Southwire Romex Brand SIMpull NM-B (nonmetallic-sheathed) cable may be used for both exposed and concealed work in normally dry locations at temperatures not to exceed 90C (with ampacity limited to that for 60C conductors) as specified in the National Electrical Code. NM-B cable is primarily used in residential wiring as branch circuits for outlets, switches, and other loads. NM-B cable may be run in air voids of masonry block or tile walls where such walls are not wet or damp locations. Voltage rating for NM-B cable is 600 volts.