Metal outlet box with snap together base and cover

A mild alloy steel is used to stamp the metal base into a configuration that provides channel shaped ribs just inboard of each end of the base. Each rib defines a downturned tab at the ends to provide a downwardly facing abutment surface adjacent each corner of the rectangular base. The cover, of the same material, has end walls that define flanges that are arranged flush with the side walls of the rectangular cover. These side walls have tabs bent around these flanges to define upwardly facing abutment surfaces. These abutment surfaces lock in place at assembly of the base and cover obviating the need for conventional screw fasteners.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to electrical outlet boxes fabricated of mild 
alloy steel, and deals more specifically with a metal box having a base of 
generally flat configuration adapted to be attached to a wall structure or 
the like, and a cover that is secured to the base without requiring 
conventional mounting screws of the like. The cover can be selected from a 
group of covers of different depth depending upon the type of electrical 
device to be accommodated therein. 
2. Description of the Prior Art 
Metal outlet boxes of the type utilizing a generally flat base and a cover 
adapted to be received by the base generally require the use of mounting 
screws for securing the cover to the base. Plastic outlet boxes have been 
provided with enough resiliency to allow snapping the components together 
without requiring the use of conventional fasteners. However, metal outlet 
boxes are generally fabricated from a mild alloy steel, and such material 
does not exhibit sufficient resiliency to permit the techniques used in 
plastic outlet boxes to be applied to the fabrication of two component 
metal outlet boxes. 
Electric switch housings of plastic have been assembled with a metal base 
as shown for example in U.S. Pat. No. 2,665,353. However, where two mild 
alloy steel components are to be snapped together difficulties arise due 
to the lack of resiliency in the mild alloy steel generally used for 
producing these products. U.S. Pat. No. 4,697,044 shows one attempt to 
avoid this problem characteristic of mild alloy steel where the snap-on 
cover of a metal casing is fabricated with a predetermined set in one 
direction so that when snapped in place the steel cover assumes a flat 
configuration in its stressed condition. In effect the steel cover has two 
conditions between which it moves in a sort of oil-canning mode without 
requiring any great degree of force to cause this oil-can type movement 
from one condition to the other. Such an approach to the design of a snap 
together metal outlet box cover and base would not be satisfactory due to 
the inherent lack of stability for the components held together solely as 
a result of this rather unstable oil-canning configuration of mild alloy 
steel sheet or plate. 
SUMMARY OF THE INVENTION 
It is a general purpose and object of the present invention to provide a 
mild alloy steel metal base and cover combination which can be assembled 
in a snap together assembly step which obviates the need for conventional 
screw fasteners, and which nevertheless secures these two components 
together in a very stable condition such that striking the cover with a 
moderate blow does not cause the cover to be disengaged from the base. 
These objects are accomplished with the present invention by providing a 
cover of mild alloy steel readily adapted to be stamped from sheet 
material and having side and end walls integrally connected to a top wall. 
The cover further includes a bottom edge defining a downwardly open 
recess. The end walls of the cover define conventional knockout openings 
adjacent to the bottom edge suitable for receiving conventional electrical 
conduits. The end walls have corner defining flanges oriented 
perpendicular to these end walls and these flanges are arranged to be 
flush with the end portions of the side walls so that clinched tabs 
defined adjacent the end portions of the side walls can be folded over 
each flange and thereby define an abutment surface which is spaced from 
the bottom edge of the cover. The base is also stamped from mild alloy 
steel sheet material and has a shape and size corresponding generally to 
that of the cover bottom edge. The base has raised ribs in the shape of 
channels extending across the base from one side to the other. Each 
channel has a top portion defining a web of the channel, and the top 
portion or web defines down-turned abutment surfaces at each end adapted 
to engage the abutment surfaces defined by the clinched tabs. Locating 
these ribs adjacent the end portions of the base, and restraining the 
exterior surfaces of the cover side by up-turned flanges on walls of the 
base provides an interference fit between the cover and the base wherein 
the abutment surfaces lock the cover to the base.

DETAILED DESCRIPTION 
Turning now to the drawings in greater detail, in its preferred form the 
present invention contemplates a two component metal electric outlet box. 
