240V wire colors are the standardized insulation color codes used to identify the ungrounded (hot), grounded (neutral), and equipment grounding conductors in a 240-volt electrical circuit. In North America, a standard 240V-only circuit uses black and red for the two hot legs, while a 120/240V circuit adds a white neutral and a bare or green ground. These color codes dictate how breakers are terminated, how receptacles are wired, and ensure safe identification of lethal voltage potentials during troubleshooting. DIYers and apprentices commonly confuse US 240V split-phase wiring with European 230/240V single-phase wiring, or mistakenly assume that all 240V appliances require a neutral wire.
The NEC Standard: US 240V Split-Phase Colors
In the US and Canada, residential 240V power is delivered via a split-phase system. The utility transformer center-taps a 240V secondary winding, providing two 120V legs that are 180 degrees out of phase with each other. If 120V is the water pressure from a single municipal pump pushing through a pipe, 240V split-phase is like having two identical pumps pushing against each other from opposite ends, doubling the pressure across the load in the middle.
The National Electrical Code (NEC) strictly governs these colors to prevent catastrophic miswiring. Here is the standard color matrix for US residential 240V circuits:
| Conductor Role | Standard Insulation Color | Alternative / Allowed Colors | NEC Article Reference |
|---|---|---|---|
| Ungrounded (Hot Leg 1) | Black | Red, Blue, or any color except white/gray/green | 200.7, 210.5 |
| Ungrounded (Hot Leg 2) | Red | Black (must be re-identified if in same cable), Blue | 200.7, 210.5 |
| Grounded (Neutral) | White | Gray, or white with a colored stripe (for larger feeders) | 200.2, 200.6 |
| Equipment Ground | Bare Copper | Green, or Green with a Yellow stripe | 250.119 |
Worked Numeric Example: Wiring a 30A Electric Dryer
Let's look at a real-world installation to see how these colors and wire sizes interact. Suppose you are running a new circuit for a standard electric clothes dryer, which requires a 120/240V NEMA 14-30 receptacle. This appliance needs both 240V for the heating element and 120V for the drum motor and control board.
The Setup:
- Breaker: 30-Amp, double-pole (takes up two slots in the panel).
- Cable: 10/3 NM-B (Non-Metallic Sheathed Cable), which contains a black, red, white, and bare copper wire.
- Receptacle: NEMA 14-30R (4-prong: X, Y, W, G).
The Wiring Sequence:
- Black Wire (Hot 1): Connects to one of the brass terminals on the double-pole breaker. At the receptacle, it terminates on the 'X' (Hot 1) blade.
- Red Wire (Hot 2): Connects to the second brass terminal on the breaker. At the receptacle, it terminates on the 'Y' (Hot 2) blade. The potential difference between Black and Red is 240V nominal.
- White Wire (Neutral): Connects to the silver neutral bus bar in the panel. At the receptacle, it terminates on the 'W' (Neutral) blade. This provides the 120V return path for the motor.
- Bare Wire (Ground): Connects to the green grounding bus bar (or bonded neutral bar in a main panel). At the receptacle, it terminates on the 'G' (Ground) pin.
Ampacity and Temperature Column Reality Check: You might look at a wire chart and see that 10 AWG THHN wire is rated for 35A or 40A. However, NEC Article 334.80 mandates that NM-B cable ampacity must be determined using the 60°C column of Table 310.16, regardless of the 90°C rating of the individual THHN conductors inside the sheath. In the 60°C column, 10 AWG copper is strictly limited to 30A. Therefore, a 30A breaker is the absolute maximum for 10/3 NM-B. If your run exceeds 100 feet, you must calculate voltage drop and likely upsize to 8 AWG to keep the drop under 3%.
Where You Meet This In Practice
You will encounter 240V color coding in several specific home and workshop scenarios, each with slight variations based on whether a neutral is actually required.
