Wiring a sub panel today. My first. The 12/2 NM was easy. Had the ripping tool to slice the yellow sheath and had no problems. But that tool mangled the 14/2 wire. I guess each wire in it is encased in the grey vinyl? How are you supposed to get the wires free? Do you have to slice each one individually with an exacto knife? I think I ruined a whole homerun because of this problem. Tips?