Scope of this technical record
Immediate or early acceleration overcurrent trips on industrial AC drives.
Repeated reset-and-run attempts can escalate semiconductor, cable and motor damage. Investigation must follow qualified isolation and OEM procedure.
Startup overcurrent route
The first useful fact is when the overcurrent appears: enable, first PWM, ramp, speed threshold or load.
Startup overcurrent timing map
Why startup overcurrent is not one fault
Overcurrent at startup can come from the machine, the motor, the cable, the parameter set, feedback hardware, current measurement, the driver stage or the output bridge. The panel text does not tell the repair shop which one is true.
The most useful first detail is timing: does the trip occur at enable before rotation, at first PWM output, during ramp, at a particular speed or only under load? That timing determines whether the route starts outside the drive or inside the inverter stage.
Repair triage map
If a module has already failed once, the gate-driver and protection path become critical. Replacing only the IGBT/IPM without verifying isolated driver supplies, gate resistors, clamp components and current-feedback evidence can produce repeat failure on the next power-up.
Startup overcurrent separation
| Observation | Likely boundary | Service meaning |
|---|---|---|
| Trip with loaded machine only | Mechanical load / ramp / motor data | Check load and parameters before boards |
| Trip as soon as PWM starts | Motor cable / output bridge / driver | Separate external output path from inverter |
| Trip after module replacement | Driver / feedback / bus stress | Do not fit another module until driver is checked |
| Trip with encoder control | Feedback phase or parameter mismatch | Verify encoder and motor data |
| Trip only after contactor closes | Output accessory / wiring | Review contactor, reactor, filter and surge device placement |
Better than a reset-and-try approach
The practical page goal is to stop the common destructive loop: reset, run, trip, replace module, trip again. The repair route should produce a first-fault timeline, motor/cable boundary, parameter snapshot and power-stage evidence before a replacement module is approved.
Field record checklist
- Trip timing relative to enable and ramp
- Motor and cable condition
- Load condition at start
- Acceleration time and motor data
- Previous module or board repair
- Static output-stage evidence
Technical basis and reference documents
This is an independent editorial technical reference. Original manufacturer documentation remains controlling for installation, repair and commissioning decisions.
Linked workflow for startup overcurrent separation.
Diagnostic workflow
Overcurrent trip appears immediately at run command, during acceleration or before stable speed is reached.
Replacement IGBT, IPM or output module fails again during power-up, enable or early load testing.
Turn this record into a qualified service request
A repair decision is much more reliable when the request includes the exact identity of the drive, the first fault evidence and the machine condition when the symptom appeared.
- Complete drive type code / MLFB or nameplate model
- Fault code, fault value and first event before reset
- When the event appears: power-up, enable, ramp, run, decel or stop
- Motor/cable connected or isolated during the symptom
- Visible board, option-card, module and connector identifiers
- Previous repair history, replacement parts and repeat-failure pattern