In US residential wiring, searching for a color wire chart usually means you need to decode two distinct coding systems: the outer NM-B (commonly called Romex) jacket color, which identifies the wire gauge and ampacity, and the internal conductor insulation color, which dictates the circuit function. For standard copper NM-B cable, White = 14 AWG (15A), Yellow = 12 AWG (20A), and Orange = 10 AWG (30A). Inside the sheath, Black and Red are hot, White is neutral, and Bare or Green is ground.
This reference guide provides the exact data tables for both the outer sheath and internal conductors, sourced directly from the National Electrical Code (NEC) and Underwriters Laboratories (UL) standards. Bookmark the quick-jump rows below for the most common hardware store runs.
The NM-B Sheath Color Wire Chart (Gauge & Ampacity)
How to Read This Table
The ampacity values in the chart below are derived from the 60°C column of NEC Table 310.16. While the individual THHN conductors inside an NM-B cable are technically rated for 90°C, NEC Article 334.80 strictly mandates that the overall ampacity of NM-B cable must be determined using the 60°C column. This is because standard residential breakers, receptacles, and switches are only tested and rated for 60°C terminations (per NEC 110.14(C)). The jacket colors themselves are standardized by UL 719 and manufacturer conventions (like Southwire and Cerro) to allow instant visual identification on the jobsite.
| Jacket Color | AWG Size | Max Ampacity (60°C) | Standard Breaker Size | Common Applications |
|---|---|---|---|---|
| White | 14 AWG | 15 Amps | 15A | General lighting, basic receptacles |
| Yellow (Most Queried) | 12 AWG | 20 Amps | 20A | Kitchen/bath receptacles, window ACs |
| Orange (Most Queried) | 10 AWG | 30 Amps | 30A | Electric dryers, water heaters, RV outlets |
| Black | 8 AWG | 40 Amps | 40A | Electric ranges, large HVAC air handlers |
| Black | 6 AWG | 55 Amps | 50A / 60A* | Subpanel feeders, EV chargers (Level 2) |
| Black | 4 AWG | 70 Amps | 70A | Large subpanels, heavy-duty shop feeders |
*Note: A 6 AWG copper wire is rated for 55A at 60°C. If your specific breaker and receptacle are explicitly marked for 75°C terminations, you may use the 75°C column (65A), but 60°C is the safe default for residential DIY.
Internal Conductor Insulation Color Codes (US NEC)
Once you strip the outer NM-B jacket, the internal conductor colors dictate how the wire must be terminated. These colors are strictly enforced by NEC Articles 200 (Neutral), 210 (Branch Circuits), and 250 (Grounding). Reversing hot and neutral or using a white wire as an ungrounded hot without proper re-identification (phase taping) are leading causes of failed electrical inspections and shock hazards.
| Insulation Color | Function | NEC Reference | Termination Rule |
|---|---|---|---|
| Black | Ungrounded (Hot) | NEC 210.5(C) | Connects to brass/gold screws on devices; to breaker hot bus. |
| Red | Ungrounded (Hot 2) | NEC 210.5(C) | Used for 240V circuits, 3-way switch travelers, or multi-wire branch circuits (MWBC). |
| White | Grounded (Neutral) | NEC 200.6(A) | Connects to silver screws on devices; to the neutral bar in the panel. Must not be switched. |
| Gray | Grounded (Neutral) | NEC 200.6(B) | Used to distinguish a second neutral in multi-voltage systems (e.g., 277V vs 480V commercial). |
| Green / Bare Copper | Equipment Ground | NEC 250.119 | Connects to green grounding screws; to the ground bar in the panel. Never carries current unless a fault occurs. |
How Derating and Installation Columns Modify Your Base Value
The ampacity numbers in the color wire chart above represent ideal, single-cable runs. In the real world, installation conditions force you to adjust (derate) those values. Understanding which column applies and how derating works prevents melted insulation and tripped breakers.
Which Column Applies to Your Installation?
Wire insulation like THHN is rated for 90°C, but your terminations (the lugs on your breaker and the screws on your receptacle) are usually only rated for 60°C or 75°C. NEC 110.14(C) dictates that you must size your wire based on the lowest temperature rating in the entire circuit loop. For almost all residential 15A, 20A, and 30A circuits, the devices are rated for 60°C. Therefore, you must use the 60°C column of Table 310.16 (as shown in Table 1). You only use the 75°C or 90°C columns for specific industrial equipment or large feeder lugs explicitly marked with those temperature ratings.
How Derating Modifies the Base Ampacity
When you bundle multiple cables together, they trap heat, reducing their ability to dissipate thermal energy. Under NEC 334.80, if you bundle more than three NM-B cables together through a framing member or inside thermal insulation for a distance greater than 24 inches without maintaining spacing, you must apply a derating factor to the 90°C ampacity of the wire, and then ensure the final derated value does not exceed the 60°C column limit.
Worked Example: You are running four 12-2 NM-B cables (8 current-carrying conductors total) bundled tightly through a wall cavity for 3 feet.
- Base 90°C ampacity for 12 AWG = 30A.
- NEC Table 310.15(C)(1) derating factor for 7-9 conductors = 70%.
- Derated Ampacity = 30A × 0.70 = 21A.
- Because 21A exceeds the 60°C column limit for 12 AWG (20A), you are legally permitted to use 12 AWG on a 20A breaker. However, if you added a fifth cable (10 conductors, 50% derating), 30A × 0.50 = 15A. You would be forced to upsize to 10 AWG wire to maintain a 20A circuit.
What the Color Wire Chart Cannot Tell You
While a color wire chart is the perfect starting point for selecting materials at the hardware store, it is not a complete engineering tool. Relying solely on jacket color and base ampacity will lead to failures in the following scenarios:
- Voltage Drop on Long Runs: The chart assumes standard run lengths. If you are running a 12 AWG circuit to a detached garage 150 feet away, the wire will safely carry 20A without melting, but the voltage at the receptacle will drop below 114V (a >5% drop on a 120V nominal system). This causes motors to overheat and lights to dim. For runs over 100 feet, you must calculate voltage drop and typically upsize the wire by one or two gauges, regardless of the breaker size.
- Conduit Fill Limits: If you strip the NM-B jacket and pull individual THHN conductors through PVC or EMT conduit, the color chart's ampacity rules change, and you must now calculate physical conduit fill percentages (NEC Chapter 9, Table 1). You cannot simply stuff as many 12 AWG wires into a 1/2-inch conduit as you want, even if the ampacity math works out.
- Aluminum vs. Copper Feeders: The NM-B jacket colors apply strictly to copper. If you are pulling SER (Service Entrance Rated) cable for a subpanel or an HVAC disconnect, you are likely using aluminum wire. Aluminum has a lower ampacity per gauge than copper and requires different torque specifications and anti-oxidant paste (like Noalox) at the terminations. Always check the wire print-line for 'CU' (Copper) or 'AL' (Aluminum).
Always verify your local jurisdiction's adopted code cycle. While the NEC provides the baseline standard, local Authorities Having Jurisdiction (AHJ) may have specific amendments regarding NM-B usage in commercial buildings or multi-family dwellings that override standard residential practices.
