GB2472912A

GB2472912A - Cable troughs

Info

Publication number: GB2472912A
Application number: GB1013758A
Authority: GB
Inventors: Duncan Laurence Chadwick; David Richard Pugh
Original assignee: THERMOPLASTIC COMPOSITES
Current assignee: THERMOPLASTIC COMPOSITES
Priority date: 2009-08-19
Filing date: 2010-08-17
Publication date: 2011-02-23
Also published as: GB201013758D0; GB0914458D0

Abstract

A cable trough (1) comprises a base wall (3a) and a pair of spaced side walls (3b) extending upwardly in use from the base wall. The cable trough has an inner wall member (5) and an outer wall member (7), a longitudinally extending void (9) being defined between the inner wall member and the outer wall member of the cable trough by a pair of web portions (11). At least one web portion is located so as to form a continuation of the inner wall member, so as to form a twin-walled portion of the cable trough. A connecting member may be shaped to be received in the void.

Description

Cable Troughs The present invention relates to cable troughs.

It is common to lay cables, such as communications or electricity cables, underground. However, it is possible for such cables to be damaged if they are laid directly into the ground. To reduce the risk of cable damage it is common practice to lay a cable inside a cable trough, which provides some measure of protection against accidental damage to the cable or cables inside it.

Typically a cable trough is of a generally U-shaped cross section defining a duct into which a cable may be laid and then, if desired, covered by a lid. Such cable troughs are usually formed in discrete sections which can 1 5 be laid end to end to form a long conduit suitable for conveying one or more cables over large distances.

* A commonly used cable trough is formed from pre-cast concrete with an unsecured lid. Although such cable troughs provide good protection for * 20 any cables they convey, those troughs have the disadvantage that they are heavy, such that specialist handling equipment is usually required when laying *** * the troughs. In order to reduce weight, such troughs are often supplied in short lengths, typically im or less. One advantage of concrete is that its * ** coefficient of thermal expansion is low enough that it does not substantially expand or contract under the range of temperatures experienced over the normal course of a year. Excessive movement due to thermal expansion and contraction can cause the trough to snake' which in turn applies stress to the cable which can resu't in failure of the cable.

A common site for laying cables is in stone ballast adjacent railway lines. In such sites low frequency vibrations caused by passing trains cause a phenomenon known as ballast pump', in which the stone ballast shifts over time. Ballast pump can cause pressure to be exerted on the side walls of a trough which can cause the trough to fail. As a result cable troughs for such sites are subject to rigorous testing. Ballast movement can also cause vertical lifting of a cable trough in the ballast over time.

According to a first aspect of the present invention there is provided a cable trough comprising a wall having an inner wall member and an outer wall member, wherein at least one void is defined between the inner wall member and the outer wall member of the cable trough so as to form a twin-walled portion of the cable trough.

Such a trough may remain substantially rigid in normal usage whilst being lighter than other cable troughs of comparable size, due to the presence of a hollow space between the wall members forming the wall of the trough.

1 5 The cable trough may comprise a base wall and a pair of spaced side walls extending upwardly in use from the base wall. The base wall may comprise the twin walled portion. A side wall may comprise the twin walled portion. Each wall may comprise a twin-walled portion.

* 20 The void may be further defined by a pair of spaced web portions. At *... least one web portion may be located so as to form a continuation of the inner wall member extending through the cable trough to contact the outer wall *:*::* member. Each web portion may be located so as to form a continuation of * the inner wall member, for example a continuation of the inner wall member of **SS.S * 25 a respective side wall. Alternatively, one web portion may be located so as to form a continuation of an inner wall member (e.g. of the base wall) and the other web portion may be defined by the outer wall member.

The cable trough may be formed of a thermoplastics material.

The cable trough may be extruded, for example from a thermoplastic polymer. Such a trough may be produced at lower cost, at higher volume and in longer lengths than a moulded thermoplastic trough.

The void may extend longitudinally from a first end face of the trough to a second end face of the trough.

The trough may further comprise a drawstring located within the void, such that a cable attached to the drawstring may be pulled through the void.

Such a drawing may be coextruded during the extrusion of the trough.

