U.S. patent number 3,643,006 [Application Number 05/120,489] was granted by the patent office on 1972-02-15 for mechanical, solderless ground wire connectors for telephonic cable shielding jackets.
This patent grant is currently assigned to Superior Continental Corporation. Invention is credited to Louis Ance.
United States Patent |
3,643,006 |
Ance |
February 15, 1972 |
MECHANICAL, SOLDERLESS GROUND WIRE CONNECTORS FOR TELEPHONIC CABLE
SHIELDING JACKETS
Abstract
Disclosed is a bonding clip adapted to be connected to a bonding
harness and for forming a joint that maintains electrical and
mechanical continuity between the shielding of one cable terminus
to another. The clip is made from a piece of metal, U-shaped in
cross section, which has two juxtapositioned terminal portions.
Each terminal portion has an aperture therein that is aligned not
only with that aperture in the opposing terminal portion but also
with an aperture through a coated cable shield. The terminal
portions have spaced-apart perforations defining inwardly extending
plastic and metal piercing protuberances whereby pressure applied
to said terminal portions by a connector means, disposed through
the apertures, exert a force to thrust said protuberances through
the plastic covering and the metal shield. Located in the aligned
apertures is a connector means that has a median shank and two
terminal portions, one of which has unconnected grooves therein and
is nested inside of an annulus sleevelike fitting that has
annuluslike protuberances on the innermost surface thereof, the
protuberances being positioned so that they mechanically interfit
and essentially fill the unconnected grooves.
Inventors: |
Ance; Louis (Hickory, NC) |
Assignee: |
Superior Continental
Corporation (Hickory, NC)
|
Family
ID: |
22390622 |
Appl.
No.: |
05/120,489 |
Filed: |
March 3, 1971 |
Current U.S.
Class: |
399/144; 174/78;
174/84C; 174/94R; 439/421; 399/196 |
Current CPC
Class: |
H01R
4/06 (20130101); H01R 4/2495 (20130101) |
Current International
Class: |
H01R
4/24 (20060101); H01R 4/00 (20060101); H01R
4/06 (20060101); H02g 015/08 () |
Field of
Search: |
;174/88R,78,94R,84R
;339/95,97,14R ;29/628 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Clay; Darrell L.
Claims
I claim:
1. In an electrical cable assembly, an electrical cable segment
having a metallic shield, a jacket of insulating material covering
said shield and a layer of plastic disposed between said jacket and
said shield and being bonded to said shield and jacket, and a
connector establishing electrical contact with said shield and
comprising a metallic member having spaced apart sections, portions
of said shield, said jacket and said layer being disposed between
said sections, with one of said sections electrically contacting
the side of said shield opposite from said layer, said sections
having protuberances extending into the space between said sections
and piercing said portions of said shield, said jacket and said
layer, a fastening member extending through aligned apertures in
said sections and said portions of said shield, said jacket and
said layer, said fastening member having a pair of terminal
portions disposed at opposite sides of said sections, one of said
terminal portions having a plurality of unconnected grooves formed
in the periphery thereof, said grooves at least partially
circumscribing said one of said terminal portions, and a sleevelike
fitting receiving said one of said terminal portions and having
inwardly extending protuberances mechanically engaging and
substantially filling said grooves, and electrically conductive
means confined between one end of said fitting and an opposing
surface of said metallic member and being retained in electrical
contact with said metallic member by said fitting.
2. The electrical cable assembly defined in claim 1, wherein said
metallic member has a U-shaped configuration in cross section, with
the legs of said U-shaped configuration forming said spaced apart
sections of said metallic member.
3. The electrical cable assembly defined in claim 1, wherein said
fitting is a metallic sleeve that is crimped on said one terminal
portion of said fastening member.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a joint that is used in concert
with a grounding harness. A grounding harness is a means to form an
electrical connection (path) and is employed to maintain the
electrical continuity in the shields in two cable segments.
