Note: Descriptions are shown in the official language in which they were submitted.
:~L385~7~ 1
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ELECTRICAL WIRING BOX AND CABLE CLAM:~?
Tnis invention relates to electrical wiring boxes.
More particularlyr it is eoncerned with electrical wiring
box arrangements having integral eable clamps.
Many known types of eleetrical wiring box and eable
elamp arrangements are of a type wherein the eable clamp
and wiring box are separate and must be assembled, either
at the time the box is manufactured, or later when the
box is wired. One such type of box and clamp, of the
type disclosed in U.S. Patent No. 3,424,856, for example,
requires that the cable be inserted in the clamp before
the elamp :LS installed in a knoc~-out opening of the
wiring box. The eable is clamped simultaneously with
the installation of the elamp deviee in the knock-out
aperture. Wiring box and elamp arrangements of this type
do not allow for removal or repositioning of the eable in
the elamp without removal of the clamp from the knoek-out
opening.
Yoke type eable elamps of the type diselosed in U.S.
Patent No. 2,973r212 clamp the eable between ~ wall of
the box and a c:d~ie gripping yoke driven against the cable
by means of a screw or bolt. This type o~ elamp involves
additional cost of manufacture, owing to the need for
thre.~ded openinys in the box wall, and to its several
parts. Moreover, the installation of a cable in boxes
fitted with such clamp devices in the field requires the
time consuming step of tightening the clamp holding serew
or bolt.
~ able clamp devices which make use of spriny-loaded
cable gripping elements have been disclosed. U.S. Patent
30 No. 2,556,977 for example, discloses one such clamp de-
vice which comprises a right angle mounting element and
spring loaded foot. The cable is gripped between one leg
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of the rigllt angle element and the spring foot. The short
length of the spring loaded cable gripping Eoot in such
clamps restric-ts them for use with a limited range of
cable diameters.
Accordingly, the present invention provides an
electr.ical wiring box arrangement comprising: an elec-
trical wiri.ng box including: a wall structure defining
front-to-rear walls and a rear wall therebetween which in
combination define a chamber within the box; said wall
structure having a knock-out region for providing a
knock-out opening for receiving non-metallic sheathed
cable, first attachment means for mounting cable clamp
means interior to said box adjacent to said knock-out
region, and first cable engaging means; and a cable clamp
means fox clamping non-metallic sheathed cable including:
a substantially flat flexible and resilient main body
portion having opposite first and second end portions, and
first and second flat surfaces; second attachment means
in said first end portion for coacti.ng with said first
attachment means to attach said cable clamp means to said
wall structure; and cable retaining means contiguous with
said second end portion providing second cable engaging
means; whereby a cable passing through a knock-out opening
of an electr:ical wiring box having said cable clamp means
attached to the wall structure thereof, deflects said
second end o: said cable clamp means inwardly into said
chamber secu:ring said cable clamp against removal from
said knock-out opening in an outward direction by the
action of said first and said second cable engaging means
bearing oppositely against said cable.
Some embodiments of the invention will now be
described, by way of example, with reference to the
accompanying drawings in which:
FIGURE 1 is a partially cut away perspective view of
a wiring box arrangement in accordance with the present
invention.
~ IGURE 2 is a perspective view of a fragment of a
wiring box in accordance with the present invention
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prior to the installation of a cable clamp in the box.
FIGURE 3 is a perspective view of an electrical
cable clamp in accordance with the present invention.
FIGURE 4 is a side view of the electrical cable
clamp of Figure 3.
FIGURE 5 is a perspective view of an electrical
cable clamp in accordance with an alternative embodiment
of the present invention.
FIGURE 6 is a side view of a fragment of an elec-
trical cable and wiring box arrangement of the presentinvention.
FIGURE 7 is a side view of a fragment of an elec-
trical cable and wring box arrangement of the present
inveiltion.
E'or a better understanding of the present invention,
together with other and further objects, advantages ancl
capabilities thereof, reference is made to the following
disclosure and appended claims in connection with the
above-described drawings.
