Of all methods used for laying underground cables the direct laying of underground cables is simple and cheapest method and due to its simplicity, it is much favored in modern practice. The direct laying of underground cables involves digging of a trench that is about 1·5 meters deep and 45 cm wide.
A layer of fine sand around 10 cm thick is used for covering the trench and then cable is laid over this sand bed. The application of sand bed averts the entry of moisture from the ground thereby protecting the cable from decay.
Once the cable is laid in trench, another layer of sand of about the same thickness (10 cm) is used for covering the cable. After application of this layer, bricks and other materials are used for providing mechanical protection to cables. If multiple cables are to be laid in the same trench, a horizontal or vertical interaxial spacing of at least 30 cm is provided in order to reduce the effect of mutual heating and also to fault on one cable does not impacts the adjacent cable. Apart from this, cables must have serving of bituminized paper and hessian tape in order to provide protection against corrosion and electrolysis.
Advantages of Directly Laying Cables
- More heat dissipation is possible in this method
- Impact of external disturbances is very less
- It is clean method
- It is most economical method of laying cables
- It is the simplest method of cable laying
- Safety of cables is ensured
Disadvantages of Directly Laying Cables
- Extension of load can be achieved only by doing a completely new excavation that might cost as much as the original work.
- Fault localization is very difficult
- It is impractical in congested areas
- Maintenance charges are very high
- The alterations in the cable network are quite difficult
Also see video below: How To Install Underground Power Cables