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 between resistance of the probes and resistance of the earth elec-
trode tested 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
example, by dampening with water the place where the probe is driven into earth, driving the probe in-
to earth in a different place or using a 80 cm-long probe. Test leads should also be checked as fol-
lows: check whether their insulation is not defective and whether the lead – banana plug – probe con-
tact areas are not corroded or loosened. In majority of cases the measurement accuracy achieved is
satisfactory. However, one should always be aware of uncertainty value the measurement is bur-
dened with.
Additional information displayed by the meter
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