Romex® is a trademarked brand name for Non-Metallic Sheathed (NM-B) cable, manufactured by Southwire. In the US electrical trade, the outer jacket color of NM-B cable is an industry-standard visual shorthand for the American Wire Gauge (AWG) and the maximum allowable ampacity of the conductors inside. White means 14 AWG (15 amps), yellow means 12 AWG (20 amps), orange means 10 AWG (30 amps), and black means 8 or 6 AWG (40 to 55 amps). This color-coding system allows electricians and inspectors to instantly verify circuit capacity at the panel or rough-in stage without stripping the sheath.
The Complete Romex Jacket Color Code Reference Table
The table below maps the standard NM-B jacket colors to their corresponding conductor sizes, maximum overcurrent protection, and typical residential applications. Note: Ampacity figures are based on the 60°C column of NEC Table 310.16, as mandated by NEC 334.80 for NM-B cable, regardless of the 90°C rating of the individual THHN conductors inside.
| Jacket Color | Conductor Size (AWG) | Max Ampacity (60°C) | Common Applications | Standard Configurations |
|---|---|---|---|---|
| White | 14 AWG | 15 Amps | General lighting, standard bedroom/living room receptacles | 14/2, 14/3 |
| Yellow | 12 AWG | 20 Amps | Kitchen/bathroom small appliance circuits, dedicated 20A outlets | 12/2, 12/3 |
| Orange | 10 AWG | 30 Amps | Electric water heaters, window AC units, heavy-duty tool circuits | 10/2, 10/3 |
| Black | 8 or 6 AWG | 40A or 55A | Electric ranges, subpanel feeders, EV charging stations | 8/3, 6/2, 6/3 |
Rows People Get Wrong (and Faded Jacket Protocols)
Even experienced DIYers make critical errors when interpreting NM-B cable. Here are the most common pitfalls and how to resolve them on the jobsite.
Mistake 1: Confusing Jacket Color with Conductor Insulation
The jacket color dictates the cable's overall capacity. The individual wire insulation colors inside dictate the circuit function. A yellow Romex cable (12 AWG, 20A capacity) will still contain black (hot), white (neutral), and bare (ground) conductors. Never assume a white jacket means the wires inside are neutrals; it simply means the entire cable assembly is rated for 15 amps.
Mistake 2: The Black Jacket Ambiguity
Unlike white, yellow, and orange, a black Romex jacket does not specify a single AWG size. It is used for both 8 AWG (40A) and 6 AWG (55A) cables. If you are pulling black NM-B from an unmarked spool, you must read the printed text on the jacket or physically measure the conductor to determine if it is safe for a 50A range circuit (requires 6 AWG) or a 40A subpanel feeder (requires 8 AWG).
Mistake 3: Ignoring the 60°C Derating Rule
The individual THHN wires inside Romex are rated for 90°C, which might suggest a 12 AWG wire could handle 30 amps. However, the National Fire Protection Association (NFPA) enforces NEC 334.80, which limits NM-B ampacity to the 60°C column because the overall PVC jacket and paper filler cannot safely dissipate heat at higher temperatures. A 12 AWG yellow Romex is strictly limited to a 20A breaker.
Safe Interpretation of Faded or Missing Markings
UV exposure, attic heat, and age can bleach a yellow jacket to look white, or rub the printed AWG text completely off. If the jacket is faded and the text is illegible, do not guess. Strip back the sheath and measure the bare copper conductor with a digital caliper:
- 14 AWG: 1.63mm (0.064 inches)
- 12 AWG: 2.05mm (0.081 inches)
- 10 AWG: 2.59mm (0.102 inches)
If your caliper reads 0.064 inches on a cable with a yellow jacket, someone likely swapped the wire or the jacket was chemically altered. Trust the copper measurement over the faded plastic.
Regional Standards: NEC NM-B vs. IEC and UK Twin & Earth
The color-coded jacket system is specific to the North American market. If you are working internationally or reading foreign schematics, the rules change entirely.
| Standard / Region | Cable Type | Jacket Color Rules | Sizing Convention | Conductor Colors |
|---|---|---|---|---|
| US / NEC | NM-B (Romex) | Color indicates AWG (White=14, Yellow=12) | AWG (American Wire Gauge) | Black (Hot), White (Neutral), Bare (Ground) |
| UK / BS 7671 | Twin & Earth | Universally Grey (or White for LSZH) | Metric mm² (1.5, 2.5, 4.0) | Brown (Line), Blue (Neutral), Green/Yellow (Earth) |
| EU / IEC | H07V-U / NYM | Usually Grey or White PVC sheath | Metric mm² | Brown (Line), Blue (Neutral), Green/Yellow (Earth) |
In the UK, the Institution of Engineering and Technology (IET) governs BS 7671. 'Twin and Earth' cable does not use jacket colors to denote size; instead, the grey jacket is standard across all sizes, and electricians rely on the printed metric text (e.g., 2.5mm² for standard 20A/32A ring mains). Similarly, IEC harmonized cables rely on the individual conductor insulation colors (per IEC 60446) rather than the outer sheath to convey any electrical information.
Frequently Asked Questions About Romex Color Codes
Can I use white Romex (14 AWG) on a 20-amp breaker?
No. NEC 240.4(D) strictly limits 14 AWG copper to a maximum 15-amp overcurrent device. If you connect white Romex to a 20-amp breaker, the breaker will not trip before the 14 AWG wire overheats and potentially starts a fire inside the wall cavity. If a circuit requires 20 amps, you must use yellow Romex (12 AWG) or larger.
What do the numbers printed on the Romex jacket mean?
The printed string, such as '14-2 w/ GND 600V NM-B', provides the exact specification. '14' is the AWG size. '2' indicates the number of current-carrying insulated conductors (black and white). 'w/ GND' confirms the presence of a bare equipment grounding conductor. '600V' is the maximum voltage rating of the insulation, and 'NM-B' is the cable type, indicating it is rated for 90°C conductors but must be treated as 60°C for ampacity.
Why is my Romex jacket color different from the wires inside?
This is a fundamental misunderstanding of cable anatomy. The outer jacket color (white, yellow, orange, black) is a manufacturing convention used solely to identify the wire gauge and ampacity of the cable assembly. The inner wire insulation colors (black, red, white) identify the electrical function of each specific conductor within that assembly. They serve two completely different identification purposes.
Is it legal to paint or tape Romex to change its jacket color?
No. NEC 334.15 requires NM-B cable to be identified and protected. Painting the jacket can obscure the manufacturer's printed specifications (AWG, voltage rating, UL listing), making it impossible for an inspector to verify the cable's rating. Furthermore, certain paints and chemical adhesives in electrical tape can degrade the PVC sheath over time, compromising its dielectric strength and fire resistance. If you need to identify a specific circuit, use approved cable tags or labels at the panel and junction boxes, not paint on the sheath.
