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ErrorLib — Industrial Fault Code Library

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Safety Stop

Safety Stop

Mitsubishi Electric · FR-D700 Inverter

What does Safety Stop mean?

The safety stop function has been activated, resulting in an immediate shutdown of the inverter outputs. This critical safety measure is typically triggered by an external safety device or a wiring issue across terminals S1 and SC, or S2 and SC, indicating an open circuit in the safety chain. If misconfigured or experiencing an internal failure, it can prevent normal operation or compromise machinery safety.

Common Causes

  • External safety device (e.g., emergency stop button, light curtain, safety gate switch) activated or faulted.
  • Wiring fault in the safety input circuit (e.g., STO terminals S1, S2), such as an open circuit or short to ground.
  • Internal fault within the inverter's safety circuit, requiring service.
  • Safety PLC or safety relay output commanding the safety stop (e.g., 0VDC to STO inputs).
  • Parameter misconfiguration relating to the safety function (e.g., incorrect Pr. 350-353 settings).

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    1. Identify and verify the state of all associated external safety devices (e-stop buttons, light curtains, interlocks) for activation.

  2. 2

    2. Measure voltage at the inverter's STO (Safe Torque Off) input terminals (e.g., S1, S2) to determine if a signal is present (e.g., 24VDC).

  3. 3

    3. Review the wiring of the safety input circuit for continuity, shorts, or damaged insulation.

  4. 4

    4. Check the status of the safety PLC or safety relay controlling the inverter's safety inputs.

  5. 5

    5. Inspect inverter safety-related parameters (e.g., Pr. 350-353) to ensure correct configuration for the application.

Browse all codes in this manual (78)
Verified technical data. Last updated: April 2026

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Source: Mitsubishi Electric FR-D700 Inverter
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