Earth Resistance Measurement (Four-Wire Method); Measurement Of The Specific Earth Resistance In Accordance With The 'Wenner' Method - Unitest TELARIS ERDE Bedienungsanleitung

Commissioning
6.3 Earth Resistance Measurement
(four-wire method)
and only possible with the accessory set, order
number:1048!
The four-wire measurement is applied instead of
the three-wire measurement when dealing with ex-
tremely low earth resistances and if the resistance
of test lead between instrument and earth connec-
tor interfere the measurement result.
Here, the earth to be measured is connected via the
connectors E and ES, the measurement selection
switch is set to "4pol" and a measurement are per-
formed as described in section 6.2.
H
S
ES
Figure 6: four-wire mesurement
6.4 Measurement of the Specific Earth
resistance in accordance with the
'Wenner' method
To perform this measurement the user re-
quires the UNITEST Earth Measurement Set
(Cat. No.1048)
To calculate the spreading resistance of earths and
earthing systems the specific earth resistance must
be determined. To calculate the specific earth re-
sistance, the measured earth resistance is used in
π
the formula: ρ = 2*
*a*RE.
This measurement is performed using four earth
rods inserted into the soil to be tested in one line at
the same distance 'a' apart. The four earth rods are
inserted into a depth of maximum 1/5th of the dis-
tance 'a'.
26
E
The earth resistance is detected up to the depth of
the distance 'a'. To avoid faulty measurements
metal pipes, cables in the earth, or in open areas
under earth waterways, or roots installed or locat-
ed in parallel must be taken into account. Addition-
ally, the specific earth resistance is subject to sea-
sonal weather-related variations.
H
S
ES
Figure 7: Specific Earth resistance measurement
Place the four earth rods for E, ES, S, H in one
line, in accordance with Figure 7. The distance
between each probes must match the value used
in the formula. Carefully place the test leads
making sure that the test leads are not parallel
to each other and do not cross to avoid coupling.
Connect test leads to earth rods according to
Figure 7.
Selct "4 pole" measurement by using selection
switch (13).
Set contact voltage by using key "UL" (11).
If required choose maunal frequency selection
by using key "auto/man" (16), and select test
frequency with key "f1/f2" (12).
Press key "Start"(14), read measurement result
on display.
After the measurement, selection can be made
between display of earth resitance (RE), auxil-
larx resistance (RS) and measurement current
(IM) by using key "Display" (8), depending on
the measurement result.
E