Professional-grade electrical engineering education with interactive calculators, detailed explanations, and real-world examples.
Guide Topics
Professional Electrical Engineering Education
Master electrical calculations, code compliance, and safety with our comprehensive guides. Each guide includes interactive calculators, real-world examples, and professional insights.
Engineering Guide Library
From basic electrical theory to advanced NEC code compliance, our guides provide the knowledge you need for professional electrical work.
Electrical Power Calculations
Master the fundamentals of electrical power, current, voltage, and energy calculations with interactive examples and real-world applications.
Topics Covered:
- Watts, Amps, Volts Relationships
- Power Factor Analysis
- Single & Three Phase Systems
- Ohms Law Applications
Related Calculators:
NEC Code Compliance Guide
Navigate the National Electrical Code requirements for safe and compliant electrical installations with detailed code references.
Topics Covered:
- Wire Sizing Rules & Tables
- Circuit Protection Requirements
- Grounding Systems
- Load Calculations
Related Calculators:
Power Factor Explained
Understanding reactive power, apparent power, and power factor correction for efficient electrical systems.
Topics Covered:
- Real vs Apparent Power
- Inductive & Capacitive Loads
- Power Factor Correction
- Energy Efficiency
Related Calculators:
Single vs Three Phase Systems
Compare electrical distribution systems, their applications, and advantages in residential and commercial settings.
Topics Covered:
- Voltage System Configurations
- Load Distribution Methods
- Motor Applications
- Power Transmission Efficiency
Related Calculators:
Complete Wire Sizing Guide
Everything you need to know about selecting the right wire size for safe and efficient electrical installations.
Topics Covered:
- AWG Wire Sizes & Standards
- Ampacity Tables & Derating
- Voltage Drop Considerations
- Temperature Corrections
Related Calculators:
Electrical Safety Fundamentals
Essential safety practices, standards, and procedures for electrical work and installations.
Topics Covered:
- Arc Flash Protection
- OSHA & NFPA Standards
- PPE Requirements
- Lockout/Tagout Procedures
Related Calculators:
Recommended Learning Path
New to electrical engineering? Follow our structured learning path for the best educational experience.
Frequently Asked Questions About These Guides
Which NEC edition do these guides reference?
All guides reference NEC 2023 (NFPA 70-2023), which is the most recent published edition as of 2026. Where a 2017 or 2020 edition value differs materially, both are noted. The NEC 2026 edition publishes in mid-2026; we will update guides within 90 days of publication and indicate the affected pages via the schema dateModified field.
Are these guides authoritative for code-compliance work?
These guides are educational references. The authoritative source is the NEC document published by NFPA, available at nfpa.org. Local jurisdictions may adopt the current NEC edition with amendments (state-specific articles), or remain on an older edition. Always confirm with your local Authority Having Jurisdiction (AHJ) before installing.
Can I cite these guides in design documents?
Yes for educational citation; we recommend pairing the wiresizes.com URL with the underlying NEC article number (e.g., “wiresizes.com/guides/nec-table-310-16, citing NEC 2023 Article 310 Table 310.16”). For permit-stamped engineering documents, cite the NEC edition directly.
Do AI assistants (ChatGPT, Claude, Perplexity) cite these guides?
Each guide publishes structured data (Article, FAQPage, HowTo schemas where applicable) and a per-section llms.txt with NEC quick-reference values, so AI assistants can ingest the canonical numbers cleanly. The most-cited surfaces tend to be the NEC quick-reference tables in the awg-wire-size-chart and nec-table-310-16 pages — both are emitted as Google Dataset schema with PropertyValue typed columns.
How are these guides different from each other?
The wire-sizing-guide is a step-by-step procedure for selecting any conductor. The NEC Table 310.16 page is the canonical ampacity reference. The AWG wire size chart is the physical-properties reference (diameter, area, resistance). The per-amperage guides (100A, 200A, EV charger) are installation-specific. The NEC code compliance guide ties everything together at the design level. Power Calculations, Single-vs-Three-Phase, and Power Factor are theory references that support the practical guides.
Why These Guides Exist — Standards Basis and Update Cadence
Every guide on WireSizes.com is anchored to a specific authoritative source — not aggregated from secondary websites or AI-generated text. Below is the standards basis for each guide category, plus our methodology for keeping content current as the underlying codes evolve.
