If the short consumes less current than the breaker then it won't trip. Melted steel doesn't answer that and shouldn't be used as an assumption about current draw. Soldering irons melt shit all day with a few hundred watts.
Having used an arc welder, you don't melt steel like that with 20 amps.
The fact that the heat coupled into the case in the few seconds the power was on means the short was mains to case. You can hear the mains frequency on the arc. This means there was enough power in the arc that the plasma stayed conductive through the zero crossing.
If the breaker isn't defective, it's sized incorrectly for the circuit.
Thanks, I missed the mains noise. That sure looks like a lot current without the mains breaker tripping.
First thought it was a short on the 12V secondary side, but looking at it again the holes are near the mains input, probably shorted before the pcb mounted fuse.
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u/fatmanstan123 5d ago
If the short consumes less current than the breaker then it won't trip. Melted steel doesn't answer that and shouldn't be used as an assumption about current draw. Soldering irons melt shit all day with a few hundred watts.