NFPA 70 — National Electrical Code Reference Guide
Quick lookup • Key articles • Formula tables • Study checklist • Exam tips
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1️⃣ General Structure & Navigation
The NEC is organized into 9 Chapters plus Annexes and an Index. Most exam questions reference Articles within Chapters 1–4 and specific topics in 5–8.
| Chapter | Coverage |
|---|---|
| 1 — General | Definitions, scope, voltage limits, code language rules (Art. 90–110) |
| 2 — Wiring & Protection | Branch circuits, feeders, services, OCPD (Art. 200–285) |
| 3 — Wiring Methods & Materials | Cable types (NM, MC, AC), raceways, conduits (Art. 300–398) |
| 4 — Equipment for General Use | Switchgear, motors, transformers, HVAC (Art. 400–490) |
| 5 — Special Occupancies | Hazardous, healthcare, assembly (Art. 500–590) |
| 6 — Special Equipment | PV, EV, signs, pools (Art. 600–695) |
| 7 — Special Conditions | Emergency systems, fire alarms (Art. 700–770) |
| 8 — Communications | Telephone, data, CATV (Art. 800–830) |
| 9 — Tables & Annexes | Conductor fill, derating, ampacity, symbols |
2️⃣ High-Frequency Exam Articles
- Art. 90–110: Purpose, definitions, terminology, conductor ID.
- Art. 210/215/220: Branch circuits, feeders, load calculations.
- Art. 230–240: Services, OCPD, disconnects.
- Art. 250: Grounding & Bonding (GEC, EGC, MBJ).
- Art. 310/312/314: Conductors, raceways, boxes, fill & derating.
- Art. 400/422/430: Flexible cords, appliances, motors.
- Art. 440/450: HVAC & transformers.
- Art. 517: Healthcare facilities.
- Art. 690/625: Solar PV and EV charging.
- Art. 700–702: Emergency & standby systems.
3️⃣ Formulas & Tables at a Glance
| Category | Formula / Table |
|---|---|
| Ohm’s Law | E = I×R | I = E÷R | P = E×I |
| Voltage Drop | %VD = (2×K×I×D)÷CM | Limit ≤ 3% branch, 5% total |
| Conductor Ampacity | Table 310.16 — Adjust for ambient & bundling |
| Conduit Fill | Ch. 9 Tables 1 & 4 — Area limits (40% typical) |
| Motor Circuit | Art. 430 — 125% FLA conductors; 175% breaker max |
| Grounding Conductor | Table 250.66 — size by largest ungrounded conductor |
| Box Fill | Art. 314 — 2.5 in³ #14 Cu, 3 in³ #12 Cu etc. |
4️⃣ Quick Reference Checklist
Tab Articles 90–110 (General Rules)
Mark load calc formulas (Art. 220)
Highlight Grounding & Bonding tables (Art. 250)
Summarize motor rules (Art. 430)
Copy ampacity & fill tables to sheet
5️⃣ Exam Tips
- Speed Indexing: Memorize chapter ranges (200s = Protection, 300s = Methods).
- Keyword Lookup: Use the Index first for fast section hits.
- Cross-Check: Verify definitions in Art. 100 before choosing answers.
- Show Work: Label units in calculations for partial credit.
- Edition Control: Practice on the same NEC year as exam.