This invention relates generally to plugs for plugging holes in relatively thin, sheet metal members or boxes and, in particular, to plugs for plugging conduit holes formed in sheet metal electrical junction boxes and control enclosures.
To simplify the task of installing electrical junction boxes and control enclosures, these structures are typically provided with a number of pre-formed conduit holes which, at the time of manufacture, are only partially formed in order to leave each hole with an easily removed "knock-out" plug. Once removed, such plugs cannot be replaced. For a number of reasons, it frequently happens that knock-out plugs are removed to result in holes which are ultimately never used. For example, changes and modifications in existing wiring may obviate the need for previously used conduit holes. Because the presence of unplugged openings in electrical junction boxes or control enclosures is undesirable both from the standpoint of safety and contamination, various plug constructions have been employed for capping unused conduit holes.
A recurrent problem in plugging such holes is that the actual hole size often varies somewhat from manufacturer to manufacturer even among holes of the same nominal "standard" dimension. Furthermore, the thickness of the sheet metal forming the boxes or control enclosures is rarely uniform among the various manufacturers. These dimensional variations complicate the task of providing plugs which function effectively, despite the variations in actual hole dimensions and sheet metal thicknesses from one box to another, to form a tight seal against the entry of dust or other foreign matter.
One prior art hole plug which is disclosed in my U.S. Pat. No. 3,366,267 offered an effective solution to the problem of hole dimension and metal thickness variations. That plug incorporated a disc having a bent angularly displaced portion formed along a chord thereof. A number of tabs along the underside of both the bent and unbent portions of the disc cooperated to securely lock the plug in the hole when the plug was inserted into the hole and pressed so as to straighten the bent portion of the disc. While this plug was effective, it is difficult to use in larger size holes since considerable force is required to straighten the bent portion when the plug diameter exceeds that required to plug a knock out hole that will receive a standard 11/4 inch electrical conduit. The use of a hammer is required in the larger size discs frequently resulting in undesirable denting and disfiguration of the disc and impairment of its sealing function.
The present invention is directed to an improved hole plug which can be effectively implemented in the larger sizes so as to provide a tight closure seal despite deviations in actual conduit hole size from standard nominal dimensions. The improved plug can be pressed into place with less force than is typically required to install similar plugs of comparable size. This reduces the possibility of denting or disfiguration of the plug disc during installation and readily adapts the plug for use in plugging large as well as small holes.
In one principal aspect of the present invention, a plug for plugging holes in sheet material includes a generally planar disc divided into a major portion and a relatively smaller minor portion joined to each other. The disc is bent along the juncture of the portions such that the minor portion is angularly displaced from the plane of the major portion. A groove is positioned at the juncture having a substantial depth relative to the thickness of the disc such that the resistance of the disc to bending along the groove is substantially reduced.
In another principal aspect of the present invention, the groove comprises a plurality of groove segments in longitudinal alignment with one another and separated from each other by lands which are of greater thickness than the depth of the groove segments.
In still another principal aspect of the present invention, each groove segment is of substantially V-shaped cross section.
In still another principal aspect of the present invention, the depth of the groove is between about 25%-60% of the thickness of the disc.
In still another principal aspect of the present invention, the disc is substantially circular and the juncture between the major and minor portions is on a chord of the disc.
These and other objects, features and advantages of the present invention will be clearly understood through consideration of the following detailed description.