Protecting electrical device assemblies during installation

An electrical device assembly, for mounting behind a wall surface, includes an electrical device mechanically attached to a mounting plate, and a rigid protector extending over the device to protect the device during wall construction. The hard metal protector enables an uninterrupted sheet of drywall or other wall facing material, hung in place over the device, to be cut through with a saw or router without risk of damaging the device by incidental contact with the cutting blade.

BACKGROUND OF THE INVENTION 
This invention relates to protecting electrical device assemblies, such as 
switches and receptacles, during installation behind wall surfaces, and to 
methods of finishing walls containing such devices. 
To facilitate field installation of wall-mounted electrical devices, such 
as electrical receptacles and switches, many such devices are now provided 
as pre-wired assemblies in which the device is mounted and wired within a 
standard junction box from which wires extend in a conduit whip for 
connecting the device to the rest of the branch circuit. Thin plastic 
covers are sometimes taped in place over the devices during assembly to 
protect against dust and paint during wall trimming. 
Such device assemblies are mounted directly to internal wall supports prior 
to the installation of the wall facing material, such as drywall. Prior to 
hanging the sheet of drywall about the front of the device, a rectangular 
hole is cut at a measured location through the drywall to expose the 
device in the finished wall. Proper positioning of the drywall hole is 
critical to ensure that the hole will be completely covered by the cover 
plate installed over the device once the wall has been finished. With the 
hole cut, the drywall is hung, taped and finished. Once wall finishing and 
painting are complete, the thin plastic dust cover in place is removed 
from the device and the cover plate is installed. 
Any improvement in the speed with which walls can be safely trimmed out can 
result in significant job-site cost savings. 
SUMMARY OF THE INVENTION 
This invention can enable faster wall construction by providing a more 
robust device assembly constructed to enable cutting the requisite access 
hole through the wall facing material after the facing material has been 
mounted without damage to the electrical device or its wiring. 
The invention features a removable, rigid protector forming a shield to 
protect the device during wall construction. By "rigid" we mean that the 
protector is stiff enough to avoid transferring a sharp impact load of 
about 10 pounds peak magnitude (such as might be applied by a saw blade 
during wall cutting) to the protected electrical device. Preferably, the 
protector is able to withstand light contact with a high speed router bit 
without being breached. 
According to one aspect of the invention, an electrical device assembly to 
be mounted behind a wall surface includes a mounting plate defining an 
aperture, an electrical device mechanically attached to the mounting plate 
and arranged to be accessed through the aperture, and a removable, rigid 
protector forming a shield across the aperture to protect the device 
during wall construction. 
In presently preferred embodiments, the protector comprises a metal plate. 
For many applications, the protector is formed of steel sheet of at least 
0.02 inch thickness, and may include a cavity for receiving an extension 
of the electrical device. 
In some embodiments, it is preferred that the outer surface of the 
protector have a Brinell hardness of at least 120. An outer hardness of 
more than about 160 Brinell is even more preferred. Many widely available 
metals, ceramics and composites have acceptable mechanical properties. 
High temperature resistance, for withstanding contact from a router bit at 
a temperature of about 1200 degrees Fahrenheit, for instance, is also 
highly desirable. 
The device may comprise an electrical receptacle or an electrical switch, 
for example, adapted to be coupled to another component of an electrical 
circuit. 
There are various useful means for releasably retaining the protector in 
position across the aperture. In some embodiments, for instance, the 
protector is releasably attached to the device by a mechanical fastener 
extending through a hole in the protector. The mechanical fastener may be 
threaded to engage mating threads of the device, or may be adapted to be 
pushed into place during assembly and pulled out to remove the protector 
from the device. In some cases, the protector is held in place by tape, a 
frangible strap, a flexible tie strap, or adhesive. Some protectors have 
side portions extending through the aperture to engage an inner surface of 
the mounting plate to hold the protector in place across the aperture. 
Some protectors form a spring clip adapted to hold the protector in place 
by grasping the device. In some cases, a headed fastener extends through 
both the device and the protector to attach the device and the protector 
to the mounting plate. The protector may define a hole for receiving the 
headed fastener, the hole through the protector having a first portion of 
sufficient diameter to pass a head of the headed fastener, and a second 
portion, contiguous with the first portion, of less than sufficient 
diameter to bass the head of the headed fastener. 
In some embodiments, the protector defines a pair of apertures for 
receiving a retaining strap. The apertures may comprise slots extending 
through opposite edges of the protector, for example. 
