16

Short Circuit

Danfoss · VLT Micro Drive FC 51

What does 16 mean?

A short circuit has been detected in the motor windings or on the motor terminals. This is a severe fault that can cause immediate and catastrophic damage to the drive's output stage if not quickly and effectively protected against, representing a major electrical failure.

Common Causes

  • Direct short circuit between two output phases (U-V, V-W, U-W) or from an output phase to ground on the motor side of the drive.
  • Catastrophic insulation failure within the motor windings, leading to a direct phase-to-phase or phase-to-ground short.
  • Damaged or faulty motor contactor (if used on the output side) creating a short between its contacts.
  • Foreign metallic object (e.g., loose screw, wire strand) bridging motor terminals or inside the motor terminal box.
  • Output filter components (e.g., dv/dt filter, sine filter) failing internally, causing a short.

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Immediately disconnect the motor cables from the drive's output terminals (U, V, W) and then power cycle the drive.

  2. 2

    Using an ohmmeter, measure resistance between all three motor output phases (U-V, V-W, U-W) and from each phase to ground at the drive's output terminals.

  3. 3

    Visually inspect the motor terminal box and the entire motor cable for any signs of physical damage, arcing, or foreign objects.

  4. 4

    Measure the resistance of each motor winding (e.g., Phase U to Phase V, V to W, W to U) directly at the motor, expecting balanced low resistance values.

  5. 5

    If an output filter or motor contactor is used, disconnect it and test the drive independently to isolate the faulty component.

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Verified technical data. Last updated: March 2026

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Source: Danfoss VLT Micro Drive FC 51