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EP1568048A1 - Fire-resistant cable - Google Patents

Fire-resistant cable

Info

Publication number
EP1568048A1
EP1568048A1 EP03811026A EP03811026A EP1568048A1 EP 1568048 A1 EP1568048 A1 EP 1568048A1 EP 03811026 A EP03811026 A EP 03811026A EP 03811026 A EP03811026 A EP 03811026A EP 1568048 A1 EP1568048 A1 EP 1568048A1
Authority
EP
European Patent Office
Prior art keywords
layer
cable
cable according
water impermeable
outer sheath
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP03811026A
Other languages
German (de)
French (fr)
Inventor
Mark Froggatt
Stephen Mason
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Draka UK Ltd
Original Assignee
Draka UK Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Draka UK Ltd filed Critical Draka UK Ltd
Publication of EP1568048A1 publication Critical patent/EP1568048A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
    • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
    • H01B3/28—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances natural or synthetic rubbers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B3/00—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties
    • H01B3/18—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances
    • H01B3/30—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes
    • H01B3/46—Insulators or insulating bodies characterised by the insulating materials; Selection of materials for their insulating or dielectric properties mainly consisting of organic substances plastics; resins; waxes silicones
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
    • H01B7/00—Insulated conductors or cables characterised by their form
    • H01B7/17—Protection against damage caused by external factors, e.g. sheaths or armouring
    • H01B7/29—Protection against damage caused by extremes of temperature or by flame
    • H01B7/295—Protection against damage caused by extremes of temperature or by flame using material resistant to flame

