If you have ever opened a wall during a renovation or watched an electrician wire a new room, you have almost certainly seen Romex wire. It is the flat, color-coded cable stapled through studs and joists in virtually every home built in the United States over the past several decades. Despite how common it is, many homeowners have questions about what it actually is, how it works, which type to use, and where it can and cannot be installed safely. This guide covers everything you need to know about Romex wire, from its construction and color coding to the safety rules that govern its use.

What is Romex Wire?

Romex wire is a brand name for non-metallic (NM) sheathed cable, the most common type of electrical wiring used in homes and light commercial buildings. It carries electricity to outlets, switches, and appliances throughout a structure.

When you purchase NM cable, it comes with three main components: the outer protective jacket, individual wire insulation, and the conductors themselves.

The outer coating is a durable 30-mil PVC jacket designed to protect the internal wires from physical damage. Each individual wire inside the jacket is also wrapped in color-coded PVC insulation, making identification easy during installation and troubleshooting.

All conductors inside Romex are made from soft, uncoated copper, which makes them flexible and easy to work with. Earlier versions used aluminum, but current electrical codes require pure copper for residential wiring.

How Romex Wire is Built

Romex bundles multiple individual wires inside one flexible, protective outer sheath. Here is what you will typically find inside:

  • Hot wires: Colored black or red, these carry the electrical current from the panel to the device.
  • Neutral wire: Always colored white, this completes the electrical circuit by returning current to the panel.
  • Ground wire: Either bare copper or covered in green insulation, this provides a safe path for electricity in the event of a fault or short circuit.

To access the inner wires during installation, electricians use a cable ripper to split the outer jacket lengthwise, then cut away the remaining material with a utility knife or wire stripper.

Romex Wire Color Coding and Sizing

The outer jacket of Romex cable is color-coded to make it easy for electricians and homeowners to identify the wire gauge and amperage rating at a glance. Here is a breakdown of what each color means:

  • White jacket (14-gauge): Rated for 15-amp circuits. Used for standard lighting and general bedroom or living room outlets.
  • Yellow jacket (12-gauge): Rated for 20-amp circuits. Used for kitchen outlets, bathrooms, garages, and dedicated appliance circuits.
  • Orange jacket (10-gauge): Rated for 30-amp circuits. Used for heavier appliances like water heaters, air conditioners, and range hoods.
  • Black jacket (8-gauge or 6-gauge): Rated for 40 to 55-amp circuits. Used for electric ranges, large subpanels, and other high-draw equipment.

What Is Romex Wire Used For?

Romex wire is designed primarily for indoor residential and light commercial electrical wiring. You will find it used in the following locations and applications:

  • Single-family and two-family homes: NM cable is the standard choice for wiring lights, receptacles, and other power needs in one- and two-family dwellings, including attached garages and unattached structures like storage sheds.
  • Concealed spaces: Romex is commonly run inside wall cavities, through bored holes in wooden studs and ceiling joists, and beneath drywall surfaces. It can also be fished behind finished walls when adding new electrical components.
  • Dry indoor areas: The National Electrical Code (NEC) specifies that NM cable is approved only for dry locations. This means it should never be installed in areas exposed to moisture, such as covered porches or patios.
  • Exposed areas with protection: In locations like unfinished basements or attics where people do not regularly spend time, Romex may be left exposed as long as it is secured properly and protected from physical damage. Where required, it should be run through conduit between sections.

What Are the Different Types of Romex Wire?

There are several types of Romex, each suited to a specific application based on the number of conductors and the wire gauge:

  • 14-2 NM cable: Contains one black hot wire, one white neutral wire, and a bare copper ground. Used for 15-amp lighting and general outlet circuits.
  • 14-3 NM cable: Adds a red wire to the standard configuration, allowing it to serve two separate circuits from the same cable run. Common in three-way switch wiring.
  • 12-2 NM cable: The most widely used cable for 20-amp household circuits, including kitchen and bathroom outlets.
  • 12-3 NM cable: Used where two hot legs are needed, such as for certain appliance circuits or multi-wire branch circuits.
  • 10-2 and 10-3 NM cable: Used for 30-amp circuits serving large appliances. The three-conductor version is often required for 240-volt appliances like electric dryers.

Where to Use Romex and Where to Avoid It

Romex is designed exclusively for dry, indoor locations. It is best suited to:

  • Runs through wooden wall studs and ceiling joists inside finished homes
  • Wiring in attics, crawl spaces, and unfinished basements when properly supported
  • Branch circuit wiring for lights, outlets, and standard household appliances

It should not be used in the following situations without additional protection:

  • Outdoors or in areas exposed to weather or moisture
  • Buried underground
  • In conduit runs that pass through wet or damp locations
  • Areas where the cable would be exposed to extreme heat or direct physical damage

When wiring in areas that require more durability, electricians typically switch to conduit-run THHN wire or cables rated for wet locations.

Advantages of Romex Wire

Romex remains the preferred choice for residential wiring for several practical reasons:

  • Safety: The thick outer PVC jacket shields the internal conductors from physical damage. The included ground wire provides a safe fault path that protects equipment and reduces the risk of electrical shock or fire.
  • Ease of installation: Unlike individual wires run through conduit, Romex bundles all conductors together in one sheath. Electricians can pull it through wall cavities and bored holes quickly, reducing labor time significantly.
  • Versatility: One cable type handles a wide range of applications, from lighting circuits to appliance feeds, making it suitable for nearly every area of a home.
  • Cost-effectiveness: Romex is less expensive than metal-clad cable or individual conduit runs, making it the economical standard for residential construction and renovation projects.
  • Code acceptance: NM cable meets the requirements of the NEC for residential applications, simplifying inspections and permit approvals.

