METREL MI 3125 - Fault Loop Impedance Measurement Procedure

MI 3125 EurotestCOMBO Fault loop impedance
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Fault loop impedance measurement procedure
 Select the Zloop or Zs rcd subfunction using the function selector switch and
¿/À keys
 Select test parameters (optional).
 Connect test cable to the Instaltest Combo.
 Connect test leads to the item to be tested (see figure 5.25 and 5.18).
 Press the TEST key to perform the measurement.
Figure 5.26: Examples of loop impedance measurement result
Displayed results:
Z..............Fault loop impedance,
ISC............Prospective fault current,
Lim ..........Low limit prospective short-circuit current value or high limit fault loop
impedance value for the UK version.
Prospective fault current I
SC
is calculated from measured impedance as follows:
Z
kUn
I
SC
SC
×
=
where:
Un ........Nominal U
L-PE
voltage (see table below),
ksc ....... Correction factor for Isc (see chapter 4.2.6).
U
n
Input voltage (L-PE)
115 V
(100 V
≤ U
L-PE
< 160 V)
230 V
(160 V
≤ U
L-PE
≤ 264 V)
Notes:
 High fluctuations of mains voltage can influence the measurement results (the
noise sign is displayed in the message field). In this case it is recommended
to repeat few measurements to check if the readings are stable.

This measurement will trip-out the RCD in RCD-protected electrical installation if
test Zloop is selected.
 Select Zs rcd to prevent trip-out of RCD in RCD protected installation.