What is Romex? What is 12/2 or 14/3 Electrical Cable?
The electrical system in most homes and businesses is wired using sheathed, insulated wire. Romex® is a brand name that is well-known for manufacturing this type of electrical wire. Romex NM cable, (pronounced rome-ecks), and competing brands of cable contain two or more insulated conductors (wires) in a flexible plastic sheath that can be run through walls, under floors, through attics and so on. All brands of flexible, sheathed cable which can be used interchangeably, though many electricians prefer to use the brand name product. The labeling for all electrical cable is standardized and so is the same regardless of who manufactures it.
Flexible sheathed cable is easier to run through holes in studs than metallic sheathed cable, it is also cheaper. Romex cable is labeled as NM-B, which means the sheathing is non-metallic cable; other brands use code "NMC". The "NM" designation is used to distinguish it from metallic sheathed (BX or AC) cable. Another designation, UF, indicates the cable is rated for direct burial in the ground (although local codes may not permit that use).
A rating of 14/3 refers to the gauge of the wire and how many conductors are in the cable. In this case, the wire gauge is fourteen (lower numbers mean larger wires) and the three indicates that there are three conductor wires in addition to a non-insulated ground wire. So, in the image above of 12/2 sheathed cable, there are two twelve gauge insulated conductors plus a bare twelve gauge ground wire.