Nonmetallic sheathed (NM-B) building cable is a flexible electrical cable consisting of three or more wire conductors (including one for grounding) bundled inside a jacket, or sheath, that is nonconductive and heat-resistant. It's lighter than armored building cable, making it easier to handle, and its pliable sheathing is easier to unspool and straighten out. It powers outlets, lighting, and appliances in residential and commercial applications. Type NM-B cable is for enclosed, interior wiring in dry locations only (typically within a wall, ceiling, or under a floor) and should not be used outdoors or anywhere it might get wet.