MI 3295 Step Contact Voltage Measuring System
Measurements
27
Specific earth resistance
For the specific earth resistance the test current is injected through two current probes
(C1/H and C2/E). The voltage probes S and ES must be placed between the current
probes (equi
distance ‘a’ between probes must be considered).
Using different distances between the test probes means that the material at different
depths is measured. By increasing the distances ‘a’ a deeper layer of ground material is
measured. More information about measuring earth resistance can be found in the
METREL handbook:
Guide for testing and verification of low voltage installations
.
Figure 7.5: Specific earth resistance measurement
Potential
The measurement is performed between an earthed accessible metal part and ground as
shown on
. The voltage between the probes is measured by a voltmeter with an
internal resistance of 1M
Ω.
Figure 7.6: Potential example