Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CABLE TRAY
BACKGROUND OF THE INVENTION
[0001] Electrical system conductors are always part of the
construction of
virtually any building whether the building is residential, business, or even
a storage
building. In most applications, local construction codes and building
techniques
dictate the use of metallic conduit mounted to various surfaces of the
building. The
necessary electrical system conductors are then drawn through the metallic
conduit
to terminate at the various control points designed within the electrical
system.
[0002] With the increase in electrical and signaling
technology, there has
also been an increase in the variety of cables used to interconnect electrical
and
electronic equipment. While the electrical industry still makes extensive use
of
copper and sometimes aluminum electrical conductors disposed within cables,
the
use of optical cables has also become widespread and there is every indication
that
the use of optical cables may surpass the current percentage of use of copper
or
aluminum conductor cables.
[0003] With the widespread use of a virtually endless
variety of electronic
equipment and devices, there has also been a constant and steady increase in
the
use of specialized electrical system conductors in raceways and mechanical
areas
that do not use normal metallic conduit. Instead, cable trays are first
installed within
the raceways and mechanical areas. Thereafter, the electrical system
conductors
and cables are placed into the cable trays where the electrical system
conductors
remain until they must be serviced or remodeled.
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[0004] One standard type of cable tray is made from an assembly of wire
rods. These rods are welded together at various angles to result in what is
usually a
channel-shaped trellis that can be used as a cable tray. These channel-shaped
cable trays are installed within the raceways and mechanical areas such that
the two
opposing sides of the channel are generally vertical while the web connecting
the
two opposing sides is mounted to face upward against gravity. The electrical
system
conductors are placed within the channel-shaped cable tray by simply locating
the
length of the wires parallel to the longitudinal axis of the channel-shaped
cable tray
and allowing the electrical system conductors to rest directly upon the metal
used to
fabricate the channel-shaped tray.
[0005] While this type of cable tray offers a simple and generally
strong
design for mounting loose electrical system conductors, the direct contact of
the
electrical system conductors onto the wire rods of the channel-shaped tray can
introduce high areas of mechanical stress on the underside of the electrical
system
conductors that can, over time and use, cause fatigue fractures to occur in
the
electrical system conductors. Such cracks not only cause severe operational
problems with the electrical devices interconnected using the electrical
system
conductors, such cracks also present a serious fire hazard.
[0006] The increased use of optical cables also presents additional
reasons for use of a cable tray that does not bend or fracture the delicate
optical
fibers within the optical cable. Such fractures can be easily caused by high
stress
point loads on an optical cable when the optical cable is resting on the wire
rods of a
standard cable tray. Such pressure points can fracture the optical fibers, but
the
sensitivity of optical fibers is such that even excessive pressure on the
optical fibers
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can affect many of the key performance characteristics of the optical cable
such as
the optical fiber's transmission signal speed, the operable bandwidth of the
optical
fiber, and the general performance integrity of the optical cable. In severe
cases,
these excessive pressures can also affect these same performance
characteristics
for copper data cables.
[0007] Various embodiments of the present invention described herein
include features and characteristics that tend to reduce the probability and
frequency
of such fatigue cracks or high stress points that can reduce the overall
performance
of both metallic and optical cables.
SUMMARY OF THE INVENTION
[0008] This invention relates to an apparatus for installing electrical
system
conductors, and more specifically to the installation of electrical system
conductors
by placement of those electrical system conductors within a uniquely designed
cable
tray. More specifically and in accordance with the various embodiments of the
present invention, a cable tray is disclosed that is made from an assembly of
interconnected metallic rods. Various embodiments of the present invention
utilize
different shaped rods to provide combinations of concentrated strength, better
rigidity,
and reduction of stress concentration points between the outer surface of the
various
shaped rods and the electrical system conductors disposed within the cable
tray.
[0009] In one aspect of the present invention, there is provided a cable
tray
comprising: a plurality of U-shaped transverse members connected to a
plurality of
longitudinal members to be in the general shape of a channel capable of
supporting
a plurality of electrical system conductors within an inside portion of the
channel,
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wherein each of the plurality of U-shaped transverse members has a cross-
sectional
shape that is substantially elliptical with a major axis and a minor axis of
different
lengths wherein the major axis is parallel to a longitudinal axis of each of
the plurality
of longitudinal members.
[00010] In another aspect, there is provided a cable tray comprising: a
plurality of U-shaped transverse members having a cross-sectional generally in
the
shape of an ellipse with a major axis and a minor axis of different lengths
and that are
connected to a plurality of longitudinal members to form an assembly generally
in the
shape of a channel, wherein the major diameter axis of the elliptic shape of
each of
the U-shaped transverse members is disposed parallel to a longitudinal axis of
each
of the plurality of the longitudinal members, such that when a set of
electrical system
conductors is placed within the cable tray, the exterior surfaces of at least
one of the
set of electrical system conductors rests upon an arcuate surface of the U-
shaped
transverse members that is generally parallel with the major diameter axis of
the
substantially elliptical shape of the U-shaped transverse members.
