FR-E700 Fault E.GF — Ground Fault

Overview

The E.GF fault code on the Mitsubishi FR-E700 series variable frequency drive (VFD) stands for Ground Fault (specifically, an output-side earth fault overcurrent). This safety trip is triggered when the VFD's internal current detection circuitry senses that current escaping to the ground (earth) line on the output terminals (U, V, W) has exceeded the drive's protective threshold during startup or operation. Its primary purpose is to shut down the output instantly, preventing catastrophic hardware destruction of the inverter's internal Insulated Gate Bipolar Transistors (IGBTs) and reducing fire hazards.

Symptoms

When an E.GF fault occurs on a Mitsubishi FR-E700 drive, the system will exhibit several of the following behaviors:

• Immediate Trip on Run Command: The drive attempts to start, but immediately stops and displays "E.GF" on the integrated PU (Parameter Unit) LED panel.
• Intermittent Tripping During Acceleration/Deceleration: The motor operates normally at low speeds but trips on E.GF at specific frequencies or during heavy load changes.
• Motor Coasting to Stop: The drive immediately cuts output power to U, V, and W, causing the connected motor to coast freely rather than performing a controlled deceleration.
• PLC Fault Signaling: The drive's internal fault relay (terminals A, B, and C) switches state, sending a digital fault input to your master PLC or SCADA system.
• Unresponsive Operation: The drive remains locked out and cannot be operated until a diagnostic reset is performed (either via the STOP/RESET key, a digital input, or a complete power cycle).

Possible Causes

Identifying the root cause of an E.GF code requires evaluating the entire drive circuit from the VFD output terminals to the motor frame. The most common causes include:

• Motor Winding Insulation Collapse: The dielectric properties of the motor winding insulation have degraded due to age, overheating, voltage spikes, or moisture. This allows current to jump from a phase winding directly to the motor frame.
• Physical Cable Damage: The motor power cable running from the VFD to the motor terminal box is pinched, cut, or worn inside the conduit, making electrical contact with the grounded conduit or cable tray.
• Moisture or Hydrocarbon Contamination: Liquid, condensation, or conductive carbon dust has accumulated inside the motor junction box or the stator enclosure, bridging the gap between active phases and ground.
• Excessive Motor Cable Length (Capacitive Leakage): Extremely long motor cable runs possess high parasitic capacitance. The high-frequency PWM switching carrier produces a leakage current directly to ground, tricking the drive's CT (current transformer) sensors into registering a ground fault.
• Internal VFD IGBT Breakdown: One or more of the internal output transistors (IGBTs) inside the FR-E700 drive has shorted directly to the aluminum cooling heatsink, which is connected to earth ground.
• Defective Current Detection Sensor: An internal CT sensor or control-board evaluation circuit inside the drive has drifted out of calibration or failed, resulting in a false E.GF trip even when the output is disconnected.
• Poor System Grounding: A missing, loose, or highly resistive ground path back to the VFD's PE (Protective Earth) terminal can cause erratic ground-potential shifts and noise spikes that mimic a real ground fault.

Step-by-Step Troubleshooting

Follow these targeted diagnostic steps to quickly locate and resolve the issue causing the E.GF fault code.

Step 1: Safety First & Lock Out Tag Out (LOTO)

Before touching any electrical terminations, isolate the VFD from the main supply voltage. Turn off the input circuit breaker, perform LOTO procedures, and wait at least 10 minutes. Use a digital multimeter (set to DC voltage) to measure across the main DC bus terminals (+ and - or P and N) to verify that the internal capacitors have fully discharged to under 24VDC.

Step 2: Isolate the VFD Outputs

Disconnect the three motor leads (U, V, and W) directly from the VFD's output terminals. Ensure the loose wires are insulated or positioned safely away from each other and from the metallic backplate.

Step 3: Run the VFD Without a Connected Motor

Turn the main power supply back on. Configure the FR-E700 drive to run in "PU" mode (local control panel mode). Press the RUN key and increase the frequency command to 15 Hz or 30 Hz.

• Result A: If the VFD immediately trips on E.GF with no wires attached to U, V, and W, the fault is internal to the VFD. The current sensors have failed or the output IGBT module is shorted. Proceed to Step 4.
• Result B: If the VFD output ramps up smoothly without tripping, the drive is functional. The problem lies downstream in the motor cable, junction box, or motor windings. Skip to Step 5.

Step 4: Verify the Drive's Output Transistors (IGBT Diode Test)

With power removed and the DC bus discharged, switch your digital multimeter to "Diode Test" mode. This test checks the state of the drive's output power module:

1. Place the Positive (+) probe on the negative DC bus terminal (N).
2. Touch the Negative (-) probe sequentially to output terminals U, V, and W. You should see a standard diode forward voltage drop of approximately 0.3V to 0.7V on each phase.
3. Reverse the probes: Place the Negative (-) probe on N and touch the Positive (+) probe to U, V, and W. The meter should display "OL" (Open Loop).
4. Place the Negative (-) probe on the positive DC bus terminal (P/+).
5. Touch the Positive (+) probe sequentially to output terminals U, V, and W. You should read the same forward diode voltage drop (0.3V to 0.7V).
6. Reverse the probes and verify "OL" is displayed.

