GEOHM 5
Instrument description
14
2.6.2 Standard four-lead test method in combination with sensitive
test clamp
Measuring selective earth resistance (test clamp E-Clip 1)
If several earthing electrodes are connected in parallel (see figure 8), then it is very
important to know the quality of each individual electrode. This is especially important
when the earthing system is intended for protection against atmospheric discharging,
because any inductance within the earthing system presents a potential danger (due to
increased resistance to high frequency pulses during the atmospheric discharge).
In order to test each electrode separately, they should be mechanically separated, but
the mechanical connections are usually very difficult to disconnect because of corroded
connection components (screws, nuts, spacers, etc.).
The main advantage of the selective measurement method with clamp is that there is no
need to mechanically disconnect the electrode under test.
Step 1
Connect test leads and sensitive test clamp (E-Clip 1) to the instrument and to the
object under test in accordance with the figure below.
Figure 8. Connection of standard 20 m long test leads and sensitive test clamp
(E-Clip 1)
!
...Ensure that the test sensitive test clamp (E-Clip 1) is connected under the E test
terminal, otherwise the parallel resistance of all other electrodes (R
E1
up to R
E4
) will be
measured!
R
E4
selective earthing resistance of electrode E4
U
test voltage
I
clamp
the current measured by sensitive test clamp
R
S
selective earth resistance
d...............probe distance, d
20 m
tolerance depending on potential gradient
4
E
clamp
S
R
I
U
R