DESCRIPTION OF THE DRAWINGS
[00011] In the accompanying drawings which form part of the specification:
[00012] Figure 1 is a perspective view of one embodiment of the present
invention showing one cable tray made from an assembly of wire rods.
[00013] Figure 2 is a vertical section view of one embodiment of the present
invention.
[00014] Figure 3 is a top view of one embodiment of the present invention.
[00015] Figure 4 is a left elevation view of one embodiment of the present
invention.
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[00016] Figure 5 is a right elevation view of one embodiment of the present
invention.
[00017] Figure 6 is a vertical cross section of the bottom portion of one
embodiment of the present invention as shown in FIG. 3.
[00018] Figures 6A, 6B, 60, and 6D are vertical cross sections similar to the
cross section of FIG. 6, but which show various geometric shapes for the
longitudinal
rods that can be used in various embodiments of the present invention.
[00019] Corresponding reference numerals indicate corresponding steps or
parts throughout the several figures of the drawings.
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[00020] While one embodiment of the present invention is illustrated in the
above referenced drawings and in the following description, it is understood
that the
embodiment shown is merely one example of a single preferred embodiment
offered
for the purpose of illustration only and that various changes in construction
may be
resorted to in the course of manufacture in order that the present invention
may be
utilized to the best advantage according to circumstances which may arise,
without
in any way departing from the spirit and intention of the present invention,
which is to
be limited only in accordance with the claims contained herein.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
INVENTION
[00021] A set of preferred embodiments of the cable tray A of the present
invention are illustrated in FIG. 1 through FIG. 6D. An example of the
physical
configuration of a preferred embodiment of the present invention is shown in
FIG. 1
where the cable tray A comprises a plurality of U-shaped transverse members 1
and
a plurality of longitudinal members 2. As is readily apparent, the plurality
of U-
shaped transverse members 1 are disposed substantially perpendicular to the
plurality of longitudinal members 2 at a general spacing of about 3.9 inches
on
center. The longitudinal members 2 of the present embodiment are generally
spaced about 2.0 inches on center.
[00022] Upon the positioning of the plurality of U-shaped transverse
members 1 and the plurality of longitudinal members 2 it will be understood by
those
skilled in the art that at substantially each point where a single U-shaped
transverse
member 1 intersects with a single longitudinal member 2, the U-shaped
transverse
member and the longitudinal member are welded together.
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[00023] This is typical throughout the entire construction of the present
embodiment of the invention with the exception of the longitudinal members 2A.
The
other longitudinal members 2 are positioned such that the outer radius of the
longitudinal member is welded against the outer radius of the adjacent U-
shaped
transverse member 1. In contrast, each of the two longitudinal members 2A is
generally located at an end 3 of the plurality of U-shaped transverse members
1.
The longitudinal members 2A are then welded in that position on the end 3 of
the
plurality of U-shaped members 2.
[00024] It will be appreciated by those skilled in the art that when the
present embodiment of the cable tray A is fully constructed, the cable tray is
in the
general shape of a channel having plurality of openings disposed between the
framework of the assembled plurality of U-shaped transverse members 1 and the
plurality of longitudinal members 2. It will also be appreciated that when
fully
assembled, the outside dimension of the cable tray A of the present embodiment
has
a width of about 3.5 inches and a height of about 1.5 inches. In alternative
embodiments of the present invention, the width and height can be readily
adjusted
to fit the dimension into which the cable tray A will be installed. In most
instances
the width and height of the assembled cable tray A will comparable to the
width and
height dimensions of standard wood construction framing material.
[00025] It will also be understood that while preferred embodiments of the
present invention as described herein show the cable tray A as being generally
channel-shaped and that the transverse members are U-shaped, the intended
scope
of this invention is not to be limited to only those embodiments that have
channel
shapes or U-shaped components. For example, other embodiments of the present
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invention include cable trays A that have a bottom and two sides where the two
sides
may be not be perpendicular to the bottom.
[00026] Other embodiments of the present invention include cable trays A
where the two sides may be flared away from the longitudinal center of the
bottom or
flared toward the longitudinal center of the bottom, thereby making the
interior angle
formed by the sides and the bottom of each such embodiment either obtuse or
acute
respectively. This is to say, the angular placement of the sides of the
present cable
tray A in relation to the bottom of the cable tray may be adjusted as needed
for
specific applications and still remain within the intended scope of the
present
invention.
[00027] In a preferred embodiment, the overall length of the cable tray A is
about 10 feet, however, the length of the cable tray A can be any other length
while
still remaining within the intended scope of the present invention.