The trough may comprise a plurality of voids. Adjacent voids may be separated by webs between the inner and outer wall members. The base wall may include at least one web which may be located so as to form a continuation of one or both of the inner wall members of the side walls.

The outer wall member of the side walls may form an acute angle with 1 5 the base wall.

The outer wall member of one or both side walls may comprise a lug.

The lug may extend longitudinally along the outer wall member of the trough. * *

* 20 One or more of the voids, for example a void in one or both side walls, may be arranged to receive a first connecting member, which may comprise *** * an elongate rod, such as a dowel. The void may comprise a cross-section *:::* complementary in shape to that of the dowel, for example a quadrilateral shape.

One or more of the voids, for example a void in the base wall, may be arranged to receive a second connecting member. Alternatively, or additionally a second connecting member may protrude from the base.

The void or one or some of the voids may be filled with a filling material.

The trough may include reinforcing, which may comprise one or more reinforcement members, which may comprise, for example glass fibres or woven tape. The reinforcing may be located by co-extrusion, or by applying the reinforcing after the extrusion.

In embodiments in which the void opens onto an end face of the cable trough, the cable trough may further comprise a first connecting member, such as a dowel, housed within the void, the first connecting member being operable to move from a first position substantially within the void to a second 1 0 position protruding from the void.

Such a cable trough may be provided with means, perhaps in the form of an actuator, to move the first connecting member from the first position into the second position.

According to a second aspect of the invention there is provided a cable trough comprising a base wall and a pair of spaced side walls extending upwardly in use from the base wall, the cable trough having an inner wall member and an outer wall member, wherein a longitudinally extending void is * 20 defined between the inner wall member and the outer wall member of the cable trough, so as to form a twin-walled portion of the cable trough, the void being defined by a pair of web portions, at least one web portion being located so as to form a continuation of the inner wall member. * **

I

According to a third aspect of the invention there is provided a cable trough system comprising a first cable trough comprising a wall having an inner wall member, an outer wall member and a first end face, wherein at least one void is defined between the inner wall member and the outer wall member so as to form a twin-walled portion of the cable trough opening onto the first end face, and a first connecting member, such as a dowel, shaped to be received at least partly in the void.

The cable trough may be in accordance with the first aspect of the invention, and may be in accordance with the second aspect of the invention, The void may extend longitudinally from the first end face of the trough to a second end face of the trough. Alternatively, or additionally, the trough may comprise a second void, discrete from the first, opening onto a second end face of the cable trough.

The system may comprise a second cable trough, the voids of the first and second cable troughs being arranged so that the first connecting member may be received in both voids at one time so as to connect the first and second cable troughs.

The system may comprise a plurality of cable troughs and first connecting members, such that the plurality of cable troughs can be connected using the plurality of first connecting members to form a cable conduit. The or each first connecting member may be flexible. * S *. *.

The or each connecting member may comprise an elongate rod such * 20 as a dowel, which may be substantially cuboid. The dowel may comprise a cross-section which is complementary in shape to that of the void, so that the dowel can be inserted into the void and possibly held in place by friction, with *, .. at least a part of the dowel protruding from the void. The cross-section of the * so dowel may be substantially quadrilateral in shape.

The first connecting member may be located, in use, in a void in a side wall, such as a void in an upper region of the side wall. Each first connecting member of a pair of first connecting members may be located, in use, in a respective void in a respective side wall. The first connecting member may be arranged to connect a first thermoplastic cable trough to a second thermoplastic cable trough.

The system may further comprise a second connecting member. The second connecting member may comprise a protrusion. The protrusion may be in the form of a tongue, and which may be tapered or wedge shaped. The second connecting member may be shaped to be inserted into a void, for example a void in a base wall of the trough.

When the second connecting member is received in the void, the protrusion may extend away from the trough, and particularly away from the base of the trough, in line with a plane defined by the base wall of the trough.

The second connecting member may extend, in use, from the base wall to the trough. The second connecting member may be arranged to connect a first thermoplastic cable trough to a conventional concrete cable trough.

