Danfoss Drives · DKDD.PB.551.A1.02 | 27
Line Contactors: When should a line contactor be used?
Soft starters can be installed with or without a line contactor.
A line contactor disconnects the SCRs from the supply when the
motor is not in use. This isolates the soft starter, and protects the
SCRs from damage due to severe overvoltage (e.g. lightning strikes)
– SCRs are most susceptible to overvoltage damage when in the o
state. The soft starter is also isolated from the supply in the event
of a trip.
A line contactor may be required by local electrical regulations and
should be AC3 rated for the motor FLC.
The line contactor can be controlled via the soft starter’s
relay output. The inrush VA rating of the contactor coil
must not exceed the rating of the soft starter’s relay
output.
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