Lenze i500 Error Code LU

Lenze PLC & VFD Major DC Bus

Model: i500 | Code: LU

Applicable Systems
i500

Symptoms

DC bus undervoltage. The DC bus voltage has dropped below the minimum required for proper drive operation.The drive cannot maintain motor control.

Possible Causes

  • Line voltage too low or voltage sag from utility
  • Line contactor or breaker opened while drive is running
  • DC bus capacitor degradation
  • Drive internal power supply module fault

Troubleshooting Steps

  1. Step 1: Check the equipment status and fault indicators to confirm the active fault code
    Fault indicator or HMI displays code LU as active
  2. Step 2: Verify all electrical connections, wiring harnesses, and connector seating
    All connections secure, no corrosion, loose pins, or damaged wires
  3. Step 3: Check the communication cable continuity and connector seating at both ends
    Cable continuity confirmed, connectors fully seated with locking tabs engaged
  4. Step 4: Verify communication parameters (baud rate, node address, protocol) match network configuration
    All communication parameters match the network setup
  5. Step 5: Inspect cable for EMI interference: check routing away from high-voltage lines and motor cables
    Cable routed away from EMI sources, shielding intact
  6. Step 6: Check terminating resistors at bus endpoints if applicable (e.g., PROFIBUS, CANopen)
    Terminating resistors installed at both bus ends
  7. Step 7: Reset the fault after restoring communication: power-cycle the affected node
    Communication restores and fault clears

How to Reset

To reset: 1) Fix the communication cable or parameter issue. 2) Power-cycle the affected node. 3) Verify communication restores. Caution: Check all nodes on the bus.

Frequently Asked Questions

  • Q: What does fault code LU mean on the Lenze i500?

    Fault LU indicates a communication fault. The equipment has lost communication with a connected device or network. Check the communication cables, connectors, and network parameters.

  • Q: Can I continue operating the equipment with fault LU active?

    No. The equipment has detected a fault condition and has taken protective action (typically stopping or derating). Continuing to operate without fixing the root cause may cause further damage. Always investigate and fix the fault before resuming operation.

Related Lenze Fault Codes

Source: Lenze i500 Frequency Inverter Operating Instructions, Lenze Documentation

Category: PLC & VFD