METHOD / TYPE OF LAYING UNDER GROUND CABLE

 the following method is used to laying underground cables.

1. Laying in Ground

A.      Direct Laying

B.      Duct/Pipe Laying or Draw in System

C.      Trough Laying or Solid System

2. Racking on the wall or on overhead structure

3. Racking in Tunnel

 

now we will discuss all the method in the description.

1. Laying in Ground

In this method, the cable is buried in the ground. it is necessary to know the condition of the soil before planting. which is include ambient temperature, the resistivity of soil, presence or absence of the corrosive material or moisture, presence of other cables and its distance, presence of water line, telephonic line, drainage line or gas line etc.

A. Direct Laying

In this method, the cable is laid directly under the ground. in which a trench 0.5 meter wide & 1.2 meter Dug is required & bed of sand 100 mm thick. now cable is laid on this sand and prevent the entry of moisture from the soil into the cable. after to place the cable on the sand, bricks are placed on the sides and above the cable also.

if there are more than 1 the cable is to lay, at that time 400 mm of distance to keep in horizontal and vertical direction, so it can prevent the heating of cable from one to another cable.

Depth of cable trench:

there is the depth of cable is depends on the voltage level of what we are using.

Up to 1.1KV _ 0.45 M

3.3KV TO 11KV _ 0.75 M

22KV TO 33KV _ 1 M

ADVANTAGES :

·         Method is Simple

·         Safe Method

·         less Costly

DISADVANTAGES:

·         Difficult to find Location of Fault

·         maintenance cost is more

·         Impurities in soil affect the sheath

·         possibility of damage the cable when re-digging.

B.   Duct / Pipe Laying or Draw in System

In this method, the trench is dug in the ground. after to dug, tube or ducts place in the trench which is made of iron galvanized or cement concrete. the cable is drawn in through the manhole.

ADVANTAGES:

·         during repairing and maintenance, we don't need digging observation

·         not necessary of armouring in the cable.

DISADVANTAGES:

·          deep and wide trench to be required

·         the initial cost is more

·         current-carrying of cable is decreased if a decrease in the heat dissipation.

APPLICATION:

·         for small length work such as workshop, railway crossing etc.

C.   Trough Laying or Solid System

in this method, trought made of cast iron, stoneware, asphalt or treated wood is kept at reasonable depth in the ground. the cable is kept in the trough and it's filled with a compound of asphalt or bitumen.

lead sheathed type cable is used.

ADVANTAGES:

·         good mechanical protection

·         impurities in soil don't affect the cable.

DISADVANTAGES:

·         more time to laying the cable

·         more time off for maintenance and repairs

·         current carrying capacity reduces

·         costly method

·         extension become difficult in future.

 

2. Racking on the wall or on overhead structure

simply in this method, cast iron (CI) bracket are filled on the wall at a certain interval. the cable is kept on the bracket.

ADVANTAGES:

·         less initial cost

·         easy maintenance

·         easy to extension

·         cant be interference with other plants

DISADVANTAGES:

·         possibility of fire

·         when sunlight on cable increase then-current carrying capacity decrease

 

3. Racking in Tunnel

In this method, first to creat the tunnel and place the cable as shown in bellow image.

ADVANTAGES:

·         no need separated rack

·         good protection against fire

DISADVANTAGES:

·         method is costly