Definitions

  • the present invention relates to fire-resistant cables.
  • it relates to electrical or telecommunications cables which are required to function in the event of a fire.
  • Systems such as fire alarm systems and close circuit television systems used in buildings, ships, and tunnels use electrical and telecommunications cables which are required to function in a fire. It may be particularly important that they continue to function in the critical early stages of a fire because they may be vital for initiating or monitoring evacuation, or guiding fire and rescue services.
  • British Standard BS5839 is the code of practice for fire alarm installations in the UK. Cables used in fire alarm systems are required to meet this standard. Historically, cables meeting BS6387 category CWZ have been deemed to meet and indeed exceed the requirements of BS5839. There are various known cable constructions which met standard BS5839 as it stood until late 2002.
  • BS5839 has now been revised with more rigorous requirements .
  • the new standard defines two grades of cable performance: "standard” and “enhanced”. Fire-resisting cables which meet these standards maintain circuit integrity when subjected to a test based on BS EN 50200. They can withstand being simultaneously exposed to flame at high temperature and mechanical shock, with subsequent or simultaneous exposure to a water spray. These tests are designed to assess the performance of a cable in a simulated fire situation.
  • a cable comprising one or more conductive cores each having an insulated covering; a layer of water impermeable material around the insulated cores; and an outer sheath of insulating polymeric material; wherein the insulating polymeric material of the outer sheath includes a nanocomposite filler.
  • the layer of water impermeable material should remain impermeable to water at the temperatures associated with a fire, for example at temperatures up to 1000°C.
  • layers of polymers such as polyethylene, which melt or burn away at high temperatures, are not suitable.
  • the outer sheath may be located immediately adjacent to the layer of water impermeable material. However, the outer sheath may be separated from the layer of water impermeable material by one or more intervening layers .
  • the intervening layer(s) may be, for example, armour layer(s), layer(s) of woven glass tape and/or further layer (s) of insulating polymeric material which includes nanocomposite filler.
  • the layer of water impermeable material is a laminated layer of a metal (e.g. an aluminium tape) and a polymer (e.g. polyester tape) .
  • a preferred material is ALI- PET tape.
  • the layer of water impermeable material is of a thickness of 10 to 80 microns (10 to 80 ⁇ m) .
  • Preferred layers have a thickness of between 20 and 50 microns.
  • the layer of water impermeable material is a tape layer which is wound helically around the layer of the cable immediately adjacent thereto (e.g. wound helically around the insulated core or cores) . It is preferred that the layer of water impermeable material completely covers the layer immediately adjacent thereto without having gaps, even when the cable is bent . In the case where the layer of water impermeable material is in the form of a tape it should be wound so that the turns of the tape overlap one another.
  • the thickness of the water impermeable layer is of 10 to 80 microns (10 to 80 ⁇ m) .
  • the cable may further comprise a layer of woven glass tape around the layer of water impermeable material . This may take the form of tape wound helically around the layer of water impermeable material .
  • the layer of water impermeable material includes a metal (e.g. includes a laminated layer of metal foil)
  • a drain wire of metal e.g. copper wire may be applied in contact with the metal (foil) to prevent or reduce build up of electrostatic charge.
  • the outer sheath of insulating polymeric material includes a nanocomposite filler. This may be a single nanocomposite filler or a mixture of two or more nanocomposite fillers.
  • a nanocomposite is a composite material which comprises sub-micronic particles dispersed in an organic matrix.
  • Preferred nanocomposite fillers are those sold under the Trade Marks NANOFIL, NANOCOR, CLOISITE.
  • Another preferred nanocomposite filler is that sold under the Trade Mark BENTONE (from Elementis) .
  • the amount of nanocomposite filler is 1 to 10%, more preferably 3 to 8%, by weight of the total weight of the insulating polymeric material present in the outer sheath.
  • the insulating polymeric material is a flame retardant polymeric material . Either a polymer that is intrinsically fire retardant or a polymer composition that is modified by the addition of ingredients that impart fire- resisting characteristics may be used.
  • the insulating polymeric material is a polymer which does not give out substantial amounts of smoke or fumes on combustion.
  • the insulating polymeric material does not contain halogens .
  • Preferred insulating polymeric materials include hydrated alumina in a polyethylene and polyethylene co-polymer composition; and magnesium hydroxide in a polyethylene and polyethylene co-polymer composition.
  • the combination of nanocomposite filler with insulating polymeric material enhances the cohesion of the outer sheath.
  • the outer sheath forms a cohesive charred outer layer (for example a crust) , or a cohesive ash layer, which is retained on the cable.
  • the nanocomposite filler binds and strengthens the ash (formed, for example, by burning of the hydrated alumina) , by forming a 3D inorganic network structure. Cracking, shattering or splitting of the sheath is prevented or delayed.
  • the cohesive layer enhances the ability of the cable as a whole to withstand flame and shock.
  • the water impermeable layer is maintained by retention of the outer sheath.
  • the water impermeable layer prevents (or delays) water from sprinkler systems etc . from reaching the conducting cores of the cable where it might lead to cable failure. It is thus possible for cables according to the invention to perform to the revised standard of BS5839.
  • the cable may include a further layer or further layers of insulating polymeric material which includes a nanocomposite filler.
  • the further layer (s) of insulating polymeric material which includes a nanocomposite filler may be located within the layer of water impermeable material and immediately adjacent thereto, so that the layer of water impermeable material surrounds and covers the layer of insulating polymeric material which includes a nanocomposite filler.
  • the further layer (s) of insulating polymeric material which includes a nanocomposite filler may be located around the layer of water impermeable material .
  • the cable further comprises a layer of porous siliceous material (used herein to mean a material permeable to gas and comprising or containing silica, silicate, or any other suitable compound having Si-0 bonds) around the insulated conductive core(s) .
