According to Sec. 334.15(B), "Cable shall be protected from physical damage where necessary by rigid metal conduit, intermediate metal conduit, electrical metallic tubing, Schedule 80 PVC conduit, ...

Once you cut into a wall, you are not just exposing studs and insulation, you are exposing the history of your home’s wiring ...

This answer is based on the 2017 NEC. A. Exposed Type NM cable must closely follow the surface of the building [Sec. 334.15(A)]. Nonmetallic-sheathed cable must be protected from physical damage by ...