I've seen the results of a nick in the wire insulation "plasma cutting" the neatest slot in the side of the EMT- without ever tripping a good breaker!
Visit any weld shop, and look at the settings on the machines. A LOT of welding is done with less than 2000 watts. Or, even, twenty amps.
It is very possible for a lot of melting to happen without tripping a breaker. We just don't appreciate just how much energy is available in a 20A/120V circuit.
