When a motor trips or insulation concern appears near capacitor-bank operation, nominal bus voltage provides little diagnostic value. Build a time-aligned record of the switching command, voltage waveform, current response and relay or drive event.
| Evidence | Question it answers | Common gap |
|---|---|---|
| One-line and capacitor-bank data | What was connected and where? | Bank step or reactor omitted |
| High-resolution event waveform | What reached the motor bus? | RMS trend used instead of event capture |
| Switching and relay logs | Did sequence and protection timing align? | Clocks not synchronised |
| Motor/drive connection data | What stress path existed? | Cable and surge-protection details missing |
Decide from a matched event
Confirm instrument bandwidth, probe location and time reference. Compare repeated events only when the bank step, load state and network configuration match. If evidence is incomplete, state the missing measurement rather than attributing the event to the motor.
Mitigation may involve switching control, reactors, surge protection, grounding or operating sequence. Select it through a coordinated power-system and motor-insulation review.
Related reading: motor voltage unbalance and overheating and motor starting methods.