How to Reset a Toshiba VF-nC3 After a Trip

When a Toshiba VF-nC3 trips because of a fault or abnormal operating condition, do not reset the inverter before identifying and removing the cause. Resetting the drive while the original problem is still present will normally result in another trip and, in some cases, may place additional stress on the inverter, motor or driven machine.

After the cause has been corrected, the VF-nC3 can be restored in several ways. Power can be switched OFF and left OFF until the operation-panel LEDs are completely extinguished. The behaviour after a power cycle depends partly on the F602 trip-hold setting.

The inverter can also be reset from an external control signal. When the reset function is assigned to a programmable input terminal, the RES and CC terminals can be used to issue the reset command. A trip-clear command may also be sent through serial communication.

Resetting the VF-nC3 from the operation panel

Press the STOP key and confirm that CLr appears on the display. After confirming that the cause of the trip has been removed, press the STOP key again to reset the inverter.

Important: Resetting the inverter is not a repair. If the same fault returns, investigate the electrical, mechanical or parameter-related cause before continuing operation.

Reset delay after OL1, OL2 and OH trips

When OL1 – inverter overload or OL2 – motor overload is active, the VF-nC3 cannot always be reset immediately. The internal thermal model requires a virtual cooling period before an external or panel reset is accepted.

OL1: approximately 30 seconds after the trip.
OL2: approximately 120 seconds after the trip.

After an OH – overheat trip, wait until the internal inverter temperature has fallen sufficiently. If OH occurs repeatedly, check the cooling fan, ventilation path, cabinet temperature and installation clearance rather than simply resetting the drive.

The inverter also cannot be reset while an external emergency-stop command remains active at the control terminals.

The motor runs in the wrong direction

With the inverter completely de-energized, interchange any two of the U, V and W motor-output phases. If direction is controlled from an external device, check the forward and reverse command inputs instead. For panel operation, verify the setting of the Fr parameter.

Note: Motor direction should be changed at the motor-output side or through the forward/reverse command. Changing the inverter input phases is not the correct method for reversing motor rotation.

The motor runs, but its speed does not change normally

First check the mechanical load. If the load is excessive, the inverter may activate stall-prevention control and automatically restrict the output frequency.

If the Soft Stall / stall-prevention function is active, the drive may reduce motor speed to avoid an overcurrent or overload trip. Therefore, a motor that refuses to accelerate is not always suffering from a frequency-reference problem.

Check maximum frequency Fh and upper-limit frequency UL. If an analog frequency reference is used, check the actual signal level, wiring and point-1 / point-2 scaling parameters.

When the problem occurs mainly at low speed, verify that torque boost ub is not excessive and check acceleration time ACC.

The motor does not accelerate or decelerate smoothly

Acceleration time ACC or deceleration time dEC may be too short for the connected mechanical load. Increase the appropriate time and observe the motor under actual operating conditions.

A very short deceleration time on a high-inertia machine can also cause regenerative energy to raise the DC-bus voltage and lead to an OP2 overvoltage trip.

Motor current is excessively high

Check the actual mechanical load, bearings, gearbox and driven machine for binding or seizure. If current is high mainly at low speed, excessive torque boost may also be contributing to the problem.

Comparing the inverter output-current display with the motor nameplate current can help determine whether the problem is caused by mechanical loading or incorrect motor-control settings.

The motor runs faster or slower than expected

Verify that the motor nameplate voltage matches the inverter and supply class. Check the base-frequency voltage parameter uLu and the configured base frequency.

A long or undersized motor cable may produce excessive voltage drop. Check cable size where necessary. On geared machines, also verify the reduction ratio and confirm that the commanded output frequency corresponds to the expected mechanical speed.

VF-nC3 parameter settings cannot be changed

Parameter editing may be restricted by the write-protection function. If F700 is set to 1 or 2, parameter changes are restricted. When parameter editing is required and operating conditions permit, set F700 to the appropriate enabled condition.

Note: Some VF-nC3 parameters cannot be modified while the inverter is running. Stop the drive before attempting to change parameters that are locked during operation.

