MPI-520 – USER MANUAL
3.4 Measurement of short circuit loop parameters
If there are residual current devices in the network tested, they should be bypassed by
bridging for the period of impedance measurement. However, it should be remembered
that the circuit tested is modified in this way and the results obtained may slightly differ
from the actual results.
Each time after completion of measurements, modifications introduced to the installa-
tion for the period of measurements should be removed and operation of the residual
current device should be checked.
The above remark does not apply to measurements of short circuit loop impedance with
the use of Z
L-PE
RCD function.
Measurements of fault loop impedance performed downstream of inverters are ineffec-
tive and their results are unreliable. This is due to the instability of internal impedance
in inverter circuits during its operation. The measurements of fault loop impedance
should not be performed directly downstream of inverters.
3.4.1 Measurement of short circuit loop parameters in L-N and L-L circuit
Set the rotary switch of function se-
lection at Z
L-N,L-L
/U
L-N,L-L
position.
Press F1 push-button if lead
length L needs to be selected.
Select lead length by means
of and push-buttons
and press ENTER push-but-
ton.
Connect test leads according to the drawing
a) for measurement in L-N circuit or
b) for measurement in L-L circuit
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