What Is Romex Wiring? Complete Guide to NM-B Cable for Home Electrical

what is romex wiring

Romex wiring is a brand name for non-metallic sheathed cable (NM-B) that contains insulated electrical wires bundled together inside a flexible plastic jacket—it's the most common type of electrical wiring used inside walls and ceilings of residential homes throughout North America. When you open a wall in almost any modern house, the flat, beige or white cable you see running between studs is most likely Romex (or a similar NM-B cable brand).

The term 'Romex' has become so ubiquitous that people use it like 'Kleenex' for tissues—asking for 'Romex' at a hardware store when they actually mean any brand of NM-B cable. This guide explains exactly what Romex wiring is, how it's constructed, where it can (and cannot) be used, and why it's become the standard for residential electrical installations.

Whether you're a homeowner trying to understand your electrical system, a DIY enthusiast planning a project, or just curious about what's behind your walls, this comprehensive guide covers everything you need to know about Romex wiring.

What Is Romex? The Technical Definition

Romex vs NM-B Cable

Romex = Brand name (manufactured by Southwire Company)
NM-B = Technical designation (Non-Metallic sheathed cable, type B)

ROMEX = BRAND NAME
(Like Kleenex is to tissues)

NM-B = TECHNICAL NAME
(Like facial tissue)

All Romex is NM-B cable
Not all NM-B cable is technically 'Romex' brand

What 'NM-B' means:

• NM = Non-Metallic sheathed cable
• -B = Type B designation (90°C rated)
• See our detailed guide: What Does NM-B Stand For?

Basic Definition

Romex wiring consists of:

• 2 or 3 insulated current-carrying wires (THHN/THWN)
• 1 bare or green ground wire
• Flexible PVC outer jacket (sheathing)

All wires pre-assembled and protected in a single, easy-to-install cable.

What Does Romex Wire Look Like?

External Appearance

ROMEX CABLE - EXTERNAL VIEW

    ┌─────────────────────────────────┐
    │                                 │ ← Flat, flexible
    │  14/2 W/G  600V                │   plastic jacket
    │  ROMEX   TYPE NM-B             │   (usually white,
    │                                 │   beige, or yellow)
    └─────────────────────────────────┘
    
    Printing shows:
    - Wire size (14/2)
    - With ground (W/G)
    - Voltage rating
    - Manufacturer name
    - Type (NM-B)

Internal Structure

ROMEX WIRE - CROSS SECTION (14/2 Example)

    ┌──────────────────────────────────┐
    │  ┌────┐  ┌────┐       ○         │
    │  │    │  │    │      bare       │ ← PVC outer
    │  │    │  │    │     ground      │   jacket
    │  └────┘  └────┘                 │
    │  Black   White                   │
    │  (Hot)   (Neutral)               │
    └──────────────────────────────────┘
    
    Individual insulated wires
    inside protective sheath

Color coding:

• Black = Hot (line, live)
• White = Neutral
• Red = Second hot (in 3-wire cable)
• Bare copper or Green = Ground

Types of Romex Wiring

By Wire Count

14/2 Romex (Most Common for Lighting)

14/2 W/G:
- 1 × 14 AWG black (hot)
- 1 × 14 AWG white (neutral)
- 1 × 14 AWG bare (ground)

Used for:

• Lighting circuits (15-amp)
• General outlets (15-amp circuits)
• Bedroom and living room outlets

12/2 Romex (Most Common for Outlets)

12/2 W/G:
- 1 × 12 AWG black (hot)
- 1 × 12 AWG white (neutral)
- 1 × 12 AWG bare (ground)

Used for:

• General outlets (20-amp circuits)
• Kitchen counter outlets
• Bathroom outlets
• Garage circuits

14/3 Romex (Three-Way Switches)

14/3 W/G:
- 1 × 14 AWG black (hot)
- 1 × 14 AWG red (hot/traveler)
- 1 × 14 AWG white (neutral)
- 1 × 14 AWG bare (ground)

Used for:

• Three-way switch circuits
• Split-receptacle circuits
• Multi-wire branch circuits

12/3 Romex

Used for:

• Three-way switches (20-amp)
• Split kitchen outlets
• Multi-wire branch circuits (20-amp)

10/2 and 10/3 Romex (Heavy Appliances)

Used for:

• Electric water heaters (10/2, 30-amp)
• Electric dryers (10/3, 30-amp)
• Window AC units (10/2, 30-amp)
• Some electric ranges

8/3 and 6/3 Romex (Large Appliances)

Used for:

• Electric ranges (8/3 or 6/3, 40-50 amp)
• Large electric dryers
• Sub-panels

Common Romex Types Summary

What Is Romex Wire Used For?