In some useful embodiments the electrical device assembly also includes a 
box attached to the mounting plate and arranged to surround the electrical 
device. 
In some cases, the protector is adapted to provide an indication of a 
characteristic of the electrical device. For instance, the protector may 
be color-coded to a list of electrical devices, or may include useful 
mounting, wiring or safety information. 
According to another aspect of the invention, a method of finishing a wall 
containing an electrical device is provided. The method includes mounting 
any of the above-described device assemblies to a wall structural member, 
covering the device assembly with a wall facing material, cutting an 
opening through the wall facing material to expose the removable protector 
protecting the electrical device, and then removing the protector to 
expose the electrical device. 
The wall facing material may be drywall, for example. 
In some cases, the step of cutting an opening includes cutting through the 
facing material adjacent the removable protector with a rotating bit. 
The step of removing the protector may include releasing a mechanical 
fastener holding the protector in place across the aperture. 
According to another aspect of the invention, a method of forming an 
electrical device assembly for mounting in a wall is provided. The device 
assembly including an electrical device mechanically attached to a 
mounting plate, and a rigid protector extending over the device to protect 
the device during wall construction. The method includes the steps of 
attaching the electrical device to the mounting plate to form a 
pre-assembly, and releasably attaching the protector to the pre-assembly 
to cover an otherwise exposed face of the electrical device. Usefully, the 
protector is adapted to protect the electrical device during wall 
construction. 
The invention can enable the advantageous use of high speed cutting tools, 
such as routers, for cutting the drywall adjacent electrical devices, by 
adequately protecting the device against the cutting bit, accidental 
contact with which can cause permanent damage to the device and 
necessitate replacement and rewiring. By enabling safe post-mounting 
drywall hole cutting, drywall installation is simplified. With a 
relatively inexpensive template, the device is readily mounted at a 
desired height and the hole router is positioned appropriately to cut the 
access hole through the installed drywall (or other wall facing material) 
directly in front of the device. 
Other features and advantages will be apparent from the following 
description and drawings, and from the claims.

DESCRIPTION OF EMBODIMENTS 
Referring to FIG. 1, pre-wired device assembly 10 contains an electrical 
device, such as an electrical switch or receptacle (outlet), contained 
within a standard steel mounting box 12 having a face plate 14 with 
flanges for mounting the assembly to a support. Wires 16 from the enclosed 
device are sheathed in conduit to form a whip 18 for electrically 
connecting the device to other components of an electrical circuit. 
Assembly 10 may be Pre-wired before delivery to the construction site, to 
be readily attached to a support and hooked up with minimal field 
electrician's time. 
Referring also to FIG. 2, assembly 10 includes a device mounting plate 20 
which is attached to the face plate 14 of the mounting box with screws 22 
and provides proper mounting features for supporting and retaining the 
electrical device 24. Various configurations of mounting plates 20 are 
commercially available for mounting different types of devices. Some 
mounting plates and boxes simultaneously accommodate multiple devices 
arranged side-by-side. 
Referring to FIG. 2A, mounting plate 20 is typically provided with threaded 
holes 21 or clips to receive threaded screws 26 (FIG. 2) for retaining the 
device. Made of stamped steel, some mounting plates have a raised area 28, 
as shown, to extend the face of the device a given distance from the face 
of the mounting box, such that the device will be properly positioned with 
respect to the surrounding wall surface in the finished wall. An aperture 
30 through the mounting plate provides clearance for the body of the 
device, for installing and removing the device from the front of the 
mounting plate. The mounting plate may be provided with flanges or other 
features to directly attach to wall support structure, or may itself be an 
integral member of the mounting box. 
Referring back to FIGS. 1 and 2, assembly 10 is also provided with a rigid 
device protector 32 that extends across the aperture of mounting plate 20 
to protect the device during shipping, installation and wall trimming. 
Protector 32 is preferably made of stamped, low-carbon steel of at least 
0.02 inch (25 gage) thickness and coated with zinc to resist corrosion. 
Ideally, the protector is able to withstand incidental contact with a high 
speed router bit, which can exceed temperatures of 1200 degrees 
Fahrenheit. A presently preferred protector is of 22 gage (0.03 inch 
thick) stamped steel, but some softer metals and even some high strength 
plastics are useful in greater thicknesses for some applications. However, 
ductile metals with a Brinell hardness of at least 120 are preferred for 
protection against high speed bits. Several protector configurations are 
discussed below with respect to other figures. Protector 32 shown in FIGS. 