  • a layer of porous siliceous material used herein to mean a material permeable to gas and comprising or containing silica, silicate, or any other suitable compound having Si-0 bonds
  • the insulated covering for the insulated conductive core(s) includes a silicone rubber.
  • the insulated covering for the conductive core(s) includes a silicone rubber and the cable further comprises a layer of porous siliceous material around the insulated core(s) and immediately adjacent the silicone rubber.
  • the layer of siliceous material completely covers the insulated cable (s).
  • Silicon dioxide is an insulating material.
  • the porous siliceous material will adsorb preferentially silicon dioxide produced by thermal decomposition of the silicone rubber insulation.
  • the porous siliceous material adsorbs and traps insulating material which would otherwise be lost (for example due to vaporisation) .
  • the surface of the porous siliceous material is exposed directly to the silicone rubber so that it can adsorb the silicon dioxide produced by pyrolysis onto its surface.
  • the porous siliceous material may be any suitable porous (preferably fibrous) material, containing silica or silicates.
  • suitable materials includes silica fibre, glass fibre, mica tape and mineral wool.
  • Glass fibre tape is a particularly preferred material, and may be wound helically around the insulated core or cores.
  • the layer of siliceous material should completely cover the insulating conductors without leaving gaps, even when the cable is bent. In the case where the material is in the form of a tape it should be wound so the turns overlap one another.
  • the water impermeable layer is located around the layer of porous siliceous material and immediately adjacent thereto.
  • a preferred layer of water impermeable material is a tape layer (for example ALI-PET tape) which is wound helically around the porous siliceous material. It is preferred that the water impermeable layer completely covers the porous siliceous material without leaving gaps, even when the cable is bent. In the case where the water impermeable material is in the form of a tape it should be wound so that the turns overlap one another.
  • the conductor core(s) may include a further layer of porous siliceous material (e.g. mica tape) immediately below the layer of silicone rubber - for example, between the silicone rubber insulation and the conductor core. If there is a further layer of porous siliceous material outside the silicone rubber (for example, immediately inside the water impermeable layer) the silicone rubber is surrounded by layers of siliceous material. In this construction the silicon dioxide due to decomposition of the silicone rubber in a fire may be firmly held by adsorption to two layers of siliceous material. This may improve the ability of the cable as a whole to maintain function while exposed to vibration.
  • porous siliceous material e.g. mica tape
  • further layers such as armoured layers can be added to further physically protect the cable.
  • the cable may further comprise a layer of armour.
  • the armour layer may be a layer of metal such a steel .
  • the armour layer may be in the form of a wire or braid.
  • a preferred layer of armour is steel wire.
  • Preferably the outer sheath is around the layer of armour and immediately adjacent thereto.
  • the cable of the invention may include a further layer or further layers of insulating polymeric material which includes a nanocomposite filler. If a layer of armour is present, the layer of armour may be around the further layer (s) of insulating polymeric material which includes a nanocomposite filler. Preferably, the layer of armour is around the further layer of insulating polymeric material which includes a nanocomposite filler and immediately adjacent thereto.
  • the cable may comprise one or more conductive cores each having an insulated covering; a layer of water impermeable material around the insulated cores; a layer of insulating polymeric material which includes a nanocomposite filler around the layer of water impermeable material; a layer of armour; and an outer sheath of insulating polymeric material; wherein the insulating polymeric material of the outer sheath includes a nanocomposite filler.
  • the layer of water impermeable material is around a further layer (s) of insulating polymeric material which includes a nanocomposite filler.
  • the layer of water impermeable material may be immediately adjacent to the further layer of insulating polymeric material which includes a nanocomposite filler.
  • the cable may comprise one or more conductive cores each having an insulated covering; a layer of insulating polymeric material which includes a nanocomposite filler around the insulated cores; a layer of water impermeable material around the layer of insulating polymeric material which includes a nanocomposite filler; a layer of armour; and an outer sheath of insulating polymeric material; wherein the insulating polymeric material of the outer sheath includes a nanocomposite filler.
  • further layers may be present, such as further layers of insulating material .
  • the further layer of insulating material is one which does not give out substantial amounts of smoke or fumes on combustion.
  • a material that does not contain halogens is used.
  • the material sold under the trade mark OHLS which consists of hydrated alumina in a polyethylene and polyethylene co- polymer composition is particularly suitable. Magnesium hydroxide in a polyethylene and polyethylene co-polymer composition is also suitable.
  • cables according to the invention may also incorporate other components known in themselves which are required by the use to which it is intended to put the cable.
  • an electrostatic sheath may be provided e.g. inside the layer of water permeable material .
  • cable it is meant a bundle of one or more conductive wires or fibre optics protected by insulating sheaths such as those used to supply electricity or in telecommunication networks .
  • the cables are used in telecommunication cables, power cables, and other cables which are parts of fire alarm installations and systems.
  • FIGURE 1 shows a cross-section through a cable embodying the invention
  • FIGURE 2 shows a side view of an armoured cable according to a second embodiment of the invention, with parts cut away.
  • the cable shown in Fig.l has two copper cores 1 each surrounded by an insulating silicone rubber covering 2.
  • the cable also includes a tinned copper earth 3.
  • Around cores 1 and earth 3 is arranged layer 4 of porous siliceous material in the form of a glass fibre tape.
  • the tape is wound helically around the insulated conductor cores 1, 2 and earth 3 with each turn of the helix overlapping the next sufficiently so that the insulated cores 1, 2 and earth 3 are completely covered with the glass fibre tape, even when the cable is bent.
