WO2000072420A1

WO2000072420A1 - Cable blocking

Info

Publication number: WO2000072420A1
Application number: PCT/GB2000/001902
Authority: WO
Inventors: Peter Van Overmeir; Bart Van Meeuwen; Luc Michiels; Jean-Marie Etienne Nolf
Original assignee: Tyco Electronics Raychem Nv; Tyco Electronics Uk Ltd.
Priority date: 1999-05-19
Filing date: 2000-05-18
Publication date: 2000-11-30
Also published as: GB9911615D0

Abstract

In a cable joint at least two cable cores (20) are exposed beyond the ends of outer jackets (60) of at least two electric power cables (30) and conductors of the at least two cores (20) are electrically connected to each other. Sealing material (25) that is substantially impervious to moisture is located around the cores (20) so as to prevent any moisture reaching the electrical connections of the conductors. Blocking material (2) is located within the joint so as to prevent the sealing material (25) from migrating away from the connections into or around the cables. A protective sleeve (40) encloses the cable connections and the sealing and blocking materials. The blocking material (2) substantially surrounds a relatively rigid support member (1) capable of maintaining spacing between the separated cores (20).

Description

WO 00/72420 . ] . PCT/GB00/01902

CABLE BLOCKING

This invention relates to a method of blocking an electric power cable joint against the ingress of water or other moisture, hereinafter referred to generally as "moisture", and to a moisture-blocked cable joint. The invention is particularly though not exclusively applicable to joints between multi-core cables, that is to say to cables containing at least two cores, and typically cables having either three or four cores, possibly with the addition of an earth core. The joint may be an in-line joint, between two cables, or it may be a branch joint, between two, three or more cables. In the case of a branch joint, the main cable may be unbroken and have a branch cable leading therefrom, or the joint may be between two main cables and a branch cable.

International Patent Application WO 91/00601 (Raychem) describes a joint between electric power cables in which at least two cable cores are exposed beyond the ends of outer jackets of at least two cables and in which conductors of the two cores are electrically connected to each other, wherein sealing material that is substantially impervious to moisture is located around the cores so as to prevent any moisture reaching the electrical connections of the conductors; wherein blocking material is located within the joint so as to prevent the sealing material from migrating away from the connections into or around the cables; and wherein a protective sleeve encloses the cable connections and the sealing and blocking materials.

Also described is a method of forming a moisture-blocked joint between at least two electric power cables; wherein outer jackets of the cables are removed to expose the cores thereof, and insulation of the cores is removed or disturbed for access to the conductors thereof; wherein electrical connection is made between the conductors of the cables; wherein sealing material that is substantially impervious to moisture is disposed around the cable cores so as to prevent any moisture reaching the electrical connections; wherein blocking material is located within the joint so as to prevent the sealing material from migrating away from the connections into or around the cables and wherein a protective sleeve is positioned around the jointed cables so as to enclose the cable connections and the sealing and blocking materials. The blocking material is thus arranged specifically to prevent migration of the water-impervious sealing material along the cable itself. This is of particular importance in the case of multi-core cables, where paths that potentially could allow transmission of moisture inherently exist in the cable and the region between the cores. The cable blocking disclosed for example in the other patent specifications mentioned in WO 91/00601 is not effective in this area since it is applied only around the outside of a plurality of conductive elements.

The seafing material may be arranged within the joint such that it encapsulates, i.e. completely encloses the electrical connections between the cables. In this case, even if moisture should find its way to the inside of the protective sleeve, whether from within the cable itself or by flowing in between the cable and the sleeve, it will be prevented from reaching the electrical connections, which are electrically the most vulnerable parts of the joint. The electrical connections in the case of a branch joint may advantageously be made by a connector, such as a compact ring connector, of known configuration, and in the case of an in-line joint, the connections may be made by crimping. The sealing material can then completely encapsulate the branch or crimp connectors. Such positioning of the sealing material thus completely ensures that any moisture escaping into the joint between the conductors and the individual core insulation cannot form a conductive path in the connection region from one conductor core to another.

The sealing material, in the case of a multi-core cable, alternatively, or additionally, may be arranged so as to block ingress of moisture from within the cable by being located in the crutch region between the cores of the cables where the cores emerge from the cable jacket. A further quantity of sealing material may then advantageously be located around the cores at the crutch region adjacent each cable jacket.

