Fuji FRENIC Inverter Alarm Codes

OC1: Instantaneous overcurrent (during acceleration)

What it means: Output current jumped above the inverter's overcurrent trip level while the motor was accelerating. On Mini and Multi the same protection also catches a short circuit or a ground fault on the output side.^{[1][2][3][4][5]}

Likely causes

• Acceleration time too short for the load inertia
• Short circuit between output phases or in the motor
• Ground fault on the output cable or motor
• Load too heavy, or sudden load swings
• Torque boost set too high
• Motor still coasting at high speed when the start command came
• Electrical noise

First checks, in this order

1. Disconnect the motor cable from U, V and W, then measure phase to phase resistance and run an insulation (megger) test on the cable and motor.
2. Lengthen the acceleration time (F07, or E10 for the second ramp).
3. Turn on the current limiter (F43, level F44) and instantaneous overcurrent limiting (H12 = 1).
4. If the motor does not stall, lower the torque boost (F09).
5. Log the motor current with a clamp meter; if the load is above the design value, reduce it or fit a larger inverter.
6. On Ace, enable auto search (H09) if the motor may be spinning at start.
7. Check grounding and cable routing, and fit surge absorbers on nearby contactor coils.

OC2: Instantaneous overcurrent (during deceleration)

What it means: Output current jumped above the overcurrent trip level while the motor was decelerating.^{[1][2][3][4][5]}

Likely causes

• Deceleration time too short for the load inertia
• Short circuit or ground fault on the output cable or motor
• Load too heavy
• Electrical noise

First checks, in this order

1. Lengthen the deceleration time (F08, or E11 for the second ramp).
2. Turn on the current limiter (F43, F44); on Ace and MEGA also the torque limiter (F40, F41, E16, E17).
3. Disconnect U, V and W and test the motor and cable for shorts and insulation.
4. Check grounding and noise sources near the drive.

OC3: Instantaneous overcurrent (at constant speed)

What it means: Output current jumped above the overcurrent trip level while the motor was running at a steady speed, usually because of a sudden load change or a wiring fault.^{[1][2][3][4][5]}

Likely causes

• Sudden load increase or a mechanical jam
• Short circuit or ground fault on the output cable or motor
• Load too heavy for the inverter
• Electrical noise

First checks, in this order

1. Check the driven machine for jams, binding or a dragging brake.
2. Log the motor current to spot sudden jumps; smooth the load or fit a larger inverter.
3. Enable instantaneous overcurrent limiting (H12 = 1).
4. Disconnect U, V and W and test the motor and cable for shorts and insulation.
5. If noise is suspected, improve grounding and enable auto-reset (H04).

OU1: Overvoltage (during acceleration)

What it means: The DC link voltage went above the overvoltage trip level while the motor was accelerating. On Mini and Multi the trip level is 400 V DC on 200 V class units and 800 V DC on 400 V class units.^{[1][2][3][4][5]}

Likely causes

• Supply voltage above the inverter's rated range
• Voltage surges on the supply, for example from power factor capacitors switching or a thyristor converter on the same line
• Acceleration too fast, so the motor overshoots and regenerates
• Electrical noise

First checks, in this order

1. Measure the input voltage and bring it within the rated range.
2. Fit a DC reactor if the supply has surges.
3. Lengthen the acceleration time (F07) or select an S-curve (H07).
4. On Ace and MEGA, consider a braking resistor.

OU2: Overvoltage (during deceleration)

What it means: The DC link voltage went above the overvoltage trip level while the motor was decelerating. This is the most common overvoltage trip: the motor acts as a generator and pushes energy back into the drive.^{[1][2][3][4][5]}

Likely causes

• Deceleration time too short for the load inertia
• Braking (overhauling) load too heavy for the inverter
• Supply voltage too high or surges on the supply
• Braking resistor missing or undersized

First checks, in this order

1. Lengthen the deceleration time (F08, E11).
2. Enable anti-regenerative control (automatic deceleration, H69) or the deceleration characteristics function (H71).
3. Set the rated voltage at base frequency (F05) to 0 to improve braking capability.
4. Fit or resize a braking resistor and set its function codes (F50, F51, F52).
5. On Ace and MEGA, use the torque limiter (F40, F41, E16, E17).
6. Measure the input voltage.

