In certain applications, parallel switching of several frequency converters on the same contactor can be required on both technical and financial grounds.

Often this is problematic, since account is not always taken of certain frequency converters' relatively high starting current - also called inrush current. For some frequency converters the inrush current can be in the range of 15-20 times the nominal maximum input current, I_L.N.

The inrush current occurs simultaneously with the contactor's contact bounce, and therefore the contact material is particularly vulnerable, as stated in the article "Danfoss CI Contactors for the VLT^® Frequency Converter's Mains Side" in The Danfoss Journal 1-1996. It is therefore very important to ensure an even, correct load of the contactor when several frequency converters are mounted on the same contactor.