1. Introduction: Symptoms and Background

In Schneider Electric’s Altivar ATV310 variable frequency drive (VFD), users may occasionally encounter the code --06 displayed on the integrated 7-segment LED screen. This condition is often accompanied by the motor being unable to start or respond to frequency commands. Although this may look like a fault, --06 is not an error code, but rather a status indication representing a special operating condition—usually “Freewheel Stop.”

This article explains the meaning of --06, identifies common causes, and walks you through practical steps to resolve the issue and restore normal operation.

2. What Does --06 Mean?

The display code --06 on the ATV310 is an operational status code indicating that the drive is currently in Freewheel Stop mode, meaning output is disabled and the motor is freely coasting. This state is not caused by a fault but is often the result of control logic, input conditions, or communication states.

Other common drive statuses include:

• --00: Drive ready (no run command)
• --01: Fast stop
• --06: Freewheel stop

While the drive is in --06, no output frequency is generated—even if run commands are issued—until the condition is cleared.

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3. Common Causes of --06 Status

Several typical reasons could trigger the --06 state:

🟠 a. Logic Input Assigned to Freewheel Stop

If a digital input (e.g., LI1–LI4) is assigned to the Freewheel Stop function and is active, the drive will enter --06.

🟠 b. Incorrect Run Command in 2-Wire or 3-Wire Mode

• In 2-wire mode (P201 = 2C), the drive needs a level-type run signal on LI1.
• In 3-wire mode (P201 = 3C), a pulse-style start and stop logic is used.
  If wiring or configuration mismatches occur, the drive may fall into --06.

🟠 c. Serial Communication Without Proper Commands

If you’re controlling the drive via Modbus or RS-485, and the master does not send a valid start command (bit 0x6 = 1), the drive enters --06.

🟠 d. Analog Input Loss or Signal Drop

When using 4–20 mA input for speed control, a loss of input signal could trigger a fallback to freewheel stop.

🟠 e. Stop Button or Remote Stop Triggered

If the STOP key on the panel or an external STOP command is active, the drive may enter --06.

🟠 f. Residual State After Power Cycle

Sometimes the drive reboots directly into --06 if the prior control signals remain unchanged.

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4. Step-by-Step Troubleshooting and Recovery

✅ Step 1: Check Control Mode and Logic Inputs

• Confirm the control mode: P201 (2-wire/3-wire/serial).
• Check P202, P203 for proper assignment of RUN/STOP logic inputs.
• Use monitor mode (parameters 800–811) to observe input signal status.

✅ Step 2: Inspect Physical Inputs

• Check if any logic inputs (e.g., LI1) are incorrectly triggered.
• Look for short circuits, faulty switches, or wiring issues.

✅ Step 3: Check Analog/Serial Communication Settings

• For analog control, verify AI1 input signal and scaling.
• For Modbus, confirm that the master is sending the appropriate control word (bit 0x6 = 1).

✅ Step 4: Clear the Freewheel Stop and Restart

Option 1: Via Panel Navigation

• Press ESC or MODE on the HMI.
• Exit back to the main screen, wait for rdY (ready) to appear.

Option 2: Power Cycle

• Power off the drive for 10 seconds, then power it back on.
• The screen should return to --00 or rdY.

Option 3: Reassign Input Functions

• Use P202 to change logic input function from Freewheel Stop to an unused input.
• Set unused inputs to No Function (typically code 00).

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5. Ensuring Stable Operation After Recovery

After returning to normal status, take the following steps to avoid future issues:

• ✅ Reassign logic inputs only when needed.
• ✅ Avoid assigning STOP or Freewheel functions to frequently active lines.
• ✅ Add debounce and safety logic in PLC/HMI control.
• ✅ Enable fault auto-restart (parameter 602.0 = 01).
• ✅ Use clear feedback loops if controlling via communication protocol.

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6. Summary Table

Step	Description
Identification	--06 is Freewheel Stop, not a fault
Analysis	Check logic input functions, run mode, communication
Resolution	Navigate panel, correct wiring or reset power
Optimization	Adjust input definitions and enable self-recovery logic

7. Conclusion

The --06 display on a Schneider ATV310 is a common condition that can interrupt motor operation but is not an error. With proper diagnosis—by inspecting control signals, input assignments, or communication—this state can be quickly cleared.

Once resolved, implementing preventive logic configuration and enabling smart restart strategies can ensure robust and continuous drive performance in both standalone and automated systems.

If issues persist, contacting Schneider’s technical support or reviewing the full parameter manual is recommended.

