>>7098173 (pb)

see

https://en.wikipedia.org/wiki/Thermal_runaway#Electrical_engineering

>Thermal runaway occurs in situations where an increase in temperature changes the conditions in a way that causes a further increase in temperature, often leading to a destructive result. It is a kind of uncontrolled positive feedback.

copper wire's resistance changes with heat in a way that increases current flow which in turn increases heat which further increases current flow…