I posted on here the other day about some suspicious 240v cable and followed the recommendations to replace it. I was already leaning that way but was kind of hoping to be told I was overthinking it. But you all confirmed what I thought. I ran close to 25’ of 10/2 cable from the second story to the basement. Nothing is wired yet because it is late and I don’t want to turn on the main breaker.
My step dad let me borrow a 50’ fishing tape and 10’ endoscope which were really helpful. I did not have to cut any walls!
You can mark it either red or black, but you already have one black wire, so it would be best to mark it red, just to differentiate it.