NEC vs IEC Wiring Standards: What's the Difference?
A comparison of the US, European, UK and Australian electrical wiring standards
Electrical wiring standards vary significantly around the world. The NEC (US), IEC 60364 (Europe), BS 7671 (UK), and AS/NZS 3000 (Australia/New Zealand) all govern safe electrical installation, but they differ in wire sizing, voltage drop limits, color codes, and protection requirements. Understanding these differences is essential when working across jurisdictions or comparing international products.
NEC (National Electrical Code) — United States
The NEC, published by NFPA, is adopted by most US states. It uses the AWG (American Wire Gauge) system, where smaller AWG numbers mean larger wires. Standard residential voltage is 120/240V single-phase. NEC requires GFCI protection in wet locations, AFCI protection in bedrooms and living areas, and recommends a maximum 3% voltage drop on branch circuits. Conductors are rated at 60°C, 75°C, or 90°C; terminals on most residential equipment are rated for 60°C or 75°C.
IEC 60364 — Europe and International
IEC 60364 is adopted (with national amendments) throughout most of Europe, Asia, and Africa. It uses the metric mm² system for wire sizing. Standard European voltage is 230V single-phase, 400V three-phase. Wire is selected from IEC standard cross-sections: 1.5, 2.5, 4, 6, 10, 16, 25, 35, 50 mm², etc. Voltage drop limits are 3% for lighting and 5% for other circuits. IEC uses brown/blue/green-yellow for live/neutral/earth (post-2004).
BS 7671 — United Kingdom
BS 7671 (the IET Wiring Regulations) is the UK standard, closely aligned with IEC 60364 but with some differences. The UK uses 230V single-phase. BS 7671 specifies voltage drop limits of 3% for lighting and 5% for power, with the design target usually 4% combined. It requires residual current devices (RCDs, equivalent to GFCI) for socket circuits and bathrooms. BS 7671 also uses the IEC color scheme: brown (live), blue (neutral), green/yellow (earth).
AS/NZS 3000 — Australia and New Zealand
The Wiring Rules (AS/NZS 3000) govern electrical installation in Australia and New Zealand. Standard voltage is 230V single-phase, 400V three-phase. Wire sizes follow IEC mm² conventions. Maximum voltage drop is 5% from supply to point of use. AS/NZS requires residual current devices (RCDs) for socket outlets. It uses the IEC color scheme in new installations: brown (active), blue (neutral), green/yellow (earth).
Practical Comparison: Wire Size for 20A at 30m
For a 20 A circuit with a 30-meter one-way run at 3% drop limit: NEC selects AWG 10 (5.26 mm², 35 A ampacity) — voltage drop 2.5%. IEC selects 6 mm² (41 A ampacity) — voltage drop 1.7%, which is the next standard size above the calculated 4.0 mm² minimum. BS 7671 (4% limit) could use 4 mm² (32 A ampacity) — voltage drop 2.6%. AS/NZS (5% limit) can use 4 mm² as well. These differences illustrate why you must check the applicable standard for each jurisdiction.
FAQ
Can I use NEC wire in a European installation?
You should match the standard to the jurisdiction. AWG wire is not listed under IEC standards and vice versa. However, for calculation purposes, the cross-sectional area (mm²) is what matters physically. An AWG 10 wire at 5.26 mm² is close to IEC 6 mm² but not identical, and the ampacity tables differ. Always use wire listed and tested to the local standard.
Which standard has the most conservative (largest) wire requirements?
It depends on the circuit. NEC's 3% recommendation and 60°C ampacity column tend to require larger wires for long runs. IEC's 230V system reduces current for the same wattage, which can allow smaller wires compared to 120V NEC circuits carrying the same power. For three-phase systems, all standards allow significantly smaller wires due to the power factor advantage.
Do all countries follow IEC or NEC?
Most countries outside North America follow IEC 60364 or a national variant of it. The US, Canada, and Mexico primarily follow NEC (or the Canadian Electrical Code, which is closely related). Japan has its own code (JIS/JEAC) but uses a 100V system. Always verify the applicable standard for the country where the installation will be made.