Romex is a trademarked brand name owned by Southwire, but in the trades, it is the universal shorthand for Non-Metallic Sheathed (NM-B) cable. The outer PVC jacket color is not an aesthetic choice; it is a standardized visual code that instantly tells you the American Wire Gauge (AWG) size and the maximum allowable ampacity of the conductors inside.
The direct answer: A White jacket indicates 14 AWG (15A max), Yellow indicates 12 AWG (20A max), Orange indicates 10 AWG (30A max), and Black indicates 8 AWG or 6 AWG (40A to 55A max). This color coding is standardized across major manufacturers to comply with NFPA 70 (National Electrical Code) and UL 719 manufacturing standards.
The Romex Color Code Chart (NEC & UL 719 Standards)
The table below is your primary reference for NM-B cable sizing. How to read this table: The "Jacket Color" is the outer sheath. The "AWG Size" refers to the thickness of the individual current-carrying copper conductors inside. The "60°C Ampacity" is the maximum continuous current the wire can safely carry under standard conditions, strictly based on the 60°C column of NEC Table 310.16. The "Max Breaker" is the highest standard overcurrent protection device you can install for that wire size per NEC 240.4(D).
| Jacket Color | AWG Size | Common Config | 60°C Ampacity | Max Breaker | Typical Application |
|---|---|---|---|---|---|
| White | 14 AWG | 14/2 or 14/3 | 15 Amps | 15A | Lighting circuits, low-draw bedroom receptacles |
| Yellow | 12 AWG | 12/2 or 12/3 | 20 Amps | 20A | Kitchen, bathroom, garage, and general receptacles |
| Orange | 10 AWG | 10/2 or 10/3 | 30 Amps | 30A | Electric water heaters, window AC units, dryers (10/3) |
| Black | 8 AWG | 8/2 or 8/3 | 40 Amps | 40A | Electric ranges, large heat pumps, subpanel feeders |
| Black (often w/ red stripe) | 6 AWG | 6/2 or 6/3 | 55 Amps | 60A* | Heavy subpanel feeders, tankless water heaters |
*Note on 6 AWG Breakers: While the base ampacity of 6 AWG copper at 60°C is 55A, NEC 240.4(B) allows you to round up to the next standard breaker size (60A) if the specific 55A breaker is not available, provided the load is not continuous.
Which Ampacity Column Applies and How Derating Works
The most common point of failure for DIY electrical work is misapplying the temperature rating of the wire. If you strip back a yellow 12/2 Romex jacket, you will see individual conductors insulated with THHN/THWN, which is rated for 90°C. However, you cannot use the 90°C ampacity column.
Per Southwire's NM-B specifications and NEC Article 334.80, the ampacity of NM-B cable must be determined using the 60°C column of NEC Table 310.16. This limitation exists because the overall cable assembly—including the outer PVC jacket and the internal paper filler—cannot safely dissipate heat at 90°C. The 90°C rating of the inner conductors is only useful for one specific purpose: calculating derating adjustments.
Calculating Derating for Bundled Cables
When you run multiple NM-B cables tightly bundled together (e.g., passing through a single bored hole in a framing member or bundling them in a conduit sleeve), the heat from adjacent cables traps thermal energy. NEC 315.15 requires you to apply an adjustment factor (derating) if you have more than three current-carrying conductors bundled together for more than 24 inches.
The Derating Rule: You apply the derating percentage to the 90°C column value, but the final derated ampacity cannot exceed the base 60°C ampacity limit.
You are running two 10/3 NM-B cables through the same bored stud hole. This gives you 6 current-carrying conductors (the bare grounds do not count).
1. Base 60°C limit for 10 AWG: 30 Amps.
2. 90°C ampacity for 10 AWG: 40 Amps.
3. Derating factor for 6 conductors (NEC Table 315.15(C)(1)): 80%.
4. Calculation: 40A × 0.80 = 32 Amps.
5. Final Limit: Because 32A exceeds the absolute 60°C cap of 30A, your maximum allowed ampacity remains 30 Amps. You must still protect this circuit with a 30A breaker.
Inner Conductor Colors and What the Chart Cannot Tell You
While the outer jacket tells you the gauge, the inner conductor colors dictate how the circuit is wired. In a standard NM-B cable, the color coding is strictly enforced by NEC Article 200 and 210.
- Black: The ungrounded (hot) conductor. Carries the 120V or 240V line voltage from the breaker to the load.
- White: The grounded (neutral) conductor. Completes the circuit back to the panel. Never use a white wire as a hot conductor in NM-B cable, as re-identifying it with tape is prohibited for cables containing multiple conductors under NEC 200.7(C)(1).
- Bare Copper: The equipment grounding conductor (EGC). Provides the fault-current path to trip the breaker. It is never counted as a current-carrying conductor for derating.
- Red: Found only in /3 cables (e.g., 12/3 or 10/3). Acts as a second ungrounded (hot) conductor for 240V appliances, multi-wire branch circuits (MWBC), or 3-way switch traveler legs.
The Limitations of the Color Code Chart
A reference chart gives you the legal baseline for ampacity, but it cannot account for the physics of long wire runs or local jurisdiction overrides. You must factor in the following edge cases before pulling wire:
- Voltage Drop: The chart assumes standard run lengths. If you are running a 12 AWG yellow Romex circuit 150 feet to a shed to power a 15A table saw, the wire is legally rated for the amperage, but the resistance of the copper will cause a voltage drop exceeding the 3% recommendation in NEC 210.19(A) Informational Note. For runs over 100 feet, you must upsize the wire (e.g., using 10 AWG orange on a 20A breaker) strictly to mitigate voltage drop, not for ampacity.
- Local AHJ Amendments: The National Electrical Code is a baseline model code. Your local Authority Having Jurisdiction (AHJ) has the final say. Municipalities like Chicago, Illinois, and New York City strictly prohibit the use of NM-B Romex in most construction, requiring all branch circuits to be pulled through metallic EMT conduit. Always check local amendments before buying bulk cable.
- Physical Protection: NM-B cannot be used where it is subject to physical damage. If you are wiring a garage or an unfinished basement, the cable must be run through bored holes in the studs or protected by running boards. You cannot simply staple Romex across the face of framing members below 8 feet where it could be impacted by stored items or vehicles.
By matching the jacket color to the correct breaker size and respecting the 60°C termination limits of your devices, you ensure your installation remains safe, code-compliant, and capable of handling the intended electrical load without thermal degradation.
