Which underground cable laying method requires re-excavation for load expansion, making modifications costly?

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RRB JE EE 22 Apr 2025 Shift 1 CBT 2 Official Paper

Answer 1

Methods of laying underground cables

Direct Laying:

This method requires digging a 1.5m deep and 0.45m wide trench, which is then covered with sand.
The cables are laid in the trench and covered with a 10 cm-thick layer of sand. To protect against mechanical injury, the trench is then covered with bricks and other materials.
If more than one cable is required to be laid in a trench, then a horizontal or vertical inter-axial spacing of 30 cm is provided to prevent mutual heating.
Direct Laying (Direct Buried Method) requires re-excavation when load expansion or modification is needed, making it costly and labor-intensive.

Draw in the system:

Ducts or conduits of cast iron or concrete or glazed stone with manholes are placed at suitable locations along the cable route. The manholes are used for pulling the cable in position.

Troughing System:

A troughing system, also known as a cable troughing system or cable raceway, is a specialized system designed to protect, organize, and route electrical cables within a defined pathway.
Cables are laid in pre-cast concrete or fiberglass troughs which are then covered.

Solid system:

Underground cables are laid in open pipes or troughs along the cable route. The troughs are usually made of asphalt, stoneware or cast iron.
Asphaltic compound is used for filling the troughs once the cable is laid in position.