OU3: Overvoltage (at constant speed)

What it means: The DC link voltage went above the overvoltage trip level while running at a steady speed. On Mini and Multi it also shows when the overvoltage happens while the inverter is stopped.^{[1][2][3][4][5]}

Likely causes

• Supply voltage too high or voltage surges on the line
• Load driving the motor (overhauling load) at steady speed
• Electrical noise

First checks, in this order

1. Measure the input voltage, also while the drive is stopped.
2. Fit a DC reactor if capacitor banks or converters on the same line cause surges.
3. If the load drives the motor, add a braking resistor (F50, F51, F52).
4. If the DC link was below the trip level when the alarm came, treat it as noise: improve grounding and enable auto-reset (H04).

LU: Undervoltage

What it means: The DC link voltage dropped below the undervoltage level. On Mini and Multi that level is 200 V DC on 200 V class units and 400 V DC on 400 V class units. On Ace, subcode 1 means low voltage while running, 2 a run command during low voltage, and 3 a trip on recovery from a momentary power failure.^{[1][2][3][4][5]}

Likely causes

• Momentary power failure or a supply dip
• Power switched back on too soon after switching off (with F14 = 1)
• Supply voltage below the rated range
• Faulty breaker, contactor or loose connection on the input
• Another large load starting on the same supply
• Supply transformer too small for the inverter's inrush current

First checks, in this order

1. Measure the input voltage and watch for dips.
2. Check the input breaker, contactor and terminal connections.
3. To restart after a short power loss instead of tripping, set F14 to 3, 4 or 5 to suit the load (Mini: 4 or 5).
4. When cycling power, wait until all keypad LEDs are off before switching on again.
5. Check whether the trip happens when the input breaker or contactor closes; if so, review the transformer size.

OL1: Motor 1 overload

What it means: The electronic thermal overload protection for motor 1 tripped: the inverter calculated that the motor has carried too much current for too long.^{[1][2][3][4][5]}

Also on: Multi manual name: Electronic thermal overload alarm 1

Likely causes

• Load too heavy
• Overload level F11 set below the motor's real continuous current, or wrong F10 and F12 settings for the motor type
• Acceleration or deceleration time too short
• Torque boost set too high

First checks, in this order

1. Measure the output current and compare it with the motor nameplate.
2. Set F11 to the motor rated current, and check F10 (motor characteristics), F12 (thermal time constant) and P99 (motor selection).
3. Lengthen the acceleration and deceleration times (F07, F08).
4. Lower the torque boost (F09) if the motor does not stall.
5. Use the overload early warning (E34) to cut the load before the trip, or fit an external thermal relay.

OLU: Inverter overload

What it means: The inverter's own internal temperature, calculated from the output current and heat sink temperature, rose too high. On Ace, subcode 1 is IGBT protection and subcode 2 is inverter overload.^{[1][2][3][4][5]}

Also on: Multi manual name: Overload

Likely causes

• Load too heavy for the inverter rating
• Surrounding temperature too high
• Acceleration or deceleration time too short
• Torque boost set too high
• Blocked airflow or clogged heat sink
• Cooling fan worn out or failed
• Very long motor cables causing high leakage current

First checks, in this order

1. Measure the output current against the inverter rating.
2. Lower the carrier frequency (F26) and enable overload prevention control (H70).
3. Lengthen the acceleration and deceleration times (F07, F08) and lower the torque boost (F09).
4. Check clearance around the inverter and clean the heat sink.
5. Check the cooling fan run time in Menu 5 Maintenance Information and check that the fan spins.
6. For long motor cables, fit an output circuit filter (OFL).

OH1: Heat sink overheat

What it means: The temperature around the heat sink rose above its limit. On Ace, subcode 6 means the inverter detected that the cooling fan stopped.^{[1][2][3][4][5]}

Also on: Ace manual name: Cooling fin overheat

Likely causes

• Cabinet or ambient temperature above the inverter's rating
• Blocked ventilation or a clogged heat sink
• Cooling fan at the end of its life or failed
• Load too heavy

First checks, in this order

1. Measure the temperature around the inverter and improve cabinet ventilation.
2. Check the clearance around the inverter and clean the heat sink.
3. Check the fan run time in Menu 5 Maintenance Information and check that the fan spins; replace it if needed.
4. Reduce the load, lower the carrier frequency (F26) and enable overload prevention control (H70).
5. On large MEGA units, check the fan power connectors CN R and CN W.

