WO1991020112A1

WO1991020112A1 - Electrical cable

Info

Publication number: WO1991020112A1
Application number: PCT/GB1991/000969
Authority: WO
Inventors: James William Roderick Males; Ian Richard Titcombe
Original assignee: Raychem Limited
Priority date: 1990-06-19
Filing date: 1991-06-17
Publication date: 1991-12-26
Also published as: GB9013689D0

Abstract

A screened electrical cable (1) is terminated by a connector (6) having an electrically conductive housing. The cable comprises a bundle of primary wires (2, 2') at least some of which are provided with electrical screens (4, 4') and the bundle is provided with an additional overall screen (5) which is connected to the conductive housing of the connector. The connector has one or more apertures (8) in the housing and at least one of the wires (2, 2') has a grounding lead extending from its screen through one of the apertures and is connected to the bundle screen outside the housing. Such a termination enables primary wire screens to be terminated within an overall screen with very little modification to an existing connector and can allow re-entry of the connector for repair.

Description

Electrical Cable

This invention relates to electrical cables and to electrical connectors for use therewith. In particular the invention relates to electrical cables that are screened against electromagnetic interface (EMI).

In many instances it is desired to employ cables that include a number of screened primary wires and an additional, overall screen that encloses the primary wires, the term "primary wires" as used herein including pairs, triplets and other multiples of wires that are enclosed in a screen. However, the termination of such cables has often proved to be a problem, in particular it has been difficult to earth the screens of the primary wires and the overall screen in a connector while providing 360° screening of the terminated assembly.

According to the present invention, there is provided a screened electrical cable that includes a connector having an electrically conductive housing, the electrical cable comprising a bundle of primary wires at least some of which are provided with electrical screens, and the bundle being provided with an additional overall screen which is connected to the conductive housing of the connector, the connector having one or more apertures in the housing providing a path between the interior and the exterior thereof, and at least one of the screened primary wires having a grounding lead extending from the its screen through the or one of the apertures and being electrically connected to the bundle screen at the exterior of the housing.

The invention has the advantage that it enables primary wire screens to be terminated within an overall screen with very little modification to an existing connector and can allow re-entry of the connector for purposes of modification or repair. In addition, it is possible to terminate cables according to the invention with little or no increase in size or weight of the connector.

Preferably the grounding lead from a primary wire screen is mechanically attached to the external surface of the connector housing. In a particularly preferred embodiment the overall screen of the cable extends over at least part of the connector housing and is in direct physical contact with part of the grounding lead or leads extending through the or each aperture. The overall screen, usually in the form of a braid, may be retained on the housing by means of a constriction member, in which case the ground leads of the primary wires may conveniently be held under the constriction member in contact with the overall braid.

A variety of means may be employed as the constriction member. For example it may comprise a jubilee clip, or circlip or the like, or it may comprise a metal ring coated with solder which is heated and forced into contact with the connecter housing. Preferably, however, the constriction member comprises a ring formed from a shape memory metal, eg. a memory nickel titanium alloy. Such a ring may be formed with an initial diameter such that it will constrict the screen into contact with the coupling body, but is expanded during manufacture to a diameter such that it can be slid into position over the connector housing and cable screen. When it has been positioned in the correct location it is heated to cause it to contract toward its original size and thereby constricts the shield. With some forms of memory metal, eg. as described in US patents Nos. 3,740,839 and 4,149,911, it is necessary to maintain the ring at a reduced temperature, eg. in liquid nitrogen, before it is installed, and contraction will occur as it warms up to ambient temperature. However, with preferred forms of memory metal, eg. as described in US patents Nos. 4,036,669, 4,067,752 and 4,095,999, the metal may be positioned on the arrangement at ambient temperature and can be heated to cause it to contract, the constriction member remaining in its reduced size when subsequently cooled to ambient temperature. In order to heat the constriction member without heating neighbouring parts of the assembly, the member may be heated by an induction heating method in which electrical contracts are positioned on opposite sides of the ring and a large alternating current is passed through the ring.

The apertures may, at least in the broadest aspect, be shielded by the overall braid, but the connector preferably includes an electrical shielding element that is located over the or each aperture to prevent transmission of electromagnetic radiation therethrough. The provision of such an element enables the size of the aperture(s) to be increased to facilitate installation of the primary wires while still retaining adequate screening. In one form of cable, the shielding element is in the form of an annular band which can be slipped over the connector housing an can be slid to a position in which it obscures the apertures.

The cable may include a conduit in which the primary wires are located and over which the overall screen extends. Such conduits are used extensively in aircraft and other automotive craft for protecting the primary wires from the environment. The conduit is employed in lengths or sections that must be terminated whenever the wiring and conduit passes throught a bulkhead, when it is necessary to form a branch-off in the wiring or when the wiring enters the relevant electrical equipment. This is achieved by connecting the end of the conduit with an appropriate form of metal coupling piece, for example a one-to-one coupling piece for an in-line connection or a T-piece for a branch in the conduit. The term "connector" as used herein refers to electrical connectors in which the primary wires are terminated, and coupling pieces of the type described, including component parts, for example adaptors, which are employed with such devices.

