Electricity: conductors and insulators – Boxes and housings – With electrical device
Reexamination Certificate
1999-06-18
2001-03-06
Kincaid, Kristine (Department: 2831)
Electricity: conductors and insulators
Boxes and housings
With electrical device
C220S003200, C248S906000
Reexamination Certificate
active
06198045
ABSTRACT:
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.
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“Two Gang—Residential Switch or Receptacle Box”, Allied Moulded Products, Inc. (p. 14). No Date.
“Slater® Plastic Boxes—Screw Mount Steel Stud Boxes”, Pass & Seymour legrand (p. 12). No Date.
Brochure: “Zip Box® Blue™—Nonmetallic Switch and Outlet Boxes”, ©Lamson & Sessions 1996. No Date.
“An Introduction To Tapping Screws”, IFI, 1981 (pp. H-1 to H-2; H-12). No Date.
“Slotted And Cross Recessed Head Tapping Screws”, Abstract of ANSI/ASME B18.6.4 (1981). No Date.
Schedule A: Measurements made by the inventor. No Date & Year.
Jones Day Reavis & Pogue
Kincaid Kristine
Patel Dhiru R
The Lamson & Sessions Co.
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