GB2105529A

GB2105529A - A cable joint including a moisture excluding envelope and a method of forming the same

Info

Publication number: GB2105529A
Application number: GB08122665A
Authority: GB
Inventors: Derek William Stenson
Original assignee: Post Office
Current assignee: Post Office
Priority date: 1981-07-23
Filing date: 1981-07-23
Publication date: 1983-03-23

Abstract

A joint between plastics sheathed cables (1 and 2) incorporates an envelope (3) enclosing the connected conductors of the joint and heat sealed to the ends of plastics cable sheaths to exclude moisture from the joint. The envelope is formed from plastics coated metal foil. The joint is completed by application of a joint sheath closure to provide mechanical strength and protection to the joint. <IMAGE>

Description

SPECIFICATION A cable joint including a moisture excluding envelope and a method of forming the same The present invention relates to a joint between at least two sheathed cable comprising a joint sheath closure for the provision of mechanical strength to the joint, and also to a method of forming such a joint.

In cable joints of various designs a cable joint sheath is provided around the ends of the joined cables and around the exposed conductors. Such a sheath may be or include, for example, a heat shrinkable sleeve or a moulded two part closure.

Whilst this sheath provides the necessary mechanical strength and protection for the joint it does not always provide an efficient seal against the ingress of moisture.

The joint of the present invention is characterised in that an envelope of plastics coated metal foil is provided around joined conductors and within the joint sheath and is sealed to ends of the cable sheaths to exclude moisture from the joint. Such an envelope can be readily formed from sheet material in any required configuration by the use of simple and known techniques thus allowing the envelope to be incorporated into various different cable joints and provide more effective sealing against moisture without modifying existing cable joint sheaths.

The invention also includes a method of forming a joint between at least two plastics sheathed cables comprising the steps of: joining associated conductors of the cables to be joined; enclosing the conductors in an envelope of plastics coated metal foil; heat sealing the envelope to ends of the cable sheaths to exclude moisture from the joint; and applying a joint closure sheath to provide mechanical strength to the joint.

In order that the invention may be well understood some embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a view of an envelope applied to a single cable joint; Figure 1 A and 1 B show details of construction of the envelope of Figure 1; Figure 2 is a view of an envelope applied to a split cable joint; Figures 2A and 28 show details of construction of the envelope of Figure 2; and Figures 3A, 3B, 4 and 5 show various ways of forming a main seam in an envelope.

Two plastics sheathed cables 1, 2 are joined as illustrated in Figure 1. Their respective conductors are joined by any conventional technique. Around the joined conductors an envelope 3 is provided.

The envelope is formed from plastics coated metal foil. Preferably the metal foil is aluminium.

In this embodiment the envelope is constructed from sheet material but a sleeve of material may be used as the starting point for construction of the envelope 3. As illustrated in Figure 1 A tucks 4 may be formed at the edges of the sheet which are to be sealed around the cable ends in order to remove fullness. The tucks 4 are formed with any suitable heat sealing tool (eg heated tongs) which melts and applies pressure to the adjacent layers of plastics coating material in order to bond them together. The main seam 5 of the envelope 3 is also preferably formed with a heat seal. The tucked edges of the material may then be heat sealed to the ends of the plastics cable sheaths.

These heat seals 6 may be formed with a wire wrap technique. Copper wire is wound around the end portion of the material over the cable sheath and heat may either be produced by passing a current through the wire or applying an external heat source which heats the wire and which in turn melts the plastics layers therebeneath to form a heat seal between the envelope and the ends of the plastics sheaths.

A similar type of envelope 3 is shown in Figure 2 except in this case the joint involves three cables 7, 8, 9. A central slit 10 in the envelope to accommodate cable ends 7 and 8 is made by heat sealing along the cut edges as shown in Figures 2A and B. The central slit terminates in an antitear hole to strengthen the slit and prevent it propagating beyond the seal. The anti-tear hole may be further reinforced by a double or folded plastics washer secured by a 'pop' rivet or similar.

Figures 3 to 5 show various ways in which the main seam 5 may be made and strengthened. As shown in Figure 3A one technique involves heat sealing adjacent edges and then folding up the edges and heat sealing again through all the layers.

Figures 4 and 5 illustrate the use of strengthening clips 11 and staples 12 respectively in addition to heat sealing the adjacent edges.

As the metal foil is impervious to water it will be appreciated that the completed envelope 3 will provide an effective seal against ingress of moisture to the conductors. In the case of smaller telecommunications cable joints which are filled with wax, synthetic resin or petroleum based greases the provision of envelope 3 substantially reduces the possibility of water vapour entering any voids in the filling and causing electrolytic corrosion. Protection for any metal foil of the envelope exposed during heat sealing and mechanical strength for the joint is provided by a joint sheath closure. Further the exposed metal foil may be protected by brushing or spraying with a plastics material or paint. Thus joints incorporating such an envelope can have a greater reliability and their life significantly extended. For larger telecommunications cables operated at air pressure up to 620mb the seal foil envelope will also provide similar advantages.

Because of the stress imposed on the envelope material by the air pressure the joint sheath closure may include adhesive tape wrapped tightly round the whole envelope and/or a heat shrinkable tubing applied over the whole joint.

It will be appreciated that joints as described may be incorporated during construction of new cable lines or whilst existing cables are being reclosed after repair work.

Claims

1. A joint between at least two sheathed cables comprising a joint sheath closure for the provision of mechanical strength to the joint, characterised in that an envelope of plastics coated metal foil is provided around conductors in the joint and within the joint sheath and sealed to ends of the cable sheaths to exclude moisture from the joint.

2. A joint as claimed in claim 1 characterised in that the cable sheaths are of plastics material and the envelope is heat sealed to the ends of the cable sheaths.

3. A joint as claimed in claim 1 or 2 wherein the metal foil is plastics coated on both sides.

4. A method of forming a joint between at least two plastics sheathed cables comprising the steps of: joining associated conductors of the cables to be joined; enclosing the conductors in an envelope of plastics coated metal foil; heat sealing the envelope to ends of the cable sheaths to exclude moisture from the joint; and applying a joint closure sheath to provide mechanical strength to the joint.

5. A joint as claimed in claim 2, wherein the envelope is formed from sheet material.

6. Ajoint substantially as herein described with reference to any of the accompanying drawings.

7. Any of the methods of forming a joint substantially as herein described with reference to the accompanying drawings.