It may well be sufficient that the blocking material merely extends axially between the sealing material and the crutch region or connection region as appropriate, or between the two or three portions of sealing material where the latter is located at the connection region and also at least one of the crutch regions. However, the blocking material may encapsulate the sealing material, and may extend completely across the joint, that is to say, it abuts or even overlaps the able jacket on each side of the joint, and is preferably sealed thereto. Preferably, the blocking material encapsulates the cable cores, between and around the cores, in the crutch region of multi-core cables.

The blocking and/or sealing material may be applied to the joint in the form of a tape or a sheet, or as a mastic or hot-melt adhesive.

Material, for example a sealant such as a mastic, that is impervious to moisture and that is suitable for use as the sealing material is known per se, as is its use in the moisture blocking of a cable, for example a telephone cable. However, in order to have a material that has sufficiently low viscosity to allow it to penetrate and seal completely the region between the three or four cores of a multi-core electrical power cable the material generally has to be non-curing or non-crosslinkable. The problem to be overcome here is that the material has to be hot (lower viscosity) in order to flow, but the cable cores are of relatively large cross-section (ranging from 1.5 mm² to 300 mm² or more, depending on the current rating of the cable), of highly thermally conductive material (usually copper or aluminium), and are close together. Thus the cores act as a very efficient heat sink. The material must not cool too much nor too quickly, nor cure, until the regions between, and around, the cores of the cable and/or the connections are substantially completely filled with the sealant. During thermal cycling of the cable in normal operation, the conductor temperature can reach as high as 95°C. At this temperature, and particularly under the influence of water pressure (which can be equivalent to a head of water of as much as 1 metre, or more) from within the cable, there is a tendency for the sealant to be physically driven away along the cable, thus allowing moisture to enter the electrically vulnerable region around the core connections, possibly leading to electrical breakdown of the cable. The problem is exacerbated by the fact that the cores of electric power cables are large and rigid (being of solid or stranded configuration), and by the requirement for making the cut-back length (and thus the exposed length of the cores) at the joint as short as possible. This means that the cores cannot be pulled far apart from each other for fear of damaging the cable jacket thus making it difficult to insert sealing material between the cores. The minimum cross-sectional area of each conductor of a low voltage electric power cable would be the region of 6 mm", with a corresponding effective core diameter of about 4 mm, whilst typical dimensions for a 1 kV cable would be 150 mm and 18 mm respectively. A typical 1 kV branch cable would have a conductor cross-

2 _ section of about 50 mm to 70 mm and a core diameter of about 12 mm.

The moisture-, and especially water-, impervious sealing material, preferably being a mastic, is advantageously chosen for its ability to form a good bond both to plyvinylchloride and to polyethylene, these being the most common materials used as insulation for plastic insulated cables. The material may, however, not bond but may form the required moisture sealing by means of external pressure applied thereto. It is also advantageous that the sealing material bond to metals, such as aluminium, used for connectors of the cable conductors. Since its positioning is in some instances such that not a great deal of heat can be expected to reach it, for example between the cores of a cable, it should be sufficiently soft at the relatively low temperatures around 40° it will in fact experience on installation of the cable joint. A composition based on a 50-50 mixture (by weight) of polyisobutylene and atactic polypropylene has been found to be particularly suitable. There is no specific requirement for this material to cure, but this would not be a disadvantage provided that good cable blocking was obtained. However, advantageously the sealing material is not rigid, thus allowing it to accommodate thermal stresses, occurring for example during load cycling of the operating cable, that result in axial movement of the cable. Although the sealing material located between the cable cores may be the same as the sealing material located around the cores, these materials can be different.

In a preferred embodiment, the sealing material in the form of a mastic has a melting point between about 91 °C and 93°C as measured by the ring and ball (R and B) softening method, or a 50% penetration between about 50°C and 54°C as measured by the thermo-mechanical analysis (TMA) method. The R and B melting point should exceed the maximum operating temperature of the cable, which for a PVC insulated cable would typically be about 70°C and for a polyethylene insulated cable would typically be about 90°C. Its viscosity advantageously has a temperature profile as given by the following table:

The material should have a water absorption of < 1 % . The sealing material should wet out the surface of the components of the joints it contacts and should peel therefrom in a cohesive manner. That is to say, its peel strength (with respect to the joint components) should be low compared with the cohesive strength of the material itself.

