Mitsubishi FR-A800 Fault EF External Fault

Getting the EF fault on your Mitsubishi FR-A800 drive? Learn how to troubleshoot the X32 signal, check digital input parameters Pr.178-Pr.189, and restore operation safely.

Mitsubishi FR-A800 Fault EF External Fault


If you are operating a Mitsubishi FR-A800 series inverter and the display suddenly trips with the EF fault code, the drive has been instructed to stop by an external device. In the Mitsubishi ecosystem, "EF" stands for External Fault.

Unlike overcurrent or overvoltage errors which indicate internal electrical stress, the EF fault is a "logic" trip. It means the drive is doing exactly what it was programmed to do: listening to a safety or process interlock and shutting down for protection. Here is a human-made guide to help you find the source of the trip and get your motor running again.

What Exactly is the EF Fault?

The EF fault is specifically linked to the X32 signal. By default, this function is not active. It only becomes a "Protective Function" if a technician has assigned the value "32" to one of the digital input terminals in the parameter settings (Pr.178 to Pr.189).

When this terminal is assigned, the drive expects a constant "ON" signal (closed contact) to run. If that contact opens (turns OFF), the drive assumes an external emergency or process failure has occurred and shuts off the output immediately to prevent damage or injury.

Common Causes of the EF Trip

  • External Interlock Triggered: A physical emergency stop, a thermal relay on the motor, or a limit switch has opened.
  • PLC Command: An overarching PLC (Programmable Logic Controller) has detected a system-wide error and dropped the "Healthy" signal to the drive.
  • Broken Wiring: A wire has vibrated loose from the digital input terminal block or has been severed in a conduit.
  • Parameter Misconfiguration: A terminal was accidentally assigned function "32" during commissioning without having the corresponding hardware wired up.

Step-by-Step Troubleshooting Guide

1. Identify the Assigned Terminal

Since the EF fault is programmable, you first need to know which physical terminal the drive is watching. Check the following parameters:

  • Pr.178 to Pr.189 (Input terminal function selection): Look for any parameter set to 32.
  • For example, if Pr.180 is set to 32, the drive is using terminal RL as the X32 signal source.

2. Check the Monitor Menu

You can verify the status of the inputs without a multimeter by using the drive's keypad:

  • Go to the Monitor menu and look at the I/O terminal status.
  • Check if the terminal identified in Step 1 is "OFF." If the icon for that terminal is not highlighted, the drive is not receiving the signal it needs to stay active.

3. Inspect the Physical Wiring

Once you know which terminal is the culprit (e.g., Terminal RM or RL):

  • Trace the wire from that terminal back to the external device.
  • Use a multimeter to measure the voltage at the terminal. Usually, this requires a 24V DC signal from the PC terminal.
  • If you measure 0V, the external circuit is open. Reset the physical E-stop button, check the external relay, or repair the broken wire.

4. Verify Safety to Restart

Important: Because this is an external fault, something outside the drive "wanted" the machine to stop. Before turning the X32 signal back ON:

  • Ensure there are no personnel working on the machinery.
  • Verify that the mechanical cause of the trip (e.g., a jammed conveyor or an empty tank) has been resolved.

How to Reset the EF Fault

  1. Restore the physical signal to the assigned terminal (Turn the X32 signal ON).
  2. The fault may clear automatically, or you may need to press the [STOP/RESET] key on the operation panel.
  3. Apply a new Start command to resume operation.

Summary Checklist

Checkpoint Action Required
Parameter Search Check Pr.178–Pr.189 for value "32".
Input Status Verify if the X32 signal is currently OFF.
External Circuit Check E-stops, PLC outputs, and thermal relays.
Wiring Ensure terminal screws are tight and wires are intact.

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