240V wire colours are the standardized insulation jackets applied to conductors to identify ungrounded (hot), grounded (neutral), and equipment grounding paths in split-phase or three-phase systems, ensuring safe termination and preventing dead shorts. Getting these colours right dictates exactly how your double-pole breaker, receptacle, and appliance lugs are terminated; swapping a hot for a neutral on a 240V circuit either trips the breaker instantly or, far worse, electrifies the appliance chassis and creates a lethal shock hazard. The most common confusion among DIYers is mixing up North American 240V split-phase colours (Black/Red/White/Green) with 208V three-phase (Black/Red/Blue), or incorrectly assuming international 230V/240V single-phase codes (Brown/Blue) apply to US and Canadian panels.
The Core Standard: North American 240V Split-Phase Colours
In North America, residential 240V is achieved via a split-phase system. The utility transformer provides two 120V legs that are 180 degrees out of phase. When measured across both legs, you get 240V; when measured from either leg to the neutral, you get 120V. The National Electrical Code (NEC) strictly mandates the insulation colours for these conductors to maintain uniformity and safety across all installations.
| Conductor Role | Standard Insulation Colour | Voltage Potential | Function in a 240V Circuit |
|---|---|---|---|
| Ungrounded (Hot 1) | Black | 120V to Neutral / 240V to Hot 2 | Carries the first half of the 240V load. |
| Ungrounded (Hot 2) | Red | 120V to Neutral / 240V to Hot 1 | Carries the second half of the 240V load. |
| Grounded (Neutral) | White (or Grey) | 0V to Ground | Carries only the unbalanced 120V return current. |
| Equipment Ground | Bare Copper or Green | 0V (unless faulted) | Provides a safe path for fault current to trip the breaker. |
Worked Numeric Example: Sizing and Colouring a 30A Dryer Circuit
To understand how these colours function under load, let us calculate and wire a standard 30-amp electric clothes dryer circuit.
Because the maximum overcurrent protection is 30A, we must use 10 AWG copper wire (rated for 30A at 60°C in NM-B cable). Here is how the colours route through the circuit:
- Black (Hot 1): Connects to one pole of the 30A double-pole breaker, runs through the 10/3 cable, and terminates on the L1 brass lug of the NEMA 14-30R receptacle.
- Red (Hot 2): Connects to the second pole of the breaker, runs through the cable, and terminates on the L2 brass lug of the receptacle. The 240V heating elements bridge across L1 and L2.
- White (Neutral): Connects to the neutral bar in the main panel, runs through the cable, and terminates on the silver neutral lug. It carries the 5A unbalanced return current for the 120V dryer motor. It does not carry the 30A heating load.
- Bare Copper (Ground): Connects to the equipment grounding bar, runs through the cable, and terminates on the green ground lug. It bonds the dryer chassis to earth.
If you mistakenly used a 10/2 cable (Black, White, Bare) and tried to use the White wire as your second hot without re-identifying it, the dryer's 120V motor would attempt to return current through the bare ground wire, creating an immediate shock hazard and violating OSHA electrical safety standards.
Where You Meet This In Practice
You will encounter North American 240V split-phase colour coding in specific high-load residential and light-commercial applications:
- Major Appliances: Electric ranges (50A, 6 AWG), clothes dryers (30A, 10 AWG), and built-in wall ovens. These almost always require the Black/Red/White/Bare configuration because they utilize both 240V for heating and 120V for electronics.
- HVAC Equipment: Central air conditioners and heat pumps. These are typically 'pure' 240V loads and only require Black/Red/Bare (no white neutral needed).
- EV Chargers: Level 2 Electric Vehicle Supply Equipment (EVSE). Most hardwired 48A chargers require 6 AWG Black/Red/Bare wire on a 60A breaker.
- Subpanels: Feeder cables running from a main panel to a subpanel (e.g., in a detached garage). These require all four colours (Black, Red, White, Green/Bare) to establish separate neutral and ground bars in the subpanel.
International Codes: UK, AU, and EU 230V/240V Single-Phase
If you are reading this from the UK, Australia, or the EU, your '240V' (nominally 230V in the EU/UK) is single-phase, not split-phase. The colour standards are entirely different, governed by IEC 60446 and regional adoptions. Confusing these with North American colours will result in catastrophic wiring errors.
| Region | Line (Hot) | Neutral | Earth (Ground) | System Type |
|---|---|---|---|---|
| UK / EU / AU (Current) | Brown | Blue | Green/Yellow Stripe | 230V/240V Single-Phase |
| UK / AU (Pre-2004/1966) | Red / Black | Black / White | Green / Green | Legacy Single-Phase |
| North America | Black / Red | White | Bare / Green | 120V/240V Split-Phase |
Notice that in the UK and Australia, Brown is the live wire carrying the full 240V potential. In North America, Brown is strictly reserved for Phase C in a 277V/480V three-phase commercial system. Never use IEC-coloured flex cable to wire a North American 240V hardwired appliance.
Decision Path: Which 240V Cable Do I Pull?
Use this decision tree to select the exact cable type and colour configuration for your 240V project. This assumes a standard North American residential split-phase system.
| Condition / Load Type | Required Conductors | Cable Type to Buy | Concrete Pick (Example) |
|---|---|---|---|
| Pure 240V Load (EV charger, baseboard heater, AC condenser, water heater) |
2 Hots + Ground (Black, Red, Bare) |
X/2 NM-B with Ground | Southwire 10/2 NM-B (for 30A) or 6/2 NM-B (for 50A) |
| Combo 240V/120V Load (Dryer, range, oven, subpanel feeder) |
2 Hots + Neutral + Ground (Black, Red, White, Bare) |
X/3 NM-B with Ground | Southwire 10/3 NM-B (for 30A) or 6/3 NM-B (for 50A) |
| Wet Locations / Conduit (Outdoor spa, underground feeder) |
Individual THHN/THWN wires pulled through PVC conduit | Individual THHN spools | Southwire THHN: Black, Red, White, Green (sized to ampacity) |
Frequently Asked Questions
Can I use a white wire as a 240V hot leg?
Yes, but only if you are using individual THHN wires in a conduit and you permanently re-identify the white wire with black or red electrical tape (or paint) at every termination point, as per NEC 200.7(C). If you are using NM-B (Romex) cable, you cannot re-identify the white wire inside the sheath; you must buy a cable that includes a black and red wire natively.
Why does my 240V baseboard heater only have Black, White, and Bare wires?
Many pure 240V heaters are manufactured with Black (Hot 1), White (Hot 2), and Bare (Ground). In this specific factory-wired scenario, the white wire is acting as a hot leg. You must connect the cable's white wire to the red wire of your branch circuit, and wrap black tape around the white wire at the junction box to mark it as a hot conductor.
Is 240V the same as 208V wire colour coding?
No. 208V is derived from a 120V/208V three-phase wye system, commonly found in commercial buildings. The standard colours for 208V three-phase are Black (Phase A), Red (Phase B), and Blue (Phase C). Connecting a 208V three-phase motor to a residential 240V split-phase (Black/Red) supply will result in the motor running at the wrong speed, overheating, and potentially burning out the windings.
Do I need a neutral for a 240V subpanel?
Yes. Even if you do not plan to use 120V circuits in the subpanel immediately, NEC Article 250.32 requires a four-wire feeder (Black, Red, White, Green/Bare) to a detached building. The neutral and ground must be kept strictly separate at the subpanel to prevent neutral return current from traveling over the equipment grounding conductor.
