Toshiba NC1 Fault Codes List

Troubleshoot your Toshiba VF-NC1 micro-drive with our updated fault code guide. Learn to interpret OC, OL, and OP trips, view the LED trip history, and reset faults.

Toshiba NC1 Fault Codes Reference Table

Below is the complete list of trip codes and alarms. Please refer to this table to match the flashing code on your micro-drive with the specific hardware issue.

Toshiba Inverter Trip Information and Remedies

Fault Code and Meaning	Cause and Remedy
OC1 / OC1P Overcurrent during acceleration	Cause: The acceleration time (ACC) is too short. The V/F setting is improper. A restart signal is input to the rotating motor after a momentary stop. A special motor (e.g. motor with small impedance) is used. Remedy: Increase the acceleration time (ACC). Check the V/F parameter. Use F301 (auto-restart) and F302 (ride-through control). Increase or decrease the carrier frequency (F300).
OC2 / OC2P Overcurrent during deceleration	Cause: The deceleration time (dEC) is too short. Remedy: Increase the deceleration time (dEC).
OC3 / OC3P Overcurrent during operation	Cause: The load fluctuates abruptly. The load is in an abnormal condition. Remedy: Reduce the load fluctuation. Check the load (operated machine).
OCR Arm overcurrent at start-up	Cause: A main circuit element is defective. Remedy: Make a service call.
OCL Overcurrent (load side at start-up)	Cause: The insulation of the output main circuit or motor is defective. The motor has too small impedance. Remedy: Check the cables and wires for defective insulation.
OP1 Overvoltage during acceleration	Cause: The input voltage fluctuates abnormally. The power supply has a capacity of 200kVA or more. A power factor improvement capacitor is opened or closed. A system using a thyristor is connected to the same power distribution line. A restart signal is input to the rotating motor after a momentary stop. Remedy: Insert a suitable input reactor. Use F301 (auto-restart) and F302 (ride-through control).
OP2 Overvoltage during deceleration	Cause: The deceleration time (dEC) is too short (Regenerative energy is too large). F305 (overvoltage limit operation) is off. The input voltage fluctuates abnormally. Remedy: Increase the deceleration time (dEC). Enable F305 (overvoltage limit operation). Insert a suitable input reactor.
OP3 Overvoltage during constant-speed operation	Cause: The input voltage fluctuates abnormally. The motor is in a regenerative state because the load causes the motor to run at a frequency higher than the inverter output frequency. Remedy: Insert a suitable input reactor.
OL1 Inverter overload	Cause: The acceleration time (ACC) is too short. The DC braking amount is too large. The V/F setting is improper. A restart signal is input to the rotating motor after a momentary stop. The load is too large. Remedy: Increase the acceleration time (ACC). Reduce the DC braking amount (F251) and the DC braking time (F252). Check the V/F parameter setting. Use F301 (auto-restart) and F302 (ride-through control). Use an inverter with a larger rating.
OL2 Motor overload	Cause: The V/F setting is improper. The motor is locked up. Low-speed operation is performed continuously. An excessive load is applied to the motor during operation. Remedy: Check the V/F parameter setting. Check the load (operated machine). Adjust OLM to the overload that the motor can withstand during operation in a low speed range.
EPH0 Output phase failure	Cause: A phase failure occurred in the output line of the main circuit. Remedy: Check the main circuit output line, motor, etc., for phase failure. Enable F605 (Output phase failure detection).
EPH1 Input phase failure	Cause: A phase failure occurred in the input line of the main circuit. The inverter may trip because of EPH1 if switching between acceleration and deceleration is done in succession at intervals of less than 1 second. Remedy: Check the main circuit input line for phase failure. Enable F608 (input phase failure detection). Set the F608 parameter to 0.
OH Overheat	Cause: The cooling fan does not rotate. The ambient temperature is too high. The vent is blocked up. A heat generating device is installed close to the inverter. The thermistor in the unit is broken. Remedy: Restart the operation by resetting the inverter after it has cooled down enough. The fan requires replacement if it does not rotate during operation. Secure sufficient space around the inverter. Do not place any heat-generating device near the inverter. Make a service call.
*UP1 Undervoltage trip (main circuit)	Cause: The input voltage (in the main circuit) is too low. Remedy: Check the input voltage. Enable F627 (undervoltage trip selection). To cope with a momentary stop due to undervoltage, enable F302 (ride-through control) and F301 (auto-restart).
EF2 Ground fault trip / Arm overcurrent	Cause: A ground fault occurs in the output cable or the motor. A main circuit element is defective. Remedy: Check the cable and the motor for ground faults. Make a service call.
E Emergency stop	Cause: During automatic operation or remote operation, a stop command is entered from the operation panel or a remote input device. Remedy: Reset the inverter.
Err2 Main unit RAM fault	Cause: The control RAM is defective. Remedy: Make a service call.
Err3 Main unit ROM fault	Cause: The control ROM is defective. Remedy: Make a service call.
Err4 CPU fault trip	Cause: The control CPU is defective. Remedy: Make a service call.
Err5 Remote control error	Cause: An error arises during remote operation. Remedy: Check the remote control device, cables, etc.
Err7 Current detector fault	Cause: The current detector is defective. Remedy: Make a service call.
EEP1 EEPROM fault 1	Cause: A data writing error occurs. Remedy: Turn off the inverter, then turn it on again. If it does not recover from the error, make a service call.
EEP2 EEPROM fault 2	Cause: Power supply is cut off during tyP operation and data writing is aborted. Remedy: Turn the power off temporarily and turn it back on, and then try tyP operation again.
EEP3 EEPROM fault 3	Cause: A data writing error occurs. Remedy: Turn off the inverter, then turn it on again. If it does not recover from the error, make a service call.
E-18 Break in analog signal cable	Cause: The signal input via VI/S3 is below the analog signal detection level set with F633. Remedy: Check the cables for breaks and change the setting of F633 if no breaks are found.
E-19 CPU communications error	Cause: A communications error occurs between control CPUs. Remedy: Make a service call.
E-20 Excessive torque boosted	Cause: The torque boost parameter (vb) is set too high. The impedance of the motor is too small. Remedy: Decrease the setting of the torque boost parameter (vb). If no improvement results, contact Toshiba Technical Support Center.
OFF ST terminal OFF	Cause: The ST-CC circuit is opened. Remedy: Close the ST-CC circuit.
nOFF Undervoltage in main circuit	Cause: The supply voltage between R, S and T is under voltage. Remedy: Measure the main circuit supply voltage. If the voltage is at a normal level, the inverter requires repairing.
rtry Retry in process	Cause: The inverter is in the process of retry. A momentary stop occurred. Remedy: The inverter is normal if it restarts after several tens of seconds. Be careful of the machine because it may suddenly restart.
Err1 Frequency point setting error	Cause: The frequency setting signals at points 1 and 2 are set too close to each other. Remedy: Set the frequency setting signals at points 1 and 2 apart from each other.
CLr Clear command acceptable	Cause: This message is displayed when pressing the STOP key while an error code is displayed. Remedy: Press the STOP key again to clear the trip.
EOFF Emergency stop command acceptable	Cause: The operation panel is used to stop the operation in automatic control or remote control mode. Remedy: Press the STOP key for an emergency stop. To cancel the emergency stop, press any other key.
HI / LO Setting error alarm	Cause: An error is found in a setting when data is reading or writing. Remedy: Check whether the setting is made correctly.
HEAd / End Display of first/last data items	Cause: The first or last data item in the data group is displayed. Remedy: Press the MON key to exit the data group.
db DC braking	Cause: DC braking in process. Remedy: The message goes off in several tens of seconds if no problem occurs.
E1 Flowing out of excess number of digits	Cause: The numeric value displayed (e.g., frequency) has a larger number of digits than the display panel. Remedy: When a frequency is displayed, decrease the setting of F702 (free unit).
StOP Momentary power failure slowdown stop prohibition	Cause: The slowdown stop prohibition function set with F302 (momentary power failure ride-through operation) is activated. Remedy: To restart operation, reset the inverter or input an operation signal again.
Init Parameters in the process of initialization	Cause: Parameters are being initialized to default values. Remedy: Normal if the message disappears after a while.
E-17 Operation panel key fault	Cause: The RUN or STOP key is held down for more than 5 seconds. The RUN or STOP key is faulty. Remedy: Check the operation panel.
E-50 Source logic switching confirmation alarm	Cause: The input terminal is switched to source logic mode. Remedy: Check whether cables are connected correctly, and then specify a proper logic. Check whether cables are connected correctly, and then reset the inverter or turn it off temporarily and turn it back on. Logics will be switched.
C, P, L, H Alarms displayed during operation	Cause: C: Overcurrent alarm P: Overvoltage alarm L: Overload alarm H: Overheat alarm Remedy: If two or more problems arise simultaneously, they blink in order C, P, L, H.

