What is the NEC?
The NEC (National Electrical Code) is the standard for safe electrical wiring and equipment installation in the United States. It is published as NFPA 70 by the National Fire Protection Association, a non-profit standards body, and its purpose is to protect people and property from the hazards of electricity: shock, fire and arc flash. It sets the minimum requirements for how to size conductors and overcurrent devices, where protection such as GFCI and AFCI is required, how to ground and bond, how to calculate services and feeders, and much more.
The NEC is not a design manual or a training course. It tells you what an installation must achieve, not how to make it efficient or convenient, and its requirements are minimums. People often say “NEC code”, which is strictly a repetition, but everyone knows what it means. It was first published in 1897, and NFPA has sponsored it since 1911.
The NEC is a model code. NFPA has no power to enforce it; states, counties and cities adopt it by law, often with amendments, and their inspectors, the authority having jurisdiction, enforce the adopted edition. That is why two electricians a few miles apart can be working to different editions, and why a calculation should always state the edition it follows.
Not to be confused with: NFPA 70E (electrical safety at work), the Canadian Electrical Code (CEC, CSA C22.1), NEC Corporation (the Japanese electronics company) or the NEC exhibition centre in Birmingham, England.
How the NEC is organised
The NEC opens with an introduction, Article 90, which sets out its scope and how it is enforced, followed by nine chapters. Each chapter is divided into numbered articles, each article into sections. A reference such as 210.8(A)(1) reads as Article 210, section 8, subsection (A), list item (1). Chapters 1 to 4 apply to every installation; chapters 5, 6 and 7 add to or change those rules for special occupancies, equipment and conditions; chapter 8 covers communications systems and stands largely on its own; chapter 9 holds tables. Informative annexes at the back, such as the load calculation examples in Annex D, explain and illustrate but are not requirements.
| Chapter | Title | What it covers |
|---|---|---|
| 1 | General | Definitions (Article 100) and general requirements such as working space, equipment ratings and terminations (Article 110); from 2026 also load calculations (Article 120) |
| 2 | Wiring and Protection | Branch circuits, feeders, services, overcurrent protection, grounding and bonding, surge protection |
| 3 | Wiring Methods and Materials | Conductors and ampacity, boxes, cables such as NM and MC, raceways such as EMT and PVC |
| 4 | Equipment for General Use | Cords, switches, receptacles, panelboards, appliances, heating, motors, air conditioning, transformers |
| 5 | Special Occupancies | Hazardous locations, health care, places of assembly, agricultural buildings, marinas, RV parks |
| 6 | Special Equipment | Signs, elevators, welders, EV charging, pools and spas, solar PV, fire pumps |
| 7 | Special Conditions | Emergency and standby systems, interconnected power sources, energy storage, Class 1, 2 and 3 circuits, fire alarms |
| 8 | Communications Systems | Telephone, antenna, coaxial and network-powered broadband systems |
| 9 | Tables | Conduit fill, conductor properties, AC impedance, Class 2 and 3 power source limits |
Each section is mandatory language (“shall”), permissive language (“shall be permitted”) or an informational note. Informational notes explain and point elsewhere but are not enforceable: the familiar 3 % and 5 % voltage drop figures, for example, sit in an informational note (210.19 Informational Note in the 2023 edition), not in a rule.
The NEC articles electricians use most
Most everyday work touches a dozen or so articles. Section numbers below are from the 2023 edition unless stated; where an edition moved a rule, we show both.
