NEC Code Quick Reference Guide
A quick-reference guide to the most commonly cited National Electrical Code (NEC) articles. Built for electricians, inspectors, and electrical engineers who need to look up code sections fast — with links to the calculators that put them into practice.
What Is the NEC?
The National Electrical Code (NFPA 70) is the benchmark for safe electrical design, installation, and inspection in the United States. Published by the National Fire Protection Association (NFPA), the NEC is updated on a three-year cycle — the current edition is NEC 2023.
Most states adopt the NEC as law, sometimes with local amendments. Whether you're pulling a permit, studying for a journeyman exam, or designing a commercial installation, knowing which NEC article applies is the first step to getting it right.
Most-Used NEC Articles — Quick Reference
| Article | Title | What It Covers | Related Calculator |
|---|---|---|---|
| 90 | Introduction | Scope, purpose, enforcement of the NEC | — |
| 100 | Definitions | Terms used throughout the NEC | — |
| 110 | Requirements for Electrical Installations | Working space, terminal ratings (110.14), conductor termination temperatures | — |
| 210 | Branch Circuits | Branch circuit ratings, GFCI/AFCI requirements, outlet spacing | Branch Circuit Calculator |
| 215 | Feeders | Feeder sizing, voltage drop considerations | Voltage Drop Calculator |
| 220 | Branch-Circuit, Feeder, and Service Load Calculations | Demand factors, load calculations, dwelling unit calculations | Load Calculation Calculator |
| 225 | Outside Branch Circuits and Feeders | Outside feeders, clearances | — |
| 230 | Services | Service entrance conductors, disconnects, overcurrent protection | Service Entrance Calculator |
| 240 | Overcurrent Protection | Breaker and fuse sizing, tap rules | Breaker Size Calculator |
| 250 | Grounding and Bonding | Equipment grounding, grounding electrode system, bonding | Grounding Calculator |
| 300 | General Requirements for Wiring Methods | Conductor routing, conduit requirements, underground wiring | Conduit Fill Calculator |
| 310 | Conductors for General Wiring | Wire ampacity (Table 310.16), temperature ratings, derating | Wire Ampacity Chart |
| 314 | Outlet, Device, Pull, and Junction Boxes | Box fill calculations, box sizing | — |
| 334 | Nonmetallic-Sheathed Cable (NM/Romex) | NM cable installation, permitted uses, securing requirements | — |
| 344–362 | Raceways (EMT, IMC, RMC, PVC, etc.) | Conduit types, fill limits, support spacing | Conduit Fill Calculator |
| 404 | Switches | Switch connections, grounding requirements | — |
| 406 | Receptacles, Cord Connectors, and Attachment Plugs | Receptacle ratings, tamper-resistant requirements | — |
| 408 | Switchboards, Panelboards, and Distribution Boards | Panel schedules, clearances, labeling | Panel Schedule Calculator |
| 410 | Luminaires, Lampholders, and Lamps | Lighting fixture installation, clearances | Lighting Calculator |
| 422 | Appliances | Appliance circuits, disconnects | — |
| 424 | Fixed Electric Space-Heating Equipment | Baseboard heaters, unit heaters, duct heaters | — |
| 430 | Motors, Motor Circuits, and Controllers | Motor FLC, overload protection, conductor sizing | Motor Starting Calculator |
| 440 | Air-Conditioning and Refrigerating Equipment | A/C circuit sizing, disconnects | — |
| 445 | Generators | Generator conductor sizing, disconnects, grounding | Generator Sizing Calculator |
| 480 | Batteries and Battery Systems | Battery room requirements, disconnect requirements | — |
| 690 | Solar Photovoltaic Systems | PV system wiring, grounding, disconnects, rapid shutdown | Solar System Calculator |
| 700 | Emergency Systems | Emergency power wiring, transfer switches, selective coordination | Emergency System Calculator |
| 705 | Interconnected Electric Power Production Sources | Utility interconnection, backfeed protection | — |
| Ch. 9 | Tables | Conduit fill areas, conductor properties, wire areas | Conduit Fill Calculator |
NEC Key Tables You Should Know
Table 210.21(B)(3)
Receptacle ratings for various circuit sizes (e.g., 15A receptacle on a 20A circuit).
