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5.8 Earth/Ground Measurements with Two Clamps
This is a quick way to measure the value of the earth.
NOTE: The two clamp method typically yields a measurement higher than the
fall of potential method since it uses a higher frequency to perform the test,
resulting in an impedance measurement.
The current clamp connected to terminal H (Z) applies a voltage to the circuit to be
measured. The value of the resulting current is determined by the impedance of
the circuit to be measured. The current flowing in the loop is measured using the
clamp connected to terminal ES (Xv). The device then calculates loop resistance
R
from these quantities.
LOOP
NOTE: Use only SR182 or MN82 current clamps, which are specially designed
to operate with the Model 6472.
1.
Set the switch to
2.
Connect a clamp to terminal H (Z) and clamp it to a point down stream from
the rod under test that is a serial path to the earth.
3.
Connect the other clamp to terminal ES (Xv) and clamp it to the rod or elec-
trode system to be measured.
Observe the following minimum distances between the two clamps in order to
avoid direct electromagnetic influences between the transmitting clamp and the
receiving clamp:
Value measured
50 to 100
100 to 500
Ground Resistance Tester Model 6472
.
R
E1
(Ω)
0 to 1
1 to 5
5 to 10
10 to 50
R
R
E2
E3
Minimum separation
MN82
0.1m (4")
0.4m (1' 04")
0.5m (1' 08")
0.7m (2' 04")
0.9m (3')
1.2m (4')
R
E
SR182
0m (0")
0.1m (4")
0.2m (8")
0.3m (1')
0.5m (1' 08")
0.5m (1' 08")
45
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