Commander SK Drive Fault Codes

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Detailed guide to diagnosing Control Techniques Commander SK trip codes. Learn to interpret OI.AC, It.AC, and HF hardware faults to minimize system downtime.

Commander SK Fault Codes Reference Table

Below is the reference list of trips for the Commander SK. Locate the mnemonic appearing on your drive’s LED display to understand the protective action taken by the drive.

Commander SK Faults and Alarms

Commander SK Diagnostics (Faults & Alarms)

Fault Code and Meaning Cause and Remedy
UV

DC bus under voltage		 Cause:
  • Low AC supply voltage.
  • Low DC bus voltage when supplied by an external DC power supply.

Remedy:
Check power supply voltage and connections.
OV

DC bus over voltage		 Cause:
  • Deceleration rate set too fast for the inertia of the machine.
  • Mechanical load driving the motor.

Remedy:
Increase deceleration ramp time or install braking resistor.
OI.AC**

Drive output instantaneous over current		 Cause:
  • Insufficient ramp times.
  • Phase to phase or phase to ground short circuit on the drives output.
  • Drive requires autotuning to the motor.

Remedy:
  • Check motor and motor cable for insulation resistance.
  • If motor or motor connections changed, re-autotune drive to motor.
OI.br**

Braking resistor instantaneous over current		 Cause:
  • Excessive braking current in braking resistor.
  • Braking resistor value too small.

Remedy:
Check braking resistor value and wiring.
O.SPd

Over speed		 Cause:
Excessive motor speed (typically caused by mechanical load driving the motor).

Remedy:
Check mechanical load and speed parameters.
tunE

Auto tune stopped before completion		 Cause:
Run command removed before autotune complete.

Remedy:
Restart autotune and maintain run command.
It.br

I2t on braking resistor		 Cause:
Excessive braking resistor energy.

Remedy:
Check braking cycle and resistor rating.
It.AC

I2t on drive output current		 Cause:
  • Excessive mechanical load.
  • High impedance phase to phase or phase to ground short circuit at drive output.
  • Drive requires re-autotuning to motor.

Remedy:
Reduce load or check motor tuning.
O.ht1

IGBT over heat based on drives thermal model		 Cause:
Overheat software thermal model.

Remedy:
Check for blocked vents or fan failure.
O.ht2

Over heat based on drives heatsink		 Cause:
Heatsink temperature exceeds allowable maximum.

Remedy:
Reduce ambient temperature or check cooling fans.
th

Motor thermistor trip		 Cause:
Excessive motor temperature.

Remedy:
Check motor cooling and load.
O.Ld1*

User +24V or digital output overload		 Cause:
Excessive load or short circuit on +24 V output.

Remedy:
Check wiring on user I/O terminals.
O.ht3

Drive over-heat based on thermal model		 Cause:
Overheat software thermal model.

Remedy:
Check drive mounting and ventilation.
cL1

Analog input 1 current mode, current loss		 Cause:
Input current less than 3 mA when 4-20 or 20-4mA modes selected.

Remedy:
Check signal source and wiring.
SCL

Serial communications loss time-out		 Cause:
Loss of communication when drive is under remote control.

Remedy:
Check serial communication cables and master controller.
EEF

Internal drive EEPROM trip		 Cause:
Possible loss of parameter values.

Remedy:
Set default parameters (see Pr 29).
PH

Input phase imbalance or input phase loss		 Cause:
One of the input phases has become disconnected from the drive (applies to 200/400 V three phase drives only, not dual rated drives).

Remedy:
Check input power supply fuses and wiring.
rS

Failure to measure motors stator resistance		 Cause:
  • Motor too small for drive.
  • Motor cable disconnected during measurement.

Remedy:
Check motor rating and connections.
CL.bt

Trip initiated from the control word		 Cause:
Control word has initiated a trip.

Remedy:
Check remote control logic.
O.ht4

Power module rectifier over temperature		 Cause:
Power module rectifier temperature exceeds allowable maximum.

