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Appendix: IT Systems
40 Symmetra MW 800 kW 3 × 400/230 V Installation - 990-1510D
In installations where the neutral is distributed, the following conditions must be fulfilled:
In the condition:
Protective devices in IT systems
The following protective devices are recognized in IT systems:
• Insulation monitoring devices
• Overcurrent protective devices
• Residual current protective devices
The following diagram shows a Symmetra
®
MW installed in a IT system:
• Earthing arrangements and protective conductors - Symmetra
®
MW in “IT installation”
is the nominal A
C
RMS voltage between phase and neutral
is the impedance of the fault loop comprising the phase conductor and the protective conductor of
the circuit
is the impedance of the fault loop comprising the neutral conductor and the protective conductor of
the circuit
is the operating current of the protective device. The disconnecting time is 5 seconds (distribution
circuits)
Z′
s
U
0
2I
a
×
-------------
≤
U
0
Z
s
Z′
s
I
a