CABLE SYSTEM FOR USE IN HAZARDOUS ENVIRONMENTS

Abstract: A method of forming a seal between a tubular cable outlet projecting from a joint enclosure (1) and a cable (21) passing through the cable outlet into the enclosure (1) in which a heat-recoverable sleeve (11) is shrunk around the cable (21) and the cable outlet (7, 8, 9); an electrically conductive, guard sleeve (13) is placed around the heat-recoverable sleeve (11) so that it substantially surrounds it and extends beyond each of its ends. The cable (21) sealed to the joint enclosure (1) can be used within a zone 1 hazardous environment, for example in a sewer. The guard sleeve (13) is preferably of stainless steel, so as to resist attack by rodents as well as enabling the joint enclosure (1) to meet zone-1 explosion-resistance requirements when the cable includes power supply conductors, for instance for powering electronic communication equipment within the enclosure (1).

Description: CABLE SYSTEM FOR USE IN HAZARDOUS ENVIRONMENTS The present invention relates to cable systems for use in hazardous environments. In particular it relates to a method of forming a seal between a cable and joint enclosure, for use within a hazardous environment, and to a formed sealed joint within a hazardous environment. Hazardous environments are areas in which the atmosphere may become explosive. Explosive atmosphere is defined as a mixture of ignitable substances in the form of gases, vapours or mixtures with air under atmospheric conditions in critically mixed ratios such that excessive high temperature, arcs or sparks may cause an explosion. According to Elex V, DIN VDE 0165-1991, endangered areas are classified into zones, according to the probability of the existence of a dangerous explosion prone atmosphere. The present invention is directed to use within so-called "zone 1" hazardous environments. A zone 1 explosive atmosphere is, according to Elex V, DIN VDE 0165-1991, a zone in which an explosive mixture can occur during normal operation. Examples of zone 1 hazardous environments include sewers, petrochemical plants and pipelines, and petrol stations. It has been proposed to use the existing infrastructure of sewers as passageways for carrying cables, for example communications or power cables. As described above, the environment within a sewer network is classified as a "zone 1" environment. In general objects to be used in zone 1 hazardous environments must satisfy the criteria set out in European Standard EN 50014:1997. In particular, it is important that any objects that are to be used within such an environment are designed such that under normal conditions of use, maintenance and cleaning , danger of ignition due to electrostatic charges is avoided, thereby avoiding possible explosions. Also the objects should be designed so that the maximum surface temperature shall not exceed a specified temperature, usually being the ignition temperature of any gasses, fluids or solids present. The value of the specified maximum temperature depends on the exact nature of the environment, and for zone 1 hazardous environments varies between 85°C and 450°C. Furthermore objects used within a zone 1 hazardous environment must be UV resistant, chemically inert, and resistant to flexing even at temperatures up to a maximum specified temperature usually corresponding to the ignition temperature of any gasses, liquids or solids present in the environment. Especially where the zone 1 hazardous environment is a sewer system, any object used within the system must also be resistant to attack by rodents. Cables known today include optical cables or copper core cables, both for communications purposes, electrical power cables, and composite cables including both optical fibres and copper conductors. Whatever the system, the usual network configurations include joint enclosures at various points in the network. The joint enclosures include means for joining, terminating, splitting, tapping etc. of the cable , in a manner well known to the man skilled in the art. Where cable networks are to be positioned within an existing conduit system, the positioning is generally such that the cable joint enclosures are easily accessed. For, example, where cable networks are to be introduced into an existing sewer system, the joint enclosures are usually arranged immediately beneath man-holes for easy access. Where cable systems are to be introduced into zone 1 hazardous environments, such as sewer networks, not only the cable jacket and the outer surface of the joint enclosure, but also the point at which the cable enters any joint enclosure, must be protected against the harsh environment. We have discovered a method and sealed system which achieves this. Accordingly a first aspect of the present invention provides a method of forming a seal between a tubular cable outlet projecting from a joint enclosure and a cable passing through the cable outlet into the enclosure, the method comprising: (i) positioning a heat-recoverable sleeve around the cable and the cable outlet, and applying heat to the sleeve to recover part of the sleeve into sealing conformity with the outlet, and part of the sleeve into sealing conformity with the cable; and (ii) positioning an electrically conductive guard sleeve around the heat- recoverable sleeve so that it substantially surrounds the heat-recoverable sleeve and extends