GB2362272A

GB2362272A - Water resistant cable connection

Info

Publication number: GB2362272A
Application number: GB0011380A
Authority: GB
Inventors: Darryl Scholfield
Original assignee: Ramar Technology Ltd
Current assignee: Ramar Technology Ltd
Priority date: 2000-05-12
Filing date: 2000-05-12
Publication date: 2001-11-14
Anticipated expiration: 2020-05-12
Also published as: GB0011380D0; GB2362272B

Abstract

A seal for a multi-core cable end, to be used at the junction of such a cable (2) and an enclosure for connected electrical equipment, is formed by injecting a solvent for the plastics material (8) which surrounds the individual conductors (6) and also forms the cable sheath (4) and then crimping the end of the cable to create a solid water impervious mass at the cable end. When used with a suitable sealing grommet at the entry point of the enclosure, this seal prevents water entering the enclosure from outside the cable as well as from within the cable sheath. The plastic material may be pvc and the solvent MEK or cyclohexanone. The solvent may contain a filler and a crimp sleeve (10) may be made of metal.

Description

2362272 Water resistant cable connection

Background of the Invention

The present invention relates to the construction of connections between cables and boxes or other enclosures for electronic equipment.

Boxes or other enclosures for electronic equipment need to be watertight since water will damage the components inside.

Technical Problems Where multi-core cable enters such an enclosure there is the possibility that water can enter through any unsealed gap in that connection. Even in cases where the connection is correctly scaled, it is still possible for water to enter the enclosure if there is a puncture in the cable sheath. Such a puncture will allow water to penetrate into the space surrounding the cores within the sheath. If the enclosure is mounted in the open air then changes in the ambient temperature can result in pressure changes within the enclosure that can cause moisture within the cable to be sucked up into the enclosure.

Punctures in the cable sheath can be caused by small animals gnawing through the cable or can appear naturally during the manufacturing process.

Moisture can also penetrate the cable sheath from the other end of the cable. Typically an enclosure with a connected cable can be supplied preassembled.

However, if it is necessary for the other end be connected on-site, the manufacturer cannot ensure that that connection will prevent the ingress of water into the cable sheath and this can obviate the effectiveness of the cable entry sealing at the other end, which is only effective to deal with moisture penetrating from outside the cable sheath rather than from within it.

There is therefore a technical problem of providing a cable entry that is resistant to water ingress through the seal at the cable entry, whether directly from the outside or from within the cable sheath.

2 Prior Art Solutions

Several approaches have been tried to deal with these possible routes for water ingress. However these usually result in a more expensive cable. Some of these involve applying compounds with adhesive - a technique which has been shown not to 5 work in this application.

Various constructions of grommets and sleeves at the point where the cable enters the enclosure have also been developed to reduce the possibility of water ingress around the cable entry.

Solution of the Invention In accordance with the present invention, there is provided a multi-core cable in which each core comprises a single conductor, which is directly coated with a first plastics material and the conductors are contained within a second plastics material sheath wherein at least one end has been sealed by the injection of a solvent for the first and second plastics materials into the sheath end and crimped in order to fuse the first and second plastics materials into a water impervious mass at the cable end.

The real breakthrough in this solution is the use of a solvent which fuses the conductor sheaths together.

Advantages of the invention Cable in which the conductors are directly coated with a plastics material such as PVC is cheaply available and is commonly used in telephone systems. This is eminently suitable for AMR purposes. Commercially available solvent cement which contains a solvent for PVC together with a filler which delays the setting process and helps to fill gaps can be used.

Preferably the cable end is crimped within an external metallic sleeve. This is convenient for fitting the cable end into commercially available sealing grommets at the point where it enters the enclosure in order to provide an effective seal against ingress of water from outside the cable sheath and enclosure through the entry point.

3 Brief Description of the Drawings

In order that the invention may be well understood an embodiment thereof will now be described, by way of example only, with reference to the accompanying diagrammatic drawings, in which:

Figure 1 shows a longitudinal section through a cable containing three plastics coated conductors; and Figure 2 shows an external view of a cable end after scaling.

Detailed Description of a Preferred Embodiment

The present invention is applicable to multi-core cable 2 such as is used in telephone systems. This cable consists of a plastic outer sheath 4 surrounding a number of insulated single conductor cores 6. The invention works best with solid core conductors rather than stranded core conductors as there will normally be some air caught between an insulating coating and a stranded conductor core.

Three such single copper wire conductors are shown in Figure 1. Each of the conductors 6 has a coating of plastics material 8 directly applied to the exterior of the conductor 6. The three insulated conductors fit loosely within the sheath 4 and are surrounded by an air gap. This type of cable is freely available commercially. Cable with more or fewer conductors than three is also suitable.

In order to prepare the cable end in order to create a water impervious seal, the sheath is first cut back to allow the conductive copper ends of the insulated conductors 6 to project. A solvent is then injected into the end of the cable. Where the plastics material 8 and the sheath 4 are both made of PVC then a suitable solvent is MARLEY (registered trade mark) solvent cement. This contains methyl ethyl ketone and cyclohexanone together with a filler which slows the setting process and provides volume to fill in the void between the cores and the sheath. Once the gap between the cores and the interior of the cable sheath has been filled a metal crimping sleeve 10 is applied to the exterior of the cable end. The act of applying the sleeve compresses the interior of the cable end expelling all residual air from that region and fusing the 4 plastics material of the sheath 4 and the coating 8 of the individual conductors into a solid, water impervious mass. Since the air spaces are completely closed by the reduction in dimensions, caused by the crimp, and since any residual crevices are filled by the molten insulator material, there is no possibility of moisture passing from 5 downstream of the sealed cable end to the free conductor ends through the cable itself.

Although PVC as both a first plastics material coating the individual cores and a second plastics material of the sheath, it is not essential for the plastics used to be identical provided a solvent can be found that will allow them to fuse together effectively.

The crimped end of the cable is well adapted to be fitted within a sealing grommet of any conventional design at the point of entry to a box or enclosure.

Claims

1. A multi-core cable in which each core comprises a single conductor, which is directly coated with a first plastics material and the conductors are contained within a second plastics material sheath wherein at least one end has been sealed by the injection of a solvent for the first and second plastics materials into the sheath end and crimped in order to fuse the first and second plastics materials into a water impervious mass at the cable end.

2. A cable as claimed in claim 1, wherein the first and second plastics materials are PVC.

3. A cable as claimed in claim 2, wherein the solvent comprises methyl ethyl ketone and/or cyclohexanone.

4. A cable as claimed in claim 1, wherein a filler is injected with the solvent.

5. A cable as claimed in claim 1, wherein the cable end is crimped within an external metallic sleeve.

6. A cable substantially as herein described with reference to the accompanying drawings.