The or each first connecting member may be provided with a securing formation arranged to resist removal from one or more of the voids, for example the securing formation may be shaped so as to provide a frictional fit within that void or voids. The securing formation may comprise serrations, barbs or ridges.One or more of the first connecting members may be provided with a spacer so as to maintain a space between two adjacent troughs.

It will be appreciated that the structural features of the cable trough * S. . . . . described with respect to the first aspect of the invention may also be applied S.....

* 25 to the cable trough of the second aspect of the invention, or the cable trough system of the third aspect of the invention.

According to a further aspect of the invention there is provided a method of repairing a cable conduit comprising positioning a repair cable trough in accordance with the first or second aspect of the invention, the cable trough further comprising a first connecting member, such as a dowel, housed within the void, the first connecting member being operable to move from a first position substantially within the void to a second position protruding from the void, such that the end face of the repair cable trough is adjacent to an end face of a second cable trough, the second trough comprising at (east one void; aligning the dowel of the repair trough with the void of the second cable trough; and causing the first connecting member to move from the first position into the second position.

The method may further comprise the step of fixing the dowel in the second position.

The present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of a cable trough; Figure 2 is a perspective view of another cable trough when carrying cables; Figure 3 is a perspective view of the cable trough of Figure 2 with connecting dowels in situ; .... Figures 3a 3b and 3c show various embodiments of connecting SI..

: dowels; * . Figure 4 is a perspective view of a repair cable trough with dowels * retracted; Figure 5 is a perspective view of the repair cable trough of Figure 4 with dowels extended; Figure 6 is a cross-sectional view similar to that of Figure 1 showing another cable trough; Figure 7 is a cross-sectional view similar to that of Figure 1 showing a further cable trough; Figure 8 is a cross-sectiona' view simi'ar to that of Figure 1 showing a cable trough comprising reinforcing; Figure 9 is a schematic drawing showing two connected cable troughs; and Figure 10 is a perspective view of another cable trough with an alternative connecting member.

Figure 1 shows a cross-section of a thermoplastic cable trough I in accordance with the invention. The cable trough 1 comprises at least one wall 3, and in this case three waIls 3 comprising a base 3a and two sides 3b of a U'. Each of the walls has an inner wall member 5 and an outer wafl member 7, with at least one wall including a void 9 between the inner wall member 5 and the outer wall member 7, so as to form a twin-walled portion of the cable trough.

In the embodiment of Figure 1 multiple voids 9 are located within the walls 3 of the cable trough 1. The voids 9 are separated by webs 11 of thermoplastic material which span between the inner 5 and outer 7 wall members of the trough.

1 5 The outer surface of the trough 1 is substantially U-shaped. However, the upright portions of the U (that is, the outer wall members of the side walls 3b) form an acute angle with the outer wall member of the base 3a. S... * * *5..

The trough comprises at least one, and in this case two, lugs or ribs 12 * *, 20 on the side walls of the trough. In this embodiment the ribs 12 extend longitudinally for the full length of the trough. S..

Figure 2 shows a perspective view of a similar cable trough la to that shown in Figure 1. The cable trough la of Figure 2 differs from that of Figure 1 only in that the cable trough Ia of Figure 2 does not comprise a longitudinal rib. It can be seen that when the trough is in use cables 13 are conveyed within a duct 15 defined between the side walls 3b and base 3a of the trough. If desired, a lid (not shown) can be used to cover the cables after they have been laid in the duct 15.

The trough 1 is formed from thermoplastics material. ThermoplasticS material is a much lighter material than the more traditional concrete; however, it is more prone to flexing and bending that concrete, which increases the risk of the trough failing and damage to the cables conveyed within occurring. We have found that by providing a twin-walled trough of the type shown in the Figures it is possible for the trough to have sufficient rigidity to resist warping under the side wall pressures present in normal use whilst still retaining the advantage that it is relatively light and easy to handle. Such a trough can be produced at relatively low cost in an extrusion process.

Furthermore, the lightness of the troughs and the use of an extrusion process means that the troughs can be produced in long lengths (for example up to 5m) making them quicker to install as less installation actions need to be taken to lay a given length of cable.

