In North America, black is hot, white is neutral, and bare or green is ground. In Europe and the post-2006 UK, brown is hot, blue is neutral, and green/yellow is ground. But relying on jacket color alone without testing is a leading cause of arc flashes and shock hazards. Installers frequently repurpose white wires as switched hots, and older homes may contain legacy color schemes that violate modern code. This reference provides the exact color codes for electrical wires across major global standards, highlights the specific rows where mistakes happen, and gives you a concrete decision path for identifying mystery wires.

The Master Wire Color Code Reference Table

The table below maps the standard conductor functions to their required insulation colors across the three major wiring frameworks. Use this as your primary bench and jobsite reference.

Conductor Function US & Canada (NEC) Europe & Modern UK (IEC 60446 / BS 7671) Old UK (Pre-2006)
Line / Hot (Single Phase) Black (or Red/Blue for multi-wire) Brown Red
Line / Hot (Phase 2 - 3-Phase) Blue (or Orange for high-leg delta) Black Yellow
Line / Hot (Phase 3 - 3-Phase) Red Grey Blue
Neutral (Grounded Conductor) White or Grey Blue Black
Earth / Ground (Equipment Grounding) Bare, Green, or Green/Yellow Green/Yellow Green (or Bare)
Switched Hot / Traveler Red, Black, Blue, Yellow (Never White/Green) Brown, Black, or Grey (with brown/black/grey sleeve) Red or Yellow
Safety Warning: Never assume a wire is dead based on its color. A white wire in a switch loop is often a 120V hot. Always de-energize the circuit, lock out the breaker, and verify with a tested CAT III or CAT IV multimeter or non-contact voltage tester (NCVT) before touching any conductor.

Regional Standards: Which Framework Applies to You?

Wire color mandates are not universal; they are dictated by the regional Authority Having Jurisdiction (AHJ) and the specific wiring standard adopted in your country.

North America: The National Electrical Code (NEC)

In the US and Canada, wire identification is governed by NFPA 70 (NEC), specifically Articles 200 (Use and Identification of Grounded and Grounding Conductors) and 250 (Grounding and Bonding). The NEC strictly reserves white, grey, and green for neutral and ground. However, it permits white to be used as an ungrounded (hot) conductor in specific scenarios, provided it is permanently re-identified at both ends.

Europe and the UK: IEC 60446 and BS 7671

Europe follows IEC 60446, which mandates brown (hot), blue (neutral), and green/yellow (earth). The UK historically used its own color code (red, black, green) but harmonized with the IEC standard in 2004, with a mandatory transition period ending in 2006. According to the UK Health and Safety Executive (HSE), any new installation or major modification must use the brown/blue scheme. If you are working in a UK home built before 2006, you will frequently encounter mixed color codes at the consumer unit, requiring extreme caution.

The 'Rows People Get Wrong' Field Notes

Even experienced DIYers and junior electricians misinterpret specific rows in the color code table. Here are the most common field errors and how to avoid them.

1. The 'White Wire as a Hot' Switch Loop

In a standard 3-way switch setup or a simple switch loop feeding a ceiling light, the 2-conductor NM-B cable running from the switch to the light contains one black wire and one white wire. The black wire brings 120V to the switch, and the white wire returns 120V to the light. That white wire is hot. NEC 200.7(C)(2) requires this white wire to be re-identified with black tape or paint at both ends, but in practice, installers frequently skip this step. If you measure 120V from a white wire to ground, it is a switched hot, not a neutral.

2. The High-Leg Delta 'Wild Leg' (Orange)

In commercial 3-phase high-leg delta systems (common in older US industrial buildings), the voltage to ground on Phase B is 208V, while Phases A and C are 120V to ground. NEC 110.15 mandates that this high leg must be identified with an orange outer finish. If you land a 120V single-phase load on the orange leg by mistake, you will instantly destroy the equipment and create a fire hazard.

3. Ground vs. Neutral Bonding Errors

People often confuse the green/bare ground wire with the white neutral wire because both read 0V to each other under normal load. However, the neutral carries return current, while the ground only carries current during a fault. Using a green wire as a current-carrying neutral in a conduit run is a severe code violation that will trip GFCI/AFCI breakers and can energize metal enclosures.

Decision Tree: Safely Identifying Faded or Miswired Cables

When you open a junction box and the colors are faded, painted over, or simply wrong, do not guess. Follow this decision-tree-table to safely identify the conductor's true function.

Visual Symptom Test Procedure (Power OFF / Power ON) Measurement Result Conclusion & Required Action
White wire is faded to gray or yellowed OFF: Test continuity to ground bar.
ON: Test voltage to ground.		 Continuity: >1 ohm.
Voltage: 120V.		 It is a Hot wire. Cap it, de-energize, and wrap it with black electrical tape to re-identify.
Red wire present in a standard 120V duplex receptacle box ON: Test voltage from red to white neutral. Voltage: 120V (switched) or 0V. It is a switch leg or traveler. If the receptacle isn't split-switched, cap the red wire with a wire nut.
Green wire used alongside black, white, and bare OFF: Test continuity from green to the load's ground pin. Continuity: <1 ohm. It is a redundant ground. If it reads continuity to a hot terminal, it is a dangerous miswire. Trace and replace.
All wires are black (e.g., in THHN conduit pulls) OFF: Use a tone generator or pull a continuity test to the panel. Tone matches breaker / Continuity to neutral bar. Identify via tracing. You must sleeve the neutral with white tape and ground with green tape at both ends per NEC 310.110.
Pro Tip: When testing continuity to identify a neutral, ensure all loads on the circuit are disconnected and the breaker is OFF. A connected load (like a smart switch or LED driver) will create a parallel path, giving you a false 'low resistance' reading on a hot wire.

Concrete Pick: Re-Identification Materials You Actually Need

When your decision tree dictates that a wire must be re-identified (such as marking a white switch-loop wire as hot, or sleeving a black THHN neutral), do not use cheap, off-brand vinyl tape. In a warm attic or a loaded panel, low-grade tape adhesive dries out, shrinks, and unravels within two years, leaving the next electrician with a mystery wire.

The Default Pick for Tape: 3M Scotch 35 Series Vinyl Electrical Tape. Specifically, buy the Scotch 35-Black (for re-identifying hots) and Scotch 35-Green (for grounds). Unlike standard black friction tape, the 35 series uses a pressure-sensitive rubber adhesive that resists UV and heat up to 221°F (105°C), and the colored vinyl itself won't fade or rub off like painted markers.

The Permanent Pick for THHN/Conduit: 3M EPS300 Adhesive-Lined Heat Shrink Tubing. Use a 3:1 shrink ratio in 3/16-inch or 1/4-inch diameter. When you apply heat, the inner meltable adhesive seals around the THHN insulation, creating a waterproof, permanent sleeve that will never slide off or unravel. It is the only method I trust for marking neutrals in commercial conduit runs.

Always terminate your troubleshooting with physical re-identification. If you figure out what a miscolored wire does, leave the panel or box safer than you found it by applying the correct 3M tape or heat shrink sleeve at both termination points.