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(11) | EP 0 138 039 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Electrical termination block for flat conductor cable |
| (57) A tansition block connector serves as a fastening point for a plurality of terminal
screws which extend through holes in the spaced-apart conductors of a flat flexible
cable. To provide fastening points for the spaced-apart screws, and to accomodate
variations in the spacing between them, mating fasteners are moveably mounted in a
housing which is formed of electrically insulating material. The moveable mounting
includes a recess in the housing for each fastener which has internal dimensions larger
than the external dimensions of the fastener, and a portion of the fastener has a
non-circular exterior configuration which cooperates with a portion of the recess
having a non circular configuration to prevent rotation of the fastener within the
recess while permitting lateral displacement of the fastener relative to the housing.
The housing is formed in two parts which define an internal shoulder which in turn
cooperates with an external shoulder on the fastener to prevent withdrawal of the
fastener from the recess when the two parts of the housing are joined together. A
conductive support plate coupled to the housing includes an electromechanically coupled
threaded fastener which cooperates with a through opening in the housing to permit
coupling of a conductor of a flat cable directly to the support sheet for grounding
purposes. |
BACKROUND OF THE INVENTION
[0001] This invention relates to electrical wiring systems utilizing flat conductor cables in lieu of coventional round wiring systems, and to accessories employed therein.
[0002] More particularly, this invention relates to terminal blocks employed in flat conductor cable wiring systems, for facilitating connections to the flat conductors.
[0003] Flat conductor cables, which comprise a plurality of conductive strips embedded in a thin insulating sleeve are finding increasing commercial use in the substitution or replacement of conventional and round wiring system. 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.
[0004] 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 connected to service modules or fittings. In a transition connection, a cable usually is connected mechanically to an insulation member, from which electrical connections are made to a conventional wiring system. Such transition junctions are normally 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 service fitting in which the flat conductor cable is connected to a standart electrical outlet.
[0005] 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 covering or other surface covering is installed. The top and bottom layers may be comprised of cold rolled 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. Generally, 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-layered, or possibly four or more-layered, composite.
[0006] 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 whithin a thin insulating sleeve which is 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 connections 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 penetrates 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 co-pending United States Patent Application Serial No. 314,964, filed October 26, 1981, assigned by Burndy Corporation, and entitled "Electrical Connection Apparatus and Procedure for Flat Conductor Cables and other similar Articles".
[0007] When transition terminal connections are made in a flat conductor cable system, the portion of the cable usually is coupled to an insulating support which is further mounted within a service module accessible to service personnel. To produce an electrical connection, a conductive surface of each conductor must be exposed, 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 mechanical force while maintaining the space between couplings independently of the cable structure itself.
[0008] It is therefore an important object of this invention to provide a transition block connector for establishing electrical connections between the conductors of flat flexible 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 spaced-apart couplings. This transition block connector also accommodates variations in the spacing between the respective couplings which are caused by variations in the spacing between conductors in various cables, and by variations in the spacing and alignment of openings in the conductors which accommodate the coupling means.
[0009] 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
[0010] The above and other objects and features of this invention 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.
[0011] The fastener members are moveable within the insulating housing, within predetermined limits, so as to accommodate variations in spacing of the 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".
[0012] 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
[0013]
Figure 1 is an "exploded" pictorial representation of a 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'.1of a portion of the flat flexible cable which is shown in end- view in Figure 3.
[0014] 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 recesses 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 with screw-threaded central openings 24 in fasteners 14. Openings 24 are shown in Figure 1. In the illustration form of the invention a conductive support sheet 48 may be coupled to the housing 10 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 known forms of fastening means may be employed to couple sheet 48 to housing 10 without departing from the scope of this invention. A threaded stud fastener 62 of conductive metal is anchored to the sheet 48 by any convenient 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.
[0015] As shown in Figure 1, the fasteners 14 comprise a generally cylndrical body portion 25 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 obvious that-other geometric configurations may be used as well within the scope of this invention.
[0016] 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.
[0017] Further, as shown in Figure 1, the housing 10 comprises a base part 32 having a mounting surfache 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 fasteners 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 direction 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 and other locations for non-circular portions of the housing and the fasteners may be provided within the scope of this invention.