The rigidity of the trough shown in Figure 1 is increased (for example, with respect to the alternative trough Ic shown in Figure 7) by the provision of the webs 11. Those webs 11 act to resist compression of the voids within the side walls and base of the trough. Two of the webs, 1 Ia and 11 b, are located so as to form a continuation of the substantially vertical portions of the inner wall member 5 (vertical' in this instance refers to the in use' orientation of the S...

S..... trough, as shown in the Figures). Similarly, two webs lic and lid are located so as to form a continuation of the horizontal portion of the inner wall * .. 20 member 5. The webs lla-d act to resist the side walls 3b being compressed inwardly into the duct 15, for example under the action of ballast pump', * providing further structUral stability to the trough. * *. * S * * SS

The bending strength and stiffness of the trough may be further improved and the coefficient of thermal expansion reduced by the addition of reinforcing. Figure 8 shows a trough Id, comprising internal reinforcing in the form of reinforcement members 31. The reinforcing could comprise any suitable number of reinforcement members 31, which could be positioned in any suitable position. In the example shown in Fig 8, a pair of first reinforcement members 31A reinforces the junctions between the side and base inner wall members 5, these members 31A having a cross sectional shape in the form of a cross. In this position, the reinforcement members 31 increase the stiffness of the trough and in particular the resistance of the walls 3 to laterally imposed forces which could cause rotation of the side walls relative to the base, and at the same time reduce the coefficient of thermal expansion.

The example shown in Fig 8 also includes pairs of second and third reinforcement members 31B, 31C which are located in the outer wall members 7 of the side walls 3b, in in-use intermediate and upper positions respectively. In both cases the reinforcement members 31B, 31C are of elongated cross sectional shape, and increase the bending strength and stiffness of the trough. The second reinforcement members 316 also increase the resistance of the walls 3 to laterally imposed forces.

Such a reinforced trough may be made by co-extruding reinforcing material at the same time as the trough. This is possible if the reinforcing 1 5 material is impregnated into a material which has a different viscosity when melted from the viscosity when melted of the thermoplastic that is used to form the trough. In one example, the reinforcing material has a relatively low S...

5... viscosity when melted compared to the surrounding material used to form the trough. Alternatively, reinforcing might be applied to the trough after it has * ** 20 been extruded or otherwise made. * * I * S.

S S..

* As thermoplastic is lighter than concrete there may be a tendency for a **::* thermoplastic trough to rise in the ground over time, due to the action of : ballast movement. The lugs 12 act to anchor the trough into the ballast to * I resist such upward movement. In addition, the acute angle of the outer wall member 7 of the side walls 3b together form a wedge which resists such upward movement as the weight of the ballast acts to hold the trough down.

Referring again to Fig 8, after the troughs are laid in position, the voids could be filled, for example, with a filling material which could be settable such as concrete, pulverised fly ash, cement or epoxy grout, or alternatively with a flowable filling material, such as a shredded scrap plastics material. In Fig 8, in-use lower voids 9A, 9B, 9C have been filled with concrete 33. The filling material acts to hold the trough in position in the ballast, and resist the aforesaid upward movement. Advantageously, the position and number of voids which are filled is selectable to suit in situ conditions.

It is normal practice when laying concrete troughs to simply butt two adjacent troughs up next to each other. This is not completely satisfactory as an installation method for thermoplastic troughs, however. Thermoplastic is more prone to thermal expansion than concrete, meaning that there is a risk of troughs moving over time, even when no ballast pump is evident, due to expansion and contraction under the range of temperatures experienced throughout a year. A method and apparatus for locating two adjacent troughs with respect to one another will now be described, with reference to Figure 3.

Figure 3 shows the cable trough Ia of Figure 2 (although the cables 13 1 5 have been omitted for clarity) comprising a pair of first connecting members or pins in the form of dowels 17 inserted into two of the voids 9, in particular voids located in an upper portion of a respective side wall. The dowels shown ** in Figure 3 are made from a flexible polymer, such as plasticized poly-vinyl-chloride (PVC) which has been moulded or otherwise shaped to fit closely into * 20 one or more of the voids of the cable trough la. The free ends of the dowels are similarly shaped so that a second cable trough can be aligned with and **. . connected to the cable trough shown by inserting the dowels 17 into the corresponding voids of the second cable trough.

less..

