GB2289804A

GB2289804A - Supporting optical fibre units

Info

Publication number: GB2289804A
Application number: GB9409918A
Authority: GB
Inventors: Malcolm Owen Jones; David Andrew Brewer; Nigel Shackleton
Original assignee: Prysmian Cables and Systems Ltd
Current assignee: Prysmian Cables and Systems Ltd
Priority date: 1994-05-18
Filing date: 1994-05-18
Publication date: 1995-11-29
Anticipated expiration: 2014-05-18
Also published as: GB2289804B; GB9409918D0

Abstract

A support for an optical fibre unit comprising at least one optical fibre comprises a tube which is adapted to be suspended from aerial supports, for receiving a fibre unit blown thereinto. The tube has at least one tensile resistant member 14 co-extensive therewith embedded in the wall thereof. The member 14 may be aramid fibre but is preferably metallic. The walls of the tube may comprise one or more layers and be loaded with carbon to dissipate static electricity. <IMAGE>

Description

Supportina Optical Fibre Units This invention relates to a support for an optical fibre unit comprising at least one optical fibre.

The invention is particularly, but not exclusively, concerned with a support which can be suspended from aerial suspension points and which comprises a tube into which an optical unit can be blown after installation of the support.

Blowing optical fibre units into a tube is a known technology and reference may be made to EP-A0108590 for a detailed description thereof. Also reference is directed to EP-A-0345968, EP-A-0521710 and to pending UK Patent Application 9320282.8 for examples of fibre units suitable for use in this technique.

A support as described in the last but one paragraph is already known and comprises two plastics tubes joined together in side-by-side relationship with one of the tubes containing a tensile resistant member and the other tube being left vacant for receiving a fibre unit blown thereinto.

The present invention provides a support for an optical fibre unit comprising at least one optical fibre, said support comprising a tube for receiving a fibre unit blown thereinto, said tube having at least one tensile resistant member coextensive therewith embedded in the wall thereof.

The invention also includes an installation comprising a support as defined in the preceding paragraph, at least a portion of which support is suspended. An optical fibre unit may be blown into the tube of the above-defined installation and the invention extends to such an installation wherein an optical fibre is received in the tube.

Preferably the outer surface of the wall of the tube of the support does not define any recesses which would retain water. The provision of such recesses in the known support is disadvantageous in that the retained water may give rise to electric problems if the support is installed near power conductors and additionally may provide a mechanical loading problem, particularly in freezing conditions.

Although the outer surface of the wall of the tube may have a cross-section which is non-circular, in the embodiment described hereinafter its crosssection is substantially circular. Similarly, although the inner surface of the wall of the tube may be non-circular, in the described embodiment it is substantially circular.

Preferably, the wall has a substantially uniform thickness.

In the above-mentioned embodiment, the tube has two said tensile resistant members embedded in the wall thereof, the passage defined by the tube being located between said two tensile resistant members.

Preferably, the or each tensile resistant member is a metallic member since it has been found that such members have more predictable tensile characteristics than for example members formed of aramid fibres, although of course members formed of aramid fibres or other tensile resistant fibres may be employed.

The wall of the tube preferably comprises plastics material and may comprise a plurality of layers. Advantageously the layer of the tube which provides the inner surface thereof, or the plastics material at least adjacent the inner surface of the wall when it does not comprise layers, is loaded with a material for dissipating static electricity. In this connection it will be understood that the presence of static electricity on the inner surface of the wall of the tube will hinder the passage of a fibre unit being blown into the tube.

In order that the invention may be better understood, the above-mentioned embodiment thereof, which is given by way of example only, will now be described with reference to the accompanying drawing in which the sole figure is a cross-section of a support for an optical fibre unit.

The illustrated support 10 comprises a tube 12 for receiving a fibre unit (not shown) blown thereinto. The tube, which is formed of plastics material, has two metallic tensile resistant, or strength, members 14 embedded in its annular wall.

The members 14 are coextensive with the tube. As shown, the inner and outer surfaces 16, 18 of the wall of the tube are substantially circular in crosssection and the wall has a substantially uniform radial thickness. The inner surface is smooth so as not to hamper the passage therethrough of a fibre unit being blown into the tube and the outer surface is free of any recesses which might retain water. Also, the substantially circular cross-section of the outer surface 18 renders easier clamping of the support 10 using known devices utilising helically configured wire than for example the known support discussed hereinbefore. The passage 20 defined by the tube is located between the members 14 which are diametrically opposite each other. The location of the members has the advantage that the tube has two planes at right angles in which it has maximum and minimum bending flexibility. Maximum flexibility occurs where the neutral axis extends through the members 14 as indicated by 22 and minimum flexibility occurs when the neutral axis extends between the members 14 as indicated at 24. This feature is advantageous in that it assists locating the support in a desired orientation for example when the support is run around a bend.

The tube may comprise a single layer or a plurality of layers. In the Figure, the dotted line 26 indicates the boundary between the inner and outer layers of a two layer tube. These layers may be made of different materials each chosen for its mechanical and/or electrical properties. For example, advantageously the inner layer is loaded with carbon for dissipating static electricity. The or each layer may be formed by extrusion and the layers of the two layer tube may be co-extruded with the members 14 being introduced between the layers during this process.

In a typical use, a length of the support 10 is installed between an aerial location and premises.

Thus, at least a portion of the support is suspended and also at least a portion may be attached to the structure of the premises. In any event the tensile strength of the support which is provided by the members 14 must be sufficient to resist axial stress on the support during installation and also support the weight of the support and any other weight loading such as caused by snow when it is suspended between aerial suspension points. After installation, possibly at some future date determined by operational requirements at-least one fibre unit is installed in the tube of the support by being blown therein.

Claims

CLAIMS:

1. A support for an optical fibre unit comprising at least one optical fibre, said support comprising a tube for receiving a fibre unit blown thereinto, said tube having at least one tensile resistant member coextensive therewith embedded in the wall thereof.

2. A support as claimed in claim 1, wherein the outer surface of the wall of said tube does not define any recesses which would retain water.

3. A support as claimed in claim 1, wherein the outer surface of the wall of the tube is substantially circular in cross-section.

4. A support as claimed in claim 1, 2 or 3, wherein the inner surface of the wall of the tube is substantially circular in cross-section.

5. A support as claimed in any one of the preceding claims, wherein the wall has a substantially uniform thickness.

6. A support as claimed in any one of the preceding claims, wherein said tube has two said tensile resistant members embedded in the wall thereof, the passage defined by the tube being located between said two tensile resistant members.

7. A support as claimed in any one of the preceding claims, wherein the or each tensile resistant member is a metallic member.

8. A support as claimed in any one of the preceding claims, wherein the wall of the tube comprises plastics material.

9. A support as claimed in claim 8, wherein the wall of the tube comprises a plurality of layers.

10. A support as claimed in claim 9, wherein the layer of the wall of the tube which provides the inner surface thereof is loaded with a material for dissipating static electricity.

11. A support as claimed in claim 8, wherein the plastics material at least adjacent the inner surface of the wall is loaded with a material for dissipating static electricity.

12. An installation comprising a support as claimed in any one of the preceding claims at least a portion of which support is suspended.

13. An installation as claimed in claim 12, wherein an optical fibre unit is received in said tube.

14. A support for an optical fibre unit substantially as hereinbefore described with reference to the accompanying drawings.