emerson commander sk fault codes

emerson commander sk fault codes – Troubleshoot your Emerson Commander SK drive with our updated 2026 fault code guide. Learn to read OU, OI.AC, and HF codes, view the trip log via CTSoft, and reset faults to minimize downtime.

The Emerson (now Nidec / Control Techniques) Commander SK is a compact, easy-to-use AC general-purpose drive. Unlike drives with full-text LCD screens, the Commander SK uses a simple LED display that flashes specific alphanumeric codes when a trip occurs (e.g., OU, OI.AC, HFxx).

This guide provides the most updated resources for 2026 to help you decipher these codes and get your motor running again safely.

Commander SK Fault Codes Reference Table

Below is the complete list of trip codes and “HF” (Hardware Fault) codes. Please refer to this table to match the flashing code on your drive’s display with the specific issue.

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 CTSoft

While the LED keypad provides a basic 2-3 character trip code, connecting your PC to the drive using the CTSoft (or the newer Connect) software allows for deeper diagnostics.

Current Trip: The software dashboard clearly displays the active trip explanation, removing the guesswork from deciphering abbreviations like “It.AC”.
Trip Log (History): The Commander SK stores the last 10 trips in Parameters 10.20 through 10.29. You can view these via the software or by unlocking “Level 2” or “Level 3” access on the keypad to see the historical sequence of failures.
Status at Trip: Advanced diagnostics can freeze-frame data such as the DC bus voltage and motor current at the moment the trip occurred, helping you identify if a spike caused the issue.

General Troubleshooting Steps

Before performing a reset, ensure you check the following key areas:

Check Input Voltage: For UU (Under Voltage) trips, ensure your AC supply is stable. For OU (Over Voltage), check if the deceleration ramp is too short for the load inertia.
Inspect Motor/Cables: For OI.AC (Over Current) or OI.br (Braking Resistor Over Current), disconnect the motor and check for phase-to-phase or phase-to-ground shorts with a megger.
Verify Cooling: For O.ht2 (Heatsink Over Temperature), ensure the drive’s internal fan is spinning and the cabinet vents are not blocked.

Frequently Asked Questions (FAQ)

Q: What does an “HF” code mean (e.g., HF20, HF25)?

A: HF stands for Hardware Fault. These are critical internal failures (such as DSP communication errors or current sensor failures) that usually cannot be reset by the user. If a power cycle (turning power off for 5 minutes and back on) does not clear an HF code, the drive typically requires repair or replacement.

Q: How do I reset an Emerson Commander SK fault?

A: You can reset the drive using one of these methods:

Press the red Stop/Reset button on the keypad.
Toggle the Enable/Reset digital input (Terminal B4) from High to Low to High.
Send a reset command via the Serial Comms or Fieldbus interface.

Q: Why is my drive flashing “tunE”?

A: This is not a fault; it indicates the drive is attempting to perform an Auto-Tune. The drive requires a Run command to complete this process. If the run command is removed before completion, it may trip on tunE.