* 25 The dowels may be fixed in place within the cable trough by any suitable means, for example screwed or glued in place. Figure 3a shows an alternative dowel 17a to those shown in Figure 3 which has been provided with a securing formation, in the form of a ridged, barbed or serrated region 19 at each end, which is designed to provide a frictional fit within a void of a cable trough. Other designs of frictional fit dowel may be used. Alternatively, the dowels need not be fixed in place at all.

Using connecting dowels as described helps multiple troughs remain aligned with each other when laid in the ground, in the case of thermal expansion and contraction of the troughs or under the action of external forces such as ballast pump. The flexible nature of the dowels allows some relative movement between adjacent troughs, which reduces the risk of the dowels or troughs breaking under load. Of course, rigid dowels may be used if required. An advantage of flexible dowels is that cable troughs may be laid around bends if desired, without the need for a customised or specially designed trough or dowel. Figure 9 shows a connection of two cable troughs 1 0 laid around a bend. It can be seen that the two troughs I are able to remain connected with an angle between their major longitudinal axes due to the flexion of dowel 17b.

If required, cable troughs of the type described herein (that is thermoplastic cable troughs comprising a void) can be easily cut or chamfered to a desired shape, perhaps to make a series of troughs laid around a corner to fit together more closely. S... * .

We have found that it may be possible to reduce the effects of thermal * ** 20 expansion on a cable trough system of the type discussed above by providing a space between two adjacent cable troughs. To that end, a dowel S..

* comprising a spacer 21 may be used, such as the dowels shown in *:*::* Figures 3b, 3c and 9.

S

*5S*SS * 25 In the event that a section of a cable trough system needs to be replaced (for example, because of wear or damage to one or more cable troughs in the system) it is possible to cut through the connecting dowels joining a damaged trough to the adjacent troughs in order to remove and replace the damaged trough. When fitting a replacement trough it may be difficult to connect replacement dowels at both ends of the trough without lifting or disturbing the rest of the cable trough system. To that end a repair trough has been designed, and that will now be described with reference to Figures 4 and 5.

Figure 4 shows a cable trough lb. As before, the trough 1 b comprises a wall 3 having an inner wall member 5, an outer wall member 7 and a first end face 23. The cable trough comprises at least one void, and in this case a plurality of voids 9, between the inner wall member and the outer wall member so as to form a twin-walled portion of the cable trough opening onto the first end face. The cable trough lb further comprises one or more, and in this case two, connecting members or dowels 25 housed within the voids 9. The dowels 25 are operable to move from a first position substantially within the void, as shown in Figure 4, to a second position protruding from the void, as shown in Figure 5.

In the example in the Figures, each dowel 25 can be moved by means of an actuator in the form of a screw 27 fixed into the dowel through a slot 29 1 5 defined in the outer wall member of the trough. When the dowel has been moved into the desired position it can be fixed in place by screwing the screw 27 further into the dowel until the screw head clamps against the cable trough (or an intermediary surface, such as a washer).

**S*S. * *

* 20 In use, such a repair trough is laid with its end 23 adjacent a cable trough that is in situ, with the dowels 25 in the first (retracted) position shown in Figure 4, in which the dowels 25 do not substantially protrude from the repair trough lb. The ends of one or more of the dowels 25 are aligned with one or more voids 9 within the trough that is in situ. Then the dowels are moved via the screw 27 into the voids of the adjacent trough. The dowels can then be fixed in place, connecting the two troughs. It will be appreciated that the dowels 25 may be arranged to be retained by friction in the voids of the adjacent trough, or may be screwed, glued or otherwise fixed in place, if desired.

The repair trough may comprise sliding dowels 25 at one end, as shown, or may comprise sliding dowels at both ends.

It will be appreciated that various modifications may be made without departing from the scope of the invention. For example, different shapes or materials may be used for the connecting dowels.

With respect to Figure 2, it will be noted that it is possible to run cables through one or more of the longitudinal voids 9 in the trough. To that end a drawstring may be provided within the or each void, for example by means of co extrusion at the time of forming the cable trough.

1 0 Figures 6 and 7 depict two alternative cross sections for a cable trough.