[0018] It can be seen most clearly in Figure 3 that the inner walls 41 which carry access openings 40 into the thickness of closure number 36 form part of the recess 12 within housing 10 which contains fastener 14.
[0019] Inside recess 12, within the body of housing 10 between 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 36 of housing 10 is assembled to base part 32.
[0020] As shown 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 22 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.
[0021] The flat flexible cable 22 is be provided with 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. Such terminal devices have been described previously in a U.S. patent application filed by one of the co-inventors named in this application.
[0022] 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 size 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 between adjacent conductors 20 of approximately 0.955" the overall outer dimension of fastener 14 may be on the order of 0.438" in such a terminal block, the overall internal dimension of the corresponding portion of recess 12, may be approximately 0.538". 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.
[0023] 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 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 which is 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.
[0024] The terminal block embodiment illustrated in the drawings, is assembled by positioning a fastener 14 in recess 12 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 recess 12 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 56 generally circumjacent the entrance to central openings 24. The contact surfaces 58 of terminal devices 52 may be firmly clamped against abutment surfaces 56 by the clamping action of screw 16 when engaged with fasteners 14. Accordingly for the purposes of this invention, and so as to avoid unnecessary distortion of cable 22, it is preferably for abutment surfaces 56 to be not substantially closer to mounting surface 34 than is access surface 38. Further, in the preferred embodiment, the thickness of the insulating material of housing 10 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.
1. A terminal block for engaging coupling fasteners extending from an electrical cable
of the type having a plurality of substanitally flat, spaced-apart, parallel conductors,
comprising:
a housing of electrically insulating material having a mounting surface and an access surface and a recess for receiving a fastener member, said access surface having
an access opening therein for giving access to said fastener member;
said recess having predetermined internal dimensions and having a portion thereof having a predetermined non-circular internal shape for cooperating with a corresponding anchor portion of a fastener member disposed within said recess;
a fastener member disposed within said recess having a central coupling opening positioned generally perpendicular to said mounting surface and having an entrance
to said coupling opening accessible through said access opening in said access surface;
said fastener member further having an anchor portion of predetermined non-circular external shape for cooperating with the non-circular internal shape portion of said recess for preventing substantial rotation of said fastener member about the central axis of said coupling opening, and having external dimensions sufficiently less than the internal dimensions of said recess for permitting lateral displacement of the axis of said coupling opening of said fastener member relative to said housing in a direction substantially parallel to said mounting surface; and,
means for preventing removal of said fastener member from said recess in a direction away from said mounting surface toward said access surface.
2. A terminal block in accordance with Claim 1 further including:
a plurality of recesses for receiving fastener members in said housing, located in spaced apart relationship; and
a plurality of fastener members disposed within said recesses;
wherein lateral displacement of said fastener members varies the distance between the spaced apart fastener members so as to accommodate variations of the spacing between coupling fasteners extending from an electrical cable which are intended to engage said fastener members.
3. A terminal block in accordance with claim 2, wherein:
said housing comprises a base part having said mounting surface thereon, and a closure part having said access surface thereon;
said access surface having a plurality of access openings therein for giving access to said plurality of fastener members;
wherein said means for preventing removal of said fastener member from said recess comprises an inner abutment surface on said closure part and a cooperating abutment shoulder on said fastener member.
4. A terminal block in accordance with claims 2 or 3, wherein:
said central coupling opening of said fastener member contains internal screw threads for engaging screw threaded fasteners extending from and electrical cable.
5. A transition block in accordance with claims 1 or 2 further including:
a conductive support plate having means thereon for coupling said housing of insulating material thereto; and a conductive fastener member electromechanically coupled to aid conductive support plate and having a threaded aperture therein extending substantially perpendicularly to the surface of said plate for receiving a threaded screw fastener;
wherein said housing has a through opening therein extending through said access surface and through said mounting surface for receiving saind conductive fastener and permitting access to the threaded aperture thereof when the mounting surface of said housing is abutted against said conductive support plate, so that a conductor of a flat cable passing over said access surface of said housing may be electrically coupled to said support plate by a screw fastener passing through said conductor and engaging said conductive fastner.
6. A terminal block in accordance with claim 5 wherein said conductive plate further
includes means thereon for couplung to a conductive metallic shield of a flat cable.