Damaged SEC

I found this at yesterday’s inspection. This is an older square D 125 amp split bus panel. The SEC on the left side overheated badly at one point. I am curious how this might have ocurred. A short at one of the branch cicuits would have tripped a breaker. The branch circuit wiring looked original and in reasonably good shape, aside from the bare wires, double tapped neutrals, and the missing strain relief.


Appears that the lug was not tight enough, or loosened over time causing heat.