Introduction

Variable frequency drives (VFDs) are critical components in modern industrial automation systems, widely used in motor control applications to achieve precise speed and torque regulation, enabling efficient production, energy savings, and extended equipment lifespan. Schneider Electric, a globally renowned electrical equipment manufacturer, offers the ATV340 series VFDs, which are known for their superior performance, high reliability, and versatile features. These drives excel in industrial applications requiring high dynamic response and precise control, such as cranes, conveyor systems, and processing machinery.

However, in practical applications, the ATV340 VFD may encounter various faults, one of which is the “Load Movement Error” (fault codes [nLdCF] or [MDCF]). This fault can disrupt production processes, potentially cause equipment damage, or pose safety risks, making timely identification and resolution essential. This document provides a detailed analysis of this fault, covering its definition, causes, diagnostic methods, solutions, and preventive measures to assist users in effectively addressing the issue.

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Fault Description

The “Load Movement Error” occurs when the load (i.e., the mechanical component driven by the motor) moves unexpectedly without any motion command. On the ATV340 VFD’s display, this fault is typically indicated as “Load Movement Error” or the code “nLdCF,” and it may also appear as “0050Hex” in hexadecimal format. According to the Schneider ATV340 programming manual, this error indicates that the system has detected abnormal load behavior during a stopped or uncontrolled state.

Fault Symptoms

• Display Indication: The VFD displays “Load Movement Error” or “nLdCF” and enters a fault protection state.
• Motor Behavior: The motor may rotate unexpectedly when not commanded, or the load may shift after the motor stops.
• System Impact: The VFD ceases output, preventing normal motor operation, which may lead to production interruptions.

This fault is particularly critical in applications like cranes or hoists, as unexpected load movement could result in dropped cargo, equipment damage, or safety hazards for on-site personnel.

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Fault Cause Analysis

The “Load Movement Error” can stem from various factors. The following are common causes based on the ATV340 programming manual and practical application experience:

1. Brake System Issues

• Brake Command Circuit Problems: Loose wiring, poor contact, or damaged components in the brake command circuit may prevent proper transmission of brake signals, causing the brake to fail.
• Brake Failure: Mechanical wear, improper adjustment, or aging of the brake itself may result in insufficient braking force, failing to prevent load movement.

2. Incorrect Parameter Settings

• Load Movement Detection Parameters: The ATV340 supports load movement detection through parameters [BRH b5] and torque threshold reference [TTR]. If [BRH b5] is not enabled (default is NO) or [TTR] is set inappropriately, it may lead to missed or false detections.
• Mismatched Motor Control Type: If the parameter [CTT] (motor control type) is not set correctly to [FVC] (standard for asynchronous motors) or [FSY] (standard for synchronous motors), it may cause control instability, leading to abnormal load movement.
• Insufficient Load Holding Time: If the parameter [MD FT] (load holding time) is set too short, the system may fail to detect load status properly after power restoration, triggering the error.

3. Mechanical System Issues

• Loose Transmission Components: Loose or damaged couplings, gears, or belts may allow the load to move even when the motor is stopped.
• Unstable Load Fixation: In hoisting applications, an unstable load center of gravity or faulty securing mechanisms may cause movement due to gravity.

4. Electrical System Issues

• Unstable Power Supply: Voltage fluctuations or momentary power interruptions may disrupt the VFD’s normal control, leading to load instability.
• Electromagnetic Interference: Strong electromagnetic interference on-site may affect the VFD’s signal processing, causing erroneous actions.

5. External Factors

• External Forces: Forces such as wind, gravity, or other external influences acting on the load may cause movement when the motor is stopped.

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Fault Diagnosis Methods

To accurately identify the cause of the “Load Movement Error,” users can follow these systematic diagnostic steps:

1. Review Fault Information

• Check Display: Note the fault code (e.g., “nLdCF” or “0050Hex”) and the “Latest Error 1 Status” on the VFD display.
• Access Fault History: Use programming software or an HMI to review the fault occurrence time and frequency to analyze triggering conditions.

2. Inspect Brake System

• Brake Command Circuit: Use a multimeter to test the continuity of the circuit wiring and verify the functionality of relays or contactors.
• Brake Condition: Manually check the brake’s engagement and release to ensure its mechanical performance is intact.

3. Verify Parameter Configuration

• Load Movement Detection: Access the parameter menu and confirm if [BRH b5] is set to “YES” (enabled). If set to “NO,” the detection function is disabled.
• Motor Control Type: Ensure the [CTT] parameter matches the motor type ([FVC] for asynchronous motors, [FSY] for synchronous motors).
• Load Holding Time: Check the [MD FT] setting, which defaults to 1 minute. Adjust it to 1–60 minutes based on application needs.

