Substantially flat fire-resistant safety cables

Abstract

A fire-resistant safety cable may include: at least two electrical conductors; an insulating layer around each of the at least two electrical conductors in order to obtain at least two separate insulated elements; and/or an outer jacket surrounding the at least two separate insulated elements. The insulating layer may be formed from at least one polymeric material capable of being converted, at least on a surface of the insulating layer, into a ceramic state at high temperatures in a fire. The at least two separate insulated elements may be untwisted and arranged so as to be parallel to each other, side by side, and separated by a space. The outer jacket may at least partially fill the space. A thickness of the outer jacket may be approximately constant over an external surface of the at least two separate insulated elements.

Claims

1. A fire-resistant safety cable, comprising: at least two electrical conductors; an insulating layer around each of the at least two electrical conductors in order to obtain at least two separate insulated elements; and an outer jacket surrounding the at least two separate insulated elements; wherein the outer jacket comprises a material comprising an ethylene/vinyl acetate copolymer, a polysiloxane, a polyolefin, a polyvinyl chloride, or a blend thereof, the material including mineral fillers capable of being converted to residual ash under an effect of high temperatures in a fire, wherein the insulating layer is formed from a polysiloxane material and a filler material comprising silica that forms, at least on a surface of the insulating layer, a ceramic state at the high temperatures in the fire, wherein the at least two separate insulated elements are untwisted and arranged so as to be parallel to each other, side by side, and separated by a space, wherein the outer jacket at least partially fills the space, and wherein a thickness of the outer jacket is approximately constant over an external surface of the at least two separate insulated elements.

2. The cable of claim 1, wherein the outer jacket comprises one or more fire-retardant fillers.

3. The cable of claim 1, wherein a material of the outer jacket is expanded.

4. The cable of claim 1, wherein when the ceramic state is formed at the high temperatures in the fire, a density of the insulating layer increases.

5. The cable of claim 1, wherein when the ceramic state is formed at the high temperatures in the fire, a volume of the insulating layer decreases.

6. A fire-resistant safety cable, comprising: at least two electrical conductors; an insulating layer around each of the at least two electrical conductors in order to obtain at least two separate insulated elements; and an outer jacket surrounding the at least two separate insulated elements; wherein the outer jacket comprises a material comprising an ethylene/vinyl acetate copolymer, a polysiloxane, a polyolefin, a polyvinyl chloride, or a blend thereof, the material including mineral fillers capable of being converted to residual ash under an effect of high temperatures in a fire, wherein the insulating layer comprises a polysiloxane material and a filler material comprising silica that forms, at least on a surface of the insulating layer, a ceramic state at the high temperatures in the fire, wherein the at least two separate insulated elements are untwisted and arranged so as to be parallel to each other, side by side, and spaced apart, wherein the outer jacket at least partially fills a region in which the at least two separate insulated elements are spaced apart, and wherein a thickness of the outer jacket is approximately constant over an external surface of the at least two separate insulated elements.

7. The cable of claim 6, wherein the outer jacket comprises one or more fire-retardant fillers.

8. The cable of claim 6, wherein a material of the outer jacket is expanded.

9. The cable of claim 6, wherein when the ceramic state is formed at the high temperatures in the fire, a density of the insulating layer increases.

10. The cable of claim 6, wherein when the ceramic state is formed at the high temperatures in the fire, a volume of the insulating layer decreases.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention and the advantages that it affords will be better understood thanks to the exemplary embodiments given below by way of nonlimiting indication, these being illustrated by the appended drawings in which:

(2) FIG. 1 is a side view of a cable according to the invention;

(3) FIG. 2 shows a cross-sectional, view of a cable having two electrical conductors according to a first embodiment;

(4) FIG. 3 shows a cross-sectional view of a cable having three electrical conductors according to a second embodiment;

(5) FIG. 4 shows a cross-sectional view of a cable having four electrical conductors according to a third embodiment;

(6) FIG. 5 shows a cross-sectional view of a cable having two electrical conductors according to a fourth embodiment;

(7) FIG. 6 shows a cross-sectional view of a cable having three conductors according to a fifth embodiment; and

(8) FIG. 7 shows a cross-sectional view of a cable having four conductors according to a sixth embodiment.

DETAILED DESCRIPTION

(9) FIG. 1 shows schematically part of a cable 1 having an axis of symmetry 2.

(10) The cable 1 according to a first embodiment, shown in FIG. 2, comprises two electrical conductors 3, two insulators 4each of the insulators 4 lying around each conductor 3 and thus forming two insulated conductors (or elements) 5and an outer jacket 6.