Lin: Input phase loss

What it means: One input phase is missing, or the voltage unbalance between the three input phases is too large.^{[1][2][3][4][5]}

Likely causes

• Broken input wire, or a faulty input breaker or contactor
• Loose screws on the main power input terminals
• Large voltage unbalance between phases
• Heavy cyclic overload causing large DC link ripple
• Single-phase power applied to a three-phase input model
• On Ace, auxiliary control power (R0, T0) taken from the supply side of the breaker

First checks, in this order

1. Measure all three input voltages at the inverter terminals.
2. Tighten the input terminal screws to the specified torque.
3. Check the input breaker, fuses and contactor.
4. If the unbalance is large, fit an AC reactor (ACR) or use a larger inverter.
5. The protection can be switched off with H98, but only do that if you know why it trips.

OPL: Output phase loss

What it means: One of the output phases to the motor is open, detected at start or during running.^{[1][2][3][4][5]}

Also on: Ace manual name: Output phase-failure detection

Likely causes

• Broken output wire
• Broken motor winding
• Loose screws on the output terminals U, V, W
• A single-phase motor connected

First checks, in this order

1. Measure the current in each output phase.
2. Tighten the U, V and W terminal screws.
3. Measure the motor winding resistance on all three phases.
4. Use only three-phase motors.

EF: Ground fault

What it means: A ground fault current flowed from the inverter output to earth. This code is listed for Ace FRN0085E2-4 and larger and for MEGA 50 HP and larger. On Mini and Multi, an output ground fault trips as OC1, OC2 or OC3 instead.^[3][4][5]

Likely causes

• Damaged motor cable insulation
• Motor winding insulation breakdown
• Water or dirt in a terminal box or junction box

First checks, in this order

1. Disconnect the motor cable from U, V and W.
2. Run an insulation (megger) test on the motor and the cable, phase to ground.
3. Replace the damaged cable, terminal or motor before restarting.

OH2: External alarm

What it means: An external device signaled a fault through a digital input set to THR (Enable external alarm trip).^{[1][2][3][4][5]}

Also on: Multi manual name: Alarm issued by an external device

Likely causes

• The external protective device wired to THR has tripped
• Broken wire or poor contact in the THR signal circuit
• THR assigned to the wrong terminal, or its logic (normal or inverted) does not match the external signal

First checks, in this order

1. Find which external device is wired to the THR input and check it.
2. Check the wiring to the terminal set to THR (one of E01 to E05, E98, E99 set to 9; Mini uses E01 to E03).
3. Check that the input logic matches the external contact (normally open or normally closed).

OH4: Motor protection (PTC thermistor)

What it means: The motor thermistor input reports that the motor is too hot. MEGA also accepts an NTC thermistor.^{[1][2][3][4][5]}

Also on: MEGA manual name: Motor protection (PTC/NTC thermistor)

Likely causes

• Motor ambient temperature too high or motor cooling fan faulty
• Motor overloaded
• Thermistor trip level (H27) set wrong
• Thermistor wiring, pull-up resistor or input switch setting wrong
• Torque boost too high, or V/f pattern not matched to the motor
• Thermistor mode (H26) switched on while no thermistor is fitted

First checks, in this order

1. Feel and measure the motor temperature, and check the motor fan and cooling fins.
2. Measure the output current and reduce the load if needed.
3. If no thermistor is fitted, set H26 to 0.
4. Check H27 against the thermistor data; on Ace set E59 = 0, H26 = 1 and the SW3/SW4 switches to C1 and PTC; on MEGA check switch SW5.
5. Check base frequency (F04) and rated voltage (F05) against the motor nameplate, and lower F09 if possible.

dbH: Braking resistor overheat

What it means: The electronic thermal model for the braking resistor tripped. The inverter calculates resistor heating from the braking load; it does not measure the resistor's surface temperature. Listed for Ace up to FRN0115E2-2, FRN0011E2-7 and FRN0072E2-4, and for MEGA 40 HP and below.^{[1][2][3][4][5]}

Also on: Mini, Multi and MEGA manual name: Braking resistor overheated

Likely causes

• Braking load heavier than planned
• Deceleration time too short
• Braking resistor function codes (F50, F51, and F52 on Ace and MEGA) not set for the fitted resistor

First checks, in this order

1. Lengthen the deceleration time (F08, E11).
2. Check the braking resistor rating against the real braking duty and use a larger resistor if needed.
3. Set F50, F51 (and F52 on Ace and MEGA) to the resistor's data; tune them while measuring the resistor surface temperature.