Such metal outlet boxes are generally fabricated from a mild alloy steel 
material which exhibits only a very limited degree of resiliency. Electric 
outlet boxes made of such material generally require screw fasteners to 
assemble the cover to the base. The base is generally attached to an 
existing wall structure or the like and the cover secured to it by screw 
fasteners. In the prior art base, a generally flat shape has been used, 
with dimpled areas suitable for receiving mounting screws (see for example 
the dimpled area indicated generally at 10 in the base of FIG. 1). By the 
same token, a prior art cover is generally provided with openings that are 
countersunk for purposes of receiving the ends of screw fasteners which 
extend from the top of the cover into the base being such that the ends 
are threadably received in threaded openings in the dimpled areas such as 
that shown at 10 in FIG. 1. 
The present invention seeks to obviate the need for use of such threaded 
fasteners for securing a stamped metal cover to a stamped metal base. As 
shown in FIG. 1, the cover 20 is adapted to be received on the base 50 and 
to be held in secure assembled relationship with respect thereto without 
the need for screw fasteners and without the threaded openings therefor in 
the base. 
The base 50 is of generally rectangular configuration corresponding in size 
and shape to the open bottom defined by the stamped metal cover 20. 
The cover 20 includes integrally formed side and end walls 22 and 24 
respectively, which cooperate to define corners for the cover, and which 
side and end walls also define a downwardly open bottom for the cover. The 
bottom edge 26 of the cover 20 is adapted to fit onto the base 50 and to 
be held in secure assembled relation with the base as described below. 
Referring more specifically to the configuration of the cover 20, FIG. 1 
shows that each corner includes a corner defining flange 28 that is 
oriented perpendicular to and is integrally connected to the end wall 24. 
Four such corner flanges are provided, each of which is integrally 
connected to one or the other of the two end walls 24,24. These flanges 
are oriented so as to be parallel to and in flush engagement with end 
portions 22a, 22a of the side walls 22,22 respectively. Further, each end 
portion of the end walls defines a tab that is adapted to be clinched in 
the position that is indicated generally at 30 in FIG. 1. These tabs 30,30 
not only serve to add additional strength to the side wall end portions 
22a, but the upper edge of each tab serves as an abutment surface 30a for 
engaging an abutment surface defined in the base 50 to be described. 
Still with reference to the cover 20, a top wall defines a generally 
rectangular opening 32 suitable for receiving an electrical device (not 
shown) such as a plug or electrical switch or other electrical device. 
Mounting holes 34 are provided in the top wall of the cover 20 for 
mounting such devices in this opening 32. The end walls of the cover 
include three knockouts 24a for providing suitable openings to receive 
conventional electrical conduits (not shown). The side walls 22 of the 
cover 20 also define knockouts 22b for the same purpose, namely to afford 
receptacles for conventional conduits (not shown). The cover shown has a 
vertical dimension or height that will accommodate most of the electrical 
devices normally encountered. However, covers of shallower or greater 
vertical dimension can also be assembled with the base to be described. 
As mentioned previously, the base 50 is adapted to be secured to an 
existing wall structure or the like, and countersunk openings 54 are 
provided in the base for this purpose. These openings 54 are provided in 
addition to the more conventional opening configuration shown at 10 and 
described previously. The conventional opening configuration shown at 10 
is intended for use as a grounding screw receptacle for use by the 
electrician who installs the box and who will accomplish the assembly of 
the cover with the base in a manner to be described. 
The base 50 is fabricated from a mild alloy steel sheet material in much 
the same manner as used in connection with the fabrication of the cover 
20. The base of the present invention preferably includes raised channel 
shaped ribs, as indicated generally at 56, the ribs extending across the 
base from one side to the other of the base. Each channel shaped rib 56 
has a flat top surface or web 56a of the channel. Each channel is 
downwardly open, and the top surface provides a convenient area for 
defining the countersunk openings 54 that receives the screws (not shown) 
that serve to secure the base 50 to a wall structure or the like (not 
shown). At each side of the base 50 a pair of up-turned flanges 58,58 are 
provided to engage the exterior surfaces of the side walls 22 of the cover 
20. 
The channel shaped ribs 56 are provided parallel to the end walls of the 
cover when the cover and base are assembled with one another, and it is an 
important feature of the present invention that abutment surfaces 60 are 
defined at the ends of these channel shaped ribs, 56 and more particularly 
by the end portions of the top wall 56a of these channel shaped ribs 56 as 
shown in FIG. 1. The top wall 56a of the channel shaped rib is wide enough 
so that when the end portions are bent downwardly as shown, they overly 
the side walls 56b of the channel shaped ribs. As so supported the end 
portions have downwardly facing abutment surfaces 60 that are adapted to 
engage the above described abutment surfaces 30a of the clinched tabs 
30,30 of the cover 20. 
