Appendix A. EMC Standard Installation GuideVFD-ED
TT system
TT: The neutral point (N) of the low voltage transformer and the equipment frames (PE) are connected
to a separate earthing point. The Neutral (N) of the transformer and electrical equipment are
connected.
IT system
IT: The neutral point of the transformer and electrical equipment are not earthed, only the equipment
frames PE are earthed.
In the IT network, the power distribution system Neutral is either not connected to earth or is earthed
via high impedance. In such a system, an insulated monitoring device is used for impedance
monitoring.
A built-in filter should be disconnected by the RFI-jumper and an external filter should not be installed
when the AC motor drive or the AC servo motor drive is connected to an IT system.
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