Output phase loss protection

What does E.LF mean?

This fault indicates a loss of one or more phases (U, V, W) on the inverter's output side, typically between the inverter and the motor. This protective function, which can be enabled by Pr. 251, stops the inverter output to prevent motor damage from unbalanced current flow. Operating a three-phase motor with a phase loss can severely overheat and damage the motor windings.

• Blown fuse in one of the motor phases (U, V, W) within the motor contactor or protective circuit.
• Loose or corroded connection on one of the output terminals (U, V, W) at the inverter, motor contactor, or motor terminal box.
• Open circuit in one of the motor windings due to internal damage or thermal stress.
• Damaged motor cable (U, V, W) leading to an open conductor.
• Parameter Pr. 251 (Output phase loss protection) is enabled and detecting a legitimate phase loss, or is overly sensitive.

Click steps to track your progress.

1. 1

   Using a multimeter, measure the line-to-line resistance (U-V, V-W, W-U) of the motor windings (motor disconnected from inverter) to check for open circuits (resistance should be balanced).

2. 2

   Check all fuses in the motor output circuit (if present) for continuity and replace any blown devices.

3. 3

   Inspect the motor output wiring connections (U, V, W) at the inverter, motor contactor, and motor terminal box for tightness and absence of corrosion.

4. 4

   Temporarily disable Pr. 251 (Output phase loss protection) if the motor and cables are confirmed stable and balanced, but re-enable after troubleshooting.

5. 5

   With the inverter operating, use a clamp-on ammeter to measure current on each output phase (U, V, W) to the motor to identify any imbalance or zero current.