Er1: Memory error

What it means: An error happened while the inverter wrote data to its internal memory.^{[1][2][3][4][5]}

Likely causes

• Power was lost while data was being written, especially during initialization or copying
• Strong electrical noise during a data write
• Faulty control board

First checks, in this order

1. Write down your function code settings, then initialize with H03 and try to reset the alarm.
2. If the reset works, enter your settings again and restart.
3. Improve grounding and wire routing if noise is likely.
4. If the alarm comes back after initialization, the control board is faulty: contact Fuji Electric.

Er2: Keypad communications error

What it means: Communication between the keypad (on Mini, the optional remote keypad) and the inverter failed.^{[1][2][3][4][5]}

Likely causes

• Broken keypad cable or poor connector contact
• On Ace, many control wires pushing the front cover so the keypad lifts
• Electrical noise
• Faulty keypad

First checks, in this order

1. Reseat the keypad connector and check the cable; replace it if needed.
2. Check that the front cover sits flat and the keypad is firmly seated.
3. Swap in another keypad to see if the alarm follows the keypad.

Er3: CPU error

What it means: The inverter's processor behaved abnormally.^{[1][2][3][4][5]}

Likely causes

• Strong electrical noise
• On small Ace units, terminals PLC and CM shorted together

First checks, in this order

1. Check grounding and separate control, communication and power wiring.
2. On Ace, check for a short between terminals PLC and CM.
3. If it repeats with good wiring, contact Fuji Electric.

Er6: Operation protection

What it means: An operation the inverter blocks was attempted: the STOP key was pressed while running from terminals or communications with STOP key priority on, or a run command was already on at power up, at alarm reset or when switching to link operation (start check function).^{[1][2][3][4][5]}

Also on: Ace manual name: Operation error

Likely causes

• STOP key pressed while running from terminals or a fieldbus, with H96 = 1 or 3
• Run command still on at power up or at alarm reset, with H96 = 2 or 3
• Run command on when switching to communication link operation
• On Ace, the forced stop input STOP switched off

First checks, in this order

1. Switch the run command off before powering up or resetting an alarm.
2. Review the control sequence so a run command is not present during these events.
3. If the behavior is not wanted, check H96.
4. On Ace, check which input is assigned to STOP (E01 to E05).

Er7: Tuning error

What it means: Motor auto-tuning failed.^{[1][2][3][4][5]}

Likely causes

• A motor phase not connected
• Motor V/f or rated current data entered wrong
• Motor cable longer than about 50 m (164 ft)
• Motor size far from the inverter size
• Special motor such as a high-speed motor
• Rotating tuning attempted with the motor brake applied

First checks, in this order

1. Check the U, V, W connections to the motor.
2. Enter the nameplate data: F04, F05, P02, P03 (and H50 to H53 where used).
3. If the brake cannot be released, use static tuning (P04 = 1) instead of rotating tuning (P04 = 2).
4. For long cables, odd motor sizes or special motors, set the motor constants (P06 to P08) by hand, or switch off auto-tuning and auto torque boost (F37 = 1).
5. On Ace, read the alarm subcode for the exact reason.

Er8: RS-485 communications error

What it means: A communication error occurred on the RS-485 link (on Ace and MEGA, communications port 1).^{[1][2][3][4][5]}

Likely causes

• Inverter communication settings do not match the host (PLC, PC)
• No-response timeout (y08) set and the host does not poll in time
• Fault in the host software, settings or hardware
• RS-485 converter wiring, settings or hardware fault
• Broken cable or poor contact
• Electrical noise
• Terminating resistor not set at the end of the line

First checks, in this order

1. Compare y01 to y10 with the host settings (address, baud rate, parity and so on).
2. Check the host program; if the timeout is not needed, set y08 = 0.
3. Check the cable and connectors for continuity.
4. Switch on the terminating resistor if the inverter is the last device (Ace: SW2/SW6).
5. Improve grounding and use an isolated RS-485 converter.

ErF: Data saving error during undervoltage

What it means: At power off, the inverter could not save data such as keypad frequency or PID commands, or values changed with the UP/DOWN inputs.^{[1][2][3][4][5]}

Likely causes

• The DC link discharged unusually fast at power off
• Electrical noise while the data was being saved
• Faulty control board

First checks, in this order

1. Find what drains the DC link quickly at power off and remove it.
2. Reset the alarm, then put the keypad frequency, PID command or UP/DOWN values back to the right settings.
3. If ErF appears at every power up, the control board is faulty: contact Fuji Electric.

