Electrical Standards

Practical guides to the electrical codes and standards engineers, installers, and students use most: the US NEC, IEC standards, UK BS 7671, and IEEE/ANSI design practice. Start with the guides below, or browse every article underneath.

NEC (US) Guides

• NEC Article 240: Overcurrent Protection, including 240.4(D) small conductor limits and a breaker sizing chart
• NEC Article 250: Grounding and Bonding, including Tables 250.66 and 250.122
• Neutral to Ground Voltage (NEC)
• Phase to Phase Clearance per NEC / NFPA 70E

IEC, BS 7671 and International Standards

• Neutral to Earth Voltage Acceptable Limits (IEC)
• Neutral to Earth Voltage per BS 7671 (UK)
• Clearance and Creepage Distance per IEC 60664
• IEC vs AS/NZS Testing Standards

High-Voltage Clearances and Spacing

• 66kV Phase to Phase Clearance
• 220kV Phase to Phase Clearance
• 400kV Phase to Phase Clearance
• 765kV Phase to Phase Clearance
• Phase to Phase Clearance for ANSI/IEEE (69-500 kV)
• Phase Spacing for Substations, Busbars and Overhead Lines

Which Standard Applies to You?

NEC (NFPA 70) governs most electrical installations in the United States and is adopted state by state, so check which edition your jurisdiction enforces. IEC standards (such as IEC 60364 and IEC 60664) are the basis for national codes in much of Europe, Asia, and the Middle East. BS 7671 is the UK wiring regulation, built on IEC principles. IEEE and ANSI standards cover utility and substation design practice. When a project crosses regions, always confirm the code adopted by the local authority.

All Electrical Standards Articles