Hardwired Water Heaters (240V Only): Standard tank water heaters do not require 120V for controls; they use 240V thermostats. Therefore, they do not need a neutral. You will typically use 10/2 NM-B (Black, White, Bare) or 12/2 NM-B for a 20A unit. Because the white wire is being used as an ungrounded hot conductor, NEC 200.7(C)(2) requires you to re-identify the white wire with black or red electrical tape, or paint, at both the panel and the heater junction box. Failing to tape the white wire is one of the most common DIY code violations.
EV Chargers (NEMA 14-50 vs Hardwired): A 50A EV charger circuit uses 6 AWG copper (or 4 AWG aluminum). If installed as a NEMA 14-50 receptacle, you must run a 4-wire setup (Black, Red, White, Bare) because the plug standard includes a neutral pin, even if the EV charger internally ignores it. If hardwired directly into a wallbox that only requires 240V, you can omit the neutral and run 6/2 cable, taping the white wire black at both ends.
HVAC Disconnects: Central air conditioners and heat pumps use 240V compressors. The outdoor disconnect box will typically receive two hot wires (Black and Red, or Black and Black-taped) and a ground. The neutral is usually not required to pass through the outdoor disconnect unless the unit has a 120V crankcase heater or control board that requires it.
International (IEC) and Three-Phase 240V Variants
If you are reading schematics for imported machinery, working in Europe, or dealing with commercial three-phase power, the US NEC colors do not apply. The International Electrotechnical Commission (IEC) standard 60446 governs colors in the UK, EU, and many other regions.
In the UK and EU, residential power is single-phase 230V (nominal, often referred to as 240V historically). The colors are entirely different:
- Line (Hot): Brown
- Neutral: Blue
- Earth (Ground): Green with Yellow stripe
The 240V Delta 'High Leg' Warning: In older US commercial buildings or specific industrial setups, you might encounter a 240V three-phase Delta system. In this configuration, two legs measure 120V to ground, but the third leg (the 'high leg' or 'wild leg') measures 208V to ground. Per NEC 110.15, this high leg must be identified by Orange insulation (or orange tape). Connecting a standard 120V load to the orange high leg will instantly destroy the appliance and create a severe fire hazard.
Frequently Asked Questions
Can I use a white wire as a hot on a 240V circuit?
Yes, but only under specific conditions. If you are using a 2-wire cable with a ground (like 10/2 NM-B) for a pure 240V load like a baseboard heater, the white wire must serve as the second hot leg. NEC 200.7(C)(2) strictly requires you to re-identify the white wire at every point where it is visible and accessible. You must wrap it with black or red electrical tape, or paint it, at both the breaker panel and the device junction box. You cannot leave it white, as future workers will assume it is a neutral.
Does a pure 240V circuit like a baseboard heater need a neutral wire?
No. A purely 240V resistive load (like baseboard heaters, well pumps, or standard water heaters) only requires two ungrounded hot conductors and an equipment grounding conductor. The current flows back and forth between the two 120V legs that are 180 degrees out of phase. Adding a neutral wire to a circuit that doesn't use 120V is a waste of copper and requires an unnecessary termination point in the panel.
Why does my old 240V range cable have a bare neutral instead of an insulated white?
Prior to the 1996 NEC revision, ranges and dryers were allowed to use a 3-wire setup where the bare equipment ground was also used as the neutral return path. This was a known shock hazard because if the bare wire broke, the chassis of the appliance could become energized at 120V. Modern code requires a 4-wire setup (separate insulated neutral and bare ground) for all new installations. If you are replacing an old range, you must either install a new 4-wire receptacle and cord, or follow the specific retrofit grounding rules in NEC 250.140.
What color is the high leg on a 240V delta system?
The high leg (or wild leg) on a 240V center-tapped delta three-phase system must be colored Orange. This is mandated by NEC 110.15. The high leg measures 208V to ground, while the other two phases measure 120V to ground. Electricians use orange to visually warn anyone working in the panel that this specific phase cannot be used for standard 120V single-phase branch circuits.