Err: Mock alarm

What it means: A test alarm generated on purpose to check the alarm sequence (alarm relay, PLC logic). Mini and Multi raise it when H45 is set to 1; Ace and MEGA raise it when a two-key combination on the keypad is held for 5 seconds or more.^{[1][2][3][4][5]}

Also on: Ace manual name: Simulated failure

Likely causes

• Someone triggered the mock alarm for testing (H45 = 1 on Mini and Multi, or the keypad key combination on Ace and MEGA)

First checks, in this order

1. Press the Program/Reset key to clear it.
2. On Mini and Multi, check that H45 is back at 0.

CoF: PID feedback wire break

What it means: The PID feedback signal (for example from a pressure or flow transmitter) is lost, as if the wire is broken.^{[1][2][3][4][5]}

Likely causes

• Broken or loose PID feedback signal wire
• Wire insulation pinched in a terminal
• Electrical noise on the feedback circuit

First checks, in this order

1. Check the feedback transmitter wiring and tighten the terminal screws.
2. Check that no terminal is clamping on the wire insulation.
3. Separate signal wires from power wires and check grounding.

OL2: Motor 2 overload

What it means: The electronic thermal overload protection for motor 2 tripped (motor 2 is selected with the motor switching input).^{[1][2][3][4][5]}

Also on: Multi manual name: Electronic thermal overload alarm 2

Likely causes

• Load too heavy for motor 2
• Motor 2 overload settings not matched to the motor
• Acceleration or deceleration time too short

First checks, in this order

1. Measure the output current while motor 2 runs.
2. On Mini and Multi, check A06, A07 and A08 (and A39 motor selection), which match F10, F11 and F12 for motor 1.
3. On Ace and MEGA, check the motor 2 versions of F10, F11 and F12.
4. Lengthen the ramps and reduce the load.

OH3: Inverter internal overheat

What it means: The air temperature inside the inverter went above its limit. On Ace, subcode 0 is internal air overheat and subcode 1 is charging resistor overheat.^[3][4][5]

Likely causes

• Cabinet or ambient temperature too high
• Poor cabinet ventilation
• On MEGA, running on single-phase power

First checks, in this order

1. Measure the temperature around the inverter and improve cabinet ventilation.
2. Check cabinet fans and filters.
3. On MEGA used on single-phase power, see section 6.7 of the MEGA instruction manual.

OH6: Charging resistor overheat

What it means: The charging resistor inside the inverter, which limits inrush current at power up, has overheated.^[1][3][4]

Likely causes

• Input power switched on and off too often
• Faulty charging circuit
• On Mini, power applied slowly through a transformer or a stabilized supply

First checks, in this order

1. Limit power cycling: Mini once per hour or less, Ace once per 30 minutes or less.
2. On Mini, switch power on with a breaker or contactor, not by ramping it up.
3. If it trips without frequent power cycling, the charging circuit is faulty: have the inverter repaired.

Er4: Option communications error

What it means: Communication between an option card and the inverter failed.^[2][3][4][5]

Also on: Multi manual name: Option card communications error

Likely causes

• Option card not seated properly in its connector
• Electrical noise

First checks, in this order

1. Power off, wait for the discharge time, then reseat the option card.
2. Check grounding and separate signal and power wiring.

Er5: Option error

What it means: The option card itself detected an error. On Ace, subcode 0 means a timeout.^[2][3][4][5]

Also on: Multi manual name: Option card error

Likely causes

• Fault reported by the option card, for example a fieldbus timeout

First checks, in this order

1. Look up the error in the option card's instruction manual.
2. Check the fieldbus or option card wiring and the master device.

ErP: RS-485 communications error (Option card)

What it means: On FRENIC-Multi, a communication error on the RS-485 link of the RS-485 option card.^[2]

Likely causes

• Option card RS-485 settings do not match the host
• No-response timeout (y18) set and the host does not poll in time
• Cable, converter or host fault
• Electrical noise

First checks, in this order

1. Compare y11 to y20 with the host settings.
2. If the timeout is not needed, set y18 = 0.
3. Check the cable, connectors and terminating resistor.

ErP: RS-485 communications error (Communications port 2)

What it means: On Ace and MEGA, a communication error on RS-485 communications port 2.^[3][4][5]

Also on: MEGA manual name: RS-485 communications error (COM port 2)

Likely causes

• Port 2 settings do not match the host
• No-response timeout (y18) set and the host does not poll in time
• Host, converter or cable fault
• Electrical noise or missing termination

First checks, in this order

1. Compare y11 to y20 with the host settings.
2. If the timeout is not needed, set y18 = 0.
3. Check the cable and connectors; on Ace set the terminating resistor switch (SW2/SW6) if the inverter ends the line.