Preferred examples of sealing mastic contain an EVA acid terpolymer (such as Elvax 4310 available from DuPont and comprising 24 % to 27 % by weight of the weight of the total composition), polyisobytylene (such as Oppanol B10, and comprising 60% to 55 % of the total composition), a tackifier resin (such as Escorez 5380, and comprising 15 % of the total composition), an antioxidant (such as Irganox 1010, and comprising 1 % of the total composition), and a silica filler (such as Aerosil 200, and comprising 0 to 2% of the composition).

The blocking material can advantageously be a fibrous material, and may comprise synthetic or glass fibres or a mixture thereof. The material may be provided as felt in strip or sheet form. Alternatively, the blocking material may comprise a closed-cell foam. Advantageously the blocking has some resilience after installation so as to enhance its conformity and contact with the cable cores. The blocking material can function solely as a physical block to prevent movement of the sealing material, and as such it need not itself seal against ingress of moisture. However, it is envisaged that the blocking material may be impregnated with a sealing material, preferably curable, so as further to restrict entry of moisture into the joint. When the blocking material is in strip or sheet form it can conveniently be inserted in one or more pieces between cable cores in regions where the cores cannot physically be prised far apart from each other.

The present invention provides an improved form of blocking material for the aforementioned purposes, wherein the fibrous or foam material surrounds a relatively (relative to the fibrous or foam material) rigid support member capable of maintaining spacing between the separated cores of a multi-core cable while the fibrous or foam material performs its blocking function of preventing the aforementioned migration of sealing material. The support member thus prevents the cores from crushing the fibrous or foam material to such an extent that the cores approach each other too closely.

It is noted that relatively rigid cable separators for separating cable cores are known per se. An example of a cable separator is disclosed in EP 0 153 174, where the separator is provided with a mastic coating. A support member surrounded by a fibrous or foam material is not disclosed. EP 0 372 936 discloses a cable separator which is not provided with a coating.

Suitable basic materials for cable blocking are known from the aforementioned WO 91/00601. The relatively rigid support member of the present invention may be made of any suitable, preferably electrically insulating material. Preferred materials include polymeric materials, perhaps high-density polyethylene or nylon, preferably in elongate rod-like form. The support member may preferably be extruded, preferably with the fibrous or foam material moulded or extruded (preferably co-extruded) around it. The support member may be of suitable shape, for example cruciform to fit between four cable cores, but may preferably be of simple elongate rod shape for convenient low-cost extrusion.

The invention includes a method of forming a cable joint, an article comprising the combination of the blocking material and the support member, and a kit of parts comprising such an article together with the other (known) components for forming the sealed cable splice.

The present invention will now further be explained with reference to an exemplary embodiment illustrated in the accompanying drawings, in which:

Figure 1 schematically shows, in perspective, an article for cable blocking according to the present invention;

Figures 2a and 2b schematically show how the article of Fig. 1 can be applied in a cable joint; Figure 3 schematically shows the position of blocking arrangements in a cut-open cable.

A preferred form of the blocking material with support member is shown in FigJ . A cable blocking article 10 comprises an extruded plastics rod 1 of substantially circular cross-section surrounded by extruded closed-cell polymeric foam 2 of substantially square or rectangular cross-section. Other cross-sectional shapes may of course be used as desired, such as a round or oval shape.

Figure 2a shows a pair of blocking articles 10 as shown in Fig 1 inserted in a first step between the cores 20 of a cable 30 seen in end view. The cores 20 are embedded in sealing material 25. The support rods 1 maintain core spacing and prevent excessive crushing of the foam 2. In Fig.2b, a mastic tape 40 (known per se) is shown wrapped around the articles 10 in a second step. Instead of the tape, a heatshrink sleeve could be applied to enclose the sealing material 25 and the blocking material 2.

Figure 3 indicates schematically the position B, B' of the blocking arrangements comprising articles 10 in relation to the cut ends of the cable sheaths 60. As can be seen, the blocking articles 10 are applied adjacent the ends of the cable sheaths.

It will be understood by those skilled in the art that the present invention is not limited to the embodiments shown and that many additions and modifications are possible without departing from the scope of the present invention as defined in the appending claims.

Claims

1. A cable joint wherein at least two cable cores (20) are exposed beyond the ends of outer jackets (60) of at least two electric power cables (30) and wherein conductors 5 of the at least two cores (20) are electrically connected to each other, wherein sealing material (25) that is substantially impervious to moisture is located around the cores (20) so as to prevent any moisture reaching the electrical connections of the conductors, wherein blocking material (2) is located within the joint so as to prevent the sealing material (25) from migrating away from the connections into or ] 0 around the cables, and wherein a protective sleeve (40) encloses the cable connections and the sealing and blocking materials, characterised in that the blocking material (2) substantially surrounds a relatively rigid support member (1) capable of maintaining spacing between the separated cores (20).

