FIRE-RESISTANT CABLE CONNECTION

Abstract

The arrangement includes a fire-resistant cable connection, a cable connection method using such a fire-resistant connection, and a line of fire-resistant cables comprising such a fire-resistant connection.

Claims

1. A connector for at least two fire-resistant cables each comprising: at least one elongated electrically-conductive element and at least one electrically-insulating sheath surrounding said elongated electrically-conductive element, the ends of said cables configured to be stripped and joined end-to-end so as to ensure a physical and electrical contact between said cables, wherein at least one layer that comprises at least one cementitious material and that surrounds a portion of each electrically-insulating sheath and said stripped and end-to-end joined ends of said cables.

2. The connector as claimed in claim 1, wherein the layer comprising at least one cementitious material is in direct physical contact with the portion of each electrically-insulating sheath that it surrounds.

3. The connector as claimed in claim 1, wherein said connector additionally comprises a metal element that makes it possible to permanently connect said stripped and end-to-end joined ends of the cables.

4. The connector as claimed in claim 3, wherein the metal element is made of copper, of copper alloy, of aluminum or of aluminum alloy.

5. The connector as claimed in claim 3, wherein the metal element is in direct physical contact with at least one portion of the stripped and end-to-end joined ends of the cables.

6. The connector as claimed in claim 1, wherein said connector additionally comprises a layer of a heat-shrinkable material.

7. The connector as claimed in claim 6, wherein the layer of a heat-shrinkable material surrounds a portion or the whole of the stripped and end-to-end joined ends of said cables or the metal element when it is used.

8. The connector as claimed in claim 6, wherein the layer of a heat-shrinkable material is in direct physical contact with the layer comprising at least one cementitious material.

9. The connector as claimed in claim 1, wherein the layer comprising at least one cementitious material has a thickness ranging from 0.5 to 5 cm.

10. The connector as claimed in claim 1, wherein the layer comprising at least one cementitious material has a length of at least L.sub.1=L.sub.0+40, L.sub.0 and L.sub.1 having units of cm, and L.sub.0 representing the length of the ends of the stripped and end-to-end joined cables.

11. The connector as claimed in claim 1, wherein the cementitious material is a solid material comprising silicon (Si), aluminum (Al), oxygen (O) and at least one element chosen from potassium (K), sodium (Na), lithium (Li), cesium (Cs) and calcium (Ca), said solid material being a geopolymer cement or being derived from a mixture of a conventional anhydrous cement and water.

12. The connector as claimed in claim 11, wherein the anhydrous cement is Portland cement or slag and fly ash cement.

13. The connector as claimed in claim 11, wherein the geopolymer cement is an aluminosilicate geopolymer cement.

14. A process for connecting at least two fire-resistant cables each comprising at least one elongated electrically-conductive element and at least one electrically-insulating sheath surrounding said elongated electrically-conductive element, said process being characterized in that it uses a connector as defined in claim 1 and in that said process comprises at least the following steps: i) a step of baring the ends of said cables intended to be connected and of end-to-end joining said bared ends of said cables, ii) a step of molding a geopolymer composition or a mixture consisting of a conventional anhydrous cement and water, around said stripped and end-to-end joined ends of said cables and a portion of each electrically-insulating sheath, and iii) a step of hardening the geopolymer composition or the mixture consisting of a conventional anhydrous cement and water, in order to form a layer that comprises at least one cementitious material and that surrounds a portion of each electrically-insulating sheath and said stripped and end-to-end joined ends of said cables.

15. A method for lengthening a fire-resistant cable line or for replacing a defective portion of a fire-resistant cable line, said method comprising the steps of: inserting a connector as defined in claim 1, into said fire-resistant cable line.

16. A fire-resistant cable line comprising at least: a first fire-resistant cable comprising at least one elongated electrically-conductive element and at least one electrically-insulating sheath surrounding said elongated electrically-conductive element, and a second fire-resistant cable comprising at least one elongated electrically-conductive element and at least one electrically-insulating sheath surrounding said elongated electrically-conductive element, the ends of said cables intended to be connected being stripped and joined end-to-end so as to ensure a physical and electrical contact between said cables, wherein said fire-resistant cable line additionally comprises a connector as defined in claim 1.

Description

EXAMPLES

[0134] The raw materials used in the examples are listed below: [0135] approximately 50 wt % aqueous sodium silicate solution of waterglass type, from Simalco, of formula Na.sub.2O.2SiO.sub.2 and with an SiO.sub.2/Na.sub.2O molar ratio of 2 approximately, [0136] tap water, [0137] potassium hydroxide, from Sigma-Aldrich, with a purity >85%, [0138] Polestar 450 aluminosilicate, from Imerys, with an Al.sub.2O.sub.3/SiO.sub.2 molar ratio of 41/55 (i.e. of 0.745 approximately).

[0139] Unless otherwise indicated, all these raw materials were used as received from the manufacturers.

