Ch 17
Grounding and electrical noise
Random limits, UC100 drops, THC noise — especially at arc start.
Never bypass the emergency stop, limit circuit, charge pump, enclosure interlock, or protective earth to keep production running.
Never touch THC arc-voltage terminals while energized. Raw plasma arc voltage can cause severe injury or death. Only a qualified person should connect arc-voltage wiring.
Record the starting condition, make one controlled change, and test again. Restore the original setting if the change did not help.
Symptom
Limits trip, USB drops, or THC voltage goes crazy when the arc starts.
Quick checks
- ☐Same program dry with plasma OFF — does fault disappear?
- ☐Work lead short path to clean metal
- ☐USB and signal cables separated from torch/work leads
Fix
Noise-control checklist
- Never remove protective earth to 'test' noise
- Optically isolated breakout between UC100 and machine
- Cross power/signal at ~90° if they must meet
- Proma Step/Dir shield ground at CNC side only (per Proma manual)
- Prevent Windows USB selective suspend
- Don't coil torch lead with signal cables
Prove it
Dry G-code → torch-signal without motion → short live straight cut while recording the exact failure moment. Ignition-only failures → work lead, separation, shielding, isolation before motor tuning.
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