Telephone cables are usually made up of a core, comprised of a
plurality of insulated electrical conductors, surrounded by a
metallic shield that is nested inside a tubular plastic outer
covering called a jacket. In order to maintain the electrical
continuity of the shield between two cable segments, a firm joint
must be created, mechanically grasping and electrically connecting
the shield of one cable terminus to the shield of a second cable
terminus.
2. Description of the Prior Art
Presently made telephone cable generally have a structure made up
of at least a core, a metallic shield and a plastic jacket. The
core is comprised of a plurality of insulated electrical
conductors, which is nested inside of a tubular-shaped metallic
shield. This shield is further nested inside of a plastic covering,
known as a jacket. It has been a standard manufacturing practice,
in the manufacture of cable, to prevent any bonding (fusion) at the
interface between a plastic film coated on the outermost surface of
the metallic shield and the plastic jacket extruded thereover,
Inhibition of fuse bonding was accomplished by: applying a
lubricant to the plastic-coated shield, and regulating the
extrusion temperature and the speed of extrusion of the jacket.
However, it has been found that when the jacket is not allowed to
adhere to the shield, the jacket, in service, has a tendency to
"run." That is to say, the outer jacket will tend to move
independently of the rest of the cable (core and shield) and "bunch
up" at certain designated spots causing the jacket, at these spots,
to buckle and subsequently rupture. Such ruptures created avenues
for moisture penetration and are obviously undesirable. In recent
technology, it has become necessary, for various and sundry
well-known reasons, to use a shield that has bonded to it a thin
coating of plastic, this plastic being a graft copolymer of
polyethylene and a monomer with reactive carboxyl group such as
acrylic acid or acrylic acid ester. Such plastics are well known
and are described in U.S. Pat. Nos. 2,987,501 and 3,027,346, the
disclosures found in these patents being herein incorporated by
express reference.
When plastic-coated shield members are used, see U.S. Pat. No.
3,233,036, the disclosure of which is herein incorporated by
reference, a great deal of care, the prior art teaches, must be
taken when extruding a plastic jacket thereover. During manufacture
of cable using a plastic-coated shield, it has been found
desirable, by prior investigators, to prevent adherence between the
outer film of the shield and the jacket extruded thereover. This
has been accomplished, as taught by the prior art, by applying a
lubricant to the laminated shield (plastic-coated shield) and by
regulating the extrusion temperature and speed of extrusion of the
jacket. The prior art teaches that a complete fusion between the
outer jacket and an outer plastic coating of the metal shield will
increase the difficulty of stripping the cable for splicing. More
often than not, this fusion bond would have the undesirable effect
of, at times, exceeding the bond force of the outer shield laminate
to the metallic shield per se so that during bending of the cable
or stripping of the jacket at cable ends, delamination of the outer
film of the shield would result, thereby exposing the metal shield
to corrosive attack.
Therefore, it would be desirable if there could be developed a
practice, plus the necessary hardware, in which telephone cable
terminus could be joined, one to another, so as to maintain the
electrical continuity between shield members firmly bonded to an
outer plastic jacket. As pointed out above, it has been the prior
art practice to require that a shield member be stripable from any
plastic jacket inside of which it was nested. This stripable
feature, the prior art declared, was necessary in order to make
adequate mechanical and electrical contact with the shield during
attachment of bonding harness from one cable reel terminus to
another.
Recently, there has been disclosure certain solderless ground wire
connectors for telephonic cable shielding jackets, designed to make
electrical and mechanical contact with a shield, laminated on one
side with a plastic. These connectors are made up of three distinct
parts plus a connector means, the connectors means being a
conventional nut and bolt arrangement. Anytime a nut and bolt
arrangement is used to form the compressive force to make
mechanical and electrical contact with plastic-coated shield
members of telephone cable, there is a tendency for such a
structure to have variations in electrical properties, namely
connection resistance that is directly attributable to the nut and
bolt arrangement. When a connection is made, using the nut-bolt
arrangement, there is always a variation in tightness applied.