1 and 2 is stamped to form a large rectangular raised area 34 for 
accommodating a duplex receptacle or a block-type device. Block-type 
devices include rocker switches and GFI outlets, for example. Raised area 
34 extends over the face of the device and provides a protective shield 
against device damage. A fastener 36 retains the protector to the rest of 
assembly 10. In this case, fastener 36 is a push-type fastener which is 
inserted through a central hole in protector 32 into a threaded boss 38 of 
duplex receptacle device 24, and is intended to be removed and discarded, 
along with protector 32, at the construction site. Other types of 
mechanical fasteners are also envisioned, examples of which are discussed 
below and shown in FIGS. 17A-17D. 
FIGS. 3A-3D illustrate the completion of an interior wall containing device 
assembly 10, mounted to a vertical wall stud 40. Although solid wooden 
studs are shown, commonly stamped metal stud members are employed in 
commercial construction. In FIG. 3A, device assembly 10 is shown already 
mounted, with its conduit whip 18 routed through stud 40 and connected to 
circuit wiring (not shown). Care is taken to record the mounted location 
of the device assembly. A simple mounting template (not shown) is useful 
for installing the device assembly at a desired height from the floor, and 
floor markers (not shown) may be employed to indicate horizontal device 
positioning. 
After all device assemblies to be mounted within the wall are in place and 
wiring completed, the drywall 42 or other wall facing material is hung 
(FIG. 3B). Either one face of each wall may be hung prior to mounting the 
electrical device assemblies (as shown), or both faces may be hung after 
the electrician's work is done. The drywall crew is able to quickly 
complete their work, as they need not stop to measure and cut openings for 
electrical switches and outlets while hanging. The hung drywall is taped 
and sanded while the electrical devices are safely shielded from sanding 
dust and drywall mud behind the wall surface. Painting may even be 
completed at this time, with the drywall protecting the electrical devices 
from paint splatter. 
Only after the drywall 42 is hung in place are the electrical device 
openings 44 cut through the drywall (FIG. 3C). The location for each 
opening 44 is readily determined with the aid of floor markings and the 
same template employed to mount the electrical devices. With the device 
protector in place, a saw or router (not shown) may be safely used to cut 
openings 44 without fear of the metal saw blade or router bit accidentally 
contacting and destroying the electrical device or its wiring. 
Final trim-out of the electrical devices entails simply removing and 
discarding protector 32 and its fastening means (FIG. 3D), and installing 
a standard device trim plate (not shown) to cover the hole 44 in the wall 
facing material. 
Many different configurations of protector 32 are envisioned. FIGS. 4-16 
illustrate samples of useful configurations. It will be understood that 
the various protector features of the individual examples shown may be 
combined in several different arrangements. 
FIGS. 4 and 5 illustrate the protector 32 as shown in the device assembly 
of FIGS. 1 and 2. The protector has overall face dimensions of about 2 by 
4 inches. It defines a central hole 46 for receiving a mechanical 
fastener, and has a broad, flat raised area 34 (of about 1.4 by 2.7 
inches) for extending across the face of a duplex receptacle or block-type 
device. The raised area extends about 0.2 inch from the face of the 
protector, and is sufficiently broad and flat to carry a manufacturer's 
logo or device installation instructions (e.g., color coding), which may 
be formed into the surface of the protector or applied as ink or decal. 
The protector 32a of FIG. 6 is for use with block-type devices without 
central face attachment means. Holes 48 are provided at each end of the 
protector, for receiving the threaded fasteners 26 holding the device to 
the mounting plate (FIG. 2). Each hole 48 has a wide area 50 broad enough 
to fit over the head of the fastener. The protector is then slid downward 
until the shanks of the fasteners are within the narrow regions 52 of 
holes 48, and the fasteners are tightened. Protector 32a is removed in the 
field by loosening the device fasteners, sliding the protector off, and 
then re-tightening the device fasteners before installing device trim. 
