GB2221355A

GB2221355A - Grounding screened cables

Info

Publication number: GB2221355A
Application number: GB8818037A
Authority: GB
Inventors: Nicholas Henry Neely; Michael William Robertson
Original assignee: Bowthorpe Hellerman Ltd
Current assignee: Bowthorpe Hellerman Ltd
Priority date: 1988-07-28
Filing date: 1988-07-28
Publication date: 1990-01-31
Also published as: GB8818037D0; WO1990001225A1; IL90916A0

Abstract

The screens of a bundle of cables are grounded by locally baring the screens of the cables and then wrapping a constant-force spring (10) around them so as to make contact with the bared screens and press together the screens of the adjacent cables. The spring (10) may then be connected to a connector to which the cables are connected.

Description

ARRANGEMENTS FOR GROUNDING SCREENED CABLES This invention relates to arrangements for grounding or earthing the screens of electrical cables.

There are currently a number of different ways of continuing or transferring the screening of a cable onto a connector. These include the use of connectors with braid tails, reverse cone clamps, iris springs and screened moulded heat-shrink tubular shapes.

There is now an increasing use of individually screened pairs, triplex and quads. The use of such cables leads to difficulties in providing continuity of their screens at their connectors.

We have now devised an arrangement for collectively grounding the screens of a bundle of individually-screened cables.

In accordance with this invention, there is provided a method of grounding the screens of a bundle of individuallyscreened cables, comprising locally baring the screens of the cables, and then wrapping a spring element around the cables so as to make contact with the bared screens.

Preferably the spring element is a so-called constant force spring, which comprises a strip of spring metal wrapped into a coil of several turns. This can be wrapped easily by hand around the bundle of cables and exerts a force radially on the cables, which force is constant over a range of diameters of the bundle of cables.

Also in accordance with this invention, there is provided an assembly of individually screened and collectively grounded cables, comprising a bundle of individually screened cables having their screens locally bared and a spring element wrapped around the cables in contact with the bared screens.

Further in accordance with this invention, there is provided a kit for collectively grounding the screens of a bundle of individually-screened cables, comprising a spring element for wrapping around the cables to make contact with locally bared regions of the screens of the cables, and means for connecting the spring element to ground.

The means for connecting the spring element to ground may comprise any of the means mentioned above for continuing a cable screen to a connector to which the cable is connected.

An embodiment of this invention will now be described by way of example only and with reference to the accompanying drawings, in which: FIGURE 1 is a perspective view of a constant force spring used in accordance with this invention for collectively grounding the screens of a bundle of individuallyscreened cables; FIGURE 2 is a side view of a bundle of cables to which a constant force spring has been applied; and FIGURE 3 is a view of the bundle of cables provided with a connector to which the constant force spring is electrically connected by a screened heat-shrink shape.

Referring to Figure 1, there is shown a constant force spring 10 which comprises a strip of spring steel which has been wrapped around a former to form a coil of several contiguous turns. This spring can be wrapped easily by hand around a bundle of cables of diameter between 1.1 and 1.8 times the internal diameter of the coiled spring. Over this range, the spring exerts a substantially constant radial force on the bundle of cables around which it is wrapped.

Referring to Figure 2, there is shown a bundle of cables 20. Each cable has its own screen and its outer insulation is stripped over a local window to bare the screen 22. All cables are similarly stripped at the same position along the length of the bundle. The constant force spring 10 is wrapped around the bundle of cables so as to make contact with the screens of the outer cables and so as to press together the screens of adjacent cables of the bundle.

The spring 10 can be applied and removed without deterioration of performance many times, so that it can be readily removed for carrying out repairs. The spring ensures a low contact resistance of approximately one milli ohm between adjacent cable screens and between itself and the screens which it contacts.

The wires of individually screened cables are often very fine, e.g. with diameters less than 0.15 mm. As the edge of the spring is often sharp, there is a possibility that it may cut such fine wires. Therefore, as protection, a piece of braid or other conductive material may be wrapped around the bundle of cables between the bared screens and the spring. If braid is used, its wires should be of greater diameter than the cable wires, and therefore e.g.

greater than 0.2 mm diameter.

Referring to Figure 3, the cable bundle is typically connected to a connector 30 and the screens, collectively connected by the spring 10, are connected to the connector 30 by a heat-shrink tubular shape 40 which is provided with an electrically conductive screen on its inner surface.

Claims

1) A method of grounding the screens of a bundle of individually screened cables, comprising locally baring the screens of the cables, and then wrapping a spring element around the cables so as to make contact with the bared screens and press together the screens of adjacent cables of the bundle.

2) A method as claimed in claim 1, in which the spring element is a constant-force spring which comprises a strip of spring metal wrapped into a coil of several turns.

3) A method as claimed in claim 1 or 2, further comprising the step of forming an electrical connection between the spring element and a connector to which the individual cables are connected.

4) An assembly of individually screened and collectively grounded cables comprising a bundle of individually screened cables having their screens locally bared and a spring element wrapped around the cables in contact with the bared screens and pressing together the screens of adjacent cables of the bundle.

5) An assembly as claimed in claim 4, in which the spring element is a constant-force spring which comprises a strip of spring metal wrapped into a coil of several turns.

6) An assembly as claimed in claim 4 or 5, further comprising means electrically connecting the spring element to a connector to which the individual cables are connected.

7) A kit for collectively grounding the screens of a bundle of individually screened cables, comprising a spring element for wrapping around the cables to make contact with locally bared regions of the screens of the cables, and means for connecting the spring element to ground.

8) A kit as claimed in claim 7, in which the spring element is a constant-force spring which comprises a strip of spring metal wrapped into a coil of several turns.

9) a kit as claimed in claim 7 or 8, in which the connecting means comprises means for connecting the spring element to a connector to which the individual cables are connected.

10) A method of grounding the screens of a bundle of individually screened cables, substantially as herein described with reference to the accompanying drawings.

11) An assembly of individually screened and collectively grounded cables, substantially as herein described with reference to the accompanying drawings.