Technical FAQs

Ask a Question

What causes USF on an ATS22 series soft starter?

Issue:
What causes USF on an ATS22 series soft starter?

Product Line:
Altistart 22 ATS22

Environment:
All models, All serial numbers.

Cause:
USF is being triggered when the starter is supplied with proper power.

Resolution:
USF is an Undervoltage Fault.  Basically, the incoming supply voltage is too low.  The following parameters affect the USF fault:

In the ConF menu, parameter UIn should be set to the nominal incoming 3 phase voltage.  The factory default is 480V.
In the PrO menu, parameter USd ( Under Voltage Threshold ) sets the threshold as a percentage of parameter UIn.  Parameter USt  (Under Voltage Time Delay ) sets the amount of time delay in seconds until a USF trip.  The voltage must remain under the threshold for the entire delay to activate the fault.

Note that the undervoltage protection feature becomes operational only after a run command has been issued.  When voltage drops to zero, the soft starter will trip immediately, overriding the time delay.

Example: 
Uln= 480V, USd = 70%, USt = 5 seconds.   So, if after a run command is issued, the incoming voltage drops to less than 336 volts (480V * 70%)  and stays there for more than 5 seconds, USF will be triggered.
Was this helpful?
What can we do to improve the information ?