| Article | Subject | Key rules | Tool or guide |
|---|---|---|---|
| 100 | Definitions | What “continuous load”, “dwelling unit” and “readily accessible” mean | — |
| 110 | Requirements for electrical installations | Working space (110.26), equipment ratings for fault current (110.9, 110.10), terminal temperature ratings (110.14(C)) | Available fault current calculator |
| 210 | Branch circuits | GFCI (210.8), AFCI (210.12), required receptacle outlets (210.52), 125 % for continuous loads (210.19(A)(1)) | GFCI requirements by edition |
| 215 | Feeders | Feeder sizing: 215.2(A)(1) in 2023, 215.4(A)(1) in 2026 | — |
| 220 (120 in 2026) | Load calculations | Dwelling load (220.41 in 2023, 120.41 in 2026), the optional method (220.82) | Residential load calculator |
| 230 | Services | Service conductors, disconnects, emergency disconnects (230.85), surge protection (230.67) | — |
| 240 | Overcurrent protection | Standard breaker and fuse ratings (240.6(A)), small-conductor limits (240.4(D)), tap rules (240.21) | — |
| 250 | Grounding and bonding | Grounding electrode conductor (250.66), equipment grounding conductor (Table 250.122), ground rods (250.53) | Ground wire size calculator |
| 310 | Conductors for general wiring | Ampacity (Table 310.16), ambient and bundling corrections, dwelling services (310.12) | Ampacity calculator |
| 314 | Boxes | Box fill (314.16) | Box fill calculator |
| 334, 358 | NM cable, EMT | The everyday wiring methods for homes and commercial work | Conduit fill calculator |
| 430, 440 | Motors; air-conditioning equipment | Motor full-load current tables, motor circuit sizing, nameplate MCA and MOCP on AC units | Wire size calculator |
| 450 | Transformers | Transformer overcurrent protection (450.3) and installation | How a transformer works |
| 625, 690, 705 | EV charging, solar PV, interconnection | EV supply equipment, PV system circuits, connecting generation to a service | — |
| Chapter 9 | Tables | Conduit fill (Chapter 9, Table 1), conductor properties (Table 8), AC impedance (Table 9) | Voltage drop calculator |
NEC editions: 2017, 2020, 2023 and 2026
The four editions still in use, with the changes most likely to affect your work:
NEC 2026
- Load calculations move from Article 220 to a new Article 120; energy management systems get Article 130.
- Dwelling unit load drops from 3 to 2 VA/ft² for services and feeders; the optional method’s first block falls from 10 to 8 kVA.
- EV chargers count at nameplate rating; continuous loads need not be counted at 125% in load calculations.
- 16 AWG copper enters Table 310.16 at 10 A; installations over 1000 V move to Articles 265 to 270.
- Outdoor dwelling outlets need GFCI protection up to 60 A.
NEC 2023
- Article 220 reorganised: the dwelling unit load gets its own section (220.41) and the lighting demand table becomes 220.45.
- First load-calculation rule for EV charging (220.57): the larger of 7,200 W or the nameplate rating.
- GFCI protection for every kitchen receptacle in a home and for twelve named appliances, including ranges and dryers; the device must be a listed Class A GFCI.
- 10 A added to the standard overcurrent device ratings, with new rules for 14 AWG copper-clad aluminum.
NEC 2020
- GFCI protection at homes extended to 250 V receptacles, all basements, damp and wet locations and outdoor outlets up to 50 A.
- Outdoor emergency disconnects for one- and two-family dwellings (230.85) and surge protection for dwelling services (230.67).
- Article 310 reorganised: the familiar ampacity table becomes Table 310.16 (it was Table 310.15(B)(16)).
- Lower general lighting unit loads for non-dwelling occupancies.
NEC 2017
- GFCI protection in non-dwelling buildings extended to receptacles up to 50 A single-phase and 100 A three-phase.
- Still the edition in force in Tennessee, and the basis for dwellings in a few states that adopt through the residential code.
The full list of calculation changes in the latest edition, with worked examples, is in 2026 NEC changes that affect your calculations, and every GFCI location from 2017 to 2026 is compared in GFCI requirements by edition.
How the NEC is written
The NEC is developed in public on a three-year cycle, and anyone may propose a change. Each cycle follows the same steps:
- Public input. Anyone submits proposed changes, with a reason, through NFPA’s online system.
