Input fuses
Low-cost line-side part to check when one phase is missing or unstable.
ABB VFD Fault 3210 — What It Means
ABB fault code 3210 (DC UNDERVOLT) indicates the DC bus voltage dropped below the minimum operating threshold. ABB ACS drives monitor the DC link voltage continuously. When input voltage sags or disappears, the DC bus capacitors discharge. Once bus voltage falls below the programmed undervoltage trip level (typically around 333 VDC on a 480V system, or 200 VDC on a 240V system), the drive trips with fault 3210 to prevent the motor from losing speed control in an uncontrolled way. This fault points to the input power supply, not the drive itself.
Common Causes
- Input power sag or interruption — Utility voltage dips below nominal, a breaker trips, or a fuse on the input supply blows. Even momentary sags during motor starting elsewhere on the same feeder can trigger 3210.
- Loose or corroded input terminals — A high-resistance connection on any input phase produces a voltage drop under load that causes DC bus undervoltage during acceleration.
- Blown input fuse or open input contactor — If one or more phases are missing from the drive’s input, the DC bus charges from fewer phases and sags when the motor loads the output.
- Line reactor failure — If a line reactor on the drive’s input is failing (open winding), effective input voltage drops and DC bus undervoltage results.
Step-by-Step Fix
- Measure input voltage under load — With the drive attempting to run, measure L1-L2, L2-L3, and L1-L3 at the drive input terminals. All three should be within 3% of each other and within ±10% of nominal. A low or missing phase is immediately obvious.
- Check input fuses and contactors — Verify all three input fuses are intact (test for continuity). If an input contactor is present, confirm all 3 poles close fully.
- Tighten input terminals — With power isolated, torque all input terminal screws to the drive manufacturer’s specification. Oxidized or undersized wire should be addressed.
- Check the utility supply — If the building is experiencing voltage sags during large motor starts elsewhere on the same panel, contact the utility or install a line conditioner.
- Reset the system — After restoring proper input voltage, reset the fault and restart. Monitor DC bus voltage readout (usually available in the diagnostics menu) during startup.
Parts Often Needed
| Part | Notes |
|---|---|
| Input fuses (class J or RK5) | Match AIC rating and current rating to drive nameplate |
| Line reactor | Install if not present; reduces voltage sag and protects drive from line transients |
| Input contactor | Replace if any pole shows excessive arcing or fails to close fully |
Need Replacement Parts?
Before ordering, match the drive part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
When to Call a Pro
Persistent undervoltage faults on a properly sized supply indicate the drive’s DC bus capacitors may have degraded (reduced capacitance allows faster sag). Capacitor testing and replacement requires a qualified drive technician.