 

How to Read NC1 Faults via LED Keypad

The NC1 is designed for simplicity. In 2026, diagnosing this drive relies on using the prominent “Monitor” button and the center dial:

• Current Fault: When the drive trips, the LED screen immediately alternates between the fault code (e.g., OC1) and the output data.
• Trip History: The NC1 stores the last 4 faults in its internal memory. Press the MON (Monitor) key repeatedly until you reach the Trip History mode (displayed as nErr or similar). Use the center dial to scroll through past errors.
• Status Monitoring: You can check the output current (`C***`) and voltage (`P***`) in real-time to see if the motor is drawing excessive amps before it trips.

General Troubleshooting Steps

Since the NC1 is often used on small motors without heavy protection, perform these checks:

1. Overcurrent (OC1/OC2/OC3): The NC1 is very sensitive to acceleration rates. If you get OC1, try increasing the Acceleration Time (Parameter ACC). Also, check for a locked rotor on the machine.
2. Overload (OL1/OL2): OL1 is Motor Overload; OL2 is Inverter Overload. This often happens if the “Motor Rated Current” (Parameter tHr) is not set correctly to match the motor nameplate.
3. Overvoltage (OP1/OP2/OP3): Because the NC1 is a small drive, it has limited braking capacity. If you get OP during deceleration, you must increase the Deceleration Time (Parameter dEC).

Frequently Asked Questions (FAQ)

Q: What does the flashing “C” or “CL” code mean?

A: This is a Current Limit alarm, not a fault. It means the motor is drawing more current than the drive allows, and the drive is automatically lowering the frequency (slowing down) to prevent an Overcurrent trip. Check your load for jams.

Q: How do I reset a Toshiba NC1 fault?

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

• Press the STOP/RESET button on the front panel twice.
• Close the digital input assigned to Reset (usually Terminal S3 or similar, depending on programming).
• Cycle the input power (Turn OFF, wait for the LED to go dark, Turn ON).

Q: Why does the display say “OFF”?

A: OFF indicates the drive is powered up and in standby mode. It is waiting for a Run command (either from the RUN button or a terminal input) and is not in a fault state.