beyond each end of the heat-recoverable sleeve, whereby the joint enclosure with the cable sealed thereto can be used within a zone 1 hazardous environment . Typically steps (i) and (ii) are carried out outside the hazardous environment, and the method comprises the additional step of: (iii) positioning the joint enclosure, with the cable sealed to the cable outlet thereof and protected by the guard sleeve, into the hazardous environment. In one embodiment the hazardous environment is a sewer system. Reference will be made throughout this specification to operation within a sewer system. It is understood that the specification applies equally to other zone 1 hazardous environments. A second aspect of the present invention provides a sealed cable system, contained within a zone 1 hazardous environment (preferably a sewer system) , the cable system comprising: (i) a cable joint enclosure comprising a cable outlet projecting therefrom; (ii) a cable passing through the cable outlet into the joint enclosure; (iii) a heat recovered sleeve that has been recovered so that part of the sleeve is in sealing conformity with the cable outlet, and part of the sleeve is in sealing conformity with surface of the cable; and (iv) an electrically conductive guard sleeve positioned substantially to surround the heat-recovered sleeve and such that it extends beyond each end of the heat recovered sleeve. The method and sealed cable system according to the invention each incorporate a heat-recoverable sleeve. Heat- recoverable sleeves are well known in the field, and are sleeves which, if heated, change their dimensional configuration. Usually, and preferred in the present invention, the heat-recoverable sleeve is heat-shrinkable, and shrinks radially when heat is applied thereto. According to a preferred method of the invention, the heat is applied by means of a hot air gun. As an alternative heat could be applied with a torch. Typically heat-recoverable sleeves comprise polymeric materials, for example cross-linked polyolefin material, especially cross-linked polyethylene. Most inexpensive, commercially available heat-recoverable sleeves are generally therefore electrically insulating. The heat-recoverable sleeves used in the present invention are typically electrically insulating, but electrically conductive sleeves could be used. Preferably the heat-recoverable sleeves are lined with adhesive to enhance the sealing. Preferably the sleeves are lined with a hot melt adhesive, which is activated by the heat applied to recover the sleeve. Adhesive lined heat- recoverable sleeve are known. Although the heat-recoverable sleeve is surrounded by the guard sleeve, gasses and liquids can pass into the space between the heat-recoverable sleeve and the guard sleeve. For example, in a sewer system, the cable system may be totally or partially immersed in dirty water, and/or may be exposed to corrosive gases such as methane within the sewer system. The material of the heat-recoverable sleeve and its adhesive lining is therefore preferably selected to be chemically inert to corrosive forces within the sewer system, e.g. to the corrosive action of the dirty water or corrosive gasses within the sewer system. The material for the heat- recoverable sleeve is preferably also UV resistant. An especially preferred material for the heat-recoverable sleeves is a cross-linked polyolefin, especially a cross- linked polyethylene, most especially cross-linked medium density polyethylene, or cross linked high density polyethylene or blends thereof. It is desirable that the heat-recoverable sleeve is recovered into sealing conformity with the cable outlet, and with the outer surface of the cable, over a significant length, preferably at least 75 mm, more preferably at least 100mm, especially preferably at least 150 mm in order to form a reliable seal. For example, in a sewer system, this length of seal ensures that the dirty water or gases do no enter the joint enclosure through the space between the cable and the cable outlet. The method and sealed cable system of the present invention include an electrically conductive guard sleeve. Preferably the guard sleeve is electrically conductive to the extent that it has an insulation resistance that does not exceed IGohm at (23+2) °C and (50+5)% relative humidity as measured in accordance with 23.4.7.8 of European Standard EN 50014:1997. Preferably the guard sleeve comprises a metal. A particularly preferred metal is steel, especially stainless steel. Other metals that could be used include aluminium, cast steel, galvanised steel and brass. As an alternative to a metal, a polymeric material with an appropriate conductivity could be used. The electrically conductive guard sleeve is arranged according to the invention such that it substantially surrounds the heat-recoverable sleeve, and extends beyond each end of the heat-recoverable sleeve. This arrangement means that the possibility of electrostatic charges building up on the insulating surface of the heat-recoverable sleeve is avoided, since it is surrounded by a mass of conductive material . The guard sleeve, may be substantially continuous in surrounding the heat-recoverable sleeve. In one embodiment the guard sleeve comprises a generally cylindrical part that may, for example, be cast metal or formed from wrapped sheet metal. In another embodiment the guard sleeve