Yaskawa A1000 Fault EF8 External Fault (Terminal S8)

Getting the EF8 fault on your Yaskawa A1000 drive? Learn how to identify the external device causing the trip, verify terminal S8 wiring, and fix H1-08 parameter errors. 

Yaskawa A1000 Fault EF8 External Fault (Terminal S8)


If you are working with a Yaskawa A1000 drive and the display suddenly trips with the EF8 fault code, the drive is doing exactly what it was programmed to do: listening to an external safety or process command. In Yaskawa terminology, "EF" stands for External Fault, and the "8" specifically points to Digital Input Terminal S8.

The good news is that an EF8 code rarely means your drive is broken. Instead, it means an external device—like a PLC, a limit switch, or a thermal relay—is telling the drive to shut down for safety. Here is how to diagnose and clear the EF8 fault systematically.

What Triggers the EF8 Fault?

The EF8 fault occurs when the Multi-Function Digital Input (MFDI) terminal S8 is activated. Depending on how the drive is programmed, this could be a "Normally Open" contact closing or a "Normally Closed" contact opening. There are three primary reasons this happens:

1. An External Device is Signaling a Fault

This is the most common cause. A physical device wired to terminal S8 has detected a problem. This could be:

  • A motor over-temperature switch (Klixon).
  • A conveyor pull-cord or emergency stop.
  • A PLC output sending a "Stop" command due to a process error.

The Fix: Trace the wire from terminal S8 to the field device. Check the status of that device. If a motor is too hot or a safety gate is open, resolve that physical issue first. Once the external device returns to a "Safe" state, the EF8 can be reset on the drive.

2. Incorrect or Loose Wiring

Vibration is a common enemy in industrial cabinets. If a wire at terminal S8 has wiggled loose or if there is a short circuit in the signal cable, the drive may interpret this as an external fault signal.

  • The Fix: Tug-test the wire at terminal S8 and the common terminal (usually SC). Ensure the insulation is not pinched in the terminal block. If you are using shielded cable, ensure the shield isn't accidentally touching the S8 input.

3. Parameter Configuration Error (H1-08)

In the Yaskawa A1000, Parameter H1-08 defines the function of terminal S8. If this parameter is set to any value between 20 and 2B, the drive is looking for an external fault on that pin.

If you aren't actually using terminal S8 for anything, but H1-08 is still set to an "External Fault" value, the drive might "ghost trip" due to electrical noise or because it's looking for a Normally Closed signal that isn't there.

  • The Fix: Check Parameter H1-08. If terminal S8 is not being used in your application, set H1-08 to F (Not Used). This will disable the EF8 monitoring on that terminal.

Decoding the Logic (Normally Open vs. Normally Closed)

If you must use an external fault input, pay attention to the specific value in H1-08:

  • Value 20: External Fault, Always Detected, Normally Open (Trips when S8 closes).
  • Value 21: External Fault, Always Detected, Normally Closed (Trips when S8 opens).

If you have a wire connected but the drive trips the moment you turn it on, you likely have the logic inverted (e.g., using an NC switch with an NO setting).

Summary Checklist

Checkpoint Action Required
Field Device Verify the sensor/relay wired to S8 is in a "Healthy" state.
Wiring Check for loose connections or broken wires between SC and S8.
Parameter H1-08 Ensure the function matches the physical wiring (NO vs NC).
Terminal Usage If S8 is empty, set H1-08 = F to disable the fault

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