ErH: Hardware error

What it means: A hardware fault was found on the control board, the power board or the link between them. On MEGA this code is listed for 60 HP and larger (230 V) and 75 HP and larger (460 V).^[2][3][4][5]

Likely causes

• Interface board not seated (Multi)
• Terminals 13 and 11 shorted together (Multi)
• Poor connection between the control board and the power board
• Inverter capacity setting on the control board wrong, or power board memory corrupted (MEGA)
• Poor connection between the control board and an option card (Multi)

First checks, in this order

1. On Multi, remove and refit the interface board until it clicks, and check for a short between terminals 13 and 11.
2. Otherwise contact Fuji Electric: a board may need replacing or the capacity setting may need correcting.

ECF: EN circuit failure

What it means: The safety enable circuit (the EN1 and EN2 safe stop inputs) failed its self-diagnosis. On Ace, subcode 10 points to the interface board and subcode 3000 to the EN inputs not matching each other.^[3][4][5]

Also on: MEGA manual name: Enable circuit failure

Likely causes

• EN1 and EN2 inputs not switching together (one high, one low)
• Interface board not seated firmly
• Electrical noise on the enable circuit (MEGA)
• Failure inside the enable (safe stop) circuit

First checks, in this order

1. Check that the safety relay or switch drives EN1 and EN2 the same way at the same time (both on or both off).
2. Check that the interface board is firmly mounted.
3. Clear the alarm by switching the power off and on; on MEGA the RST input cannot reset it.
4. If it comes back, the enable circuit is faulty: contact Fuji Electric for repair.

FUS: Fuse blown

What it means: The DC fuse inside the inverter has blown, which points to a short circuit inside the inverter. On MEGA this code is listed for 125 HP and larger (230 V) and 150 HP and larger (460 V).^[3][4][5]

Also on: Ace manual name: DC fuse-blowing

Likely causes

• Internal short circuit in the inverter
• Large surges or noise from the supply

First checks, in this order

1. Do not keep cycling power.
2. Check the supply for surges and noise, and add protection if needed.
3. Have the inverter repaired by Fuji Electric.

PbF: Charger circuit fault

What it means: The contactor that bypasses the charging resistor after power up did not operate. Listed for Ace FRN0203E2-4 and larger and for MEGA 60 HP and larger (230 V) and 125 HP and larger (460 V).^[3][4][5]

Also on: Ace user's manual heading: Charge circuit fault

Likely causes

• Connector CN R on the power board set to NC on a normal AC-fed connection
• Input breaker switched on and quickly off again after wiring
• On MEGA, running on single-phase power

First checks, in this order

1. For a normal AC supply (not DC bus fed), set connector CN R on the power board to FAN.
2. Wait until the DC link has discharged, reset the alarm, then switch power on again; do not flick the breaker on and off.

OS: Overspeed

What it means: The motor ran faster than allowed, about 1.2 times the maximum frequency (F03).^[3][4][5]

Also on: Ace manual name: Overspeed protection

Likely causes

• Number of motor poles (P01) or maximum frequency (F03) set wrong
• Speed controller gain too low, so speed overshoots (MEGA)
• Noise on the encoder (PG) wiring (MEGA)
• Speed limit function settings d32, d33 (MEGA)

First checks, in this order

1. Set P01 to the motor pole count and F03 to the right maximum frequency.
2. On MEGA, check d32 and d33, raise the speed control gain (d03) if speed overshoots, and check encoder cable shielding.

PG: PG wire break

What it means: The pulse generator (encoder) signal is lost, as if a wire is broken.^[3][4][5]

Likely causes

• Broken or loose encoder wire between the encoder and the option card
• Electrical noise on the encoder circuit
• On Ace, pulse train input PIN not assigned for positioning with the pulse counter

First checks, in this order

1. Check the encoder cable, connector and terminal screws, and look for pinched insulation.
2. Separate the encoder cable from power wiring and check shield grounding.
3. On Ace, check that E05 is set to the pulse train input PIN when positioning is used.

