MI 3295 Step Contact Voltage Measuring System
Measurements
26
Figure 7.3: Contact/Touch voltage measurement
As the test current is usually only a small fraction of the highest fault current the measured
voltages must be up scaled according to following equation:
Gen
Fault
Measured
C
S
I
I
U
U
,
U
S,C
………..calculated Step or Contact/Touch voltage in case of fault current
U
Measured
….measured voltage during the test
I
Fault
………..maximal earth current in case of a fault
I
Gen
………..injected test current
Earth resistance
For the earthing resistance test a voltage and current probe (serves as auxiliary earth) are
used. Because of the voltage funnel it is important that the test electrodes are placed
correctly. More information about measuring earth resistance can be found in the METREL
handbook:
Guide for testing and verification of low voltage installations
.
Figure 7.4: Earth resistance measurement
