The standard US wire color code for 120V/240V AC branch circuits uses black or red for hot (ungrounded), white or gray for neutral (grounded), and bare copper or green for ground (equipment grounding conductor). For standard ungrounded DC circuits, red is positive and black is negative. However, color alone is never a guarantee of safety; prior owners, imported machinery, and degraded insulation frequently violate the National Electrical Code (NEC). Always verify with a meter before touching a conductor.
The Complete US Wire Color Code Reference Table (NEC)
The following table outlines the standard conductor identification required by the National Fire Protection Association (NFPA) under NEC Articles 200, 210, and 250. This applies to standard US residential, commercial, and light industrial installations.
| Function | 120V / 208V / 240V AC | 277V / 480V AC | Ungrounded DC Power | Standard Screw Terminal |
|---|---|---|---|---|
| Hot 1 (Phase A) | Black | Brown | Red (Positive) | Brass / Gold |
| Hot 2 (Phase B) | Red (or Blue for 3-phase) | Orange (or Violet) | Black (Negative) | Brass / Gold |
| Hot 3 (Phase C) | Blue | Yellow | N/A | Brass / Gold |
| Neutral (Grounded) | White or Gray | White or Gray (with phase tape) | White (if grounded) | Silver |
| Ground (Equipment) | Bare Copper or Green | Bare Copper or Green | Green or Bare | Green |
Rows People Get Wrong & How to Read Faded Wires
Knowing the chart is only half the battle. In the field, you will encounter miswired panels, faded insulation, and non-standard configurations. Here is how to interpret the most commonly misunderstood rows and safely verify unknown wires.
The High-Leg Delta (Orange) Confusion
In a 240V 3-phase high-leg delta system (common in older commercial buildings), the B-phase winding has a center tap to ground. This creates a 'wild leg' that measures 208V to ground instead of the standard 120V. NEC 110.15 mandates this specific high-leg must be marked Orange. The mistake? Apprentices frequently confuse this 240V orange high-leg with the 277V/480V Phase B orange. If you land a 120V coil on a high-leg orange wire, the coil will violently fail. Always measure Phase-to-Ground on all three hots before terminating; if one reads ~208V, you have a high-leg delta.
Bootleg Grounds and Neutral Bonds
A 'bootleg ground' occurs when a previous worker jumpered the neutral (silver) screw to the ground (green) screw on a 3-prong receptacle to trick a tester. This is incredibly dangerous because if the neutral wire breaks upstream, the metal chassis of any plugged-in appliance becomes energized at 120V. To catch this, remove the receptacle cover and look for a bare copper wire or jumper bridging the silver and green screws.
Protocol for Faded or Missing Wire Markings
Old rubber-insulated wires (pre-1960s) often turn uniformly dark brown or black, making color identification impossible. Furthermore, THHN insulation in hot attics can fade or become brittle. When markings are compromised, follow this OSHA-compliant verification sequence using a digital multimeter (DMM) or a two-pole voltage tester (like a Fluke T+):
- De-energize and Isolate: Turn off the breaker and verify the circuit is dead. Separate all wire nuts and ensure no conductors are touching.
- Re-energize and Measure Hot-to-White: Turn the breaker back on. Measure between the known hot (black) and the unknown white wire. If it reads ~120V, the white wire is functioning as the neutral.
- Measure Hot-to-Ground: Measure between the hot and the bare/green wire. It should also read ~120V. If it reads 0V, you have an open ground or a miswired panel.
- Measure White-to-Ground: This is the critical test. It should read less than 2V (ideally <0.5V). If it reads 120V, the white wire is actually a hot conductor (likely a switch leg), and your actual neutral is missing or broken.
Regional & Standard Variants: NEC vs IEC vs Old UK
If you are wiring a home in the US, the NEC chart above is your law. However, if you are repairing imported European machinery (like a Festool dust extractor or a 3-phase CNC router), working on a boat with ABYC standards, or troubleshooting equipment in regions using IEC standards, the colors change drastically. Connecting a US 4-wire plug to an IEC-wired machine without tracing will cause a dead short if you tie the IEC Blue (Neutral) to the US Ground.
| Function | US / Canada (NEC / CEC) | Europe / UK / AU (IEC 60446) | Old UK (Pre-2004 BS 7671) |
|---|---|---|---|
| Phase 1 (Hot) | Black | Brown | Red |
| Phase 2 (Hot) | Red | Black | Yellow |
| Phase 3 (Hot) | Blue | Grey | Blue |
| Neutral | White or Gray | Blue | Black |
| Earth / Ground | Bare, Green, or Green/Yellow | Green with Yellow Stripe | Green |
When to Apply Which Standard
- US NEC: Applies to all fixed building wiring, branch circuits, feeders, and service entrances in the United States. Governed locally by the Authority Having Jurisdiction (AHJ). For deeper residential safety practices, refer to the Electrical Safety Foundation International (ESFI) wiring guidelines.
- IEC 60446: Applies to the internal wiring of imported machinery, European appliance cords, and fixed wiring in the UK, EU, Australia, and New Zealand. If you open a control panel on a German-manufactured lathe, expect Brown/Black/Grey/Blue.
- Old UK Colors: You will only encounter these in UK homes wired before April 2004. The most dangerous trap here is the neutral: Old UK used Black for neutral, but IEC uses Black for Phase 2 (Hot). If you are adding a new IEC-compliant circuit to an old UK consumer unit, you must sleeve the old black neutral wires with blue markers to prevent a future electrician from treating them as live phases.
Ultimately, wire color is a secondary identification method. The primary identification is always a physical measurement with a calibrated meter. Treat every conductor as live until you have personally verified its potential difference to a known ground.