ErE: Speed inconsistency / Excessive speed deviation

What it means: The measured motor speed differs too much from the speed command.^[3][4][5]

Also on: MEGA manual name: Speed mismatch or excessive speed deviation

Likely causes

• Wrong motor pole count (P01) or encoder settings (MEGA: d15 to d17)
• Overload, or a mechanical brake still applied
• Current limiter (F43, F44) or torque limiter (F40) holding the speed down
• Motor parameters not matching the motor
• Motor phases U, V, W connected in the wrong order
• Encoder wiring broken, or A and B phases swapped

First checks, in this order

1. Check P01 and the encoder settings.
2. Check the load and that the brake releases.
3. Check F44, F43 and F40.
4. Run auto-tuning (P04).
5. Check the motor wiring order and the encoder wiring (swap A and B if the direction is wrong).

Ero: Positioning control error

What it means: The position error grew too large during servo lock or position control (MEGA also during synchronous control).^[3][4][5]

Likely causes

• Position loop gain too low
• Completion range set wrong
• Excessive deviation detection level set too tight
• Encoder feedback pulses missing

First checks, in this order

1. Servo lock: adjust J97 (gain) and d03 (speed control P gain), and check J99 (completion range).
2. Ace: check the excessive deviation level d78; MEGA synchronous control: check d72 and d78.
3. Check the encoder wiring and connections.

ErD: Step-out detection

What it means: A permanent magnet synchronous motor fell out of step (lost synchronism). On Ace the same code also covers a failed magnetic pole position detection at start.^[1][3][4]

Likely causes

• Motor constants not matching the motor (F04, F05, P01 to P03, P60 to P64)
• Starting torque too low or acceleration too fast
• Starting current too high for a light load
• On Ace, pole position detection mode (P30) or starting frequency hold time (F24) not suited to the motor

First checks, in this order

1. Enter the motor data and run auto-tuning.
2. Adjust the acceleration time and the reference current at start (P74); for a motor running alone in a test, set P74 to 80% or less.
3. On Ace, match P30 to the motor type and check F24.

dbA: Braking transistor broken

What it means: The inverter detected a fault in its braking transistor (the switch that drives the braking resistor).^[3][4][5]

Also on: MEGA manual name: Braking transistor error

Likely causes

• Failed braking transistor
• Braking resistor value too low or resistor wired wrong

First checks, in this order

1. Check the braking resistor value against the specification and check its wiring.
2. Have the inverter repaired by Fuji Electric.

OL3: Motor 3 overload

What it means: The electronic thermal overload protection for motor 3 tripped.^[5]

Likely causes

• Load too heavy for motor 3
• Motor 3 overload settings not matched to the motor
• Ramps too short or torque boost too high

First checks, in this order

1. Measure the output current while motor 3 runs.
2. Check the motor 3 versions of the overload settings (equal to F10, F11, F12 for motor 1).
3. Lengthen the ramps and reduce the load.

OL4: Motor 4 overload

What it means: The electronic thermal overload protection for motor 4 tripped.^[5]

Likely causes

• Load too heavy for motor 4
• Motor 4 overload settings not matched to the motor
• Ramps too short or torque boost too high

First checks, in this order

1. Measure the output current while motor 4 runs.
2. Check the motor 4 versions of the overload settings (equal to F10, F11, F12 for motor 1).
3. Lengthen the ramps and reduce the load.

nrb: NTC wire break error

What it means: The NTC motor thermistor circuit reads as open.^[5]

Likely causes

• Broken thermistor wire in the motor cable
• Motor ambient temperature extremely low (below minus 30 C, minus 22 F)
• Failed NTC thermistor

First checks, in this order

1. Check the thermistor wires in the motor cable.
2. Measure the NTC thermistor resistance.
3. Check the temperature around the motor.

ECL: Customizable logic failure

What it means: A customizable logic setting error was found, typically because the logic operation selection was changed while running.^[3][4]

Likely causes

• Customizable logic selection (U00) changed during operation

First checks, in this order

1. Check U00 and only change it while the inverter is stopped.

ErT: CAN communications failure

What it means: A communication error occurred on the CAN bus link.^[3][4]

Likely causes

• Baud rate (y24) different from the host
• Fault in the host controller software, settings or hardware
• Broken cable or poor contact
• Electrical noise

First checks, in this order

1. Compare y24 with the host baud rate.
2. Check the host controller.
3. Check cable continuity and connectors, and improve noise protection.

