What Does Romex or NM Mean?

Romex 12/2 NM Wire
Romex 12/2 NM wire. Amazon.com

Romex® is the brand name for a non-metallic (NM) building wire made by Southwire that is widely used by professional electricians and DIYers alike.  Romex is used for many common household electrical projects like outlets and lights.

The "NM" designation does not refer to the wire itself; the wire is copper.  Nor does it refer to the jackets around the wires; those jackets are made of color-coded PVC (polyvinyl chloride)--black, white, and red.

Instead, NM pertains to the sheathing--a 30 mil-thick PVC jacket--that binds the individual wires together.  This is in contrast to metallic sheathed wire, which has the same internal wires with the only difference being the outer covering.

NM is used to refer to any type of electrical wiring sheathed in a plastic coating, not just Romex brand.

Romex Brand vs. Other Brands of NM Wire

The debate goes on:  Is there any reason to buy the more expensive Romex brand NM wire when you can buy other brands for far less?  Is the plastic sheathing on brand-name Romex easier to rip and easier to strip than other brands?  Is the copper wire itself better than with other brands?

Romex does have SIMpull®, an embedded slippery coating on the sheathing.  It reduces friction when pulling the cable through studs and other difficult passages.  Other brands have begun to incorporate a similar coating, as well.

You will find no appreciable difference in the copper wire found in Romex vs. the wire in other brands.

 The wire gauge will be the same and the metallic content the same, too.

Some electricians may have an individual preference.  Walking around any job site, you will see all brands of NM wiring. Since Romex® may be pricier than other brands of NM wire, the electrician could end up using any brand of wire.

Compare Prices on Romex Brand Wire

  • Romex® 12-2 Wire. When starting any large-scale electrical project, begin with the big 100 ft. rolls.  Those 25 ft. rolls deplete quickly.  Having larger spools ensure that you can make long runs without having to splice wires.
  • Romex® 14-2 Wire. This is a thinner gauge wire mainly for lighting applications and 15A outlets.  It is a staple of home electrical work.

Romex and Other NM vs. Other Types of Electrical Wiring

It is definitely easier for the lesser experienced homeowner to work with plastic-sheathed wiring.   Unless you currently have metal sheathed wiring and want to continue the tradition, there is little reason for you to work with this type of wire.

Romex or any type of NM is:

  • NM wire is lighter than metallic sheathed wiring, so easier to handle.
  • Easier to unspool and straighten out because the PVC sheathing is pliable.
  • Easier to pull through holes in studs because of the smooth sheathing.  In the case of Romex (and some other brands), coating is added that makes the sheathing more slippery.
  • Quicker to cut--just use a set of side-cutting pliers. Smaller gauges can even be snipped with the cutters on a wire stripper.
  • Cheaper than metal-sheathed wiring.  The metal sheathing itself drives up costs, as opposed to the extremely low cost of producing plastics.
  • Easier to rip back the cable sheathing--it is just plastic, not metal.  Though a ripping tool makes your job easier, you can still cut the sheathing with a utility knife and rip it back by hand. 
  • Quicker to tack up, as you can use light-weight plastic clips.

All factors considered, DIY electricians will find their projects easier and cheaper to complete when using NM wiring.

Names and Trademarks

The name comes from the Rome Cable Corp. of Rome, NY, which originally produced the wire. 

The "Rome" part comes from the company's name. No one is quite sure where the "x" came from, though.  It may have been added to make the name more attractive or it may be playing off the name "BX" for metal armored cable.

Rome Cable was founded in 1936 and filed for bankruptcy in 2003. Now the Romex® brand is owned by Southwire and is an actual trademarked brand.

 

So, even though many electricians like to call NM wire romex, there is really no such thing as a lower-case generic "romex" but trademarked Romex® instead. Just like Kleenex or Jell-O.

As Romex mentions on its website, they "vigorously monitor and protect the use of the Romex brand."