may comprise an open configuration, for example a metal mesh. Either a continuous or an open configuration will function substantially to prevent electrostatic charges building up on the insulating surface of the heat-recoverable sleeve. The guard sleeve is preferably also resistant to flexing, even at elevated temperatures, especially at temperatures higher than 85°C. This preferred characteristic of the guard sleeve protects the heat-recoverable sleeve contained within it from damage by any object leaning towards the sleeve within the hazardous environment. The preferred heat-shrinkable polyolefinic recoverable sleeve would typically be softened at temperatures of about 85°C, and in the absence of the more rigid guard sleeve surrounding it would therefore be damaged by a leaning object. Where the present invention is to be used within a sewer system, the guard sleeve is preferably also sufficiently strong to be resistant to rodent attack. For example a continuous cylindrical cast stainless steel sleeve of thickness 2mm, or a piece of sheet stainless steel of thickness 1mm, wrapped to form a continuous cylinder, would satisfy this rodent resistant criteria. Preferably the guard sleeve has a thickness of at least 0.4mm. The guard sleeve is generally tubular. It may be closed in cross section, or it may be open in cross-section, e.g. it may comprise two half-shells which are held together in operation. The parts may be mechanically or otherwise held together, or may simply be placed in adjacent, or near- adjacent relationship to each other. The material of the guard sleeve is also selected to be chemically inert, and UV resistant. Most metals will satisfy these criteria Stainless steel is especially preferred. Also cast steel, galvanised steel, aluminium and brass may be used. The combination of a heat-recoverable (preferably polymeric) sleeve, with a more rigid conductive guard sleeve, therefore provides a good, UV resistant, chemically resistant seal between the cable outlet and the cable (by means of the recoverable sleeve) , while ensuring that the system is resistant to static charges and consequent explosions, protected from rodents, and protected from damage from leaning objects (by means of the guard sleeve) . The heat- recoverable sleeve and the guard sleeve therefore operate together to provide an effective system for use in a zone 1 hazardous environment. The cable used in the method and sealed system of the present invention may carry optical fibres or electrical conductors (e.g. copper), or both. In one embodiment according to the invention the cable carries optical fibres and electric conductors for powering so-called "active electronics" within the joint enclosure. The electric conductors may power routers or the like within the joint enclosure . Typically the joint enclosure comprises a generally box- shaped housing with one or more tubular outlets projecting therefrom for receipt of cables. The housing may comprise a base and a lid which can be separated to access the jointing region within the housing to allow network connections to be made. The tubular cable outlets may be any shape in cross section, but are generally circular or oval in cross-section. Usually there will be a plurality of outlets, e.g. four to ten outlets. Typically circular cross-section outlets receive individual cables, and oval outlets receive a cable loop from which a tap is to be taken. The joint enclosure will generally contain splice trays, optical fibre organisers, electronic circuit boards, etc, depending on the nature of the cable entering, and the connection required within the joint enclosure. So far the method steps and sealed system discussed above have been directed towards forming a seal between the cable and the cable outlet into which it passes. Where cables are damaged part way along their length, away from the junction between the cable and the joint enclosure, then if the cables (either optical cables or electrical cables) are unfilled, gasses, water, or other fluids may enter the joint enclosure through the cable itself. The seal described so far, between the outside of the cable and the cable outlet, can not prevent passage of these fluids through the cable itself. Therefore, a preferred embodiment of the method of the present invention comprises sealing the interior of the cable in addition to sealing between a tubular cable outlet and a cable. The step of sealing the interior of the cable is preferably carried out by pouring a resin into the interior of the cable. The resin is preferably introduced after the step of recovering the heat- recoverable sleeve aground the cable and the cable outlet. Where a plurality of cable outlets project from the joint enclosure, e.g. from a lid of a joint enclosure, the resin- pouring step is conveniently carried out by pouring a mass of resin into the lid of the joint enclosure. Some resin will flow into each cable as desired, and some into the annular space between the cable and the cable outlet. Provided the resin is poured after the heat-recoverable sleeves are recovered, no resin will escape from the cables and enclosure. Generally the resin pouring step is carried out before the cable is stripped for jointing in the joint enclosure. A suitable resin is a two part curable polyurethane or epoxy resin. As described above, the surrounding mass of an electrically conductive