When you strip back a jacket of NM-B cable or pull THHN through a conduit, the insulation colors are not random manufacturer choices. They are strict legal designations defined by the National Electrical Code (NEC) in the US and IEC 60446 internationally. The direct answer for standard US 120V/240V AC residential wiring is: Black, Red, or Blue for hot (ungrounded); White or Gray for neutral (grounded); and Bare, Green, or Green/Yellow for ground (equipment grounding).
However, mixing up US and European standards, or AC and DC conventions, can lead to catastrophic faults or failed inspections. This reference guide provides the master wire color code chart, explains how to read the columns, and clarifies what this chart can and cannot tell you about your circuit.
The Master Wire Color Code Chart (NEC & IEC Standards)
| Standard / System | Function | Mandatory / Standard Colors | Common Use Case |
|---|---|---|---|
| US NEC AC (120/208V) | Hot (Ungrounded) - Phase A | Black | Standard 120V branch circuits, switches |
| US NEC AC (120/208V) | Hot (Ungrounded) - Phase B | Red | 240V appliances, 3-way traveler wires |
| US NEC AC (120/208V) | Hot (Ungrounded) - Phase C | Blue | 3-phase commercial panels |
| US NEC AC (All) | Neutral (Grounded) | White or Gray | Return path for 120V/277V circuits |
| US NEC AC/DC (All) | Ground (Equipment Grounding) | Bare, Green, or Green/Yellow | Fault current path, panel bonding |
| US NEC AC (277/480V) | Hot (Ungrounded) - Phases A, B, C | Brown, Orange, Yellow | High-voltage commercial/industrial 3-phase |
| US NEC DC | Positive (Ungrounded) | Red (or White with red stripe) | Solar PV strings, battery banks, automotive |
| US NEC DC | Negative (Grounded/Ungrounded) | Black (or White with black stripe) | Solar PV return, DC load negative |
| IEC AC (EU/UK/AU) | Hot (Line) - Single or 3-Phase | Brown, Black, Gray | Standard 230V/400V international wiring |
| IEC AC (EU/UK/AU) | Neutral | Blue | International 230V return path |
| IEC AC/DC (All) | Protective Earth (Ground) | Green/Yellow Stripe | International fault current path |
Applying the Chart: Derating, Columns, and Limitations
Knowing the colors is only the first step. You must know how to apply this wire color code chart to your specific physical installation and understand its boundaries.
Which Column Applies to Your Installation?
If you are wiring a residential home, commercial building, or standard solar array in the United States, you must strictly follow the US NEC AC or US NEC DC columns. The IEC columns apply if you are working in Europe, the UK, Australia, or importing pre-wired machinery (like a European CNC router or solar inverter) that must be integrated into a local system. Never mix IEC blue (neutral) with US blue (Phase C hot) in the same panel.
The 'Derating Rows' Misconception
When consulting electrical reference tables, you might be searching for how derating rows modify the base value. It is a common point of confusion to mix up electrical tables. Derating rows modify base ampacity values in wire sizing charts (like NEC Table 310.16), adjusting current capacity for ambient heat or conduit bundling. A wire color code chart contains no derating rows because a wire's legal color designation is absolute; it does not scale, degrade, or change based on environmental factors or conduit fill. If you are calculating breaker size, you need an ampacity chart, not this color reference.
What This Table Cannot Tell You
This chart dictates function, not capacity. What this table cannot tell you is the wire’s insulation rating (THHN vs. XHHW), its voltage limit (300V NM-B vs. 600V THHN), or its physical ampacity. A 14 AWG black wire and a 2 AWG black wire share the exact same color code but carry vastly different loads (15A vs. 95A+). Always verify the wire gauge and insulation stamp printed on the jacket alongside the color.
Common Edge Cases and Code Exceptions
The NEC provides specific exceptions where standard colors can be repurposed, provided they are properly re-identified.
- White Wire as a Hot (Switch Legs & Travelers): In older switch loops, or when using standard 2-wire or 3-wire NM-B cable for 3-way switches, you may be forced to use the white wire as a hot traveler or switch leg. NEC Article 200.7(C)(2) permits this only if the white wire is permanently re-identified at both ends with black or red electrical tape or heat shrink. (Note: NEC 2011 and later requires the white wire to be used as the hot feed down to the switch, and the black wire as the switched hot up to the light, eliminating the need to re-identify the white wire in standard single-pole loops).
- Multi-Wire Branch Circuits (MWBC): When running a 240V circuit split into two 120V legs sharing a single neutral, you must use Black and Red for the two hot legs, and White for the shared neutral. The two hot breakers must be on opposite phases and tied together with a handle tie or a 2-pole breaker to prevent overloading the neutral.
- High-Leg Delta Systems: In older commercial 240V 3-phase Delta systems, the 'wild leg' or 'high leg' (which measures 208V to neutral instead of 120V) must be colored Orange, regardless of the standard phase sequence. This is a strict NEC 110.15 requirement to prevent electricians from accidentally connecting 120V single-phase loads to a 208V phase.
Wire Color Code Chart FAQ
Can I use white wire for a switch leg or traveler without taping it?
Under modern NEC rules (2011 and newer), if you are wiring a standard single-pole switch loop using 2-wire NM-B cable, the white wire must be used as the constant hot feed down to the switch, and the black wire is used as the switched hot returning to the light. In this specific configuration, the white wire is naturally functioning as a hot and does not require black tape. However, if you are wiring a 3-way switch and using the white wire in a 3-wire cable as a traveler, you must re-identify it with black or red tape at both termination points.
What color is the ground wire in older homes or knob-and-tube wiring?
Homes built before the 1960s (often using knob-and-tube or early ungrounded NM cable) typically do not have an equipment grounding conductor at all. If a ground wire was retrofitted later, it might be bare copper, green, or occasionally a mismatched color if installed improperly. If you open an outlet box and find only a black and a white wire with no bare or green wire, the circuit is ungrounded. You cannot simply swap in a 3-prong outlet; you must either run a new ground wire back to the panel, or install a GFCI outlet labeled 'No Equipment Ground' to meet NEC 406.4(D)(2) safety requirements.
Does the wire color code chart apply to low-voltage thermostat or data cables?
No. The NEC color code chart applies to line-voltage power circuits (Class 1). Low-voltage wiring, such as thermostat cables (Class 2), ethernet, or alarm systems, falls under NEC Article 725 and Article 800. Thermostat wire typically uses 18 AWG solid conductors in Red (24VAC hot), White (heat call), Yellow (cooling call), Green (fan call), and Blue (common). While these colors are industry standard for HVAC, they are not legally mandated by the NEC in the same strict manner as line-voltage power conductors.
