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1625
Users Manual
The Influence of Potential Gradient Areas on Earth Resis-
tance Measurement
To pick off the true voltage drop from the earthing resistance (= the resistance
between the earth electrode and the soil potential F
probe is set outside the potential gradient area of all connected earth electrodes
and the auxiliary earth electrode H.
V
I1
E1
A probe positioned inside a potential gradient area leads to incorrect measuring
results. As it can be seen in the picture above, probe voltages U
probes S
and S
deliver a value too low, which also means that the earthing
1
2
resistance appears to be lower than it actually is(low resistance). Probe S
U
on the other hand, picks up a value too high which indicates a worse (high
S4
resistance) earthing conditions.
Only probe S
picks up the correct voltage between earth electrode and soil
3
potential F
.
E
For that reason it is advisable to repeat each measurement with repositioned
probes and only to regard a measurement as successful and accurate if several
subsequent measurements result in the same values.
Normally, a distance of 20 m to the earth electrode and to the probes to each
other is sufficient.
80
I
U
S1
U
S2
V
I2
S1
S2
E2
U
S1
U
S2
) it is to be assured that the
E
U
G
G
U
S2
V
S3
U
S3
F
E
I
U
S4
V
H
S4
U
S4
U
G
edw059.eps
and U
of
S1
S2
with
4
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