  • the glass fibre of the tape layer 4 is immediately adjacent the silicone rubber covering 2 of the cores 1.
  • the silicone rubber is cured before the glass tape is applied.
  • a layer of water impermeable material 5 in the form of ALI- PET tape of thickness 50 microns surrounds the glass tape layer 4.
  • the layer of ALI-PET tape 5 is wound helically around the glass tape layer 4 in a similar way to that of tape 4 so that each turn of the helix overlaps the next sufficiently so that the glass tape layer 4 is completely covered with the layer 5 of water impermeable material, even when the cable is bent.
  • the outer sheath 6 is made up of material sold under the mark OHLS (RTM) , which consists of hydrated alumina in a polyethylene and polyethylene co-polymer composition, to which has been added nanocomposite filler Nanofil-15 from S ⁇ dchimie in an amount of 6% by weight of the OHLS (RTM) material . It will be understood that the outer sheath 6 may also be made by mixing the components which together form OHLS (RTM) with the required amount of nanocomposite filler Nanofil-15.
  • RTM OHLS
  • the silicone rubber coating 2 When a cable according to the invention such as the cable just described is exposed to a fire, the silicone rubber coating 2 will decompose to yield a considerable amount of silicone dioxide.
  • the layer of porous siliceous material (glass tape layer 4) preferentially adsorbs the silicon dioxide and holds it in place, providing an insulated silicone dioxide coating for the conductive cores of the cable.
  • the outer sheath 6 burns and chars on exposure to flame but is sufficiently cohesive to retain the ALI-PET tape layer 5 around the glass tape layer 4.
  • the ALI-PET layer 5 prevents water (e.g from fire sprinkler sprays) from reaching the glass tape layer 4 and the silicone dioxide (caused by combustion of silicone rubber insulation 2) adsorbed thereon and is thus prevented or delayed from reaching the conductive core(s) 1 of the cable. Cable failure due to short circuiting is thus prevented or delayed.
  • a sample of the cable shown in Fig.l and discussed above was tested for maintenance of circuit integrity. The test described below exceeds the requirements of BS EN50200.
  • BS EN50200 Using the apparatus and set up of BS EN50200, a sample of the cable was exposed to flame at a temperature of 930°C with simultaneous mechanical shock for a period of 60 minutes. After the required period of exposure to flame and shock without water spray, and with the flame and shock still being applied, the water spray is started. The application of water is continued for 60 minutes.
  • the water spray was applied by a water spray bar consisting of a metallic tube (copper or stainless steel) of thickness 1 mm and overall diameter 15.5 mm, closed at one end and open at the other to allow the inflow of water.
  • the tube had one row of 17 holes of 0.85 mm diameter drilled on 30 mm centres and was positioned centrally with respect to the test sample of cable of Fig.l.
  • the water spray bar was supplied by water at a flow rate of 0.8 litres per minute. The resulting water spray was centralised around the burned and/or burning portion of the test sample.
  • the cable shown in Fig.2 has four copper cores 51 (two copper cores are not shown) .
  • Each copper core 51 is made of stranded copper (7 strands of diameter 2.2mm which are circularised and compacted) and is of nominal diameter 5.9mm and cross section 25mm 2 .
  • Each copper core 51 is surrounded by a layer of mica tape 59.
  • the tape 59 is of 0.1mm thickness and is wound helically around the core 51 with each turn of the helix overlapping the next sufficiently so that each of the cores 51 is completely covered with a layer of mica tape 59.
  • Each mica tape surrounded core 51, 59 has a surrounding layer of an insulating covering 52 of material sold under the trade mark XL-OHLS which consists of hydrated alumina in a polyethylene and polyethylene co-polymer composition.
  • the layer 52 is applied by extrusion so that it surrounds the mica tape layer 59 and is immediately adjacent layer 59.
  • the layer 52 has a radial thickness of 0.9mm.
  • the overall diameter of each XL-OHLS and tape surrounded core 51, 59, 52 is 8.27mm.
  • a layer of water impermeable material 55 in the form of ALI-PET tape of thickness 50 microns surrounds the insulated cores 51, 59, 52.
  • the layer of ALI-PET tape 55 is wound helically around the cores 51 so that each turn of the helix overlaps the next sufficiently so that the cores are completely covered with the layer 55 of water impermeable material, even when the cable is bent.
  • the layer of ALI-PET tape 55 is of thickness 73 microns (the thickness of Aluminium is 50 microns and the thickness of PET is 23 microns) .
  • a layer of woven glass tape may be wound helically around the layer of water impermeable material 55 (not shown in Fig 2) .
  • a nanocomposite layer 61 made up of material sold under the mark OHLS (RTM) , which consists of hydrated alumina in a polyethylene and polyethylene co-polymer composition, to which has been added nanocomposite filler Nanofil-15 from S ⁇ dchimie in an amount of 6% by weight of the OHLS (RTM) material.
  • RTM OHLS
  • the layer 61 is applied by extrusion and is of 0.9mm radial thickness .
  • a layer 75 of steel wire armour (radial thickness 1.6mm) surrounds the nanocomposite layer 61.
  • the layer 75 is made up of 44 steel wires of thickness 1.6mm which are laid and twisted in a manner which is well known in the art.
  • An outer sheath 56 is also made up of material sold under the mark OHLS (RTM) to which has been added nanocomposite filler Nanofil-15 from S ⁇ dchimie in an amount of 6% by weight of the OHLS (RTM) material.
  • RTM OHLS
  • the outer sheath 6 and the layer 61 may also be made by mixing the components which together form OHLS (RTM) with the required amount of nanocomposite filler Nanofil-15.
  • the outer sheath 56 is applied on the armoured layer 75 by extrusion and is of radial thickness 1.5mm.
  • the water impermeable layer 55 and nanocomposite sheath 56 function in a similar manner to the equivalent components in the embodiment of Fig 1 as described above.
  • cable is able to maintain function in the event of a fire and prevent or delay failure due to short circuiting.
  • the armour layer 75 and additional layer of nanocomposite 61 may provide additional physical protection and resistance to damage due to vibration and physical shock.
  • the structure is similar to that shown in Fig 2 with the positions of nanocomposite layer 61 and water impermeable material 55 interchanged so that the layer of water impermeable material 55 surrounds the further (i.e. non-sheath) layer of insulating polymeric material which includes a nanocomposite filler (layer 61) .

