THHN building wire is 19-strand, 600-V, uncoated copper wire available in sizes ranging from 4 to 14 gauge sizes. It’s suitable for use in wet or dry locations. MTW-type wire is available in 19- and 26-strand, 600-V bare, annealed copper, in 10- to 16-gauge sizes. It is primarily used in control cabinets, machine tool applications and appliance wiring applications. Both wire types are UL-, cUL-, CSA- and NEMA-rated.