material around the heat-recoverable sleeve substantially prevents the build up of a static charge on the surface of the heat-recoverable sleeve. The outer surface of the main length of the cable passing through the hazardous environment, e.g. passing along the length of a sewer pipe, is generally polymeric. Typically this outer surface of the cable is protected from static-charge build up by earthing it at regular distances. For example cleats may be attached to secure it to the internal surface of the sewer pipe every 2 metres. The joint enclosure itself is generally made from a metallic or other conductive part, so there is no static charge build-up on the enclosure itself. An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, wherein: Figure 1 is a perspective view of a joint enclosure having a plurality of cable outlets projecting therefrom, and heat- recoverable sleeves and guard sleeves to be sealed onto the cable outlets; and Figure 2 is a sectional view showing one heat-recoverable sleeve and corresponding guard sleeve sealed onto one cable outlet of Figure 1. Referring to the drawings, Figure 1 shows a stainless steel joint enclosure 1 containing optical fibre organiser trays, and electronic boards (not shown) , The metal enclosure 1 comprises a body portion 3 and a lid 5 which can be separated to access the interior of the enclosure for forming connections and the like. Six cable outlets 7,8 that are generally circular in cross-section, and one cable outlet 9 that is generally oval in cross-section project from the lid 5 of the joint enclosure 1. Some of the circular cross- section outlets 7, and the oval outlet 9 are open, ready for receipt of a cable. Others of the circular cross-sectioned outlets 8 are sealed. The seals may be broken during the lifetime of the system where network modifications are needed. Typically each outlet projects by a distance of about 300mm. Appropriately sized, adhesive-lined, heat- shrinkable polyethylene sleeves 11 are provided for each cable outlet 7,9. The sleeves are a loose fit around the outlets 7, 9 prior to heating. The sleeves 11 are tubes of closed cross-section which are threaded over the end of the cable before it is inserted into the respective cable outlet 7. Heat-shrinkable polymeric sleeves 11 are typically 350mm in length. Stainless steel guard sleeves 13 and 15 are provided for fitting around shrunk sleeves 11. The guard sleeves 13, 15, are tubular and are longer than the shrinkable sleeves 11. Guard sleeve 15, for the oval cross- sectioned cable outlet 9, is of open cross-section, comprising two mating half-shells. Guard sleeve 13, for the circular cross-sectioned cable outlet 7, is of closed cross- section. The guard sleeve 13 of closed cross-section must be threaded over the end of the cable 21 before it is inserted into its respective cable outlet 7. The guard sleeve 15 of open cross-section can be applied later. Each guard sleeve 13, 15 is wider at its end 19 nearest to the enclosure 1, than it is at its other end 17. According to the method of the invention, heat- shrinkable sleeve 11, and guard sleeve 13 are threaded over the end of a cable 21, and then cable 21 is inserted into a cable outlet 7 projecting from lid 5 of the joint enclosure 1. The sleeve 11 is then heated by a hot air gun, causing it to shrink into sealing conformity with the outlet 7 and with the outer surface of cable 21. The guard sleeve 13 is then positioned over the shrunk sleeve 11 so that it substantially surrounds it, and extends beyond each end of the sleeve 11. The sleeve 11 is in sealing conformity with the outlet 7 over a length of about 150 mm, and with the outer jacket of the cable over a length of about 150 mm. Figure 2 shows the arrangement after sleeve 11 has been shrunk, and after the stainless steel guard 13 has been positioned. After the sleeve 11 has been shrunk onto the cable outlets 7 and 9, the lid 5 is inverted (so that the cable outlets extend downwards from the lid 5) and a thermosetting resin (not shown) is poured into the lid 5 so that it flows into the cables 21 and into the annular spaces between the cables 21 and the sleeves 11. It is prevented from passing into the joint enclosure itself by the sealing of sleeve 11 onto each cable outlet. The resin cools and sets and prevents any corrosive gasses which might enter the cables through damaged parts along the length of the cable, entering the joint enclosure. The next step is for the cables 21 to be stripped for connection within the joint enclosure 1. The application of the sleeves 11, 13 and 15, and the stripping of the cable, and jointing work within the enclosure is carried out outside of a sewer, with access to the sewer via a man hole. Then the completed system, with 5 sleeves 11, 13, 15 installed is introduced into the sewer. The joint enclosure 1 is earthed, and the stainless steel sleeve 13, which substantially surrounds the polymeric sleeve 11, ensures that no electrostatic charges build up on the insulating surface of the sleeve 11. The guard sleeves 13, 10 15 also protect the sleeve 11 from rodent damage, and protect the sleeve 11, which softens during recovery, from damage from leaning objects. The sleeve 11 itself provides a fluid resistant seal preventing ingress of corrosive liquids or gases between the outer surface of the cable and the cable 15 outlet through which the cable passes.