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  • Physics & Mathematics (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Insulated Conductors (AREA)

Abstract

A cable comprising one or more conductive cores each having an insulated covering; a layer of water impermeable material around the insulated cores; and an outer sheath of insulating polymeric material; wherein the insulating polymeric material of the outer sheath includes a nanocomposite filler.

Description

FIRE-RESISTANT CABLE
The present invention relates to fire-resistant cables. In particular it relates to electrical or telecommunications cables which are required to function in the event of a fire.
Systems such as fire alarm systems and close circuit television systems used in buildings, ships, and tunnels use electrical and telecommunications cables which are required to function in a fire. It may be particularly important that they continue to function in the critical early stages of a fire because they may be vital for initiating or monitoring evacuation, or guiding fire and rescue services.
British Standard BS5839 is the code of practice for fire alarm installations in the UK. Cables used in fire alarm systems are required to meet this standard. Historically, cables meeting BS6387 category CWZ have been deemed to meet and indeed exceed the requirements of BS5839. There are various known cable constructions which met standard BS5839 as it stood until late 2002.
BS5839 has now been revised with more rigorous requirements . The new standard defines two grades of cable performance: "standard" and "enhanced". Fire-resisting cables which meet these standards maintain circuit integrity when subjected to a test based on BS EN 50200. They can withstand being simultaneously exposed to flame at high temperature and mechanical shock, with subsequent or simultaneous exposure to a water spray. These tests are designed to assess the performance of a cable in a simulated fire situation.
There is a need for fire-resistant cables which meet the new, more rigorous, BS5839 standard, particularly the enhanced performance category.
According to the present invention there is provided a cable comprising one or more conductive cores each having an insulated covering; a layer of water impermeable material around the insulated cores; and an outer sheath of insulating polymeric material; wherein the insulating polymeric material of the outer sheath includes a nanocomposite filler.
The layer of water impermeable material should remain impermeable to water at the temperatures associated with a fire, for example at temperatures up to 1000°C. Thus, layers of polymers such as polyethylene, which melt or burn away at high temperatures, are not suitable.
The outer sheath may be located immediately adjacent to the layer of water impermeable material. However, the outer sheath may be separated from the layer of water impermeable material by one or more intervening layers . The intervening layer(s) may be, for example, armour layer(s), layer(s) of woven glass tape and/or further layer (s) of insulating polymeric material which includes nanocomposite filler.
Preferably, the layer of water impermeable material is a laminated layer of a metal (e.g. an aluminium tape) and a polymer (e.g. polyester tape) . A preferred material is ALI- PET tape. Preferably, the layer of water impermeable material is of a thickness of 10 to 80 microns (10 to 80 μm) . Preferred layers have a thickness of between 20 and 50 microns.
Preferably the layer of water impermeable material is a tape layer which is wound helically around the layer of the cable immediately adjacent thereto (e.g. wound helically around the insulated core or cores) . It is preferred that the layer of water impermeable material completely covers the layer immediately adjacent thereto without having gaps, even when the cable is bent . In the case where the layer of water impermeable material is in the form of a tape it should be wound so that the turns of the tape overlap one another.
Preferably the thickness of the water impermeable layer is of 10 to 80 microns (10 to 80 μm) . The cable may further comprise a layer of woven glass tape around the layer of water impermeable material . This may take the form of tape wound helically around the layer of water impermeable material .
If the layer of water impermeable material includes a metal (e.g. includes a laminated layer of metal foil) a drain wire of metal e.g. copper wire may be applied in contact with the metal (foil) to prevent or reduce build up of electrostatic charge.
The outer sheath of insulating polymeric material includes a nanocomposite filler. This may be a single nanocomposite filler or a mixture of two or more nanocomposite fillers.
A nanocomposite is a composite material which comprises sub-micronic particles dispersed in an organic matrix. Preferred nanocomposite fillers are those sold under the Trade Marks NANOFIL, NANOCOR, CLOISITE. Another preferred nanocomposite filler is that sold under the Trade Mark BENTONE (from Elementis) . Preferably the amount of nanocomposite filler is 1 to 10%, more preferably 3 to 8%, by weight of the total weight of the insulating polymeric material present in the outer sheath. Preferably the insulating polymeric material is a flame retardant polymeric material . Either a polymer that is intrinsically fire retardant or a polymer composition that is modified by the addition of ingredients that impart fire- resisting characteristics may be used. Preferably the insulating polymeric material is a polymer which does not give out substantial amounts of smoke or fumes on combustion. Preferably the insulating polymeric material does not contain halogens . Preferred insulating polymeric materials include hydrated alumina in a polyethylene and polyethylene co-polymer composition; and magnesium hydroxide in a polyethylene and polyethylene co-polymer composition.
The combination of nanocomposite filler with insulating polymeric material enhances the cohesion of the outer sheath. Thus, when exposed to fire, the outer sheath forms a cohesive charred outer layer (for example a crust) , or a cohesive ash layer, which is retained on the cable. It is believed that the nanocomposite filler binds and strengthens the ash (formed, for example, by burning of the hydrated alumina) , by forming a 3D inorganic network structure. Cracking, shattering or splitting of the sheath is prevented or delayed. The cohesive layer enhances the ability of the cable as a whole to withstand flame and shock. The water impermeable layer is maintained by retention of the outer sheath. The water impermeable layer prevents (or delays) water from sprinkler systems etc . from reaching the conducting cores of the cable where it might lead to cable failure. It is thus possible for cables according to the invention to perform to the revised standard of BS5839.
The cable may include a further layer or further layers of insulating polymeric material which includes a nanocomposite filler. The further layer (s) of insulating polymeric material which includes a nanocomposite filler may be located within the layer of water impermeable material and immediately adjacent thereto, so that the layer of water impermeable material surrounds and covers the layer of insulating polymeric material which includes a nanocomposite filler. The further layer (s) of insulating polymeric material which includes a nanocomposite filler may be located around the layer of water impermeable material .
