12/2 CU NM-B W/G is an indoor wire used in residential electrical wiring. The ?NM? stands for non-metallic, which refers to the flexible, generally PVC sheathing surrounding the cable. The ?B? represents a heat rating of 194° Fahrenheit. Wire is sized by the American Wire Gauge (AWG) system. 12/2 is for common residential wiring: light fixtures, receptacle and small appliances such as microwaves. The larger the number means the smaller the wire. NM-B can run behind walls and ceiling, inside floor cavities and other unexposed areas. It is not designed for running along the outside of a wall, such as in an unfinished basement. Use NM-B indoors only, in spaces that are dry and free from moisture. Exposure to water can subject the wires to corrosion. Since the insulation is rated to handle only a certain level of heat, you’?ll want to avoid placing wires near heat sources such as hot water pipes or heating ducts. Also, do not bury NM-B in cement, concrete, plaster or underground. Size 25’.