. In both conditions, the conduit connection at the box meets prevailing UL Standard 514 regarding conduit and fittings. 
     The outlet box  10  includes a unitary outlet body  30  formed of die cast aluminum. The body includes a rectangular base wall  32  circumscribed by forwardly projecting longitudinally spaced parallel end walls  34  and transversely spaced parallel side walls  36  terminating at an upper rim  38 . The interior surfaces of the walls provide a forwardly opening wiring cavity  40 . The outlet box  10  includes three access ports; ports  42 ,  44  at the end walls  34 , and port  46  at the base wall  32 . As representatively shown for the side port  42  in  FIGS. 10 and 11 , an annular body or lug  50  is integrally formed with the associated wall  34 . The lug  50  includes a central bore  52  having an outwardly opening portion provided with internal pipe threads  54  and inwardly terminating at an inwardly extending annular flange  56 . The threads  54  are adapted to receive, with the bushing  12  removed, the threaded end  17  of the larger conduit  16 , and with the bushing  12  installed, the threaded end  17  of the smaller conduit  18 . The axial length of the threads is sufficient to receive typical threaded conduits to providing at least about five thread turns for pull strength in accordance with regulatory requirements. 
     The outlet box  10  is provided with apertured mounting plates  58  carried on upwardly projecting threaded posts  59  at the end walls adjacent the rim for accommodating mounting of electrical devices, such as switches and receptacles and/or cover plates. In final assembly, the box, cover plate and conduit connections provide a weatherproof assembly. 
     Referring to  FIGS. 1 and 3  through  9 , the reducer bushing  12  comprises a one-piece annular body  60  formed of a suitable material such as a zinc die casting. The bushing  12  has an exterior pipe threaded section  62  and an interior pipe threaded section  64 . The body  60  frontally terminates with an annular rim  66  and rearwardly terminates with an annular base  68 . The outer threaded section  62  an outer diameter substantially the same as the rim  60 . The interior threaded section  64  extends rearwardly from a frustoconical entry surface  74  to the base  68 . 
     The rim  66  includes a pair of diametrically opposed frontally opening U-shaped slots  80 , providing wide diameter reacting surfaces for facilitating the insertion and removal of the bushing  12  with a simple tool, such as a screwdriver or other bladed device. A plurality of circumferentially spaced, axially aligned V-shapes grooves  90  are formed in and across the external threads to form a helical series of serrated thread sections  92 . The grooves  90  extend rearwardly from the base of the rim. The grooves  90  are effective for limiting the removal torque necessary for remove the bushing without damage to the outlet box and for reducing the overall weight of the bushing and the manufacturing costs thereof. For the described outlet box accepting ½ and ¾ in. conduit, a circumferential series of six aligned grooves  90  are provided. 
     An enlarged thread interruption or ferrule  92  is formed at a center portion of the outer threaded section  62 . In assembly, the interruption  92  is deformed and swaged against the threads  54  of the outlet box lug  50  to increase the bushing breakaway torque sufficient to insure that the conduit  18  will be removable without rotating the bushing  12 . The removal torque, however, does not limit the manual removal of the bushing using a screwdriver at the larger diameter slots  80 . Referring to  FIGS. 4 and 9 , the interruption comprises a local cylindrical sleeve at an intermediate turn of the thread  62 . The interruption  92  terminates radially at the diameter of the threads and the outer wall projects axially from the sides of the thread. The interruption  92  includes an outwardly opening counterbore  94  whereby the interruption  92  has a thin cylindrical wall  96 . Upon insertion, the wall  96  is deformed and establishes an increased mechanical engagement with the lug to increase the breakaway torque. For ¾ inch to ½ inch reducer bushing, an interruption having an axial length of about 0.030 inch, an outer diameter of 0.034 inch and an inner diameter of about 0.018 inch provides sufficient torque resistance to prevent busing rotation upon removal of a firmly seated inner conduit. The hollow cylindrical configuration promotes the swaging during installation, however, solid construction and/or alternative cross sectional shapes may obviously be utilized. 
     In assembly as shown in  FIGS. 2 and 11 , the bushing  12  is threaded into an outlet box opening until the base seats against the flange  56 , manually and/or using a tool torquing at the slots thereby swaging the interruption  92  against the threads  54 . At seating, the rim of the bushing  12  is slightly exposed beyond the outlet box outer wall  34  thereby allowing the user of tools of varying widths. The outlet box  10  thus enables the installer to adapt for conduit sizes without the need for separately obtained adapters, and to source a single box design for multiple conduits applications. 
     While the invention has been described with reference to outlet boxes furnished with the bushings installed, it is apparent that the bushings may be used as a separate component for existing boxes and compatible box designs for providing the versatility and advantages in accommodating differing sized conduits. 
     The above description is intended to be illustrative of the preferred embodiment, and modifications and improvements thereto will become apparent to those in the art. Accordingly, the scope of the invention should be construed solely in accordance with the appended claims.