Primary Residential Applications

1. Inside Walls and Ceilings (Most Common)

Romex is designed for concealed residential wiring:

✅ Inside finished walls

• Between studs
• Protected from damage
• Dry locations only

✅ Above ceilings

• Running to light fixtures
• Between floors
• Attic spaces (with protection)

✅ Under floors

• In crawl spaces (if dry)
• Between joists
• Basement ceilings

2. Residential Circuits

Lighting circuits:

• Ceiling lights
• Wall switches
• Recessed lighting
• Ceiling fans

Outlet circuits:

• Bedroom outlets
• Living room outlets
• Dining room outlets
• Home office circuits

Kitchen circuits:

• Counter outlets (20-amp required)
• Small appliance circuits
• Refrigerator circuit

Bathroom circuits:

• Outlet circuits (20-amp, GFCI)
• Exhaust fans
• Vanity lights

Appliance circuits:

• Dishwasher
• Garbage disposal
• Microwave (dedicated)
• Electric water heater
• Dryer

3. Where Romex Is Code-Approved

NEC (National Electrical Code) allows Romex in:

✅ One and two-family dwellings

• Single-family homes
• Duplexes
• Townhouses

✅ Multi-family dwellings

• Inside individual units
• Protected locations
• Not in common areas

✅ Dry locations

• Inside conditioned spaces
• Protected from moisture

✅ Concealed installations

• Inside walls
• Above ceilings
• Under floors

Where Romex CANNOT Be Used

Code-Prohibited Locations

❌ Exposed in garages (below 8 feet)

• Must use conduit or BX cable
• Protection from physical damage required

❌ Exposed in unfinished basements

• Many jurisdictions require protection
• Use BX cable or conduit for exposed runs
• Check local codes

❌ Outdoor installations

• Not rated for weather exposure
• Use conduit with THWN wire or UF cable

❌ Wet or damp locations

• Bathrooms (exposed wiring)
• Laundry rooms (exposed)
• Any location subject to moisture

❌ Embedded in concrete

• Not approved for concrete pour
• Use conduit

❌ Underground burial

• Not rated for direct burial
• Use UF cable or conduit

❌ Commercial buildings (most cases)

• Typically requires conduit or MC cable
• Check local commercial codes

❌ Exposed to physical damage

• High-traffic areas
• Where subject to impact
• Use protected methods

Is Romex Wiring Safe?

Yes—When Properly Installed

Common question: 'Is romex wiring safe?'

Answer: Romex is completely safe when:

• ✅ Correctly sized for the circuit
• ✅ Properly installed per NEC code
• ✅ Used in approved locations only
• ✅ Protected from physical damage
• ✅ Secured and supported correctly

Safety Features of Romex

Modern Romex (NM-B) includes:

1. 90°C temperature rating
   • Won't melt under normal loads
   • Safety margin for temperature rise
2. Color-coded wires
   • Prevents incorrect connections
   • Clear identification
3. Ground wire included
   • Equipment grounding
   • Shock protection
4. Flame-retardant jacket
   • Inhibits fire spread
   • Meets fire safety standards
5. Clearly marked
   • Wire size printed on jacket
   • Voltage rating visible
   • Easy verification

When Romex Can Be Unsafe

Improper use creates hazards:

❌ Wrong size for circuit

• Overheating risk
• Fire hazard
• Must match breaker size

❌ Damaged insulation

• Exposed conductors
• Shock hazard
• Short circuit risk

❌ Used in prohibited locations

• Code violations
• Moisture damage
• Physical damage risk

❌ Poor connections

• Overheating
• Arcing
• Fire risk

Why Is Romex 'Illegal' in Some Places?

Addressing the Misconception

Search query: 'why is romex illegal'

Truth: Romex is NOT illegal—but it has limitations.

Where People Think It's 'Illegal'

1. Commercial buildings:

• Not actually illegal
• Code typically requires conduit or MC cable
• Fire-rating requirements
• Easier future changes

2. Some cities/jurisdictions:

• Local amendments to NEC
• May require armored cable or conduit
• Chicago historically required conduit everywhere
• New York City has specific requirements

3. Exposed locations:

• Not illegal, just not approved
• Must use protected methods
• BX cable or conduit required

4. Canada:

• Different electrical code (CEC)
• Uses different cable types (Loomex)
• Not technically 'Romex'

The Reality

Romex is legal and widely used when:

• Installed per NEC requirements
• Used in approved locations
• Properly sized and protected
• Meets local code amendments

Not 'illegal'—just has specific approved uses.

Romex vs Other Wiring Methods

Romex vs BX Cable (Armored Cable)

When to choose BX over Romex:

• Exposed installations (basements, garages)
• Better physical protection needed
• Code requires protected cable
• See our guide: What Is BX Cable Used For?

Romex vs Conduit + THWN Wire

When to choose conduit over Romex:

• Outdoor installations
• Exposed wiring
• Commercial buildings
• Underground runs
• Maximum protection needed
• See our guide: What Is Electrical Conduit?

