GB2186123A - Cable ladder - Google Patents

Abstract

A cable ladder 1 has a demountable cover 3 made of intumescent thermoplastic fire-retarding material. In a fire the material melts and sinks down to coat the cables 2 while a further rise in temperature produces a cellular ceramic-like coating around the cables. Such a material is disclosed in US Patent No. 4,543,281 and can comprise an ethylene copolymer, with 50-450 parts by weight of aluminium hydroxide per 100 parts of polymer and 100-600 parts by weight of calcium carbonate or calcium-magnesium carbonate per 100 parts of polymer. <IMAGE>

Description

SPECIFICATION Cable ladder The present invention relates to an arrangement in connection with cable ladders, in which the cables in the cable ladder are covered with a fire retarding material.

Cables can be protected against fire either by building into the cables themselves the desired fire retarding properties, or the fire protection can be implemented externally by sectionalizing, fire protecting paint or similar.

The fire protection can have several aims, for example to prolong the time of operation during a fire, prevent ignition, prevent the spreading of fire and reduce the effect of the fire. The external means which are used today for achieving a fire protection of cables, include fire insulation of the cable ladders by means of for example layers of rockwool or ceramic fibre, by painting the cables with a foamable paint, wrapping the cables with a fire retarding tape, or covering the ladders with fire proof mats.

However, there exists an increasing requirement that the fire protecting means which are used, must not substantially aid in the smoke development, the development of corrosive gases or poisonous environment as such. Neither should the fire protecting means to any degree reduce the loading properties of the cables.

Most of the fire protecting methods used today entail substantial disadvantages, especially as regards the installation, "retrofitting" and maintenance of the cables in the cable ladders.

From international published application WO 80/02086 (PED-LOW) there is known a flameor fire-protective material which in connection with cable ladders or cable trays can be put over the cables in a form of a layer by spraying or by application with a brick layer's tool.

However, this known material forms a flexible layer around all the cables, a fact which complicates the replacement or later installation of cables.

The present invention provides an arrangement in connection with cable ladders which enables a simple and effective mounting and replacement of cables in a cable ladder, the maintenance and "retrofitting" being made simple.

According to the invention the fire retarding material takes the form of one or more covers adapted to the cable ladder for simple mounting and demounting, and the cover is made from a thermoplastic extrudable material having fire resistant properties, the material upon temperature rise being subjected to melting and sinking down upon the cables to cover them, further influence of the fire triggering the fire retarding properties of the material.

Such material can be of the type which is disclosed in US patent No. 4.543.281, to which attention is directed for full information.

This arrangement will reduce the risk of ignition, prevent spreading of fire and increase the time of operation of the cables in the cable tray in case of fire.

The protection of the cable ladder itself and the underside of the cables can be realized by coating thereof with the same material, or by other means.

The cover or covers can preferably be provided with holes or slits for ventilation of the cable ladder during normal conditions of operation. The openings should preferably be arranged such that they will be closed by fire, either by expansion of the material or by the sinking of the cover onto the cables.

To prevent spreading of fire along the cable ladder it may be sufficient to use covers having a length of 1 to 2 meters along certain sections of the cable ladder. In this case the ventilation holes or slits may be deleted because the cable ladder can be ventilated at the ends of the covers.

The system is devised to function with both horizontal and inclined parts of the cable ladder. For vertical parts there must be used other means, for example the provision of sections or similar.

In the following the invention will be further disclosed, reference being had to the attached drawing which illustrates an embodiment of the arrangement according to the invention.

On the drawing there is depicted a section of a cable ladder or tray 1, taking the form of a U-shaped trough in which there are arranged a plurality of cables 2. Along the cable tray 1 there is provided a cover 3 which is adapted to the cable tray 1 for simple mounting and demounting.

The cover 3 is provided with ventilation openings, for example in the form of perforations 4 which are made in the top surface of the cover 3, or in the form of slits 5 made in the side surfaces of the cover 3.

It is to be understood that the cover 3 is made from a thermoplastic extrudable material having fire resistant properties, and the material will upon a rise in temperature melt and sink down onto the cables for the coating thereof, a further influence of fire initiating the fire retarding properties of the material.

It is important that the material from which the cable tray cover 3 is made from, can be manufactured through a thermoplastic extrusion, and that it at the same time can prevent spreading of fire in case a fire should occur.

Aside from the fact that the material shall have fire retarding properties and should be extruded in profiles, it is preferably free from halogens.

For example, the cable tray cover can be manufactured by extrusion of the material which is disclosed in Norwegian Patent Application 83.4495, said material having such a property that it under the influence of heat will become soft at a temperature of approximately 95"C, and in dependence of the melting viscosity which changes with temperature, it will then during the influence of heat sink down onto the cables for the covering thereof as a protective coating. The material also has the property that it develops water vapour which foams the material and creates an atmosphere of water vapour around the cable tray.