Preferably the cable further comprises a layer of porous siliceous material (used herein to mean a material permeable to gas and comprising or containing silica, silicate, or any other suitable compound having Si-0 bonds) around the insulated conductive core(s) . Preferably, the insulated covering for the insulated conductive core(s) includes a silicone rubber.
In a preferred embodiment of a cable according to the invention the insulated covering for the conductive core(s) includes a silicone rubber and the cable further comprises a layer of porous siliceous material around the insulated core(s) and immediately adjacent the silicone rubber. Preferably the layer of siliceous material completely covers the insulated cable (s).
Thermal decomposition of the silicone rubber polymer due to the heat of a fire results in various products including silicon dioxide. Silicon dioxide is an insulating material. The porous siliceous material will adsorb preferentially silicon dioxide produced by thermal decomposition of the silicone rubber insulation. Thus, the porous siliceous material adsorbs and traps insulating material which would otherwise be lost (for example due to vaporisation) . In a preferred embodiment the surface of the porous siliceous material is exposed directly to the silicone rubber so that it can adsorb the silicon dioxide produced by pyrolysis onto its surface.
The porous siliceous material may be any suitable porous (preferably fibrous) material, containing silica or silicates. Examples of suitable materials includes silica fibre, glass fibre, mica tape and mineral wool. Glass fibre tape is a particularly preferred material, and may be wound helically around the insulated core or cores. The layer of siliceous material should completely cover the insulating conductors without leaving gaps, even when the cable is bent. In the case where the material is in the form of a tape it should be wound so the turns overlap one another.
If the porous siliceous material is present it is preferred that the water impermeable layer is located around the layer of porous siliceous material and immediately adjacent thereto. A preferred layer of water impermeable material is a tape layer (for example ALI-PET tape) which is wound helically around the porous siliceous material. It is preferred that the water impermeable layer completely covers the porous siliceous material without leaving gaps, even when the cable is bent. In the case where the water impermeable material is in the form of a tape it should be wound so that the turns overlap one another.
If the insulated covering for the conductive core(s) includes a silicone rubber the conductor core(s) may include a further layer of porous siliceous material (e.g. mica tape) immediately below the layer of silicone rubber - for example, between the silicone rubber insulation and the conductor core. If there is a further layer of porous siliceous material outside the silicone rubber (for example, immediately inside the water impermeable layer) the silicone rubber is surrounded by layers of siliceous material. In this construction the silicon dioxide due to decomposition of the silicone rubber in a fire may be firmly held by adsorption to two layers of siliceous material. This may improve the ability of the cable as a whole to maintain function while exposed to vibration.
Optionally, further layers such as armoured layers can be added to further physically protect the cable.
The cable may further comprise a layer of armour. The armour layer may be a layer of metal such a steel . The armour layer may be in the form of a wire or braid. A preferred layer of armour is steel wire. Preferably the outer sheath is around the layer of armour and immediately adjacent thereto.
The cable of the invention may include a further layer or further layers of insulating polymeric material which includes a nanocomposite filler. If a layer of armour is present, the layer of armour may be around the further layer (s) of insulating polymeric material which includes a nanocomposite filler. Preferably, the layer of armour is around the further layer of insulating polymeric material which includes a nanocomposite filler and immediately adjacent thereto. The cable may comprise one or more conductive cores each having an insulated covering; a layer of water impermeable material around the insulated cores; a layer of insulating polymeric material which includes a nanocomposite filler around the layer of water impermeable material; a layer of armour; and an outer sheath of insulating polymeric material; wherein the insulating polymeric material of the outer sheath includes a nanocomposite filler.
In another embodiment the layer of water impermeable material is around a further layer (s) of insulating polymeric material which includes a nanocomposite filler. The layer of water impermeable material may be immediately adjacent to the further layer of insulating polymeric material which includes a nanocomposite filler. The cable may comprise one or more conductive cores each having an insulated covering; a layer of insulating polymeric material which includes a nanocomposite filler around the insulated cores; a layer of water impermeable material around the layer of insulating polymeric material which includes a nanocomposite filler; a layer of armour; and an outer sheath of insulating polymeric material; wherein the insulating polymeric material of the outer sheath includes a nanocomposite filler.
Optionally, further layers may be present, such as further layers of insulating material . Preferably the further layer of insulating material is one which does not give out substantial amounts of smoke or fumes on combustion. Preferably a material that does not contain halogens is used. The material sold under the trade mark OHLS which consists of hydrated alumina in a polyethylene and polyethylene co- polymer composition is particularly suitable. Magnesium hydroxide in a polyethylene and polyethylene co-polymer composition is also suitable.
It will be appreciated that cables according to the invention may also incorporate other components known in themselves which are required by the use to which it is intended to put the cable. For example an electrostatic sheath may be provided e.g. inside the layer of water permeable material .
By cable it is meant a bundle of one or more conductive wires or fibre optics protected by insulating sheaths such as those used to supply electricity or in telecommunication networks . Preferably the cables are used in telecommunication cables, power cables, and other cables which are parts of fire alarm installations and systems.
The present invention will now be described in more detail by way of example with reference to the accompanying drawings, in which : FIGURE 1 shows a cross-section through a cable embodying the invention; and
FIGURE 2 shows a side view of an armoured cable according to a second embodiment of the invention, with parts cut away.
