A wire color code standardizes the function of electrical conductors to prevent shock hazards, short circuits, and equipment damage. Because global standards differ drastically, assuming a wire's function based on a single region's rules can be fatal. Below is the master reference for North American, modern European, and legacy UK systems.
The Master Wire Color Code Reference Table
The following table maps conductor functions to their mandated insulation colors across the three most common residential and commercial frameworks. Always verify your local jurisdiction's adopted code before terminating any connections.
| Conductor Function | NEC (US & Canada) | IEC 60446 (EU & Modern UK) | Old UK (Pre-2004 BS 7671) |
|---|---|---|---|
| Protective Earth (Ground) | Green, Green/Yellow Stripe, or Bare | Green/Yellow Stripe | Green/Yellow Stripe (or Bare in very old installs) |
| Neutral (Grounded Conductor) | White or Gray | Blue | Black |
| Line 1 (Hot / Phase 1) | Black (120/208V) or Brown (277/480V) | Brown | Red |
| Line 2 (Hot / Phase 2) | Red (120/208V) or Orange (277/480V) | Black | Yellow |
| Line 3 (Hot / Phase 3) | Blue (120/208V) or Yellow (277/480V) | Gray | Blue |
| High-Leg Delta (Wild Leg) | Orange (Mandated by NEC 110.15) | N/A (Rare in EU) | N/A |
For detailed code requirements, refer to the National Fire Protection Association (NFPA) NEC guidelines or the Institution of Engineering and Technology (IET) BS 7671 standards for UK installations.
Rows People Get Wrong (and How to Fix Them)
Even experienced DIYers and junior electricians misinterpret specific color code edge cases. Here are the most common points of failure on the jobsite.
White vs. Gray Neutrals in Commercial Panels
In residential 120V/240V systems, white is universally neutral. However, in commercial 277V/480V three-phase systems, the OSHA and NEC mandate gray for the neutral. This prevents a 277V neutral from being accidentally spliced to a 120V neutral in a shared junction box, which would instantly overload the 120V neutral and cause a fire. If you are pulling wire in a commercial building, buy gray THHN for your neutrals.
The 208V vs. 480V Three-Phase Trap
Notice in the NEC column that Line 1, 2, and 3 change colors depending on the system voltage. Black/Red/Blue is strictly for 120V/208V systems. If you are wiring a 277V/480V system, the hots must be Brown/Orange/Yellow. Mixing these up during a panel retrofit can lead to catastrophic equipment failure if a 208V motor is accidentally fed 480V.
High-Leg Delta (The Orange Wild Leg)
Found in older commercial buildings, a high-leg delta transformer provides 120V/240V three-phase power. Two of the phases measure 120V to neutral, but the third phase (the "wild leg" or "high leg") measures 208V to neutral. The NEC strictly requires this high leg to be identified by an orange wire (or orange phase tape). If you connect a standard 120V appliance between the orange leg and neutral, the appliance will explode.
Safe Interpretation When Markings Fade or Go Missing
When working on legacy knob-and-tube, sun-faded THHN in conduit, or old cloth-covered Romex, the original insulation color may be completely illegible. Here is the professional workflow for identifying mystery conductors.
- Isolate and De-energize: Shut off the main breaker if the specific branch circuit cannot be positively identified.
- Perform a Continuity Test: With the power OFF, use a multimeter in continuity mode. Disconnect the suspected neutral from the bus bar and test it against the ground bus. A reading near 0 ohms indicates it is likely a neutral or a bonded ground.
- Beware of Phantom Voltage: When testing faded wires in metal conduit or MC cable with a high-impedance digital multimeter, you may read 40V-60V on a completely dead wire due to capacitive coupling from adjacent live wires. Switch your meter to "LoZ" (Low Impedance) mode, or use an old-school solenoid tester (like a Wiggy), which ignores phantom voltage.
- Apply Phase Tape: Once you have positively identified a conductor's function using a tone generator or live-testing (with proper PPE), you must re-identify it. NEC 310.12 requires that re-identification be done with colored electrical tape or sleeving at every point the conductor is accessible (both ends and every junction box splice).
Frequently Asked Questions
Can I use white wire for hot if I wrap it in black tape?
Yes, but with strict limitations. Under NEC 310.12(A)(1), you are permitted to re-identify a white or gray wire as a "hot" (ungrounded) conductor only if it is part of a multiconductor cable (like 12/2 or 14/2 NM-B Romex). You must wrap it with black or red phase tape at both the panel and the device end. However, if you are pulling individual THHN wires through conduit, you cannot pull a white wire and tape it; you must purchase properly colored THHN.
What is the wire color code for 240V split-phase appliances?
For heavy appliances like electric dryers, ranges, or subpanels in the US, you are dealing with 240V split-phase. The standard color code is:
- Hot 1: Black
- Hot 2: Red (or a second Black wire)
- Neutral: White (required if the appliance has 120V control boards, timers, or lights)
- Ground: Bare copper or Green
Why does my older house have white wires connected to switches?
This is a legacy "switch loop." Prior to the 2011 NEC update (which required a dedicated neutral wire in every switch box for smart switches), electricians used 2-wire cables to drop power from a ceiling fixture down to a wall switch. The black wire carried the switched hot up to the light, and the white wire was used to bring the constant hot down to the switch. Because it was functioning as a hot wire, code required it to be taped black. In older homes, electricians often skipped the tape. If you see a white wire connected to a single-pole switch, treat it as an ungrounded hot conductor and test it accordingly.