Furthermore, a nut and bolt arrangement has the property of losing
its original tightness, over a period of time; thus resulting in
some visible mechanical deterioration as well as significant
electrical contact resistance.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a cross-sectional view of a metal shield fuse bonded to a
plastic jacket forming a part of an electrical and mechanical joint
made according to the instant invention; and,
FIG. 2 is a graph showing a plot of contact resistance against
number of temperature cycles (-40.degree. to +140.degree. F.) data,
for two types of joints: one made according to the instant
invention and one made using a nut-and-bolt type connector
means.
DESCRIPTION OF A PREFERRED EMBODIMENT
Shown in FIG. 1 is a metal shield coated on one side with a graph
polymer of polyethylene and a monomer with reactive carboxyl group,
such as acrylic acid or acrylic acid ester. This graph polymer is
termed as a "fuse bond." It is this layer of plastic that is bonded
to the metal shield as well as to the plastic jacket. It will be
remembered that this fuse bond is normally achieved during the
extrusion step of the manufacturing process of the cable.
The composite laminate made up of the plastic jacket, fuse bond and
metal shield, is tightly gripped and in electrical contact with the
clip bond combination, which is made up of a piece of metal,
U-shaped in cross section, connector means 2 and annulus fitting 3.
The U-shaped piece of metal is composed of three portions, namely a
median portion connected to two terminal portions indicated by
reference character 1. The terminal portions contain spaced-apart
perforations 8 defining inwardly extending plastic and metal
piercing protuberances 6. These two terminal portions face
oppositely one from another and form the "legs" of the
aforementioned U-shaped configuration. Protuberances 6 pierce not
only the metal shield but also the fuse bond and plastic jacket
laminate as shown.
Each terminal portion has an aperture in it that is not only
aligned with that aperture in the opposing terminal portion but
also with an aperture in the plastic jacket fuse bond metal shield
laminate. Within these three apertures, connector means 2 is
disposed. Connector 2 is made up of a median (shank) portion and
two terminal portions. One of these terminal portions has a
dimension that is larger than the apertures in the metal clip
terminal portions. The other terminal portion of connector means 2
has nonconnecting annular grooves disposed therein. One end of jack
5, which is a piece of metal with a hole in it, is connected to the
grounding harness and is disposed around the connector means 2 to
form the electrical connection between that shield shown in FIG. 1
and another shield which is connected to the other end of the
grounding harness (not shown).
An annuluslike fitting 3, which prior to being affixed to connector
means 2 possessed no inwardly protruding protrusions like that
shown at 4, is slipped over that terminus portion of connector
means 2 where the unconnected grooves are located. By means of a
special tool, not shown, compression is applied to the thus
assembled joint, more specifically connector usually aluminum, out
of which annulus fitting 3 is formed.
As a result of this compression, metal is caused to flow into those
unconnecting grooves disposed in one terminal portion of connector
means 2. The compression rendered by this special tool is a
function of that compression energy that is required to make the
metal of annulus fitting 3 cold flow into those grooves previously
described. If, by chance, insufficient compression energy were
applied, using the special tool previously mentioned and not shown,
there would be no cold flow of the metal of fitting 3. Thus, there
would be no connection between annulus fitting 3 and connector
member 2. Therefore, by using the special tool in this particular
combination, there is absolute assurance that a predetermined
amount of compressive force will be exerted on connector 5 U-shaped
metal clip 1 and 7, the plastic jacket, fuse bond and metal shield
laminate, if there is adherence of annulus 3 to connection member
2. If there has been insufficient compressive force rendered to
annulus 3 and connection member 2 by the tool, then there will be
insufficient protuberances 4 and thus no connection.
