Note: Descriptions are shown in the official language in which they were submitted.
517
ELECTRICAL TERMINATION BLOCK FOR FLAT CONDUCTOR CABLE
BACKGROUND OF THE INVENTION
This invention relates to electrical wiring
systems utilizing flat conductor cables in lieu of
conventional round wiring systems, and to accessories
employed therein.
More particularly, this ir,vention relates to
terminal blocks employed in flat conductor cable wiring
systems9 for facilitating connections to the flat
conductors.
Flat conductor cables, which comprise a
plurality of conduc~ive strips embedded in a thin
insulating sleeve are finding increasing commercial use
in the substitution or replacement of conventional and
round wiring systems. By permitting wiring arrangements
which may-be placed under certain floor coverings such
as carpeting, flat conductor cable systems eliminate the
need for extensive behind-the-wall electrical
installations~ the tacking oF wiring to baseboards, and
the inclusion of duct work in the walls and floors of
buildings under construction which are meant to house
conventional wiring systems. Flat conductor wiring
systems utilize the floor surface itself as the wiring
bed.
Several under-carpet wiring systems have been
offered commercially: one of these is the FLEXWAY
(trademark of Burndy Corporation) cable wiring system.
In these systems, numerous and different types of cable
connections are made which are analagous to the several
types of connections used in conventional wiring
systems; that is, flat conductor cables are tapped,
spliced, connected to transition junctions, and
15 connected to service modules or fittings. In a
transition connection, a cable usually is connected
mechanically to an insulating member, from which
electrical connections are made tc a conventional wiring
system. Such transition junctions are normally
20 contained within an enclosure which can be opened for
access. A service module or fitting is an enclosure in
which a flat conductor cable is mounted and connected to
an insulating support, from which power is tapped for
direct use by a consumer. An example of this would be a
25 service fitting in which the flat conductor cable is
connected to a standard electrical outlet.
Cable systems of this type are often installed
in three layers: a bottom protective layer which
directly contacts the surface on which the wiring system
is to be laid; a middle layer which is the flat
conductor cable itself; and a top protective layer, over
which the floor coverirg or other surface covering is
installed. The top and bottom layers may be comprised
of cold rolied steel , and either one or both may be
used to "ground" the entire electrical system.
Alternatively, the bottom layer may be
insulating plastic, either beneath and in addition to
the lower matallic layer, or in lieu thereof.
~enerally, the plastic insulating layer is in the range
of several mils to about 25 mils thick. The thickness of
the cable itself depends upon the exact gauge, but
generally is of the order of 10 to 25 mils; and the
metallic grounding shield layers range in thickness
between 5 and 15 mils. Therefore the total structure
remains very thin despite the three-]ayered, or possibly
four or more-layered, composite.
As previously mentioned, flat conductor cables
are comprised of a plurality of conductive strips which
are separated and insulated from each other and are
enclosed within a thin insulating sleeve which is
-- 'I --
typically a plastic Material, such as for example, polyester.
The conductive strips are usually formed of copper or a copper
alloy, and the number of strips per cable can vary from several
to a large number, depending upon the extensiveness of the
wiring system contemplated. Taps, splices, transition connec-
tions and terminal connections are produced by clamping
conductive connectors of various sorts onto the conductive
portions of the cable. Squeeze-clamp connectors with teeth
which penetrate the cable insulation have been used, and a
novel cable connection arrangement has been introduced
recently by Burndy Corporation as part of -the above
referenced FLEXWAY* under-carpet wiring system. This
electrical connection arrangement comprises the use of a
hollow rivet connector which penetra-tes through an aperture
in the cable and is compressed into an eyelet shape so as
to electro-mechanically engage the cable conductor.
The apparatus and method of producing such a novel connection
is described in detail in United States Patent No. 4,446,330
issued May 1, 19~4, assigned to Burndy Corporation, and
entitled "Electrica] Connection Apparatus And Procedure
For Flat Conductor Cables And Other Similar Articles".
When transition -terminal connections are made
in a flat conductor cable system, the por-tion of the
* Trade Mark
5~
cable usually is coupled to an insulating support which
iâ further mounted within a service module accessible to
service personnel. To produce an electrical connection,
a conductive surface of each conductor must be exposed,
5 and a conductive coupling means must be provided to form
an electrical connection between the conductive surface
and an external conductor or utilization device. These
connections are subject to two significant requirements:
(1) The conductive coupling means which engage the
respective spaced apart conductors of the cable
generally must be electrically insulated from each
other, and (2) the conductive coupling means must join
the external conductors to the cable conductors with
significant mechanic;al force while maintaining the space
15 between couplings independently of the cable structure
itself.
It is therefore an important object of this
invention to provide a transition block connector for
establishing electrical connections between the
20 conductors of flat flexible cable and external
conductors or utilization devices, which provides for
firm mechanical clamping of external conductors to the
flat cable while maintaining mechanical and electrical
separation of the respective spac~d-apart couplings.
25 This transition block connector also accommodates
variations in the spacing between the respective
couplings which are caused by variations in the spacing
between onductors in various cables, and by variations
in the spacing and alignment of openings in the
conductors which accommodate the coupling means.