Figure 6 shows a cable trough ic comprising a single void 9, the rest of the trough being solid. Such a trough is lighter than an all solid trough, although not as light as those depicted in the other Figures. Figure 7 shows a cable trough Id having a single void such that substantially the entire trough is twin- 1 5 walled. Such a trough is very light, but not as strong as those shown in Figures 1 to 5, due to the absence of internal webs. It is considered that the troughs shown in Figures 1 to 5 provide a good compromise between weight and strength. * *

It will also be appreciated that various features of the invention, for * ** * example, the use of connecting dowels, the provision of lugs on the trough *** side waUs, and the acute angle of the trough side walls, may be advantageously used with cable troughs formed from other materials. For example, a concrete trough may be provided, perhaps by casting or drilling, with recesses in its end faces into which a dowel can be received. The invention therefore is not limited to thermoplastic cable troughs.

All the troughs shown have voids extending the full longitudinal length of the trough. As discussed, this is because the applicant intends primarily to produce cable troughs using extrusion. However, it will be appreciated that troughs with one or more fully enclosed void still retain the advantage of being lighter than a solid trough, whilst having a larger cross section, and hence an increased rigidity with respect to a single walled trough of the same mass.

It will be understood that the system of dowels for connecting cable troughs discussed above may not be suitable for connecting the thermoplastic cable troughs described herein to a conventional concrete cable trough, because conventional concrete cable troughs do not include suitably located voids. Figure 10 shows a cable trough connecting system which is suitable for use with existing concrete cable troughs.

A cable trough le is shown in Figure 10 which includes a second connecting member 41 shaped to be received in a void located in the centre of the base wall of the cable trough le. The connecting member 41 comprises a generally wedge shaped protrusion 43 extending from the void along a central longitudinal axis of the trough. The wedge shaped protrusion is shaped to fit into a complementary shaped cut out provided in a 1 5 conventional cable trough (not shown), so as to interlock with the conventional cable trough.

It will be appreciated that the shape of the protrusion can be selected as desired, depending on the shape of the cut out. In addition, it will be understood that the second connecting member can be removed from the * ** recess in the cable trough and possibly replaced with a second connecting *..

* member of a different shape, if required. * ** * * * * **

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

Claims 1. A cable trough comprising a base wall and a pair of spaced side walls extending upwardly in use from the base wall, the cable trough having an inner wall member and an outer wall member, wherein a longitudinally extending void is defined between the inner wall member and the outer wall member of the cable trough, so as to form a twin-walled portion of the cable trough, the void being defined by a pair of web portions, at least one web portion being located so as to form a continuation of the inner wall member.
2. A cable trough according to claim 1, wherein the twin-walled portion is located in the base wall.
3. A cable trough according to claim 2, wherein the void is defined by two web portions, each web portion being located so as to form a continuation of the inner wall member of a respective side wall. S...

*:
4. A cable trough according to claim 1, wherein the twin-walled portion is **SSSS * * located in a side wall. * S * * *.
5. A cable trough according to claim 4, wherein the void is defined by two web portions, one of which is located so as to form a continuation of the inner * S. wall member of the base wall *SS*S. * .
6. A cable trough according to any one or claims I to 5, wherein the void extends longitudinally from a first end face of the trough to a second end face of the trough.
7. A cable trough according to any preceding claim, wherein the trough comprises a plurality of voids.
8. A cable trough according to claim 7, wherein adjacent voids are separated by webs between the inner and outer wall members.
9. A cable trough according to claim 8, wherein a first void is provided in a side wall, the first void being defined by a web which is located so as to form a continuation of the inner wall member of the base wall, and a second void is provided in the base wall, the second void being defined by a pair of webs, each of which are located so as to form a continuation of the inner wall member of a respective side wall.
10. A cable trough according to claim 9, wherein both side walls include a void defined by a web which is located so as to form a continuation of the inner wall member of the base wall.
11. A cable trough according to any preceding claim, wherein the outer wall member of the side wall forms an acute angle with the outer wall member of 1 5 the base wall.
12. A cable trough according to any preceding claim, wherein the outer wall member of one or both side walls comprises a lug. * ** *. 20
13. A cable trough according to claim 12, wherein the lug or lugs extend longitudinally along the outer wall member of the side walls.

