GB2026191A - Cables - Google Patents

Abstract

A cable structure has its conductive members 2 enclosed within a sheath 3 of a plastics material, and this sheath is itself enclosed within an armouring layer formed by tapes of glass-type material helically wrapped over the sheath. This armouring layer itself has an oversheath 6 of an electrically insulating material. The cable actually described uses optical fibre conductors but the invention is applicable where the conductors are metallic ones for electricity. In either case the cable has a central strength member 1 formed of a glass-type material. <IMAGE>

Description

SPECIFICATION Cables This invention relates to cable constructions, both for conventional metallic conductor cables and for optical fibre cables, especially when intended for direct burial.

Conventional cables for direct burial use metallic armouring, e.g., extruded or welded aluminium, steel tape, brass tape. The armouring serves several purppses, thus it absorbs installation stresses, gives crush/inpact resistance, and gives rodent or termite resistance. It normally needs protective coatings to prevent corrosion.

Such combinations tend to be heavy and costly, and it is an object of this invention to provide a cable structure which overcomes or at least minimizes the above disadvantages.

According to the present invention there is provided a cable structure in which the conductive members are enclosed within a sheath of a plastics material which sheath is itself enclosed within an armouring layer formed of tapes of glass type material helically wrapped over the sheath, and in which the armouring layer has an oversheath also of an electrically insulating material.

According to the present invention there is further provided an optical fibre cable structure which includes a central strength member, a number of optical fibre cables disposed about the periphery of the strength member, a sheath of a plastics material overlaying the optical fibre cables, an armouring layer overlaying the plastics sheath, which layer is formed of silica or high silica glass tapes helically wrapped over the sheath, and an oversheath of a thin plastics material overlaying the armouring layer.

An embodiment of the invention will now be described with reference to the accompanying drawings, in which Figure lisa cross-section of an optical fibre cable embodying the invention, while Figure 2 is a somewhat simplified side view of the cable of Figure 1.

In the cable shown there is a central cylindrical strength member 1, which can be steel, or a non-metallic material such as coated aramid fibre or glass braid. In the present case in which the conductors are glass optical fibres, the glass braid is a preferred choice. Such a non-metallic cable has the merit that it is immune to electro-magnetic interference.

The strength member 1 is surrounded by a number of sheathed and clad optical fibre light conductors such as 2, which fibres are overlayed by a sheath 3 of a plastics material. This sheath is separated from the fibres by a layer 4 of a tape, with or without a strength member. This tape layer 4 may consist of two or more tapes of a silica or high silica glass wound with opposed layers.

The sheath 3 is overlayed with two or more layers of tapes of silica or high silica glass applied with alternating lay. These tapes have a hard protective coating applied immediately after drawing to maintain high strength.

Finally the sheath 3 is covered by an outer layer 6 which is a hard thin plastics oversheath, preferred materials being polyamide and polypropylene.

The above arrangement has all of the advantages of the conventional cable, plus the additional advantages of lower weight and cost. Further, the materials used, being similar to the optical fibres have consistency with the fibres.

1. A cable structure in which the conductive members are enclosed within a sheath of a plastics material which sheath is itself enclosed within an armouring layer formed of tapes of glass-type material helically wrapped over the sheath, and in which the armouring layer has an oversheath also of an electrically insulating material.

2. A cable structure as claimed in claim 1, and which contains a number of electrical conductors.

3. A cable structure as claimed in claim 1 or 2 and which contains a number of optical fibres.

4. An optical fibre cable structure which includes a central strength member, a number of optical fibres, disposed about the periphery of the strength member, a sheath of a plastics material overlaying the optical fibre cables, an armouring layer overlaying the plastics sheath, which layer is formed of silica or high silica glass tapes helically wrapped over the sheath, and an oversheath of a thin plastics material overlaying the armouring layer.

5. An optical fibre cable structure substantially as described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Cables This invention relates to cable constructions, both for conventional metallic conductor cables and for optical fibre cables, especially when intended for direct burial. Conventional cables for direct burial use metallic armouring, e.g., extruded or welded aluminium, steel tape, brass tape. The armouring serves several purppses, thus it absorbs installation stresses, gives crush/inpact resistance, and gives rodent or termite resistance. It normally needs protective coatings to prevent corrosion. Such combinations tend to be heavy and costly, and it is an object of this invention to provide a cable structure which overcomes or at least minimizes the above disadvantages. According to the present invention there is provided a cable structure in which the conductive members are enclosed within a sheath of a plastics material which sheath is itself enclosed within an armouring layer formed of tapes of glass type material helically wrapped over the sheath, and in which the armouring layer has an oversheath also of an electrically insulating material. According to the present invention there is further provided an optical fibre cable structure which includes a central strength member, a number of optical fibre cables disposed about the periphery of the strength member, a sheath of a plastics material overlaying the optical fibre cables, an armouring layer overlaying the plastics sheath, which layer is formed of silica or high silica glass tapes helically wrapped over the sheath, and an oversheath of a thin plastics material overlaying the armouring layer. An embodiment of the invention will now be described with reference to the accompanying drawings, in which Figure lisa cross-section of an optical fibre cable embodying the invention, while Figure 2 is a somewhat simplified side view of the cable of Figure 1. In the cable shown there is a central cylindrical strength member 1, which can be steel, or a non-metallic material such as coated aramid fibre or glass braid. In the present case in which the conductors are glass optical fibres, the glass braid is a preferred choice. Such a non-metallic cable has the merit that it is immune to electro-magnetic interference. The strength member 1 is surrounded by a number of sheathed and clad optical fibre light conductors such as 2, which fibres are overlayed by a sheath 3 of a plastics material. This sheath is separated from the fibres by a layer 4 of a tape, with or without a strength member. This tape layer 4 may consist of two or more tapes of a silica or high silica glass wound with opposed layers. The sheath 3 is overlayed with two or more layers of tapes of silica or high silica glass applied with alternating lay. These tapes have a hard protective coating applied immediately after drawing to maintain high strength. Finally the sheath 3 is covered by an outer layer 6 which is a hard thin plastics oversheath, preferred materials being polyamide and polypropylene. The above arrangement has all of the advantages of the conventional cable, plus the additional advantages of lower weight and cost. Further, the materials used, being similar to the optical fibres have consistency with the fibres. CLAIMS

1. A cable structure in which the conductive members are enclosed within a sheath of a plastics material which sheath is itself enclosed within an armouring layer formed of tapes of glass-type material helically wrapped over the sheath, and in which the armouring layer has an oversheath also of an electrically insulating material.

2. A cable structure as claimed in claim 1, and which contains a number of electrical conductors.

3. A cable structure as claimed in claim 1 or 2 and which contains a number of optical fibres.

4. An optical fibre cable structure which includes a central strength member, a number of optical fibres, disposed about the periphery of the strength member, a sheath of a plastics material overlaying the optical fibre cables, an armouring layer overlaying the plastics sheath, which layer is formed of silica or high silica glass tapes helically wrapped over the sheath, and an oversheath of a thin plastics material overlaying the armouring layer.

5. An optical fibre cable structure substantially as described with reference to the accompanying drawings.