In US residential and commercial AC wiring governed by the National Electrical Code (NEC), the standard color code for a 120V/240V branch circuit is Black (or Red) for Hot, White (or Gray) for Neutral, and Bare Copper (or Green) for Equipment Ground. However, knowing the conductor colors is only half the battle; the outer jacket color dictates the wire type, temperature rating, and how you must calculate ampacity derating.

The Master AC Wiring Color Code Chart (NEC & IEC)

Bookmark Quick-Jumps: The most queried values on the bench are the 120V Hot (Black), Neutral (White), Equipment Ground (Bare/Green), and 240V Split-Phase Hots (Black and Red). If you are working with international equipment or IEC-compliant panels, note that the EU/UK standard flips the hot and neutral colors compared to the US.

How to read this table: The 'NEC (US/CA)' column applies to all installations governed by NFPA 70 in North America. The 'IEC 60446 (EU/UK)' column applies to European and modern British installations. The 'Notes' column highlights critical re-identification rules and common field exceptions. Always default to your local Authority Having Jurisdiction (AHJ) if regional amendments exist.
Table 1: AC Conductor Color Codes (Source: NFPA 70 / IEC 60446)
Function NEC (US / Canada) IEC 60446 (EU / UK) Field Notes & Exceptions
120V Hot (Line 1) Black Brown Always the primary ungrounded conductor.
240V Hot (Line 2) Red Black Used for split-phase 240V (US) or second phase in 3-phase.
Neutral (Grounded) White or Gray Blue Must be white/gray. Never use white for a hot wire without re-identification.
Equipment Ground Bare, Green, or Green/Yellow Green/Yellow Stripe Never carries current under normal operation. Green/yellow is globally recognized.
Switched Leg Any color except White/Green/Bare Brown or Black Often black or red. If using 2-wire cable, the white wire must be taped black.
3-Way Travelers Red, Black, or Blue Brown, Black, Gray No strict NEC color mandate, but red/black is standard practice for travelers.
3-Phase (Line 3) Blue (120/208V) or Yellow (277/480V) Gray US 3-phase colors vary by voltage class; verify with a meter before touching.

Wire Jacket Colors, Temperature Columns, and Derating

A common mistake among DIYers and junior apprentices is confusing conductor insulation color with cable jacket color. While conductor color tells you the circuit function, the outer jacket color of NM-B (Romex) or the insulation color of individual THHN wires in conduit tells you the temperature rating. This directly dictates which ampacity column applies to your installation and how derating rows modify your base value.

Which Column Applies to Your Installation?

NEC Table 310.16 provides ampacity columns for 60°C, 75°C, and 90°C. Here is the hard rule: Your termination points (breakers, lugs, receptacles) dictate your maximum allowable ampacity, not the wire itself. Most residential breakers and receptacles under 100A are rated for 75°C, but NEC 110.14(C) forces you to use the 60°C column for circuits rated 100A or less (which covers 14, 12, and 10 AWG wire) unless the equipment is explicitly marked otherwise. You can use 90°C wire (like THHN), but you must terminate at the 60°C or 75°C ampacity limit.

How Derating Rows Modify the Base Value

When you pull more than three current-carrying conductors in a single conduit, or when ambient temperatures exceed 86°F (30°C), you must apply derating factors per NEC 310.15. This is where the 90°C column saves your project.

The Derating Calculation: You apply the derating percentage to the 90°C column ampacity, not the 60°C column. If the resulting derated value is still higher than your 60°C termination limit, you can still use the wire at its 60°C ampacity. If the derated 90°C value drops below the 60°C limit, the derated value becomes your new, lower maximum.

Table 2: Wire Jacket / Insulation Colors & Derating Baselines
Wire Type / Jacket Color Conductor Insulation Base Temp Rating Derating Starting Point
White NM-B (14 AWG) Color-coded PVC 60°C (140°F) Derate from 60°C column. Highly restrictive in hot attics.
Yellow NM-B (12 AWG) Color-coded PVC 60°C (140°F) Derate from 60°C column. Standard for 20A branch circuits.
Orange NM-B (10 AWG) Color-coded PVC 60°C (140°F) Derate from 60°C column. Used for 30A dryers/water heaters.
Black/Red/Blue THHN Nylon-coated PVC 90°C (194°F) Derate from 90°C column. Ideal for conduit runs requiring bundling.
White/Gray THHN Nylon-coated PVC 90°C (194°F) Derate from 90°C column. Must be used for grounded neutral conductors.
Ambient Temperature Trap: If you run NM-B cable across ceiling joists in an attic that reaches 110°F (43°C), you must apply an ambient temperature correction factor. Because NM-B is limited to the 60°C column, a 12 AWG wire (20A base) derates to roughly 14.6A in a 110°F attic. You must upsize to 10 AWG or switch to 90°C THHN in conduit to maintain a legal 20A circuit.

What the Chart Cannot Tell You (Edge Cases & Field Realities)

Color code charts provide the baseline rules, but they do not account for legacy wiring, specific switching topologies, or multi-wire branch circuits. Here is what the table leaves out, and how to handle it on the jobsite.

1. Switch Loops and Re-Identification

In a standard switch loop powering a ceiling light, power arrives at the light fixture first. A 2-wire cable (e.g., 12/2 NM-B) drops down to the switch. By necessity, the white wire in that cable must be used as the hot feed down to the switch, and the black wire returns as the switched leg. NEC 200.7(C)(2) strictly requires that the white wire used as a hot must be permanently re-identified at both ends with black paint, tape, or a marker. If you open a junction box and see a white wire with black electrical tape wrapped around it, treat it as an ungrounded hot conductor.

2. Multi-Wire Branch Circuits (MWBC)

An MWBC uses two hot wires (typically Black and Red) on opposite phases of a 240V split-phase system, sharing a single White neutral wire. The chart tells you Black and Red are hot, but it doesn't warn you that the shared neutral carries the unbalanced load. If you are working on an MWBC, you must use a 2-pole breaker or approved handle ties. Turning off only the black wire's breaker leaves the red wire live, and the shared white neutral will still be carrying return current from the red circuit. Always measure neutral-to-ground voltage with a non-contact meter or multimeter before assuming a white wire is safe to touch.

3. Legacy and Knob-and-Tube Wiring

If you are working in a home built before 1950, discard the color code chart entirely. Early cloth-insulated wiring often used black for both hot and neutral, or faded colors that are now indistinguishable. Furthermore, old 3-way switch configurations often used white wires as travelers without re-identification. In these environments, you must map the circuit manually using a tone generator and a digital multimeter, verifying every single conductor's status before making splices.

4. The 'Traveler' Color Void

While the chart lists Red and Black for 3-way switch travelers, the NEC does not actually mandate a specific color for travelers. In commercial jobs using 12/3 or 14/3 NM-B, you will use the red and black. But in conduit pulls with THHN, an electrician might use Blue, Yellow, and Brown for travelers. Never assume a wire is a neutral just because it isn't black or red in a multi-gang switch box; always trace it or test it.