S
14. A cable trough according to any preceding claim, wherein one or more of the voids is arranged to receive a connecting member.
15. A cable trough according to any preceding claim, wherein the cable trough is formed of a thermoplastics material.
16. A cable trough according to claim 15, wherein the cable trough is formed of a thermoplastic polymer.
17. A cable trough according to claim 15 or claim 16, wherein the cable trough is extruded.
18. A cable trough according to any preceding claim, wherein the trough further comprises a drawstring located within the or a void, such that a cable attached to the drawstring may be pulled through the void.
19. A cable trough according to claim 18, as dependent on claim 17, wherein the drawstring is coextruded during the extrusion of the trough.
20. A cable trough according to any preceding claim, wherein the trough 1 0 includes reinforcing.
21. A cable trough according to claim 20, wherein the reinforcing comprises glass fibres or woven tape.
22. A cable trough according to claim 20 or claim 21, wherein the reinforcing is located at or adjacent the web portions.
23. A cable trough according to any preceding claim, wherein the cable trough further comprises a first connecting member housed within the void, the first connecting member being operable to move from a first position * .* * substantially within the void to a second position protruding from the void. *..
24. A cable trough according to claim 23, wherein the cable trough is provided with an actuator to move the first connecting member from the first position into the second position.
25. A cable trough according to any preceding claim, wherein a void is filled with a fifing material.
26. A cable trough comprising a wall having an inner wall member and an outer wall member, wherein at least one void is defined between the inner wall member and the outer wall member of the cable trough so as to form a twin-walled portion of the cable trough.
27. A cable trough system comprising a first cable trough comprising a wall having an inner wall member, an outer wall member and a first end face, wherein at least one void is defined between the inner wall member and the outer wall member so as to form a twin-walled portion of the cable trough opening onto the first end face, and a first connecting member shaped to be received in the void.
28. A cable trough system according to claim 27, wherein the void extends longitudinally from the first end face of the trough to a second end face of the trough.
29. A cable trough system according to claim 27, wherein the trough comprises a second void, discrete from the first, opening onto a second end 1 5 face of the cable trough.
30. A cable trough system according to any one of claims 27 to 29, wherein the system comprises a second cable trough, the voids of the first and second * cable troughs being arranged so that the first connecting member may be *.. 20 received in both voids at one time so as to connect the first and second cable * ..troughs. * S.
31. A cable trough system according to claim 30, wherein the system comprises a plurality of cable troughs and first connecting members, such that the plurality of cable troughs can be connected using the plurality of first connecting members to form a cable conduit.
32. A cable trough system according to any one of claims 27 to 31, wherein the first connecting member is flexible.
33. A cable trough system according to any one of claims 27 to 31 wherein the first connecting member is substantially rigid.
34. A cable trough system according to any one of claims 27 to 33, wherein the first connecting member is provided with a securing formation arranged to resist removal from one or more of the voids.
35. A cable trough system according to claim 34, wherein the securing formation comprises serrations, barbs or ridges.
36. A cable trough system according to any one of claims 27 to 35, wherein one or more of the first connecting members comprises a spacer arranged in use to maintain a space between two adjacent troughs.
37. A cable trough system according to any one of claims 27 to 36, wherein one or more of the cable troughs in the system comprises the cable trough of any one of claims I to 26.
38. A cable trough system according to any one of claims 27 to 37 wherein the or each first connecting member comprises a dowel. 1 *.*
39. A cable trough system according to any one of claims 27 to 38 further *.. 20 comprising a second connecting member. * **

S
40. A cable trough system according to claim 39, wherein the second * * connecting member comprises a protrusion extending in use from the base wall of a cable trough.
41. A cable trough substantially as described herein, with reference to the accompanying drawings.
42. A cab'e trough system substantially as described herein, with reference to the accompanying drawings.
43. Any novel subject matter or combination including subject matter disclosed, whether or not within the scope of or relating to the same invention as any of the preceding claims. * SI ** ** SS I S * * * SU ** * * S.IS * *I I. * * ISS 55S55 I *