Ground Fault Alarm (Drive Trip)

What does ALARM 1 mean?

This alarm signal from the ground fault monitor (option +Q954) is explicitly recommended to be connected for immediate drive tripping upon detection of a ground fault in IT (ungrounded) systems. The contact is normally closed when no ground fault is present and has a load capacity of 250 V AC, 2 A. Be aware that the ground fault monitor performs self-testing, which might momentarily activate this signal, necessitating careful distinction between actual faults and test sequences.

• Insulation breakdown in motor winding or power cable due to aging, moisture ingress, or mechanical abrasion.
• Damage to a power semiconductor component (e.g., IGBT, rectifier diode) within the drive, creating a direct leakage path to ground.
• Severe contamination (conductive dust, metal shavings, process fluids) on power busbars or terminal blocks inside the drive or motor connection box, creating a low-resistance path.
• Excessive capacitive leakage current to ground from long, unshielded motor cables in an IT (ungrounded) system, exceeding the drive's detection threshold (e.g., P3-10, Ground Fault Trip Level).
• Faulty wiring or incorrect installation of the ground fault monitor (option +Q954) leading to erroneous detection or signal interpretation.

Click steps to track your progress.

1. 1

   De-energize and lock out power to the drive. Verify zero voltage at input terminals L1, L2, L3 and output terminals T1, T2, T3 using a CAT III rated multimeter.

2. 2

   Disconnect all motor phase conductors (U, V, W) from the drive output terminals. Measure insulation resistance between each motor phase and the motor frame ground (PE) using a megohmmeter (e.g., 1000V DC test voltage). A reading below 1 Megohm indicates a motor or cable fault.

3. 3

   Measure insulation resistance between each drive output phase (T1, T2, T3) and the drive chassis ground (PE) with motor disconnected. A reading below 1 Megohm suggests an internal drive fault.

4. 4

   Inspect the ground fault monitor (+Q954) connection terminals X1:1 and X1:2 for secure wiring and proper contact.

5. 5

   Verify drive parameter P3-10 (Ground Fault Trip Level) is set appropriately for the IT system and does not trigger prematurely due to normal capacitive leakage.

6. 6

   Visually inspect the drive's power section (IGBTs, rectifiers, busbars) for signs of arcing, discoloration, or component damage indicative of a short to ground.