Read out the result.
Resistance of current electrode
Resistance of voltage electrode
The value of additional uncertainty,
generated by the resistance
of auxiliary electrodes
Repeat the measurements (steps 2, 11, 12) moving the
voltage a few meters - placing it farther and closer to the
measured earth electrode. If R
E
measurement results dif-
fer from one another by more than 3 %, the distance of
the current electrode from the earth electrode being test-
ed should be considerably increased and the measure-
ments should be repeated.
Measurement of resistance-to-earth may be carried out if voltage of interfer-
ences does not exceed 24 V. Voltage of interferences is measured up to the
level of 100 V, but above 50 V it is signalled as dangerous. The meter must not
be connected to voltages exceeding 100 V.
- Particular attention should be paid to quality of connection between the object being tested and the
test lead – the contact area must be free from paint, rust, etc.
- If resistance of test probes is too high, R
E
earth electrode measurement will be burdened with addi-
tional uncertainty. Particularly high uncertainty of measurement occurs when a small value of re-
sistance-to-earth is measured with probes that have a weak contact with earth (such a situation oc-
curs frequently when the earth electrode is well made and the upper soil layer is dry and slightly con-
ductive). In such a case, the ratio of resistance of the probes to resistance of the tested earth elec-
trode is very high and consequently, uncertainty of measurement that depends on this ratio is also
very high. The uncertainty is displayed on the screen in the column of additional results. In order to
reduce the uncertainty, it is recommended to improve the contact between the probe and soil, for ex-
ample, by dampening with water the place where the probe is driven into earth, driving the probe into
earth in a different place or using a 80 cm-long probe. Check also the test leads for possible insula-
tion damage and for corroded or loosened connection between the banana plug and the test lead. In
majority of cases the achieved measurement accuracy is satisfactory. However, you should always
be aware of the uncertainty included in the measurement.
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