CA1248189A

CA1248189A - Communications cable

Info

Publication number: CA1248189A
Application number: CA000477461A
Authority: CA
Inventors: Michael J. Cowley; John R. Osterfield
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: 1989-01-03
Also published as: BR8501227A; EP0160393A1; GB8408539D0; GB2157063A; ES286317Y; EP0160393B1; GB8507844D0; ES286317U; GB2157063B; AU4039885A; DE3566320D1

Abstract

ABSTRACT

COMMUNICATIONS CABLE

A communications cable comprises a plurality of coaxial elements (1) which are stranded around a central structure (2). The central structure (2) is resiliently deformable to allow limited displacement of the coaxial elements (1) when the cable is subjected to bending during installation. The central structure may com-prise simply a tube of plastics or rubber material, or a plurality of tubes laid-up together.

Description

~;~4l 3:~89 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 facilitating cabling from switching points at the centre 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, particularly telephone. As a consequence, the television cables are liable to be subjected to a combination of pulling tensions and bending forces which are higher than those experienced when laying multiple-element coaxial cables for long distance telecommunicatiorl trunk links. We have Eound that the coaxial elements on or around -the axis of the cable are the most liable to suffer deformation under the higher forces to which the cable is subjected. Further, ~e have now devised a mul-tiple-element coaxial cable which overcomes this problem.
In accordance with this invention, there is provided a communications cable which comprises a resiliently deformable central structure and a plurality of coaxial elements stranded around that structure. The resiliently deformable central structure may comprise simply a tube of plastics or rubber material, and will , ~48~

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 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 elernents arranged in two layers (one of l2 elements and the other of 18 elements) around a central tube.
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 elements 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 websradiating from its axis, with or without a central reinforcing member.
The cable, and particularly the tube Ol tubes, may be filled with a water impermea~le medium such as petroleum jelly to prevent mi~ration 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.
3o An embodiment of this invention will now be described, by way of example only, with reference to the accompanying drawings, in which:
Fi~ure 1 is a cross-~ection through a communications cable in accordance with this invention;
and ~24 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 elemellts are stranded il~ the same or oppo-site directions of lay anci are separated ~y a ~inciing 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 mvisture barrier 5 is bonded.
The tube 2 is selected of optimum characteris-tics to resist permanent collapse but to undergo resilient deformation during dynamic bending of the cable cluring 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 to-gether and for example around a central member. Also~
-the or each tube may comprise a semi-air-spaced tube as shown in Figure 2, wherein the tube is formed internally with a pluraiity of longitudinal webs 7 radiating from the axis, with or without a reinforcing member along this axis.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A communications cable comprising a central support structure and a plurality of coaxial elements stranded about the said structure and mounted for limited radial displacement within the cable, wherein the said support structure is of tubular form and is resiliently deformable to permit said limited radial displacement.

2. A cable according to claim 1, wherein the said elements are arranged in two concentric layers about the support structure.

3. A cable according to claim 1, wherein the central support structure comprises a single tube.

4. A cable according to claim 1, wherein the central support structure comprises a plurality of laid-up tubes.

5. A cable as claimed in claim 4, wherein the 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 claim 3, wherein the or each tube is formed internally with a plurality of longitudinal webs.

8. A cable as claimed in claim 7, wherein the said webs radiate from the axis of the or each tube along which axis a reinforcing member may extend.

9. A cable as claimed in claim l, 2 or 3, wherein a plastics sheath extending over said coaxial elements has a moisture barrier bonded to its inner surface.

10. A cable as claimed in claim 4, wherein the or each tube is formed internally with a plurality of longitudinal webs.

11. A cable as claimed in claim 5, wherein the or each tube is formed internally with a plurality of longitudinal webs.

12. A cable as claimed in claim 10 or 11, wherein the said webs radiate from the axis of the or each tube along which axis a reinforcing member may extend.