The protector 32b of FIGS. 7 and 8 requires no separate mechanical 
fasteners. It is provided with wings 54 extending from opposite edges of 
the protector, that extend through the aperture 30 of the mounting plate 
and engage inner surfaces 56 of the mounting plate to retain the protector 
in place over the device. Flexure of wings 54 maintains pressure between 
the mounting plate and the protector wings. The protector may otherwise 
bear against the face of the device, or opposite edges 58 may bear against 
the outer surface of the mounting plate. To install protector 32b, one 
wing 54 is first inserted through aperture 30 and under a corresponding 
edge of the mounting plate, with the protector skewed toward the inserted 
wing. The exposed wing 54 is then flexed and inserted beneath the opposite 
edge of the mounting plate aperture, and the protector is centered across 
the aperture. This process is reversed to remove the protector at the job 
site. 
Protector 32c of FIGS. 9 and 10 is configured for use with a standard wall 
switch 60, and has a narrow raised area 62 forming a rectangular pocket 62 
to receive the switch lever 64. Protector 32c is made of thin spring steel 
and is held in place by spring arms 66 integrally formed with and 
extending from the protector to engage the back face of the switch body. 
To install protector 32c, spring arms 66 are elastically splayed outward 
and snapped about the back of the switch body as the protector is moved 
into place. The protector is readily removed by simply grasping and 
pulling on its raised area 62. 
The switch protector 32d of FIGS. 11 and 12 is configured to be retained by 
the fasteners mounting the switch to the mounting plate. It may be 
provided with a pair of spaced apart holes 68, as shown, or a pair of 
slots 70 (shown in dashed outline). Slots 70, which extend through edges 
of the protector, are useful for accommodating switch devices having 
various mounting screw spacings. 
The raised regions for accommodating switch levers or device faces may be 
formed in many shapes. FIGS. 13 and 14 illustrate a switch protector 32e 
having a trapezoidal raised area 72 with large drawing draft angles. 
The switch protector 32f of FIGS. 15 and 16 is stamped to have edges that 
extend down over the edges of a raised region 28 of a mounting plate (FIG. 
2A), thereby helping to prevent dust and paint spray from entering the 
device assembly between the face of the mounting plate and the back of the 
protector. Protector 32f extends across the entire aperture of the 
mounting plate, and is particularly useful in dusty environments. Two 
rectangular holes 76 through the protector on either side of the switch 
lever housing 62 are sized to receive a standard plastic tie strap for 
strapping the protector to the device. 
The protectors discussed above may be conveniently ganged to protect 
multiple devices in the same device assembly. For instance, a receptacle 
protector 32 is shown in dashed outline in FIG. 15, ganged with a switch 
protector 32f. Adjacent protectors are preferably overlapped. 
FIGS. 17A-17D illustrate examples of types of mechanical fasteners useful 
for retaining device protectors to device assemblies. FIG. 17A shows a 
plastic push pin fastener 36 having a head 78 and a pair of extending 
fingers 80 with distal barbs 82. Pin fastener 36 is pressed into a 
threaded hole of the device assembly to hold the protector in place, and 
is removed by prying it out of its hole, either directly or by lifting an 
edge of the protector. Barbs 82 are configured to grip threads when 
fingers 80 are flexed inward as the fastener is inserted. FIG. 17B shows a 
standard threaded screw 36a which is adapted to be torqued with a standard 
screwdriver. The male threads of screw 36a engage female threads on the 
device assembly to retain the protector. FIG. 17C shows a two-part push 
pin 36b. The molded plastic body of the push pin has a head 80 and 
extending fingers 82 which are inserted into a threaded hole of the device 
assembly. Once inserted, an inner piston 84 extending through head 80 is 
permanently pushed down between fingers 82 to splay the fingers outward to 
press against the female threads of the hole. Pin 36b is removed like pin 
36, by prying. FIG. 17D shows a mechanical fastener 36c having a tapered 
male thread 86 or other tapered gripping element, which is pressed into a 
threaded hole. Thread 86 may be formed of molded plastic, for instance, 
which deforms when inserted and locks the fastener in place. The fastener 
is removed either by twisting, or by prying or pulling. Other types of 
mechanical fasteners, such as those commonly known as "Christmas 
tree"-type fasteners, may also be employed. 
The device protector may be temporarily retained by other fastening means. 
For instance, it and a device may be wrapped with tape. Adhesive 88, 
hot-melt glue or double-sided tape may be employed to releasably adhere 
the protector to the device (FIG. 2). As mentioned above with respect to 
FIG. 16, and shown in FIG. 18, a plastic tie strap 90 may be wrapped about 
the protector and device and later clipped for removal. Flexible 
twist-ties, similar to those commonly used as bread loaf bag closures, may 
be employed. 
There are yet other embodiments which will be found to be within the scope 
of the following claims.