What You Need to Know About Romex Wiring

When I was a commercial electrician, I spent much of my time bending pipe and pulling metal-clad cable through cavernous ceiling expanses in hospitals, dorms and even a sports stadium. I had almost no experience with house wiring. I had put in a few light fixtures and even had a comically disastrous experience with wiring a ceiling fan.

But when it came to most residential work, I had no clue.

So when I got the chance to wire a Habitat for Humanity house, I jumped at the opportunity. First of all, what a great organization. Second, wiring a home would give me valuable experience I lacked at the time. I was especially interested in working more with Romex cable, aka nonmetallic sheathed cable. You’ve probably seen this yellow or white-sheathed cable in your own home— it’s by far the most common way to bring power from your electrical panel to the many things in your house that need it.

If you want to understand house wiring, you’ve got to know about Romex. Here’s everything I’ve learned about Romex wiring in my career, from those early days working with Habitat for Humanity to today.

What Is Romex Wiring?

Romex is the brand name of a nonmetallic (NM) sheathed electrical cable manufactured by Southwire. The “nonmetallic” designation refers to the protective sheath that covers the electrical conductors (wires). It is the most recognizable NM cable in the electrical industry, so much so that the term has become genericized much like Band-Aid or Kleenex (even though other brands of NM cable exist).

Romex comes in several sizes, and like other electrical conductors is measured in American Wire Gauge (AWG). Common residential sizes are 14 AWG, 12 AWG and 10 AWG, but larger sizes exist up to 2 AWG (the larger the AWG, the smaller the wires). Depending on the size, the conductors can be single solid wires, or stranded, which means multiple individual strands wound together. The electrical conductors are insulated, while the ground wire is either bare or insulated.

Romex comes in two, three or four-conductor cables, plus the ground wire. These cables are labeled using their AWG followed by the number of conductors. For example, Romex with 14 AWG and two conductors is referred to as “14/2”.

Remember that the number of conductors refers only to the hot(s) and neutral(s) in the cable, not the ground. So, if you’re buying 14/2 Romex, that’s a hot, neutral and ground. Even though there are technically three wires in the cable, the ground wire is not captured by the 14/2 designation.

What Is Romex Wire Used For?

Romex/NM is used primarily for residential wiring. Here are some places where Romex wire is commonly found.

• One- and two-family dwellings. Romex and other NM cable can be used in houses and duplexes to wire lights, receptacles and other common power needs, including in attached and detached garages and outbuildings such as storage sheds.
• Dry locations. The NEC has specific definitions of wet, dry and damp locations, and NM cable can only be used where it’s dry. This means you can’t run it along the ceiling of your porch or patio, even if the area is covered.
• Concealed. Concealed means that you can run Romex behind walls, floors and ceilings. So, if you’re wiring a new house, the NM cable travels within and through the studs behind the drywall. You can even “fish” it behind walls after the finishing is done, like if you want to add a new receptacle or light where there wasn’t one before.
• Exposed. In attics, basements, crawlspaces and other places where you don’t do your primary living, NM cable can be exposed (visible). You must secure it properly and keep it protected from physical damage, though. You can even protect it with conduit, say, if you need to poke through a wall from one basement room to another.

When Should Romex Not Be Used?

Romex is versatile and commonly used in many residential applications. It can’t be used everywhere, though.

The National Electric Code (NEC) governs its use, but always also consult your local building codes. Chicago, for example, does not allow the use of NM cable except in very limited circumstances. The exact reasoning is lost to history, but the general consensus is that using metal raceways instead of in-wall wiring is safer from fire. (Chicago had a famously huge fire in 1871.)

Here are some other Romex restrictions:

• Wet and damp locations. Keep Romex and other NM cable inside your home, garage or shed. If you need to run a cable out to a freestanding yard light or under the eaves of your porch, choose a cable rated for wet locations, like UF (underground feeder cable).
• As service-entrance cable. The wires coming into your electrical panel from the transformer outside your house cannot be NM cable.
• Embedded in a concrete slab. This goes back to the wet locations thing. Any concrete or masonry in contact with the earth, including a slab or a basement block wall, is considered a wet location.
• Buried in the ground. The soil is a wet location, so again, Romex is a no-no. Note also that the inside of the conduit that is located outdoors or in the ground is also a wet location, so you cannot get around this rule by running Romex through the conduit outside.

Romex Buying Considerations

So now that you know where Romex and other NM cable can and cannot be used, which one do you choose for your home renovation? Even though Romex is a popular brand, all NM cable is pretty similar. That’s because the NEC requires that NM cable used in electrical installations be listed by an accredited testing laboratory, like UL or Intertek.

“Listed” in this case means that the manufacturer conformed to rigorous technical specifications. In the United States, it will be hard to find an unlisted NM cable. Just make sure you’re buying from a reputable store or online retailer, and check the specs.

Once you’ve determined that the product is listed and available, your next considerations are deciding how much you want to spend, and getting the right size for your installation. In your home, 14/2 is used for 15-amp circuits, and 12/2 goes with 20-amp circuits. Larger circuits, for your dryer, range and HVAC, require bigger wires. Consult a licensed electrician if you have any questions about what goes where.

Romex Wire Recommendation

When you go to the local hardware store, home improvement center or electrical supply retailer looking for NM cable, chances are Southwire’s Romex Brand SIMpull will take up the majority of shelf space. It’s a quality NM cable with decades of market dominance. The SIMpull coating is a proprietary addition that makes it easy to pull Romex through studs and wall cavities.

Depending on your store of choice, another popular and quality brand of NM cable is Cerrowire, which has its own easy-pull coating called SLiPWire. These two brands are comparable in price, with 250 feet of 14/2 costing about $100 at a typical home store.