The material which comprises a combination of ethylene copolymer, aluminium hydroxide and calcium carbonate and/or calcium-magnesium carbonate will at temperatures above 200"C due to the polymeric matrix component start to swell and develop a porous thermally insulating material. The swelling of the material is in the range of 30-40% on a linear basis, i.e. larger than 100% on a volume basis.

On heating the material from ambient temperature to a temperature about 1200 C, it will undergo a series of complex chemical and physical transformations, the material then providing a cellular structure rendering favourable fire protecting properties, i.e. the material is converted to a ceramic-like substance. The cellular structure to which the flame resistant material has been converted, after being subjected to a fire, can have sufficient mechanical integrity to be self-supporting and to be resistant to moderate mechanical attack, particularly as it is believed that the polymer and even the carbon content of the barrier material at elevated temperatures are pyrolyzed to, for instance CO and C0.

It is to be understood that the cover 3 has a shape which is adapted to the cable ladder or tray 1 for simple mounting and demounting. The perforations 4 or the slits 5 in the cover can appropriately be arranged such that they during a fire become closed either by swelling of the fire retardent material or by the sinking thereof down on to the cables 2.

The cable tray 1 illustrated on the Figure extends horizontally, but it is to be understood that corresponding covers 3 also can be used for inclined cable trays. However, for vertical parts thereof, special measures must be taken, for example by the provision of sections or similar.

The basic principle of the present arrangement is the shaping of a cover for a cable tray, such that is has an optimal form as regards the handling thereof, and as regards the mechanical protection of the cables, as well as the cooling thereof, the cover not being permanently connected with the cable tray or the cables.

The material in the cover is to be choosen such that it is mechanically strong enough against handling and other influences at ambient temperature, but softens at higher temperatures (100-200"C), such that the cover will collapse and sink down onto the cables for the coating thereof. The material should be a polymeric composition which prevents the spreading of fire, and which is difficult to ignite.

This is achieved through the use of previously known fire retarding polymers, for example conventional forms of modified PVC or fire retarding PE. For many applications it is a desire not to use materials which include halogens, and it is then possible to use for example copolymers of polyethylene which are filled with a great part of ATH and other non organic fillers. A special subgroup of such materials are disclosed in US Patent No.

4.543.281 in which in addition to the above mentioned properties, there are disclosed materials which at high temperatures develop a cellular ceramic.

A preferred covering material comprises a thermoplastic matrix, 50-450 parts by weight of a filler comprising aluminium hydroxide related to 100 parts of the matrix, as well as 100-600 parts by weight of material selected from calcium carbonate and calcium-magnesium carbonate related to 100 parts of the matrix; it may also include 11-30 parts by weight of elasticizer, 0-10 parts by weight of polymer softening agent, 8-15 parts by weight of lubricating agent, 8-15 parts by weight of calcium oxide and 1 part by weight of colouring agent.

Claims (10)

1. A cable ladder for cables and one or more covers for easy mounting on and demounting from the ladder and made from thermoplastic extrudable material having fire resistant properties-, said material being such that upon undue temperature rise it melts and sinks down on the cables and that further influence of fire triggers its fire retarding properties.

2. A ladder and cover(s) according to claim 1 wherein the cover material is of the type disclosed in US Patent No. 4,534,281.

3. A ladder and cover(s) according to claim 1 or 2 wherein the ladder has a coating of material corresponding to that of the cover.

4. A ladder and cover(s) according to any of claims 1 to 3 wherein at least one cable cover has ventilation holes or slits.

5. The use of a fire or flame resistant material which can be extruded thermoplastically to unspecified profile length, as a cover for a cable ladder, the material upon temperature increase due to a fire being subject to melting and sinking down on to the cables for the coating thereof and the protection of the cables against fire.

6. The use of a fire or flame resistant material, comprising a thermoplastic matrix, 50-450 parts by weight of a filler comprising aluminium hydroxide related to 100 parts of the matrix, as well as 100-600 parts by weight of material selected from calcium carbonate and calcium-magnesium carbonate related to 100 parts of the matrix in extruded form as a cover for cable ladders.

7. The use of a material as defined in claim 5 or 6, as a cover for cable ladders, the material also comprising 11-30 parts by weight of elasticizer, 0-10 parts by weight of polymer softening agent, 8-15 parts by weight of lubricating agent, 8-15 parts by weight of calcium oxide and 1 part by weight of colouring agent.

8. The use of material as defined in claim 5, 6 or 7, in extruded form, as a cover for cable ladders, the ladder being provided with ventilation openings in the form of holes and/or slits which during a fire become closed either by swelling of said material or by the sinking down of the cover onto the cables in the cable ladder.

9. A cable ladder cover substantially as herinbefore described.

10. A covered cable ladder substantially as hereinbefore described.