Another object of this invention is to provide
a transition connector for connecting the ground
conductor of a flat cable to a metallic shielding layer
associated with a flat cable without resort to external
wires or additional lengths of other conductors.
SUMMARY OF THE INVENTION
- The above and other objects and features of
- this inventions are accomplished by providing for use in
a flat conductor cable service module, a transition
- block connector which provides spaced-apart fastener
members moveably mounted in spaced-apart relation in an
insulating housing for threadedly engaging screw
threaded terminal fasteners that have been positioned in
openings in the conductors of a flat cable and are in
electrical engagement with the conductors.
The fastener members are moveable within the
insulating housing, within predetermined limits, so as
to accommodate variations in spacing of tne terminal
screws which project through the cable conductors, while
maintaining a predetermined electrical and mechanical
separation between the respective fasteners, and between
the fasteners and "ground".
A conductive support sheet can be coupled to
the insulating housing to provide for grounding
connectors between the ground conductor of a flat cable
and a metallic shield layer of an installed system. By
providing a conductive threaded fastener coupled to the
support sheet and positioned so that it may be aligned
with a through opening in the insulating housing, a
direct ground connection can be achieved between the
cable and the conductive support sheet.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is an "exploded" pictorial representation of d
terminal block in accordance with this invention;
Figure 2 is a pictorial representation of an assembled
terminal block in accordance with this invention,
mounted on a substrate, with terminal screws aligned in
position for assembly;
Figure 3 is an "exploded" cross-sectional view oF a
terminal block with a conductive support sheet and
attached conductive fastener in accordance with this
invention, showing a flat flexible cable and terminal
screws aligned for assembly; and
Figure 4 is a pictorial representation of a portion of
the flat flexible cable which is shown in end-view in
Figure 3.
Now, referring to the drawings more specifically, and
particularly at first to Figure 3: The terminal block of
this invention may be seen to comprise a housing 10
having recess,es 12 containing fastener members 14. In
use, terminal screws 16, extending through holes 18 in
the spaced-apart conductors 20 of a flat flexible cable
22, are threadedly engaged with screw-threaded central
openings 24 in fasteners 14. Openings 24 are shown in
Figure l.
In the illustration form of the invention a conductive
support sheet 48 may be coupled to the housing lO by
means of clamping screws 46 which engage threaded
openings 60 in the sheet. Although threaded openings
have been shown it is clear that other and different
kno~n forms of fastening means may be employed to couple
sheet 48 to housing lO without departing from the scope
t~
of t~is invention. A threaded stud fastener 62 of
conductive metal is anchored to the sheet 48 by any
convenien~ means such as staking to form a secure
electro mechanical connection between the sheet and the
stud. The function of stud fastener 62 is further
explained later in the text of this specification.
As shown in Figure 1, the fasteners 14 comprise a
generally cylindrical body portion 26 and an anchor
portion 28 which has a non-circular exterior
configuration; it can be seen that the non-circular
configuration of anchor portion 28 in the illustrated
embodiment is generally square or rectangular, but it is
considered ~bvious that other geometric configurations
may be used as well within the scope of this invention.
Between body portion 26 and anchor portion 28 of
fastener 14, a shoulder 30 is formed, facing generally
in the direction of the opening 24. The function of
shoulder 30 is explained later in the text of this
specification.
Further~ as shown in Figure 1, the housing 10 comprises
a base part 32 having a mounting surface 34 thereon, and
a closure part 36 having an access surface 38 thereon.
A pluralty of access openings 40 extend through the
access surface to permit access to the central openings
24 of ~asteners 14 which are disposed within recesses 12
which are -Formed in base portion 32 of housing 10. The
exterior dimensions of fasteners 14 measured in a
direction generally normal to the central axis of the
central openings 24 are sufficiently less than the
internal dimensions of recesses 12 measured in a
d.rection generally parallel to base surface 34 of
housing 10, so as to permit lateral displacement of axis
24 of fasteners 14 relative to housing 10. The interior
configuration of recesses 12 is selected to be generally
congruent with, but larger than the exterior
configuration of anchor portion 28, so as to permit
lateral displacement of the fasteners 14 within the
recess 12, while substantially preventing rotation of
fasteners 14 about axes substantially parallel to the
central axis of openings 24. Although fasteners 14 are
shown in this embodiment to have non-circular anchor
portions remote from the entrance to openings 24, and
congruent non-circular portions of recesses 12 are shown
to be formed in base portion 32 of housing 10, it is
considered obvious to one of ordinary skill in this art,
that different arrangements are possible ancl other
locations for non-circular portions of the housing and
the fasteners may be provided within the scope of this
invention.
It can be seen most clearly in Figure 3 that the inner
3 ~
walls 41 which carry access openings 40 into the
thickness of closure number 36 form part of the recess
1? within housing 10 which contains fastener 14.
Inside recess 12, ~ithin the body of housing 10 bet~een
mounting surface 34 and access surface 38 a shoulder 42
is formed facing in a direction generally away from
access openings 40 toward the interior of the housing.