- First draft. Code-making panels, made up of manufacturers, electricians and contractors, inspectors, utilities, insurers, testing laboratories and users, meet and act on every input.
- Public comment. The first draft is published, and anyone can comment on it.
- Second draft. The panels act on the comments and ballot the result; a correlating committee checks consistency across the code.
- Technical meeting and issue. Remaining disputes can be raised at NFPA’s technical meeting, and the Standards Council then issues the new edition.
Between editions, urgent fixes come as tentative interim amendments (TIAs) and errata. Because the process is open, the reasoning behind each change is published with the drafts, which is often the best explanation of what a new rule is for.
How NEC adoption works
Most states adopt the NEC statewide through an electrical board, fire marshal, labor department or building code council, typically a year or two after NFPA publishes an edition, and often with amendments. A few have no statewide electrical code for general construction and leave adoption to cities and counties. Some states adopt the NEC for commercial work but cover one- and two-family homes through the International Residential Code, which can mean a different edition for houses.
Our NEC adoption tracker lists the edition in force in every state, the District of Columbia and Puerto Rico, with effective dates, pending updates and official sources, and it is free to download as CSV or JSON. As of 2026-10-14, 9 states enforce the 2026 edition and 20 the 2023 edition, and 21 jurisdictions have a newer edition adopted or in review. Always check for local amendments too: large cities such as Chicago and New York City publish their own electrical codes.
Why the NEC edition matters in calculations
Editions differ in both numbers and section references. The same 2,000 ft² house calculates a few amperes lower under the 2026 NEC than under 2023 because the dwelling unit load dropped from 3 to 2 VA/ft². The rule for upsizing an equipment grounding conductor is 250.122(B) in 2023 and 250.122(D) in 2026. The ampacity table was Table 310.15(B)(16) in 2017 and Table 310.16 from 2020. Feeder conductor sizing moved from 215.2(A)(1) to 215.4(A)(1).
Every NEC calculator on electrician.wiki is edition-aware: pick 2017, 2020, 2023 or 2026 and both the numbers and the cited sections follow. When you open a calculator we preselect the edition used in your state, and any result you share carries its edition in the link. Start with the NEC wire size calculator, the dwelling load calculation or the conduit fill calculator.
NEC vs other electrical codes
| Code | Where | Published by | Revised |
|---|---|---|---|
| NEC (NFPA 70) | United States, and the basis for codes in several other countries | NFPA | Every 3 years |
| CEC (CSA C22.1) | Canada, adopted province by province | CSA Group | Every 3 years |
| BS 7671 | United Kingdom | IET and BSI | By amendment; currently 2018+A4:2026 |
| IEC 60364 | The international base for most national wiring rules outside North America | IEC | Part by part |
The NEC sizes conductors in AWG and kcmil from ampacity tables and protects people with GFCIs; IEC-based codes size cables in mm² from installation methods and correction factors and protect people with RCDs and disconnection times. The physics is the same, but numbers do not carry across. Our codes by country page compares them in more detail.
How to read the NEC
NFPA offers free read-only access to the current NEC online after registration, and sells printed, PDF and subscription versions, plus the NEC Handbook with commentary. Use the edition your jurisdiction has adopted, not simply the newest. Never rely on unofficial copies of the code text: they are often out of date, incomplete or missing amendments. On this site we summarise requirements in our own words and cite the section and the edition, so you can check the rule in the book your inspector uses.
Our NEC guides and tools
- NEC adoption by state: which edition applies where, with sources and downloads.
- 2026 NEC changes: Article 120, the 2 VA/ft² dwelling load, EV chargers and more.
- GFCI requirements by edition: every location and limit from 2017 to 2026.
- Grounding and bonding: Article 250 explained, with the GEC and EGC tables worked through.
- Residential load calculator: standard and optional methods for 2017 to 2026.
- Ampacity calculator and box fill calculator: Table 310.16 and 314.16, edition by edition.