What causes USF on an ATS22 series soft starter?
Altistart 22 ATS22
All models, All serial numbers.
USF is being triggered when the starter is supplied with proper power.
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.
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.