Instructions

GMC-I Messtechnik GmbH 43
10.11 Earthing Resistance Measurement, Battery Powered
– Measurement of Soil Resistivity ρ
E
(only MPRO & MXTRA)
General
Measurement of Soil Resistivity
The determination of soil resistivity is necessary for the planning of
earthing systems. Reliable values need to be ascertained which
take even the worst possible conditions into account (see “Geo-
logic Evaluation” on page 44).
Soil resistivity is decisive with regard to the magnitude of an earth
electrode’s dissipation resistance. Soil resistivity can be measured
with the PROFITEST MASTER using the method according to Wen-
ner.
Four earth spikes of greatest possible length are driven into the
ground in a straight line at distance d from one another, and are
connected to the earth tester (see figure above).
The earth spikes usually have a length of 30 to 50 cm. Longer
earth spikes can be used for soil which demonstrates poor con-
ductivity (sandy soil etc.). The depth to which the earth spikes are
driven into the ground may not exceed one twentieth of distance
d.
Note
Erroneous measurement may result in the event that pip-
ing, cables or other underground metal conduits run par-
allel to the measuring setup.
Soil resistivity is calculated as follows:
ρ
E
=2π ⋅ d ⋅ R
Where:
π = 3.1416
d = distance in m between two earth spikes
R = ascertained resistance value in Ω (this value corresponds to R
E
as
determined with the 4-wire method)
Connection
➭ Position the spikes for the probe and the auxiliary electrode at
equal distances (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.
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:
ρ
E
(Rho)
❑ Transformer ratio: irrelevant in this case
❑ Distance d for measurement of
ρ
E
: adjustable from 0.1 to 999 m
Start Measurement
ES ESH
dd d
R
E