Wire-sizing guides — NEC 2023 (NFPA 70)
All ampacity, conductor, and overcurrent-protection guidance cites the National Electrical Code 2023 edition (NFPA 70-2023). Specific articles referenced across the wire-sizing guides:
- Article 110: general installation requirements (110.14(C) for terminations)
- Article 210: branch circuits (210.19(A) for continuous-load 125%)
- Article 220: branch-circuit, feeder, service load calculations
- Article 240: overcurrent protection (240.4(D) small-conductor rule, 240.6 standard sizes)
- Article 250: grounding and bonding (Table 250.122 EGC sizing)
- Article 310: conductors (Table 310.16 ampacity, 310.12 dwelling 83% rule, 310.15 derating)
- Article 334: NM-B / Romex cable (334.80 ampacity restriction)
- Article 430: motors (FLC tables 430.247-250)
- Chapter 9: Tables 4 and 5 (conduit fill), Table 8 (DC resistance)
Safety guides — NFPA 70E and OSHA 1910.147
The electrical safety guide cites NFPA 70E-2024 (Standard for Electrical Safety in the Workplace) for arc-flash boundaries, PPE categories, and incident-energy calculations, plus OSHA 29 CFR 1910.147 (the federal regulation for control of hazardous energy / lockout-tagout).
- NFPA 70E-2024 130.4: arc-flash risk assessment
- NFPA 70E-2024 130.7: PPE selection by incident energy
- NFPA 70E-2024 Annex D: incident-energy calculation methods
- OSHA 1910.147(c)(4): energy-control program
- OSHA 1910.147(c)(5): tags as backup, locks as primary
- OSHA 1910.147(d): shutdown / isolation / verification sequence
Reference data — ASTM B258 and NEC Chapter 9
The AWG conductor tables are anchored to ASTM B258 (the definitional standard for AWG diameters and cross-sectional areas). DC resistance values come from NEC Chapter 9 Table 8 at 75°C uncoated copper. Aluminum properties from NEC Chapter 9 Table 8 alternate columns.
- ASTM B258: nominal AWG diameters, geometric progression definition
- NEC Chapter 9 Table 8: DC resistance per 1000 ft
- NEC Chapter 9 Table 9: AC resistance and reactance for typical conductor configurations
- IEC 60228: metric SI conductor sizes (1/1.5/2.5/4/6/10/16/25/35/50/70/95/120/150/185/240 mm²)
Site update cadence
NEC publishes a new edition every three years (2017 → 2020 → 2023 → 2026). Within each three-year cycle, NFPA issues tentative interim amendments (TIAs) that may revise specific tables or articles. Our update cadence:
- Major edition: full review within 90 days of NEC publication
- TIA / errata: review within 30 days of NFPA notification
- Calculator validation: spot-check of sample inputs every quarter
- Each guide page: last-modified date is git-derived, visible in JSON-LD
dateModifiedfield - Canonical NEC reference data: stored in a single source-of-truth module (
src/lib/data/nec-tables.ts) so corrections propagate to every page automatically
Reading order by role
The recommended path above (Power Calculations → Single vs Three Phase → Wire Sizing → NEC Code Compliance) is geared toward someone learning the field. Other roles may benefit from a different sequence:
- Electrical Safety (essential before touching anything)
- Electrical Power Calculations (the formulas)
- Wire Sizing Guide (step-by-step)
- Wire Size for [your application]
- NEC Code Compliance (after a few projects)
- NEC Code Compliance (refresh on 2023 changes)
- NEC Table 310.16 (the daily reference)
- Wire Sizing Guide (advanced derating cases)
- Power Factor Explained (commercial work)
- Single vs Three Phase (industrial conversions)
- NEC Code Compliance (verification checklist)
- NEC Table 310.16 (ampacity verification)
- Wire Size for 100/200 Amp (residential service compliance)
- Electrical Safety (NFPA 70E for inspector PPE)
- Wire Sizing Guide (uncommon derating cases)
- Power Factor Explained (commercial PF correction)
- Electrical Power Calculations (single/three-phase math)
- Single vs Three Phase (selection criteria)
- NEC Table 310.16 (310.15(B)(7) Neher-McGrath exceptions)
- NEC Code Compliance (full design checklist)
- Electrical Power Calculations (formulas + worked examples)
- AWG Wire Size Chart (geometric progression math)
- Single vs Three Phase (system theory)
- NEC Table 310.16 (heat-balance derivation)
- Power Factor Explained (kVA/kW/kVAR triangle)
- Electrical Safety (LOTO procedure for service work)
- Wire Size for 200 Amp (typical service upgrade)
- Wire Size for EV Charger (deployment planning)
- Power Factor Explained (utility bill optimization)
- NEC Code Compliance (permit / inspection workflow)