Toshiba VF-nC3 Fault Codes and Remedies

OC1 0001 – Overcurrent during acceleration
The VF-nC3 has detected excessive output current while the motor is accelerating. Common causes include an acceleration time that is too short, incorrect V/f settings, restarting a motor that is already rotating or using a motor with unusually low impedance.

Remedy: Increase ACC and check the V/f parameters. If the motor is already rotating when a start command is issued, review F301 auto-restart and F302 ride-through control. For special motors, the PWM carrier-frequency settings may also require adjustment.

The VF-nC3 uses F300 for PWM carrier frequency. Parameter F316 selects whether the carrier frequency can be reduced automatically; F316 = 1 enables automatic reduction.

OC2 0002 – Overcurrent during deceleration
The deceleration time may be too short for the motor and mechanical load.

Remedy: Increase dEC. If required, set F316 = 1 so that the inverter can automatically reduce carrier frequency under appropriate operating conditions.

OC3 0003 – Overcurrent during constant-speed operation
A sudden load change or abnormal mechanical condition can cause current to rise even though the commanded frequency is constant.

Remedy: Reduce rapid load fluctuations and inspect the driven machine for binding, impact loading or another abnormal condition. The F316 carrier-frequency control setting may also be checked where appropriate.

OCL 0004 – Load-side overcurrent at start-up
The insulation of the motor cable, output circuit or motor winding may be defective. A motor with unusually low impedance can also cause this trip.

Remedy: Check the U-V-W motor cables, wiring and motor insulation. Do not repeatedly reset an OCL trip until insulation or wiring faults have been ruled out.

OCA 0005 – Arm overcurrent at start-up
This fault can indicate an abnormal condition in the inverter main power circuit.

Remedy: After confirming that the motor and output wiring are not shorted, have the inverter power stage inspected by qualified service personnel. Repeated reset attempts are not recommended.

EPHI 0008 – Input phase failure
One phase of the main-circuit input may be missing, or the DC-link capacitor condition may have deteriorated.

Remedy: Check the main input circuit, fuses, contactors, terminals and phase-to-phase voltages. Input phase-loss detection is associated with parameter F608. If the supply is correct and the trip persists, the main-circuit capacitors should also be inspected.

EPHO 0009 – Output phase failure
One motor output phase may be open between the inverter and the motor.

Remedy: Check U-V-W output wiring, terminals and motor windings. Output phase-loss detection is associated with parameter F605.

OP1 000A – Overvoltage during acceleration
Abnormal variation of the incoming supply voltage can raise the inverter DC-bus voltage. This condition is more likely on a high-capacity supply, where power-factor correction capacitors are switched, or where thyristor equipment and other distortion-producing loads share the same distribution system.

Remedy: Check the power supply. Toshiba recommends considering a suitable input reactor where the supply capacity is 200 kVA or more, is very large compared with the inverter capacity, or where significant waveform distortion is present. If the motor is already rotating when restarted, also review F301 and F302.

OP2 000B – Overvoltage during deceleration
The most common cause is excessive regenerative energy caused by a deceleration time that is too short. Abnormal incoming voltage can also contribute to the trip.

Remedy: Increase dEC. Check F305 overvoltage-limit operation and inspect the supply voltage. If the power system requires it, install a suitable input reactor. High-inertia applications that require rapid stopping may also need an appropriate regenerative braking system.

OP3 000C – Overvoltage during constant-speed operation
Supply-voltage disturbances may cause this fault, but a mechanical load can also drive the motor above the commanded inverter speed and return regenerative energy to the DC bus.

Remedy: Check the incoming supply and mechanical load. Where required, use a suitable input reactor. Applications that continuously generate regenerative energy may require an optional braking module and correctly sized braking resistor.

Continue with VF-nC3 fault information:
+ VF-nC3 Troubleshooting and Fault Index
+ VF-nC3 Fault Codes – OL1, OL2, OH, EEPROM, EF2 and other trips
+ VF-nC3 Fault Codes – ETN1, E-18, CPU and alarm messages

VF-nC3 related resources:
+ Toshiba VF-nC3 Main Page
+ VF-nC3 User Manuals and Technical Documents
+ Toshiba Drives Main Page
+ AC Drive / VFD Main Page