[00028] Those skilled in the art will appreciate that the plurality of U-
shaped
transverse members 1 and the plurality of longitudinal members 2 may be of any
type of material strong enough to support the weight to which the cable tray A
is
expected to support. In a preferred embodiment, the plurality of U-shaped
members
1 and the longitudinal members 2 are made from a galvanized wire in accordance
with ASTM A641. The zinc plating of the present embodiment is electrodeposited
zinc having a Type III Finish and Service Condition One in accordance with
ASTM
B633. Alternatively, the finish of the material may also be a polyester powder
coating having a general thickness of about 1.2 mils to about 3.0 mils. In yet
other
alternative embodiments of the present invention, the plurality of U-shaped
transverse members and the plurality of longitudinal members 2 are made from
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either carbon steel Brite Basic Wire in accordance with A510, Grade 1008, or
alternatively, 304 & 306 Stainless Steel. To ensure that the assembled cable
tray A
shown in some preferred embodiments has a generally consistent geometric shape
and balance, the angular formations within the assembled cable tray should not
vary
by more than about + 3 degrees; the overall camber should not exceed 0.5
inches
over each ten foot length of cable tray; and, the twist should not exceed 0.5
inches
over each ten foot length of the cable tray.
[00029] Although the general characteristics of the cable tray A are
substantially described and disclosed above, variations in the geometric shape
of the
plurality of U-shaped transverse members 2 provide a variety of preferable
strength
characteristics and resistance to combat fatigue cracking and abrasion of the
electrical system conductors.
[00030] More specifically, when electrical system conductors are installed in
a prior art style cable tray having round or square U-shaped transverse
members,
the geometry of those member shapes causes the outer surface of the electrical
system conductor to rest upon a relatively sharp corner or small radius. This
results
in the weight of the electrical system conductor being transferred onto the
cable tray
at the sharp corner or small radius of the round or square shaped transverse
rod.
This generates a mechanical rise in the stress load at those very concentrated
points
and can more easily result in chaffing or fatigue cracks in the metallic
electrical
conductor, the optical fiber within the cable, or the cable's insulation.
Various
embodiments of the present invention tend to reduce this stress concentration
area
by incorporating alternative geometric shapes for the plurality of U-shaped
transverse members 2.
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[00031] For example, the embodiment of the cable tray A as shown in FIG.
1, FIG. 2, FIG. 3, FIG. 4, FIG. 5, and FIG. 6 show the plurality of U-shaped
transverse members to be generally obround in shape (FIG. 6), having a height
of
about 3.5 mm and a width of about 6.5 mm. When the obround shape is used, a
flat
portion 4 of each of the plurality of U-shaped transverse members 1 rests upon
the
outer radius of each of the longitudinal members 2. This orientation of the
obround
U-shaped transverse member 1 positions the opposite flat face 5 of the obround
shape upward to face the bottom of the electrical system conductors when the
electrical system conductors are placed within the cable tray A. As can be
seen, the
point load between the electrical conductor and the transverse members 1 is
significantly lower in the present embodiment than the old art embodiment
because
the surface area of the obround flat surface 5 reduces the loading per square
inch
against the bottom of the electrical conductor.
[00032] In this same manner, the plurality of U-shaped transverse members
1 can be made using rods that provide yet other geometric shapes that tend to
reduce the point loading between the electrical system conductors in the cable
tray A
and the plurality of U-shaped transverse members 1 of the cable tray. For
example,
the plurality of u-shaped transverse members 2 may be elliptically shaped as
shown
by member 1A in FIG. 6A. In other embodiments of the present invention, the
plurality of transverse U-shaped members may be in the shape of a square
having
substantially rounded corners as shown by member 1B in FIG. 6B. In yet other
embodiments of the present invention, the plurality of U-shaped transverse
members
may be in the shape of an extremely flattened elliptical as shown by member 1C
in
FIG. 6C. Finally, in yet another embodiment of the present invention, the
plurality of
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U-shaped transverse members may be in the shape of an elliptical rod that has
been
halved as shown by member 1D in FIG. 6D. It is appreciated that the U-shaped
transverse member may be of yet other geometric shapes while still remaining
with
the intended scope of this invention and act to reduce the point loading on
the
electrical system conductors placed in the cable tray, with the primary
limiting factor
for the chosen geometric shape, and the dimension of that shape, being the
shape's
ability to provide the structural integrity to carry the weight of the number
of electrical
system conductors to b disposed within the cable tray A.
[00033] In each of the above geometric shapes it is understood that a goal
is to select a shape that proffers the flattest surface area to the bottom
surface of the
electrical conductor to thereby reduce the point loading between the cable
tray A and
the electrical conductor residing within the cable tray. Thus, in each shape
identified
for the present invention, the intent is to generate a structural system where
the
contact point load on an electrical conductor placed within the cable tray
such that
the surface of the U-shaped transverse members contacts the electrical
conductor
placed within the cable tray is less than the contact point load of a cable
tray having
U-shaped members that are in the shape of one of either a substantially sharp
cornered square, a substantially sharp cornered rectangle, a substantially
sharp
cornered triangle, or a circle.
[00034] While the above description describes various embodiments of the
present invention, it will be clear that the present invention may be
otherwise easily
adapted to fit any configuration where a cable tray is required. Additionally,
as
various changes could be made in the above constructions without departing
from
the scope of the invention, it is also intended that all matter contained in
the above
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description or shown in the accompanying drawings shall be interpreted as
illustrative and not in a limiting sense. The scope of the invention should be
determined by the appended claims and their legal equivalents, rather than by
the
examples given.
