What Is Romex or NM Electrical Cable?

Romex 12/2 NM Wire

The individual electrical wires used for wiring circuits in most residential applications are contained in a cable bundle that is protected by vinyl plastic sheathing. The term non-metallic (NM) is used to describe this type of cable, to distinguish it from the other common form of wiring. Anytime you see the term NM cable, it refers to this kind of wiring—individual conductors contained in a bundle protected by vinyl plastic sheathing. For homeowners and professional electricians running new circuits or extending old circuits inside walls and ceilings, NM cable is the material normally used.

Romex® is the specific brand name for a non-metallic (NM) building wire made by Southwire. In other words, Romex® is technically just one brand of NM cable. However, the term Romex is often used generically (though inaccurately) to describe any type of NM cable, no matter which manufacturer made it.

NM Defined

The NM designation refers to the outer jacket of the cable, indicating that it is a non-metal material. This outer sheathing is a 30 mil-thick PVC jacket that serves to bundle the individual wire conductors together and protect them. This is in contrast to metallic sheathed cable or conduit wiring, in which the individual conductors are instead protected by some form of a metal coil or metal or plastic conduit.

Despite the NM label, the individual electrical conductors within the cable are indeed metal—normally copper that is jacketed with color-coded PVC (polyvinyl chloride). The individual conductors normally have black, white, and red insulation. Also present within the NM cable is a bare copper grounding wire.

NM cable comes in many wire gauges, but most household circuits will use 12-gauge or 14-gauge wire, with either two or three conductors inside (plus a bare copper ground wire). For example, a cable labeled "14-2 with ground" will have two insulated conductors with 14-gauge wire plus a bare copper grounding wire. This cable is used for 15-amp circuits. A cable labeled "12-3 with ground" will have three 12-gauge insulated conductors (white, black, and red) plus the bare copper grounding wire. A 12-gauge cable is rated for 20-amp circuits.

Is Romex Brand Superior?

Romex® is a very well-known brand of NM cable, but it is also somewhat more expensive. The only real advantage to Romex® is that it includes SIMpull®, an embedded slippery coating on the sheathing that reduces friction when pulling the cable through studs and other difficult passages. Other brands have begun to incorporate a similar coating, as well. Other than this, you will find no appreciable difference in the copper wire found in Romex® when compared to other brands. The wire gauge will be the same and the metallic content is exactly the same.

Professional electricians have individual preferences, and if you walk around a large job site where several electricians are working, you might see all brands of NM wiring being used. One electrician might choose a cheaper brand to save money, while another might prefer Romex®. There poses no problem, as the various brands of NM cable can be mixed in the same electrical system—or even in the same circuit—without causing any difficulty.

NM Wiring Versus Other Types

NM wiring is very common in residential wiring, but it is also possible to wire a home using metallic sheathed cable or conduit. NM wiring has many advantages that make it the most popular type of wiring, especially for homeowners:

  • NM wire is lighter than metallic sheathed wiring, so it is easier to handle.
  • NM is easier to unspool and straighten out because the PVC sheathing is pliable.
  • It is easier to pull through holes in studs because of the smooth sheathing. In the case of Romex® (and some other brands), a coating is added that makes the sheathing more slippery.
  • NM cable is easier to cut—just use a set of side-cutting pliers. Smaller gauges can even be snipped with the cutters on a wire stripper.
  • It is cheaper than metal-sheathed wiring. 
  • NM cable is easier to strip since the sheathing is plastic, not metal. Though a ripping tool makes your job easier, you can also cut the sheathing with a utility knife and rip it back by hand. 
  • NM cable is easier to attach to framing members, requiring only light-weight plastic cable staples.

All factors considered DIY electricians will find their projects easier and cheaper to complete when using NM wiring. Remember, though, that there are situations in which NM cable cannot be used, such as outdoors or when wiring is exposed along the face of foundation walls. In these instances, the electrical code calls for conduit installations.

The Romex Brand

The Romex name derives from the Rome Cable Corp. of Rome, NY, which originally produced the cable. The company was founded in 1936 and filed for bankruptcy in 2003. Today, the Romex brand is owned by the Southwire company as a trademark. As the company mentions on its website, they "vigorously monitor and protect the use of the Romex brand." In other words, the term Romex should be used to refer only to NM cable made by the Romex® company, not NM cable from other manufacturers.