It System; Criteria For Earthing System And Emc - Delta C2000 series User Manual

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
Availability of
energy
EMC behavior
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)
Good
Excellent
Few equipotential - Neutral and PE are
the same
Problems:
- Need to handle - Circulation of
the high leaking disturbance
currents problem of currents in exposed
the device conductive parts
(high magnetic-field
- High fault current radiation)
(transient
disturbances) - High fault currents
(transient
disturbances)
TN-C TT
Good Good
RCD is mandatory
Poor Good
Medium fault current
(< a few dozen
amperes)
Good Good
Poor Good
(prohibited)
- Over-voltage risk
- Equipotential
Problems:
- Need to handle the
high leaking
currents problem of
the device
- RCD (Residual-
current device)
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
Excellent
Poor
(should be avoided)
- Over-voltage risk
- Common–mode
filters and surge
arrestors must
handle the phase
to phase voltage.
- RCDs subject to
nuisance tripping
when common-
mode capacitors
are present
- Equivalent to TN
system for second
fault