Table 220.12
General lighting loads by occupancy type (VA per square foot).
Table 250.66
Grounding electrode conductor sizing based on largest service-entrance conductor.
Table 250.122
Minimum equipment grounding conductor sizing based on overcurrent device rating.
Table 310.16
Conductor ampacity — the most referenced table in the entire NEC. View Ampacity Chart →
Table 314.16(A)
Metal box fill — maximum number of conductors allowed per box size.
Table 430.250
Motor full-load currents for three-phase motors at various voltages.
Table 430.248
Motor full-load currents for single-phase motors at various voltages.
Chapter 9, Table 1
Conduit fill percentages — 40% for 2+ conductors, 53% for 1 conductor. Conduit Fill Calculator →
Chapter 9, Table 4
Conduit dimensions and internal areas for each raceway type (EMT, IMC, RMC, PVC).
Chapter 9, Table 5
Wire cross-sectional areas (including insulation) used for conduit fill calculations. Conduit Fill Calculator →
Frequently Asked Questions
What is the current NEC edition?
The current edition is NEC 2023 (NFPA 70-2023). The National Electrical Code is updated on a 3-year cycle. Some states and jurisdictions still enforce older editions such as NEC 2020 or NEC 2017, so always check which edition your local authority having jurisdiction (AHJ) has adopted.
Is the NEC a law?
The NEC itself is a standard published by the National Fire Protection Association (NFPA), not a law. However, most states and municipalities adopt it — sometimes with local amendments — as part of their building codes, making it legally enforceable. Always verify which edition and amendments apply in your jurisdiction.
What is NEC Table 310.16?
Table 310.16 is the most referenced table in the NEC. It lists allowable ampacities for insulated conductors rated 0–2000 volts installed in raceways, cables, or direct-buried, based on a 30°C (86°F) ambient temperature with no more than 3 current-carrying conductors in a raceway or cable. Ampacity must be derated for higher temperatures or more conductors.
What NEC article covers grounding?
Article 250 covers all grounding and bonding requirements in the NEC, including equipment grounding conductors, grounding electrode systems, bonding of services, and grounding of separately derived systems.
What is the NEC 80% rule?
NEC 210.20(A) and 215.3 require that where a branch circuit or feeder supplies continuous loads (loads expected to run for 3 hours or more), the overcurrent device rating must be not less than 125% of the continuous load. In practice, this means a continuous load must not exceed 80% of the breaker rating. For example, a 20A breaker should carry no more than 16A of continuous load.
How often is the NEC updated?
The NEC is updated every 3 years. Recent editions include NEC 2017, NEC 2020, and NEC 2023. The next edition will be NEC 2026. Each new cycle incorporates changes based on public proposals, public comments, and committee actions to improve electrical safety.
Related Electrical Calculators
Wire Sizing Calculator
Select the correct wire gauge for any circuit based on NEC ampacity tables and voltage drop limits.
Calculate Wire Size →Load Calculation Calculator
Perform NEC Article 220 load calculations for dwelling units, commercial buildings, and feeders.
Calculate Electrical Load →Conduit Fill Calculator
Calculate conduit fill per NEC Chapter 9 tables. Supports EMT, IMC, RMC, PVC, and flexible conduits.
Calculate Conduit Fill →Voltage Drop Calculator
Check voltage drop for branch circuits and feeders to stay within NEC recommended limits.
Calculate Voltage Drop →Wire Ampacity Chart
Interactive NEC Table 310.16 ampacity chart with temperature correction and conduit fill derating.
View Ampacity Chart →Breaker Size Calculator
Determine the correct overcurrent protection per NEC Article 240, including the 80% continuous load rule.
Calculate Breaker Size →