User Manual

GMC-I Messtechnik GmbH 39
10.8 Earthing Resistance Measurement, Battery Operated – 4-Pole (only MPRO & MXTRA)
4-Wire Method
The 4-wire method is used in the case of high cable resistance
between the earth electrode and the instrument terminal.
The resistance of the cable between the earth electrode and the
“E” terminal at the instrument is measured in this case.
Figure 10.8.1:Measurement of Earthing Resistance with 4-Wire Method
Connection
➭ Position the spikes for the probe and the auxiliary electrode at
least 20, respectively 40 meters from the electrode (see figure
above).
➭ Make sure that no excessively high contact resistances occur
between the probe and the ground.
➭ Attach the PRO-RE adapter (Z501S) to the test plug.
➭ Connect the probes, the auxiliary electrode and the electrode
via the 4 mm banana plug sockets at the PRO-RE adapter.
In doing so, observe labeling on the banana plug sockets.
Note
In the case of the 4-wire method, the earth electrode is
connected to the “E” and “ES” terminals with two sepa-
rate measurement cables, the probe is connected to the
“S” terminal and the auxiliary earth electrode is connected
to the “H” terminal.
Note
The measurement cables must be well insulated in order
to prevent shunting. In order to keep the influence of pos-
sible coupling to a minimum, the measurement cables
should not cross each other or run parallel to each other
over any considerable distance.
Select Measuring Function
Select Operating Mode
The selected operating mode is displayed inversely:
white battery icon against black background.
Set Parameters
❑ Measuring range: AUTO, 50 kΩ, 20 kΩ, 2 kΩ, 200 Ω, 20 Ω
❑ Connection type: 4-pole
❑ Transformer ratio: irrelevant in this case
❑ Distance d (for measuring
ρ
E
): irrelevant in this case
Start Measurement
Potential Gradient Area
Information regarding suitable positioning of the probe and the
auxiliary earth electrode can be obtained by observing voltage
characteristics or dissipation resistance in the ground.
The measuring current from the earth tester which flows via the
earth electrode and the auxiliary earth electrode causes a given
potential distribution in the form of a potential gradient area (see
also Figure 10.8.3: on page 40). Resistance distribution is analo-
gous to potential distribution.
Dissipation resistance of the earth electrode and the auxiliary
earth electrode differs as a rule. The potential gradient area and
the resistance gradient area are thus not symmetrical.
Dissipation Resistance of Small Scope Earth Electrodes
The arrangement of the probe and the auxiliary earth electrode is
very important for correct determination of the dissipation resis-
tance of earth electrodes.
The probe must be positioned between the earth electrode and
the auxiliary earth electrode within the so-called neutral zone (ref-
erence earth) (see also Figure 10.8.2: on page 40).
The voltage or resistance curve is thus nearly horizontal within the
neutral zone.
Proceed as follows in order to select suitable probe and auxiliary
earth electrode resistances:
➭ Drive the auxiliary earth electrode into the ground at a dis-
tance of roughly 40 meters from the earth electrode.
PROFITEST MPRO, PROFITEST MXTRA
SHESE
E
SH
≥ 20 m ≥ 20 m
R
E