L-AL: Light alarm

What it means: A minor fault chosen as a light alarm is active. The inverter keeps running, shows L-AL and can switch the L-ALM output. Which faults count as light alarms is set with H81 and H82.^[3][4][5]

Likely causes

• Any condition set as a light alarm, for example DC fan lock, overload early warning, lifetime alarm or reference loss

First checks, in this order

1. Read the cause in Menu 5 Maintenance Information: Ace items 5_36 to 5_39, MEGA LALM1 to LALM4 on the LCD.
2. Fix the cause, then press the Program/Reset key in Running mode to return to the normal display.
3. To wire it to a PLC, assign L-ALM (data 98) to a digital output (Ace: E20, E21 or E27). When an alarm is set as a light alarm, relay 30A/B/C does not switch for it (Ace).

FAL: DC fan locked

What it means: Light alarm: a DC cooling fan has stopped turning. On MEGA it is listed for 75 HP and larger (230 V) and 125 HP and larger (460 V).^[3][5]

Also on: Ace manual name: Detect DC fan lock

Likely causes

• Fan blocked by dirt or debris
• Fan worn out or failed
• Fan power connection problem

First checks, in this order

1. Look at the fan while the inverter is powered and check it spins.
2. Clean or replace the fan, then clear the light alarm.

OH: Heat sink overheat early warning

What it means: Light alarm: the heat sink is getting close to the OH1 trip temperature.^[3][5]

Also on: Ace manual name: Cooling fin overheat early warning

Likely causes

• High cabinet temperature
• Dirty heat sink or weak cooling fan
• Heavy load

First checks, in this order

1. Treat it like an early OH1: check ventilation, clean the heat sink, check the fan and reduce the load.

OL: Motor overload early warning

What it means: Light alarm: the motor current is above the early warning level set in E34 (timer E35), before the OL1 trip.^[3][4][5]

Also on: Ace manual name: Overload early warning

Likely causes

• Load rising toward the motor overload limit

First checks, in this order

1. Measure the output current and reduce the load.
2. Check E34 and E35.

LiF: Lifetime alarm

What it means: Light alarm: a part with a limited life (such as the DC link capacitors or the cooling fans) has reached its estimated replacement point.^[3][5]

Likely causes

• Normal aging of life-limited parts

First checks, in this order

1. Check the life data in Menu 5 Maintenance Information.
2. Plan replacement of the worn part (see the list of periodic replacement parts in the manual).

rEF: Reference command loss detected

What it means: Light alarm: the analog frequency command was lost (for example a broken wire). With E65 set, the inverter keeps running at a set frequency.^[3][5]

Likely causes

• Broken or loose analog reference wire
• Faulty reference source (PLC output, potentiometer, transmitter)

First checks, in this order

1. Check the analog reference wiring and the signal source.
2. Check E65.

PID: PID alarm

What it means: Light alarm: the PID control alarm condition is active (process value outside its set alarm range).^[3][5]

Also on: Ace manual name: PID alarm output

Likely causes

• Process value away from the set point or limits
• Feedback transmitter problem

First checks, in this order

1. Check the process and the feedback transmitter.
2. Check the PID alarm settings.

UTL: Low torque detection

What it means: Light alarm: output torque fell below the set low torque level, which often means a broken belt or coupling or a pump running dry.^[3][5]

Also on: MEGA manual name: Low torque output

Likely causes

• Mechanical link broken (belt, coupling)
• Load lost, for example a pump running dry

First checks, in this order

1. Check the driven machine and its mechanical links.
2. Check the low torque detection settings.

PTC: PTC thermistor activated

What it means: Light alarm: the motor PTC thermistor has reached its activation level, reported as a warning instead of an OH4 trip.^[3][5]

Likely causes

• Motor running hot from overload or poor cooling

First checks, in this order

1. Check the motor load and cooling.
2. Check H26 and H27.

rTE: Machine life (Cumulative motor running hours)

What it means: Light alarm: the motor's total running hours reached the maintenance setting.^[3][5]

Also on: MEGA manual name: Inverter life (Motor cumulative run time)

Likely causes

• Preset run-hour maintenance interval reached

First checks, in this order

1. Carry out the planned maintenance on the motor and machine.
2. Check the run-hour data in Menu 5 Maintenance Information.

CnT: Inverter life (Number of startups)

What it means: Light alarm: the number of motor starts reached the maintenance setting.^[3][5]

Likely causes

• Preset start-count maintenance interval reached

First checks, in this order

1. Carry out the planned maintenance.
2. Check the start count in Menu 5 Maintenance Information.