At first blush, it might seem that a nut and bolt arrangement, used
as a connector means, would be roughly equivalent to that connector
means envisioned by the instant invention, namely Elements 2, 3 and
4 of FIG. 1. If such an equivalency were in fact true, then one
would anticipate that not only the mechanical but the electrical
characteristics exhibited by that joint shown in FIG. 1 would be
the same, whether or not connector means shown in the combination
of Elements 2, 3 and 4 were employed or a nut and bolt arrangement
were substituted for these elements. Experimentation and data taken
from such experimentation has proven this not to be the case,
namely that the connector means combination of Elements 2, 3 and 4
is not an electrical equivalent, from the standpoint of contact
resistance, of a nut and bolt arrangement.
FIG. 2 is a graph showing a plot of connection resistance data
against a given number of temperature cycles (-40.degree. to
140.degree. F.) for two types of joints, namely one having the same
configuration as shown in FIG. 1 (" " data plot) and another having
the same configuration in FIG. 1 except that Elements 2, 3 and 4
were replaced by a nut and bolt arrangement ("X" data plot).
Contact resistance in ohms was measured for both joint types and
ploted against the number of cycles these joints were subjected,
using a temperature cycle of -40.degree. to +140.degree. F. As will
be seen by FIG. 2, the initial contact resistance of a joint, made
according to the instant invention, was lower than that made using
another joint using a nut and bolt arrangement. Over the 100
temperature cycles shown in FIG. 2, the joint made according to the
instant invention maintained and increased that contact resistance
differential between itself and a joint using a nut and bolt
arrangement. Observing the type "X" data plots, which form the
uppermost curve and characterizes the contact resistance of the nut
and bolt type connector joint, it is readily seen that in
comparison to that joint made according to the instant invention,
the connection resistance of the nut-and-bolt-type joint connector
increased significantly over a period of 100 temperature
cycles.
Inasmuch as the connection resistance of connectors joining bonding
harnesses to respective shields of cable terminuses is highly
important, it is immediately obvious that the joint formed
according to the instant invention gives an unexpected result.
Because of this characteristic, it is far more proficient in
maintaining electrical continuity from one cable segment shield to
another. The results shown by FIG. 2 are not only surprising in the
sense that one would expect the electrical characteristics of the
nut and bolt arrangement to be essentially the same as that
arrangement envisioned by the instant invention, but also in the
sense that a nut and bolt arrangement would appear to exert
essentially the same compression as that exerted by connector means
made from Elements 2, 3 and 4. Notwithstanding this fact, after 100
temperature cycles between -40 to 140.degree. F., it was physically
noticeable that the mechanically compression exerted by the nut and
bolt arrangement was significantly less than it was at the
beginning of the temperature cycles, whereas the compression
exerted by that arrangement envisioned by the instant invention was
essentially unchanged. Furthermore, field trials in the state of
Montana have shown that vibrations caused by normal highway traffic
tend to loosen a nut and bolt arrangement. Inasmuch as the grooves
of Element 4 are unconnected, the connector means of the instant
invention is unaffected by vibration.
In summary, it can be readily seen that the instant invention sets
forth a simple but yet effective means of establishing not only a
mechanical but an electrical contact with a cable shield member.
Furthermore, this contact, both electrical and mechanical, can be
made with a shield coated and/or laminated to a piece of plastic.
This mechanical and electrical contact is one that will withstand
not only vibrations that tend to loosen a nut and bolt arrangement,
but also many severe temperature cycles. Additionally the joint
will maintain an extremely desirable level of mechanical
compressive force and at the same time exhibit an electrical
contact resistance that is not only much lower in value than one
would expect using other conventional connector means but also more
constant in value over a period of time. The presently disclosed
connector means employs the use of metal cold flow and therefore
demands that a given amount of compressive force be exerted before
a connection can be made. Such a feature insures that the
compressive force under which the joint is subjected is sufficient
to achieve desired electrical and mechanical properties.
* * * * *