Wiring Guide  

Wires and Gauge:  Household indoor wire is commonly referred as  is Romex and or NM wire It's often used in a generic sense to refer to any type of non-metallic sheathed electrical cable. More to the point, it's electrical wiring sheathed in a plastic coating

All NM "non-metallic"   cable has a series of numbers stamped on the outside of the polyvinyl sheath. They tell you how many wires it contains and what their gauge is. For example, a cable that says 14-3 contains three separate wires, each of which is 14 gauge. Gauge lets you know how much electricity a wire can conduct. It is rated according to the American Wire Gauge, or the AWG, and refers to the thickness of the wire. The smaller the number is, the thicker the wire will be. Therefore, 12-gauge wire would be thicker than 14-gauge wire. 

• Conductor wires are usually color coded – black and/or red are hot, white is neutral
• 12-2 Gauge wire has 2 wires plus a ground , 12-3 wire has three wires plus a ground
• Typical electric heater will use a  12-2, 10-2, 8-2 or 6-2 wire gauge ( wire size is base on amps and distance from circuit breaker box to appliance
• 12-3, 10-3, 8-3 wire is used 3-way switches, split receptacles, major appliances like stoves, and dryers
• Ground wires are usually bare but sometimes may be surrounded by green insulation
• Same wire is used for 120 volt or 240 Volt applications
• Wire size is base gauge, the larger the number the thinner  the wire and less electricity can go through it
•  household Wire gauge size goes from 14 gauge to 2 gauge
• Wire size is base on amp load the electrical appliance your installing
• Romex and NM wire It's basically the same thing, Romex owned by Southwire and is an actual trademarked brand

Applications: NM wire is designed to be placed in walls, ceilings, floor cavities and other unexposed areas. It is for indoor use only and should be located in spaces that are dry and free from moisture, as exposure to water can subject the wires to corrosion. To determine which type of  wire is best suited to specific household applications, consult an electrician