WO1994008377A1

WO1994008377A1 - Cable duct access unit

Info

Publication number: WO1994008377A1
Application number: PCT/GB1993/002011
Authority: WO
Inventors: Thomas Kevin Shannon
Original assignee: North West Cable Communications Limited
Priority date: 1992-09-26
Filing date: 1993-09-27
Publication date: 1994-04-14
Also published as: AU4829493A; GB9220482D0

Abstract

A cable duct access unit for connection into a cable duct network has a junction box (1) and an upper sleeve section (2). The junction box (1) has an upstanding chamber (7), through which services may be introduced into said network. The upstanding chamber (7) is slidingly engageable with said sleeve section (2) by means of interconnecting grooves (6) and ribs (5). The arrangement provides for vertical adjustment of the height of the unit to permit easy installation and adjustment if the ground level is altered.

Description

CABLE DUCT ACCESS UNIT
This invention relates to a cable duct access unit for a cable duct or conduit particularly, but not exclusively, for use in telephone or cable television (CTV) services.

Networks of cables of the CTV type comprise main underground ducts with a multiplicity of subsidiary ducts which branch from a main duct and terminate adjacent to, or in the vicinity of a potential user, for example, a short distance from the exterior wall of a house or other building. A main underground duct may be provided when a new estate of houses is constructed. When a householder wishes to be connected to a network it is necessary to provide cables from the underground ducts to a desired location within the building.

One well known underground duct system for CTV has a characteristic "swept tee" style of construction. This design of duct system has cable pulling chambers installed in footpaths above and along the length of the underground ducts. The pulling chambers facilitate the introduction and installation of a cable into an existing CTv network. Typically these chambers are positioned at about 80m intervals along the footpath. However, it is often difficult to install cable pulling chambers in ideal positions along footpaths because of the, congestion of other utility services installed.

Known cable pulling chambers commonly comprise a pre-formed plastic chamber of a fixed depth which is designed to emulate concrete chambers which are cast in situ. It is necessary that the pulling chamber access opening is larger than the duct system itself and this makes installation of the chamber in the footpath difficult. A further disadvantage with this known type of chamber is that the fixed depth of the chamber means that expensive and time consuming alterations are often needed to install the chamber so that it fits flush with the ground surface.

Furthermore, if after installation the local authority decides to resurface the pavement or road, the new surface may cover the access opening of the chamber thereby preventing or hindering access to it.

It has been necessary to ensure that this does not happen. Present arrangements have involved use of extensions or replacements, installation of which is time consuming, costly and may involve disruption to the services provided to customers.

It is an object of the present invention to obviate or mitigate the aforesaid disadvantages.

According to the present invention there is provided a cable duct access unit for connection into a cable duct network, the access unit comprising a junction box having a substantially upright chamber portion through which services may be introduced into said network; and an upper sleeve section engageable with said upright chamber portion, said sleeve section being substantially vertically adjustable relative to said upright chamber portion.

The cable duct access unit of the present invention has the advantage that the height of the unit may be adjusted for easy installation. The sleeve section may be moved to a position such that the upper surface or edge of the sleeve section is flush with the level of surface access which may be a footpath, road or other ground surface. This means that the cable duct access unit may be readjusted if for example the height of the footpath or road is altered.

Preferably, one or more apertures are provided in the junction box to accept one or more duct sections. The cable duct access unit can therefore be used in a single length of duct or at a node where one or more duct sections meet. In many types of cable duct networks ducts many junctions between ducts may occur at substantially perpendicular angles.

The external surface of the upright portion of the junction box may have a plurality of ribs and the internal surface of the sleeve section may have a plurality of grooves to engage with the ribs. This facilitates engagement of the sleeve section and upright portion of the junction box. Vertical adjustment of the unit is achieved by sliding the sleeve section vertically with respect to the junction box.

Alternatively the sleeve section and the upright portion of the junction box may be threaded.

The sleeve section may have a protruding flange around the periphery of the lower edge of the sleeve section. The flange facilitates positioning and installation of the unit.

The cable access unit according to the present invention may have an aperture or duct entrance of a similar geometrical arrangement as that found in existing "swept tee" duct systems.

Therefore, the unit eliminates the need for a separate swept tee duct unit.

Specific embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:
Fig. 1 shows plan and side elevations of a cable duct access unit in accordance with the present invention with three duct entrances; and
Fig. 2 shows plan and side elevations of a cable duct access unit in accordance with the present invention with four duct entrances.

Figure 1 illustrates a cable duct access unit which is to be fitted into an underground cable duct network (not shown). The cable duct access unit is generally of plastics material and comprises a fixed duct junction box 1 and an upper sleeve section 2. The junction box 1 and the upper sleeve section 2 are rectangular in cross-section and are open to provide a rectangular chamber 3 in the unit through which a cable may be introduced or drawn into the underground duct system.

