Earth Resistance Measurement (Four-Wire Method) - BEHA UNITEST TELARIS ERDE 8986 Manual De Instrucciones

6.2 Earth Resistance Measurement (three-wire
method) (only possible with the accessory
set, order number: 1048!)
Measurements in dangerous proximity to elec-
trical systems should only be carried out in con-
junction with clear instructions from a responsible
electrical specialist and must not be carried out
alone.
The earth measurements instrument functions in
accordance with the current-voltage measurement
principle. The so-called three-wire procedure is
used, determining the grounding resistance by
using three wires. A constant current is fed into the
earth via outputs auxiliary ground "H" and ground
"E". The voltage drop between probe and ground is
measured via probe input "S", and consequently the
earth resistance is determined and displayed.
4 Locate earth rods for auxiliary ground, probe
and ground, in one line if possible, as described
in figure 6.2.
4 Distance between probe and ground, or probe
and auxiliary ground must be at least 20 m. The
conductors should not be parallel to each other
and should not cross to avoid couplings.
4 Connect test leads to test instruments and
earthe rods/ground.
4 Select "3 pole" measurement range (13).
4 Set contact voltage (11).
4 Automatic (16) or manual (12) frequency selec-
tion and press key "Start"(14).
4 Read measurement result from display.
4 Exchange auxiliary ground "H" and ground "E" by
H S
Earth Resistance Measurement (three-wire method)
E
6.2
simple exchange of socket plugs.
4 Now press key "Start"(14), read measurement
result on display.
4 If the value displayed strongly deviates from the
first measured value, proceed as follows:
4 Relocate the probe approximately 1 ... 2 m to-
wards ground and then towards auxiliary
ground. If the instrument shows the same mea-
surement results for
surement layouts, the probe is located outside
the voltage funnel generated by ground and aux-
iliary ground, within the range of the reference
ground.
4 If the instrument shows a larger deviation, the
probe could be within the voltage funnel of the
ground or auxiliary ground. To avoid this situa-
tion, two possibilities are available:
A: Increase distance between ground and auxiliary
ground, or
B: Locate the probe (as shown in figure 6.3.1) onto
a point of the straight line, outside the voltage
funnel and repeat the measurement.
Also refer to display indications in chapter 7.0
6.2.1
all three mea-
25