In North America (NEC), standard 120V/240V AC wiring uses black or red for hot, white or gray for neutral, and bare or green for ground. In Europe and the modern UK (IEC 60446), brown is live, blue is neutral, and green-and-yellow is earth. However, assuming a wire is safe based solely on its jacket color is a leading cause of residential electrical shock. The table below provides the exact mapping, followed by the critical exceptions and testing protocols you need to know before touching a terminal.
The Master AC Wiring Color Code Reference Table
The following spec-sheet-table maps the standard conductor functions across the four most common regional frameworks. Read the 'Function' column to understand the electrical role, then cross-reference your region's column to identify the correct insulation color.
| Function | US / Canada (NEC) | Europe / Intl (IEC 60446) | UK (Post-2004) | UK (Pre-2004) |
|---|---|---|---|---|
| Line 1 (Hot/Phase 1) Carries current from source to load. |
Black | Brown | Brown | Red |
| Line 2 (Hot/Phase 2) Second hot leg (240V or 3-phase). |
Red | Black | Black | Yellow |
| Line 3 (Hot/Phase 3) Third hot leg (3-phase systems). |
Blue | Grey | Grey | Blue |
| Neutral (Grounded) Carries return current; bonded to ground at service. |
White or Grey | Blue | Blue | Black |
| Ground / Earth (PE) Safety path for fault current; carries no normal load. |
Bare, Green, or Green/Yellow | Green/Yellow | Green/Yellow | Green |
Sources: NFPA 70 (National Electrical Code), IEC 60446 Standard.
Regional Variants and 'Rows People Get Wrong'
While the table above covers standard installations, real-world panels and junction boxes are full of code-mandated exceptions and historical legacy wiring. Here are the specific rows and scenarios where DIYers and junior electricians make dangerous assumptions.
The White Wire Switch Loop Exception (NEC)
In standard US residential wiring, a white wire is strictly a neutral. However, in older switch loops (where power goes to the light fixture first, then down to the switch), a 2-wire cable is used. The white wire in this cable is used as the hot feed down to the switch. Under NEC Article 200.6 and 404.2, this white wire must be re-identified with black tape or paint at both ends. If you see a white wire connected to a brass (hot) screw on a switch, do not assume it is a neutral.
The High-Leg Delta 'Orange' Wire (US 3-Phase)
In older US commercial buildings with a 240V 3-phase high-leg delta service, the B-phase (high leg) measures 208V to ground instead of the standard 120V. The NEC (Article 110.15) mandates this high leg must be colored orange. Connecting a standard 120V appliance between the orange high-leg and neutral will instantly destroy the appliance and create a fire hazard.
UK Pre-2004 vs Post-2004 Harmonization
The UK changed its wiring colors in 2004 to harmonize with European IEC standards. The most dangerous mix-up occurs when extending circuits in older homes. A pre-2004 black wire was a neutral, but in modern IEC wiring, a black wire is a Line 2 (hot). If you splice a new IEC blue neutral to an old UK black neutral without proper testing and labeling, you risk introducing a dead short or energizing a neutral bus bar. Always use a properly rated voltage tester to verify legacy UK wiring before making splices.
Safe Interpretation When Markings Are Faded or Missing
Insulation fades, painters tape falls off, and previous homeowners ignore color codes entirely. When you open a junction box and face a bundle of identically colored wires, or wires where the insulation is degraded, you must rely on measurement, not visual inspection. Follow this bench-and-jobsite proven sequence to identify unknown AC conductors safely.
- De-energize and Lock Out: Turn off the breaker supplying the circuit. Verify it is dead using a non-contact voltage tester (NCVT) and a digital multimeter (DMM) set to AC Voltage (>200V range). Test the DMM on a known live source first to prove the meter works (Live-Dead-Live test).
- Isolate and Separate: Disconnect all wires from the device (outlet/switch) and separate them so they do not touch each other or the metal box.
- Energize and Test for Hot: Turn the breaker back on. Use the NCVT to identify which wires trigger the alarm. Confirm with the DMM by measuring between the suspected hot wire and the bare metal grounding bus. A reading of 114V–126V (in a 120V system) confirms the ungrounded (hot) conductor.
- Identify the Neutral: With the hot wire identified, measure between the remaining unknown wires and the hot wire. The wire that reads 114V–126V is the neutral. (The ground wire will read 0V to 120V relative to the hot wire if the grounding system is intact, but you can distinguish it by checking continuity to the panel ground bus with the power OFF).
- Mark and Document: Once identified, immediately wrap the correct colored electrical tape (black for hot, white for neutral) around the wire at least three times, covering at least 1 inch of insulation, per NEC identification requirements.
AC Wiring Color Code FAQ
Can I use a white wire for a hot connection?
Yes, but only under specific conditions outlined in NEC Article 200.6. A white wire can be used as an ungrounded (hot) conductor in a switch loop, or in a multi-conductor cable (like 12/3 NM-B) where the white wire is used as a traveler or a second hot leg for a 240V appliance. However, you must permanently re-identify the white wire with black or red tape, paint, or heat-shrink tubing at every point where the insulation is visible. If you fail to re-identify it, the next person working on the panel will assume it is a neutral and risk a fatal shock.
What color is the ground wire in a 3-phase AC system?
The ground (equipment grounding conductor) color does not change based on the number of phases. In North America, it remains bare copper, green, or green-with-a-yellow-stripe. In IEC and modern UK standards, it is strictly green-and-yellow. The phase conductors (hots) change colors to accommodate the extra legs (e.g., Brown, Black, Grey in IEC), but the safety earth remains universally standardized to prevent catastrophic grounding errors.
Why does my outlet have a black, white, and red wire?
If you open a standard 120V duplex receptacle and find a black, a red, and a white wire (plus ground), you are likely looking at a split-receptacle circuit or a multi-wire branch circuit (MWBC). In a split-receptacle setup, the brass tab on the hot side of the outlet is broken off. The black wire feeds the top half (always hot), while the red wire feeds the bottom half (switched by a wall switch for a lamp). In an MWBC, the black and red wires are on two different breaker poles sharing a single white neutral. Always use a 2-pole breaker or handle tie for MWBCs to ensure both hot legs disconnect simultaneously.
Is it safe to mix NEC and IEC color codes in the same panel?
No. Mixing regional color codes in the same enclosure is a severe safety hazard and a direct violation of NEC Article 110.12, which requires neat and workman-like installation with clear identification. If you are integrating imported European machinery (wired with brown/blue IEC colors) into a US facility, you must transition the wiring at a dedicated junction box or disconnect switch. Use clearly labeled terminal blocks to step from IEC colors to NEC colors (e.g., Brown to Black, Blue to White), and apply permanent warning labels to the inside of the panel door indicating the presence of dual-standard wiring.