4. Inspect Mechanical System

• Transmission Components: Check for looseness or wear in couplings, gears, or other components.
• Load Fixation: Ensure the load is securely fixed in the stopped state and not subject to external forces.

5. Monitor Electrical Environment

• Power Quality: Use a voltmeter to monitor input voltage, ensuring it remains within the VFD’s acceptable range (typically 380V ±15%).
• Electromagnetic Interference: Assess whether strong interference sources, such as high-power equipment or unshielded cables, are present on-site.

6. Observe Load Behavior

• Under safe conditions, disconnect the motor power and observe whether the load moves due to external forces or mechanical looseness.

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Fault Resolution Measures

Based on the identified causes, the following are specific solutions:

1. Repair Brake System

• Circuit Repair: Replace damaged wiring or components to ensure accurate brake command transmission.
• Brake Adjustment: Repair or replace the brake to ensure sufficient braking force and timely response.

2. Optimize Parameter Settings

• Enable Detection Function: Set [BRH b5] to “YES” to activate load movement detection.
• Adjust Torque Threshold: Configure [TTR] based on load characteristics to ensure appropriate detection sensitivity.
• Match Control Type: Set [CTT] to [FVC] or [FSY] to align with the motor type.
• Extend Holding Time: Adjust [MD FT] to an appropriate value (e.g., 5 minutes) to prevent false alarms after power restoration.

3. Strengthen Mechanical System

• Tighten Components: Secure or replace loose transmission components.
• Secure Load: Add fixing mechanisms to ensure load stability.

4. Improve Electrical Environment

• Stabilize Power Supply: Install a voltage regulator or UPS to maintain stable voltage.
• Reduce Interference: Shield control circuits and optimize equipment layout to minimize electromagnetic interference.

5. Clear Fault Code

• Reset Operation: After resolving the issue, use the [ATR] (automatic fault reset) or [RSF] (reset fault) parameter to clear the error code. If necessary, reset [MTBF] (load holding delay) by powering off and restarting the device.

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Preventive Measures

To reduce the likelihood of “Load Movement Error,” users can implement the following preventive measures:

1. Regular Maintenance

• Brake System: Inspect the brake and its circuit monthly, replacing worn components promptly.
• Mechanical System: Regularly tighten transmission components to prevent looseness.

2. Standardized Parameter Management

• Parameter Backup: Save parameter configurations after commissioning for quick restoration after faults.
• Periodic Review: Check critical parameters (e.g., [BRH b5], [CTT]) quarterly to ensure correctness.

3. Personnel Training

• Operational Standards: Train operators on proper VFD usage to avoid errors.
• Emergency Handling: Teach basic fault diagnosis skills to improve response capabilities.

4. Optimize Operating Environment

• Power Protection: Ensure a stable power supply to avoid fluctuations.
• Interference Mitigation: Optimize wiring to reduce electromagnetic interference.

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Conclusion

The “Load Movement Error” is a common fault in Schneider ATV340 VFDs, potentially caused by brake system failures, incorrect parameter settings, mechanical looseness, electrical issues, or external forces. Through systematic diagnosis—reviewing fault information, inspecting brake and mechanical systems, and adjusting parameters—users can effectively identify and resolve the issue. Additionally, preventive measures such as regular maintenance, standardized operations, and environmental optimization can significantly reduce fault occurrences, ensuring long-term stable equipment operation.

In industrial automation, promptly and accurately addressing VFD faults is critical to maintaining production efficiency and safety. This document aims to provide practical guidance to help users better understand and manage the ATV340’s “Load Movement Error,” enhancing their confidence and capability in equipment management.

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I. Overview

In modern industrial automation control systems, inverters play an extremely crucial role. The ATV630 series inverters launched by Schneider Electric are widely used in fields such as fans, pumps, and compressors, offering energy efficiency, flexible control, and extensive communication capabilities. However, during actual use, users may occasionally encounter a fault message on the screen indicating “Safety Function Error,” often accompanied by a status display of “STO,” indicating that the inverter is in a safe shutdown state.

This article provides a detailed analysis of the meaning of this error, its possible causes, wiring considerations, and practical methods for troubleshooting and resolving the fault.

II. Fault Meaning Analysis

On the ATV630 inverter, the “Safety Function Error,” or SAFF (Safety Function Fault), is a type of fault related to the STO (Safe Torque Off) safe shutdown function.

2.1 Overview of STO Function

STO (Safe Torque Off) is a safety function compliant with the IEC 61800-5-2 standard. Its primary role is to quickly disconnect the motor torque by shutting off the power output to the motor without cutting off the main power supply of the inverter.

