Open transition transfer The Filax is an open transition (break before make) transfer switch. The maximum load transfer time is 16ms. The load is normally supplied by the priority source, and is transferred to the alternate source if: The voltage of the priority source drops below the threshold value. The frequency of the priority source drops below the low frequency threshold value, or increases beyond the high frequency threshold value. Reverse transfer from the alternate source to the priority source is initiated when the priority source has operated within the voltage and frequency reverse switching limits during 30s.