It is a nonmetallic sheathed cable consisting of two or more insulated conductors having an outer sheath of moisture resistant, nonmetallic material. The conductor insulation is rubber, neoprene, thermoplastic or a moisture resistant flame retardant fibrous material. There are two types: NM and NMC - described earlier. Romex should be secured between boxes with straps. It is not used underground but can be used in residential garages. One disadvantage is that it can be mechanically broken. It can not be used in commercial structures, nor in concrete and can not be buried.