Claims: Clai s : 1. A method of forming a seal between a tubular cable outlet projecting from a joint enclosure and a cable passing through the cable outlet into the enclosure, the method comprising: (i) positioning a heat-recoverable sleeve around the cable and the cable outlet, and applying heat to the sleeve to recover part of the sleeve into sealing conformity with the outlet, and part of the sleeve into sealing conformity with the cable; and (ii) positioning an electrically conductive, guard sleeve around the heat-recoverable sleeve so that it substantially surrounds the heat-recoverable sleeve, and extends beyond each end of the heat- recoverable sleeve; whereby the cable sealed to the joint enclosure can be used within a zone 1 hazardous environment. 2. A method according to claim 1, wherein steps (i) and (ii) are carried out outside a zone 1 hazardous environment system, and wherein the method comprises the additional step of: (iii) positioning the cable joint enclosure, with the cable sealed to the cable outlet thereof and protected by the guard sleeve, into the zone 1 hazardous environment. 3. A method according to claim 1 or 2, wherein the zone 1 hazardous environment is a sewer system. 4. A method according to any preceding claim, wherein the heat-recoverable sleeve is a heat-shrinkable polymeric sleeve, preferably adhesive-lined. 5. A method according to claim 4, wherein the heat- shrinkable polymeric sleeve has an electrically insulating outer surface. 6. A method according to any preceding claim, wherein the guard sleeve comprises a metal. 7. A method according to any preceding claim, wherein the guard sleeve comprises stainless steel. 8. A method according to any preceding claim, wherein the guard sleeve has a continuous outer surface. 5 9. A method according to any of claims 1 to 17, wherein the guard sleeve comprises a mesh. 10. A method according to any preceding claim wherein the guard sleeve comprises steel having a thickness of at least 0.4mm. 10 11. A method according to any preceding claim, comprising forming a seal within the cable by pouring a resin into the cable. 12. A method according to claim 11, wherein the joint enclosure comprises a lid having a plurality of cable 15 outlets projecting therefrom, the method comprising positioning the lid such that the cable outlets project downwards therefrom, and pouring resin into the lid such that it flows into the cables. 13. A sealed cable system, contained within a zone 1 20 hazardous environment, the cable system comprising: (i) a cable joint enclosure comprising a cable outlet projecting therefrom (ii) a cable passing through the cable outlet into the joint enclosure; 25 (iii) a heat recovered sleeve that has been recovered so that part of the sleeve is in sealing conformity with the cable outlet, and part of the sleeve is in sealing conformity with surface of the cable; and (iv) an electrically conductive guard sleeve positioned 30 around the heat recovered sleeve such that it substantially surrounds the heat recovered sleeve and extends beyond each end of the heat recovered sleeve. 14. A cable system according to claim 13, wherein the hazardous environment is a sewer system. 35 15. A cable system according to claim 13 or 14, wherein the cable contains optical fibres 16. A cable system according to claim 13, 14 or 15 wherein the cable contains, or additionally contains, electrical conductors . 17. A method of forming a seal between a tubular cable outlet projecting from a joint enclosure and a cable passing through the cable outlet into the enclosure, substantially as described with reference to the drawings . 18. A cable system substantially as described with reference to the drawings .

Inventors: WHITESMITH PETER JOHN, WHITESMITH, PETER, JOHN
Applicants: CORNING COMMUNICATIONS LTD, WHITESMITH PETER JOHN, CORNING COMMUNICATIONS LIMITED, WHITESMITH, PETER, JOHN
Application year: 1999
Main classification: H02G15
IPC codes: G02B6, H02G1, H02G3, H02G15, H05K7