Romex (NM-B Cable)
Affiliate link — we may earn a commissionRomex is the brand name for non-metallic sheathed cable (NM-B), the standard wiring for residential circuits in the US. The outer jacket is a flat, usually white or yellow plastic sheath containing two or three insulated conductors plus a bare ground wire. Common sizes: 14/2 (14-gauge, 2 conductors) for 15-amp circuits, 12/2 for 20-amp circuits, 10/3 for 30-amp circuits like dryers and AC units. The first number is the wire gauge (lower = thicker = more ampacity). You cut and strip Romex with a cable ripper and wire strippers, and drill through studs and joists to route it.
Why It Matters
If you're running new circuits, adding outlets, or doing any residential electrical work, you're working with Romex. Using the wrong gauge for the circuit amperage creates a fire hazard. 14-gauge wire on a 20-amp breaker can overheat before the breaker trips. Match the wire gauge to the breaker rating: 14 for 15A, 12 for 20A, 10 for 30A.