Remedy:
Check airflow and ambient temperature.
C.dAt

SmartStick data does not exist		 Cause:
New/empty SmartStick being read.

Remedy:
Program the SmartStick or use one with valid data.
C.Acc

SmartStick read/write fail		 Cause:
Bad connection or faulty SmartStick.

Remedy:
Re-seat SmartStick or replace it.
C.rtg

SmartStick/drive rating change		 Cause:
Already programmed SmartStick read by a drive of a different rating.

Remedy:
Use SmartStick compatible with drive rating.
O.cL

Overload on current loop input		 Cause:
Input current exceeds 25 mA.

Remedy:
Check analog input source.
HFxx trip

Hardware faults		 Cause:
Internal drive hardware fault.

Remedy:
See Commander SK Advanced User Guide.
OVL.d

I x t overload (I = current, t = time)		 Cause:
Motor current overload detected.

Remedy:
Reduce motor current (Load).
hot

Heatsink/IGBT temperature high		 Cause:
Drive thermal model limits approached.

Remedy:
Reduce ambient temperature or reduce motor current.
br.rS

Braking resistor overload		 Cause:
Braking resistor thermal limit approached.

Remedy:
See Menu 10 in the Commander SK Advanced User Guide.
AC.Lt

Drive is in current limit		 Cause:
Load requires more current than the limit set.

Remedy:
See Menu 10 in the Commander SK Advanced User Guide.
FAIL

Failed attempt to read stick		 Cause:
An attempt has been made to read the stick when the drive was not disabled or tripped, or the stick is read-only.

Remedy:
Ensure drive is disabled before reading SmartStick.
 

How to Read Commander SK Faults via Parameters

In 2026, the Commander SK’s built-in trip log remains the most reliable way to diagnose intermittent failures. You can access the last 10 trips directly through the keypad by navigating to Menu 10.

  • Trip History (Pr 10.20 to 10.29):
    • Pr 10.20: Displays the most recent trip.
    • Pr 10.21 – 10.29: Displays the 9 previous trips.
  • Diagnostic Software: If you have the CTSoft or the newer Connect software and a serial lead (CT-USB-Cable), you can view the trip log on your PC. This provides a timestamp (in run-hours) and the operating conditions at the time of the trip.
  • SmartStick & LogicStick: If your drive is equipped with a SmartStick, the trip history is often backed up to the stick, allowing you to transfer logs to another drive or a PC for analysis.

Frequently Asked Questions (FAQ)

Q: What is the difference between a Trip and a Warning?

A: A Trip (Solid code) shuts down the drive output to protect the motor and drive. A Warning (Flashing code) indicates the drive is nearing a limit—such as O.Ld1 (Load Warning)—but it will keep the motor running unless the condition worsens.

Q: How do I reset a Commander SK trip?

A: Once the cause of the fault has been cleared, you can reset the drive by:

  • Pressing the Red Reset Button on the drive’s keypad.
  • Cycling the Main Power (wait for the display to clear completely before turning it back on).
  • Toggling the Drive Enable signal (typically Terminal B2).
  • Using the Reset Command via Modbus RTU if the drive is networked.

Q: Where is the trip history stored?

A: The trip history is stored in the drive’s non-volatile memory in Menu 10. New trips automatically shift older trips down the log, with the 11th oldest trip being deleted. This log survives power cycles.

Q: What does “ih” mean on the display?

A: “ih” stands for Inhibit. This is not a fault; it means the drive is in a safe state and cannot run because the Enable signal (Terminal B2) is missing. Once the signal is applied, the display will change to “rd” (Ready).

Q: My drive shows “It.AC,” what should I check?

A: This stands for I²t on AC current (Motor Overload). Check if the motor is mechanically jammed, if the “Pr 06” (Motor Rated Current) is set correctly, or if the load has increased beyond the motor’s capacity.

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