The copper wires that create a circuit for residential electrical services such as GFCI outlets, lights, wall outlets, and more must run parallel in a tightly packed bundle, but they also must not contact each other. Running every individual wire separately would be logistically difficult: thus the need for a tight bundle. Yet if bare wires were allowed to touch, the circuit would not work. Wires must remain close yet stay separate.
Over the many decades that electricity has been powering homes, these parallel wires have been bundled and separated in several different ways. The most common and efficient way of creating this separated-wire bundle is with Romex brand and other non-metallic (NM) sheathed electrical cable.
What Is Non-Metallic (NM) Electrical Cable?
The non-metallic (NM) designation refers to the outer sheathing that bundles individual wires together like a cable. This is in contrast to metallic sheathed cable or conduit wiring, in which the bundle of individual conductors is protected by some form of a metal coil or metal conduit. Typically, there are three parts to NM electrical cable: outer cable sheathing, wire insulation, and wire.
NM electrical cable's outer sheathing is a 30 mil-thick PVC jacket that serves to bundle the individual wire conductors and to protect them. The sheathing is extremely tough. This is necessary to withstand the stress inflicted on the sheathing when the cable is pulled through holes in studs.
To make connections with devices, cable sheathing is ripped laterally with a metal device called a cable ripper. At the end of the rip, the remaining attached sheathing is cut off with a utility knife, scissors, or with the snipping portion of a wire stripper.
Wires within the sheathing are insulated with color-coded PVC (polyvinyl chloride). The individual conductors normally have black, white, and red insulation. Also present within the NM cable is a copper grounding wire that is usually left uncoated and bare but sometimes is coated in green PVC. Often, paper will be added within the cable as a separator. This paper can be snipped and discarded in the ripped portion of the cable.
To connect to devices, wire insulation is stripped from the copper wire with a manual wire stripper. A series of holes in the wire stripper correlates with different wire diameters, or gauges. For example, choose the hole labeled "12" to strip the insulation from 12-gauge wire.
Despite the NM label, the individual electrical conductors within the cable are indeed metal—normally about 65-percent copper.
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 the bare copper ground wire). For example, a cable labeled "14-2 with ground" will have two insulated conductors with 14-gauge wires plus a bare copper grounding wire. This cable is used for 15-amp circuits and often powers circuits from panels and individual devices. 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.
What Is Romex Brand Electrical Cable?
Romex is the brand name of a non-metallic (NM) sheathed electrical cable made by Southwire Company, LLC of Carrollton, Georgia.
Southwire notes that they "vigorously monitor and protect the use of the Romex brand." While this is common legal boilerplate language for many products, with Southwire and Romex it is more of critical concern since the word Romex is widely used by electricians and some consumers in a generic sense to refer to all NM-sheathed electrical wire. Within the world of building products, the word Romex is often used in the same way that Kleenex is used to refer to any tissue: generically and erroneously. So, strictly speaking, the term Romex should be used to refer only to NM sheathed electrical cable made by Southwire Company under the Romex brand, not NM cable from other manufacturers.
Origin of Romex Brand Wire
The Romex name comes from Rome Cable Corp. of Rome, New York, which originally produced the cable. The company was an industry leader until it filed for bankruptcy in 2003 and its factory was largely demolished in 2010. Rome Cable Corp. was also a major source of aluminum wire produced by its parent company Alcoa. Aluminum wire is inferior to copper wire and its presence is considered to be dangerous in your home. In 1964, Alcoa was court-ordered to divest itself of Rome Cable Corp.
While the prefix of Romex certainly applies to the company that produced it, the origin of the suffix (-x) is not clear. It may mean that the wire at the time was experimental or it may have simply been a convenient method of creating a brand name.
Romex Brand vs. Other NM Wire Brands
Romex brand NM-sheathed is not the only brand of NM wire but it is the predominant brand in North American sales. One feature of 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. As required by electrical codes, the wire gauges will be the same and the metallic content the same, too.
Professional electricians have individual preferences. 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.
NM Wiring Pros and Cons
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. With all factors considered, do-it-yourself electricians will find their projects easier and cheaper to complete when using NM wiring. NM wiring presents a huge amount of advantages to the do-it-yourselfers, as opposed to other materials.
- NM wire can be installed in plastic boxes and does not require the extra step of grounding the box itself.
- NM wire is lighter than metallic sheathed wiring, so it is easier to handle.
- NM wire 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, a coating is added that makes the sheathing more slippery.
- NM cable is easier to cut with just a set of side-cutting pliers. Smaller gauges can even be snipped with the wire stripper.
- NM wire is cheaper than metal-sheathed wiring.
- NM cable is easier to rip 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.
There are situations in which NM cable cannot be used, such as outdoors (with the exception of UF-type cable, which is rated for direct burial) or when wiring is exposed along the face of foundation walls. In these instances, the electrical code calls for conduit installations. This cable also needs to have some sort of protection in certain applications, or when not inside a wall. It also cannot be used above drop ceilings in light commercial applications.