(11) The two insulated conductors 5 are arranged so as to be parallel to each other and side by side in the longitudinal mid-plane P of the cable 1. They are in contact with each other, which means that there is no space present between the adjacent elements.

(12) The outer jacket 6 is deposited on the insulated elements 5 and surrounds the insulated elements 5 so as to define at least two faces that are substantially plane and parallel to each other and to the longitudinal mid-plane P.

(13) In cross-section, the cable has an approximately rectangular shape and in particular an outline having two plane faces parallel to the plane P that contains the axes of the two conductors 3 and two rounded lateral portions.

(14) The material of the insulator 4 is preferably a polysiloxane which includes in particular a silica-type reinforcing filler. The insulator 4 preferably comprises a single polysiloxane layer.

(15) The outer jacket 6 preferably consists of an EVA, optionally containing fillers such as metal oxides or hydroxides.

(16) According to another embodiment (not shown) similar to that shown in FIG. 2 apart from the shape of the outer jacket 6 in cross section, the outer jacket 6 has an external profile that substantially matches the shape of the envelope of the insulated elements 5 so that the cable is in cross section a figure of 8 shape.

(17) The cable of FIG. 3 differs from that of FIG. 2 in that an additional insulated element 5 is introduced into the outer jacket 6, the axis of this additional insulated element 5 lying in the longitudinal mid-plane P of the cable 1.

(18) The cable of FIG. 4 differs from that of FIG. 3 in that an additional insulated element 5 is introduced into the outer jacket 6, the axis of this additional insulated conductor 5 lying in the longitudinal mid-plane P of the cable 1.

(19) The cable of FIG. 5 differs from that of FIG. 2 in that a space 7 separates the two insulated elements 5 and in that the outline of the outer jacket follows substantially the envelope of the insulating layers 4.

(20) The cable of FIG. 6 differs from that of FIG. 5 in that three insulated elements 5 are shown.

(21) The cable of FIG. 7 differs from that of FIG. 5 in that four insulated elements 5 are shown.

(22) The spaces 7 in FIGS. 5, 6 and 7 are preferably filled with the material of the jacket, such as an EVA. These spaces 7 preferably measure from 0.1 mm to 20 mm, better still from 1 mm to 3 mm.

EXAMPLES

Example 1

(23) Two cables A and B were tested according to French standard NP C 32-070.

(24) Cable A was a substantially flat fire-resistant cable according to the invention. Cable B (comparative cable) was a fire-resistant cable identical to cable A except that cable B was round.

(25) Two different compositions of cables A and B were tested: 21.5 mm.sup.2 (composition 1) and 31.5 mm.sup.2 (composition 2).

(26) According to the French standard NF C 32-070, a fire-resistant cable must withstand a voltage of about 500 V during the rise in temperature up to 920 C. over 50 minutes, then at a constant temperature of about 920 C. for about 15 minutes.

(27) All the cables tested met this minimum value required by the standard.

(28) Next, the cables were tested by progressively increasing the voltage until a short circuit occurred.

(29) The results of the latter testswhich are given in Tables 1 and 2show that the flat cable of the present invention is capable of withstanding higher voltages than those withstood by the comparative round cable.

(30) This is because the data of the tables show that cables A according to the invention withstand higher voltages than those withstood by cables B, or else that they withstand the same voltage but for a longer period of time than that of cables B.

(31) TABLE-US-00001 TABLE 1 CABLE A (Invention) Composition 1 Composition 2 1st 65 at 500 V OK 65 at 500 V OK series 5 at 600 V OK 5 at 600 V OK 5 at 700 V OK 5 at 700 V OK 5 at 800 V OK 2 at 800 V 430 at 900 V 2nd 65 at 500 V OK 65 at 500 V OK series 5 at 600 V OK 5 at 600 V OK 5 at 700 V OK 5 at 700 V OK 340 at 800 V 5 at 800 V OK 5 at 900 V OK 130 at 1000 V

(32) TABLE-US-00002 TABLE 2 CABLE B (Comparative cable) Composition 1 Composition 2 1st 65 at 500 V OK 65 at 500 V OK series 10 at 600 V 5 at 600 V OK 5 at 700 V OK 0 at 800 V 2nd 65 at 500 V OK 65 at 500 V OK series 5 at 600 V OK 5 at 600 V OK 226 at 700 V 5 at 700 V OK 5 at 800 V OK 0 at 900 V