In North America, the standard 120 volt color code for single-phase AC branch circuits is Black for Hot (Line), White for Neutral, and Bare or Green for Ground. This is mandated by the National Electrical Code (NEC) Articles 200 and 250. If you are wiring outside the US and Canada, the IEC standard applies (Brown for Live, Blue for Neutral, Green-Yellow for Earth). Never trust wire color blindly in older homes; always verify with a multimeter before touching a conductor.
The Complete 120 Volt Color Code Reference Table
The following spec-sheet-table defines the exact conductor colors, their physical terminal destinations on standard devices, and the NEC article governing their use. This applies to standard 120V, 15A and 20A residential and commercial branch circuits.
| Function | NEC Conductor Color | Allowed Alternatives | Device Terminal Screw | NEC Article |
|---|---|---|---|---|
| Hot (Line/Ungrounded) | Black | Red, Blue (in conduit) | Brass (Gold) | 200.2, 310.110(C) |
| Neutral (Grounded) | White | Gray, White with 3+ stripes | Silver | 200.2, 200.6 |
| Ground (Equipment Grounding) | Bare Copper | Green, Green with Yellow Stripe | Green | 250.118, 250.119 |
Regional Variants: NEC vs. IEC vs. Legacy UK
While the 120 volt color code above is standard in the US, Canada, and parts of South America, international projects or imported machinery may use different schemes. The IEC standard is technically designed for 230V nominal systems, but the same color codes apply to 120V control circuits and step-down transformer secondaries in industrial panels.
| Standard / Region | Hot / Live | Neutral | Ground / Earth | Where It Applies |
|---|---|---|---|---|
| NEC (US/Canada) | Black | White | Bare / Green | North American 120V/240V split-phase |
| IEC (Global/EU) | Brown | Blue | Green-Yellow | EU 230V, global industrial control panels |
| Old UK (Pre-2004) | Red | Black | Green | Legacy UK wiring (now harmonized to IEC) |
| Old US (Pre-1950s) | Black / Red | White / Gray | None (ungrounded) | Knob-and-tube, early cloth-braided NM |
If you are working on an imported piece of European equipment (like a CNC router or espresso machine) wired to IEC standards, do not assume the blue wire is safe to touch just because it resembles a US neutral. Always verify the machine's specific wiring diagram, as internal 120V step-down transformers may use local EU color codes on the secondary side.
The 'Rows People Get Wrong' Field Notes
Experienced electricians know that the NEC allows specific exceptions to the standard 120 volt color code. Misinterpreting these exceptions is the leading cause of shocks during DIY fixture swaps.
- Gray Neutrals in 120V: Gray is technically reserved for the neutral of 277V/480V systems. However, in commercial 120V control circuits pulled from a 480V panel, you may encounter gray neutrals. Treat gray exactly like white: it is a current-carrying grounded conductor.
- Red Wires in 120V Circuits: Red is rarely used in standard 12/2 NM-B cable. If you see a red wire in a 120V ceiling box, it is almost always the 'switched hot' returning from a wall switch, or a traveler in a multi-way switch setup. The black wire is likely the constant hot.
- Green vs. Bare: Both are equipment grounds. Bare copper is standard in residential NM-B (Romex) cable. Green insulation is used when pulling individual THHN wires in metal or PVC conduit. They are electrically identical and terminate on the same green busbar or device screw.
Decision Path: Choosing and Routing Your 120V Conductors
Use this decision-tree-table to select the correct cable and routing method for your specific 120V project. This terminates in a concrete material pick.
| Project Scenario | Environment | Required Action | Concrete Material Pick |
|---|---|---|---|
| Adding a standard 15A or 20A wall receptacle | Interior drywall, residential | Run non-metallic sheathed cable | 14/2 NM-B (15A) or 12/2 NM-B (20A) |
| Wiring a dedicated 120V workshop tool (e.g., lathe) | Garage, exposed studs | Run individual wires in protected raceway | 12 AWG THHN (Black, White, Green) in 1/2' EMT |
| Installing an outdoor 120V GFCI receptacle | Exterior, wet location, buried | Run direct burial cable or wet-rated conduit | 12/2 UF-B cable or THWN-2 in Schedule 80 PVC |
| Wiring a 120V control circuit inside an industrial panel | Inside a metal enclosure | Use flexible conduit and machine tool wire | 14 AWG MTW (Black, White, Green) in liquidtight |
Safe Interpretation When Markings Are Faded or Missing
In homes built before the 1960s, or in DIY-renovated properties, wire insulation may be faded, painted over, or entirely the wrong color. Never assume a wire's function based on color alone in an older home. According to Electrical Contractor Magazine, improper re-identification of conductors is a frequent code violation and a severe shock hazard.
To safely identify unknown 120V wires, follow this strict multimeter verification protocol. You must use a CAT III 600V (or higher) rated digital multimeter.
- De-energize and Open: Turn off the breaker. Open the junction box or device. Separate the wires so no bare copper is touching.
- Energize and Set Meter: Turn the breaker back on. Set your multimeter to AC Voltage (V~), ensuring the range is at least 200V.
- Test Hot to Ground: Place the black probe on the suspected hot wire and the red probe on a known, clean metal ground (like a metal box or the bare ground wire). A reading of 114V to 126V confirms it is the Hot conductor.
- Test Hot to Neutral: Keep the black probe on the confirmed Hot wire. Move the red probe to the suspected Neutral. You should read 114V to 126V.
- Test Neutral to Ground: Move the black probe to the suspected Neutral and the red probe to the known Ground. The reading must be less than 2V (ideally 0.0V to 0.5V). If you read 120V here, your 'neutral' is actually a hot wire, or you have an open neutral fault upstream.
- De-energize and Label: Turn the breaker off again. Verify dead. Apply colored electrical tape or heat shrink to properly re-identify the wires before terminating them.
Always terminate your work by torquing terminal screws to the manufacturer's specification (typically 12 to 14 in-lbs for standard 15A/20A receptacles) and ensuring no bare copper is exposed outside the terminal clamp. Color codes are your first line of defense, but a verified multimeter reading is your final authority.