If you read 0.00V, a very low resistance, or a short circuit on any of these checks, the VFD's internal power module has physically failed. The VFD must be repaired or replaced.

Step 5: Test the Motor Cabling & Windings with a Megohmmeter

If the VFD passed the test in Step 2, the ground fault is in your field cabling or motor. Never connect a Megohmmeter (Megger) directly to the VFD output terminals! High test voltages will destroy the drive's sensitive electronics.

1. Keep the motor cables disconnected from the VFD output terminals.
2. Set your Megohmmeter to 500VDC (or 1000VDC check your motor's rating—typically 500VDC is standard for 460V class motors).
3. Connect the negative ground lead of the Megger to the structural enclosure ground block (PE).
4. Connect the positive probe of the Megger to motor phase lead U (disconnected from VFD). Initiate the insulation test and record the resistance value after 1 minute.
5. Repeat the test for motor leads V and W to ground.
6. Evaluation:
   • Excellent: Resistance values over 100 Megohms.
   • Marginal/Fair: Resistance values between 10 Megohms and 100 Megohms. This may hold up in dry conditions but could trip during high relative humidity or load surges.
   • Failed: Resistance values below 1 Megohm. This indicates an active insulation breakdown to ground. Proceed to Step 6 to isolate the cable from the motor.

Step 6: Separate Motor from Field Cable

If you observed a failed insulation test in Step 5, open the motor junction box located on the motor housing. Disconnect the field cables from the internal motor windings.

1. Use the Megohmmeter to test only the field cable leads (from the VFD panel end, with both motor and VFD isolated).
2. Use the Megohmmeter to test the motor windings directly from their lead terminals to the physical motor frame.

This final test isolates the exact location of the insulation breakdown, telling you if the issue is a damaged buried cable conduit or a burnt motor winding.

Recommended Actions

Once you have pinpointed the location of the ground fault, implement the appropriate corrective action:

• If the Motor Winding is Damaged: Have an authorized motor rewind shop rebuild the stator insulation, or replace the motor with a modern, high-grade inverter-duty motor equipped with Class F or H insulation.
• If the Power Cable is Faulty: Replace the line with high-quality, VFD-rated shielded power cable. Run the cable in a dedicated metal conduit to shield against electromagnetic interference (EMI) and reduce capacitive coupling to neighboring circuits.
• If Cable Run is Exceptionally Long: If your run is longer than 50 meters, the E.GF code might be caused by high-frequency capacitive leakage currents. Access the FR-E700 parameters and lower the PWM Carrier Frequency via Parameter 72 (e.g., reduce it from 14.5 kHz to 2 kHz or 1 kHz). This reduces the switching frequency and lowers capacitive ground leakage.
• If Environmental Contaminants are Found: Thoroughly dry out any condensation using space heaters, clean any carbon dust deposits out of the motor junction box, and replace degraded junction box gaskets to prevent future water ingress.

Recommended Replacement Parts

When replacing damaged components to resolve the E.GF code, select high-grade parts designed to withstand high $dV/dt$ voltage spikes:

• Inverter-Duty Motor: Ensure the replacement motor is rated for VFD use with corona-resistant insulation (such as NEMA MG1 Part 31 standards).
• VFD-Rated Cable: Use proper VFD cable featuring three-phase conductors plus symmetrical grounds within an overall foil/braid shield (e.g., Belden or Southwire VFD cable).
• Output Reactor / dV/dt Filter: If your system requires long cable runs, install a three-phase output reactor between the VFD and the motor to suppress capacitive leakage currents.
• Replacement Mitsubishi FR-E700 VFD: If your internal IGBT diode test failed, contact your distributor for a direct replacement unit (e.g., FR-E720-030-NA or FR-E740-080-NA).

Related Articles

• /knowledge/replacement/mitsubishi-fre700-to-fre800-migration-guide
• /knowledge/compatibility/vfd-shielded-cable-selection-standards
• /knowledge/guide/how-to-megger-test-a-three-phase-motor

FAQ

Q: Can I bypass or disable the E.GF fault in the FR-E700 parameter list?

A: No. The E.GF code is a critical hardware assessment fault designed to safeguard the VFD's internal power semiconductor components from catastrophic explosion. It cannot be disabled, adjusted, or bypassed via parameter options.

Q: Why does the E.GF error code only trip after running the motor for several minutes?

A: This is typical of thermal expansion or environmental ingress. As the motor runs, its windings heat up and thermally expand, which can cause micro-cracks in the insulation to make temporary contact with the grounded stator core. Additionally, internal condensation in a cold motor can evaporate under thermal load, temporarily creating water vapor that conductive-bridges sensitive components until it settles.

Q: What is the difference between an E.GF fault and an E.OC1 / E.OC2 / E.OC3 overcurrent fault?

A: While both relate to path current, E.OC indicates a short circuit running phase-to-phase (from U to V, V to W, etc.) or a mechanical overload pulling excessive load current. E.GF indicates a path current leak going directly to output earth ground/frame ground.

Q: What will happen if I continuously reset the drive to clear the E.GF fault without troubleshooting?

A: Doing this is highly dangerous and will likely destroy the VFD's output transistors entirely. Every time you reset the VFD and apply a voltage pulse to a direct ground fault, you subject the internal IGBTs to extreme physical, thermal, and magnetic stresses. Always diagnose and clear the physical ground fault before powering the system back up.