Danfoss VLT, Pocket Manual, Page: 15 / 64

VLT ® Soft Starter Pocket Guide 15
Bypass contactors bridge out the SCRs when the motor is running at
full speed, eliminating heat dissipation during run. This allows the soft
starter to be installed in enclosures without the need for forced-air
cabinet ventilation.
If a soft starter is installed in a totally sealed enclosure (>IP54) it must
be bypassed.
Bypass contactors should be AC1 rated for the motor FLC (the bypass
contactor does not carry start current).
Soft starters may be internally or externally bypassed:
MCD 200 soft starters are internally bypassed,
with built-in bypass relays.
MCD3000 soft starters provide relay outputs to control an
externally connected bypass contactor. Dedicated bypass
terminals mean motor protection still operates even when
the soft starter is bypassed.
Bypass Contactors:
When should a bypass contactor be used?