MI 3290 Earth Analyser
Appendix C
–Functionality and placing of test probes
149
Measurement 2
Distance from earthing electrode E/ES to voltage probe S shall be:
S
a
d
d
1
1
2
38
,
0
52
,
0
Measurement 3
Distance from earthing electrode E/ES to voltage probe S shall be:
S
a
d
d
1
1
2
38
,
0
72
,
0
In case of a properly selected d1 the result of measurements 2 and 3 are symmetrical around
the result of measurement 1. The differences (measurement 2- measurement 1, measurement 3
- measurement 2) must be lower than 10 %. Higher differences or non-symmetric results mean
that the voltage funnels influence the measurement and the d1 should be increased.
Notes:
Initial uncertainty of measured resistance to earth depends on distance between
electrodes d1 and size of earthing electrode a. It can be seen in Table C.4.
d1/a
Uncertainty
[%]
5
10
10
5
50
1
Table C.4:
Influence of d1/a ratio to initial uncertainty
It is advisable for the measurement to be repeated at different placements of test probes.
The test probes shall also be placed in the opposite direction from tested electrode (180°
or at least 90°). The final result is an average of two or more partial results.
According to IEC 60364-
6 the distances S’-S (measurement 2) and S’’-S (measurement
3) shall be 6 m.
Equilateral placement
Figure C.5:
Equilateral placement
Measurement 1
Distance from tested earthing electrode to current probe H and voltage probe S should be at
least:
a
d
5
2