Romex vs UF Cable (Underground Feeder)

When to use UF instead of Romex:

• Outdoor wiring
• Underground burial
• Wet locations
• From house to shed/garage

Romex Installation Requirements

NEC Code Requirements

Support and securing:

• Within 12 inches of boxes
• Every 4.5 feet along runs
• Use proper cable staples

Protection:

• Through studs: drill holes 1.25' from edge
• Through notches: add steel plate protection
• No sharp edges or objects

Bending radius:

• Minimum 5× cable diameter
• Avoid tight bends (damages wires)

Box fill:

• Calculate conductor count
• Don't overfill boxes
• Follow NEC Chapter 3 requirements

Common Installation Mistakes

Romex Wire Sizes and Ampacity

Quick Reference

Important: Circuit breaker must match wire size:

• 14 AWG → Maximum 15-amp breaker
• 12 AWG → Maximum 20-amp breaker
• Never oversize breaker for wire

For complete sizing charts and ampacity tables, see: Romex Wire Size Chart: Complete Guide ← Coming soon

Romex in Conduit: Can You Do It?

Short Answer: Yes, But...

Question: 'Can you run romex in conduit?'

Answer: Yes, NEC allows it, but it's usually not the best choice.

Why Run Romex in Conduit?

✅ Physical protection

• Short exposed sections
• Transition through walls
• Protection from damage

✅ Already installed conduit

• Existing conduit runs
• Easier than removing conduit

Why NOT Run Romex in Conduit?

❌ Takes up more space

• Romex jacket adds bulk
• Limits number of cables
• Harder to pull

❌ Better alternatives exist

• Individual THWN wires more efficient
• Easier to pull
• More circuits in same conduit

❌ Not ideal for long runs

• Friction from jacket
• Difficult to pull
• Time-consuming

For detailed analysis, see: Can You Run Romex in Conduit? Code Requirements ← Coming soon

Romex Wiring Diagram Basics

Simple Circuit Example

BASIC ROMEX LIGHTING CIRCUIT

┌─────────────────┐
│  Circuit Breaker│
│     Panel       │
└────────┬────────┘
         │ 14/2 Romex
         │ (Black, White, Ground)
         │
    ┌────▼────┐
    │ Switch  │ ← Black wire switched
    │  Box    │   White continuous
    └────┬────┘   Ground to box
         │ 14/2 Romex
         │
    ┌────▼────┐
    │ Light   │
    │ Fixture │
    └─────────┘

Three-Way Switch Circuit

THREE-WAY SWITCH WITH 14/3 ROMEX

Panel ──14/2──► Switch 1 ──14/3──► Switch 2 ──14/2──► Light
              (Source)    (Travelers)  (Load)
              
14/3 contains:
- Black (hot)
- Red (traveler)
- White (neutral)
- Ground

For complete wiring diagrams, consult:

• NEC handbook
• Licensed electrician
• Manufacturer instructions

Frequently Asked Questions

What does 'Romex' stand for?

Romex is a brand name, not an acronym. It's manufactured by Southwire Company. The technical name is NM-B (Non-Metallic sheathed cable, type B).

Can I use Romex in my garage?

Partially:

• ✅ Concealed in walls/ceilings
• ✅ Above 8 feet (exposed)
• ❌ Below 8 feet (exposed) — use BX or conduit

Is Romex the same as NM-B?

Yes and no:

• Romex is a specific brand of NM-B cable
• NM-B is the technical designation
• Like saying 'Kleenex' vs 'facial tissue'
• All Romex is NM-B; not all NM-B is Romex brand

How long does Romex last?

30-50+ years when properly installed in appropriate locations. Romex from the 1960s-1970s still functions in many homes. Lifespan depends on:

• Installation quality
• Environmental conditions
• Proper sizing
• Protection from damage

Can Romex be used outdoors?

No. Romex is rated for dry locations only. For outdoor use:

• Use conduit with THWN wire
• Use UF (Underground Feeder) cable
• Use weatherproof methods

What's the difference between Romex and THHN wire?

Romex = Complete cable (multiple THHN wires + ground in plastic jacket) THHN = Individual insulated wire (used inside conduit)

Romex contains THHN-type wires pre-assembled in a jacket.

Conclusion

Romex wiring (NM-B cable) is the standard electrical wiring method for residential homes, consisting of insulated wires bundled together in a flexible plastic jacket for easy installation inside walls and ceilings. While 'Romex' is technically a brand name, it has become the common term for all non-metallic sheathed cable used in home electrical systems.

Key takeaways:

• Romex = NM-B cable (brand name vs. technical name)
• Used inside walls/ceilings in dry locations only
• Not for outdoor, wet, or exposed locations (use BX, conduit, or UF cable)
• Completely safe when properly installed per NEC code
• Available in various sizes (14/2, 12/2, 10/2, etc.) for different circuits
• Most economical residential wiring method (faster, cheaper than conduit)
• Not 'illegal' but has specific approved uses

Understanding what Romex is, where it can be used, and how it compares to other wiring methods ensures safe, code-compliant electrical installations in your home.

Related Guides:

• What Does NM-B Stand For? - Technical details on NM-B designation
• What Is BX Cable Used For? - When to use armored cable instead
• What Is Electrical Conduit? - Understanding conduit systems
• Romex Wire Size Chart ← Coming soon
• Can You Run Romex in Conduit? ← Coming soon

Planning electrical work? Always follow local electrical codes, obtain required permits, and consider hiring a licensed electrician for complex installations. Improper electrical work is dangerous and may violate building codes.