GB2252866A

GB2252866A - Flexible electrically insulated electric conductor

Info

Publication number: GB2252866A
Application number: GB9127199A
Authority: GB
Inventors: Gordon Carl Baker
Original assignee: Phillips Cables Ltd
Current assignee: Phillips Cables Ltd
Priority date: 1991-01-03
Filing date: 1991-12-23
Publication date: 1992-08-19
Also published as: AU9011591A; GB9100034D0; GB9127199D0; CA2058696A1

Abstract

A flexible electrically insulated electric conductor comprises a plurality of wires 1, a flexible barrier 2 of plastics material and at least one layer 3 of electrically insulating material. The plastics material of the barrier 2 e.g. urethane polymer, polyester or polyamide, is substantially tougher than the material or materials of the overlaying layer or layers 3 e.g. EPDM, and is of such radial thickness as to inhibit penetration by a broken wire 1 of the conductor. The flexible conductor may be used for domestic electrical appliances and electrically operated tools or a core of a flexible multi-core power cable. In the latter case, the plastics material of the barrier 2 will incorporate carbon black rendering it semi-conductive; the insulating layer 3 may also be semi-conductive. In another embodiment, Figure 2, the barrier (12) is of semiconductive polyurethane surrounded by successive layers of semiconductive polyolefin (13), EPDM (14) and semiconductive polyolefin (15). <IMAGE>

Description

AN IMPROVED FLEXIBLE ELECTRICALLY INSULATED ELECTRIC CONDUCTOR This invention relates to flexible electrically insulated electric conductors of the kind comprising a plurality of wires stranded, bunched or otherwise assembled together and surrounded by at least one layer of electrically insulating material. Flexible electrically insulated electric conductors of this kind include flexible electrically insulated cords for connection to domestic electrical appliances such as, for example, electric irons, lamps and electrically operated devices used in a kitchen, and flexible single core and multi-core power cables incorporating one or more than one flexible electrically insulated electric conductor for connection to electrically operated tools and equipment used in industry, e.g. equipment incorporating a reeling and de-reeling facility, and by a handyman.

We have found that, over a period of time, frequent flexing of a flexible electrically insulated electric conductor can cause a wire of the conductor to break and an end part of such a broken wire sometimes penetrates outwardly into and through the overlying layers or layers of electrically insulating material. A flexible electrically insulated electric conductor which is connected to an electrical appliance and which has a live wire or live wires protruding through its electrically insulating layer or layers is extremely dangerous, especially if handled with damp hands - as may be the case where the electrical appliance to which the flexible electrically insulated electric conductor is connected is in a kitchen.

It is an object of the present invention to provide an improved flexible electrically insulated electric conductor of the kind described in which the aforesaid risk is eliminated or at least substantially reduced.

According to the invention, the improved flexible electrically insulated electric conductor comprises a plurality of wires stranded, bunched or otherwise assembled together, a flexible barrier of plastics material surrounding and immediately adjacent the conductor throughout its length and, overlying the flexible barrier, at least one layer of electrically insulating material, the plastics material of the flexible barrier being substantially tougher than the material or materials of the overlying layer or layers and being of such radial thickness as to inhibit penetration by a broken wire of the conductor.

The flexible barrier may be in the form of an extruded layer of said plastics material or it may be in the form of one or more than one layer of helically applied tape of said plastics material. In the latter case, where the flexible barrier comprises two or more layers of helically applied tape of said plastics material, preferably adjacent layers of helically applied tapes will be of opposite hand to one another.

Preferably, the flexible barrier has a radial thickness lying in the range O.Old to O.10d, where d is the overall diameter of the bare conductor.

The plastics material of the flexible barrier preferably is a relatively tough polymeric material; suitable relatively tough polymeric materials include urethanes, polyurethanes, thermoplastic polyurethane elastomers, polyesters and polyamides.

Where the layer immediately overlying the flexible barrier is of electrically insulating plastics material, the plastics material of the flexible barrier may itself have electrically insulating properties or it may be rendered semi-conductive by the incorporation of carbon black or other electrically conductive filler so that the flexible barrier also constitutes a semi-conductive conductor screen or shield.

Where the layer immediately overlying the flexible barrier is of a semi-conductive plastics material and constitutes a conductor screen or shield, the plastics material of the flexible barrier will incorporate carbon black or other electrically conductive filler rendering the plastics material of the flexible barrier semiconductive.

Since the plastics material of the flexible barrier may constitute a part of the electrical insulation of the conductor or a part of the semiconductive conductor screen or shield, the overall diameter of the improved flexible electrically insulated electric conductor need be no greater than that of a comparable flexible electrically insulated electric conductor in which no flexible barrier is incorporated.

The invention also includes a multi-core flexible power cable in which at least one of the cores is an improved flexible electrically insulated electric conductor as hereinbefore described.

The invention is further illustrated by a description, by way of example, of two preferred flexible electrically insulated electric conductors with reference to the accompanying drawing, in which: Figure 1 is a transverse cross-sectional view, drawn on an enlarged scale, of a preferred flexible electrically insulated cord for connection to a domestic electrical appliance, and Figure 2 is a transverse cross-sectional view, drawn on an enlarged scale, of a core of a preferred flexible multi-core power cable for connection to industrial equipment incorporating a reeling and dereeling facility for the cable.

