Last week at work we had a problem where the carpenter installing medicine cabinets sent a screw through one of our NM cables and caused a short. My apprentice suggested that in lieu of tearing into a lot of sheetrock to re-run the swichtleg to the vanity light, we could just cut into the rock in the one spot where the screw hit, splice the romex there and be done. He said that there was a "UL-approved" splicing device, approved for in-the-wall splices, and that he had personally used one of these devices in the past.
My reading of NEC 300.15 would expressly forbid such a practice and I have never before heard of such an "approved" device. Anyone else?
Tyco Electronics makes a NM cable interconnection device that is designed to be concealed in the wall. Care needs to taken that there is no violation of the NEC.
For more information on these devices see the following sections of the 2005 NEC. 545.13, 550.15(K), 551.47(O), 552.48(N) and 690.32. These are the only places in the 2005 NEC that permits the interconnection device. For more information see UL file number E57250.