15 2. A cable joint according to claim 1 , wherein the sealing material (25) encapsulates the electrical connections between the cables (30).

3. A cable joint according to claim 1 or 2, wherein the blocking material (2) prevents any longitudinal expansion of the sealing material (25).

20

4. A cable joint according to any preceding claim, comprising at least one connector arranged electrically to interconnect the cores of the cables (30), wherein the sealing material (25) encapsulates the or each connector.

25 5. A cable joint according to any preceding claim, wherein the blocking material (25) completely encloses each cable at the region where the cores are exposed beyond the outer jackets (60).

6. A cable joint according to any preceding claim, wherein each cable (30) is a multi- 30 core cable, and wherein the blocking material (2) is located in the crutch region of each cable between the cores (20) where the cores emerge from the cable jacket (60).

7. A cable joint according to any preceding claim, wherein the blocking material (2) extends over each cable jacket (60).

8. A cable joint according to any preceding claim, wherein the sealing material (25) comprises a mastic or a hot-melt adhesive.

9. A cable joint according to any preceding claim, wherein the blocking material (2) comprises a fibrous material, preferably felt or glass or synthetic fibrous material, or more preferably a closed-cell foam.

10. A cable joint according to any preceding claim, wherein the blocking material (2) comprises a sealant.

11. A cable joint according to claim 10, wherein the sealant is curable, preferably being a hot-melt adhesive.

12. A cable according to any preceding claim, wherein the protective sleeve (40) is bonded, preferably by hot-melt adhesive, on to the cable jackets (60).

13. A cable joint according to any preceding claim, wherein the sleeve (40) comprises a polymeric material having fibres embedded therein.

14. A cable joint according to any preceding claim, wherein the sleeve (40) is a recoverable sleeve, preferably a heat-recoverable sleeve.

15. A cable joint according to any preceding claim, wherein the sealing material (25) is provided as an inner layer of the protective sleeve.

16. A method of forming a moisture-blocked joint between at least two electric power cables (30), wherein outer jackets (60) of the cables are removed to expose the cores (20) thereof, and insulation of the cores is removed or disturbed for access to the conductors thereof, wherein electrical connection is made between the conductors of the cables, wherein sealing material (25) that is substantially impervious to moisture is disposed around the cable cores (20) so as to prevent any moisture reaching the electrical connection, wherein blocking material (2) is located within the joint, so as to prevent the sealing material from migrating away from the connections into or around the cables; and wherein a protective sleeve (40) is positioned around the jointed cables so as to enclose the cable connections and the sealing and blocking materials, characterised in that the blocking material (2) substantially surrounds a relatively rigid support member (1) capable of maintaining spacing between the separated cores (20).

17. A method according to claim 16, wherein the sealing material (25) is applied so as completely to enclose the electrical connections between the cables (30).

18. A method according to claim 16 or claim 17, wherein at least one connector is applied to the cables so as to interconnect the cores thereof; and wherein the sealing material (25) is positioned so as to encapsulate the or each connector.

19. A method according to any of claims 16 to 18, wherein the blocking material (25) is positioned between and around the cores (20) so as completely to enclose each cable (30) at the region where the cores are exposed beyond the outer jackets (60).

20. A method according to any of claims 16 to 19, wherein each cable (30) is a multi- core cable, and wherein the sealing material (25) is disposed in the crutch region of each cable between the cores (20) where the cores emerge from the cable jacket

(60).

21. A method according to any of claims 16 to 20, wherein the blocking material (25) prevents any longitudinal expansion of the sealing material (25).

22. A method according to any one of claims 16 to 21 , wherein the blocking material (2) is disposed so as to extend over each cable jacket (60).

23. A method according to any of claims 16 to 22, wherein the protective sleeve (40) comprises a recoverable sleeve of polymeric material having fibres embedded therein, and is recovered around the cable joint, preferably being sealed on to the cable jackets (60).

24. A method according to any of claims 16 to 23, wherein the sealing material (25) is applied to the joint as an inner layer of the protective sleeve (40).

25. An article (10) for use in a joint or method according to any preceding claim, comprising the said blocking material (2) substantially surrounding the said support member (1).

26. A kit of parts for forming a joint according to any of claims 1 to 15, including an article (10) according to claim 25.