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The circuit only has one load: the IT system transformer. Taking into consideration the ex-
planation in section 710.537.6 as well as the manufacturer's technical data for the contactor,
the maximum possible fuse (F1 or F2) for the contactor can be calculated as follows:
I
= Manufacturer's technical data regarding max. fuse x 0.45
v
The fuse must match the fuse specified by the manufacturer of the selected IT system trans-
former.
The rated operational current I
I
= Manufacturer's technical data for the switching contact with consideration of
e
AC-3 conditions x 0.45
This rated operational current must be greater than the rated operational current of the IT
system transformer.
4.1.2
Selecting a fuse with several loads
This circuit branches into several load groups. The result is that every fuse of every load
group is moved downstream of the changeover module. Regardless of this, the maximum
possible fuse is calculated in the same way as described above.
The rating of this fuse (F1 or F2) must be coordinated with the rating of fuse F3 (and of
course F4 and F5) so that selective shutdown is ensured. The fuse specified by the manufac-
turer for the IT system transformer must therefore be at least two stages smaller in rating
than the fuse calculated using the formula above for the changeover module. Of course, the
total nominal current for the changeover module must be calculated from the sum and simul-
taneity factor of all load groups connected, and the required or minimum rated current cal-
culated according to the formula above.
The values listed in the ordering information apply for the changeover modules.
16
All manuals and user guides at all-guides.com
of the changeover module is calculated as follows:
e
F1
F2
2
2
Changeover module
Contactors with latching
F3
F4
F5
Circuit breaker
Installation and connection
TGH1322en/06.2009
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