|Electrical Installation - Basic Vocational Knowledge|
|3. Laying of underground cables|
The cable marking informs about:
- type of cable,
- construction of cable
- material and shape of conductors
- cross section of cable.
Cables are being supplied on cable drums in case of larger quantities.
Laying of underground cables is done from the cable drum into cable ditches.
Underground cables are placed 0.70 m deep into the ground at least.
The distance between two underground cables is to be approx. 0.20 m.
Below temperatures of +4°C underground cable is to be laid in warmed up condition in urgent cases only.
When running out cable the following points of emphasis are to be observed:
- the minimum bending radius must not be undercut,
- cables must not be dragged on the ground when being laid,
- underground cables are to be covered. Cables without coverage will have to be dug-in 1.00 m if these cables have a concentric phase conductor,
- every 3 to 5 m underground cables are to be provided with marking tape.
When removing the insulation from underground cables, the individual, insulation layers of the cable are to be removed. Minimum insulation lengths which must remain after stripping are to be adhered to. Cable joints are being made by sleeves and by means of cable terminations. In practical use are sleeves resp. cable terminations of cast iron, plastic or cast-resin.
Conductor connections are mainly made via cable terminals. For this, stamped cable terminals are being preferred to screwed, soldered and welded cable terminals. Stamped cable terminals are stamped on by means of hydraulic or mechanical stamping tools. In this tools matching stamp inserts are to be used.
After laying, the underground cables are tested for adherence to the required insulation resistance. The fixed minimum insulation values are to be kept.
Preparation of the underground cable will be decisive for its life.