MI 3101 EurotestAT: Appendix D
IT supply systems
108
133 V
133 V
L1
L2
230 V
133 V
L3
230 V
230 V
Optional
high
impedance
N
(Optional)
IMD
Figure D.1: General IT supply system
Three phase star connection, optional delta connection.
Optional neutral line.
Single-phase connection is also possible.
Various system voltages – not only three phase 230 V as indicated above.
One faulty connection of any line to PE is treated as first fault and is regular but it has to
be repaired as soon as possible.
IEC 60364-4-41
: In IT systems the following monitoring devices and protective devices
may be used:
-
Insulation monitoring devices (IMDs),
-
Residual current monitoring devices (RCMs),
-
Insulation fault location systems,
-
Overcurrent protective devices,
-
Residual current protective devices (RCDs).
NOTE
: Where a residual current operating device (RCD) is used, tripping of the RCD in the
event of a first fault cannot be excluded due to capacitive leakage currents.
Testing of IT supply system is slightly different to standard tests in TN / TT system.
D.3 Measurement guides
The user has to select the IT supply system in the instrument before testing it. The
procedure for selecting the IT supply system is defined in chapter
4.4.2 Supply system, Isc
factor, RCD standard.
Once the IT system is selected the instrument can be used
immediately. The instrument keeps selected IT system when it is turned off.
When the instrument detects appropriate voltage levels for selected IT system, the
terminal voltage monitor shows IT system icon
IT
.