Example 1: Process for Connecting Two Fire-Resistant Cables in Accordance with the Invention

[0140] 1.1. Preparation of an Aluminosilicate Geopolymer Composition (Step ii.sub.0)

[0141] An alkali metal silicate solution is prepared by mixing 1000 g of an aqueous sodium silicate solution, 300 g of water and 180 g of potassium hydroxide. Then 600 g of aluminosilicate were mixed with the alkali metal silicate solution to form an aluminosilicate geopolymer composition.

[0142] Said aluminosilicate geopolymer composition comprised 54% by weight approximately of solids relative to the total weight of said composition.

[0143] The aluminosilicate geopolymer composition had the following molar composition of formula (I):

0.54SiO.sub.2:0.16Al.sub.2O.sub.3:0.1K.sub.2O:2.3H.sub.2O(I)

1.2. Connection of Two Fire-Resistant Cables

[0144] Two identical cables were used in the present example. Each cable comprised four elongated electrically-conductive elements made of copper having a cross section of 50 mm.sup.2, each of the four elongated electrically-conductive elements made of copper being insulated by an electrically-insulating layer, and an electrically-insulating sheath surrounding said insulated four elongated electrically-conductive elements made of copper. The electrically-insulating layers were based on a crosslinked polyorganosiloxane. The electrically-insulating sheath was of HFFR type based on an ethylene/vinyl acetate copolymer (EVA).

[0145] The ends of said cables intended to be connected were stripped.

[0146] Next, a tube made of heat-shrinkable material sold by Huber-Suhner Suisse under the reference Sucofit was placed around said cables and in particular around the stripped ends of said cables. The tube was able at this stage to be moved manually along the longitudinal axis of the cables, in particular in order to be able to view the stripped ends and join them end-to-end manually. The stripped ends of said cables were thus joined end-to-end manually and permanently connected using a metal element (conventional connector) by crimping.

[0147] Finally, the tube made of heat-shrinkable material was again moved along the longitudinal axis of the cables so as to position it at the stripped and end-to-end joined ends of said cables (i.e. connection zone); then it was shrunk by heating, so as to form a layer consisting of said heat-shrinkable material. The stripped and end-to-end joined ends of said cables permanently covered by the layer consisting of said heat-shrinkable material were thus obtained.

[0148] The geopolymer composition prepared in example 1.1 was molded around the layer consisting of a heat-shrinkable material with the aid of a cylindrical mold.

[0149] The assembly (cables and connector) was then dried at ambient temperature for 24 hours, then removed from the mold.

[0150] FIG. 1 is a schematic representation of the process in accordance with the present invention.

[0151] The process described in FIG. 1 relates to the connection of two fire-resistant cables (1A, 1B) each comprising an elongated electrically-conductive element (2A, 2B) and an electrically-insulating sheath (3A, 3B) surrounding said elongated electrically-conductive element (2A, 2B).

[0152] According to a first step i), the ends that are intended to be connected of said cables (1A, 1B) were stripped and joined end-to-end.

[0153] Next, according to a step ii), the stripped and end-to-end joined ends (2a, 2b) are permanently connected using a metal element (4) by crimping (connection zone).

[0154] Finally, according to a step ii), a geopolymer composition is molded around said stripped and end-to-end joined ends (2a, 2b) of said cables (1A, 1B) and a portion (3a, 3b) of each electrically-insulating sheath (3A, 3B).

[0155] After step iii) of hardening the geopolymer composition at ambient temperature, a layer (5) comprising at least one geopolymer cement is formed around the metal element (4), said stripped and end-to-end joined ends (2a, 2b) of said cables (1A, 1B) and a portion (3a, 3b) of each electrically-insulating sheath (3A, 3B).

1.3. Connector Performance

[0156] The cable connector comprising a layer of geopolymer cement and a metal element was evaluated with regard to the flame resistance performance. The assembly was placed in a furnace and exposed to a temperature close to 1000 C. for 2 hours.

[0157] FIG. 2 represents images of the cable connector before the exposure test at a temperature close to 1000 C. for 2 hours (FIG. 2a) and of the cable connector after the test (FIG. 2b).

[0158] As can be seen in FIG. 2, after the test, the residual mechanical cohesion of the geopolymer cement layer (5) indicates that the geopolymer cement protects the connection zone defined by the stripped and end-to-end joined ends (2a, 2b) of the cables (1A, 1B). The electrically-insulating layers (6A, 6B) respectively underneath each electrically-insulating sheath (3A, 3B) of each of the cables (1A, 1B) surrounding the elongated electrically-conductive elements (2A, 2B) are very slightly deteriorated. Consequently, the geopolymer cement layer (5) very greatly limits the heat transfers. Furthermore, it has been noted that the internal portion of the connection zone is completely intact and that no trace of degradation or of overheating is visible. The electrically-insulating sheath (3A, 3B), for its part, does not withstand such temperatures and is degraded by combustion.