I'm getting ready to replace the breaker panel in my condo and I found some scary damage in one of the cables coming into the box from the top, just at the knock out hole (see picture). The damage black wire seems to be almost gone. It looks like I would need to add a piece of wire to extend it to the breaker that is connected. what is the best way to do this? I should be able to do whatever is needed since I'll have the old breaker box off.
I've been living here for 18 years and that breaker (not AFCI/GFCI) has never tripped. I wonder if this happened before my time.