In electrical wiring, a 'voltage color code' does not mean stripes on a wire tell you its exact voltage rating like a resistor's bands indicate ohms. Instead, it refers to the insulation color standard used to identify the system voltage class, phase, and function. For standard US residential 120/240V split-phase systems, the voltage color code dictates Black and Red for hot legs, White for neutral, and Green/Bare for ground. For commercial 277/480V three-phase systems, the code shifts entirely to Brown, Orange, Yellow, Gray, and Green.

⚠️ MAINS VOLTAGE SAFETY WARNING: Never rely solely on wire color to determine if a circuit is dead. Colors can be miswired, faded, or repurposed. Always de-energize the breaker, apply lockout/tagout (LOTO), and verify the circuit is dead using a known-working CAT III or CAT IV digital multimeter or non-contact voltage tester before touching any conductor. Local codes may require a licensed electrician for panel work.

The Master Voltage & Phase Color Code Table

The table below maps the exact insulation colors required for the most common AC voltage systems. This is your primary reference for pulling wire through conduit or terminating a new subpanel. Note that these colors apply to the insulation of individual conductors (like THHN/THWN-2 in conduit), not necessarily the outer jacket of a cable assembly (like NM-B/Romex), though the internal conductors follow the same logic.

System Voltage & Phase Phase A (L1) Phase B (L2) Phase C (L3) Neutral (N) Ground (PE) Governing Standard
120/240V Split-Phase (US Residential) Black Red N/A White Green / Bare NEC (NFPA 70)
120/208V 3-Phase (US Commercial) Black Red Blue White Green / Bare NEC (NFPA 70)
277/480V 3-Phase (US Industrial) Brown Orange Yellow Gray Green / Bare NEC (NFPA 70)
230/400V 3-Phase (EU / UK / AU) Brown Black Gray Blue Green/Yellow Stripe IEC 60446
230V Single-Phase (EU / UK / AU) Brown N/A N/A Blue Green/Yellow Stripe IEC 60446
Old UK Colors (Pre-2006) Red (L1) / Yellow (L2) / Blue (L3) (See L1/L2/L3) Black Green / Bare BS 7671 (Legacy)

Sources: Electrical Construction & Maintenance (ECM) on NEC Color Coding; The IET Wiring Regulations (BS 7671 / IEC alignment).

Rows People Get Wrong (And How to Fix Them)

Misinterpreting a voltage color code doesn't just trip a breaker; it destroys equipment and creates lethal shock hazards. Here are the most common mistakes made on the bench and in the field:

1. The White vs. Gray Neutral Mix-Up

In the US, White is strictly the neutral for 120V and 208V systems. If you are wiring a 277/480V system, the neutral must be Gray. Using a white wire for a 277V neutral is a direct NEC violation (Article 215.12). If a technician later assumes that white wire is a 120V neutral and touches it while it's carrying 277V return current, the result is fatal. Always stock gray THHN when pulling 480V feeders.

2. The Orange Wire Identity Crisis

Orange means two completely different things depending on the transformer feeding your panel:

  • In a 277/480V system: Orange is Phase B (the middle phase).
  • In a 120/240V High-Leg Delta system: Orange is the 'wild leg' or 'high leg' (usually Phase B), which measures 208V to ground instead of the standard 120V. Connecting a standard 120V appliance to this orange wire will instantly fry the appliance's power supply.
Pro-Tip: If you see an orange wire in a US panel, immediately grab your multimeter and measure from that orange wire to the ground bar. If it reads ~208V, you are looking at a High-Leg Delta. If it reads ~277V, you are in a 480V Wye system.

3. Blue in IEC vs. NEC

If you are working on an imported European machine (IEC 60446), Blue is the Neutral. However, if you are wiring a US 120/208V commercial panel (NEC), Blue is Phase C (a hot leg carrying 120V to ground). Never assume a blue wire is safe to touch just because you are used to European appliance wiring standards.

