GB2157063A

GB2157063A - Communications cable

Info

Publication number: GB2157063A
Application number: GB08507844A
Authority: GB
Inventors: John Richard Osterfield; Michael John Cowley
Original assignee: Prysmian Cables and Systems Ltd
Current assignee: Prysmian Cables and Systems Ltd
Priority date: 1984-04-03
Filing date: 1985-03-26
Publication date: 1985-10-16
Also published as: ES286317U; EP0160393A1; CA1248189A; GB8408539D0; GB2157063B; AU4039885A; ES286317Y; DE3566320D1; EP0160393B1; GB8507844D0; BR8501227A

Description

1 GB 2 157 063 A 1

SPECIFICATION

Communications cable This invention relates to a communications cable which comprises a plurality of coaxial elements.

In cable television systems, use of such cables is envisaged when the multiple star configuration is employed, the multiple-element coaxial cable facili tating cabling from switching points at the centre 75 of each star. For installing these cables in built-up areas, the ducts which are to receive the cables are already crowded with cables for other uses, partic ularly telephone. As a consequence, the television cables are liable to be subjected to a combination 80 of pulling tensions and bending forces which are higher than those experienced when laying multi pie-element coaxial cables for long distance tele communication trunk links. We have found that the coaxial elements on or around the axis of the cable 85 are the most liable to suffer deformation under the higher forces to which the cable is subjected. Fur ther, we have now devised a multiple-element coaxial cable which overcomes this problem.

In accordance with this invention, there is pro- 90 vided a communications cable which comprises a resiliently deformable central structure and a plu rality of coaxial elements stranded around that structure. The resiliently deformable central struc ture may comprise simply a tube of plastics or rub- 95 ber material, and will deform when the cable is subjected to dynamic bending so as to give the coaxial elements limited freedom to displace and avoid being deformed. For example, whereas a conventional cable might have 30 coaxial elements 100 arranged in 3 layers with 4 elements at the centre, then a layer of 10 elements and finally a layer of 16 elements, a cable in accordance with this invention might have the 30 coaxial elements arranged in two layers (one of 12 elements and the other of 18 105 elements) around a central tube. We have found that the provision of a resiliently deformable cen tral structure is sufficient to prevent the coaxial elements being permanently deformed during han dling and installation and that no other measures 110 such as embedding the coaxial elements in a cush ioning material are required.

Instead of a single tube, the central structure may comprise a plurality of resiliently deformable tubes laid-up together, for example say 6 tubes stranded around a central member which may or may not itself be resiliently deformable. Even a single tube could be helically applied around such a central member. The first layer of coaxial ele ments would be stranded in the opposite direction of lay to the underlying tube or tubes.

The or each tube may comprise a semi-air spaced tube, i.e. with internal longitudinal webs ra diating from its axis, with or without a central rein forcing member.

The cable, and particularly the tube or tubes, may be filled with a water impermeable medium such as petroleum jelly to prevent migration of water along the cable should it penetrate the sheath at any point.

The tube or tubes may serve as carriers for other cable elements, such as optical fibres or control wires.

An embodiment of this invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a cross-section through a communications cable in accordance with this invention; and Figure 2 is a cross-section, on an enlarged scale, through an alternative form of resiliently deformable tube from which the central structure of the cable may be made.

Referring to Figure 1 of the drawings, there is shown a communications cable comprising a plurality of coaxial elements 1 stranded as two layers (of 12 and 18 elements respectively) around a resiliently deformable central structure 2, which in the example shown comprises a single, hollow plastics tube. The two layers of coaxial elements are stranded in the same or opposite directions of lay and are separared by a winding of paper tape 3 around the inner layer. A further winding of paper tape 4 is applied around the outer layer of coaxial elements and the cable is completed by a plastics sheath 6 to the inner surface of which a metal foil moisture barrier 5 is bonded.

The tube 2 is selected of optimum characteristics to resist permanent collapse but to undergo resilient deformation during dynamic bending of the cable during installaiton, so that the coaxial elements have some freedom to move and avoid being deformed and damaged themselves. The tube 2 may comprise soft PVC, reinforced PVC or polyethylene for example, or a rubber or elastomeric material.

As mentioned previously the central structure may instead comprise a plurality of tubes laid-up together and for example around a central member. Also, the or each tube may comprise a semiair-spaced tube as shown in Figure 2, wherein the tube is formed internally with a plurality of longitudinal webs 7 radiating from the axis, with or without a reinforcing member along this axis.

Claims

1. A communications cable comprising a plurality of coaxial elements stranded around a central structure which is resiliently deformable to allow limited displacement of the coaxial elements when the cable is subjected to bending during installation.

2. A cable as claimed in claim 1, wherein the coaxial elements are arranged in two layers around said central structure.

3. A cable as claimed in claim 1 or 2, wherein said central structure comprises a tube.

4. A cable as claimed in claim 1 or 2, wherein central structure comprises a plurality of laid-up tubes.

5. A cable as claimed in claim 4, wherein said tubes are laid-up around a central member.

6. A cable as claimed in claim 3, 4 or 5, wherein the or each tube comprises a plastics material.

7. A cable as claimed in any one of claims 3 to 2 GB 2 157 063 A 2 6, wherein the or each tube is hollow.

8. A cable as claimed in any one of claims 3 to 6, wherein the or each tube is formed internally with a plurality of longitudinal webs.

9. A cable as claimed in claim 8, wherein said webs radiate from the axis of the or each tube along which axis a reinforcing member may ex tend.

10. A cable as claimed in any one of the pre- ceding claims, wherein a plastics sheath extending over said coaxial elements has a moisture barrier bonded to its inner surface.

11. A communications cable substantially as herein described with reference to the accompany- ing drawings.

Printed in the UK for HMSO, D8818935, 8' '85, 7102. Published by The Patent Office, 25 Southampton Buildings, London, WC2A lAY, from which copies may be obtained.