GB2327529A - Fire-resistant electric cable - Google Patents

Abstract

A fire-resistant electrical cable has one or more individual insulated conductors (1) housed within an external insulating sheath (6). The conductors are surrounded within the sheath, by a plurality of layers (3, 5) composed wholly or partially of aluminium and serving as a fire-resistant barrier. An uninsulated earth continuity conductor (4) may be disposed between the layers. Each layer may be made of aluminium and plastics, with one plastic surface and one aluminium surface.

Description

ELECTRICAL CABLE This invention relates to a fire-resistant electrical cable in which an electrical conductor means having one or more individual insulated conductors, is housed within an external insulating sheath, and a fireresistant barrier is disposed between the sheath and conductor means.

Various fire-resistant electrical cables have already been proposed embodying internal fire barrier layers, but these can sometimes lack the necessary integrity under fire conditions and/or are complex to manufacture and correspondingly expensive.

According to the present invention, the conductor means is surrounded, within the sheath, by a plurality of layers composed wholly or partially of aluminium and serving as a fire resistant barrier.

Preferably, each layer is of aluminium/plastics material, the two surfaces of each layer being predominantly aluminium and predominantly plastics respectively.

In one convenient arrangement, the innermost layer is arranged with the aluminium surface facing outwards away from the conductor means.

Typically, the cable is provided with an uninsulated earth continuity conductor which is conveniently disposed between the layers.

Preferably, the outermost layer is arranged with its aluminium surface innermost and the earth continuity conductor is in contact with the aluminium surfaces of both layers to provide electromagnetic screening.

The invention will now be described, by way of example, with reference to the accompanying drawings in which: Figure 1 is an end view of one form of the electrical cable of the invention, and Figure 2 is an exploded view of part of the cable of Figure 1.

The illustrated cable has three conductors 1, typically of solid or stranded copper, according to requirements. Each conductor 1 is surrounded by an insulating layer 2, typically of silicon rubber. The insulated conductors may be arranged in linear parallel relationship, as shown, or may be twisted together into a formation having a generally circular cross-section.

The assembled insulated conductors are covered by a first aluminium/plastics layer 3, of which one surface is predominantly aluminium and the other predominantly plastics, the plastics content serving as a flexible support. The layer 3 is arranged in contact with the insulated conductors with its aluminium surface 3A facing outwardly. The aluminium content of this layer 3 forms an effective fire barrier around the insulated conductors.

In the particular embodiment described, the cable is provided with a bare earth continuity conductor 4 which lies outside the insulated conductors and against the aluminium outer surface of the fire protective layer 3. As can be seen from the drawing, the conductor 4 is arranged so that it lies at least partially within one of the interstices formed between the insulated conductors and conveniently follows this throughout the length of the cable.

Surrounding all of the assembled insulated conductors is a further aluminium/plastics layer 5 similar to the layer 3 and arranged with its aluminium surface 5A facing inwardly, in this case in contact with the earth continuity conductor 4. The primary function of this layer is to make excellent connection with the conductor 4 along its whole length and thereby provide effective electrical screening, whilst also serving as a further fire protection barrier of effectiveness similar to the layer 3.

Finally, the above described assembly of conductors and layers is enveloped within an outer sheath 6 which is preferably of plastics material having low smoke properties and giving nil halogen emission when under fire conditions.

The use of a pair of layers of aluminium/plastics material is found to be very advantageous in terms of simplicity of construction and assembly, with the aluminium of the aluminium/plastics layers acting to provide a very effective flame barrier under fire conditions, as well as effective screening under normal conditions. This barrier remains in position both during and after combustion and silicon dioxide formed by burning of the silicon rubber insulation layers 2 is held in position around the conductors and allows the cable to function normally under load conditions for 3 hours at 9500C both during and after a combustion situation. The cable of the invention also provides enhanced resistance to vibration and the application of water which is conventionally applied to extinguish combustion.

Claims (7)

1. A fire-resistant electrical cable comprising electrical conductor means having one or more individual insulated conductors housed within an external insulating sheath, the conductor means being surrounded, within the sheath, by a plurality of layers composed wholly or partially of aluminium and serving as a fire-resistant barrier.

2. A cable according to Claim 1, wherein each layer is of aluminium/plastics material, the two outer surfaces of each layer being predominantly aluminium and predominantly plastics respectively.

3. A cable according to Claim 2, wherein the innermost layer is arranged with its aluminium surface facing outwards away from the conductor means.

4. A cable according to any one of the preceding claims, wherein an uninsulated earth continuity conductor is provided.

5. A cable according to Claim 4, wherein the uninsulated conductor is disposed between the layers.

6. A cable according to any one of the preceding claims, wherein the outermost layer is arranged with its aluminium surface innermost and the earth continuity conductor is in contact with the respective aluminium surfaces of the layers to provide electromagnetic screening.

7. A fire-resistant electrical cable substantially as hereinbefore described, with reference to the accompanying drawings.