Referring to the drawing figures, an electrical
wiring box arrangement in accordance with one embodiment
of the present invention is shown in Figure 1. An
electrical wiring box 10 is comprised of a front-to-rear
wall structure including end walls 12 and 14, side walls
16 and 18, and rear wall 20 which define a chamber within
the box for receiving an electrical wiring device such as
a switch or plug receptacle (not shown). Ears 22 and 24,
integral respectively with end walls 12 and 14 are pro-
vided with threaded openings for mounting an electricalwiring device in the box chamber.
The wall structure of the wiring box 10 is provided
with knock-out regions, typified by region 26 formed in
end wall 12. Each knock-out region 26 is provided with
a tool-receiving aperture 28 for prying the knock-out
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region from the wall structure to form a knock-out
opening such as 30, shown in Figure 1 with the knock-out
region removed.
The knock-out regions may form a portion of the
front-to-rear wall structure, or of the rear wall struc-
ture of the wiring box 10. But in any configuration of
the knock-out regions it is preferred that the knock-out
regions be located immediately adjacent to the inter-
section of one wall and another. This preferred orien-
tation is shown in Figure 1 by way of example whereknock-out region 26 is located in end wall 12 immediately
adjacent to the intersection of end wall 12 and rear wall
20. Removal of a knock-out region situated immediately adjacent
to the i~tersection of two walls provides a knock-out
opening such as 30 which permits an electrical wiring
cable to pass through one wall and lie directly along
the intersecting wall.
The wall structure of wiring box 10 is further pro-
vided with one or more protrusions or ridges for gripping
or engaging a non-metallic sheathed cable. In a prefer-
red embodiment shown in Figure 1, the cable engaging
protrusion is a series of substantially parallel ridges
or scored lines 32, 34, or 36 embossed in rear wall 20.
The protrusion is preferrably located in a wall which
intersects a wall having one or more knock-out regions
and in proximity to the knock-out region. For example,
protrusion 32 is formed in rear wall 20 proximal to
knock-out opening 30 in end wall 12.
As seen best in Figure 6, this relative orientation
of a knock-out opening and wall protrusion allows a non-
metallic sheathed electrical cable 38 to pass through a
knock-out opening in one wall 40 and to lie along a
second wall 42 with the cable 38 contacting the protru-
sion 44 in the second wall 42.
An electrical wiring hox arrangement in accordance
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with this i~vention further inclu~es a cable clamp device.
A preferred embodiment of the cable clamp device 50 is
shown in Fiyure 3. The clamp is formed of a sheet of
substantially flat flexible and resilient material such
as metal or plastic, preferably thin gage steel.
The cable clamp 50 is preferably bifurcated into
two leg portions 52 and 54 although cable clamps having
single or multiple leg portions are contempleted as
falling within the scope of this invention.
Each leg portion, as for example leg portion 52
compri.ses a substantially flat main body portion 56 with
end portions 60 and 62. Each leg portion 52 and 54 is
jnined l.aterally to the other at their respective end
portions 62 and 66. Slit 68 which bifurcates or divides
l~ cable clamp 50 permits each leg portion 52 or 54 to flex
ind~pesldently of the other. Slit 68 ends in a strain
relievi.ng aperture 70 which minimizes shearin~ stresses
in cable clamp 50 when one leg portion is flexed inde-
pendently of the other.
A cable retaining portion of each leg portion is
C~ll ti.guous with the end portion of each leg. For example,
foot portion 72, contiguous with end portion 60 of leg 52,
provides for retaining non-metallic sheathed electrical
~able. As can better be seen in the lateral view of
cable clamp S0 in Figure 4, the first surface 80 of foot
portion 74 forms an acute dihedral angle ~ with. :th~ fixst
surface 82 of the main body portion of-cable clamp 50. It
has been found tha-t optimal cable.clamping action occurs whe~
~ is between 75 and 90, preferably about 80. The heel
84 formed at the vertex of the dihedral angle formed by
the second surface 86 of foot portion 74 where it inter-
sects the second surface 88 of the main body portion of
the cable clamp 50 provides a cable engaging edge for
clamping or securing a cable sheath when the clamp is in
use.
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An alternative embodiment of the cable clamp device
of this invention is shown in Figure 5. In the embodiment
shown there clamp 90 is provided with serrations 92 and
94 at the vertex of the dihedral angels formed, for ex-
ample, by foot portions 96 and 98 meeting main body por-
tions 100 and 102 of legs 104 and 106, respectively. The
serrations provide addition cable gripping or engaging
capability and may conveniently be formed by making a
series of holes in the body of the clamp prior to folding
the clamp material to produce the foot portion.
