User Manual
Product description
3.3 Functional principle of the SIRIUS 3RW30 and 3RW40 soft starters
SIRIUS 3RW30 / 3RW40
22 Manual, 10/2010, 535199502000 DS 03
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Figure 3-8 Starting current asymmetry
Note
If wye-delta starters are exchanged for soft starters in an existing system, you should check
the fuse ratings in the feeder in order to avoid false tripping. This is particularly important in
connection with heavy-duty starting or if the fuse that is installed has already been operated
close to the thermal tripping limit with the wye-delta assembly.
All elements of the main circuit (such as fuses, motor starter protectors, and switching
devices) must be dimensioned for direct starting and according to the on-site short-circuit
conditions, and ordered separately.
For recommended fuse and motor starter protector ratings for the feeder with soft starter,
refer to chapter Technical data (Page 127).