Wire Color Code Reference
Overview
NEC-compliant wire color identification for residential and light-commercial systems. Quick-reference for techs who work across both new construction (clean color discipline) and renovation (where prior owners' "creative" wiring undermines every color assumption). Mis-identifying a conductor causes shock injuries and equipment damage - when in doubt, verify with a meter, never assume from color.
Reference Table
Single-phase 120/240 V (standard residential)
| Conductor | Color | Notes |
|---|---|---|
| Hot (line 1) | Black | Common general-purpose hot |
| Hot (line 2) | Red | Second hot leg on 240 V circuits, or switch leg |
| Hot (additional) | Blue | Used as switch traveler or third hot |
| Neutral (grounded) | White or gray | Carries return current at zero potential |
| Equipment ground | Bare copper or green | Bonded to panel ground bus |
| Switch leg (re-marked) | Often white with black tape | Older code; flag any white wire feeding a switch loop |
Three-phase 120/208 V (light commercial)
| Conductor | Color | Notes |
|---|---|---|
| Phase A | Black | |
| Phase B | Red | |
| Phase C | Blue | |
| Neutral | White or gray | |
| Equipment ground | Green or bare |
Three-phase 277/480 V (commercial)
| Conductor | Color | Notes |
|---|---|---|
| Phase A | Brown | |
| Phase B | Orange | High leg on 240 V high-leg deltas (per NEC 110.15) |
| Phase C | Yellow | |
| Neutral | Gray | |
| Equipment ground | Green |
Low-voltage (24 V controls, doorbells, thermostats)
| Conductor | Color | Notes |
|---|---|---|
| Red | Power (R or RH on thermostats) | |
| White | Heat call (W) | |
| Yellow | Cooling call (Y) | |
| Green | Fan call (G) | |
| Blue or black | Common (C) | |
| Orange / Brown | Reversing valve (O or B) on heat pumps |
Notes
- Re-marked white wires: NEC permits identifying a white wire as a hot conductor by wrapping it with electrical tape (black or red) - but ONLY in cable assemblies (Romex / NM-B) where you can't easily swap conductor colors. Loose-conductor circuits should never have a re-marked white. If you see one in a junction box, treat the entire installation with suspicion and verify every other conductor with a meter.
- Orange "high leg": In old 240 V high-leg delta systems (rare but still in service in some industrial-zoned homes), phase B is the "wild" leg at 208 V to ground. Treating this as a normal 120 V circuit will destroy whatever you plug into it.
- Aluminum branch wiring (1965 - 1973) uses the same color code but the wire is silver instead of copper. Aluminum-to-copper connections require COPALUM or AlumiConn connectors per NEC; standard wire nuts are a fire hazard.
- Knob-and-tube (pre-1950) often has cloth-insulated wires with no color discipline. Verify every conductor; replace whenever the wire is exposed during other work.
Color is a clue, not a guarantee. Always verify with a meter before contact, especially on renovation work. The DIY homeowner who wired a sub-panel "right" by their own logic has caused more electrician injuries than every utility lineman job combined.
References
- NEC Article 200.6 (Identification of Grounded Conductors)
- NEC Article 200.7 (Use of Grounded Conductor)
- NEC Article 210.5 (Identification of Branch Circuits)
- NEC Article 250.119 (Identification of Equipment Grounding Conductors)