I'm doing some work up in my attic, installing plywood decking over my garage for storage. During installation, I accidentally rubbed the edge of one plank of plywood against a run of NM-B, tearing its outer insulation. (The inner paper-like sheath is not damaged.)
If both ends of this run of NM-B were accessible I would just replace it completely. Unfortunately, it is the line running from my garage's overhead light, to the light switch mounted on the wall. I'm pretty certain this run will be stapled to the stud, a few inches above the switch gang, which means I can't pull it out. (It is also inaccessible for other reasons, such as: the point at which it descends through the plate down to the switch gang is directly below my A/C unit, in the attic.)
Since neither the paper sheath nor the insulated conductors inside were damaged, I'm wondering if it would be acceptable (NEC-wise) to just wrap electrical tape around the scarred portion. After the repair, this section will be hidden under the plywood decking that I am installing. (Not intentionally, that's just the way the cookie crumbles.)
I also found something at HD called 'liquid electical tape'.
Best Answer
I'd trust the old reliable electrical tape over the liquid stuff.
Section 334.116 of the NEC (USA National Electric Code) talks about the sheath in very generic terms: it has to be flame retardant and moisture resistant, etc. There is nothing particularly special or magic about the requirements.
I'd inspect the wire very very carefully, maybe even remove the paper to ensure nothing is going on below, wrap it, then mention and show it to the local inspector when your job is inspected. Maybe even write a note on the cable in sharpie.
The worst case is you have to splice the cable into a junction box that forever more must be accessible.