Referring to Figure 1, the preferred flexible electrically insulated cord comprises a conductor 1 consisting of a multiplicity of wires bunched together, a flexible barrier 2 of extruded electrically insulating polyurethane surrounding and immediately adjacent the conductor throughout its length and, overlying the flexible barrier, a layer 3 of extruded electrically insulating ethylene propylene diene rubber (EPDM). The bare conductor 1 has an overall diameter of 10.5 mm and the flexible barrier 2 has a radial thickness of approximately 0.3 mm and is sufficiently tough to inhibit penetration of the flexible barrier by a broken wire of the conductor. The flexible electrically insulated cord has an overall diameter of 14.8 mm.

Referring to Figure 2, the preferred flexible multi-core power cable comprises three substantially identical flexible cores laid up together and surrounded by an overall cable sheath, one of which cores is illustrated in the Figure. The core comprises a conductor 11 consisting of a plurality of wires stranded together, a flexible barrier 12 of extruded semiconductive polyurethane surrounding and immediately adjacent the conductor throughout its length, a layer 13 of extruded semi-conductive polyolefin overlying the flexible barrier which, in combination with the layer 13, constitutes a conductor screen or shield, a layer 14 of extruded electrically insulating ethylene propylene diene rubber (EPDM) overlying the layer 13 and a layer 15 of extruded semi-conductive polyolefin overlying the layer 14 and constituting a dielectric screen or shield.

The bare conductor 11 has a diameter of 10.5 mm and the flexible barrier 12 has a thickness of 0.3 mm and is sufficiently tough to inhibit penetration of the flexible barrier by a broken wire of the conductor. The core has an overall diameter of 19.8 mm.

As has been previously indicated, since the electrically insulating flexible barrier 2 of the preferred flexible electrically insulated cord constitutes a part of the electrical insulation of the conductor 1 of the preferred flexible electrically insulated cord and the semi-conductive flexible barrier 12 constitutes a part of the conductor screen or shield of the conductor 11 of the core of the preferred flexible multi-core power cable, the overall diameters of the preferred flexible electrically insulated cord and of the preferred flexible multi-core power cable need be no greater than that of comparable cords and cables in which no flexible barrier is provided.

Claims

1. A flexible electrically insulated electric conductor comprising a plurality of wires stranded, bunched or otherwise assembled together, a flexible barrier of plastics material surrounding and immediately adjacent the conductor throughout its length and, overlying the flexible barrier, at least one layer of electrically insulating material, the plastics material of the flexible barrier being substantially tougher than the material or materials of the overlying layer or layers and being of such radial thickness as to inhibit penetration by a broken wire of the conductor.

2. A flexible electrically insulated electric conductor as claimed in Claim 1, wherein the flexible barrier is in the form of an extruded layer of said plastics material.

3. A flexible electrically insulated electric conductor as claimed in Claim 1, wherein the flexible barrier is in the form of one or more than one layer of helically applied tape of said plastics material.

4. A flexible electrically insulated electric conductor as claimed in Claim 3 in which the flexible barrier comprises two or more layers of helically applied tape of said plastics material, wherein adjacent layers of helically applied tapes are of opposite hand to one another.

5. A flexible electrically insulated electric conductor as claimed in any one of the preceding Claims, wherein the flexible barrier has a radial thickness lying in the range 0.01d to 0.10d, where d is the overall diameter of the bare conductor.

6. A flexible electrically insulated electric conductor as claimed in any one of the preceding Claims, wherein the plastics material of the flexible barrier is a relatively tough polymeric material selected from urethanes, polyurethanes, thermoplastic polyurethane elastomers, polyesters and polyamides.

7. A flexible electrically insulated electric conductor as claimed in any one of the preceding Claims in which the layer immediately overlying the flexible barrier is of electrically insulating plastics material, wherein the plastics material of the flexible barrier has electrically insulating properties.

8. A flexible electrically insulated electric conductor as claimed in any one of Claims 1 to 6 in which the layer immediately overlying the flexible barrier is of electrically insulating plastics material, wherein the plastics material of the flexible barrier is rendered semi-conductive by the incorporation of carbon black or other electrically conductive filler so that the flexible barrier also constitutes a semi-conductive conductor screen or shield.

9. A flexible electrically insulated electric conductor as claimed in any one of Claims 1 to 6 in which the layer immediately overlying the flexible barrier is of a semi-conductive plastics material and constitutes a conductor screen or shield, wherein the plastics material of the flexible barrier incorporates carbon black or other electrically conductive filler rendering the plastics material of the flexible barrier semi-conductive.

10. A multi-core flexible power cable in which at least one of the cores is a flexible electrically insulated electric conductor as claimed in Claim 8 or 9.

11. A flexible electrically insulated electric conductor substantially as hereinbefore described with reference to and as shown in Figure 1 of the accompanying drawing.

12. A flexible electrically insulated electric conductor substantially as hereinbefore described with reference to and as shown in Figure 2 of the accompanying drawing.