According to another aspect, the invention provides an arrangement for terminating a screened cable, which comprises an electrical connector having an electrically conductive housing, a constriction member for gripping a screen of the cable against the housing, one or more apertures extending through the connector housing between the interior and the exterior thereof, and a shielding element that is capable of being positioned over the or each aperture to prevent transmission of electromagnetic radiation therethrough.

One form of cable and arrangement according to the present invention will now be described by way of example with reference to the accompanying drawing which is a sectional elevation along the axis of an adaptor.

Referring to the accompanying drawing an electrical cable 1 comprises a number of screened primary wires 2,2' enclosed in a flexible plastics conduit 3, having a helically profiled outer surface. The primary wires 2,2' are shielded against EMI by means of primary wire braids 4,4' and the entire cable is enclosed in an overall braid 5.

The conduit 3 and overall braid 5 are terminated by a connector or coupling piece (not shown) and associated spin-coupling adaptor 6 formed from nickel or cadmium plated aluminium. The adaptor 6 has an internal screw thread 7 which matches the helical profile of the conduit 3 and enables the adaptor 6 to be screwed onto the end of the conduit.

The adaptor 6 is provided with a number of apertures 8, in this case about four apertures, extending around the circumference of the adaptor and located at the same axial position. One of the primary conduit 3 and enables the adaptor 6 to be screwed onto the end of the conduit.

The adaptor 6 is provided with a number of apertures 8, in this case about four apertures, extending around the circumference of the adaptor and located at the same axial position. One of the primary wires, wire 2, is provided with a grounding lead 9 that extends from the its braid 4 through one of the apertures 8 to the exterior of the surface, whereupon it is folded flat against the. outer surface of the adaptor 3. The grounding lead 9 may be connected to the primary wire braid 4 by an appropriate means, for example as shown, the connection is made using a dimensionally heat-recoverable solder connector device 10. The other of the primary wires, wire 2' has had its braid 4' removed from the central insulated conductor and pulled into a thin tail 12 which extends through an aperture 8 and its flattened against the surface of the adaptor as in ground lead 9.

The overall braid 5 of the cable extends over the rearward part of the adaptor up to annular shoulder 13. Once the braid 5 has been pushed onto the adaptor a metal annular band 15 is pushed over the braid 5 until it also abuts the shoulder 13 and a memory metal ring 16 is recovered over the overall braid 5 and adaptor 3 to retain the braid 5 in place and to trap any ground leads 9 and earth tails 12 of the primary wires. The annular band 15 serves two purposes: it acts as a spacer to ensure that the memory metal ring 16 is correctly positioned and it obscures the apertures 8, thereby preventing or reducing EMI transmission through them.

The surface transfer impedance of the adaptor was determined in general accordance with IEC 96. The results are shown graphically in Figure 2.

Claims

Cteimg:

1. A screened electrical cable that includes a connector having an electrically conductive housing, the electrical cable comprising a bundle of primary wires at least some of which are provided with electrical screens, and the bundle being provided with an additional overall screen which is connected to the conductive ^' housing of the connector, the connector having one or more apertures in the housing providing a path between the interior and the exterior thereof, and at least one of the screened primary wires having a grounding lead extending from its screen through the or one of the apertures and being electrically connected to the bundle screen at the exterior of the housing.

2. A cable as claimed in claim 1, wherein the grounding lead is mechanically attached to the external surface of the connector housing

3. A cable as claimed in claim 1 or claim 2, wherein the overall screen extends over at least part of the connector housing and is in direct physical contact with part of the grounding lead or leads extending through the or each aperture.

4. A cable as claimed in claim 3, wherein the overall screen is retained on the connector housing by means of a constriction member that grips the screen.

5. A cable as claimed in claim 4, wherein the constriction member is formed from a shape memory alloy.

6. A cable as claimed in any one of claims 1 to 5, wherein the connector includes a shielding element that is located over the or each aperture to prevent transmission of electromagnetic radiation therethrough.

7. A cable as claimed in any one of claims 1 to 6, wherein the primary wire screens are in the form of braids and an extended length of the braid of a primary wire forms the grounding lead of that primary wire.

8. A cable as claimed in any one of claims 1 to 6, wherein a grounding lead is electrically connected to the screen of the primary wire.

9. A cable as claimed in any one of claims 1 to 9, wherein the connector includes more than one aperture.

10. A cable as claimed in any one of claims 1 to 9, wherein the primary wires are enclosed in a conduit about which the overall screen is located.

11. An arrangement for terminating a screened cable, which comprises an electrical connector having an electrically conductive housing, a constriction member for gripping a screen of the cable against the housing, one or more apertures extending through the connector housing between the interior and the exterior thereof, and a shielding element that is capable of being positioned over the or each aperture to prevent transmission of electromagnetic radiation therethrough.