Component reference
Welder Varistor Surge Protection Faults
A shorted varistor can cause power-on trip; an aged/open varistor leaves the input unprotected.
Component role
Do not only replace the varistor. Check input voltage, surge history, rectifier bridge and downstream short before powering again.
Repair evidence table
| Evidence | Meaning | Action |
|---|---|---|
| Burned / cracked MOV | Surge clamp failed | Replace rated part and inspect input bridge. |
| Zero ohms across MOV | Shorted protection device | Remove/replace only after isolating input circuit. |
| No visible damage | Does not prove healthy | Check if overvoltage event damaged other parts. |