Cable Conduit System

the aggregate of pipelines and inspection devices used in laying, installing, and servicing cables. Devices for concealed installation of cables in buildings are a variety of cable conduit systems. A complete cable conduit system includes shafts (in the basements of buildings) that contain central station equipment for electrical communications, and collecting mains and ducts, in which the cables run exposed, without pipes, and on special supports.

Underground cable conduit systems have span lengths of up to 125 m between inspection devices. Such systems are constructed using either single conduits or packs of several conduits arranged as a unit. They are buried in the earth, mainly under sidewalks, at a depth of 0.4-1.8 m. Conduits are made of concrete, ceramics, asbestos cement, polyethylene, plolyvinyl chloride, and tarred fibers. Their inside diameter is usually 100 mm (conduits with a diameter of 55 to 90 mm are in limited use); they are 1-6 m long. Conduits of each type are joined in such a way as to ensure maximum water-tightness and provide sufficient mechanical strength. To provide an adequate water runoff, the conduits and units of a system are laid with a slope, either from one inspection device to the next or from the midpoint of a span to both sides, with each side sloping toward an inspection device.

In a conduit system for communications cables, the underground inspection devices (manholes and chambers) are classified according to design, dimensions, and dimensional proportions (standard and special types); according to configuration, which depends on the direction and number of conduits or conduit units (straight-through, angular, branching, or station-type); according to material (brick or reinforced concrete; the latter type is subdivided into built-up and cast types); according to design load (for conduits installed under sidewalks, a truck-load of 20 kilonewtons; for conduits installed under the roadway, a trailer load of 300 kilonewtons); according to standard dimensions, which depend on the number of channels entering from the station (large or small chambers; small, medium, or large manholes; or of a station type for 3,000, 6,000, 10,000, and 20,000 channels); and according to the shape (retangular, oval, polyhedral, or ellipsoidal).

An underground cable conduit system provides access to thecables at any time (through the inspection devices), thus elimi-nating the necessity of cutting the pavement and excavating.Such access is required for inspection, repair, and replacement, as well as for development of the cable system to the ultimateplanned size.