If you’ve opened an electrical panel or peeked behind a wall during a remodel, you’ve almost certainly seen flat plastic-sheathed cable in white, yellow, or orange. That’s Romex. Understanding what is Romex wiring matters because it’s the most common type of electrical cable in modern American homes, and knowing how to identify it tells you a lot about your circuits before you ever touch a wire. Romex is a brand name for non-metallic sheathed cable, often shortened to NM cable, and it has been wiring houses since the 1920s.
The Basics: NM Cable Explained
Romex is a registered trademark owned by Southwire, but the name has become the generic term the way “Kleenex” stands in for tissue. Technically you’re looking at NM-B cable, where “NM” means non-metallic and “B” indicates the conductors are rated for 90 degrees Celsius. Inside the flat plastic jacket you’ll find two or three insulated copper conductors plus a bare copper ground wire.
The sheathing protects the conductors from moisture, abrasion, and minor physical damage. Each insulated wire carries current: black is typically hot, white is neutral, and red serves as a second hot in three-conductor cable. The bare wire is your equipment ground. This bundled design is why Romex installs so much faster than running individual conductors through conduit, and it’s the main reason builders rely on it for residential work.
Reading the Color Code and Gauge
One genuinely useful feature of modern Romex is the color-coded jacket, standardized around 2001. The outer sheath color tells you the wire gauge and amperage at a glance, which speeds up both installation and troubleshooting.
- White jacket: 14-gauge wire, rated for 15-amp circuits — lighting and general receptacles.
- Yellow jacket: 12-gauge wire, rated for 20-amp circuits — kitchen and bathroom outlets.
- Orange jacket: 10-gauge wire, rated for 30-amp circuits — dryers, water heaters, window AC.
- Black jacket: 8 or 6-gauge, for 40 to 60-amp loads like ranges and subpanels.
- Gray jacket: Underground feeder (UF) cable, not standard NM.
The printing on the jacket also lists the conductor count followed by a “G” for ground. So “12-2 G” means two 12-gauge conductors plus a ground, while “14-3 G” means three 14-gauge conductors plus a ground. Matching gauge to amperage is non-negotiable: putting 14-gauge wire on a 20-amp breaker is a fire hazard and a code violation.
Where Romex Can and Cannot Be Used
Romex is designed for dry, protected interior locations — inside finished walls, ceilings, attics, and the framing of a typical home. The National Electrical Code permits it in most one- and two-family dwellings, which covers the vast majority of houses in the U.S.
There are hard limits, though. You cannot run standard NM cable in wet or damp locations, bury it directly in the ground, or leave it exposed where it might get hit. Garages and basements are gray areas: exposed Romex usually needs protection from physical damage, often by running it through conduit or keeping it above 8 feet. Some municipalities, including parts of Chicago and New York City, ban Romex entirely in favor of metal conduit, so always check your local amendments before buying a single roll.
How Romex Compares to Conduit and Armored Cable
Builders choose Romex over conduit mainly for speed and cost. A 250-foot roll of 12-2 Romex runs roughly $130 to $180, and a competent installer can pull it through a stud wall in a fraction of the time conduit demands. Conduit, by contrast, requires bending pipe, securing it, and then fishing individual THHN conductors through — labor that easily doubles or triples the job cost.
Armored cable, known as BX or MC, splits the difference. It wraps the conductors in a flexible metal sheath, giving better physical protection than Romex while still being faster than conduit. MC cable costs more per foot, typically $1 to $2 versus $0.30 to $0.60 for Romex, and it’s the common choice in commercial buildings and jurisdictions that restrict plastic-jacketed cable.
Working With Romex Safely
If you’re doing your own work where permitted, a few practices keep installations safe and inspector-friendly. Strip the outer jacket with a dedicated cable ripper rather than a utility knife, which can nick the insulation underneath. Leave at least 6 to 8 inches of free conductor inside each box for connections.
Secure the cable with a staple within 8 inches of every plastic box and every 4.5 feet along its run. Where Romex passes through a stud less than 1.25 inches from the edge, install a metal nail plate to keep future drywall screws from piercing it. And always confirm your gauge matches the breaker — this single check prevents the most common DIY wiring fire risk.
Common Romex Sizes and What They Power
Matching the right cable to each circuit is the heart of a safe install, and a quick reference saves a lot of second-guessing at the hardware store. Most household lighting and standard wall outlets run on 14-2 Romex protected by a 15-amp breaker. Kitchen counter outlets, bathroom receptacles, and garage circuits step up to 12-2 on a 20-amp breaker because they routinely run higher-draw appliances.
Larger loads need heavier copper. A 30-amp electric dryer or water heater typically uses 10-3 or 10-2 cable, while an electric range or oven drawing 40 to 50 amps calls for 8-3 or 6-3. Three-conductor cable like 14-3 or 12-3 carries that extra red wire for three-way switch setups, where two switches control the same light from different locations. Knowing these pairings lets you read a panel and immediately understand what each circuit feeds and whether it was wired to code.
When to Call a Licensed Electrician
Plenty of homeowners swap an outlet or add a light fixture without trouble, but anything involving the main panel, new circuits, or service upgrades belongs to a licensed electrician. Most jurisdictions require a permit and inspection for new wiring, and insurance claims can be denied for unpermitted work. Expect to pay $50 to $130 per hour for a licensed pro, plus materials.
Understanding what is Romex wiring gives you the vocabulary to talk intelligently with an electrician, spot obvious problems like undersized cable, and make smarter decisions during a renovation. Whether you handle small jobs yourself or hand the big ones off, knowing your cable is the foundation of safe home electrical work.
