Delta C2000 Series User Manual page 675

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 a
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.
Criteria for earthing system and EMC
Safety of
Personnel
Safety of property
TN-S
Good
Continuity of the PE Continuity of the PE
conductor must be conductor must be
ensured throughout ensured throughout
the installation the installation
Poor
High fault current High fault current
(around 1kA) (around 1kA)
TN-C TT
Good Good
RCD is mandatory
Poor Good
Medium fault current
(< a few dozen
amperes)
8
IT
Good
Continuity of the PE
conductor must be
ensured throughout
the installation
Good
Low current at the
first fault (< a few
dozen mA) but high
current at the
second fault