Cable clamp 50 is attached to the wall structure of
wiring box 10 adjacent a knock-out region as can best be
seen in Figure 1. As shown there, the end walls are pro-
vided with attachment tabs or ears such as tabs 4~ and 4g
in end wall 14. Although tabs or ears formed in the wall
. structure are the preferred means for attaching cable
clamps in accordance with this invention because of their
ease and low cost of fabrication, other ~asteners such as
screws, bolts, or rivets passing through apertures in the
wall structure may also be used.
A detail of the attachment tabs or ears, prior to
attachment of a cable clamp is shown in the partial cut-
away view of wiring box 10 shown in Figure 2. Tabs or
ears 46 and 48 are formed from end wall 14 and protrude
or extend inwardly into the interior chamber o~ box 10.
Tabs 46 and 48 are formed in the same wall as that having
knock-out regions and, prior to attachment of a cable
clamp, are essentailly perpendicular to the wall struc-
ture.
Referring again to Figure 3, slotted apertures 76
and 78 in end portions 62 and 66 of cable clamp 50 are
spaced apart to receive tabs 46 and 48. The clamp 50 is
shown in Figure 1 attached to end wall 14 where tabs 46
and 48 are shown bent over or crimped to secure end por-
35 tions 62 and 66 of clamp 50 to wall 14. Cable clamp 50
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is attached to a wall which is also provided with knock- !
out regions. The relative positions of the clamp and
knock-o~-lt regions is preferably such that the foot por-
tion of the cable clamp is spaced apart from the adjacent
wall bearing the cable engaging protrusion. The spacing
is preEerably sligh~ly less than the diameter of the
cable to be clamped in the knock-out aperture. For ex-
ample, in Figure 1, cable clamp 50 is shown attached to
end wall 14 in such a position that foot 72 is spaced
slightly apart from rear wall 20 which bears cable en-
gaging protrusion 34.
This relative configuration of the cable engaging
wall protrusion and the cable engaging foot portion of
the cable clamp permits a non-metallic sheathed cable to
be clamped in a knock-out opening as shown in Figure 6.
An electrical cable 38 is inserted through wall 40, flex-
j ing or deflecting the free end of cable clamp 50 inwardly
into the box chamber, with the cable lying along wall 42
and contacting or engaging protrusion 44. The resiliency
of cable clamp 50 causes the heel 84 of the clamp 50 tobear against the cable, in turn forcing the cable against
protrusion 44. Any attempts to pull the cable from the
knock-out in an outward direction only increases the
forces of the clamp and protusion bearing oppositely
~5 against the cable.
However, a clamped cable is easily removed from, or
repositioned in, a knock-out opening by prying the free
end of the cable clamp away from the cable as shown in
Figure 7. ~he bit of a screwdriver 110 or like tool is
inserted in tool-receiving tab 114 prying the heel 84 of
the clamp 50 away from the cable in the direction of the
arrow.
The preferred configuration of the tool-receiving
tab is shown in Figures 3 and 4. The tab 114 is formed
of a portion of foot 74 forming a more acute angle ~
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with the main body portion than does the foot portion
itself.
To prevent excessive flexure or deflection of a
cable clamp leg portion into the box chamber, wiring
box arrangements in accordance with this invention are
provided with tabs to restrain the cable clamp. For
exa~ple, in a rectangular wiring box having mutually
orthogonal or perpendicular end, side, and rear walls,
the restraining tabs are preferably located in a wall
orthogonal to the wall having the attached cable clamp
and the wall having the cable engaging protrusion.
Thus, as shown in Figure 1, restraining tab 120 is lo-
cated in side wall 16, proximate to the main body portion
of cable clamp 50 attached to end wall 14; cable engaging
protrusion 34 is located in rear wall 20. Excessive
bending of a cable clamp leg portion into the box chamber
causes the main body portion of the clamp to contact the
restraining tab, preventing further inward flexure of the
clamp leg.
While there have been shown and described what are
at present believed to be the preferred embodiments of
the invention, it will be obvious to those skilled in the
art that various changes and modifications may be made
therein without departing from the scope of the invention
as defined by the appended claims.
