Metal-stud electrical box

The invention relates to the use of drill-pointed screws to attach electrical boxes to heavy gauge metal studs. The drill-pointed screws of the invention are at least two inches long and have a length to thread diameter ratio of at least 12 to 1. The electrical boxes of the invention have brackets that form a relatively steep angle to the stud, such a steep angle having proven necessary to get the drill-pointed screws to penetrate the metal. The electrical boxes may also include a second set of brackets that angle more shallow angle with the stud surface and are more suitable for use with nails. The electrical boxes are preferable made of extra-thick relatively shatter resistant engineered plastic and are preferably formed so that they can be vertically stacked in a nested fashion.

FIELD OF THE INVENTION
 This invention relates to electrical boxes and means and methods for
 mounting them on metal studs.
 BACKGROUND OF THE INVENTION
 During housing construction, many electrical boxes are typically mounted on
 wall studs to accommodate electrical equipment such as outlets and
 switches. In the last decade, it has become increasingly common for these
 wall studs to be made of a metal, especially steel. Mounting an electrical
 box on a metal stud can be difficult and the time required to mount all
 the electrical boxes called for in a construction project can be
 substantial.
 Prior art electrical boxes have been designed for mounting on wooden studs
 by means of nails or screws. These boxes are usually provided with
 external mounting brackets on their tops and bottoms. Generally, the
 brackets are angled away from the boxes to provide space for the operation
 of a hammer, screwdriver, or drill. This is particularly important when
 the electrical box is of the longer multi-gang type. The mounting brackets
 are also commonly angled toward the front of the box to further facilitate
 access to them during installation.
 While these prior art electrical boxes can be mounted to very light gauge
 metal studs by means of nails or screws, they cannot be so mounted to
 heavier gauge metal studs such as load-bearing studs. Heavier gauge metals
 are not penetrated by ordinary nails and screws. Clamps have been used as
 an alternative mounting means. Mounting with clamps, however, is
 cumbersome and slow in comparison to mounting by nails or screws.
 SUMMARY OF THE INVENTION
 An object of the present invention is to provide an electrical box and
 mounting means that satisfies the demands of modern housing construction,
 including the need for electrical boxes that attach to metal studs. Such a
 mounting means is a drill-pointed screw.
 When the electrical box mounting brackets guide the screws at an angle that
 is too far from perpendicular to a steel stud and the steel is of gauge 18
 or thicker, and particularly if the steel is of gauge 16 or thicker, the
 drill-pointed screws will dance and slip across the surface of the steel
 without effectively penetrating it. For there to be effective penetration
 of the steel, the screw must be directed at an angle that is no more than
 about 14 degrees from perpendicular to the stud surface. Therefore, one
 aspect of the invention is an electrical box with external mounting
 brackets that guide fasteners into a stud at an angle within about 14
 degrees of the perpendicular.
 For electrical boxes generally, and for multi-gang electrical boxes in
 particular, it was unexpected that there would be an angle at which a
 fastener guide would allow ready access for an installation tool while
 being steep enough for a drill-pointed screw to penetrate the metal. For
 all electrical boxes, angling the fastener guides away from the box
 facilitates the operation of installation tools. For multi-gang electrical
 boxes this angle must be particularly steep. Whereas for single gang
 electrical boxes the space on the stud opposing side of the electrical box
 can be of use for the operation of a hammer, screwdriver or drill,
 particularly when an extra-long fastener is used, for multi-gang
 electrical boxes this space is of no use at all.
 An angle of about 14 degrees from the perpendicular is too shallow to allow
 ready mounting of an electrical box with a hammer and nails. Thus, the new
 electrical boxes could potentially present a contractor with the necessity
 of stocking two types of electrical boxes, one for use with nails and the
 other for use with drill-pointed screws. To avoid this inconvenience, a
 preferred embodiment of the invention has two sets of fastener guides, one
 for nails, the other for drill-pointed screws. The nail guides form angles
 that are 20 degrees or more from the perpendicular.
 The drill-pointed screws of the present invention are also new. These
 drill-pointed screws have a greater length to major thread diameter ratio
 than prior art drill-pointed screws, the screws of the invention have a
 length of 1.5 to 3.25 inches, a major thread diameter between 0.110 and
 0.160 inches, and a length to major thread diameter ratio of at least 12
 to one. The drill bit point is generally no more than about 0.25 inches
 long and the threaded portion is generally at least 1 inch long.
 An electrical box with brackets accommodating two sets of fastener guides
 tends to be somewhat voluminous. To compensate for this disadvantage, a
 further aspect of this invention is an electrical box that is shaped to
 allow nested stacking. This feature reduces shipping costs, eases the
 handling of large quantities of boxes, and is convenient for contractors
 and end users.
