In North America (NEC), a standard 4-wire electrical cable (like 14/4, 12/4, or 10/4 NM-B) uses Black (Line 1), Red (Line 2), White (Neutral), and Bare/Green (Ground). In Europe and the modern UK (IEC 60446), a 4-core cable typically uses Brown (Line 1), Black (Line 2), Grey (Line 3 or Neutral), and Green/Yellow (Ground). Because color codes dictate how current flows and where shock hazards exist, misinterpreting these colors is the fastest way to destroy an appliance or cause a fatal fault.
Below is the definitive reference for 4-conductor cables across major global standards, followed by the practical physics of how these wires behave in split-phase and 3-phase systems.
Master 4-Wire Color Code Reference Table
The table below maps the standard 4-wire configurations for residential split-phase (US/Canada), harmonized European/UK systems, legacy UK installations, and Australasian standards. Use this as your primary bench and jobsite reference.
| Conductor Function | US / Canada (NEC 120/240V) | EU & Modern UK (IEC 60446) | Old UK (Pre-2004) | Australia / NZ (AS/NZS 3000) |
|---|---|---|---|---|
| Line 1 (Hot / Phase A) | Black | Brown | Red | Red (or Brown) |
| Line 2 (Hot / Phase B) | Red | Black | Yellow (or Black) | White (or Black) |
| Neutral / Line 3 | White (or Grey) | Grey (or Blue for N) | Blue | Black (or Blue) |
| Equipment Ground | Bare Copper or Green | Green/Yellow Striped | Green/Yellow (or bare) | Green/Yellow Striped |
Note: In 3-phase Wye configurations (common in EU commercial and US light commercial), the 4th wire is the Neutral (White/Grey in NEC, Blue in IEC), and the Ground is run separately in conduit or as a 5th wire. The table above reflects the most common residential 4-core cable layouts.
What Each Conductor Actually Does in Practice
To troubleshoot or install a 4-wire cable, you need to understand the electrical physics of the circuit, not just memorize colors. Let us break down the standard US 10/4 NM-B cable used for a 240V electric dryer or range.
The Split-Phase Hot Legs (Black and Red)
In a US 120/240V split-phase system, the black and red wires are connected to opposite legs of the main service panel's bus bars. Each leg carries 120V relative to ground, but because they are 180 degrees out of phase, the potential difference between the black and red wires is 240V. The heating elements in your dryer or range use this 240V potential to draw high wattage without requiring massive current (amps), which allows you to use 10 AWG or 8 AWG wire instead of much thicker conductors.
The Neutral Return (White)
The white wire carries only the unbalanced return current. If your dryer uses 240V for the heating element but 120V for the control board, drum motor, and interior light, the white wire completes the 120V circuit. If Leg A (Black) draws 20A for the heater and the motor, and Leg B (Red) draws 20A for the heater, the neutral carries 0A. If the motor draws 3A on Leg A, the neutral carries exactly 3A back to the panel. It is sized to handle the maximum 120V load, not the full 240V load.
The Fault Path (Bare/Green)
The ground wire carries zero current during normal operation. Its sole purpose is to provide a low-impedance path back to the main bonding jumper in the panel. If a hot wire breaks and touches the metal chassis of the appliance, the ground wire allows enough current to flow instantly to trip the breaker. Never use the ground as a neutral return. The old practice of 'bootlegging' a 3-wire dryer cord to a 4-wire outlet by bonding neutral to ground at the appliance was banned by NEC 250.140 because a broken neutral would energize the appliance chassis with 120V.
Rows People Get Wrong & Faded Wire Troubleshooting
Color codes are useless if the installer broke the rules or if the insulation has degraded. Here are the most common field errors and how to safely verify your wires.
The 'Rows People Get Wrong' Gotchas
- Assuming White is Always Neutral: Under NEC 200.7(C)(2), a white wire in a cable assembly can be used as a hot (ungrounded) conductor if it is permanently re-identified with black tape or paint at every termination point. You will frequently see this in 240V baseboard heaters, AC disconnects, and 3-way switch travelers. Always test white wires with a meter before touching them.
- The Old UK Red/Black Trap: If you are working in a UK home wired before 2004, a red wire is Line (Hot) and a black wire is Neutral. If you treat this like a modern IEC or US cable and assume Black is a second Hot leg, you will create a dead short across 230V when you connect your device. The UK Health and Safety Executive (HSE) strictly outlines these transition hazards in older properties.
- Confusing 3-Phase Grey with Neutral: In commercial IEC 3-phase systems, Brown, Black, and Grey are all 400V phase conductors. Grey is not a neutral in a 3-phase motor feed. The neutral is strictly Blue.
Safe Interpretation Protocol for Faded or Unmarked Wires
When you open a junction box and find four wires where the colors are painted over, sun-faded, or covered in drywall mud, do not guess. Follow this exact multimeter protocol using a CAT III or CAT IV rated meter (like a Fluke 117):
- De-energize and Lock Out: Turn off the breaker and verify the panel is dead using a non-contact voltage tester (NCVT).
- Identify the Ground via Continuity: Set your multimeter to continuity (the diode/beep setting). Place one probe on the bare metal junction box or a known ground screw, and touch the other probe to each wire. The wire that reads less than 1.0 ohms (and beeps) is your Equipment Ground.
- Identify the Neutral via Resistance: With power still OFF, measure resistance between the remaining wires and the ground. The neutral will often show a very low resistance (a few ohms) back to the panel's neutral bus, while the hot legs will read infinite resistance (OL).
- Verify Hots with Live Voltage: Restore power. Set your meter to AC Voltage. Measure between the suspected Hot wires and the confirmed Ground. You should read nominal voltage (120V in the US, 230V in the EU/UK). Measure between the suspected Neutral and Ground; this should read less than 2V. If Neutral-to-Ground reads 120V, your neutral is open or broken upstream.
Regional Standards & Safe Interpretation Rules
Knowing which standard applies to your region prevents catastrophic wiring errors, especially when importing appliances or working on international equipment.
Which Standard Applies to You?
- North America (US & Canada): Governed by the NFPA 70 (National Electrical Code) and the Canadian Electrical Code (CEC). Standard residential 4-wire cables are NM-B (Romex) or THHN in conduit. Colors are strictly Black, Red, White, Green/Bare.
- Europe, UK, and Most of the World: Governed by IEC 60446 (now superseded by IEC 60445 but colors remain identical). Standard cables are PVC or LSZH (Low Smoke Zero Halogen). Colors are Brown, Black, Grey, Blue, Green/Yellow.
- Australia & New Zealand: Governed by AS/NZS 3000. While they have largely harmonized with IEC colors (Brown, Black, Grey, Blue, Green/Yellow) for new installations, older homes still feature the legacy Red, White, Black, Green scheme. Always test before trusting the colors in Australasian retrofits.
When to Stop and Call a Professional
If you open a panel or appliance junction box and find a 4-wire cable where the ground wire is being used as a current-carrying neutral, or where a white wire is feeding a 240V load without any black re-identification tape, you are looking at a code violation and a severe shock hazard. Local Authorities Having Jurisdiction (AHJ) require that any reconfiguration of service-level wiring, subpanel feeders, or permanent appliance hardwiring be performed or inspected by a licensed electrician. Use this reference to understand your system and diagnose faults, but defer to licensed professionals for final termination and code compliance.
