Delta CT2000 Series User Manual page 625

Chapter 19 EMC Standard Installation GuideCT2000 Series
Criteria for earthing system and EMC
Safety of
Personnel
Safety of
property
Availability of
energy
EMC behavior
TN-S
Good
Continuity of the Continuity of the
PE conductor
PE conductor
must be must be ensured
ensured throughout the
throughout the installation
installation
Poor
High fault High fault
current (around current (around
1kA) 1kA)
Good
Excellent
(prohibited)
Few - Neutral and PE
equipotential are the same
Problems: - Circulation of
- Need to handle
disturbance
the high currents in
leaking exposed
currents conductive
problem of the parts (high
device magnetic-field
radiation)
- High fault
current - High fault
(transient currents
disturbances) (transient
disturbances)
TN-C TT
Good Good
RCD is
mandatory
Poor Good
Medium fault
current (< a few
dozen amperes)
Good Good
Poor Good
- Over-voltage
risk
- Equipotential
Problems:
- Need to handle
the high
leaking
currents
problem of the
device
- RCD
(Residual-
current device)
19-12
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