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j. The Earth enhancement material shall be supplied in sealed, moisture proof bags. These
bags shall be marked with Manufacturer’s name or trade name, quantity etc.
k. Shall not require periodic charging treatment nor replacement and maintenance.
l. Shall not dissolve, decompose or leached out with time.
m. Shall not pollute the local water table be environment friendly.
n. Shall not be explosive.
o. Shall not cause burns, irritation to eye, skin etc.
6. Construction of Unit Earth :
a. A hole of 100mm to 125mm dia shall augured to a depth of about 2.8 meters.
b. The earth electrode shall be inserted into this augured hole.
c. It will be penetrating into the soil by gentle driving on the toe of the rod using a sledge
hammer . Here natural soil is assumed to be available at the bottom of the electrode so
that min.150 mm of the electrode shall be instated in the natural soil.
d. RDSO approved earth enhancement material min.
e. approximately 30-35 kg shall be filled into the augured hole in slurry form and allowed
to set.
f. After the material gets set,
g. the diameter of the composite structure shall be of minimum 100mm dia covering
entire length of the hole.
h. Remaining portion of the hole shall be covered by the soil which is taken out during
auguring.
i. A copper strip of 150mmx25mmx6mm shall be exothermically welded to main earth
electrode for taking the connection to the main equi-potential earth bus bar in the
equipment room and to other earth pits ,if any.
j. Exothermic weld material shall be UL listed and tested as per provisions of IEEE 837
by NABL/ILAC member labs.
k. The main earth pit shall be located as near to the main equi-potential earth bus bar in
the equipment room as possible.
7. Construction of loop Earth by providing multiple earth pits:
Since it is not possible to achieve a low resistance values of less than one ohm with
one pit, it is required to install a ring earth consisting of 2 to 4 pits depending upon the
soil resistivity. Following method is shall be adopted to construct the ring earth.
a. The procedure mentioned above for one pit under item 6 , shall be repeated for
installing 2 to 4 such earth pits. It will be ensured that the distance between the
successive earth pits shall be min.3 mtrs and maximum upto twice the length of the
electrode i.e. 6 mtrs approx..
b. The number of pits required shall be decided based on the resistance achieved for the
earth pits already installed as the properties of the soil play a major role.
c. These earth pits shall than interlinked using 25mmx2mm copper tape to form a loop
using exothermic welding technique.. The interconnecting cable / bus bar shall be
buried at depth not less than 500mm below the ground level. This interconnecting bus
bar shall also be covered with earth enhanced compound. These connection shall be
Signature of contractor Page 9 of 104 Dy CSTE/Proj/IRPMU/CNB