 When a conventional electrical box made of a relatively shatter resistant
 engineered plastic is firmly attached to a heavy gauge metal stud by means
 such as a drill-pointed screw, the walls of the box, which are ordinarily
 about 0.08 inches thick, have a tendency to bow. Therefore, another aspect
 of the invention is an electrical box made of a relatively shatter
 resistant plastic having walls that are thicker than those of prior art
 relatively shatter resistant electrical boxes, the boxes of the present
 invention have wall thicknesses of about 0.10 inches, preferably about
 0.12 inches.
 Another aspect of the invention is a method for mounting an electrical box
 to a metal stud that comprises mounting the electrical box using
 drill-pointed screws, preferably with the drill-pointed screws entering
 the stud at an angle of about 14 degrees from the perpendicular.

DETAILED DESCRIPTION OF THE INVENTION
 FIGS. 1 through 4 show a two gang electrical box of the present invention.
 Referring to FIG. 1, the two gang electrical box 1 has a front 2, a back
 3, and four sides, which are a stud facing side 4, a distal side 5, a top
 side 6, and a bottom side 7. The front is open to allow access to the
 interior of the box. The stud facing side 4 has projections 8 and 9 that
 fix the position of the box relative to a stud when stud facing side 4 is
 placed against a flat stud surface. Projections 8 are intended to rest
 against a stud surface to which the box is to be attached Projections 9
 are intended to lie over the front edge of the stud and to fix the
 position of the front of the box so that it lines up with a sheet of
 drywall subsequently placed over the stud. When the box is mounted on the
 right side of a vertically oriented stud, the top side 6 will be above the
 bottom side 7, although the situation would be reversed if the box were
 mounted on the left side of the stud.
 The top 6 and the bottom 7 each have mounting bracket frames 10. Each of
 these mounting bracket frames has a nail guide 11 and a screw guide 12.
 When projections 8 are resting against the surface of a stud, fasteners
 mounted in these guides will make determinate angles with an imaginary
 line that is perpendicular to the stud surface. Whether or not a box is
 provided with projections 8, this position in which these angles are
 determined is the position of the box relative to the stud when the stud
 facing side of the box is pressed up against the stud. This position fixes
 the angle made by the fastener guides with the stud surface. The angle
 that the guides make with the stud surface while the box is in this
 position, which angle can be measured in terms of degrees from the
 perpendicular, determines whether the fasteners will effectively penetrate
 the stud, at least in the case of a drill-pointed screw and a heavy gauge
 metal stud.
 As shown in FIG. 2, fastener guides 11 and 12 angle towards the front of
 the box 2 at an angle of 10 degrees as they extend away from the stud
 facing side 4. As shown in FIG. 3, fastener guides 11 and 12 also angle
 away from the top 6 and bottom 7 sides of the box as they extend from the
 stud facing side 4. If the box is mounted on the side of a vertical
 positioned stud, the screw guides make an angle of 10 degrees with the
 horizontal whereas the nail guides make an angle of 30 degrees. These
 angles make it easier to install the fasteners when the box is being
 mounted within a wall.
 Another way of describing the angles made by the fastener guides, or
 equivalently, the angles made by fasteners mounted in the fastener guides,
 is in terms of projections. When the stud facing side 4 of the box 1 is
 pressed up against a stud, the front of the box 2 lies in a plane
 perpendicular to the plane of the stud surface. When the angles the
 fastener guides make with a perpendicular to the stud surface are
 projected onto the plane of the front of the box, these angles are 10
 degrees for the screw guides and 30 degrees for the nail guides, as shown
 in FIG. 3. When the angles the fastener guides make with a perpendicular
 to the stud surface are projected onto a plane that is perpendicular to
 both the stud surface and the plane of the front of the box, the projected
 angles are all 10 degrees, as shown in FIG. 2.
 Being angled 10 degrees away from the horizontal and 10 degrees towards the
 front of the box, the screw guides make a total angle which is about 14
 degrees from perpendicular to the stud surface. Once again, these angles
 are measured relative to a flat stud surface and assuming the box is
 positioned properly with its stud facing side pressed against that
 surface.
 As shown in FIG. 4, fastener guides 11 and 12 are made up of top surfaces
 16 and opposing bottom surfaces 17. This arrangement holds a fastener
 firmly in position without unduly hindering its installation.
 As can be seen in FIGS. 1, 2, and 4, each of the sides 4, 5, 6, and 7 jogs
 towards the interior of the box at a point 15 that is approximately midway
 between the front of the box 2 and the back 3. Sides 4 and 5 jog in by a
 distance that is slightly greater than the thickness of the sides. Sides 6
 and 7 jog in by a greater distance, which is slightly greater than the
 thickness of these sides at the points where they bulge inward to
 accommodate electrical device mounting holes 13. These jogs allows
 identical boxes 1 to be stacked in a vertically nested fashion. That is,
 the back 3 of one box 1 can be slid thorough the front 2 of another
 identical box to a distance that is approximately half way to the back 3.
 Placing the jog approximately midway between the front of the box and the
 back provides the greatest benefit, although a significant benefit would
 still be achieved if the offset occurred only about one quarter of the way
 from the front to the back.