2.2 Meaning of SAFF Fault

According to Schneider’s official manual, the specific definitions and possible causes of SAFF (safety function error) are as follows:

Possible Causes:

• Inconsistent states (high/low) of the STOA and STOB inputs for more than 1 second;
• Debounce time timeout;
• Internal hardware failure (modules related to safety functions).

Solutions:

• Check the wiring of the STOA and STOB digital inputs;
• Verify that jumpers are reliably connected;
• Contact Schneider’s official technical support if necessary;
• Clear the fault by performing a power reset.

III. Wiring Principles and Common Error Analysis

The STO function of the ATV630 typically uses terminals “STOA” and “STOB” to receive 24V inputs. Both ports must be at a high level simultaneously for the inverter to operate.

3.1 Standard Wiring Method

STOA ←→ 24VDC

STOB ←→ 24VDC

If the safety function is not used, “STOA” and “STOB” can be connected to “24V” respectively using short jumpers on the terminal block.

For example, in the picture you uploaded, the yellow jumpers connect “STOA→24V” and “STOB→24V,” which is theoretically correct.

3.2 Common Wiring Errors

• Connecting only one STO port (e.g., only STOA):
  This leads to inconsistent states between the two, triggering the SAFF.
• Loose or poor contact wiring:
  Loose plugs, oxidation, or insufficient tightening can cause intermittent faults.
• Incorrect jumper placement or use of non-industrial-grade wires:
  This can result in high-frequency interference or open circuits in the wiring.

IV. Detailed Troubleshooting and Resolution Steps

Step 1: Check STO Wiring

• Turn off the power and open the terminal cover;
• Verify that both STOA and STOB are connected to 24V and ensure reliable connections;
• If the safety circuit is not used, short-circuit “STOA” and “STOB” using industrial-grade copper wires;
• Use a multimeter to measure the voltage of STOA and STOB relative to ground to confirm it is around 24V.

Step 2: Observe Parameter Status

From the current control panel screenshot:

• ETA state word = 0x0050
• ETI state word = 0x0003
• Cmd word = 0x0006
• Drive state = STO

This indicates that the inverter has detected that the STO signal is not satisfied, preventing it from running.

Step 3: Fault Clearance Method

According to the manual, SAFF-type faults must be cleared by power cycling:

• Disconnect all main and control power supplies;
• Wait 15 minutes for the DC bus capacitors to fully discharge;
• Ensure correct wiring before reapplying power;
• Press the “STOP/RESET” button or use the rP parameter to restart the product;
• The fault should be cleared. If it persists, consider hardware issues or the use of an external safety circuit mode.

V. Extended Analysis: Is Enhanced Safety Function Enabled?

In certain applications, enhanced safety function modules (such as safety relays, Pilz, Sick, etc.) may be enabled, requiring STOA and STOB to be closed through these certified devices. If you have enabled “safety module enable (e.g., parameters such as SDI, IFSB, etc.),” the following situations may occur:

• The wiring appears correct, but the inverter’s internal logic judges it as illegal;
• The safety circuit must be closed within a specific time window; otherwise, a timeout will occur.

Check Parameters
Access the menu via the graphic terminal:
[Full Menu] → [Input/Output Configuration] → [Safety Function Allocation]
Check whether parameters such as “STO Input Allocation” and “Fault Reset Allocation” are controlled by external signals.

VI. Practical Suggestions and Summary

1. When using default jumpers, ensure:

• Use a dual-core yellow wire to jump STOA and STOB to 24V;
• Ensure good contact, no oxidation, and no broken strands;
• Avoid cross-wiring with other I/Os.

2. When enabling safety functions, it is recommended to configure:

• Use external safety modules compliant with PLe/SIL3 levels;
• Use example wiring diagrams provided by Schneider to avoid logical confusion;
• Configure digital inputs to monitor the status of the safety circuit (e.g., DI5/DI6 to monitor STO feedback).

3. Fault clearance sequence:

• Eliminate the root cause of the fault;
• Ensure correct wiring;
• Perform a RESET or power cycle;
• Check whether “Fault Reset” and “STO Configuration” are activated in the menu.

VII. Conclusion

Although the “Safety Function Error” is a common protection mechanism in the ATV630 series, its underlying principle is to protect equipment and personnel safety. Understanding its working mechanism and control logic is crucial. Proper handling of STO ports and parameter configuration is the basic prerequisite for ensuring the safe operation of the equipment.

Through the systematic explanation in this article, readers should now be able to independently address such issues, quickly locate and accurately resolve them, and avoid situations where equipment cannot operate due to “STO false alarms.”