In the US, the National Electrical Code (NEC) mandates black or red for ungrounded (hot) conductors, white or gray for grounded (neutral) conductors, and bare copper or green for equipment grounding conductors in standard 120V/240V AC branch circuits. However, global standards differ significantly, and real-world jobsite conditions often present faded, re-purposed, or misidentified wires that require careful verification.
The Complete NEC Wire Color Code Reference Table
The table below maps standard AC power circuit functions to their required insulation colors across the three major wiring standards. Use this as your primary bench and jobsite reference when identifying conductors in panels, junction boxes, and device enclosures.
| Function | NEC (US / Canada) | IEC 60446 (EU / Global) | Old UK (Pre-2004) |
|---|---|---|---|
| Hot (Line 1) | Black | Brown | Red |
| Hot (Line 2) | Red (or Blue for 277V/480V) | Black | Yellow |
| Hot (Line 3) | Blue (or Yellow for 277V/480V) | Grey | Blue |
| Neutral (Grounded) | White or Grey | Blue | Black |
| Ground (Equipment) | Bare Copper or Green | Green with Yellow Stripe | Green |
Rows People Get Wrong (and How to Fix Them)
While the table above is the baseline, real-world wiring often deviates due to specific NEC exceptions, multi-wire branch circuits (MWBC), or previous DIY mistakes. Here are the specific scenarios where the standard color code misleads people.
1. 240V Appliances Using 12/2 NM-B Cable
When wiring a 240V baseboard heater or a window AC unit using standard 12/2 NM-B (Romex) cable, the circuit requires two hot legs and a ground, but no neutral. The cable contains a black wire, a white wire, and a bare ground. In this scenario, the white wire is acting as an ungrounded (hot) conductor. According to NEC 200.7(C)(1), this white wire must be permanently re-identified at every point where the cable terminates (both at the panel and the device) using black electrical tape or black paint. A common, dangerous mistake is leaving the white wire unmarked, leading a future worker to assume it is a safe neutral.
2. Switched Legs and 3-Way Travelers
In a standard single-pole switch loop (common in older homes wired before the 2011 NEC update required a dedicated neutral at switch boxes), the white wire carries hot power up to the switch, and the black wire carries the switched hot down to the light. The white wire here is hot. For 3-way and 4-way switches, the "traveler" wires connecting the switches can technically be any color except white, gray, green, or bare. While red and black are standard for travelers, you will frequently encounter blue, yellow, or even purple THHN wires in conduit acting as travelers.
3. Multi-Wire Branch Circuits (MWBC)
An MWBC shares a single neutral (white) wire between two hot legs (black and red) that are on opposite phases (240V between them). If you disconnect the shared white neutral while one of the hot legs is still energized, the neutral wire becomes energized at 120V through the connected loads. Never assume a white wire is safe to touch just because it is white; always verify it is dead at the termination point.
Safe Interpretation When Markings are Faded or Missing
On the bench or in older homes, you will encounter wires where the insulation has faded, become brittle, or is completely missing. In homes built between the 1920s and 1950s using cloth-sheathed wiring, the original black and white rubber insulation often degrades into identical shades of muddy brown. Here is the professional protocol for identifying unknown conductors.
- De-energize and Verify: Turn off the main breaker or the specific branch circuit. Use a non-contact voltage tester (NCVT) followed by a digital multimeter (DMM) to confirm 0V between the suspected conductor and a known ground.
- Continuity Testing (Dead Circuit): If the wires are disconnected at both ends, use the continuity setting on your DMM. Connect a long jumper wire to one end of the mystery wire and test for continuity at the other end. This is the safest way to map out faded knob-and-tube or old cloth NM cables without energizing them.
- Voltage Testing (Live Circuit): If you must test an energized circuit to find a lost neutral, use a CAT III rated DMM. Measure Line-to-Ground (should read ~120V) and Line-to-Neutral (should read ~120V). Then measure Neutral-to-Ground. A true, healthy neutral will read less than 1V (often 0.1V to 0.5V) relative to ground under normal load. If Neutral-to-Ground reads 120V, you have an open neutral, and that white wire is currently carrying the full return current and is highly dangerous.
- Re-Identification: Once identified, immediately apply colored heat-shrink tubing or high-quality vinyl electrical tape (like 3M Super 33+) to re-establish the proper NEC color code. Do not rely on masking tape or office tape, which dries out and falls off within a year.
Frequently Asked Questions
Can I use white wire for hot if I tape it black?
Yes, but with strict conditions. Under NEC 200.7(C)(1), you can re-identify a white or gray grounded conductor to serve as an ungrounded (hot) conductor, but it must be permanently re-identified at every location where the conductor is visible and accessible. A single wrap of black tape at the panel is a code violation if the other end inside a junction box or device enclosure remains white. Furthermore, for conductors 4 AWG or larger, re-identification is permitted at the time of installation, but for smaller wires (like 14, 12, or 10 AWG in NM-B cable), you cannot simply strip the white insulation off; you must tape or paint over the existing white insulation.
What color is the ground wire in a 1960s house?
If the house was wired in the early 1960s with early versions of NM-B (Romex) with a ground, the equipment grounding conductor will be a bare copper wire. If the house was wired with individual THHN/THWN conductors pulled through metal conduit (EMT or rigid), the ground wire will have green insulation. However, many homes built in the 1950s and early 1960s used ungrounded NM cable (only black and white wires) or relied on the metal conduit itself as the ground path. If you open a 1960s outlet box and see only black and white wires, assume there is no equipment ground unless you can verify continuity from the box to the panel ground bus using a DMM.
Does the NEC wire color code apply to DC and low voltage?
The standard NEC color codes in the table above apply primarily to AC power and light circuits (Articles 210, 215, 220). For DC systems, such as solar photovoltaic (PV) arrays governed by NEC Article 690, the rules differ. While red and black are industry standards for DC positive and negative, NEC 690.41 requires specific identification for PV source and output circuits. For low-voltage data and control wiring (like Ethernet, RS-485, or 24V AC thermostat wire), the NEC does not mandate specific colors, but industry standards (like TIA/EIA-568 for network cables) dictate the color pairs to prevent crosstalk and ensure proper pinouts.
Why is my neutral wire reading 120V to ground?
If you measure 120V between a white neutral wire and a bare copper ground, you have an "open neutral" condition. This means the neutral wire is disconnected somewhere between your testing point and the main panel's neutral bus bar. Because the circuit's hot wire is still connected to a load (like a lightbulb or appliance), the 120V potential is passing through the load and energizing the disconnected neutral wire. This is an extreme shock hazard. Turn off the breaker immediately and trace the circuit to find the broken wire nut, failed backstab connection, or loose terminal screw causing the open circuit.
