Emerson Unidrive SP Error Code OC

Emerson PLC & VFD Critical Drive

Model: Unidrive SP | Code: OC

Applicable Systems
Unidrive SP Commander SK EV2000 Mentor MP

Symptoms

The drive trips and displays OC (Overcurrent). The output current has exceeded the drive's overcurrent trip threshold. This is a critical fault that immediately cuts the motor output to protect the IGBT modules.

Possible Causes

  • Motor or output cable short circuit between phases or to ground
  • Sudden mechanical load increase or shock load during operation
  • Acceleration time too short causing excessive current draw
  • IGBT module failure or current detection circuit fault

Troubleshooting Steps

  1. Step 1: Disconnect the motor and output cable, then run the drive in no-load mode
    If OC trips without motor, the drive's IGBT or detection circuit is faulty
  2. Step 2: Measure motor winding insulation with a 500V megger
    Phase-to-phase and phase-to-ground resistance should exceed 1Mohm
  3. Step 3: Check output cable for damage, especially at bends and cable glands
    Replace any cable with damaged insulation
  4. Step 4: Verify the acceleration time parameter is appropriate for the load
    Increase acceleration time if the load inertia is high

How to Reset

To reset: 1) Fix the short circuit or load issue. 2) Press the RESET key or cycle power. 3) Restart. Caution: Never reset OC without locating the cause; repeated overcurrent trips can destroy the IGBT modules.

Frequently Asked Questions

  • Q: What is the OC trip threshold?

    The overcurrent trip level is typically 200-300% of the drive's rated output current, depending on the model. The exact value is specified in the Unidrive SP Advanced User Guide. The trip is instantaneous to protect the IGBT from thermal damage.

  • Q: How do I distinguish between a motor short and a drive fault?

    Disconnect the motor cable at the drive output. If OC trips again without the motor connected, the drive is faulty. If it runs fine, the fault is in the motor or cable.

Related Emerson Fault Codes

Source: Emerson Control Techniques Unidrive SP Advanced User Guide, 2023

Category: PLC & VFD