Fagor DDS Series Hardware Manual page 237

IT diagram
Distribution diagram that has no direct connection to ground and the
conductive parts of the installation are connected to ground.
SECONDARY
WINDING OF THE
LINE TRANSFORMER
OF THE PLANT
F. H6/6
IT type distribution diagram.
MANDATORY. With an IT distribution diagram, always install the DDS
system to mains through an isolating transformer.
With IT type distribution diagrams, the differential breaker is used assuming
that the capacitance of mains with respect to ground is large enough to
ensure that a minimum fault current flows with the same magnitude as that
of the operating differential current assigned. Otherwise, its use is not
necessary.
INFORMATION. Note that with an IT type distribution diagram, mains can also
i
be controlled through an isolation watching device. Both protection
measurements are compatible with each other.
See figure F. H6/6 for properly installing the DDS system with an IT type
distribution diagram.
SECONDARY
WINDING OF THE
LINE TRANSFORMER
OF THE PLANT
L1
L2
L3
DIFFERENTIAL
BREAKER
MAINS
FILTER
DDS
   Power line connection
IT diagram
L1
L2
L3
DIFFERENTIAL
BREAKER
MAINS
FILTER
DDS
HARDWARE
6.
DDS
Ref.1912
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