Why does the ATS46 or ATS48 get a phase fault PHF when attempting to start?


02 August 2023

ATS46 / ATS48 getting a PHF when attempting to start.

Product Line:
ATS46 and ATS48 soft starters


Open circuit between ATS and motor, open or bad connection on input line power, shorted SCR or bypass contactor, high power factor.

Possible Causes & Solutions:
  • Mains supply failure greater than 500ms when run command is present. (verify that line voltage is sufficient, stable and present on L1-L2-L3 terminals. If an isolation contactor is used, it must close within 200ms of a run command)
  • Motor current draw less than 10% of the nominal starter rating. (verify that load is present and motor is pulling sufficient current because current draw must be more than 10% of the controller rating while running without a shorting contactor)
  • SCR failure (suspect this to be case if fault occurs immediately upon start - can verify SCRs by measuring from L1 to T1, L2 to T2, L3 to T3, then reverse the meter leads and retest.  For the ATS46,  the control board must be totally removed.  When making this measurement one should see at least 50k ohms on all 6 measurements. If less, then suspect have a bad SCR in that phase
  • Power factor greater than 95% lagging
  • If the fault is detected after completion of the acceleration ramp, ensure the proper connection of the shorting contactor, if used. The output of the the shorting contactor must be connected to terminals A2-B2-C2, and must close within 200 milliseconds of reaching full speed.
  • Can occur if shorting contactor does not drop out within 500ms of stop (Look at associated relay which may be dropping it out due to noise)
    • Confirm whether the shorting contactor is the issue by removing contactor out of the system by disconnecting and see if the Soft Starter will run without getting the PHF fault.
  • Check for open phases including:
    • Blown Fuses
    • Open or loose power connections
  • Check connections to measurement board to confirm they are secure and clean
  • Verify the motor and the output wiring are good
  • If you suspect external and load issue, you can test with smaller motor or same motor with SST (in level 3 for ATS46 or drC menu for ATS48) ON which is test on low power motor or maintenance mode -- If current is the issue, then with this on the unit should get up to speed and run.  NOTE: SST parameter will reset to OFF after a power cycle.
  • Verify that there are no devices on line or load side such as contactors or overloads that may be open.
  • If the motor can be run across the line, measure current on each phase. They should be equal. An imbalance could indicate a bad motor.

Additionally verify wiring to shorting contactor. It may have wires reversed on the contactor input as compared to the contactor output. Terminal A1 should go through shorting contactor to terminal A2, Terminal B1 should go through shorting contactor to terminal B2 and terminal C1 should go through shorting contactor to terminal C2.