 The sides of the box may be otherwise shaped to accommodate nested
 stacking. The sides of the box may angle steadily inward along the
 distance from the front of the box to the back of the box. The lower
 portions of the box may be provided with indentations to accommodate
 corresponding inward bulges in the upper portions of the box, such as
 bulges created to accommodate electrical device mounting holes.
 Electrical boxes shaped to accommodate nested stacking may be produced in
 families having various numbers of gangs. Within such a family, each
 electrical box can be nested within any other electrical box having an
 equal or lesser number of gangs,
 As shown in FIG. 3, the box 1 has eight flexible cable clamps 14.
 Electrical cables can be slid into the box through these clamps. Once the
 cables are installed, the clamps hold the cables securely in place.
 The box 1 has two pairs of electrical device mounting holes 13, making it a
 two-gang electrical box. Fixtures, such as light switches and electrical
 receptacles, can be mounted in the box by means of these holes. Although
 the invention has thus far been described with reference to the two gang
 electrical box 1, it encompasses electrical boxes with any number of
 gangs. FIG. 5 shows a three gang electrical box 18 of the present
 invention. FIG. 6 shows a four gang electrical box 19 of the present
 invention. FIG. 7 shows a single gang electrical box 20 of the present
 invention.
 Ceiling boxes can also be made in accordance with the present invention.
 FIGS. 8 and 9 show a ceiling box 21. It has a front 2, a back 3, and a
 stud facing side 4, and a rounded side 28. The stud facing side has a
 projection 9 that fits over the edge of a stud when side 4 is pressed up
 against the stud. Although box 21 has four electrical device mounting
 holes 13, it is not considered a multi-gang electrical box. Box 21 has
 indentations 22 in the lower portions of its rounded side 28. These
 indentations facilitate vertical stacking and correspond to bulges 23 in
 the upper portions of the box's rounded side 28, which bulges accommodate
 the electrical device mounting holes 13.
 The boxes 1, 18, 19, 20, and 21 are single piece, injection molded, and
 made of a relatively shatter resistant engineered plastic. Thermoplastics,
 such as polycarbonate, polyvinylchloride, and Valox.TM. are considered
 relatively shatter resistant engineered plastics. Thermoset plastics, such
 as phenolic resin and polyester resin plastics, on the other hand, are not
 considered relatively shatter resistant.
 FIGS. 10 and 11 show a drill-pointed screw 30 of the present invention. The
 screw has a drill bit portion 31, a threaded portion 32, a shaft portion
 33, and a head portion 34. The drill bit portion 31 and the shaft portion
 33 each have a diameter of 0.108 inches. The major diameter of the threads
 of the threaded portion 32 is slightly greater, being 0.133 inches. The
 pointed end 35 of the drill bit portion 31 forms an angle of 59 degrees
 with the axis of the screw. The drill bit portion 31 is 0.19 inches long.
 The threaded portion 32 is 1.06 inches long and has 20 threads per inch.
 The shaft portion 33 is 1.38 inches long. The total length of the screw 30
 is 2.75 inches.
 The head portion 34 comprises a washer portion 36 and a hex nut portion 37.
 The washer portion is 0.285 inches in diameter and 0.020 inches thick. The
 hex nut is of the 0.250 inch type. The head portion 34 is also provided
 with Phillips No. 2 slots 38.
 Drill-pointed screws have one or more sharp cutting edges on their drill
 bit ends that function to cut away material from the surface the screw is
 being driven into. The hole thus created has a diameter that is less than
 the major thread diameter. When the threads enter the hole created by the
 drill bit point, they cut or form a matching thread in the sides of the
 hole. Examples of drill-pointed screws are given in SAE (Society of
 Automotive Engineers) J78, pages H-69 thru 76, in Fastener Standard (6th
 ed. 1988), the entire volume of which is incorporated herein by reference.
 As an added convenience to the user, it may be advantageous to pre-install
 fasteners within the fastener guides. FIG. 5 shows a three gang electrical
 box with pre-installed nails 26. FIG. 6 shows a four gang electrical box
 with pre-installed screws 27. The four gang electrical box of FIG. 9 has a
 flange 24 distal from the box's stud facing side. The flange 24 is
 penetrated by two holes 25 for receiving fasteners. This flange is
 designed to rest against and attach to a short piece of stud and thus
 facilitate the alignment of the box with a sheet of dry wall installed
 over and around the box.
 As an added convenience to the user, it may be advantageous to pre-install
 fasteners within the fastener guides. FIG. 8 shows a three gang electrical
 box with pre-installed nails 26. FIG. 9 shows a four gang electrical box
 with pre-installed screws 27. The four gang electrical box of FIG. 9 has a
 flange 24 distal from the box's stud facing side. The flange 24 is
 penetrated by two holes 25 for receiving fasteners. This flange is
 designed to rest against and attach to a short piece of stud and thus
 facilitate the alignment of the box with a sheet of dry wall installed
 over and around the box.