Page 110 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

System earthing

The earthing associated with current carrying conductor is normally essential to the security of the system is
known as system earthing. The system earthing is done at generating stations and substations.
Equipment earthing
Earthing of non-current carrying metal work and conductor which is essential for the safety of human life and
animals and the property is generally known as equipment earthing.
Pipe earthing
Pipe earthing is done by permanently placing a pipe in wet ground. The pipe can be made of steel, galvanized iron
or cast iron. Usually GI pipes having a length of 2.5m and an internal diameter of 38mm are used. The pipe should
be placed at least l.25m below the ground level through 19mm GI pipe. Earth electrode should be surrounded by
alternate layers of charcoal and salt for a distance of around 15 this is to maintain the moisture level and to obtain
lower earth resistance. The earth lead of sufficient gauge should be firmly connected to the electrode and it should
be carried in a GI pipe at a depth of 60cm below the ground level.A funnel having a wire mesh is provided at the
top of 19mm diameter pipe for water poured during summer season.
Advantages

The area of the pipe with soil is more compared with plate earthing, hence more leakage current can earth.

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CITS : Power - Electrician & Wireman - Lesson 20-25 CITS : Power - Electrician & Wireman - Lesson 20-25