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Why does my ATS48 soft starter show PHF fault when stopping the motor?

Issue:
Why does my ATS48 soft starter show PHF fault when stopping the motor?

Product Line:
ATS48 soft starters

Environment:
All models, All serial numbers

Cause:
Information unavailable in current literature.

Resolution:
PHF is caused by too great of an imbalance in the current draw of the output phases.  If one phase is pulling considerably more or less current than the other two, PHF can occur.   PHF can also occur if one or more output phases are pulling no current (open phase).

If PHF is occurring when stopping the motor, the most common cause is found when there is a contactor between the output of the starter and the motor that is opening before the soft starter has received the command to stop.  The soft starter will display PHF fault within 200ms. of the output contactor opening if it has not received a command to stop yet.  If you are using an output contactor between the motor and the starter, make sure that it stays closed until the soft starter has stopped sending power to the motor and it displaying "RDY".






Customer has an output contactor between the starter and the motor.  This contactor opens as soon as their run command is removed.  The soft starter is configured for Freewheel stop but if the contactor opens before the starter receives the command to stop, the PHF fault will occur.  I advised adding a time delay of at least .5 seconds after the run command is removed before the output contactor is allowed to open.

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