In the United States, the National Electrical Code (NEC) strictly dictates the color code for electrical wiring in US residential and commercial installations to prevent shock hazards and ensure consistent troubleshooting. For standard 120/240V split-phase AC power, black and red are ungrounded (hot) conductors, white or gray are grounded (neutral) conductors, and bare copper or green are equipment grounding conductors.
However, wire colors change depending on the voltage class (such as 277/480V three-phase) and the specific application (like switch loops). Below is the definitive reference chart, followed by critical field exceptions that trip up even experienced DIYers.
The Complete US Electrical Wiring Color Code Table
The NEC (specifically Articles 200, 210, and 250) separates wiring colors by system voltage and current type. Use this table as your primary bench and jobsite reference. Note that these apply to the individual wire insulation inside a cable or conduit, not the outer jacket of NM-B (Romex) cables.
| Function | 120/240V AC (Single-Phase) | 277/480V AC (3-Phase Wye) | DC Power (Solar/Low Voltage) |
|---|---|---|---|
| Hot / Ungrounded (Line 1) | Black | Brown | Red (or Positive +) |
| Hot / Ungrounded (Line 2) | Red | Orange | Black (or Negative -) |
| Hot / Ungrounded (Line 3) | Blue (Rare in residential) | Yellow | N/A |
| Neutral / Grounded | White or Gray | Gray (White for 120V taps) | White or Gray |
| Equipment Ground | Bare Copper or Green | Bare Copper or Green | Bare Copper or Green |
Regional Variants & Standard Clashes (NEC vs. IEC vs. Old UK)
If you are importing machinery, working on RVs with international components, or reading schematics for imported electronics, you will encounter non-US color codes. The US relies on the NEC (NFPA 70), while most of the world uses IEC 60446. Mixing these up on a 240V control board can result in a dead short or a lethal shock.
| Conductor Function | US Standard (NEC) | EU / International (IEC 60446) | Old UK (Pre-2006) |
|---|---|---|---|
| Line / Hot (L1) | Black | Brown | Red |
| Line / Hot (L2) | Red | Black | Yellow |
| Line / Hot (L3) | Blue | Gray | Blue |
| Neutral (N) | White or Gray | Blue | Black |
| Earth / Ground (PE) | Green, Green/Yellow, or Bare | Green/Yellow | Green |
The Neutral Trap: Notice that in the IEC standard, Blue is the neutral wire. In the US, blue is occasionally used as a hot wire for 120/208V three-phase systems or as a traveler in complex switch loops. If you wire an imported European appliance assuming the blue wire is hot (US style), you will bond the chassis to the phase voltage.
The "Rows People Get Wrong" Field Notes
The NEC table above is the baseline, but real-world jobsite conditions and specific code exceptions create edge cases that cause failed inspections and tripped breakers. Here are the most common misinterpretations of the US color code.
1. The White Wire Used as a Hot Conductor
Under NEC Article 200.7(C)(1), a white wire can be used as an ungrounded (hot) conductor in specific scenarios, most notably in switch loops or when pulling 240V-only circuits (like a baseboard heater or water heater) using 2-conductor NM-B cable. The catch: The white wire must be permanently re-identified at every location where it is visible and accessible. You must wrap the ends with black or red electrical tape, or use heat-shrink tubing, to indicate it is carrying line voltage. If you open a switch box and see a white wire with no tape connected to a brass screw, assume it is hot.
2. Green vs. Bare Copper (Isolated Grounds)
While both green and bare copper serve as equipment grounding conductors, green insulation is specifically required when pulling an Isolated Ground (IG) through a metallic conduit. In hospitals or data centers (NEC Article 250.146(D)), an insulated green wire is run alongside the circuit to prevent stray high-frequency noise from traveling on the metal conduit back to the sensitive equipment. Never use a bare wire for an isolated ground circuit.
3. Faded THHN in Older Panels
If you are working in a commercial panel from the 1970s or 1980s, the PVC insulation on THHN wires often degrades, turning black, red, and white wires into a uniform, dirty gray. Safe interpretation: Do not guess. Treat every conductor as energized. Shut off the main breaker, verify the bus bars are dead with a tested multimeter (measuring phase-to-phase and phase-to-ground), and use a tone tracer or continuity tester to identify circuit origins before disconnecting anything.
Frequently Asked Questions
What is the color code for electrical wiring in US 240V circuits?
For standard residential 240V circuits (like electric dryers, ranges, or HVAC condenser units), you are using two hot legs of the split-phase system. The color code requires Black and Red for the two hot lines, White for the neutral (if the appliance requires 120V for controls, like a dryer timer), and Bare/Green for the ground. If the circuit is a pure 240V load (like a water heater) and uses 10/2 NM-B cable, the cable will contain a Black, a White, and a Bare wire. In this case, the white wire is acting as the second hot leg and must be marked with black tape at both the panel and the appliance connection.
Does the US color code for electrical wiring apply to 3-phase panels?
Yes, but the colors scale up. For standard 120/208V three-phase wye systems (common in US commercial strip malls and offices), the hot phases are Black, Red, and Blue, with White as the neutral. For higher voltage 277/480V three-phase systems (used for heavy HVAC and industrial lighting), the hot phases shift to Brown, Orange, and Yellow, with Gray as the neutral. The high-leg delta system (240V 3-phase) is a notorious exception: the "wild leg" or "high leg" (which measures 208V to ground instead of 120V) must be identified by Orange insulation per NEC 110.15, regardless of the overall system voltage.
How to test the color code for electrical wiring in US homes when faded or painted over?
Painters frequently spray over outlet wires, and heat degrades jacket colors over decades. To safely identify wires when colors are obscured:
1. Turn off the main breaker and verify zero voltage at the panel.
2. Disconnect the suspect wires from the device (outlet/switch).
3. Turn the main breaker back on (keeping branch breakers off).
4. Turn on one branch breaker at a time.
5. Use a non-contact voltage tester to find which wire energizes.
6. Turn the breaker off, verify dead, and use a multimeter in continuity mode to trace the wire back to its source. Always re-wrap the tested wires with fresh, correctly colored electrical tape before re-terminating.
Does the US color code for electrical wiring apply to low-voltage thermostat wire?
No. The NEC color codes apply to line-voltage (over 50V) power distribution. Low-voltage control wiring (like 18 AWG or 20 AWG thermostat wire, doorbell wire, or alarm sensor wire) follows manufacturer conventions, not the NEC. In standard 5-wire HVAC thermostat cable, Red is 24VAC power (R), White is heat (W), Yellow is cooling (Y), Green is the fan (G), and Blue/Black is the common (C). Always check the control board schematic on the specific furnace or air handler, as older systems may use entirely different color mappings.