The junction box 1 has a lower portion with three apertures or duct entrances 4 which are designed to engage adjacent duct sections of the underground duct network (not shown). The junction box 1 has an upstanding upper portion 7 which has a plurality of ribs 5 and grooves 6 in its exterior surfaces. The interior surface of the sleeve section 2 has similar ribs 5 and grooves 6.

The sleeve section 2 has outwardly directed flanges 8, 9 around its upper and lower edges respectively.

The junction box 1 is slightly smaller in rectangular cross section than the sleeve section 2. This allows the sleeve 2 to slide over the upstanding portion 7 of the junction box 1. The ribs 5 of the junction box 1 slidingly engage the grooves 6 of the sleeve section 2 so as to permit vertical adjustment of the sleeve 2 relative to the junction box 1.

Alternatively, the sleeve section and the upright portion of the junction box may be threaded. This arrangement has the advantage that the sleeve section and the junction box do not become easily detached or displaced, for example, by a large downward force on the upper edge or surface of the sleeve section. Vertical adjustment of the unit to align the upper surface of the sleeve section with ground level is achieved by rotating the sleeve section relative to the junction box.

The surfaces of the unit are contoured to have gradual curves in areas where damage to a cable may result as it is introduced or pulled through the unit into the underground duct network. In particular, the unit has internal curved surfaces 10 between the upstanding portion 7 of the junction box 1 and the incoming or outgoing duct which surfaces prevent possible cutting or abrasion damage to a cable as it is pulled through the access unit.

Grooves (not shown) are provided in the internal surface of the sleeve section 2 and chamber 3. These grooves guide a cable as it is pulled or drawn into the duct network, for example during installation of a service to a building or customer.

In use, the unit is accommodated in a trench in which the cable duct or ducts are buried and is set in place with concrete. The junction box 1 is set to a depth so that the flange 9 of the sleeve section 2 rests on the surface of the concrete with the upper flange 8 of the sleeve section 2 flush with the ground or other surface. If vertical readjustment of the unit is necessary, for example after resurfacing of a road or repair of a footpath or pavement, then the sleeve section 2 is exposed and raised so that it is flush with the new ground level. The gap created between the surface of the original concrete and the flange 9 is grouted or filled with suitable materials.

Hence the flange 9 facilitates positioning and installation of the unit.

The use of this arrangement reduces the ingress of water, dirt and insects into the underground duct system.

The present invention thus obviates the need for reinstallation of, or expensive and time consuming repairs to the access unit when road or footpath repairs are made. Access to the cable duct network is not hindered and subsequent installation of cables or services into the duct can be performed easily.

The unit has parallel sides which engage the surfaces of a duct trench wall. This arrangement allows for accommodation within an existing trench. As the unit engages the surfaces of the trench-walls it stays in place without the need for using other tools to hold it in place as it is installed. Furthermore, a unit with this construction may be used to support the walls of a trench being constructed and thereby reduce the time and materials required for installing trench supports during construction.

Figure 2 shows a similar cable duct access unit in accordance with the present invention. The access unit shown has four duct entrances 21 and would be suitable for use at a network node where two ducts cross, at substantially perpendicular angle, and require joining. Therefore, use of this access unit would allow inspection and installation of cables or services into any one of the four underground ducts.

The junction box and sleeve section may be polygonal in crosssection with an aperture located in each face. A cable access unit may be used to gain access to a node or point at which more than two ducts meet. A cable access unit which accommodates two duct sections may have apertures or duct entrances at substantially 900 angles to one another.

Claims

CLAIMS:

1. A cable duct access unit for connection into a cable duct network, the access unit comprising a junction box having a substantially upright chamber portion through which services may be introduced into said network; and an upper sleeve section engageable with said upright chamber portion, said sleeve section being substantially vertically adjustable relative to said upright chamber portion.

2. A cable duct access unit according to claim 1 in which one or more apertures are provided in the junction box to accept one or more duct sections of the cable duct network.

3. A cable duct access unit according to claim 1 or 2 in which the external surface of the upright portion of the junction box has a plurality of ribs and the internal surface of the sleeve section has a plurality of grooves which slidingly engage with said ribs.

4. A cable duct access unit according to claim 1 or 2 in which the sleeve section and the upright portion of the junction box are threadedly engaged.

5. A cable duct access unit according to any preceding claim in which the sleeve section has an outwardly protruding flange around the lower edge of the sleeve section.

6. A cable duct access unit according to any preceding claim in which an internal surface interconnecting the upright chamber portion and the remainder of the junction box is curved.

7. A cable duct access unit according to any preceding claim in which the unit has parallel side walls.

8. A cable duct access unit substantially s-hereinbefore described with reference to the accompanying drawings.