Regional Standards: Which Code Governs Your Bench?

Your physical location and the origin of the equipment you are wiring dictate which voltage color code you must follow. Presenting a single region's practice as universal is a recipe for failed inspections.

  • NEC (NFPA 70): Applies to the United States, and heavily influences Canada (CEC) and parts of Latin America. If you are pulling wire in a US jurisdiction, NEC Article 210.5 (branch circuits) and 215.12 (feeders) are your legal requirements. Note that the NEC does not strictly mandate phase colors for 120/208V or 120/240V systems nationally, but Black/Red/Blue and Black/Red are the universally enforced industry standards that local AHJs (Authorities Having Jurisdiction) expect to see.
  • IEC 60446 / HD 308 S2: Applies to the European Union, the United Kingdom (via BS 7671), Australia, New Zealand, and much of Asia/Africa. This standard is strictly enforced and highly harmonized. The Green/Yellow striped earth wire is sacred; using green/yellow for anything other than protective earth is a severe violation.
  • Legacy / Old UK Colors: If you are troubleshooting a UK/AU home built before 2006 (or 2000 in AU), you will encounter Red (Live) and Black (Neutral). Treat old black wires as hot if they are part of a switch loop, and always verify with a meter, as color transitions in junction boxes are notoriously messy.

Faded, Missing, or Non-Standard Markings: Safe Interpretation

On the jobsite, you will frequently open a junction box to find wires where the insulation has faded to a dirty off-white, or where a previous handyman used a white wire as a hot leg and forgot to wrap it in black electrical tape. Here is the exact decision path for safe interpretation when markings fail:

  1. Isolate and De-energize: Turn off the main breaker for the panel feeding the box. Verify dead at the panel.
  2. Perform a Continuity Test: With power off, use your multimeter's continuity/beep setting. Identify the ground wire by testing continuity between the bare/green wire and the metal box or a known grounding electrode. This is your only trusted reference point.
  3. Energize and Measure (Line-to-Ground): Turn the breaker back on. Keeping one probe firmly on the verified ground, touch the other probe to each unknown wire.
    • Reads 0V: This is likely your neutral (or a disconnected hot).
    • Reads 120V / 230V (Nominal System Voltage): This is a hot/line conductor, regardless of its faded color.
    • Reads 208V / 277V / 400V: You are in a multi-phase system and measuring a high-leg or line-to-line bleed.
  4. Re-Mark the Wire: Once identified, de-energize again and wrap the ends of the wires with properly colored phase tape (e.g., black tape on a faded hot wire, white tape on a verified neutral) to restore the voltage color code for the next technician.

Decision Tree: Picking the Right Wire Color for Your Next Run

Stop guessing at the supply house. Use this decision path to determine exactly which spools of THHN/THWN-2 to buy for your next conduit pull.

IF your project is... AND the system voltage is... THEN buy these exact THHN colors:
Residential Subpanel / Range / Dryer 120/240V Split-Phase Black, Red, White, Green
Commercial Office Receptacles / Lighting 120/208V 3-Phase Wye Black, Red, Blue, White, Green
Industrial Motor / HVAC Rooftop Unit 277/480V 3-Phase Wye Brown, Orange, Yellow, Gray, Green
Exporting a control panel to the EU/UK 230/400V 3-Phase Brown, Black, Gray, Blue, Green/Yellow
Low Voltage Control / DC Electronics < 50V AC / < 120V DC Red (VCC/+), Black (GND/-), Yellow/Blue (Signals)

The Default Recommendation: If you are a US-based hobbyist or DIYer working on a standard home workshop addition, your default pick is always Black (Hot), White (Neutral), and Green/Bare (Ground) for 120V circuits, adding Red only when you are explicitly wiring a 240V split-phase load like a welder outlet or water heater. Never use green or bare copper for anything other than equipment grounding, and never use white for a hot leg without permanently re-identifying it with black phase tape at every termination point.