As so constructed and arranged, the cover 20 can be forcibly applied to the 
base as a result of which the upwardly facing abutment surface 30a of the 
clinched tab 30 will engage the downwardly facing surface 60 of the 
down-turned channel top wall 56a. This engagement occurs adjacent all four 
corners and more particularly in spaced relationship to the four corners 
of the cover. 
Still with reference to the base 50, a plurality of barbed tongues 62 are 
defined at the ends of the base and these barbed tongues 62,62 correspond 
in location with the three knockout openings 24a of the cover. As so 
constructed and arranged a conventionally shaped conduit can conveniently 
be secured to the base to assist in holding the conduit in place while the 
installer or electrician provides wires to the electrical outlet box 
location and prior to assembly of the cover. Depending on how many 
conduits are to be received at the electrical outlet box, one or more 
knockouts 24a or 22b will be removed to provide the desired arrangement of 
outlet box and conduits in a particular installation. Tongues 62,62 are 
also provided in the side walls of the base 50 and are aligned with the 
single knockout 22b provided in the side wall of the cover as described 
previously. A center knockout 64 in the base 50 may be provided to 
accommodate wiring to and from the electrical outlet box from the wall 
structure to which the base is attached. 
FIGS. 2, 3 and 4 illustrate the cover in conventional three view 
arrangement, the abutment surfaces defined by the clinched tabs 30 being 
illustrated at 30a in these views. FIG. 3 shows the generally U-shaped 
configuration for each of the end walls 24,24 and also illustrates the 
flanges 28 defined integrally with these end walls and abutting the inside 
of each side wall 22. FIGS. 2 and 3 show the conduit knockouts 24a and 
22b. 
FIGS. 5, 6 and 7 illustrate in typical three view arrangement the 
configuration of the stamped metal base 50. FIGS. 6 and 7 illustrate the 
specific configuration for each of the tongues 62,62. These tongues are of 
conventional configuration and adapted to be received in the open ends of 
conventionally configured conduits (not shown) which conduits have a shape 
corresponding to the shape of the knockouts 24a and 22b in the cover 20. 
FIGS. 5 and 7 illustrate in some detail the configuration for the 
down-turned tabs that serve to define the downwardly facing abutment 
surfaces 60 which cooperate with the upwardly facing surfaces 30a of the 
tabs 30 of the cover 20. FIG. 6 clearly shows the channel shaped 
configuration for each of the ribs that provide stiffening for the base 50 
in the area of these abutment surfaces. FIG. 5 illustrates the 
configuration for the up-turned flanges 58,58 that serve to engage the 
exterior surface of each cover side wall 22. Note that FIG. 2 shows 
cutouts as indicated generally at 22c for receiving the portion of the 
base 50 that extends horizontally outwardly to provide the up-turned 
flanges 58,58 described previously. At the lower left hand portion of FIG. 
5 one corner of the box 20 is shown to illustrate the relationship between 
the corner of the box 20 and the up-turned flange 58 with respect to the 
down-turned flange on the end of the rib. It should be noted that this 
down-turned tab and its abutment surface 60 is located generally between 
the corner of the cover 20 and the immediately adjacent up-turned flange 
58 of the base. This geometry provides for limited resiliency of the cover 
side wall 22 and allows an interference fit to be achieved between these 
three points with the result that the abutment surfaces 30a and 60 engage 
one another with sufficient force to remain assembled securely together 
even when subjected to forces that would otherwise result in knocking the 
cover away from its base but for the unique geometries for the affected 
areas of these stamped mild alloy (soft) steel components. 
Another feature of the present invention attributable to the elimination of 
the need for screw fasteners is due to the fact that a single base 
geometry can accept covers of different height. This requirement, also 
true of the prior art covers, requires screw fasteners of different length 
when used to assemble a conventional cover to a conventional base. With 
the present invention no fasteners are required. Hence, covers of various 
height can be assembled with a common base configuration without any screw 
fasteners of different length. This advantage leads to economies of both 
supply and inventory requirements, and to economics realized during 
installation.