The cable shown in Fig.l has two copper cores 1 each surrounded by an insulating silicone rubber covering 2. The cable also includes a tinned copper earth 3. Around cores 1 and earth 3 is arranged layer 4 of porous siliceous material in the form of a glass fibre tape. The tape is wound helically around the insulated conductor cores 1, 2 and earth 3 with each turn of the helix overlapping the next sufficiently so that the insulated cores 1, 2 and earth 3 are completely covered with the glass fibre tape, even when the cable is bent.
The glass fibre of the tape layer 4 is immediately adjacent the silicone rubber covering 2 of the cores 1. The silicone rubber is cured before the glass tape is applied. A layer of water impermeable material 5 in the form of ALI- PET tape of thickness 50 microns surrounds the glass tape layer 4. The layer of ALI-PET tape 5 is wound helically around the glass tape layer 4 in a similar way to that of tape 4 so that each turn of the helix overlaps the next sufficiently so that the glass tape layer 4 is completely covered with the layer 5 of water impermeable material, even when the cable is bent.
Around the layer of water impermeable material 5 is outer sheath 6. The outer sheath 6 is made up of material sold under the mark OHLS (RTM) , which consists of hydrated alumina in a polyethylene and polyethylene co-polymer composition, to which has been added nanocomposite filler Nanofil-15 from Sϋdchimie in an amount of 6% by weight of the OHLS (RTM) material . It will be understood that the outer sheath 6 may also be made by mixing the components which together form OHLS (RTM) with the required amount of nanocomposite filler Nanofil-15.
When a cable according to the invention such as the cable just described is exposed to a fire, the silicone rubber coating 2 will decompose to yield a considerable amount of silicone dioxide. The layer of porous siliceous material (glass tape layer 4) preferentially adsorbs the silicon dioxide and holds it in place, providing an insulated silicone dioxide coating for the conductive cores of the cable. The outer sheath 6 burns and chars on exposure to flame but is sufficiently cohesive to retain the ALI-PET tape layer 5 around the glass tape layer 4. The ALI-PET layer 5 prevents water (e.g from fire sprinkler sprays) from reaching the glass tape layer 4 and the silicone dioxide (caused by combustion of silicone rubber insulation 2) adsorbed thereon and is thus prevented or delayed from reaching the conductive core(s) 1 of the cable. Cable failure due to short circuiting is thus prevented or delayed.
Example 1 - Cable Testing
A sample of the cable shown in Fig.l and discussed above was tested for maintenance of circuit integrity. The test described below exceeds the requirements of BS EN50200. Using the apparatus and set up of BS EN50200, a sample of the cable was exposed to flame at a temperature of 930°C with simultaneous mechanical shock for a period of 60 minutes. After the required period of exposure to flame and shock without water spray, and with the flame and shock still being applied, the water spray is started. The application of water is continued for 60 minutes.
The water spray was applied by a water spray bar consisting of a metallic tube (copper or stainless steel) of thickness 1 mm and overall diameter 15.5 mm, closed at one end and open at the other to allow the inflow of water. The tube had one row of 17 holes of 0.85 mm diameter drilled on 30 mm centres and was positioned centrally with respect to the test sample of cable of Fig.l. The water spray bar was supplied by water at a flow rate of 0.8 litres per minute. The resulting water spray was centralised around the burned and/or burning portion of the test sample.
The cable continued to function for the duration of the test . The cable shown in Fig.2 has four copper cores 51 (two copper cores are not shown) . Each copper core 51 is made of stranded copper (7 strands of diameter 2.2mm which are circularised and compacted) and is of nominal diameter 5.9mm and cross section 25mm2. Each copper core 51 is surrounded by a layer of mica tape 59. The tape 59 is of 0.1mm thickness and is wound helically around the core 51 with each turn of the helix overlapping the next sufficiently so that each of the cores 51 is completely covered with a layer of mica tape 59. Each mica tape surrounded core 51, 59 has a surrounding layer of an insulating covering 52 of material sold under the trade mark XL-OHLS which consists of hydrated alumina in a polyethylene and polyethylene co-polymer composition. The layer 52 is applied by extrusion so that it surrounds the mica tape layer 59 and is immediately adjacent layer 59. The layer 52 has a radial thickness of 0.9mm. The overall diameter of each XL-OHLS and tape surrounded core 51, 59, 52 is 8.27mm.
A layer of water impermeable material 55 in the form of ALI-PET tape of thickness 50 microns surrounds the insulated cores 51, 59, 52. The layer of ALI-PET tape 55 is wound helically around the cores 51 so that each turn of the helix overlaps the next sufficiently so that the cores are completely covered with the layer 55 of water impermeable material, even when the cable is bent. The layer of ALI-PET tape 55 is of thickness 73 microns (the thickness of Aluminium is 50 microns and the thickness of PET is 23 microns) .
Optionally, a layer of woven glass tape may be wound helically around the layer of water impermeable material 55 (not shown in Fig 2) .
Around the layer of water impermeable material 55 (or, if present, the layer of woven glass tape) there is, in this embodiment, a nanocomposite layer 61 made up of material sold under the mark OHLS (RTM) , which consists of hydrated alumina in a polyethylene and polyethylene co-polymer composition, to which has been added nanocomposite filler Nanofil-15 from Sύdchimie in an amount of 6% by weight of the OHLS (RTM) material. The layer 61 is applied by extrusion and is of 0.9mm radial thickness . A layer 75 of steel wire armour (radial thickness 1.6mm) surrounds the nanocomposite layer 61. The layer 75 is made up of 44 steel wires of thickness 1.6mm which are laid and twisted in a manner which is well known in the art. An outer sheath 56 is also made up of material sold under the mark OHLS (RTM) to which has been added nanocomposite filler Nanofil-15 from Sύdchimie in an amount of 6% by weight of the OHLS (RTM) material. As with the embodiment of Fig 1, it will be understood that the outer sheath 6 and the layer 61 may also be made by mixing the components which together form OHLS (RTM) with the required amount of nanocomposite filler Nanofil-15. The outer sheath 56 is applied on the armoured layer 75 by extrusion and is of radial thickness 1.5mm.
It will be appreciated that the water impermeable layer 55 and nanocomposite sheath 56 function in a similar manner to the equivalent components in the embodiment of Fig 1 as described above. Thus, cable is able to maintain function in the event of a fire and prevent or delay failure due to short circuiting. The armour layer 75 and additional layer of nanocomposite 61 may provide additional physical protection and resistance to damage due to vibration and physical shock.
In a further embodiment (not shown) , the structure is similar to that shown in Fig 2 with the positions of nanocomposite layer 61 and water impermeable material 55 interchanged so that the layer of water impermeable material 55 surrounds the further (i.e. non-sheath) layer of insulating polymeric material which includes a nanocomposite filler (layer 61) .