Safety and Regulation Requirements for Romex Wire

Working with Romex requires attention to code compliance and basic safety principles. Here are the key requirements to keep in mind:

  • Hire a licensed electrician: For any project involving new wiring or panel connections, a licensed electrician is the safest option. They understand how to navigate local amendments to the NEC and ensure the work passes inspection.
  • Use the correct tools: A cable ripper, wire stripper, and proper connectors are essential for clean, safe Romex installation. Improper stripping can nick the conductor insulation and create a future fault point.
  • Follow NEC guidelines: The NEC provides specific rules about how NM cable must be run, supported, and terminated. Cables must be secured within 12 inches of every box and at intervals not exceeding 4.5 feet.
  • Protect from environmental hazards: Avoid running Romex through areas with direct sunlight, moisture, or mechanical hazard without appropriate protection. UV exposure degrades the PVC jacket over time.

Important NEC Safety Practices for NM Cable

The National Electrical Code outlines several specific practices that apply to Romex installations:

  • Overload prevention: Never connect more load to a circuit than the wire gauge is rated to handle. Overloading a 14-gauge wire on a 20-amp breaker, for example, causes the wire to overheat well before the breaker trips. Match the wire gauge, breaker size, and connected load carefully. An electrician can help you determine the right combination for your project.
  • Inspect before installing: Check all cable for cuts, nicks, or fraying of the outer sheath before pulling it through walls. Damaged Romex must be replaced, not repaired with tape.
  • Avoid moisture exposure: Even brief or indirect water contact can compromise the insulation inside the jacket and increase the risk of shock or short circuit over time.
  • Ground every connection: The bare copper ground wire must be connected to the designated grounding terminal in every outlet, switch, and panel connection. Skipping this step eliminates the fault protection the ground wire provides.
  • Secure the cable properly: NM cable must be fastened at every penetration point through framing and at regular intervals along its run to prevent sagging, pinching, or shifting that could damage the jacket.

Conclusion

In summary, Romex wire is the go-to solution for residential electrical wiring because it is safe, affordable, easy to install, and widely accepted by electrical codes across the United States. Understanding how it is built, where it is appropriate to use, and how to handle it correctly helps ensure every installation meets both safety standards and inspection requirements.

If you are uncertain about any aspect of a Romex installation, consulting a qualified electrician is always the right call. A properly wired home protects the people living in it and maintains its value for years to come.

Frequently Asked Questions About Romex Wire

Is Romex the same as NM-B wire?

Yes. Romex is a brand name owned by Southwire, while NM-B is the official NEC designation for the same product. The term became so widely used that electricians now say “Romex” to mean any non-metallic sheathed cable regardless of manufacturer. If a cable jacket reads “NM-B” with a gauge and conductor count printed on it, it is the same thing.

Can you run Romex through conduit?

The NEC permits it in limited situations, typically to protect the cable from physical damage over a short distance. The drawback is that the bundled jacket traps heat inside the conduit, which requires you to derate the ampacity of the cable. For longer conduit runs, individual THHN conductors are the better and more code-friendly choice.

How long does Romex wire last?

Properly installed Romex in a dry location can last the lifetime of the building. Research on homes built from the 1960s onward found that undisturbed NM cable retained near-new electrical properties decades later. Most failures occur at connection points and devices, not in the wire itself.

What is the difference between NM, NMC, and NM-B?

NM is rated for dry locations only. NMC has a moisture-resistant jacket that also allows use in damp locations like unfinished basements. NM-B is the current standard, indicating conductors rated to 90 degrees Celsius, though ampacity is calculated at 60 degrees to match standard residential terminations. Nearly all Romex sold today is NM-B.

Can you splice Romex wire inside a wall?

No. The NEC requires every splice to be made inside a listed junction box that remains accessible without cutting into the wall. Burying wire nuts or splice connectors inside a sealed wall cavity is a code violation. The correct fix is to install an accessible blank-cover junction box at the splice point or replace the full cable run.

How do you read the printing on a Romex jacket?

“12/2 NM-B” means 12-gauge wire with two insulated conductors plus a bare ground. “14/3 NM-B” means 14-gauge wire with three insulated conductors (black, white, red) plus a ground. The jacket color confirms the gauge quickly, but the printed text is the definitive reference. Newer Romex also includes a production date printed on the jacket.

Is Romex allowed in commercial buildings?

The NEC does not permit NM cable in buildings taller than three stories or in most commercial construction. Local codes can be even stricter. Chicago, for example, prohibits NM cable in nearly all applications and requires conduit wiring instead. Always verify local code before using Romex outside a single-family or two-family home.

What is the difference between Romex and UF cable?

Romex is for dry indoor use only. UF (underground feeder) cable has a solid plastic core that encases each conductor individually, making it waterproof and rated for direct burial and outdoor use. A simple way to tell them apart: UF cable cannot be rolled between your fingers because the plastic fills every gap inside the jacket, while Romex feels flexible and pliable. Use UF cable for outdoor circuits and underground runs.