This shoulder 42 within the recess, cooperates with
shoulder 30 on the surface of fastener 14 to prevent
withdrawal of the fastener from recess 12 when closure
part 3~ of housing 10 is assembled to base part 32.
As show~ in Figures 1 and 2, in addition to access
openings 40 and recesses 12, housing 10 includes through
openings 44 which extend through access surface 38 as
well as through mounting surface 34 for receiving
fastener members 46 to secure the terminal block to a
suitable substrate such as conductive support sheet 48.
Housing 10 also include a through opening 45 which
extends through access surface 38 and mounting surface
34 for receiving a terminal screw 17 which can extend
through a ground conductor 20 of a flat flexible cable
2~ and engage a stud fastener 62 on conductive sheet 48
for the purpose of providing an electrical "ground"
connection between the conductor 20 and conductive
~shield layers connected to support sheet 48.
11
~he ~lat fle~ible cable 22 i5 be provided ~ith
conductive terminal devices 52 which extend through the
conductors 20 and are secured to the insulation 54 of
the cable for the purpose of reinforcing the conductors,
maintaining electrical contact, and for providing
secure clamping surfaces for the terminal screws 16.
In a typical embodiment of this invention, the flat
flexible cable 22 may be 0.020" thick with a center to
center spacing between adjacent conductors 20 of 0.955".
Terminal screws 16 and 17 may be screw thread si~e 8-32
UNC-2A with a corresponding internal thread provided in
the central openings 24 of fasteners 14~and binding
heads preferably may be used. For use with a flat cable
of these dimensions, the difference between the interior
dimensions of recesses 12 and the exterior dimensions of
fasteners 14 preferably may be selected to permit
relative lateral displacement of each fastener 14 plus
or minus 0.050" from its normal centerline position.
For example, in a terminal block intended for use with
cable having center-to-center spacing betwee~n adjacent
con.ductors 20 of approximately 0.955", the overall
outer dimension of fastener 14 may be on the order of
12
s~
0 43S" in such a terminal block~ the overall internal
dimension of the corresponding portion of recess 12, may
be approximately 0.53~". Because it is generally
important to accommodate or permit displacement of
fasteners 14 relative to housing 10 in -a direction
parallel to the center line of the flat cale, as well as
in the lateral direction, the difference between the
exterior dimensions of fasteners 14 and the inner
dimensions of recesses 12 may be the same in both
directions. However, it must be understood that
dimensions may be selected to permit different limits of
excursion of the fasteners in different directions,
without departing from the scope of this invention.
With respect to preventing rotation of
fasteners 14 about any axis generally parallel to the
axis of central opening 24, referred to previously, it
is noted that this is necessary for proper engagement of
screws 16 with the threaded receptacle openings 24; it
would be difficult to achieve threaded coupling of the
screw within the receptacle opening if the fastener is
free to rotate about a parallel axis. For the purposes
of this invention therefore, it can be seen that in
addition to the necessary differences between the inner
dimensions of recess 12 and the outer dimensions of
fastener 14 which permit lateral displacement of the
fasteners relative to the housing 10, it is also
~ 2~
necessary that the maximum overall dimension of some
part of fastener 14 measured in a direction generally
perpendicular to the central access of opening 24, must
be greater than an overall interior dimension of a
corresponding part of recess 12 so as to provide the
interference between the fastener and the recess ~hich
i, necessary to prevent rotation. In the illustrated
embodiment, this objective is achieved by the fact that
the diagonal dimension of the generally square
anchor-portion 28 oF fastener 14 is greater than the
space between either of the opposite sides of the
generally rectangular recess 12.
The terminal block embodiment illustrated in the
drawings, is assembled by positioning a fastener 14 in
recess lZ in the base part 32 of housing 10, and then
positioning the closure part 36 in abutting relation
with the base part 10 such that the generally
cylindrical portions 26 of the fasteners are surrounded
by wall portions portions 41 which form part of rPces 12
20 inclosure part 36, and the central openings 24 are
exposed through access openings 40. In a preferred
embodiment, each fastener 14 has an abutment surface ~6
generally circumjacent the entrance to central openings
24. The contact surfaces 58 of terminal devices 52 may
25 be firmly clamped against abutment surfaces 56 by the
clamping action of screw 16 when engaged with fasteners
14
14. Accordingly, tor the purposes of this invention,
and so as to avoid unnecesary distortion of cable 22, it
is preferable for abutment surfaces 56 to be not
substantially closer to mounting surFace 34 than is
access surface 33. Further, in the preferred
embodiment, the thickness of the insulating material
of housing lO between mounting surface 34 and the
nearest inner surface of recess 12 should be sufficient
to satisfy applicable standards for electrical
insulation between an energized conductive fastener 24
and any conductive surface or substrate which may be
abutted against mounting surface 34, at commonly used
electrical voltages.
Variations and modifications of the connector
disclosed herein will become obvious to persons skilled
in this art as a result of this disclosure and
accordingly such variations and modifications are
considered to be within the scope of this invention.
