GB2221341A - An insulated electrical conductor - Google Patents

Abstract

An electrical cable has a conductive core and an insulating outer sheath, the sheath being heat set to take up a non-straight form. The sheath is preferably of non-plasticised nylon. The shape of a cable run using the cable can be predetermined by heat setting the sheath so that the cable run will return to its designed position after being displaced from it. Preferably the conductive core has a minimum of 100 strands to make it more flexible. The cable is for use in an automobile. <IMAGE>

Description

AN INSULATED ELECTRICAL CONDUCTOR This invention relates to a flexible insulated electrical conductor, particularly for automotive applications.

Insulated conductors have a conductive core usually of metal and an insulating sheath, usually of a plastics material. The metal conductive core is capable of plastic deformation and can be bent to any desired shape but has no memory of its previous shape once it has been bent again.

When assembling and when servicing motor vehicles it is desirable to ensure that the ends of the conductors align themselves with the point of the structure to which they are to be connected. While it is possible to pre-bend metal cored conductors, once the conductor has been bent away from its initially set position, it has no way of returning to the original position.

According to the present invention there is provided an electrical conducting cable having a conductive core and an insulating outer sheath, the sheath being heat set to take up a non-straight form.

The sheath is of a heat settable plastics material, and a suitable material is nylon. Nylon 11 and 12 are preferred. Nylon also has advantageous wear resistance characteristics.

With this cable, the shape of the cable run can be pre- determined by heat setting the nylon outer sheath, so that this determines the path of the cable and also provides a 'memory' which will assist the cable to return to its designed position after having been deformed.

In order to make the core more flexible, i.e. so that any deformation of the core is overcome by the preset imparted to the sheath, the core can be made of a large number of thin wires rather than a small number of thick wires.

The nylon should be non-plasticised to ensure that it has the necessary elastic rather than plastic properties and can be extruded on to the cable in the conventional manner. The heat setting of the sheath is carried out after the cable has been manufactured, and at temperatures higher than any under bonnet temperatures but not high enough to damage or destroy the sheath.

The core construction is also important to the invention. A core with a large number of thinner strands will be inherently more flexible than a core with a smaller number of larger strands, and it is preferred that the core in accordance with the invention has at least 100 strands.

The invention will now be further described, by way of example, with reference to the accompanying drawing which is a schematic view of part of a conductor in accordance with the invention.

The drawing shows a conductor with a multi-strand core 12 and a Nylon sheath 14. The sheath is heat set to form a bend 16 of predetermined position and radius.

Normally the end of the conductor will be fitted with a terminal of some form by which it can be connected to, for example, a vehicle battery. When the conductor is temporarily disconnected from the battery, it may be pushed aside to enable the battery to be removed but the restoring force provided by the modulus of the sheath will be greater than the modulus of the wire core so that the conductor will always want to take up its designed position and shape.

Conventional cables have a plasticised PVC outer sheath with a multi-stranded copper wire core. In such a cable, the modulus of the wire core is very much greater than that of the sheath.

Comparative tests were carried out between Cable A representing the Prior Art, and Cable B in accordance with the invention. Both cables had similar electrical characteristics.

The cables were made up as follows: A - PVC insulation, plasticised, nominal 8mm outside diameter - Copper core, 49 strands of 0.61mm diameter B - Nylon insulation, non-plasticised, nominal 8mm outside diameter - Copper core, 126 strands of 0.40mm diameter.

Tests were carried out to determine the load/deflection characteristics of the cables A and B, of the sheaths and of the cores of both cables, in accordance with the Three Point Bend test method ISO 178. The table below gives the load (in Newtons) required for a 5mm deflection in this test.

Cable A 9 Newtons Sheath A 2 Newtons Core A 7 Newtons Cable B 27 Newtons Sheath B 23 Newtons Core B 3 Newtons It will be seen from these results that in the prior art cable A, 77% of the resistance to deflection is provided by the core and only 22% by the sheath. In contrast, in the cable B in accordance with the invention, 85% of the resistance is provided by the sheath and only 12% by the core. Typically the modulus of the non-plasticised nylon sheath can be 2,350 N/mm2

Claims (6)

1. CLAIMS 1. An electrical conducting cable having a conductive core and an insulating outer sheath, the sheath being heat set to take up a non-straight form.
2. 2. A cable as claimed in Claim 1, wherein the sheath is of non-plasticised nylon.
3. 3. A cable as claimed in Claim 1 or Claim 2, wherein the conductive core is made up of a minimum of 100 strands.
4. 4. A cable as claimed in Claim 1, wherein the sheath makes a contribution of more that 50% to the rigidity of the cable.
5. 5. A cable as claimed in Claim 4, wherein the sheath makes a contribution of more than 75% to the rigidity of the cable.
6. 6. An electrical conducting cable substantially as herein described with reference to the accompanying drawing.