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What is the difference between transition and level settings of the two wire control type (tct) parameter in Altivar drives?

Issue:
What is the difference between TRANSITION and LEVEL settings of the Two wire Control Type (TCT) parameter in Altivar drives?

Product Line:
Altivar 12,312,32,61,71 series drives and various obsolete models excluding the ATV21 and ATV212 series.

Environment:
All models, all serial numbers.

Cause:
Drive displays NST as soon as power is applied or when power is reapplied after a power outage.  When NST Status is not expected and does not power the motor.

Resolution:
Parameter TCT (Two-wire Control Type) determines the function of the drive when a run command is present on the drive at the time main power is applied to the drive.

If TCT is set to TRANSITION (TRN) The drive requires a transition from not having a run command to having a run command AFTER main power has been applied before it will start.  If the run command is already present on the drive when main power is applied to the drive the display will show NST and the drive will not start the motor.   Removing the run command after main power is applied will cause the display to change to RDY and then reapplying the run command will cause the drive to start and run.   This setting is designed to prevent a drive from powering the motor if the run command is already present at the time main power i applied to the drive.  This would be useful in situations where you would not want a motor to automatically restart after a power outage when you have a maintained run command.  

If TCT is set to LEVEL (LEL) it does not require the run command to transition after main power is applied.  If the run command is present and sufficient power is available to the drive to power the motor, it will start the motor and allow it to run, if no other fault is present.   This would be useful in situations where you do want the motor to automatically restart after a power outage  when you have a maintained run command, or in situations where you want the drive to power the motor any time main power is applied to the drive.

There are several other conditions that can cause NST to be displayed on the screen of the drive.  NST is an indication that the drive is in Freewheel Stop Mode, it is a status and not an actual fault.  If you are experiencing an NST status on your drive when you are not expecting it, rule out the TCT setting as a possible cause and continue to eliminate possible causes until the source of the problem is found.
 
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