Claims

C L A I M S :
1. A cable comprising one or more conductive cores each having an insulated covering; a layer of water impermeable material around the insulated cores; and an outer sheath of insulating polymeric material; wherein the insulating polymeric material of the outer sheath includes a nanocomposite filler.
2. A cable according to claim 1 wherein the layer of water impermeable material is impermeable to water at temperatures associated with a fire.
3. A cable according to claim 1 or 2 wherein the outer sheath is located immediately adjacent to the layer of water impermeable material .
4. A cable according to any of claims 1, 2 or 3 wherein the layer of water impermeable material is a laminated layer of a metal and a polymer.
5. A cable according to any preceding wherein the thickness of the water impermeable layer is between 10 and 80 microns.
6. A cable according to any preceding claim wherein the nanocomposite material is selected from those sold under the trade marks Nanofil, Nanocor, Bentone or Cloisite.
7. A cable according to any preceding claim wherein the amount of nanocomposite filler is between 1% and 10% of the total weight of the outer sheath.
8. A cable according to any preceding claim wherein the insulated covering for the conductive core(s) includes a silicone rubber and the cable further comprises a layer of porous siliceous material around the insulated core(s) and immediately adjacent the silicone rubber.
9. A cable according to claim 8 wherein the surface of the porous siliceous material is exposed directly to the silicone rubber .
10. A cable according to claim 8 or 9 wherein the layer of water impermeable material surrounds the layer of porous siliceous material.
11. A cable according to any preceding claim which further comprises a layer of armour.
12. A cable according to claim 11 wherein the outer sheath surrounds the layer of armour and is immediately adjacent thereto .
13. A cable according to any preceding claim which comprises a further layer of insulating polymeric material which includes a nanocomposite filler.
14. A cable according to claim 13 further which includes a layer of armour, wherein the layer of insulating polymeric material is within the layer of armour.
15. A cable according to claim 13 wherein within the layer of water impermeable material surrounds the further layer of insulating polymeric material which includes a nanocomposite filler.
16. A cable substantially as hereinbefore described with reference to Fig 1 of the attached drawings .
17. A cable substantially as hereinbefore described with reference to Fig 2 of the attached drawings .
EP03811026A 2002-11-13 2003-11-12 Fire-resistant cable Withdrawn EP1568048A1 (en)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GB0226508A GB0226508D0 (en) 2002-11-13 2002-11-13 Fire-resistant cable
GB0226508 2002-11-13
PCT/GB2003/004902 WO2004044927A1 (en) 2002-11-13 2003-11-12 Fire-resistant cable

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EP1568048A1 true EP1568048A1 (en) 2005-08-31

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WO (1) WO2004044927A1 (en)

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US7579397B2 (en) 2005-01-27 2009-08-25 Rensselaer Polytechnic Institute Nanostructured dielectric composite materials
DE102005017112A1 (en) * 2005-04-13 2006-10-26 Siemens Ag Moisture-repellent protective layer for a winding head of an electrical machine
GB2448778B (en) * 2007-05-18 2010-04-14 Draka Uk Ltd Fire-resistant cable
US8796372B2 (en) 2011-04-29 2014-08-05 Rensselaer Polytechnic Institute Self-healing electrical insulation
CN103337278A (en) * 2013-06-28 2013-10-02 无锡市新阳光电缆有限公司 High-temperature resistant twisted-pair cable
US20160348357A1 (en) * 2015-05-27 2016-12-01 Clarkwestern Dietrich Building Systems Llc Fire resistant framing accessory
US11486150B2 (en) 2016-12-20 2022-11-01 Clarkwestern Dietrich Building Systems Llc Finishing accessory with backing strip
ES1184958Y (en) * 2017-05-29 2017-08-30 Llona Maria Iciar Zubelzu Flame retardant cable protection cover
US11885138B2 (en) 2020-11-12 2024-01-30 Clarkwestern Dietrich Building Systems Llc Control joint
USD1026252S1 (en) 2020-11-12 2024-05-07 Clarkwestern Dietrich Building Systems Llc Control joint

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