If you are buying non-metallic sheathed cable (NM-B), the jacket color tells you exactly what size wire is inside and what breaker it can safely terminate on. Here is the direct answer: White is 14 AWG (15A), Yellow is 12 AWG (20A), Orange is 10 AWG (30A), and Black is 8 or 6 AWG (40A–55A).

'Romex' is technically a registered trademark of Southwire, but it has become the genericized term for all NM-B cable in the US. While the jacket color dictates the wire gauge, the actual ampacity is governed by strict thermal limits in the National Electrical Code (NEC). Below is the complete reference chart, the internal conductor breakdown, and the decision tree you need to pick the exact right cable for your next rough-in.

The Romex Wire Color Chart (Jacket & Conductor Standards)

How to read this table: This chart maps the outer PVC jacket color to the American Wire Gauge (AWG) of the internal conductors and the maximum Overcurrent Protective Device (OCPD) or breaker size. The ampacity values are sourced from the NEC Table 310.16 (60°C column) and the physical cable specifications are governed by the UL 719 Standard for Nonmetallic-Sheathed Cables. Always look at the 'Max Breaker' column to determine your circuit limit, not the 90°C rating printed on the internal wire insulation.

Jacket Color AWG Size Conductor Config Max Breaker (OCPD) Standard Use Case
White 14 AWG 14/2 or 14/3 15 Amps Lighting circuits, bathroom fans, low-draw bedroom receptacles.
Yellow 12 AWG 12/2 or 12/3 20 Amps Kitchen small appliance, bathroom GFCI, garage, and general living room receptacles.
Orange 10 AWG 10/2 or 10/3 30 Amps Electric water heaters, window AC units, dryers (10/3), and RV receptacles.
Black 8 AWG 8/2 or 8/3 40 Amps Electric ranges, cooktops, and large HVAC air handlers.
Black 6 AWG 6/2 or 6/3 55 Amps Subpanel feeders (short runs), tankless electric water heaters, EV chargers (hardwired).
Bench Tip: Modern Southwire Romex uses SIMpull technology—a lubricated jacket that drastically reduces friction. If you are pulling 12/2 through bored framing holes, a quick spray of wire pulling lubricant on the jacket will save your arms and prevent micro-tears in the PVC sheath.

Internal Conductor Colors: What’s Inside the Jacket?

When you strip back the outer PVC sheath, you will find individual THHN/THWN-2 equivalent conductors wrapped in a paper separator. Here is the strict color code for the internal wires:

  • Black: Ungrounded conductor (Hot). Carries the 120V or 240V line voltage.
  • White: Grounded conductor (Neutral). Carries the return current. Never use this as a hot wire unless re-identified with black tape or paint at both terminations (NEC 200.7).
  • Bare Copper: Equipment Grounding Conductor (EGC). Provides the fault current path to trip the breaker.
  • Red: Second ungrounded conductor (Hot 2). Found only in /3 cables (e.g., 12/3). Used for 240V appliances, 3-way switch travelers, or multi-wire branch circuits (MWBC).

Ampacity, Derating, and the 60°C Rule

A common point of confusion is why a 12 AWG wire inside a yellow Romex jacket is rated for 20A, while a standalone 12 AWG THHN wire in a conduit is rated for 30A.

Which Column Applies to Your Installation?

You must always use the 60°C column of NEC Table 310.16 for NM-B cable. NEC Article 334.80 explicitly states that the ampacity of NM-B cable shall not exceed that of a 60°C conductor, regardless of the fact that the individual wires inside the jacket are marked 90°C. The 90°C rating is only permitted to be used as a starting point for derating calculations.

How Derating Modifies the Base Value

Derating becomes critical when you bundle multiple NM-B cables together. According to NEC 310.15(C)(1), if you run more than three current-carrying conductors through a single bored hole in a framing member (and they are bundled tightly without spacing), you must apply an adjustment factor.

Worked Numeric Example:
Imagine you bore a single hole through a stud and pull four 12/2 yellow Romex cables through it to feed four different 20A receptacle circuits.

  1. You have 8 current-carrying conductors (the bare grounds do not count).
  2. NEC Table 310.15(C)(1) dictates a 70% adjustment factor for 7-9 conductors.
  3. Using the 90°C column for derating math: 12 AWG at 90°C is 30A.
  4. 30A × 0.70 = 21A.
  5. Because 21A is greater than the 60°C baseline of 20A, the 12 AWG cable is still legally permitted to be protected by a 20A breaker.

However, if you pulled five 12/2 cables (10 conductors, 50% derating), the math becomes 30A × 0.50 = 15A. Your 12 AWG wire is now legally derated below the 20A breaker size. You would be forced to upsize to 10 AWG (Orange) to maintain a 20A circuit.

Decision Tree: Which Romex Color Do You Actually Need?

Use this decision path to terminate your search and pick the exact cable for your project. Do not guess; match your load to the row below.

If Your Load / Circuit Is... And the Breaker Size Is... Then Buy This Exact Cable
Standard lighting, ceiling fans, or bathroom exhaust 15 Amp White 14/2 NM-B (with bare ground)
Kitchen countertops, bathroom GFCI, garage, or outdoor receptacles 20 Amp Yellow 12/2 NM-B (with bare ground)
3-way or 4-way switch loops requiring travelers 15 or 20 Amp White 14/3 or Yellow 12/3 NM-B
Standard electric water heater (up to 4500W) 30 Amp Orange 10/2 NM-B (with bare ground)
Electric dryer or 120/240V multi-wire branch circuit 30 Amp Orange 10/3 NM-B (Black, Red, White, Bare)
Electric range, oven, or cooktop (up to 8.8kW) 40 Amp Black 8/3 NM-B (Black, Red, White, Bare)
Safety & Code Caveat: Never install NM-B (Romex) in wet or damp locations, buried directly in the earth, or embedded in poured concrete. For those applications, you must use UF-B (Underground Feeder) cable or individual THWN-2 conductors inside a raceway. Always de-energize the panel and verify dead with a tested multimeter before terminating any conductors.

What This Chart Cannot Tell You (Edge Cases & Code Limits)

While the jacket color chart is your primary lookup tool, it does not account for physics or local jurisdiction amendments. Keep these three limitations in mind before loading your cart:

1. Voltage Drop Over Distance

The chart assumes standard run lengths. If you are running a 120V circuit more than 100 feet from the panel to a detached garage or shed, a 12 AWG yellow jacket will result in unacceptable voltage drop (exceeding the recommended 3% limit). In long-run scenarios, you must upsize the wire (e.g., using 10 AWG Orange on a 20A breaker) purely to maintain voltage, not to increase ampacity.

2. Conduit Fill and Heat Dissipation

Some DIYers attempt to use Romex inside PVC conduit for long underground or in-wall runs to 'protect' it. NM-B is not rated for the heat dissipation characteristics of long conduit runs. If you must sleeve NM-B through a short section of conduit (e.g., dropping down a block wall to a receptacle), the conduit must be sized large enough to prevent jamming, and you must calculate conduit fill based on the elliptical cross-section of the flat cable, not just the individual wires.

3. Local AHJ Amendments

The NEC is a model code; your local Authority Having Jurisdiction (AHJ) has the final say. Many municipalities in the US have amended the code to ban 14 AWG (White) entirely for residential branch circuits, mandating a minimum of 12 AWG (Yellow) for all 15A and 20A receptacle and lighting circuits to reduce fire risk and future-proof the home. Always check your local municipal building department's electrical amendments before buying white-jacketed cable.