AC Wire Color Code Guide: US, UK, and EU Standards Explained

In the US (NEC), black is hot, white is neutral, and bare or green is ground. In the EU, UK, and Australia (IEC), brown is hot, blue is neutral, and green/yellow is ground. However, relying on a single regional chart is a fast track to a shock hazard, especially when dealing with legacy wiring, switch loops, or 240V appliance circuits where standard colors are intentionally repurposed. Below is the exact reference data you need to wire safely and legally.

Global AC Wire Color Code Standards (NEC vs. IEC)

The two dominant frameworks for AC wiring are the US National Electrical Code (NEC) and the International Electrotechnical Commission (IEC 60445) standard, which governs the EU, Australia, New Zealand, and the UK (post-2004). Use this table as your primary bench reference.

What these rows mean in practice:

• Line (Hot): Carries the full source voltage (120V/230V nominal) from the breaker to the load. Touching this while grounded will result in a severe shock.
• Neutral: The return path for current back to the transformer. While it is bonded to ground at the main service panel, it carries the same current as the hot wire under load. Never treat a neutral wire as a safe, de-energized conductor.
• Earth/Ground: A safety path that only carries current during a fault. It connects to the metal chassis of appliances to trip the breaker if a hot wire touches the case.

For authoritative code references, consult the NFPA 70 (National Electrical Code) for North American installations, or the IET BS 7671 Wiring Regulations for UK and IEC-aligned regions.

The 'Rows People Get Wrong' Trap

Memorizing the table above is only half the battle. The most dangerous electrical faults occur when standard colors are legally repurposed or when regional standards clash. Here are the specific rows and scenarios where DIYers and junior techs make critical errors.

240V Appliance Circuits (US/Canada)

When wiring a 240V baseboard heater, EV charger, or water heater using standard 2-wire NM-B cable, you are using both the black and white wires as hot legs (Line 1 and Line 2). There is no neutral in this circuit. The white wire must be re-identified with red or black phasing tape at the panel and the appliance terminal block. Failing to do so is a direct NEC violation and a massive shock risk for the next person working on the panel.

The Old UK vs. IEC Black Wire Clash

If you are working on a UK property wired before 2004 (or an older Commonwealth country that hasn't updated), a black wire is the Neutral. However, under the modern IEC 60445 standard used across the EU and modern UK, a black wire is Line 2 (Hot) in a 3-phase system, or sometimes used as a switched live. Mixing up legacy UK black (neutral) with modern IEC black (hot) will instantly energize a chassis you assumed was safe.

Solid Green vs. Green/Yellow Grounding

Historically, the US used solid green for equipment grounding, while the rest of the world used green with a yellow stripe. Modern NEC revisions now permit green/yellow, but you will still find solid green in older US panels. Never use solid green for a current-carrying neutral or hot conductor, as it is universally recognized as a safety ground.

Safely Identifying Wires When Colors Are Faded or Missing

In older homes, wire insulation degrades. White jackets turn yellow or brown from heat, bare copper oxidizes to dark green, and previous homeowners frequently paint over exposed Romex in basements. When visual color codes fail, you must rely on electrical verification.

Never assume a wire's function based on a faded jacket. Follow this verification sequence:

1. De-energize and Isolate: Turn off the main breaker or the specific branch circuit. Use a non-contact voltage tester (NCVT) on the outside of the cable, then open the junction box and test the exposed conductors. Verify the NCVT is working on a known live circuit before and after testing.
2. Visual Inspection and Stripping: If the outer jacket is painted or degraded, strip back 1 inch of the individual conductor insulation to expose clean copper. Do not rely on the color of the outer NM-B jacket; look at the inner insulation (though heat discoloration can still affect this).
3. Live Voltage Testing (Requires Extreme Caution): If you must identify an unknown circuit while energized, use a digital multimeter (DMM) set to AC Voltage (V~).
   • Measure Conductor A to Known Ground (e.g., a bare copper wire in the box or a metal junction box). If you read nominal line voltage (114-126V in the US, 220-240V in the EU), Conductor A is your Hot.
   • Measure Conductor B to Known Ground. If you read less than 2V, Conductor B is your Neutral. (Note: You may read 'phantom voltage' of 10-40V on a neutral due to capacitive coupling; a low-impedance DMM or a solenoid voltage tester like a Wiggy will bleed this off and read near zero).
   • Measure Hot to Neutral. You should read full nominal line voltage.
4. Re-identify Immediately: Once identified, wrap the correct colored vinyl electrical tape (e.g., 3M Super 33+) around the wire at the termination point and at the panel. If a white wire is confirmed as a hot leg in a switch loop, wrap it entirely in black tape at both ends.

Color codes are a vital first layer of safety, but they are only as reliable as the installer who pulled the wire. When in doubt, treat every conductor as energized until your meter proves otherwise.