Home FAQs Motor Circuit Configurations Bypass Contactors: When and how should they be used?

Bypass Contactors: When and how should they be used?

Bypass contactors bridge out a soft starter’s SCRs when the motor is running at full speed. This eliminates heat dissipation from the SCRs during run state.

Some soft starters include built-in bypass contactors, others require an external bypass contactor.

Q39

Bypass contactors:

  • allow soft starters to be installed in sealed enclosures
  • eliminate the cost of forced-air cabinet ventilation
  • save energy by eliminating SCR losses during run

Bypass contactors should be AC1 rated for the motor FLC. The AC1 rating is adequate because the bypass contactor does not carry start current or switch fault current.