Ra : Measurement Of Global Earth Resistance (M73, M74, M75) - HT MULTITEST M72 User Manual

4.11. RA : MEASUREMENT OF GLOBAL EARTH RESISTANCE (M73, M74, M75)
Disconnect all loads connected to the lower end of the RCD as they could
introduce additional leakage currents, thus nullifying the test results. Is possible to
perform measurement on plants whose phase to earth rated voltage is up to
265V. Do not use the instrument on plants whose interlinked rated voltage is
higher than 550V.
Fig. 12: Connection of the instrument's terminals during Ra
1. Turn on the instrument
2.
Press the arrow keys to select Ra
By pressing MODE select the test current among the possible values 15mA
MODE
3.
and 100mA which turn cyclically at each key pressure
PEAK
If a RCD is present, select a lower current value than the nominal current
value of the device. Otherwise the RCD could trip during the measurement
and therefore prevent it from being executed.
4. By selecting a test current of 100mA you will get also the value of the prospective short
circuit current phase to earth, calculated according to the formula I
Z is the global earth resistance value
PE
U is the nominal phase to earth voltage whose value is: 127V if 100V ≤ V
N
As an alternative:
5. Insert the black and green cables in the corresponding input terminals of the
instrument. If necessary insert the croco climps on the test probes
6. Connect the green cable of the instrument to the protective conductor (earth) and
the black cable to the phase conductor (as shown in Fig. 12)
MULTITEST M72 - M73 - M74 - M75
CAUTION
CAUTION
230V if 150V ≤ V
EN - 33
test
U
= where:
N
CC Z
PE
< 150V
measured
< 265V
measured