Different Methods Of Underground Cable Laying

Different Methods Of Underground Cable Laying

There are three three different methods of laying underground cable:

1. Direct Laying
2. Draw in system
3. Solid system

1. Direct Laying:

This method of laying of cable is simple and cheap. For laying of cable a trench about Ion 1.2 m deep and 0.5 m wide is dug.

Direct Laying Of Cable

A layer of 10 cm thickness of line sand is spread and cable is laid.

After laying of cable, it is covered with another layer of sand about 10 cm. A wall of bricks is provided on either side and top of the cable.

This method is preferred for cables with efficient steel tape or wire armoring. Since the posses excellent protection against mechanical damage.

When more than one cable is to be laid in the same trench then the minimum 30-40 cm spacing is provided between them and the gap is filled with sand.

Such arrangement avoids the mutual heating with another cables. 

Drawbacks Of Direct Laying Method

1. Localization of fault is difficult. 
2. Maintenance cost is high.
3. Extension of load necessities completely new excavation. 
4. Changes of damage of cable during excavation work carried out for maintenance or expansion.
5. Due to pressure of impurities in soil, cable sheath may sometimes undergo chemical changes which may damage the cable.

2. Draw in System :

In congested areas where excavation is expensive and inconvenient, then square draw in system of cable laying is preferred.

Draw in System Method

In this method, conduit or duct of glazed stone or cast iron or concrete are laid in the ground.

Manholes are provided at regular intervals.

Separate pipe and ducts are provided for each cable laid in the same duct.

The cables are then pulled into position from manholes.

For curved ducts the diameter of the pipe is kept larger to facilitate arranging cables into ducts.

The depth of the trench should be such that the top pipe remains at least 0.6 m below the ole ground level.

Normally a spacing of 0.25 m to 0.75 m is maintained between the two adjacent pipes. The cables to be laid in this way need not be armored but must be provided with serving.

Advantages Of Draw in System Method

1. There are very less chances of occurrence of fault due to strong structure.
2. Any repairs, addition to the cable network is simple and can be made without opening the ground.
3. Due to absence of arranging cable jointing is much simpler.

Disadvantages Of Draw in System Method

1. Initial cost of laying of cable is very high.
2. Heat dissipation is less due to close grouping of cables.

3. Solid System :

In solid system of laying of cables, the cable is laid in troughing, in an open trench/channel dug out in earth along the cable route.

Solid System Method

The troughing is filled with bituminous or asphastic compound and covered over. Cables laid in this manner are usually plain lead covered since it afford good mechanical protection.

This method of laying underground cables is rearly used because of its high cost. Also its success depends upon skilled, labour and favorable weather conditions.

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