HT instruments М75 - Manual (Page 35)

M72 - M73 - M74 - M75
EN - 33
4.15. RA : MEASUREMENT OF GLOBAL EARTH RESISTANCE (M73, M74, M75)
CAUTION
 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. 13: Connection of the instrument’s terminals during test
1. Turn on the instrument
2. Press the arrow keys to select Ra
3. By pressing MODE/PEAK select the test current among the possible values 15mA and
100mA which turn cyclically at each key pressure
CAUTION
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
CC
= PE
N
Z
U
where:
Z
PE
is the global earth resistance value
U
N
is the nominal phase to earth voltage whose value is:
127V if 100V ≤ V
measured
< 150V
230V if 150V ≤ V
measured
< 265V
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. 13)
Or:
5. Insert the Shuko cable in the input terminals of the instruments
6. Insert the Shuko cable in a power socket (as shown in Fig. 13). The picture
represents the connection to power socket