In the near future i want to change my 100amp box to a 200amp box in my basement, i am an industrial electrician but i don't deal with residential that much i want to put the new box next to or with in a couple feet of the old panel my question is if the existing romex is not long enough to reach what is the best (safest) and code compliant way to extend the romex to reach the new panel. any advice would be great or refer to code book so i can look up the section.
