What Is Romex Used For?

Romex is commonly used for permanent indoor branch circuits that supply receptacles, lighting, switches, and some fixed appliances. The cable must be installed in an approved dry location and protected from physical damage. The conductor size and number must match the circuit design, breaker, load, and applicable electrical code.

Can Romex Be Used Outdoors or in Wet Locations?

Standard NM-B cable is generally intended for dry locations, so it is not the default choice for outdoor or wet areas. Outdoor wiring may require a listed cable, individual conductors in conduit, or another approved wiring method. The location, exposure, protection, and local code determine the correct option.

Is 12/2 Romex Always Safe on a 20-Amp Breaker?

No. 12/2 cable is commonly associated with 20-amp branch circuits, but safe installation also depends on cable type, insulation rating, terminals, circuit length, load, box connections, and local code. A breaker should not be increased simply to stop nuisance trips. The full circuit must be evaluated first.

Glossary

What is a Romex?

Romex is a brand name commonly used for nonmetallic-sheathed cable, or NM cable, used in residential and light commercial wiring. The cable contains insulated copper conductors, a bare or insulated grounding conductor, and a protective plastic jacket. Romex commonly supplies branch circuits for receptacles, lighting, switches, and other permanently installed equipment.

Sources reviewed: National Fire Protection Association, National Electrical Code, Occupational Safety and Health Administration, Electrical Standards

Quick Facts About Romex

Key Takeaways About Romex

Romex usually means nonmetallic-sheathed cable, not a specific wire size or electrical circuit.
The cable jacket protects insulated conductors and a grounding conductor during indoor installation.
Wire gauge, conductor count, and ampacity must match the circuit breaker and connected load.
NM cable is generally intended for dry locations and must follow electrical code requirements.
Outdoor, wet, exposed, or high-impact locations may require conduit or another wiring method.

Understanding Romex

Romex is a widely used name for nonmetallic-sheathed cable. People also call it NM cable or NM-B cable. Southwire owns the Romex brand. Many people use the word for similar products from other manufacturers. A typical cable contains two or more insulated conductors. It also has a grounding conductor and an outer jacket. The jacket uses nonmetallic material.

Related glossary terms: Branch Circuit, Conduit, Electrical Code.

The insulated conductors carry current to and from a load. The grounding conductor provides a low-resistance path during some faults. The outer jacket keeps the conductors together. It also protects them during normal installation. Common examples include 14/2 cable for many 15-amp circuits. Another example is 12/2 cable for many 20-amp circuits. The correct choice depends on the complete installation and applicable code.

How Romex Works, Is Measured, or Is Used?

NM-B cable is identified by conductor count and wire gauge. A label may say 12/2 with ground. The first number describes the copper conductor size. The second number identifies two insulated conductors. The phrase with ground identifies an equipment grounding conductor. A 12/3 with ground cable has three insulated conductors. It also has one grounding conductor.

Electricians route branch circuits from a panelboard to receptacles, switches, lights, and fixed equipment. The circuit breaker protects conductors from excessive current. The insulation rating and cable listing define where installers may use the cable. NM cable is common inside finished walls, ceilings, and other dry areas. Installers must protect it from nails, screws, abrasion, heat, moisture, and damage.

Installation also requires correct box connections, cable support, conductor stripping, and grounding. Each cable must enter an approved junction box or wiring enclosure. This applies when a splice or termination occurs. The cable jacket should stay intact where it enters the box. The cable mustn't fill the box beyond its permitted capacity.

Why Romex Matters?

Electrician in a black cap examines an open electrical breaker panel inside a workshop

Romex cable can reduce installation time. Several conductors stay enclosed in one jacket. Its design also helps installers identify the cable assembly. It helps them route a complete circuit through a wall. These benefits don't remove the need to check conductor size, circuit load, protection, and installation conditions.

Choosing the wrong cable can cause overheating, nuisance breaker trips, damaged insulation, or an unsafe grounding path. A cable rated for dry locations doesn't automatically suit a damp or wet location.National Electrical Code sets rules for wiring methods, protection, support, box fill, and locations. Local authorities may apply adopted amendments during inspection.

When Romex Matters Most?

Electrical remodeling often requires a choice between NM cable, conduit, and another approved wiring method. NM cable may fit an enclosed, dry wall cavity. Conduit may be needed where wiring stays exposed or faces impact. Existing cable also needs inspection before reuse. Age, damage, overloading, and unapproved changes can affect circuit safety.

Pay close attention when adding a receptacle, replacing a panel, finishing a basement, or installing a large appliance. A new load may require a dedicated circuit, a different conductor size, or updated protection. Before work begins, check the cable markings, breaker rating, grounding path, box capacity, and local permit requirements. These checks help prevent hidden defects. Such defects may surface during an inspection or emergency repair.

How to Evaluate Romex?

Read the jacket marking for conductor size, conductor count, temperature rating, and cable type.
Confirm the circuit breaker rating matches the permitted ampacity of the installed conductors.
Check that cable runs stay in approved dry locations and receive protection from physical damage.
Inspect every box for secure cable entry, intact sheathing, grounding, and adequate box volume.
Ask whether local code, permits, or inspection rules require a different wiring method.

Related Concepts Compared

Romex vs. THHN Wire

THHN is an individual insulated conductor, while Romex normally contains multiple conductors inside one jacket. THHN is often pulled through conduit.

Romex vs. Conduit

Conduit is a raceway that protects and routes individual wires. Romex is a complete cable assembly and is not itself a conduit.

Romex vs. BX Cable

BX commonly refers to armored cable with a metal sheath. Romex uses a nonmetallic outer jacket and has different installation requirements.

Romex vs. Wire Gauge

Wire gauge describes conductor size, such as 12 AWG or 14 AWG. Romex describes the cable assembly that may contain conductors of different gauges.

Expert Note

Do not identify cable only by jacket color. Manufacturers may use colors to suggest wire size, but the printed jacket marking is the controlling source for conductor size, cable type, and ratings.

Common Mistakes or Myths About Romex

Treating every plastic-jacketed cable as suitable for outdoor, wet, or exposed installation.
Matching cable color to breaker size without reading the printed jacket marking.
Removing too much outer sheathing inside a junction box.
Installing a larger breaker to stop trips without checking conductor size and circuit load.
Leaving cable unsupported or unprotected near holes, edges, or finished surfaces.

Romex in Practice: A Real-World Example

A homeowner adds a basement receptacle to an existing 120-volt circuit. An electrician may run 12/2 NM-B cable if the circuit design, breaker, location, and local code allow it. The installer still checks box fill, cable support, grounding, and protection before closing the wall.

Sources & Further Reading on Romex

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