GB2120464A - Cable duct - Google Patents

Abstract

A cable duct, particularly for laying across roads to protect temporary traffic light cables, is made of resilient rubber or plastics material with an isosceles trapezoidal cross- section. The narrower of the two parallel faces 2 serves as the top and the wider one 1 as the base, the latter having downwardly feathered edge portions 4 to ensure that the duct hugs the ground. One or two longitudinal internal passages 5 are provided, and a cable may be placed therein through a resiliently closed longitudinal slit 6 in the top 2 or bottom 1 face. The slit 6 may be held closed with adhesive. Face 1 may have a tread to improve its grip on the road. <IMAGE>

Description

SPECIFICATION Improvements relating to cable ducts This invention relates to cable ducts, and is primarily intended for use in conjunction with temporary traffic lights.

When there are road works of any magnitude, temporary traffic lights are usually installed at opposite ends, and in order to work properly they must be in mutual communication. This is generally achieved by a cable and, as it is usually impractical to suspend it at a sufficient height to clear all traffic, it is normally laid across the road when the lights at the respective ends of the obstruction have to be on opposite sides. This is especially advisable if a microwave radar sensing device is used for vehicle actuation of the lights. A radar system can easily be upset by receding vehicles, and one measure to avoid this is always to have the detector installation on the light standard at the 'near' side of the road where the radar beam can be more easily concentrated on the oncoming traffic. This inevitably means a cable across the road.

Another vehicle detection system employs an inductive loop which responds by some form of pulse when a vehicle passes over it In a permanent system, the loops can be buried just below the road surface. However, in a temporary one this is not practical, and the loop has to be laid on the road.

Hitherto, no really satisfactory means of protecting cables or loops laid on the road has been developed. They are of course laid in an area where vehicles are braking and accelerating, and where engineering works give rise to stones and debris on the nearby road surface. Even a well sheathed cable does not survive long in such conditions, and unless it is very securely pegged down at short intervals it can be picked up and wrapped around vehicle wheels. Securing to the ground is a nuisance and an expense, and can also damage the road surface.

The aim of this invention is to provide a better means of protecting cables and loops in such circumstances.

According to the present invention there is provided a cable duct comprising a strip of rubber or plastics material of generally isosceles trapezoidal cross-section, with an internal longitudinal passage.

Access to this passage may be by means of a closable slit along the strip. Such closure is generated by the elasticity of the strip itself, which can be deformed to allow the cable to be entered, but when released automatically reverts to its trapexoidal shape and closes the slit. The cable can be removed by ripping it thorugh the slit, which parts locally and then recloses.

Conveniently the slit is along the top of the strip, but it can be along the bottom so that the strip would have to be inverted for entry and extraction of the cable.

If the cable is expected to be in place for a long time, corresponding to the strip's useful life, the closure may be augmented by adhering the faces of the slit together.

However, with a reasonably stiff cable and a not excessively long duct, it has been found that the cable can be threaded through by feeding it in at one end. The slit is then not necessary. If the cable will not itself feed through by being pushed from one end, a pilot wire or cord may be threaded through first and used to pull the cable into position.

Preferably the edges of the base are feathered downwardly so that when the strip is laid these edges meet the ground first and are deformed upwardly as the main body settles down. The edges are therefore resiliently urged against the ground and help resist lifting.

Such a duct may have just a single passage for a multi-core cable to cross a road, but there may be two or even more passages. The double passage version can be adapted to take a loop for inductive detection, by providing interconnections between the two passages.

For a better understanding of the invention, some constructional forms will now be described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a cross-section of a duct for a cable, and Figure 2 is a cross-section of a duct for two cables or for an inductive loop.

The duct of Figure 1 is a rubber strip of generrally isosceles trapezoidal cross-section, having a base 1, a top face 2 and shallow inclined sides 3. These meet the base 1 in downwardly turned feathered edge portions 4 which are deformed resiliently upwardly when the strip is laid on the ground. Along the centre of this strip there is a substantially circular section passage 5 with a normally closed vertical slit 6 between it and the top face 2. A cable 7 is housed in this passage.

For short lengths the cable may be inserted endwise through the passage 5, the slit 6 remaining closed. However, this may not be practical for certain lengths and types of cable, in which case the slit 6 can be opened by "hogging" the strip in the transverse direction. The cable can then be pressed down into the passage 5, and when the strip is released, it resumes the shape shown, with the slit closed. The cable can be subsequently removed by grasping a part which projects from one end of the strip and pulling upwardly, the resilience of the strip allowing the slit to part locally and then rejoin.

Instead of the slit 6 leading from the passage 5 to the top face 2, it could lead downwardly to the base 1.

Figure 2 shows a similar arrangement, but with two passages 8 for twin cables or the longer legs of an elongate loop which normally will extend half way across the road. Interconnecting ducts can be formed between the passages 8 for housing the shorter legs of the loop. The twin core cable leading to the loop may be housed in a single passage strip such as that of Figure 1.

If a wider loop is desired, a protective duct can be made up from Figure 1 strips.

As mentioned above, the slit 6 may not be necessary and could then be omitted in either the single or twin passage version of the duct, but these alternatives will not be illustrated.

It is important that the strip should remain in position, and the feathered edge portions might not be sufficient in themselves to keep the strip "hugging" the road. To increase the grip, therefore, the underside of either strip may be formed with corrugated, pimpled or other types of thread.

Claims (9)

1. A cable duct comprising a strip of rubber or plastics material of generally isosceles trapezoidal cross-section, with an internal longitudinal passage.

2. A cable duct as claimed in claim 1, wherein access to the passage is provided by a closable slit along the strip, the strip having an elasticity enabling it to be deformed to open the slit and allow a cable to be entered and then to revert to its trapezoidal shape re-closing the slit.

3. A cable duct as claimed in claim 2, wherein the slit is along the narrower of the two parallel sides which, in use, is the top of the strip.

4. A cable duct as claimed in claim 2, wherein the slit is along the wider of the two parallel sides which, in use, is.the base of the strip.

5. A cable duct as claimed in claim 2, 3 or 4, wherein the opposed faces of the slit are adhered together subsequent to the entry of the cable.

6. A cable duct as claimed in claim 1 wherein the passage is accessible only from the ends of the strip.

7. A cable duct as claimed in any preceding claim, wherein the edge portions of the wider of the two parallel sides, which in use serves as the base of the strip, are feathered downwardly.

8. A cable duct as claimed in any preceding claim, wherein a further internal longitudinal passage is formed in said strip.

9. A cable duct substantially as hereinbefore described with reference to Figure 1 or Figure 2 of the accompanying drawing.