This article describes how to dimension Danfoss CI contactors to VLT^® frequency converters´motor side, or dimension CI-TI^TM contactors and termal relays when several motors are connected on the same frequency converter.

On dimensioning of contactors and termal relays on the VLT^® frequency converter's motor side there are three primary factors to consider:

• The motor's starting current
• The rated output current, I_VLT,N
• The frequency range in which the converter is to work

The discharge capacity in the screened cables, the output current's harmonics and the position of contactor and thermal relay are secondary aspects.