1) Four spikes are driven into the ground in a straight line 15 meters apart. The spikes are connected to terminals on an earth resistance tester. 2) The resistance range is selected and the potentiometer is set to 5 to observe the null detector needle. 3) The generator handle is rotated to obtain a null deflection, indicating the earth resistance value corresponding to the dial reading multiplied by the resistance range.

1. CHAPTER THIRTEEN
PRACTICALS ON EARTH MEASUREMENTS
Measurement of Earth Resistance by using I.T.L. Earth Resistance Tester
(Model ET-1/10 )
Steps
The procedure for measuring the earth resistance is given in the following.
• Drive four spikes into ground in a straight line at an equal distance of 15 meters
in-between spikes.
• Connect the spikes to the terminals.- the first to C1, the second to P1, the third to
P2 and the fourth to C2.
• Select the resistance range using selector switch.
• Keep the potentiometer knob at 5 on the dial scale calibrated 0 to 10.
• Rotate the handle of the generator slowly and watch the deflection of the null
detector. If the needle deflects to right the earth resistance is less and if the needle
deflects to left then the earth resistance is more than 5 set on the dial.
• Increase or decrease the potentiometer knob to obtain null deflection.
• If null can not be obtained, change the position of the selector switch to higher or
lower range and repeat steps 4 to 6.
• Rotate the handle of the generator at about 160 to 180 R.P.M. and adjust the
potentiometer until "NULL" is obtained.
To know the value of the earth resistance multiply the dial reading by the value of the
range. To know the resistance of the earthing device ,connect the terminals C1 and P1 to
earthing device and P2 and C2 for spikes at a distance of 15 meters and meters in a straight
line and repeat steps 3 to 9. If the meter pointer is not steady, then increase or decrease the
cranking speed to obtain "NULL" point.
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P1 P2
C1 C2
A B C SOIL D