The Romex color code is not a strict NEC mandate, but rather a universal manufacturing standard established by Southwire and adopted across the US electrical industry. The outer PVC jacket color of NM-B (Non-Metallic Sheathed) cable instantly tells you the American Wire Gauge (AWG) and the maximum safe ampacity of the conductors inside. Here is the definitive reference chart.
The Standard Romex Color Code Chart (NEC / NM-B)
The following table maps the outer jacket color to the internal wire gauge, maximum ampacity (based on the 60°C column per NEC Table 310.16 for standard residential branch circuits), and the maximum standard breaker size. This applies to standard indoor NM-B cable.
| Jacket Color | AWG Size | Max Ampacity (60°C) | Max Breaker Size | Common Use Cases | Standard Configurations |
|---|---|---|---|---|---|
| White | 14 AWG | 15 Amps | 15A | General lighting, low-draw receptacles, bathroom fans | 14/2, 14/3 |
| Yellow | 12 AWG | 20 Amps | 20A | Kitchen counter outlets, laundry, standard bedroom/living room receptacles | 12/2, 12/3 |
| Orange | 10 AWG | 30 Amps | 30A | Electric water heaters, window AC units, dryers (120V control circuits) | 10/2, 10/3 |
| Black | 8 AWG or 6 AWG | 40A (8 AWG) / 55A (6 AWG) | 40A or 60A | Electric ranges, EV chargers, subpanel feeders, central AC disconnects | 8/2, 6/2, 6/3, 4/2 |
| Grey (UF-B) | Varies (14-6 AWG) | Depends on AWG | Depends on AWG | Direct burial, outdoor lighting, shed feeds (Not standard indoor Romex) | 14/2, 12/2, 10/2, etc. |
Rows People Get Wrong (And How to Avoid Costly Mistakes)
Even experienced DIYers and apprentice electricians misinterpret Romex color codes. Here are the most frequent errors and how to avoid them.
1. Putting White Romex (14 AWG) on a 20A Breaker
This is the most dangerous and common mistake. A homeowner might swap a 15A breaker for a 20A breaker because 'the lights keep tripping,' not realizing the white Romex feeding the circuit is only rated for 15A. Under NEC 240.4(D), 14 AWG copper must be protected at 15A. If you push 18A through a 14 AWG wire on a 20A breaker, the breaker won't trip, but the wire will overheat, melt its insulation, and potentially start a fire inside the wall cavity.
2. The Black Jacket Ambiguity
Notice that the black jacket row in the table lists both 8 AWG and 6 AWG (and sometimes 4 AWG). Southwire and other manufacturers use black jackets for all heavy-gauge NM-B cables. You absolutely cannot tell if a black Romex cable is rated for 40A or 60A just by looking at the jacket color. You must read the stamped text on the side of the cable or measure the conductor diameter. Never assume a black cable is 6 AWG without verifying.
3. Confusing Jacket Color with Wire Insulation Color
Beginners often confuse the outer jacket with the internal wires. A 'White Romex' cable does not contain only white wires. A standard 12/2 yellow Romex contains a black (hot), a white (neutral), and a bare copper (ground) wire inside. The jacket color dictates the gauge; the internal insulation colors dictate the circuit function.
4. Assuming UF-B (Grey) Follows the Same Rules
Underground Feeder (UF-B) cable is almost always grey, regardless of whether it is 14 AWG, 12 AWG, or 10 AWG. If you are working on an outdoor circuit or a shed feed and see grey cable, you cannot use color to determine the gauge. You must read the printing or measure the wire.
International Equivalents: Romex vs. Twin & Earth vs. EU Harmonized
The color-coded jacket system is unique to North America (NEC). If you are reading this from the UK, EU, or Australia, your regional standards use different cable types and color conventions. Here is how the US system compares to international equivalents.
| Region / Standard | Cable Type | Jacket Color | Internal Wire Colors (Line / Neutral / Earth) | Gauge Identification Method |
|---|---|---|---|---|
| US / Canada (NEC) | NM-B (Romex) | White, Yellow, Orange, Black | Black / White / Bare Copper | Jacket color + Printed AWG |
| UK (BS 7671) | Twin & Earth | Grey (PVC) | Brown / Blue / Bare (Green-Yellow sleeve) | Printed mm² (e.g., 1.5mm², 2.5mm²) |
| UK (Pre-2004 Legacy) | Twin & Earth | Grey or White | Red / Black / Bare (Green-Yellow sleeve) | Printed mm² (Danger: old colors still exist in walls) |
| EU (IEC 60446) | NYM Cable | Grey or White | Brown / Blue / Green-Yellow | Printed mm² (e.g., 1.5mm², 2.5mm², 4mm²) |
| Australia / NZ (AS/NZS 3000) | TPS (Thermoplastic Sheathed) | White or Grey | Active (Brown/Red) / Neutral (Blue/Black) / Earth (Green-Yellow) | Printed mm² |
Key Takeaway for International Readers: In regions using metric sizing (mm²), the jacket color does not indicate the wire size. A 1.5mm² cable (roughly 15 AWG, used for 10A lighting) and a 2.5mm² cable (roughly 13 AWG, used for 16A/20A ring mains) both use identical grey PVC jackets in the UK and EU. You must always rely on the printed text on the sheath.
What to Do When Jacket Markings Are Faded, Painted, or Missing
In older homes, or after a sloppy painting job, the printed text on Romex can be completely obscured. The jacket might also be sun-faded in an attic, making yellow look white, or orange look yellow. Here is the professional protocol for safely identifying wire gauge when visual cues fail.
Method 1: The Wire Stripper Gauge Test
Do not guess. Take a known offcut of 12 AWG and 14 AWG solid copper wire. Use the stripping holes on a high-quality wire stripper (like the Klein Tools 11055). If the wire fits snugly in the 14 AWG hole and strips cleanly without scoring the copper, it is 14 AWG. If it requires the 12 AWG hole, it is 12 AWG. Scoring the copper reduces its cross-sectional area and creates a hot spot.
Method 2: Digital Caliper Measurement (The Most Accurate)
If you have a digital caliper, strip a small section of the insulation and measure the bare copper conductor's diameter. This removes all guesswork and bypasses faded jackets entirely.
- 14 AWG: 1.628 mm (0.0641 inches)
- 12 AWG: 2.053 mm (0.0808 inches)
- 10 AWG: 2.588 mm (0.1019 inches)
- 8 AWG: 3.264 mm (0.1285 inches)
- 6 AWG: 4.115 mm (0.1620 inches)
Measure at least three different points along the bare wire and average the results, as copper drawing can have microscopic variances. If your caliper reads 2.05mm, you are holding 12 AWG wire, regardless of whether the jacket is painted white, yellow, or covered in drywall mud.
Method 3: The Cross-Section Area Comparison
If you lack tools, cut a clean, flush cross-section of the wire with heavy flush cutters. Hold it directly against a known, verified sample of 12 AWG and 14 AWG wire. The difference in cross-sectional area between 14 AWG (2.08 mm²) and 12 AWG (3.31 mm²) is visually massive—12 AWG is roughly 60% thicker in area than 14 AWG. If you are ever in doubt, assume the smaller gauge (14 AWG) and protect the circuit with a 15A breaker until you can verify with proper tools.
